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ACVM Veterinary Microbiology study materials
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ACVM Veterinary Microbiology practice questions

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Question 1Bacteriology

Which bacterial structure is the primary target of the Gram stain's crystal violet retention?

  1. The cytoplasmic membrane phospholipids
  2. The lipopolysaccharide of the outer membrane
  3. The capsular polysaccharide
  4. The peptidoglycan layer of the cell wall Correct answer.

Explanation

Crystal violet is trapped by the thick peptidoglycan meshwork of gram-positive cells after iodine mordanting and alcohol decolorization. Gram-negative cells lose the dye because their thin peptidoglycan cannot retain it.

Question 2Bacteriology

A gram-positive coccus that grows in clusters and is catalase-positive is most likely which genus?

  1. Staphylococcus Correct answer.
  2. Micrococcus
  3. Enterococcus
  4. Streptococcus

Explanation

Clustered gram-positive cocci that produce catalase are characteristic of Staphylococcus. Streptococci and enterococci are catalase-negative and typically form chains or pairs.

Question 3Bacteriology

Which culture medium is selective for gram-negative enteric bacilli by inhibiting gram-positive organisms with bile salts and dyes?

  1. Chocolate agar
  2. Mannitol salt agar
  3. Blood agar
  4. MacConkey agar Correct answer.

Explanation

MacConkey agar contains bile salts and crystal violet that suppress gram-positive growth, and lactose with a pH indicator to distinguish lactose fermenters. It is the standard selective and differential medium for enteric gram-negative rods.

Question 4Bacteriology

Which organism is the most common cause of community-acquired urinary tract infection in dogs?

  1. Proteus mirabilis
  2. Pseudomonas aeruginosa
  3. Escherichia coli Correct answer.
  4. Staphylococcus pseudintermedius

Explanation

Escherichia coli accounts for the majority of uncomplicated canine urinary tract infections. Other organisms such as Proteus and staphylococci occur less frequently and are more often associated with complicating factors.

Question 5Bacteriology

Which bacterial genus is an obligate intracellular pathogen transmitted by ticks and causes granulocytic anaplasmosis?

  1. Anaplasma Correct answer.
  2. Borrelia
  3. Bartonella
  4. Leptospira

Explanation

Anaplasma species are obligate intracellular rickettsial organisms that infect granulocytes and are tick-transmitted. Bartonella and Borrelia are extracellular or facultatively intracellular and have different vector relationships.

Question 6Bacteriology

Which test detects bacterial endotoxin by forming a gel clot in the presence of lipopolysaccharide?

  1. Coombs test
  2. Latex agglutination for capsule
  3. CAMP test
  4. Limulus amoebocyte lysate assay Correct answer.

Explanation

The Limulus amoebocyte lysate assay uses horseshoe crab amoebocyte lysate, which clots in response to endotoxin. It is a sensitive method for detecting gram-negative lipopolysaccharide.

Question 7Bacteriology

Which statement best describes the nature of bacterial endotoxin?

  1. A heat-labile protein secreted by living gram-positive cells
  2. A polysaccharide capsule that resists phagocytosis
  3. A heat-stable lipopolysaccharide of the gram-negative outer membrane Correct answer.
  4. A peptidoglycan fragment that activates complement

Explanation

Endotoxin is lipopolysaccharide located in the outer membrane of gram-negative bacteria; its lipid A component is heat-stable and pyrogenic. Exotoxins, by contrast, are heat-labile proteins secreted by bacteria.

Question 8Bacteriology

Which bacterial shape describes a curved, comma-shaped organism such as Vibrio?

  1. Coccus
  2. Bacillus
  3. Vibrio Correct answer.
  4. Spirillum

Explanation

Vibrio organisms are curved or comma-shaped rods, a morphology named after the genus. Bacilli are straight rods and cocci are spherical.

Question 9Bacteriology

A gram-negative rod from a dog's wound is oxidase-positive, grows at 42°C, and produces a green pigment on culture. Which organism is most consistent with these findings?

  1. Pasteurella multocida
  2. Escherichia coli
  3. Pseudomonas aeruginosa Correct answer.
  4. Salmonella enterica

Explanation

Oxidase positivity, growth at 42°C, and blue-green pigment (pyocyanin) are classic features of Pseudomonas aeruginosa. The other listed organisms are oxidase-negative or fail to grow at elevated temperature.

Question 10Bacteriology

A gram-positive rod isolated from a ruminant abortion is catalase-positive, motile at 25°C but not 37°C, and shows umbrella motility. Which organism is most likely?

  1. Bacillus anthracis
  2. Erysipelothrix rhusiopathiae
  3. Listeria monocytogenes Correct answer.
  4. Corynebacterium renale

Explanation

Listeria monocytogenes is a catalase-positive, gram-positive rod with tumbling motility that is expressed at 25°C but not 37°C, producing an umbrella pattern in semisolid medium. It is a recognized cause of abortion in ruminants.

Question 11Bacteriology

Which organism is a major cause of contagious bovine mastitis that grows as gram-positive cocci in chains and is catalase-negative?

  1. Streptococcus agalactiae Correct answer.
  2. Staphylococcus aureus
  3. Trueperella pyogenes
  4. Escherichia coli

Explanation

Streptococcus agalactiae is a catalase-negative, chain-forming gram-positive coccus and a classic cause of contagious mastitis spread from cow to cow. Staphylococcus aureus is catalase-positive and occurs in clusters.

Question 12Bacteriology

Which feature distinguishes the CAMP test result of Listeria monocytogenes from that of Streptococcus agalactiae?

  1. Listeria enhances hemolysis of Streptococcus agalactiae but not of Staphylococcus aureus
  2. Listeria produces a positive CAMP reaction only on blood agar with sheep erythrocytes
  3. Both show synergistic hemolysis, but Listeria enhances hemolysis of Staphylococcus aureus rather than being enhanced Correct answer.
  4. Listeria is CAMP-negative while Streptococcus agalactiae is CAMP-positive

Explanation

The CAMP test uses a Staphylococcus aureus streak; Listeria monocytogenes enhances hemolysis near the staphylococcal line, whereas Streptococcus agalactiae enhances hemolysis near a different indicator organism. The reaction depends on the specific indicator strain used.

Question 13Bacteriology

A gram-negative, microaerophilic, curved rod is cultured from aborted ovine tissue and grows best at 37°C in a microaerobic atmosphere. Which genus is most likely?

  1. Salmonella
  2. Campylobacter Correct answer.
  3. Brucella
  4. Yersinia

Explanation

Campylobacter species are curved gram-negative rods that grow best under microaerobic conditions and are recognized causes of ovine abortion. Salmonella, Brucella, and Yersinia are not microaerophilic curved rods.

Question 14Bacteriology

Which organism is the causative agent of strangles in horses?

  1. Streptococcus equi subsp. equi Correct answer.
  2. Rhodococcus equi
  3. Corynebacterium pseudotuberculosis
  4. Streptococcus zooepidemicus

Explanation

Streptococcus equi subsp. equi causes strangles, a highly contagious upper respiratory infection of horses. Rhodococcus equi causes pneumonia in foals, and S. zooepidemicus is associated with opportunistic respiratory and genital infections.

Question 15Bacteriology

A gram-negative rod isolated from a pig with septicemia is oxidase-negative, lactose-negative, and produces hydrogen sulfide on triple sugar iron agar. Which organism is most likely?

  1. Actinobacillus pleuropneumoniae
  2. Escherichia coli
  3. Salmonella enterica Correct answer.
  4. Pasteurella multocida

Explanation

Salmonella enterica is oxidase-negative, generally lactose-negative, and produces hydrogen sulfide, which appears as blackening in TSI agar. Escherichia coli is a lactose fermenter and typically does not produce H2S.

Question 16Bacteriology

Which organism is the primary cause of caseous lymphadenitis in sheep and goats?

  1. Corynebacterium pseudotuberculosis Correct answer.
  2. Burkholderia mallei
  3. Trueperella pyogenes
  4. Mycobacterium avium subsp. paratuberculosis

Explanation

Corynebacterium pseudotuberculosis produces caseous lymphadenitis, characterized by abscesses in superficial lymph nodes. The organism is a gram-positive pleomorphic rod and is spread via contaminated wounds and fomites.

Question 17Bacteriology

Which organism is the agent of contagious caprine pleuropneumonia?

  1. Pasteurella multocida
  2. Mycoplasma capricolum subsp. capripneumoniae Correct answer.
  3. Bibersteinia trehalosi
  4. Mannheimia haemolytica

Explanation

Mycoplasma capricolum subsp. capripneumoniae is the specific cause of contagious caprine pleuropneumonia, a severe respiratory disease of goats. The other organisms cause different respiratory syndromes.

Question 18Bacteriology

Which organism is the most likely cause of a gram-negative, oxidase-positive, non-lactose-fermenting rod isolated from a cat bite wound?

  1. Pasteurella multocida Correct answer.
  2. Pseudomonas aeruginosa
  3. Escherichia coli
  4. Salmonella enterica

Explanation

Pasteurella multocida is a gram-negative, oxidase-positive coccobacillus commonly found in the oral flora of cats and dogs and is a leading cause of bite wound infections. It is non-lactose-fermenting on MacConkey agar.

Question 19Bacteriology

A gram-positive rod isolated from a horse's respiratory tract grows as small, rough colonies and is catalase-positive. Which organism is most likely?

  1. Rhodococcus equi Correct answer.
  2. Bacillus anthracis
  3. Streptococcus equi
  4. Corynebacterium pseudotuberculosis

Explanation

Rhodococcus equi is a gram-positive, catalase-positive pleomorphic rod that causes pneumonia in foals and forms mucoid colonies on culture. It is a soil organism that can be recovered from the respiratory tract of affected animals.

Question 20Bacteriology

Which mechanism best explains the action of the diphtheria toxin produced by Corynebacterium diphtheriae?

  1. Cleavage of host cell membranes by phospholipase activity
  2. Formation of pores in host membranes
  3. Inhibition of protein synthesis by ADP-ribosylation of elongation factor 2 Correct answer.
  4. Activation of adenylate cyclase by ADP-ribosylation of G proteins

Explanation

Diphtheria toxin ADP-ribosylates elongation factor 2, blocking protein synthesis and causing cell death. This mechanism is shared with exotoxin A of Pseudomonas aeruginosa.

Question 21Bacteriology

Which organism is the causative agent of Johne's disease in cattle?

  1. Mycobacterium avium subsp. paratuberculosis Correct answer.
  2. Mycobacterium tuberculosis
  3. Mycobacterium leprae
  4. Mycobacterium bovis

Explanation

Mycobacterium avium subsp. paratuberculosis causes Johne's disease, a chronic granulomatous enteritis of ruminants. It is an acid-fast organism that requires long incubation periods for culture.

Question 22Bacteriology

A gram-positive rod isolated from a soil sample grows aerobically and forms endospores that are centrally located and do not bulge the sporangium. Which genus is most likely?

  1. Listeria
  2. Corynebacterium
  3. Clostridium
  4. Bacillus Correct answer.

Explanation

Bacillus species are aerobic or facultatively anaerobic, spore-forming gram-positive rods with centrally located endospores. Clostridium species are anaerobic spore formers, while Corynebacterium and Listeria do not form spores.

Question 23Bacteriology

Which organism is the agent of glanders, a disease of equids characterized by respiratory and cutaneous lesions?

  1. Actinobacillus equuli
  2. Burkholderia mallei Correct answer.
  3. Pseudomonas aeruginosa
  4. Burkholderia pseudomallei

Explanation

Burkholderia mallei is the obligate pathogen that causes glanders in horses, mules, and donkeys. Burkholderia pseudomallei is a soil saprophyte that causes melioidosis but is not the glanders agent.

Question 24Bacteriology

Which feature of the bacterial cell envelope is most directly responsible for the endotoxic activity of gram-negative bacteria?

  1. Lipid A of lipopolysaccharide Correct answer.
  2. The peptidoglycan cross-links
  3. O-antigen polysaccharide side chains
  4. Porin proteins in the outer membrane

Explanation

Lipid A is the hydrophobic anchor of lipopolysaccharide and is the biologically active portion that triggers the innate immune response. The O-antigen and porins contribute to other functions but are not the principal endotoxic moiety.

Question 25Bacteriology

A gram-negative rod isolated from a bovine respiratory outbreak is non-hemolytic on blood agar, oxidase-positive, and fails to grow on MacConkey agar. Which organism is most likely?

  1. Pasteurella multocida
  2. Actinobacillus pleuropneumoniae
  3. Mannheimia haemolytica
  4. Histophilus somni Correct answer.

Explanation

Histophilus somni is a gram-negative rod that requires enriched media and does not grow on MacConkey agar; it is oxidase-positive and generally non-hemolytic. Mannheimia haemolytica is hemolytic, and Pasteurella multocida grows on MacConkey agar.

Question 26Bacteriology

Which bacterial structure is the primary target of lysozyme, causing cell lysis?

  1. Lipopolysaccharide in the outer membrane
  2. The cytoplasmic membrane bilayer
  3. Peptidoglycan in the cell wall Correct answer.
  4. The polysaccharide capsule

Explanation

Lysozyme hydrolyzes the beta-1,4 glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, weakening the wall and causing lysis. Gram-positive walls are more exposed, so they are more susceptible.

Question 27Bacteriology

Which term describes bacteria that require oxygen at reduced concentrations of roughly 2 to 10 percent for optimal growth?

  1. Facultative anaerobes
  2. Aerotolerant anaerobes
  3. Obligate anaerobes
  4. Microaerophiles Correct answer.

Explanation

Microaerophiles grow best at oxygen levels below atmospheric concentration because they need oxygen for respiration but are inhibited by full ambient oxygen. Examples include Campylobacter and Helicobacter species.

Question 28Bacteriology

Which type of bacterial toxin is a protein that is secreted by living bacteria and is typically heat-labile?

  1. Lipoteichoic acid
  2. Peptidoglycan fragment
  3. Endotoxin
  4. Exotoxin Correct answer.

Explanation

Exotoxins are actively secreted proteins produced by living bacteria, are generally heat-labile, and are often highly specific in their action. Endotoxins are cell-wall lipopolysaccharide released on lysis and are heat-stable.

Question 29Bacteriology

Which bacterial genus is characterized as gram-positive cocci arranged in grape-like clusters that are catalase-positive?

  1. Enterococcus
  2. Streptococcus
  3. Staphylococcus Correct answer.
  4. Micrococcus

Explanation

Staphylococcus species are gram-positive cocci in irregular clusters, are catalase-positive, and grow in high salt. The clustering reflects division in multiple planes.

Question 30Bacteriology

Which culture medium is selective for gram-negative enteric bacilli because bile salts and dyes inhibit gram-positive organisms?

  1. Columbia colistin-nalidixic acid agar
  2. MacConkey agar Correct answer.
  3. Blood agar
  4. Chocolate agar

Explanation

MacConkey agar contains bile salts and crystal violet, which inhibit gram-positive bacteria, and lactose with a pH indicator that differentiates lactose fermenters. Blood and chocolate agars are enriched, non-selective media.

Question 31Bacteriology

Which organism is a gram-positive, spore-forming rod that causes anthrax in livestock and humans?

  1. Corynebacterium pseudotuberculosis
  2. Bacillus anthracis Correct answer.
  3. Trueperella pyogenes
  4. Clostridium perfringens

Explanation

Bacillus anthracis is an aerobic, gram-positive, endospore-forming rod that forms the agent of anthrax. Its spores persist in soil and are the infectious form.

Question 32Bacteriology

Which bacterial structure is the target of the coagulase test used to distinguish Staphylococcus aureus from coagulase-negative staphylococci?

  1. Bound coagulase converting fibrinogen to fibrin Correct answer.
  2. Urease hydrolyzing urea to ammonia
  3. Oxidase transferring electrons to cytochrome c
  4. Catalase degrading hydrogen peroxide

Explanation

The coagulase test detects the enzyme that converts fibrinogen to fibrin, clumping plasma; S. aureus is coagulase-positive while most other staphylococci are negative. It is a key presumptive identification step.

Question 33Bacteriology

Which organism is the primary cause of tuberculosis in cattle, a chronic granulomatous disease affecting the respiratory tract and other organs?

  1. Mycobacterium leprae
  2. Nocardia asteroides
  3. Mycobacterium avium subsp. paratuberculosis
  4. Mycobacterium bovis Correct answer.

Explanation

Mycobacterium bovis is the member of the tuberculosis complex that primarily affects cattle, producing granulomas in lungs and lymph nodes. It is a slow-growing acid-fast bacillus.

Question 34Bacteriology

A gram-negative, oxidase-positive, curved rod is isolated from a dog with diarrhea and grows at 42°C under microaerophilic conditions. Which genus is most likely?

  1. Salmonella
  2. Escherichia
  3. Campylobacter Correct answer.
  4. Bordetella

Explanation

Campylobacter species are curved gram-negative rods that are oxidase-positive and microaerophilic, with several species growing at 42°C. Their curved morphology and growth requirements are characteristic.

Question 35Bacteriology

A gram-positive, catalase-negative coccus in chains is beta-hemolytic and bacitracin-sensitive. Which organism is most likely?

  1. Streptococcus pyogenes Correct answer.
  2. Enterococcus faecalis
  3. Staphylococcus aureus
  4. Streptococcus agalactiae

Explanation

Streptococcus pyogenes (Lancefield group A) is beta-hemolytic and bacitracin-sensitive, distinguishing it from group B streptococci. It is catalase-negative and forms chains.

Question 36Bacteriology

Which organism is a gram-negative, non-spore-forming coccobacillus that causes tularemia and is highly infectious to humans handling infected rabbits?

  1. Brucella abortus
  2. Yersinia pestis
  3. Pasteurella multocida
  4. Francisella tularensis Correct answer.

Explanation

Francisella tularensis is a tiny gram-negative coccobacillus that causes tularemia and is transmitted by contact with infected lagomorphs, ticks, or deer flies. It requires enriched media with cysteine for culture.

Question 37Bacteriology

A gram-negative rod from a cow with mastitis grows on MacConkey agar as lactose-negative colonies and is oxidase-negative. Which organism is most likely?

  1. Pseudomonas aeruginosa
  2. Klebsiella pneumoniae
  3. Escherichia coli
  4. Salmonella enterica Correct answer.

Explanation

Salmonella enterica is a lactose-negative, oxidase-negative gram-negative rod, unlike the lactose-fermenting coliforms. Pseudomonas would be oxidase-positive and often pigmented.

Question 38Bacteriology

Which organism is a gram-positive, non-spore-forming rod that causes mastitis and abscesses in livestock and is typically beta-hemolytic and catalase-positive?

  1. Listeria monocytogenes
  2. Trueperella pyogenes Correct answer.
  3. Bacillus subtilis
  4. Erysipelothrix rhusiopathiae

Explanation

Trueperella pyogenes is a gram-positive, non-spore-forming, catalase-positive rod that is beta-hemolytic and causes suppurative infections including mastitis and abscesses. It is a common opportunistic pathogen of livestock.

Question 39Bacteriology

Which organism is a gram-negative, oxidase-positive, non-lactose-fermenting rod that is a major cause of otitis externa in dogs and often produces a sweet grape-like odor?

  1. Bordetella bronchiseptica
  2. Pseudomonas aeruginosa Correct answer.
  3. Proteus mirabilis
  4. Escherichia coli

Explanation

Pseudomonas aeruginosa is oxidase-positive, non-lactose-fermenting, and produces pigments and a characteristic grape-like odor. It is a common cause of canine otitis externa.

Question 40Bacteriology

A gram-positive rod isolated from a sheep's liver grows anaerobically, is spore-forming, and produces a lecithinase reaction on egg yolk agar. Which organism is most likely?

  1. Clostridium novyi Correct answer.
  2. Listeria ivanovii
  3. Bacillus cereus
  4. Corynebacterium renale

Explanation

Clostridium novyi is an anaerobic, spore-forming gram-positive rod that is lecithinase-positive and causes infectious necrotic hepatitis in sheep. Its anaerobic growth and lecithinase activity support the identification.

Question 41Bacteriology

Which organism is a gram-negative, oxidase-positive, non-lactose-fermenting rod that causes bovine respiratory disease and is often identified by a characteristic musty odor?

  1. Bordetella bronchiseptica Correct answer.
  2. Haemophilus somnus
  3. Pasteurella multocida
  4. Mannheimia haemolytica

Explanation

Bordetella bronchiseptica is a gram-negative, oxidase-positive rod that grows on MacConkey agar and has a characteristic musty odor. It is associated with respiratory disease in a range of species.

Question 42Bacteriology

A gram-positive coccus from a sheep with pneumonia is catalase-positive, oxidase-negative, and grows as mucoid colonies. Which organism is most likely?

  1. Staphylococcus aureus Correct answer.
  2. Lactococcus lactis
  3. Enterococcus faecium
  4. Streptococcus pneumoniae

Explanation

Staphylococcus aureus is a catalase-positive, oxidase-negative gram-positive coccus that can produce mucoid colonies, particularly when encapsulated. It is a recognized cause of suppurative pneumonia in ruminants.

Question 43Bacteriology

Which organism is a gram-negative, microaerophilic, spiral-shaped bacterium that causes abortion in sheep and is transmitted by ingestion of contaminated feed or water?

  1. Coxiella burnetii
  2. Leptospira interrogans
  3. Campylobacter fetus subsp. fetus Correct answer.
  4. Brucella ovis

Explanation

Campylobacter fetus subsp. fetus is a microaerophilic, spiral-shaped gram-negative organism that causes ovine abortion, typically after ingestion of contaminated material. Its morphology and growth requirements are characteristic.

Question 44Bacteriology

A gram-negative rod from a pig with pneumonia is oxidase-positive and non-hemolytic on blood agar. Which organism is most likely?

  1. Salmonella choleraesuis
  2. Escherichia coli
  3. Pasteurella multocida
  4. Actinobacillus pleuropneumoniae Correct answer.

Explanation

Actinobacillus pleuropneumoniae is a gram-negative, oxidase-positive, non-hemolytic rod that is a major cause of porcine pleuropneumonia. It requires NAD for growth.

Question 45Bacteriology

Which mechanism best explains how the toxin produced by Clostridium tetani causes spastic paralysis?

  1. Blocking acetylcholine receptors on the motor end plate
  2. Increasing release of acetylcholine at the neuromuscular junction
  3. Blocking release of inhibitory neurotransmitters from inhibitory interneurons Correct answer.
  4. Degrading acetylcholine in the synaptic cleft

Explanation

Tetanospasmin cleaves synaptobrevin in inhibitory interneurons, preventing release of GABA and glycine, so motor neurons fire unopposed and spastic paralysis results. The toxin does not act at the motor end plate itself.

Question 46Bacteriology

A gram-negative, oxidase-positive, non-lactose-fermenting rod is isolated from a horse with genital tract infection and abortion. Which organism is most likely?

  1. Taylorella equigenitalis Correct answer.
  2. Klebsiella pneumoniae
  3. Pseudomonas aeruginosa
  4. Salmonella abortus-equi

Explanation

Taylorella equigenitalis is a fastidious, oxidase-positive, non-lactose-fermenting gram-negative rod that causes contagious equine metritis and abortion. Its growth requires enriched media and it is not a typical coliform.

Question 47Bacteriology

Which mechanism best explains the action of the toxin produced by Clostridium botulinum at the neuromuscular junction?

  1. Stimulating acetylcholinesterase activity
  2. Blocking postsynaptic acetylcholine receptors
  3. Cleaving SNARE proteins to prevent acetylcholine vesicle fusion Correct answer.
  4. Increasing calcium influx into the motor nerve terminal

Explanation

Botulinum neurotoxin cleaves SNARE proteins in the motor nerve terminal, preventing fusion of acetylcholine vesicles and causing flaccid paralysis. It acts presynaptically by inhibiting transmitter release.

Question 48Bacteriology

Which organism is a gram-negative, oxidase-positive, non-lactose-fermenting rod that causes melioidosis and is often resistant to many antibiotics?

  1. Pseudomonas fluorescens
  2. Burkholderia pseudomallei Correct answer.
  3. Bordetella bronchiseptica
  4. Acinetobacter baumannii

Explanation

Burkholderia pseudomallei is an oxidase-positive, non-lactose-fermenting gram-negative rod that causes melioidosis and is intrinsically resistant to many antibiotics. It is a soil organism in tropical regions.

Question 49Bacteriology

A gram-positive rod isolated from a ruminant abortion is catalase-positive, motile at 25°C but not at 37°C, and shows a narrow zone of beta-hemolysis on sheep blood agar. Which organism is most likely?

  1. Listeria monocytogenes Correct answer.
  2. Listeria innocua
  3. Erysipelothrix rhusiopathiae
  4. Corynebacterium pseudotuberculosis

Explanation

Listeria monocytogenes is catalase-positive, motile at 25°C but not at 37°C, and produces a narrow zone of beta-hemolysis, distinguishing it from non-hemolytic Listeria species. These features are used in identification from abortion material.

Question 50Bacteriology

Which mechanism best explains the action of the toxin produced by Clostridium perfringens type A in gas gangrene?

  1. ADP-ribosylation of elongation factor 2
  2. Phospholipase C activity that lyses cell membranes Correct answer.
  3. Blocking release of inhibitory neurotransmitters
  4. Activation of adenylate cyclase

Explanation

Alpha-toxin of Clostridium perfringens is a phospholipase C that hydrolyzes membrane phospholipids, causing cell lysis and tissue necrosis in gas gangrene. This enzymatic activity is central to its local tissue destruction.