Master the Microbiology – Anaerobic Bacteriology section for your laboratory certification exams with our extensive bank of 91 multiple-choice questions (MCQs). Designed to match the latest syllabi for ASCP MLS, AMT MLT/MT, AIMS, CSMLS, IBMS, HAAD/DOH, DHA, and MOH exams, this focused set helps you strengthen both knowledge and exam technique. Each question is crafted to test core concepts, practical applications, and problem-solving skills—ideal for targeted revision, practice, and confidence building.
90 MCQs (1821-1910):
- Which of the following best describes anaerobic bacteria?
a) Require oxygen for growth
b) Grow in the presence of oxygen but prefer low oxygen levels
c) Cannot grow in the presence of oxygen
d) Use oxygen but cannot survive without it - Which genus is considered a gram-positive anaerobic cocci?
a) Clostridium
b) Peptostreptococcus
c) Bacteroides
d) Fusobacterium - What is the primary habitat of anaerobic bacteria in the human body?
a) Skin surface
b) Gastrointestinal tract
c) Lungs
d) Bloodstream - Which method is most commonly used to create an anaerobic environment for culture?
a) Candle jar
b) GasPak jar
c) CO₂ incubator
d) UV sterilization - Which anaerobic bacterium is most commonly associated with gas gangrene?
a) Bacteroides fragilis
b) Clostridium perfringens
c) Peptococcus niger
d) Actinomyces israelii - Which gram-negative anaerobic rod is most frequently isolated from human infections?
a) Bacteroides fragilis
b) Fusobacterium nucleatum
c) Prevotella melaninogenica
d) Veillonella parvula - Which test is helpful in differentiating Clostridium species from Bacillus species?
a) Gram stain
b) Catalase test
c) Oxidase test
d) Indole test - Which of the following is a characteristic of Bacteroides fragilis group?
a) Non-spore forming, gram-negative rods
b) Spore-forming, gram-positive rods
c) Aerobic cocci
d) Acid-fast bacilli - Which anaerobic bacterium is implicated in “pulmonary actinomycosis”?
a) Fusobacterium necrophorum
b) Actinomyces israelii
c) Clostridium botulinum
d) Veillonella parvula - Which of the following specimens is least suitable for anaerobic culture?
a) Abscess aspirate
b) Blood culture
c) Throat swab
d) Deep wound tissue - Which environment is most suitable for strict anaerobes?
a) 21% oxygen
b) Microaerophilic conditions
c) Absence of oxygen
d) High humidity and oxygen - Which anaerobe is most associated with intra-abdominal infections?
a) Bacteroides fragilis
b) Fusobacterium necrophorum
c) Clostridium tetani
d) Veillonella parvula - The presence of a “double zone of hemolysis” on blood agar is characteristic of:
a) Clostridium perfringens
b) Clostridium difficile
c) Fusobacterium nucleatum
d) Bacteroides fragilis - Which anaerobic gram-positive rod produces terminal spores and causes tetanus?
a) Clostridium botulinum
b) Clostridium difficile
c) Clostridium tetani
d) Clostridium perfringens - Which method is best for transporting anaerobic specimens?
a) Cotton swab in saline
b) Anaerobic transport vial with reducing medium
c) Dry sterile container
d) Refrigerated plastic bag - Which of the following is NOT a recommended specimen for anaerobic culture?
a) Pus from deep abscess
b) Cerebrospinal fluid
c) Throat swab
d) Tissue biopsy from deep wound - Which anaerobe is associated with “Lemierre’s syndrome”?
a) Fusobacterium necrophorum
b) Clostridium perfringens
c) Actinomyces israelii
d) Bacteroides fragilis - Which biochemical test is useful for identifying Bacteroides fragilis group?
a) Indole test
b) Catalase test
c) Bile esculin hydrolysis
d) Urease test - The “Nagler reaction” is used to detect the toxin of:
a) Clostridium difficile
b) Clostridium perfringens
c) Clostridium tetani
d) Clostridium botulinum - Which anaerobe is part of normal oral flora but can cause brain abscesses?
a) Actinomyces israelii
b) Clostridium botulinum
c) Fusobacterium nucleatum
d) Veillonella parvula - Which reducing agent is commonly added to anaerobic culture media to maintain low redox potential?
a) Thiosulfate
b) Sodium thioglycolate
c) Methylene blue
d) Phenol red - Which anaerobic bacterium produces neurotoxins that block acetylcholine release?
a) Clostridium perfringens
b) Clostridium botulinum
c) Clostridium tetani
d) Fusobacterium necrophorum - Which anaerobic gram-negative rod produces black colonies due to pigment production?
a) Prevotella melaninogenica
b) Bacteroides fragilis
c) Fusobacterium nucleatum
d) Veillonella parvula - What is the purpose of resazurin in anaerobic media?
a) Carbon source
b) pH indicator
c) Redox indicator
d) Oxygen scavenger - Which anaerobic gram-positive rod is associated with pseudomembranous colitis?
a) Clostridium tetani
b) Clostridium botulinum
c) Clostridium difficile
d) Clostridium septicum - Which anaerobic technique involves displacement of oxygen with another gas before inoculation?
a) GasPak method
b) Anaerobic glove box
c) Pre-reduced media
d) CO₂ incubator - The “reverse CAMP test” is useful for identification of:
a) Clostridium perfringens
b) Clostridium difficile
c) Actinomyces israelii
d) Fusobacterium necrophorum - Which anaerobe has a characteristic “bread crumb” colony appearance?
a) Bacteroides fragilis
b) Fusobacterium nucleatum
c) Actinomyces israelii
d) Veillonella parvula - Which anaerobic organism can cause botulism in infants from honey consumption?
a) Clostridium difficile
b) Clostridium botulinum
c) Clostridium tetani
d) Clostridium perfringens - Which anaerobe is best detected using KVLB (Kanamycin-Vancomycin-Laked Blood) agar?
a) Bacteroides fragilis
b) Fusobacterium necrophorum
c) Prevotella melaninogenica
d) Veillonella parvula - Which of the following groups of specimens would be acceptable for anaerobic culture?
a) Vaginal swab, eye swab
b) Intraoral surface swab, leg tissue
c) Pleural fluid, brain abscess fluid
d) Urine, sputum - The optimal collection method for a wound specimen for anaerobic culture is a:
a) Swab of lesion obtained before antibiotics
b) Swab of lesion obtained after antibiotics
c) Syringe filled with pus, obtained before antibiotics
d) Syringe filled with pus, obtained after antibiotics - Acceptable specimen sources for anaerobic bacteria culture include:
a) Sputum
b) Stool
c) Suprapubic bladder aspiration
d) Vaginal swab - Anaerobic infections differ from aerobic infections in that they:
a) Usually respond favorably to aminoglycoside therapy
b) Usually arise from exogenous sources
c) Are typically polymicrobic
d) Have Gram stains less helpful in diagnosis - Which anaerobe is inhibited by sodium polyanethol sulfonate (SPS)?
a) Bacteroides fragilis
b) Cutibacterium acnes
c) Peptostreptococcus anaerobius
d) Veillonella parvula - For presumptive identification of non-spore-forming pleomorphic gram-positive bacilli (likely Cutibacterium acnes) from anaerobic blood cultures, perform:
a) Beta-hemolysis and oxidase tests
b) Catalase and spot indole tests
c) Esculin hydrolysis
d) Gelatin hydrolysis - Anaerobic gram-positive bacilli with subterminal spores and swarming colonies from a peritoneal abscess are likely:
a) Bacillus cereus
b) Clostridium septicum
c) Eggerthella lenta
d) Bifidobacterium dentium - To identify large gram-positive bacilli with double-zone hemolysis (suggesting Clostridium perfringens), use:
a) Glucose fermentation test
b) Oxidase test
c) Egg yolk agar plate
d) Bile tolerance test - An organism from a peritoneal abscess growing black colonies on BBE agar, nonpigmented, catalase-positive, and indole-negative is:
a) Acidaminococcus
b) Bacteroides
c) Porphyromonas
d) Prevotella - Thin gram-negative bacilli with tapered ends, indole-positive, lipase-negative, and bile-inhibited from an empyema are likely:
a) Bacteroides distasonis
b) Prevotella melaninogenica
c) Fusobacterium nucleatum
d) Clostridium septicum - For Clostridioides difficile culture, use ________ medium, where colonies appear ________.
a) BBE; black
b) Brucella agar; red-pigmented
c) CCFA; yellow, ground glass
d) CNA; double-zone hemolytic - Growth on both aerobic and anaerobic plates at 24 hours indicates the organism is a(n):
a) Nonfermenter
b) Obligate anaerobe
c) Aerobe
d) Facultative anaerobe - Presumptive evidence of anaerobic bacteria in a clinical specimen is:
a) Presence of a single bacterial species
b) Gas production in thioglycolate broth
c) Growth on anaerobic blood agar
d) Foul, putrid odor - Gram stain of a thigh wound shows gram-positive spore-forming bacilli. No growth aerobically after 3 days suggests incubation should be:
a) On chocolate agar
b) Extended to 5 days
c) Under 5% CO₂
d) Anaerobically - After 48 hours, growth only on the anaerobic plate requires:
a) Reincubation for 24 hours
b) Gram stain and identification
c) Requesting blood cultures
d) Bauer-Kirby susceptibility test - Anaerobic, box-car shaped, beta-hemolytic gram-positive bacilli from a foot wound are likely:
a) Actinomyces israelii
b) Clostridium perfringens
c) Bacillus subtilis
d) Eggerthella lenta - The most common anaerobic bacterium isolated from soft tissue infections and bacteremia is:
a) Bacteroides fragilis
b) Fusobacterium nucleatum
c) Porphyromonas asaccharolytica
d) Clostridium perfringens - Sodium polyanethol sulfonate (SPS) in blood cultures inhibits:
a) Bacteroides fragilis
b) Cutibacterium acnes
c) Peptostreptococcus anaerobius
d) Fusobacterium nucleatum - Anaerobic gram-negative bacilli that grow on BBE agar and hydrolyze esculin to form black colonies are likely:
a) Porphyromonas
b) Prevotella
c) Bacteroides fragilis
d) Fusobacterium - Brick-red fluorescence under UV light in anaerobic cultures suggests:
a) Clostridium difficile
b) Prevotella melaninogenica
c) Bacteroides ovatus
d) Veillonella parvula - Which anaerobe requires bile for growth?
a) Fusobacterium necrophorum
b) Porphyromonas asaccharolytica
c) Bacteroides fragilis
d) Clostridium perfringens - Gram-variable bacilli clustered on vaginal epithelial cells (“clue cells”) indicate:
a) Lactobacillus
b) Gardnerella vaginalis
c) Mobiluncus
d) Peptostreptococcus - Reverse CAMP test positivity is characteristic of:
a) Streptococcus agalactiae
b) Clostridium perfringens
c) Actinomyces israelii
d) Bifidobacterium - Anaerobic infections are LEAST likely to originate from:
a) Brain abscess
b) Diabetic foot ulcer
c) Oropharyngeal swab
d) Intra-abdominal abscess - The “safety-pin” morphology on Gram stain is characteristic of:
a) Clostridium tetani
b) Bacteroides fragilis
c) Fusobacterium nucleatum
d) Yersinia pestis (anaerobic variant) - Which medium is selective for Bacteroides?
a) Thiosulfate citrate bile salts (TCBS)
b) Bacteroides bile esculin (BBE)
c) Charcoal yeast extract (CYE)
d) Campylobacter blood agar - A foul odor in a wound culture suggests:
a) Pseudomonas aeruginosa
b) Staphylococcus aureus
c) Anaerobic bacteria
d) Streptococcus pyogenes - Which anaerobic bacterium is most often linked to botulism from improperly canned foods?
a) Clostridium botulinum
b) Clostridium perfringens
c) Bacteroides fragilis
d) Actinomyces israelii - The primary energy source for most anaerobic bacteria is:
a) Aerobic respiration
b) Anaerobic respiration or fermentation
c) Photosynthesis
d) Nitrogen fixation - Which anaerobe is commonly part of the skin microbiota and can cause prosthetic joint infections?
a) Peptostreptococcus anaerobius
b) Clostridium septicum
c) Cutibacterium acnes
d) Veillonella parvula - What is the main inhibitory effect of oxygen on anaerobic bacteria?
a) Denaturation of ribosomal proteins
b) Oxidative damage to essential enzymes
c) Disruption of DNA replication
d) Inhibition of lipid synthesis - Which anaerobic pathogen is associated with foodborne illness involving reheated meats?
a) Clostridium botulinum
b) Clostridium perfringens
c) Fusobacterium nucleatum
d) Prevotella intermedia - The term “obligate anaerobe” means:
a) Can survive with or without oxygen
b) Requires oxygen for survival
c) Killed by prolonged oxygen exposure
d) Prefers low oxygen but tolerates some - Which anaerobe is linked with Lemierre’s syndrome involving septic thrombophlebitis of the internal jugular vein?
a) Fusobacterium nucleatum
b) Fusobacterium necrophorum
c) Bacteroides thetaiotaomicron
d) Actinomyces gerencseriae - Which anaerobic gram-negative rod is bile-resistant and catalase-positive?
a) Prevotella melaninogenica
b) Fusobacterium nucleatum
c) Bacteroides fragilis
d) Veillonella parvula - Which anaerobe is known for “molar tooth” colony morphology?
a) Actinomyces israelii
b) Clostridium septicum
c) Veillonella parvula
d) Bifidobacterium adolescentis - Which organism produces a neurotoxin that causes flaccid paralysis?
a) Clostridium tetani
b) Clostridium botulinum
c) Fusobacterium necrophorum
d) Bacteroides fragilis - Which medium contains hemin and vitamin K to enhance anaerobe recovery?
a) MacConkey agar
b) Brucella blood agar
c) CCFA agar
d) TCBS agar - Which anaerobe can cross the placenta causing neonatal sepsis?
a) Clostridium perfringens
b) Fusobacterium nucleatum
c) Prevotella bivia
d) Veillonella parvula - Which feature helps differentiate Clostridium difficile from other Clostridium spp.?
a) Lecithinase production
b) Toxin A and Toxin B production
c) Lipase positivity
d) Gas gangrene formation - Which anaerobe is associated with sulfur granules in draining sinuses?
a) Actinomyces israelii
b) Clostridium septicum
c) Fusobacterium necrophorum
d) Prevotella melaninogenica - Which anaerobic infection is often accompanied by a foul-smelling discharge?
a) Staphylococcus aureus infection
b) Pseudomonas aeruginosa infection
c) Anaerobic bacterial infection
d) Streptococcus pyogenes infection - Which anaerobic rod can cause myonecrosis without trauma?
a) Clostridium septicum
b) Bacteroides fragilis
c) Fusobacterium nucleatum
d) Actinomyces israelii - Which anaerobic gram-negative coccus is part of normal oral flora?
a) Veillonella parvula
b) Peptostreptococcus anaerobius
c) Bacteroides fragilis
d) Prevotella melaninogenica - Which antibiotic is most active against many anaerobic infections?
a) Gentamicin
b) Metronidazole
c) Ciprofloxacin
d) Vancomycin - Which anaerobe is a major cause of intrauterine infections after prolonged rupture of membranes?
a) Fusobacterium nucleatum
b) Bacteroides fragilis
c) Clostridium perfringens
d) Prevotella bivia - Which anaerobic bacterium is gram-positive, spore-forming, and produces a potent alpha toxin?
a) Clostridium perfringens
b) Clostridium tetani
c) Clostridium botulinum
d) Actinomyces israelii - Which specimen is appropriate for anaerobic culture?
a) Surface wound swab
b) Deep aspirate from abscess
c) Saliva sample
d) Sputum sample - Which gas mixture is typically used in anaerobe jars?
a) 80% nitrogen, 10% hydrogen, 10% CO₂
b) 50% oxygen, 50% CO₂
c) 70% nitrogen, 20% oxygen, 10% CO₂
d) 100% nitrogen - Which anaerobe is catalase-negative and produces indole?
a) Fusobacterium nucleatum
b) Bacteroides fragilis
c) Clostridium septicum
d) Veillonella parvula - Which anaerobic bacterium is associated with Vincent’s angina (trench mouth)?
a) Fusobacterium nucleatum
b) Prevotella melaninogenica
c) Actinomyces israelii
d) Bacteroides fragilis - Which anaerobic gram-negative bacillus is non-pigmented and saccharolytic?
a) Bacteroides fragilis
b) Porphyromonas asaccharolytica
c) Prevotella melaninogenica
d) Veillonella parvula - Which organism shows “drumstick” shaped spores on microscopy?
a) Clostridium tetani
b) Clostridium botulinum
c) Clostridium septicum
d) Clostridium difficile - Which anaerobic bacteria are most often involved in aspiration pneumonia?
a) Bacteroides and Fusobacterium
b) Pseudomonas and Klebsiella
c) Lactobacillus and Corynebacterium
d) Escherichia coli and Proteus - Which anaerobe is part of normal vaginal flora but can cause pelvic inflammatory disease?
a) Bacteroides fragilis
b) Prevotella bivia
c) Fusobacterium necrophorum
d) Actinomyces israelii - Which anaerobic infection often follows human bite wounds?
a) Pasteurella multocida
b) Eikenella corrodens and anaerobes
c) Bacteroides fragilis only
d) Staphylococcus aureus only - Which pigment is produced by Porphyromonas species?
a) Black pigment from hemin breakdown
b) Green pigment from pyoverdine
c) Blue pigment from pyocyanin
d) Yellow pigment from carotenoids - Which anaerobe produces a “horse stable” odor in culture?
a) Clostridium difficile
b) Clostridium septicum
c) Clostridium tetani
d) Clostridium botulinum - Which anaerobic culture method uses pre-reduced, anaerobically sterilized media?
a) Streak plating in ambient air
b) Broth dilution method
c) PRAS technique
d) Ziehl-Neelsen method - Which anaerobic bacterium is most often isolated from diabetic foot infections?
a) Bacteroides fragilis
b) Clostridium septicum
c) Fusobacterium nucleatum
d) Prevotella melaninogenica
Answer Key
Answer Key:
- c) Cannot grow in the presence of oxygen
- b) Peptostreptococcus
- b) Gastrointestinal tract
- b) GasPak jar
- b) Clostridium perfringens
- a) Bacteroides fragilis
- b) Catalase test
- a) Non-spore forming, gram-negative rods
- b) Actinomyces israelii
- c) Throat swab
- c) Absence of oxygen
- a) Bacteroides fragilis
- a) Clostridium perfringens
- c) Clostridium tetani
- b) Anaerobic transport vial with reducing medium
- c) Throat swab
- a) Fusobacterium necrophorum
- c) Bile esculin hydrolysis
- b) Clostridium perfringens
- c) Fusobacterium nucleatum
- b) Sodium thioglycolate
- b) Clostridium botulinum
- a) Prevotella melaninogenica
- c) Redox indicator
- c) Clostridium difficile
- a) GasPak method
- a) Clostridium perfringens
- c) Actinomyces israelii
- b) Clostridium botulinum
- c) Prevotella melaninogenica
- c) Pleural fluid, brain abscess fluid
- c) Syringe filled with pus, obtained before antibiotics
- c) Suprapubic bladder aspiration
- c) Are typically polymicrobic
- c) Peptostreptococcus anaerobius
- b) Catalase and spot indole tests
- b) Clostridium septicum
- c) Egg yolk agar plate
- b) Bacteroides
- c) Fusobacterium nucleatum
- c) CCFA; yellow, ground glass
- d) Facultative anaerobe
- d) Foul, putrid odor
- d) Anaerobically
- b) Gram stain and identification
- b) Clostridium perfringens
- a) Bacteroides fragilis
- c) Peptostreptococcus anaerobius
- c) Bacteroides fragilis
- b) Prevotella melaninogenica
- c) Bacteroides fragilis
- b) Gardnerella vaginalis
- b) Clostridium perfringens
- c) Oropharyngeal swab
- d) Yersinia pestis (anaerobic variant)
- b) Bacteroides bile esculin (BBE)
- c) Anaerobic bacteria
- a) Clostridium botulinum
- b) Anaerobic respiration or fermentation
- c) Cutibacterium acnes
- b) Oxidative damage to essential enzymes
- b) Clostridium perfringens
- c) Killed by prolonged oxygen exposure
- b) Fusobacterium necrophorum
- c) Bacteroides fragilis
- a) Actinomyces israelii
- b) Clostridium botulinum
- b) Brucella blood agar
- b) Fusobacterium nucleatum
- b) Toxin A and Toxin B production
- a) Actinomyces israelii
- c) Anaerobic bacterial infection
- a) Clostridium septicum
- a) Veillonella parvula
- b) Metronidazole
- a) Fusobacterium nucleatum
- a) Clostridium perfringens
- b) Deep aspirate from abscess
- a) 80% nitrogen, 10% hydrogen, 10% CO₂
- a) Fusobacterium nucleatum
- a) Fusobacterium nucleatum
- a) Bacteroides fragilis
- a) Bacteroides fragilis
- a) Bacteroides and Fusobacterium
- b) Prevotella bivia
- b) Eikenella corrodens and anaerobes
- a) Black pigment from hemin breakdown
- a) Clostridium difficile
- c) PRAS technique
- a) Bacteroides fragilis
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
Tags:
#ASCPMLS #MLSexam #LabTech #MedicalLaboratory #BOCexam #FreePracticeQuestions #QualityControl #LaboratorySafety
