MicroBiology MCQs with Answer and Explanations | Chapter 71

Answer: The lowest temperature at which the microorganisms grow

The minimum growth temperature refers to the lowest temperature at which a specific microorganism can reproduce and maintain a population. Below this temperature, essential metabolic processes become too slow or stop entirely, preventing growth.

The other options are incorrect:

• The growth of organisms at lowest temperature: This phrasing is a bit vague. Growth refers to the increase in population, not just the ability to survive at low temperatures.
• The maximum temperature at which the growth is stable: This describes the maximum growth temperature, not the minimum.
• None of these: While the wording could be improved in some options, “The lowest temperature at which microorganisms can grow” accurately defines the minimum growth temperature.

Answer: Thermophiles

Thermophiles are microorganisms that thrive at high temperatures, with an optimum growth temperature exceeding 45°C. They have adaptations that allow them to function in hot environments like hot springs, deep sea vents, and compost heaps.

The other options are incorrect:

• Mesophiles: These organisms prefer moderate temperatures, typically ranging from 20°C to 45°C.
• Psychrophiles: These cold-loving microbes have optimal growth at temperatures below 15°C and can even survive freezing conditions.
• None of these: While the other options represent different temperature preferences, thermophiles are specifically adapted to high temperatures.

Answer: Faculative anaerobes

Facultative anaerobes are versatile organisms that can grow with or without oxygen. They possess the metabolic machinery for both aerobic respiration (utilizing oxygen for energy production) and anaerobic respiration (generating energy without oxygen). They can switch between these pathways depending on the oxygen availability in their environment.

The other options are incorrect:

• Aerobes: These organisms strictly require oxygen for growth and cannot survive in its absence.
• Anaerobes: Anaerobic organisms are poisoned by oxygen and rely solely on anaerobic respiration for energy production.
• Strict aerobes: This term is synonymous with aerobes, emphasizing their absolute dependence on oxygen.

Answer: Microaerophilic

Microaerophiles are organisms that require a reduced concentration of oxygen (typically lower than the atmospheric level of 21%) for optimal growth. They cannot tolerate high oxygen levels and may have limited oxygen-processing enzymes, making them susceptible to oxygen toxicity.

The other options are incorrect:

• Aerophilic: This term is often used interchangeably with aerobic, referring to organisms that thrive in the presence of atmospheric oxygen levels.
• Aerobic: Similar to aerophilic, aerobic organisms function best in environments with atmospheric oxygen concentrations.
• Anaerobic: Anaerobic organisms do not require oxygen and in fact, some are even poisoned by it. They rely on anaerobic respiration for energy production.pen_spark

Answer: Sodium Thioglycollate

Sodium thioglycollate is a reducing agent commonly used in microbiology to create anaerobic conditions in culture media. It acts by scavenging dissolved oxygen in the medium, promoting the growth of anaerobic bacteria that would otherwise be inhibited by oxygen.

The other options are incorrect:

• Nitrous acid: Nitrous acid (HNO₂) has various uses in chemistry but isn’t typically used for creating anaerobic conditions in culture media.
• Citrate: Citrate is a chelating agent that can bind to metal ions, but it doesn’t have a significant impact on oxygen levels in culture media.
• None of these: While the other options aren’t used for this specific purpose, sodium thioglycollate is a well-established method for creating anaerobic environments for bacterial growth.

Answer: Cyanobacteria

Cyclic phosphorylation is a process of photosynthetic electron transport that occurs in the thylakoid membrane of chloroplasts or similar structures in photosynthetic bacteria, including Cyanobacteria. During cyclic phosphorylation, electrons travel through the electron transport chain and return to the reaction center chlorophyll molecule, generating ATP without the release of oxygen.

The other options are incorrect:

• Algae: While algae are photosynthetic organisms, cyclic phosphorylation is not a process exclusive to algae. Algae may utilize cyclic phosphorylation under specific conditions, but it is not a defining characteristic of algae as a group.
• Bacteria: While some bacteria are capable of photosynthesis, not all bacteria perform cyclic phosphorylation. Bacterial photosynthesis can vary in its mechanisms and may include cyclic or non-cyclic electron transport pathways depending on the species and environmental conditions.
• Plants: Plants perform oxygenic photosynthesis, which involves both cyclic and non-cyclic phosphorylation processes. However, cyclic phosphorylation is not unique to plants and is not the primary pathway utilized in plant photosynthesis.

Answer: Meromixis

Meromixis is a type of fertilization where only a portion of the sperm cell, specifically the nucleus, fuses with the egg cell. This results in an offspring with a combination of parental genetic material, but not a complete set of chromosomes from each parent.

The other options are incorrect:

• Exozygote: This term isn’t commonly used in biology. It might be a misspelling of “heterozygote,” which refers to an organism having different alleles for a particular gene.
• Mitosis: Mitosis is a cell division process that produces genetically identical daughter cells. It doesn’t involve fertilization or the creation of a zygote.
• Meiosis: Meiosis is a cell division process that halves the chromosome number, leading to the formation of gametes (sperm and egg cells) with a single set of chromosomes. It’s not directly involved in mesozygote formation.

Answer: S.typhi

Salmonella typhi, the bacteria responsible for typhoid fever, cannot synthesize all its essential amino acids, including tryptophan. It relies on acquiring tryptophan from its environment for growth and survival.

The other options are incorrect:

• H. influenzae (Haemophilus influenzae): While H. influenzae also requires some essential amino acids, tryptophan is not one of them. It can synthesize tryptophan on its own.
• Vibrio cholerae: Similar to H. influenzae, Vibrio cholerae can produce its own tryptophan and doesn’t require it from external sources for growth.
• Neisseria gonorrhoeae (Gonococci): N. gonorrhoeae, the bacteria causing gonorrhea, has similar amino acid synthesis capabilities as H. influenzae and Vibrio cholerae. It can synthesize tryptophan internally.

Answer: Presence of CO2

Tubercle bacilli, which cause tuberculosis, are aerobic obligates. This means they require oxygen (O2) for growth, but not in high concentrations. However, they also benefit from the presence of carbon dioxide (CO2). CO2 helps them utilize oxygen more efficiently and creates a more favorable environment for their growth.

The other options are incorrect:

• Absence of O2: As mentioned above, tubercle bacilli are aerobic obligates and require oxygen for growth. They wouldn’t be able to grow in its absence.
• Presence of O2: While they need oxygen, they don’t thrive in high oxygen environments.
• None of these: Both oxygen and CO2 play a role in their optimal growth, making this answer incorrect.

Answer: Synchronous growth

The growth curve of bacteria typically includes the lag phase, exponential (log) phase, stationary phase, and decline phase. Synchronous growth, which refers to a population of cells that are all in the same phase of the cell cycle at a given time, is not a phase included in the traditional growth curve of bacteria.

The other options are incorrect:

• Lag phase: This is the initial adaptation period in bacterial growth.
• Stationary phase: This phase occurs when growth reaches a plateau due to limitations.
• Decline phase: This phase represents the decrease in bacterial population due to death.

Answer: Log phase

During the log phase, bacteria are actively dividing and growing. Their cellular processes are most robust, making them more susceptible to the action of antibiotics. Antibiotics often target essential processes like cell wall synthesis or protein production, which are highly active during rapid growth.

The other options are incorrect:

• Decline phase: In the decline phase, bacteria are dying or stressed due to depleted resources. Their cellular processes are winding down, making them less susceptible to antibiotics.
• Stationary phase: Similar to the decline phase, bacteria in the stationary phase are not actively growing and dividing. Their reduced metabolic activity makes them less vulnerable to antibiotics that target growth processes.
• Lag phase: During the lag phase, bacteria are primarily adapting to the environment and preparing for growth. Their cellular processes are not yet fully geared up for rapid division, making them somewhat less susceptible to antibiotics compared to the log phase.

Answer: Cyt o

Cytochrome o is a specific type of cytochrome found in some bacteria. Unlike most cytochromes that function as electron carriers in the electron transport chain, cytochrome o has a unique ability. It can directly react with molecular oxygen (O2) as the terminal electron acceptor in some bacterial respiratory pathways.

The other options are incorrect:

• Cyt b (Cytochrome b): Cytochrome b is a common cytochrome found in both bacteria and mitochondria. It participates in the electron transport chain but doesn’t directly react with oxygen.
• Cyt c (Cytochrome c): Similar to cytochrome b, cytochrome c is another electron carrier in the respiratory chain and doesn’t interact directly with oxygen.
• Cyt d (Cytochrome d): Cytochrome d is less common than cytochromes b and c. While its exact function can vary depending on the bacteria, it typically functions as an electron carrier within the respiratory chain, not directly interacting with oxygen.

Answer: Acetic acid

Microorganisms can utilize various pathways to generate acetyl-CoA (acetyl Coenzyme A), a crucial intermediate molecule in cellular metabolism. One common pathway for many microbes is the acetate oxidation pathway. This pathway breaks down acetic acid into acetyl-CoA, releasing energy in the process.

The other options are incorrect:

• Pyruvic acid: While pyruvate can be converted to acetyl-CoA through the action of pyruvate dehydrogenase complex, this is a different pathway compared to the acetate oxidation pathway.
• α-ketoglutaric acid and Fumaric acid: These are intermediates within the Krebs cycle (citric acid cycle) used for energy production. They are not typically the starting points for acetyl-CoA generation in most microorganisms.

Answer: Plasmids

Plasmids are small, circular, self-replicating DNA molecules found in bacteria (and sometimes archaea and eukaryotes) that are separate from the main chromosomal DNA. They often carry genes that provide bacteria with additional benefits, such as antibiotic resistance or the ability to utilize specific nutrients.

The other options are incorrect:

• Cosmids: These are artificially created DNA molecules that combine features of plasmids and viral vectors. They are larger than plasmids and can hold more foreign DNA, making them useful for cloning larger genes.
• Plasmomeros: This term is not commonly used in biology. It might be a misspelling of plasmodesmata, which are channels that connect plant cells.
• Plastids: These are membrane-bound organelles found in plant and some protist cells. They come in different forms, such as chloroplasts for photosynthesis and chromoplasts for pigment storage. Plastids contain their own DNA, but it is different from plasmids.

Answer: All of the above

All the listed options are examples of DNA viruses.

• Adenovirus: These viruses can cause a variety of illnesses, including the common cold, conjunctivitis, and gastroenteritis.
• Bacteriophage T1-T6: These are well-studied viruses that infect bacteria. They are used in various research applications, such as gene cloning and bacterial identification.
• Papovavirus: This family of viruses includes some that can cause warts and cervical cancer.

Answer: Bacteriophage F C

Bacteriophage F C is a bacteriophage, which is a virus that infects bacteria. Bacteriophages have DNA genomes, not RNA genomes. Therefore, it is not an RNA virus.

The other options are incorrect:

• Reoviruses: Reoviruses are RNA viruses that infect animals, including humans. They are named for “respiratory enteric orphan viruses” because they were originally isolated from the respiratory and gastrointestinal tracts.
• Retroviruses: Retroviruses are RNA viruses that use reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell’s genome. Examples include HIV and HTLV-1.
• Dahlia mosaic virus and Bacteriophages F × 174, M12, M13: These are not RNA viruses. Dahlia mosaic virus is a plant virus, and Bacteriophages F × 174, M12, M13 are bacteriophages, both of which have DNA genomes.

Answer: A few no. of genes are transferred

Specialized transduction is characterized by the transfer of a limited region of bacterial DNA alongside the viral DNA of the phage. This typically involves only a few genes adjacent to the location where the phage DNA integrates into the bacterial chromosome.

The other options are incorrect:

• Large amount of DNA is transferred: This describes generalized transduction, where a random and potentially large fragment of bacterial DNA gets packaged with the phage DNA.
• Whole DNA is transferred: Neither specialized nor generalized transduction involves transferring the entire bacterial genome.
• None of these: While the other options are incorrect, some specialized transduction events might involve transferring a slightly larger number of genes than “a few.” However, it’s still a targeted transfer compared to the randomness of generalized transduction.

Answer: Exogenate

During transformation, the recipient cell takes up external DNA from the environment. This external DNA source is called the exogenate.

The other options are incorrect:

• Endogenate: This refers to something produced within an organism or cell. In transformation, the DNA comes from outside the recipient cell.
• Mesozygote: This describes a cell with an intermediate number of alleles for a particular gene, not relevant to the source of DNA in transformation.
• Merosite: This term refers to a motile daughter cell produced by some parasitic protists during asexual reproduction. It’s not related to the transfer of genetic material in transformation.

Answer: Transformation

Transformation is the process by which a competent bacterial cell takes up free, naked DNA from the surrounding environment and incorporates it into its own genome. This allows the recipient bacterium to acquire new genetic traits.

The other options are incorrect:

• Transduction: In transduction, genetic material is transferred between bacteria via a viral vector (bacteriophage). The phage carries bacterial DNA from a donor cell and injects it into a recipient cell.
• Conjugation: Conjugation involves a physical connection (sex pilus) formed between two bacterial cells. Through this connection, a donor cell transfers a plasmid (piece of DNA) directly to a recipient cell.
• Cell fusion: This process involves the merging of entire cells, combining their complete genomes. It’s not the typical mechanism for gene transfer in bacteria, although some bacterial species can exhibit a form of cell fusion.

Answer: Treponema pallidum

Syphillis is a sexually transmitted disease caused by the bacterium Treponema pallidum. This spiral-shaped bacterium can cause various stages of infection if left untreated, potentially leading to serious health complications.

The other options are incorrect:

• Staphylococcus aureus: This is a common bacterium that can cause various infections, including skin infections, pneumonia, and food poisoning. However, it is not responsible for syphilis.
• Yersinia pestis: This bacterium causes the bubonic plague, a serious historical disease transmitted by rodents. It is not linked to syphilis.
• Streptococcus syphilitis: There is no known bacterial species named Streptococcus syphilitis. Streptococcus is a genus of bacteria that can cause various infections, but not syphilis.

Answer: Basophilic

Negri bodies, which are hallmarks of rabies infection, stain with a basic dye, meaning they have an affinity for basic structures. Basophilic refers to having an affinity for basic stains and typically describes structures rich in RNA (ribonucleic acid). Negri bodies contain viral RNA associated with rabies virus replication, hence their basophilic nature.

The other options are incorrect:

• Eosinophilic: Eosinophilic describes structures that stain with acidic dyes. Negri bodies stain the opposite way.
• Neutrophilic: This term refers to a type of white blood cell, not a staining property.
• Acidophilic: This refers to structures with an affinity for acidic stains. Negri bodies don’t stain with these.

Answer: Candida utilis

Candida utilis is the widely used yeast for the production of single-cell protein (SCP). It is a non-pathogenic yeast that can efficiently convert various substrates such as hydrocarbons, alcohols, and sugars into high-quality protein biomass, which can be used as a nutritional supplement in animal feed and human food production.

The other options are incorrect:

• Saccharomyces cerevisiae: While this is a very common yeast used in bread making and fermentation, it’s not typically the primary choice for SCP production due to its lower protein content compared to Candida utilis.
• Rhizopus: This is a mold, not a yeast. Molds are not typically used for SCP production because they are filamentous and difficult to process.
• All of the above: While all these yeasts can potentially be used for SCP production, Candida utilis is the most widely used due to its efficiency and suitability.

Answer:

Louis Pasteur is credited with developing the first vaccines for several diseases, including:

• Chicken cholera: In the late 1870s, Pasteur discovered that he could weaken the chicken cholera bacteria by growing them in specific conditions. This weakened form could then be used to vaccinate chickens, providing them with immunity to the full-fledged disease.
• Anthrax: Pasteur’s work on anthrax vaccines came shortly after his success with chicken cholera. He developed a method to attenuate (weaken) the anthrax bacteria, allowing for vaccination in animals.
• Rabies: Pasteur’s rabies vaccine was a breakthrough discovery in the 1880s. He developed a method to weaken the rabies virus in rabbits and then use it to create a vaccine that could protect humans and animals from the deadly disease.

Answer: All of the above

All three methods listed can be used to attenuate (weaken) organisms for inoculation purposes, particularly in the development of live attenuated vaccines.

• Growing it at a temperature higher than optimum: Exposing the organism to a higher than ideal temperature can introduce mutations that make it less virulent (cause less disease) while potentially retaining its ability to stimulate an immune response.
• Passage through animals of different species which are less susceptible to it: By repeatedly passing the organism through a series of animals with a lower susceptibility, the organism can adapt and lose some of its virulence towards the original host.
• Continuous cultivation in presence of antagonistic substance: Growing the organism in the presence of substances that hinder its growth or virulence can select for mutations that make it less harmful.

Answer: Motile organ

H antigens, also known as flagellar antigens, are present in motile organs of bacteria. These antigens are composed of flagellar proteins and are involved in bacterial motility, enabling bacteria to move through their environment using flagella.

The other options are incorrect:

1. Non-motile organ: This option is incorrect because H antigens are not present in non-motile organs. H antigens are specifically associated with motility and are found in structures such as flagella.
2. Both a & b: This option is incorrect because H antigens are only present in motile organs (flagella). Non-motile organs do not possess H antigens.
3. None of these: This option is incorrect because H antigens are indeed present in motile organs (flagella).

Answer: All of these

The agglutination test is a versatile tool used in microbiology for various purposes related to bacteria:

• Identification of isolated bacteria: By observing agglutination patterns (clumping) of bacteria with specific antibodies, scientists can help identify the type of bacteria present in an isolate.
• Typing of bacterial strains: Agglutination tests can be used to differentiate between different strains of the same bacterial species. Antibodies specific for certain surface antigens on the bacteria can help distinguish between closely related strains.
• Study of antigenic structure of bacteria: Agglutination tests with different antibodies can reveal information about the antigenic makeup of a bacterium. By analyzing which antibodies cause agglutination, scientists can learn about the different antigens present on the bacterial surface.

Answer: Pyogenic

Pyogenic refers to bacteria that have the ability to produce pus, a thick, white or yellow fluid filled with white blood cells, dead tissue, and bacteria. These bacteria are often responsible for causing skin and soft tissue infections.

The other options are incorrect:

• Pyoderm: This term specifically refers to a skin infection caused by pyogenic bacteria. While related, it’s a narrower term than pyogenic which describes the pus-producing nature of the bacteria themselves.
• Pyrogen: This term refers to a substance that causes fever. While some pus-forming bacteria might also be pyrogenic (fever-causing), not all pyogenic bacteria necessarily induce fever.
• None of the above: Pyogenic is a well-established term used in microbiology to describe bacteria capable of producing pus.

Answer: Bacitracin

Bacitracin is a bactericidal chemotherapeutic agent, meaning it kills bacteria rather than merely inhibiting their growth. It interferes with bacterial cell wall synthesis, leading to cell lysis and death.

The other options are incorrect:

• Chloramphenicol: Chloramphenicol is a bacteriostatic antibiotic that inhibits bacterial protein synthesis. It prevents the formation of peptide bonds in the bacterial ribosome, thereby halting bacterial growth.
• Novobiocin: Novobiocin is a bacteriostatic antibiotic that inhibits bacterial DNA gyrase, an enzyme involved in DNA replication. By interfering with DNA replication, novobiocin prevents bacterial growth.
• Tetracycline: Tetracycline is a bacteriostatic antibiotic that inhibits bacterial protein synthesis by binding to the bacterial ribosome and blocking the attachment of aminoacyl-tRNA molecules. This action prevents the elongation of the peptide chain during protein synthesis, thereby halting bacterial growth.

Answer: Protozoa

Kinetosomes are structures found at the base of cilia and flagella in eukaryotic cells. These hair-like structures help cells move or propel fluids. Protozoa are single-celled eukaryotes, and many species use cilia or flagella for locomotion or feeding.

The other options are incorrect:

• Algae: Some algae have flagella, but the basal structures are not typically called kinetosomes. They might be referred to as basal bodies.
• Fungi: Fungal cells lack cilia and flagella, and therefore don’t have kinetosomes.
• Viruses: Viruses are not cells and don’t have these cellular structures.

Answer: Penicillin

Penicillin is a classic antibiotic that contains a β-lactam ring in its molecular structure. This ring structure is crucial for penicillin’s mechanism of action, as it binds to enzymes essential for bacterial cell wall synthesis.

The other options are incorrect:

• Erythromycin: This antibiotic belongs to the macrolide class and does not contain a β-lactam ring. It works by inhibiting protein synthesis in bacteria.
• Tetracyclines: Similar to erythromycin, tetracyclines are another class of antibiotics that lack a β-lactam ring. They primarily interfere with bacterial protein synthesis.
• Chloramphenicol: While the name sounds similar, chloramphenicol also doesn’t possess a β-lactam ring. It functions by inhibiting bacterial protein synthesis at the ribosome level.

Answer: Vancomycin

Vancomycin is the antibiotic produced by Streptomyces orientalis. It’s a glycopeptide antibiotic known for its effectiveness against some gram-positive bacteria, including those resistant to other antibiotics like penicillin.

The other options are incorrect:

• Streptomycin: This antibiotic is produced by a different species, Streptomyces griseus. It works by inhibiting bacterial protein synthesis.
• Penicillin: Penicillin is produced by the mold Penicillium notatum. It works by inhibiting bacterial cell wall synthesis.
• Both a and b: Neither Streptomycin nor Penicillin are produced by Streptomyces orientalis.

Answer: Streptomyces venezuelae

Chloramphenicol is an antibiotic originally isolated from the bacterium Streptomyces venezuelae. It was one of the first broad-spectrum antibiotics discovered and is still used in some cases today.

The other options are incorrect:

• Streptomyces griseus: This bacterium produces the antibiotic streptomycin, not chloramphenicol.
• Streptomyces pyrogenes: While there are many Streptomyces species known to produce various antibiotics, Streptomyces pyrogenes is not a known source of chloramphenicol.
• None of these: Streptomyces venezuelae is the established source from which chloramphenicol was first isolated.

Answer: Multiplication of bacteria and toxins in blood

Septicaemia, also known as sepsis, is a life-threatening condition characterized by the presence of pathogenic microorganisms (usually bacteria) and their toxins in the bloodstream. It occurs when these microorganisms enter the bloodstream and multiply, leading to systemic inflammation and potentially severe organ dysfunction.

The other options are incorrect:

• Bacteria in blood: While the presence of bacteria in the blood is a hallmark of septicemia, it’s not just the presence alone. Their multiplication and toxin production are crucial aspects.
• Toxin in blood: Toxins can be present in the blood due to various reasons, but septicemia specifically involves toxins released by bacteria multiplying in the bloodstream.
• Pus in blood: Pus is a thick, white or yellow fluid formed by white blood cells and dead tissue. While pus formation can be associated with infections that might lead to septicemia, pus itself isn’t the defining characteristic of septicemia.

Answer: Spirochaete

Lyme disease is caused by a specific type of bacteria called a spirochaete. Spirochetes are spiral-shaped bacteria known for their motility. In the case of Lyme disease, the culprit is the bacterium Borrelia burgdorferi.

The other options are incorrect:

• Bacteria: This is a broader category that includes spirochetes. However, not all bacteria cause Lyme disease.
• Fungi: Fungal infections are different from bacterial infections and wouldn’t cause Lyme disease.
• Virus: Lyme disease is not caused by a virus. Viruses are different pathogens altogether.

Answer: Staph. aureus

Toxic shock syndrome (TSS) is primarily caused by Staphylococcus aureus (Staph. aureus) bacteria. These bacteria produce toxins that can cause a widespread inflammatory response in the body, leading to the characteristic symptoms of TSS.

The other options are incorrect:

• Staph. albus: While Staphylococcus albus is another species of staphylococcus bacteria, it’s not typically associated with causing TSS.
• Strep. viridana: Streptococcus viridans is a type of streptococcus bacteria. While some streptococcal species can cause other illnesses, Streptococcus viridans is not a known cause of TSS.
• None of these: Staph. aureus is the most common bacterial culprit behind toxic shock syndrome.

Answer: P. falciparum

Blackwater fever is a severe complication that can arise from malaria infection. The most common parasite associated with blackwater fever is Plasmodium falciparum.

The other options are incorrect:

• P. vivax: While Plasmodium vivax is a type of malaria parasite, it’s not the most common cause of blackwater fever.
• P. ovale: Similar to P. vivax, Plasmodium ovale is another malaria parasite but not the primary culprit behind blackwater fever.
• None of these: Plasmodium falciparum is the established leading cause of blackwater fever among malaria parasites.

Answer: M. tuberculosis

The Mantoux test is a skin test specifically designed to detect infection with Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB).

The other options are incorrect:

• Cynaobacteria: Cynaobacteria are a group of photosynthetic bacteria not related to Mycobacterium tuberculosis. The Mantoux test wouldn’t detect them.
• Clostridia: Clostridia is a genus of bacteria that includes some species known to cause diseases like tetanus and botulism. The Mantoux test is not designed to detect Clostridia infections.
• Both a and b: Neither cyaobacteria nor clostridia are involved in tuberculosis, so the Mantoux test wouldn’t detect them.

Answer: All of these

All of the listed antibiotics (Bacitracin, Penicillin, and Cyclosporine) can act on the cell wall of microbes, although their mechanisms differ slightly:

• Bacitracin and Penicillin: These are classic antibiotics that primarily target the cell wall of bacteria. They work by inhibiting the synthesis or disrupting the structure of essential components in the bacterial cell wall, ultimately leading to cell death.
• Cyclosporine: This antibiotic is a bit different. While it does have some effect on fungal cell wall synthesis, its primary target is the immune system. It is used to suppress the immune system in certain cases, such as after organ transplantation to prevent rejection.

Answer: Fleming

Sir Alexander Fleming, a Scottish physician and microbiologist, is credited with discovering penicillin in 1928. He observed that a mold (later identified as Penicillium notatum) inhibited the growth of bacteria in his culture dish. This discovery paved the way for the development of penicillin antibiotics, revolutionizing the treatment of bacterial infections.

The other options are incorrect:

• Pasteur: Louis Pasteur was a French biologist and chemist known for his work on germ theory, pasteurization, and vaccines. While he made significant contributions to microbiology, he is not credited with discovering penicillin.
• Koch: Robert Koch was a German physician and microbiologist famous for his postulates that established the germ theory of disease. He also discovered the causative agents of several diseases, but not penicillin.
• None of these: While other scientists made significant contributions to the development of penicillin antibiotics, Fleming’s initial discovery of its antimicrobial properties is the foundation.

Answer: a and b

While penicillins are generally ineffective against mycoplasmas because they lack a cell wall, a key target for penicillins, other antibiotics are the drugs of choice for treating mycoplasma infections.

• Tetracyclines: These antibiotics are typically the first-line treatment for mycoplasma infections. They work by inhibiting protein synthesis in bacteria, including mycoplasmas. Doxycycline is a commonly used tetracycline for this purpose.
• Erythromycin: This is another effective antibiotic against mycoplasmas. It works by binding to the ribosomes of bacteria and stopping protein synthesis. Erythromycin and other macrolide antibiotics are often used when tetracyclines are contraindicated or in cases of severe infection.

The other options are incorrect:

• Penicillins: As mentioned earlier, penicillins are not effective against mycoplasmas due to the lack of a cell wall target.

Answer: Mycoplasma phages

Viruses that specifically infect bacteria are called bacteriophages (or phages for short). Since mycoplasmas are a type of bacteria, the viruses that infect them are indeed mycoplasma phages. These phages can play a role in regulating mycoplasma populations and potentially even influence their virulence (disease-causing ability) in some cases.

The other options are incorrect:

• Bacteriophages: This is a general term for all viruses that infect bacteria, but it doesn’t specify the host being mycoplasmas.
• Virions: Virion is a general term for a complete, infectious virus particle. While technically accurate, it doesn’t specify the host (mycoplasmas) in this context.
• Tiny strains: This doesn’t accurately describe mycoplasma phages. They are viruses with specific characteristics, not just “tiny strains” of anything.

Answer: Prokaryotic intracellular parasites

Rickettsiae are prokaryotic intracellular parasites. They are obligate intracellular bacteria that replicate only within the cytoplasm of eukaryotic host cells. They are responsible for various diseases in humans, such as typhus fever and Rocky Mountain spotted fever.

The other options are incorrect:

• Unicellular organisms: This is true, but not specific enough.
• Presence of 70S ribosomes: This is shared by many bacteria.
• It causes hemolysis in human beings: This is not always the case for Rickettsiae infections.

Answer: R.orinetalis

The causative agent of scrub typhus is Rickettsia orientalis. Scrub typhus is a disease caused by infection with Orientia tsutsugamushi, which was previously classified under the genus Rickettsia but is now recognized as a distinct genus.

The other options are incorrect:

• R. quintana: Rickettsia quintana is the causative agent of trench fever, not scrub typhus. Trench fever is transmitted by the human body louse.
• R. rickettsii: Rickettsia rickettsii is the causative agent of Rocky Mountain spotted fever, not scrub typhus. It is transmitted by ticks.
• R. prowazekii: Rickettsia prowazekii is the causative agent of epidemic typhus, not scrub typhus. It is transmitted by human body lice.

Answer: Prototheca

Prototheca is the algae genus that is pathogenic to humans. It is an achlorophyllous, yeast-like algae that can cause infections in humans, particularly in immunocompromised individuals. Prototheca species are associated with a range of conditions, including cutaneous, ocular, and systemic infections.

The other options are incorrect:

• Cephaloeuros: Cephaloeuros is a genus of green algae, commonly found in freshwater habitats. It is not pathogenic to humans and is not associated with human infections.
• Ulothrix: Ulothrix is a genus of green algae, typically found in freshwater environments. It is not pathogenic to humans and is not associated with human infections.
• Macrocystis: Macrocystis is a genus of brown algae, commonly known as kelp. It is not pathogenic to humans and is not associated with human infections.

Answer: Enteric fever

Salmonella typhi is the causative organism of enteric fever, also known as typhoid fever. This bacterial infection primarily affects the digestive system.

The other options are incorrect:

• Undulant fever: This disease is caused by Brucella bacteria, not Salmonella typhi. It’s characterized by relapsing cycles of fever, sweating, and fatigue.
• Remittent fever: This is a general term for a fever that comes and goes but doesn’t follow a regular pattern. It can be caused by various pathogens, including Salmonella typhi, but isn’t specific to Salmonella typhi infection.
• Dengue fever: This viral infection is caused by a mosquito-borne flavivirus and has distinct symptoms like high fever, muscle and joint pain, and a characteristic rash.

Answer: Gall bladder

In enteric fever, the organ lodging the maximum number of the organism is the gall bladder. Salmonella typhi, the causative organism of enteric fever (typhoid fever), can reside in the gall bladder, forming biofilms and persisting for extended periods even after apparent recovery from the acute illness. From the gall bladder, the bacteria can intermittently shed into the intestine, contributing to the persistence of the infection and potential transmission to others.

The other options are incorrect:

• Liver: While Salmonella typhi can also localize in the liver during enteric fever, the organ lodging the maximum number of the organism is the gall bladder.
• Small intestine: While the small intestine is the primary site of infection and inflammation during enteric fever, the maximum number of organisms is typically found in the gall bladder, where they can persist.
• Large intestine: Enteric fever primarily affects the small intestine rather than the large intestine, and the maximum number of organisms is not typically found in the large intestine.

Answer: Bacteraemia in first week

Enteric fever, caused by Salmonella Typhi, leads to bacteria entering the bloodstream (bacteremia) during the first week of infection. This is a hallmark symptom and contributes to the characteristic fever associated with the disease.

The other options are incorrect:

• Carrier in 90%: While some individuals become carriers (asymptomatic but shedding bacteria) after infection, the rate is closer to 1-5%, not 90%.
• All serotypes cause the disease: Only specific serotypes of Salmonella, primarily Salmonella Typhi and to a lesser extent Salmonella Paratyphi A, B, and C, cause enteric fever. Other serotypes might cause food poisoning but not the full-blown enteric fever illness.
• Rosy spots on 18th day: Rosy spots, which are faint pink rashes on the abdomen, are a classic symptom of enteric fever, but they typically appear around the first week, not necessarily on the 18th day. 

Answer: Meningitis

Escherichia coli (E. coli) can cause various infections, including urinary tract infections (UTIs), septic infections of wounds, and diarrhea. However, meningitis is not typically caused by E. coli in healthy individuals.

The other options are incorrect:

• Urinary tract infections: E. coli is a common cause of urinary tract infections, particularly in women. It is the most common bacterial pathogen isolated from urine cultures in cases of UTIs.
• Septic infections of wounds: E. coli can cause septic infections of wounds, particularly in hospital settings or in individuals with compromised immune systems.
• Diarrhea: Certain strains of E. coli, such as enterotoxigenic E. coli (ETEC) and enteropathogenic E. coli (EPEC), can cause diarrhea through the production of enterotoxins and by attaching to the intestinal lining, respectively.

Answer: Corynebacterium diphtheriae

Diphtheria is a respiratory illness caused by the bacterium Corynebacterium diphtheriae. This specific bacterium produces a toxin that damages tissues in the throat and nose, leading to the characteristic thick membrane formation and breathing difficulties associated with diphtheria.

The other options are incorrect:

• C. Bovis: Corynebacterium Bovis is a different species within the Corynebacterium genus. While it can cause infections in cattle, it’s not implicated in human diphtheria.
• C. Jeikeium: Corynebacterium Jeikeium is another species within the genus. It can occasionally cause opportunistic infections in immunocompromised individuals, but it’s not known to cause diphtheria.
• C. equi: Corynebacterium equi is yet another species that primarily infects horses and other equines. It’s not associated with human diphtheria.

Answer: Klebs and Loeffler

The causative organism of diphtheria, Corynebacterium diphtheriae, was discovered and identified by German bacteriologists Edwin Klebs and Friedrich Löffler in 1884. Their work on isolating and characterizing the bacteria played a crucial role in understanding and developing treatments for diphtheria.

The other options are incorrect:

• Robert Koch: Robert Koch was another prominent microbiologist who made significant contributions to bacteriology. He discovered the causative agents of anthrax, tuberculosis, and cholera, but not diphtheria.
• Lois Pasteur: Louis Pasteur was a renowned French microbiologist known for his work on vaccines, pasteurization, and the germ theory of disease. While his contributions were fundamental to microbiology, he wasn’t involved in identifying the cause of diphtheria.
• Volhard and Fahr: Volhard and Fahr were German physicians known for their work in nephrology (kidney diseases). Their research areas did not encompass identifying the causative agent of diphtheria.