MicroBiology MCQs with Answer and Explnation | Chapter 61

Answer: Darting movement

“Darting movement.” Vibrio, the causative organism of cholera, exhibits darting movement, characterized by rapid, dart-like movements in water.

The other options are incorrect:

• Gliding movement: This movement is seen in bacteria like Myxobacteria, not in Vibrio.
• Pseudopodial movement: This movement involves the extension of pseudopods, typically seen in amoebas, not in Vibrio.
• None of these: This option simply states that none of the provided movements are correct, which is inaccurate as Vibrio does exhibit a specific type of movement, i.e., darting movement.

Answer: DNA or RNA

Viruses can contain either DNA or RNA, but not both within the same virus particle. Their genetic material is the essential component for replication, and it can be single or double-stranded depending on the specific virus.

The other options are incorrect:

• Cell membrane: Viruses do not have a cell membrane of their own. They can acquire an envelope from the host cell membrane during the replication process, but this is not a defining characteristic.
• Cell wall: Similar to the cell membrane, viruses lack a cell wall. Cell walls are structures found in bacteria and some other organisms for rigidity and protection, but not needed by viruses.

Answer: Proteins

Bacterial pili are hair-like structures primarily composed of a specific protein called pilin. These pilin subunits assemble to form the long, thin fibers that project from the bacterial surface.

The other options are incorrect:

• Carbohydrates: While bacteria can have carbohydrates on their surface in the form of capsules or lipopolysaccharides, pili themselves are not made of carbohydrates.
• Lipids: Lipids are fatty molecules found in cell membranes, but they are not the main building block of pili.
• Minerals: Minerals are inorganic elements that can be important for bacterial functions, but they are not a significant component of pili.

Answer: Breakdown of organic compounds

Bacteria play a crucial role in the carbon cycle by acting as decomposers. They break down dead organic matter from plants, animals, and other organisms. Through this process, they release carbon back into the atmosphere as carbon dioxide (CO2) which can then be reused by plants during photosynthesis.

The other options are incorrect:

• Photosynthesis: While some bacteria, like cyanobacteria, can perform photosynthesis, this is not the primary role of most bacteria in the carbon cycle. Photosynthesis is the process by which plants and some other organisms capture carbon dioxide to create organic compounds.
• Chemosynthesis: Chemosynthesis is a process where certain bacteria use chemical energy to synthesize organic molecules. While it contributes to the carbon cycle, it’s not the main role of most bacteria.
• Assimilation of nitrogen compounds: Although some bacteria can fix nitrogen from the atmosphere (convert it into a usable form), this is not their primary function in the carbon cycle.

Answer: Fruit juices

Louis Pasteur’s early fermentation experiments primarily focused on understanding the spoilage of beverages, particularly wine. He used fruit juices as his main model system to study the process of fermentation and the role of microorganisms.

The other options are incorrect:

• Milk: While Pasteur later made significant contributions to milk preservation through pasteurization, his initial fermentation experiments did not heavily involve milk.
• Food material: This is too broad an answer. Fermentation can occur in various food materials, but Pasteur’s initial focus was on beverages like fruit juices.
• Both Milk and Fruit juices: There’s no evidence that milk was a central focus in Pasteur’s first fermentation experiments.

Answer: Paul Ehrlich

While all the scientists listed made significant contributions to medicine, Paul Ehrlich is credited as the “Father of Chemotherapy” for his pioneering work in developing drugs specifically targeting infectious diseases. He proposed the concept of a “magic bullet” – a drug that would selectively target and kill pathogens without harming the host.

The other options are incorrect:

• Joseph Lister: Lister is known for his work on antiseptics and promoting sterile surgical techniques, which greatly reduced infections but is not directly related to chemotherapy.
• Elie Metchnikoff: Metchnikoff was a key figure in immunology, studying the body’s defense mechanisms against pathogens. His contributions are important for understanding the immune system’s role in fighting infections, but not directly related to developing chemotherapeutic drugs.
• None of these: Although the others didn’t propose modern chemotherapy, Ehrlich’s work laid the foundation for this field of treatment.

Answer: Klein Berger

Emmy Klieneberger-Nobel, sometimes referred to as Klein Berger, discovered L-forms in 1935. These are cell wall-deficient variants of bacteria that can arise from various bacteria species.

• Louis Pasteur: While a prominent microbiologist, Pasteur’s discoveries focused on areas like fermentation and germ theory of disease, not L-forms.
• Robert Koch: Koch is known for his postulates to establish the causative agent of a disease. His work did not involve the discovery of L-forms.
• Antony van Leeuwenhoek: A pioneer in microscopy, Leeuwenhoek observed and described microorganisms, but L-forms were not identified until much later.

Answer: Howard Ricketts

Howard Ricketts is credited with identifying the causative organism of Rocky Mountain spotted fever in 1906. He conducted extensive research on the disease, isolating the bacteria and demonstrating its transmission through ticks.

The other options are incorrect:

• da Rocha-lima: While some sources mention da Rocha-lima in connection with Rocky Mountain spotted fever, his contributions were likely related to identifying a similar tick-borne disease in South America. Ricketts’ work is widely recognized as the first description of the specific bacteria causing Rocky Mountain spotted fever.
• Both Howard Ricketts and da Rocha-lima: Although da Rocha-lima might have been studying a related disease, Ricketts’ work is the definitive discovery for Rocky Mountain spotted fever.
• Robert Koch: Robert Koch made significant contributions to microbiology, but his focus was not on Rocky Mountain spotted fever. He is known for his postulates to establish the cause of infectious diseases.

Answer: F.W. Twort

The discovery of viral infection in bacteria, also known as bacteriophages, is attributed to F.W. Twort in the early 1900s. He observed a phenomenon where bacterial cultures seemed to be cleared of bacteria by an unknown agent.

The other options are incorrect:

• De’Herelle (Felix d’Herelle): While Felix d’Herelle independently discovered bacteriophages around the same time as Twort, Twort’s observations are often credited as the first.
• Beijernick (Martinus Beijerinck): Beijerinck is known for his work on the tobacco mosaic virus, one of the first discovered viruses, but not directly related to bacteriophages.
• Jwanoksy (Dimitri Ivanovsky): Ivanovsky played a crucial role in the discovery of viruses by demonstrating a filterable infectious agent in tobacco plants, but his work wasn’t focused on bacteria.

Answer: Mycoplasms

Mycoplasmas are a unique group of bacteria that lack a rigid cell wall. This allows them to be very flexible and able to squeeze through very small spaces. They are the smallest self-replicating organisms known.

The other options are incorrect:

• Spirochetes: Spirochetes are a type of bacteria known for their helical or spiral shape. They do have a cell wall, although it can be complex and contribute to their motility.
• Actinomycetes: These are bacteria known for their thread-like growth and ability to form spores. They possess a cell wall, often with a unique composition compared to other bacteria.
• Methanogens: Methanogens are a group of archaea, another type of prokaryote. They have a cell wall, although its composition can differ from that of bacteria.

Answer: Lysozyme

Lysozyme is an enzyme that specifically targets and breaks down glycosidic bonds in the peptidoglycan layer of bacterial cell walls. This weakens the cell wall and can lead to lysis (bursting) of the bacteria.

The other options are incorrect:

• Reductase: Reductases are a class of enzymes involved in reduction reactions, not specifically designed to break down bacterial cell walls.
• Protease: Proteases are enzymes that break down proteins, not the carbohydrate structures found in bacterial cell walls.

Answer: Cellulose hydrolyzing microorganisms

Straw is primarily composed of cellulose, a complex carbohydrate that humans and many other animals cannot digest. Cows, however, have a four-chambered stomach (rumen) that houses a complex ecosystem of microorganisms. These microbes, including bacteria, fungi, and protozoa, produce enzymes called cellulases. Cellulases break down cellulose into simpler sugars like glucose, which the cow can then absorb and use for energy.

The other options are incorrect:

• Protein hydrolyzing bacteria: While cows do have bacteria that break down proteins in their food, straw is low in protein and cellulose digestion is the key challenge.
• Lipid hydrolyzing microorganisms: Straw contains minimal lipids (fats), and these wouldn’t be a primary target for digestion.
• Amino acid degrading bacteria: Amino acids are the building blocks of proteins, and as mentioned above, protein content in straw is low. Cellulose breakdown is the more crucial function for cows utilizing straw.

Answer: Agrobacterium tumefaciens

Agrobacterium tumefaciens has found extensive use in genetic engineering work in plants due to its ability to transfer DNA into plant cells. It is commonly used as a vector in plant biotechnology to introduce desired genes into plants, making it a valuable tool in genetic engineering.

The other options are incorrect:

• Clostridium septicum: This bacterium is an obligate anaerobe (requires an oxygen-free environment) and causes gas gangrene. It is not used in plant genetic engineering.
• Xanthomonas oriza: This bacterium is a plant pathogen that causes bacterial blight of rice. While it can infect plants, it is not used for genetic engineering purposes.
• Bacillus coagulens: This bacterium has some probiotic properties and may be found in certain food products. It is not typically used in plant genetic engineering.

Answer: Protein and rRNA

Bacterial ribosomes are composed of two main components: protein and ribosomal RNA (rRNA). These components work together to facilitate the process of protein synthesis by translating mRNA into protein.

The other options are incorrect:

• Protein and DNA: Bacterial ribosomes do not contain DNA. DNA serves as the genetic material and is located in the bacterial chromosome or plasmids, not in ribosomes.
• Protein and mRNA: mRNA (messenger RNA) is involved in protein synthesis, but it is not a component of ribosomes. Ribosomes read mRNA to synthesize proteins.
• Protein and tRNA: tRNA (transfer RNA) is involved in protein synthesis by carrying amino acids to the ribosome, but it is not a structural component of ribosomes. Ribosomes interact with tRNA during the process of translation.

Answer: Bacteria

Bioleaching is primarily done by bacteria. It is a process where microorganisms, particularly certain types of bacteria, are used to extract metals from ores. These bacteria oxidize the metals in the ore, making them soluble and allowing for their extraction.

The other options are incorrect:

• Protozoa: While some protozoa can interact with and even consume bacteria, they are not typically involved in bioleaching processes.
• Algae: Algae are photosynthetic organisms and wouldn’t be directly involved in mineral breakdown for metal extraction as seen in bioleaching.
• All of the above: Although bacteria are the main players, protozoa and algae are not generally used in bioleaching.

Answer: Chemostat

A chemostat is the apparatus used to maintain a continuous culture in microbiology. It controls the flow rate of nutrients into a bioreactor while simultaneously removing an equal volume of culture to keep the culture volume constant.

The other options are incorrect:

• Autostat: There is no apparatus known as an “Autostat” in microbiology. This option is incorrect.
• Thermostat: A thermostat is a device used to regulate temperature, not to maintain a continuous culture. This option is incorrect.
• Both Chemostat and Thermostat: While a chemostat is indeed used for maintaining continuous cultures, a thermostat is not relevant to this context. This option is partially incorrect.

Answer: Coxiella

Coxiella is the genus most likely to contain organisms capable of surviving high temperatures. It includes the species Coxiella burnetii, which is known for its ability to survive extreme heat, making it resistant to standard disinfection methods.

The other options are incorrect:

• Vibrio: While some Vibrio species can tolerate moderate temperatures, they are generally mesophilic, meaning they prefer moderate temperatures for growth.
• Pseudomonas: Similar to Vibrio, most Pseudomonas species are mesophilic. High temperatures can inhibit their growth.
• Torula: This genus typically refers to a type of yeast. Most yeasts are also mesophilic and cannot survive extremely high temperatures.

Answer: Chemostat

A chemostat is the apparatus used to maintain a continuous culture in microbiology. It controls the flow rate of nutrients into a bioreactor while simultaneously removing an equal volume of culture to keep the culture volume constant.

The other options are incorrect:

• Autostat: There is no known apparatus called an “Autostat” in microbiology. This option is incorrect.
• Thermostat: A thermostat is a device used to regulate temperature, not to maintain a continuous culture. This option is incorrect.
• Both Chemostat and Thermostat: While a chemostat is used for maintaining continuous cultures, a thermostat is unrelated to this context. This option is incorrect.

Answer: Nessler’s reagent test

Nessler’s reagent test detects the presence of ammonia (NH₄⁺) produced by the deamination of amino acids by bacteria. Deamination removes the amino group (NH₂) from the amino acid, resulting in the formation of ammonia and a keto acid.

The other options are incorrect:

• Proteolytic test: This test identifies bacteria that can break down proteins into peptides and amino acids. It doesn’t directly detect deamination of amino acids.
• Lactose test: This test determines a bacterium’s ability to ferment lactose, a sugar. It’s not related to amino acid deamination.
• Rose indole reagent test: This test detects the presence of indole, a specific product formed by some bacteria during tryptophan metabolism. It’s not a general test for amino acid deamination.

Answer: Corynebacterium

Diphtheria is a respiratory illness caused by the bacterium Corynebacterium diphtheriae. This bacterium produces a toxin that damages tissues in the throat and nose, causing difficulty breathing and other serious complications.

The other options are incorrect:

• Staphylococcus: Staphylococcus is a genus of bacteria commonly associated with skin infections like boils and impetigo. While some Staphylococcus species can cause more severe infections, they are not responsible for diphtheria.
• Streptococcus: Streptococcus is another genus of bacteria known for causing various infections, including strep throat and pneumonia. Similar to Staphylococcus, Streptococcus species are not the culprit behind diphtheria.

Answer: Measles

Koplik spots are tiny, white bumps with a red halo that appear on the inner cheeks (buccal mucosa) in the early stages of measles. They are considered a highly characteristic sign of the disease.

The other options are incorrect:

• Rubella: Rubella, also known as German measles, typically doesn’t present with Koplik spots. Its rash may have some similarities to measles, but it doesn’t involve these specific mouth lesions.
• Mumps: Mumps is a viral infection that primarily affects the salivary glands. While it can cause swelling in the cheeks and mouth, it doesn’t cause Koplik spots.
• Influenza: Influenza, commonly known as the flu, is a respiratory illness caused by a virus. It doesn’t involve Koplik spots or any mouth lesions.

Answer: Lysogen

A bacterium containing a prophage, which is the integrated form of a bacteriophage (virus) genome within the bacterial chromosome, is called a lysogen. The prophage replicates passively along with the bacterial DNA during cell division.

The other options are incorrect:

• Lytic: The lytic cycle refers to the cycle of viral replication where the virus actively replicates within the host cell and causes its lysis.
• Lytogen: “Lytogen” isn’t a recognized term in the context of phage-bacteria interactions.

Answer: Botulism

Botulism is considered the most infectious foodborne disease. It is caused by the bacterium Clostridium botulinum, which produces potent neurotoxins. Ingestion of even small amounts of the toxin can lead to severe illness, including paralysis and potentially death.

The other options are incorrect:

• Tetanus: Tetanus is not typically transmitted through food; it is caused by the bacterium Clostridium tetani and is commonly associated with wound contamination.
• Dysentery: Dysentery is usually caused by bacteria such as Shigella or protozoa such as Entamoeba histolytica, and it is transmitted through contaminated food or water, but it is not considered the most infectious foodborne disease.
• Gas gangrene: Gas gangrene is caused by Clostridium perfringens and is typically associated with contaminated wounds, not foodborne transmission.

Answer: Influenza

Influenza is an example of a common airborne epidemic disease. It is caused by influenza viruses that can spread through the air via respiratory droplets when an infected person coughs, sneezes, or talks.

The other options are incorrect:

• Typhoid: Typhoid fever is typically transmitted through contaminated food and water, not through airborne transmission.
• Encephalitis: Encephalitis refers to inflammation of the brain, which can be caused by various factors including viruses transmitted by mosquitoes or ticks, but it is not typically transmitted through airborne routes.
• Malaria: Malaria is transmitted through the bite of infected mosquitoes, primarily Anopheles mosquitoes, and is not considered an airborne disease.

Answer: Prophage

A prophage is a viral genome that has become integrated into the genome of a bacterial host. Prophages are typically found in lysogenic bacteria, where they remain dormant until triggered to enter the lytic cycle.

The other options are incorrect:

1. Temperate phage: This term refers to a bacteriophage that can undergo both lytic and lysogenic cycles but does not specifically denote integration into the bacterial genome.
2. Bacteriophage: While bacteriophages infect bacteria, not all bacteriophages integrate into the bacterial genome.
3. Metaphage: “Metaphage” is not a recognized term in virology or microbiology.

Answer: Lipolytic microbes

The rancidity of stored foods is primarily due to the activity of lipolytic microbes, which break down fats (lipids) present in the food, leading to the development of off-flavors and odors associated with rancidity.

The other options are incorrect:

• Toxigenic microbes: While some microbes can produce toxins that can cause foodborne illness, these toxins aren’t directly responsible for rancidity.
• Proteolytic microbes: These microbes break down proteins and wouldn’t be the primary culprit behind fat and oil spoilage.
• Saccharolytic microbes: These microbes ferment sugars, which can contribute to spoilage in some cases, but they aren’t the main cause of rancidity in fats and oils.

Answer: Infectious virus particles

Virion refers to a complete, infectious virus particle that is capable of infecting a host cell and replicating within it.

The other options are incorrect:

• Non-infectious particles: This term refers to virus particles that are unable to infect host cells and replicate, which do not qualify as virions.
• Incomplete particles: Incomplete particles may lack essential components required for infectivity, and they are not considered virions.
• Defective virus particles: Defective virus particles have mutations or deletions in their genome that render them non-functional or less efficient in infecting host cells. They are not considered typical virions.

Answer: Attenuation

Attenuation refers to the process of reducing the virulence or pathogenicity of microorganisms, typically through methods such as serial passage in laboratory conditions or genetic manipulation, while still maintaining their ability to induce immunity.

The other options are incorrect:

• A virulence: “A virulence” is not a recognized term in microbiology. This option is incorrect.
• Inactivation: Inactivation refers to rendering microorganisms non-viable or inactive, which may not necessarily reduce their virulence but rather eliminates their ability to cause infection. This option is incorrect.
• Freezing: Freezing may preserve microorganisms but does not inherently reduce their virulence.

Answer: WIDAL test

The WIDAL test is used for the serological detection of antibodies against Salmonella enterica serotype Typhi, the causative agent of typhoid fever. It detects specific antibodies produced by the body in response to infection with Salmonella Typhi.

The other options are incorrect:

• ELISA: ELISA (Enzyme-Linked Immunosorbent Assay) is a versatile technique used for various serological tests, but it is not specific to the detection of typhoid fever.
• Rosewaller test: There is no widely recognized test known as the “Rosewaller test” for the detection of typhoid fever.
• Western blotting: Western blotting is a laboratory technique used for the detection and analysis of proteins, and it is not typically used for the detection of typhoid fever.

Answer: Virulent

A bacteriophage capable of only lytic growth is called virulent. Virulent phages infect bacterial cells, replicate within them, and ultimately cause the lysis of the host cell to release progeny phages.

The other options are incorrect:

• Temperate: Temperate phages are capable of both lytic and lysogenic growth. They can integrate their DNA into the host genome (lysogeny) or undergo a lytic cycle.
• Avirulent: Avirulent refers to non-pathogenic or non-virulent strains of microorganisms. It does not specifically describe phages capable of only lytic growth.

Answer: Kleb’s hofflers bacillus

The diphtheria bacillus is named after the two scientists who discovered it in 1884: Edwin Klebs and Friedrich Löffler.

The other options are incorrect:

• Friedländer’s bacillus: This refers to Klebsiella pneumoniae, a bacterium that can cause pneumonia and other infections.
• Frchs bacillus: This is likely a misspelling and doesn’t correspond to a known bacillus associated with diphtheria.
• Koch’s bacillus: This refers to Mycobacterium tuberculosis, the bacterium responsible for tuberculosis.

Answer: Gram positive

Acridine dyes are more effective against Gram-positive bacteria. They work by binding to the DNA of bacteria and interfering with its replication and transcription processes, ultimately leading to bacterial cell death.

The other options are incorrect:

• Gram negative: Acridine dyes are less effective against Gram-negative bacteria due to the presence of an outer membrane that acts as a barrier, limiting the penetration of these dyes. This option is incorrect.
• Ricke Hsia: “Ricke Hsia” does not correspond to any recognized term related to microbiology or bacteriology. This option is incorrect.
• Mycoplasma: Mycoplasma bacteria lack a cell wall, making them resistant to many antibiotics and dyes that target cell wall synthesis. Acridine dyes may not be particularly effective against Mycoplasma

Answer: Chromatophores

Chromatophores are pigment-bearing structures found in bacteria. These structures are responsible for bacterial pigmentation and can vary in color depending on the type of pigment present.

The other options are incorrect:

• Chloroplast: Chloroplasts are organelles specific to plant cells and some protists. They contain chlorophyll and are the primary site of photosynthesis in these organisms. Bacteria don’t have chloroplasts.
• Protoplast: A protoplast is a bacterial cell that has had its cell wall removed. It doesn’t refer to a pigment-bearing structure.
• Spheroplast: Similar to a protoplast, a spheroplast is a bacterial cell with a partially degraded cell wall. It’s not a structure specifically associated with pigments.

Answer: H.C. Gram

This method allows for the classification of bacteria into two large groups based on their cell wall structure: Gram-positive and Gram-negative.pen_spark

The other options are incorrect:

• A.H. Gram: There is no recognized scientist with the initials “A.H. Gram” associated with the development of the Gram stain.
• N.C. Gram: Similarly, there is no recognized scientist with the initials “N.C. Gram” associated with the development of the Gram stain.
• H.A. Gram: This option is a slight variation of the correct answer but does not accurately represent the scientist who developed the Gram stain

Answer: Rickettsias

Rickettsias are a group of intermediate pathogens between bacteria and viruses that are intracellular parasites. They are responsible for diseases such as Rocky Mountain spotted fever and typhus.

The other options are incorrect:

• Mycoplasmas: While Mycoplasmas are also small bacteria lacking a cell wall, they are not obligate intracellular parasites. They can survive and replicate outside of host cells.
• Prions: Prions are infectious agents composed solely of misfolded proteins. They lack genetic material and do not replicate in the same way as bacteria or viruses.
• Virusoides: Virusoids are small, single-stranded RNA molecules that depend on a helper virus for replication. They are not considered a separate group of pathogens and are associated with specific viral infections.

Answer: Gram positive bacteria

Bacillus is a genus of rod-shaped, Gram-positive bacteria. They are classified based on their cell wall structure, which stains purple in the Gram staining procedure. Bacillus species are widespread in nature and can be found in soil, water, and even in the human gut.

The other options are incorrect:

• Gram negative bacteria: Gram-negative bacteria have a different cell wall structure compared to Gram-positive bacteria. They stain pink in the Gram staining process.
• Virus: Viruses are much smaller and simpler than bacteria. They lack a cell wall and many other cellular components, and they reproduce by hijacking the host cell machinery.
• Viroid: Viroids are even smaller and simpler than viruses. They consist solely of a short, single-stranded RNA molecule and cannot reproduce on their own.

Answer: Entamoeba histolytica

Entamoeba histolytica is a single-celled parasite responsible for amoebic dysentery in humans. This parasite infects the intestines, causing symptoms like diarrhea, abdominal pain, and fever.

The other options are incorrect:

• Plasmodium: This parasite causes malaria, a mosquito-borne disease affecting red blood cells. It is not linked to amoebic dysentery.
• Paramecium: Paramecium is a free-living ciliate, a type of protist commonly studied in biology labs. It doesn’t infect humans and is not related to amoebic dysentery.
• Yeast: Yeast is a fungus, and while some yeasts can cause infections, they are not responsible for amoebic dysentery.

Answer: Prophage

A prophage is a viral genome that has been integrated into the DNA of a bacterium, becoming dormant and replicating along with the host genome until it is triggered to enter the lytic cycle.

Incorrect Options:

• Temperate Phage: This is essentially synonymous with a prophage. It refers to a phage that can enter a dormant state within the bacterial genome.
• Bacteriophage: While bacteriophages are viruses that infect bacteria, not all of them become integrated into the bacterial genome like a prophage.
• Metaphage: This term doesn’t have a specific biological meaning in the context of viral integration into bacterial genomes. It seems to be a combination of “meta” (meaning beyond or transcending) and “phage” (referring to a virus that infects bacteria), but it’s not a recognized term in virology.

Answer: Transduction

Transduction is the recombination process facilitated by phages, where bacterial DNA is transferred from one bacterium to another via a virus (bacteriophage) vector during the lytic cycle of the phage.

The other options are incorrect:

• Conjunction: Conjugation is a process of genetic transfer in bacteria that involves direct cell-to-cell contact via a conjugation bridge. It does not involve phages.
• Transformation: Transformation is the process where bacteria take up free DNA from their environment and incorporate it into their genome. It doesn’t involve phages directly.
• Transfection: Transfection is a laboratory technique where foreign DNA is introduced into cells, typically eukaryotic cells, using non-viral methods such as chemical or physical means. It does not involve phages or bacterial recombination.

Answer: Iodine

Iodine is used as a mordant in Gram staining. It helps to fix the crystal violet dye to the bacterial cell wall, enhancing its retention during the staining process.

The other options are incorrect:

• Crystal Violet: Crystal violet is a primary stain used in the Gram staining process to initially stain all bacterial cells.
• Saffranin: Saffranin is a counterstain used in Gram staining to stain Gram-negative bacteria after the decolorization step.
• All of these: This option is incorrect because not all of the options listed are mordants. Crystal violet and saffranin are stains used in the Gram staining process, but only iodine functions as a mordant in this context.

Answer: Cell-wall

Parasitic forms must contain a cell wall for protection, structural integrity, and defense against host immune responses.

The other options are incorrect:

• Capsule: While some parasitic forms may have capsules for evasion of host immune responses, not all parasitic forms necessarily have capsules.
• Endospores: Endospores are a dormant, resistant structure formed by certain bacteria for survival under harsh conditions. Not all parasitic forms produce endospores.
• Flagella: Flagella are used for motility and may or may not be present in parasitic forms depending on their lifestyle and habitat requirements. They are not a mandatory characteristic of parasitic forms.

Answer: Differential staining

Gram staining is a classic example of a differential staining technique used to differentiate between different types of bacteria based on their cell wall composition, specifically the presence or absence of a thick peptidoglycan layer.

The other options are incorrect:

• Simple staining: Simple staining involves the use of a single dye to color cells uniformly. Gram staining involves multiple steps and different dyes, making it a form of differential staining rather than simple staining.
• Negative staining: Negative staining is a technique where the background is stained instead of the cells, leaving the cells unstained and visible as clear areas. Gram staining doesn’t follow this principle.

Answer: Rhodococcus agilis

Rhodococcus agilis is a motile species of cocci. It possesses flagella, enabling it to move.

The other options are incorrect:

• Staphylococcus: Staphylococcus species are typically non-motile cocci.
• Meningococcus: Meningococcus refers to Neisseria meningitidis, which is non-motile.
• Gonococcus: Gonococcus refers to Neisseria gonorrhoeae, which is non-motile.

Answer: All of them

Aspergillus fumigatus is a versatile fungus known to cause infections in birds, animals, and humans. It is found ubiquitously in the environment and can lead to a variety of infections in different host species.

The other options are incorrect:

• Birds: Aspergillus fumigatus can infect birds, so
• Animals: Aspergillus fumigatus can infect animals as well, making
• Man: Aspergillus fumigatus can indeed infect humans,

Answer: Straphylococci

Enterotoxins responsible for food poisoning are primarily secreted by certain strains of Staphylococci, particularly Staphylococcus aureus. These toxins can contaminate food and cause gastrointestinal illness when ingested.

The other options are incorrect:

• Enterococci: While Enterococci can cause infections, they are not typically associated with food poisoning due to enterotoxins.
• Entamoeba histolytica: Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery, but it does not secrete enterotoxins associated with food poisoning.
• Enterobacteriaceae: Enterobacteriaceae is a large family of bacteria, some of which can cause foodborne illness, but the primary agents responsible for food poisoning through enterotoxin secretion are Staphylococci, not Enterobacteriaceae.

Answer: Ordinarily an aerobe but can grow in absence of O2

Facultative anaerobes are organisms that can grow in the presence or absence of oxygen. They prefer aerobic conditions but can switch to anaerobic metabolism when oxygen is unavailable.

The other options are incorrect:

• Only grow anaerobically: This describes obligate anaerobes, which cannot survive in the presence of oxygen.
• Only grow in the presence of O2: This describes obligate aerobes, which require oxygen for growth.
• Ordinarily an anaerobe but can grow with O2: This describes aerotolerant anaerobes, which can tolerate oxygen but do not use it for growth.

Answer: 2 – 8%

Moderate anaerobes require oxygen in concentrations ranging from 2% to 8% for growth. They can tolerate higher levels of oxygen compared to obligate anaerobes but still prefer low oxygen environments.

The other options are incorrect:

• 0%: This describes obligate anaerobes, which cannot grow in the presence of oxygen.
• < 0.5%: This value is too low for moderate anaerobes, as they require oxygen in higher concentrations.
• 5 – 10%: This range is too high for moderate anaerobes. It overlaps more with the oxygen requirements of microaerophiles.

Answer: Chromophores

Chromophores are pigment-bearing structures in bacteria responsible for their coloration. These pigments can vary and contribute to bacterial characteristics such as color, UV protection, and other functions.

The other options are incorrect:

• Mesosomes: Mesosomes are invaginations of the plasma membrane in bacteria and are not involved in pigment-bearing structures.
• Plasmids: Plasmids are extrachromosomal DNA elements that often carry accessory genes but are not pigment-bearing structures.
• Mitochondria: Mitochondria are membrane-bound organelles found in eukaryotic cells responsible for energy production through respiration. They are not present in bacteria.

Answer: Treponema pallidum

Spirochetes are a group of spiral-shaped bacteria, and Treponema pallidum is a species of spirochete bacteria that causes syphilis, a sexually transmitted infection.

The other options are incorrect:

• Gonococci: Gonococci are diplococci bacteria, meaning they occur in pairs, and they cause gonorrhea. They are not spirochetes.
• Staphylococci: Staphylococci are spherical-shaped bacteria that occur in clusters and are responsible for various infections, but they are not spirochetes.
• Streptococci: Streptococci are spherical-shaped bacteria that occur in chains and can cause a variety of infections, but they are not spirochetes.

Answer: Teichoic acids are absent

Gram-negative bacteria have a thin cell wall composed of a peptidoglycan layer surrounded by an outer membrane. Unlike Gram-positive bacteria, they do not have teichoic acids in their cell wall structure.

The other options are incorrect:

• Thick: This describes the cell wall of Gram-positive bacteria, which have a thick layer of peptidoglycan.
• Lipids are present: Lipids are indeed present in the outer membrane of Gram-negative bacteria, so this statement is not accurate.