Prepare for the ASCP MLS exam with 40 fresh multiple-choice questions on bacterial identification methods. Covers biochemical tests, selective media, automated systems, and molecular diagnostics.
Bacterial identification is a cornerstone of diagnostic microbiology, helping laboratory professionals accurately detect pathogens and guide patient care. This practice set focuses on the methods used to differentiate and identify clinically important bacteria.
The questions cover a wide range of traditional and modern laboratory techniques, including:
- Biochemical tests (catalase, oxidase, indole, urease, bile esculin, CAMP, hippurate hydrolysis, carbohydrate fermentation).
- Selective and differential media (MacConkey agar, chromogenic media, mannitol salt agar, X and V factor requirements for Haemophilus).
- Rapid and automated methods (API strips, VITEK, MALDI-TOF mass spectrometry).
- Molecular approaches (16S rRNA sequencing, nucleic acid amplification tests, whole-genome sequencing).
- Specialized tests (string test for Vibrio, reverse CAMP for Clostridium, D-test for inducible clindamycin resistance, India ink for Cryptococcus).
This set of 40 fresh MCQs is designed for medical laboratory students and professionals preparing for certification exams such as ASCP MLS, AMT, or state licensure tests. Practicing these questions will strengthen your understanding of bacterial identification techniques used in real-world clinical labs.
100 MCQs (2341-2440):
- Which test is used to differentiate Staphylococcus aureus from other staphylococci?
a) Oxidase
b) Catalase
c) Coagulase
d) Optochin susceptibility - The optochin disk is used for the identification of:
a) Haemophilus influenzae
b) Group A beta-hemolytic streptococci
c) Streptococcus pneumoniae
d) Enterococcus - Which of the following tests is used to identify Streptococcus agalactiae?
a) Bacitracin susceptibility
b) CAMP test
c) Bile esculin hydrolysis
d) Hippurate hydrolysis - Gamma-hemolytic streptococci that blacken bile esculin agar but do not grow in 6.5% NaCl broth are most likely:
a) Group B Streptococcus
b) Enterococcus
c) Group D Streptococcus (Streptococcus bovis group)
d) Streptococcus pneumoniae - A positive CAMP test is indicative of:
a) Streptococcus pyogenes
b) Streptococcus agalactiae
c) Staphylococcus aureus
d) Enterococcus faecalis - Which test is used to distinguish Enterococcus from group D streptococci?
a) Growth in 6.5% NaCl
b) PYR hydrolysis
c) Bacitracin susceptibility
d) Optochin susceptibility - The ONPG test detects the presence of:
a) Beta-lactamase
b) Beta-galactosidase
c) Cytochrome oxidase
d) Catalase - Which of the following is a reliable test for Neisseria gonorrhoeae identification?
a) Maltose fermentation
b) Glucose fermentation
c) Sucrose fermentation
d) Lactose fermentation - Moraxella catarrhalis can be differentiated from Neisseria species by its:
a) Oxidase positivity
b) DNase production
c) Carbohydrate utilization
d) Gram stain morphology - The satellite phenomenon is associated with which organism?
a) Neisseria meningitidis
b) Haemophilus influenzae
c) Streptococcus pneumoniae
d) Staphylococcus aureus - Which of the following is used to differentiate Listeria monocytogenes from Corynebacterium species?
a) Catalase test
b) Motility at 25°C
c) Gram stain
d) Hemolysis on blood agar - A positive bile solubility test is characteristic of:
a) Streptococcus viridans
b) Streptococcus pneumoniae
c) Enterococcus faecalis
d) Streptococcus agalactiae - Which test is used to detect beta-lactamase production?
a) Oxidase test
b) Nitrocefin test
c) Indole test
d) Urease test - The porphyrin test is used to determine the need for which factor in Haemophilus species?
a) X factor (hemin)
b) V factor (NAD)
c) Both X and V factors
d) Neither X nor V factor - Which of the following is a key characteristic of Pseudomonas aeruginosa?
a) Lactose fermentation
b) Oxidase negativity
c) Growth at 42°C
d) Nonmotile - Which organism is positive for phenylalanine deaminase?
a) Escherichia coli
b) Klebsiella pneumoniae
c) Proteus mirabilis
d) Shigella sonnei - The HACEK group of organisms requires which condition for growth?
a) Anaerobic environment
b) 5–10% CO₂
c) High salt concentration
d) Low pH - Which test is used to differentiate Acinetobacter from Moraxella?
a) Oxidase test
b) Motility test
c) Growth on MacConkey agar
d) All of the above - Which of the following is a nonfermenter?
a) Escherichia coli
b) Klebsiella pneumoniae
c) Pseudomonas aeruginosa
d) Proteus mirabilis - The indole test is used to differentiate:
a) E. coli from Klebsiella
b) Proteus from Providencia
c) Shigella from Salmonella
d) Enterobacter from Serratia - Which of the following is a positive quality control organism for the bile esculin test?
a) Staphylococcus aureus
b) Streptococcus pyogenes
c) Enterococcus faecalis
d) Escherichia coli - The reverse CAMP test is used to identify:
a) Clostridium perfringens
b) Streptococcus agalactiae
c) Staphylococcus aureus
d) Listeria monocytogenes - Which of the following is used to differentiate Micrococcus from Staphylococcus?
a) Catalase test
b) Modified oxidase test
c) Coagulase test
d) Bacitracin susceptibility - A positive hippurate hydrolysis test is indicative of:
a) Streptococcus pyogenes
b) Streptococcus agalactiae
c) Enterococcus faecalis
d) Streptococcus pneumoniae - Which test is used to identify Streptococcus pneumoniae?
a) Bacitracin susceptibility
b) Optochin susceptibility
c) CAMP test
d) PYR test - The ability to grow in 6.5% NaCl is characteristic of:
a) Streptococcus bovis
b) Streptococcus pneumoniae
c) Enterococcus
d) Streptococcus pyogenes - Which of the following is used to differentiate Proteus mirabilis from Proteus vulgaris?
a) Indole test
b) Urease test
c) Citrate test
d) H₂S production - The enzyme detected by the oxidase test is:
a) Catalase
b) Cytochrome c oxidase
c) Peroxidase
d) Superoxide dismutase - Which of the following is a key test for identifying Vibrio cholerae?
a) Oxidase test
b) Urease test
c) Citrate test
d) Phenylalanine deaminase - The test that uses tetramethyl-p-phenylenediamine is the:
a) Catalase test
b) Oxidase test
c) Indole test
d) Coagulase test - A catalase-negative, gram-positive coccus that hydrolyzes hippurate is most likely:
a) Streptococcus pyogenes
b) Streptococcus agalactiae
c) Enterococcus faecalis
d) Staphylococcus epidermidis - The test used to detect inducible clindamycin resistance in staphylococci is called the:
a) CAMP test
b) D test
c) PYR test
d) Bacitracin test - Which of the following organisms is bile-esculin positive but does NOT grow in 6.5% NaCl?
a) Enterococcus faecium
b) Streptococcus bovis
c) Streptococcus pneumoniae
d) Streptococcus agalactiae - A gram-negative diplococcus that is oxidase-positive, ferments glucose, but not maltose is:
a) Neisseria meningitidis
b) Neisseria lactamica
c) Neisseria gonorrhoeae
d) Moraxella catarrhalis - A positive “string test” is indicative of which genus?
a) Klebsiella
b) Vibrio
c) Aeromonas
d) Pseudomonas - Which set of biochemical results is characteristic of Escherichia coli?
a) TSI A/A, Gas +, H₂S –, Indole +, Motility +
b) TSI K/A, Gas –, H₂S –, Indole –, Motility –
c) TSI K/A, Gas +, H₂S +, Indole –, Motility +
d) TSI A/A, Gas +, H₂S +, Indole +, Motility – - The primary purpose of the satellite test is to identify the requirement for:
a) X factor (Hemin)
b) V factor (NAD)
c) Both X and V factors
d) Cysteine - Which organism is known for its “swarming” motility on blood agar?
a) Proteus mirabilis
b) Pseudomonas aeruginosa
c) Klebsiella pneumoniae
d) Escherichia coli - A gram-positive bacillus that is catalase-positive, motile at 25°C, and exhibits “tumbling” motility is:
a) Corynebacterium diphtheriae
b) Listeria monocytogenes
c) Bacillus cereus
d) Clostridium perfringens - The ability to hydrolyze urea rapidly (within minutes) is a key characteristic of:
a) Proteus vulgaris
b) Klebsiella pneumoniae
c) Helicobacter pylori
d) Pseudomonas aeruginosa - A gram-negative rod that is oxidase-positive, nonfermentative, and produces a blue-green pigment is:
a) Acinetobacter baumannii
b) Stenotrophomonas maltophilia
c) Pseudomonas aeruginosa
d) Burkholderia cepacia - Which test is used to differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci?
a) Bile solubility
b) Hippurate hydrolysis
c) VP test
d) Nitrate reduction - A positive PYR test is useful for the identification of:
a) Streptococcus pyogenes and Enterococcus
b) Staphylococcus aureus and Staphylococcus epidermidis
c) Neisseria meningitidis and Neisseria gonorrhoeae
d) Escherichia coli and Klebsiella pneumoniae - The HACEK group of organisms is most commonly associated with:
a) Urinary tract infections
b) Nosocomial pneumonia
c) Bacterial endocarditis
d) Gastroenteritis - A gram-negative coccobacillus that requires both X and V factors for growth is:
a) Haemophilus influenzae
b) Haemophilus parainfluenzae
c) Bordetella pertussis
d) Brucella melitensis - Which of the following is a key characteristic of the genus Bacteroides?
a) Strict aerobe
b) Susceptible to vancomycin
c) Resistant to colistin
d) Bile-resistant - A positive CAMP test shows:
a) Enhanced hemolysis between two organisms
b) Hydrolysis of hippurate
c) Reduction of nitrate
d) Production of cytochrome oxidase - The compound tetramethyl-p-phenylenediamine is used in the:
a) Catalase test
b) Coagulase test
c) Oxidase test
d) Indole test - A gram-positive coccus that is novobiocin-resistant is most likely:
a) Staphylococcus saprophyticus
b) Staphylococcus epidermidis
c) Staphylococcus aureus
d) Micrococcus luteus - Which organism produces a “fried egg” colony morphology on solid media?
a) Mycoplasma pneumoniae
b) Chlamydia trachomatis
c) Mycobacterium tuberculosis
d) Nocardia asteroides - The ability to produce deoxyribonuclease (DNase) is a characteristic of:
a) Serratia marcescens
b) Shigella sonnei
c) Salmonella Typhi
d) Yersinia enterocolitica - A gram-negative rod that is urease-positive, motile, and produces H₂S on TSI agar is:
a) Proteus mirabilis
b) Klebsiella pneumoniae
c) Escherichia coli
d) Providencia stuartii - The reagent used in the spot indole test is:
a) Kovac’s reagent
b) Oxidase reagent
c) 3% Hydrogen peroxide
d) 1% Alpha-naphthol - A positive test for phenylalanine deaminase will result in a:
a) Green color after adding ferric chloride
b) Red color after adding Barrett’s reagent
c) Blue color after adding oxidase reagent
d) Yellow color after adding nitric acid - Which of the following is a non-spore-forming, anaerobic gram-positive bacillus?
a) Clostridium difficile
b) Actinomyces israelii
c) Bacillus anthracis
d) Listeria monocytogenes - The “beaten copper” appearance is characteristic of which organism’s colony?
a) Corynebacterium diphtheriae
b) Listeria monocytogenes
c) Bacillus anthracis
d) Erysipelothrix rhusiopathiae - Which test is used to differentiate Klebsiella pneumoniae from Enterobacter cloacae?
a) Motility
b) Indole
c) Citrate
d) Urease - A gram-negative rod that is oxidase-positive and ferments glucose would be classified as a:
a) Nonfermenter
b) Enteric
c) Vibrionaceae
d) Fastidious gram-negative rod - The ability to hydrolyze esculin in the presence of bile is a characteristic of:
a) Group A streptococci
b) Group B streptococci
c) Enterococci and group D streptococci
d) Pseudomonas aeruginosa - The primary stain used in the acid-fast staining procedure is:
a) Crystal violet
b) Carbol fuchsin
c) Methylene blue
d) Safranin - Which molecular technique is commonly used for bacterial genus-species identification by targeting conserved genetic regions?
a) MALDI-TOF
b) 16S rRNA gene sequencing
c) Gram staining
d) Oxidase test - The API (Analytical Profile Index) system helps in identification using:
a) Genetic sequencing
b) Biochemical test panels
c) Serotyping
d) Phage typing - A rapid method distinguishing lactose fermenters from non-fermenters on agar is:
a) Blood agar
b) Mannitol salt agar
c) Eosin methylene blue agar
d) Nutrient agar - In blood culture processing, the first step after detecting growth is typically:
a) Biochemical testing
b) Serotyping
c) Gram stain
d) Whole genome sequencing - IMViC stands for:
a) Indole, Mannitol, Voges–Proskauer, Catalase
b) Indole, Methyl red, Voges–Proskauer, Citrate
c) Indole, Motility, VP, Catalase
d) Indole, MR, VP, Coagulase - The oxidase test detects:
a) Catalase enzyme
b) Cytochrome c oxidase
c) Lactose fermentation
d) Indole production - Phenotypic identification of bacteria is most often supplemented by:
a) Gram staining alone
b) Molecular tests like DNA sequencing
c) Only colony color
d) Acid-fast staining - Which molecular marker is most widely used in phylogenetic bacterial classification?
a) 23S rRNA
b) 16S rRNA
c) gyrB
d) ITS region - Label-free bacterial identification through Fourier Transform Light Scattering is:
a) A biochemical test
b) A molecular method
c) An optical technique
d) A staining procedure - The IMViC pattern for Escherichia coli is:
a) +, +, –, –
b) –, –, +, +
c) +, –, +, –
d) –, +, –, + - MALDI-TOF identifies bacteria via:
a) DNA sequencing
b) Mass spectrometry of cell proteins
c) Biochemical reactions
d) Gram reaction - Selective and differential media support growth and identification by:
a) Genotypic methods
b) Direct staining
c) Combining selective inhibition and visual differentiation
d) Only inhibiting unwanted bacteria - 16S rRNA sequencing still performs well even when:
a) Culture yields many contaminants
b) Prior antibiotic use is present
c) Sample is environmental soil
d) Bacteria are gram-positive - Biochemical tests in 96-well substrates analyze:
a) Morphology
b) Antibiotic susceptibility
c) Multiple substrate utilization simultaneously
d) Gram type only - For precise strain-level subtyping, molecular techniques may include:
a) Gram stain
b) Serotyping or whole-genome sequencing
c) Catalase testing
d) Colony morphology alone - The API20NE strip is primarily used to identify:
a) Enterobacteriaceae
b) Non-enteric Gram-negative bacilli
c) Gram-positive cocci
d) Anaerobes - In blood culture identification, colony features help guide:
a) Staining method only
b) Selection of biochemical tests
c) Sequencing directly
d) MALDI-TOF exclusively - The IMViC test series is especially useful for identifying:
a) Gram-positive cocci
b) Coliforms like Enterobacteriaceae
c) Acid-fast bacteria
d) Spirochetes - Oxidase test helps differentiate:
a) Pseudomonads from Enterobacteriaceae
b) All fermenters vs non-fermenters
c) Gram + vs Gram –
d) Only between Streptococci species - Serotyping for bacterial identification involves:
a) Genetic sequencing
b) Detecting surface antigens via specific antibodies
c) Gram staining
d) Optochin sensitivity - Whole-genome sequencing provides:
a) Only genus-level info
b) Subspecies and strain-level resolution
c) Gram status
d) Only biochemical profiles - Differential staining used for respiratory pathogens includes:
a) Gram stain only
b) Acid-fast or special stains based on organism type
c) None—culture only
d) Capsule stain exclusively - Biolog multiwell plates identify bacteria via:
a) Serotyping
b) Antibiotic resistance
c) Metabolic phenotype patterns
d) Gram reaction - DNA–DNA hybridization in bacterial ID serves to:
a) Identify motility
b) Compare genetic relatedness between organisms
c) Detect catalase
d) Measure growth rate - GC content analysis helps in:
a) Assessing peptidoglycan thickness
b) Taxonomic identification at genetic level
c) Determining fermentation pathways
d) Differentiating oxidase production - Traditional phenotypic techniques include:
a) Whole-genome sequencing
b) Staining, culturing, biochemical tests
c) MALDI-TOF only
d) Only selective media - Immunological identification methods rely on detecting:
a) DNA sequences
b) Specific microbial antigens or antibodies
c) Enzyme activity
d) Colony color - NAAT stands for:
a) Non-Antigenic Agglutination Test
b) Nucleic Acid Amplification Technique
c) Neuro-Acid Antibody Test
d) Non-culture Anaerobic Assay Technique - Direct microscopy as an ID method is considered:
a) A serological test
b) A non-culture technique
c) A biochemical panel
d) Molecular sequencing - Immunochromatographic testing identifies pathogens via:
a) DNA profiling
b) Antibody-antigen reactions on test strips
c) Gram staining
d) Heat fixation patterns - Chromogenic media aids identification by:
a) Using antibodies
b) Producing color changes specific to organisms
c) Sequencing DNA
d) Only inhibiting growth - Direct examination, growth, and analysis of cultures are:
a) Only molecular steps
b) Sequential traditional identification steps
c) Immunological tests
d) None of the above - India ink is typically used for:
a) Acid-fast staining
b) Simple stain only
c) Negative staining to visualize capsules
d) Gram-negative rod detection - Dark-field microscopy is most useful for detecting:
a) E. coli
b) Treponema pallidum
c) Staphylococcus aureus
d) Bacillus anthracis - Chromogenic, molecular, immunologic tests are examples of:
a) Phenotypic methods
b) Non-traditional identification techniques
c) Only culture-based methods
d) Only Gram-dependent tests - Catalase presence is tested by adding hydrogen peroxide and looking for:
a) Color change
b) Bubble formation
c) Colony swelling
d) Hemolysis - Subtyping below species level may involve:
a) Gram staining alone
b) Identification of plasmids, toxins, or serotypes
c) Only culture morphology
d) Only catalase testing - Multilocus sequence typing (MLST) identifies:
a) Colony color
b) Sequence types using several conserved genes
c) Only 16S rRNA sequences
d) Biochemical reaction speed - Biochemical test plates like the substrate panels help identify bacteria by:
a) Genetic profiling
b) Observing utilization of various substrates visually
c) Measuring turbidity only
d) Only discerning Gram type - Molecular phylogeny complements phenotypic ID by:
a) Being slower than culture
b) Confirming species based on genetic relationships
c) Ignoring biochemical traits
d) Only for viral diagnostics
Answer Key
Answer Key:
- c) Coagulase
- c) Streptococcus pneumoniae
- c) Bile esculin hydrolysis
- c) Group D Streptococcus (Streptococcus bovis group)
- b) Streptococcus agalactiae
- a) Growth in 6.5% NaCl
- b) Beta-galactosidase
- b) Glucose fermentation
- b) DNase production
- b) Haemophilus influenzae
- b) Motility at 25°C
- b) Streptococcus pneumoniae
- b) Nitrocefin test
- a) X factor (hemin)
- c) Growth at 42°C
- c) Proteus mirabilis
- b) 5–10% CO₂
- a) Oxidase test
- c) Pseudomonas aeruginosa
- a) E. coli from Klebsiella
- c) Enterococcus faecalis
- a) Clostridium perfringens
- b) Modified oxidase test
- b) Streptococcus agalactiae
- b) Optochin susceptibility
- c) Enterococcus
- a) Indole test
- b) Cytochrome c oxidase
- a) Oxidase test
- b) Oxidase test
- b) Streptococcus agalactiae
- b) D test
- b) Streptococcus bovis
- c) Neisseria gonorrhoeae
- b) Vibrio
- a) TSI A/A, Gas +, H₂S –, Indole +, Motility +
- b) V factor (NAD)
- a) Proteus mirabilis
- b) Listeria monocytogenes
- c) Helicobacter pylori
- c) Pseudomonas aeruginosa
- a) Bile solubility
- a) Streptococcus pyogenes and Enterococcus
- c) Bacterial endocarditis
- a) Haemophilus influenzae
- d) Bile-resistant
- a) Enhanced hemolysis between two organisms
- c) Oxidase test
- a) Staphylococcus saprophyticus
- a) Mycoplasma pneumoniae
- a) Serratia marcescens
- a) Proteus mirabilis
- a) Kovac’s reagent
- a) Green color after adding ferric chloride
- b) Actinomyces israelii
- c) Bacillus anthracis
- a) Motility
- c) Vibrionaceae
- c) Enterococci and group D streptococci
- b) Carbol fuchsin
- b) 16S rRNA gene sequencing
- b) Biochemical test panels
- c) Eosin methylene blue agar
- c) Gram stain
- b) Indole, Methyl red, Voges–Proskauer, Citrate
- b) Cytochrome c oxidase
- b) Molecular tests like DNA sequencing
- b) 16S rRNA
- c) An optical technique
- a) +, +, –, –
- b) Mass spectrometry of cell proteins
- c) Combining selective inhibition and visual differentiation
- b) Prior antibiotic use is present
- c) Multiple substrate utilization simultaneously
- b) Serotyping or whole-genome sequencing
- b) Non-enteric Gram-negative bacilli
- b) Selection of biochemical tests
- b) Coliforms like Enterobacteriaceae
- a) Pseudomonads from Enterobacteriaceae
- b) Detecting surface antigens via specific antibodies
- b) Subspecies and strain-level resolution
- b) Acid-fast or special stains based on organism type
- c) Metabolic phenotype patterns
- b) Compare genetic relatedness between organisms
- b) Taxonomic identification at genetic level
- b) Staining, culturing, biochemical tests
- b) Specific microbial antigens or antibodies
- b) Nucleic Acid Amplification Technique
- b) A non-culture technique
- b) Antibody-antigen reactions on test strips
- b) Producing color changes specific to organisms
- b) Sequential traditional identification steps
- c) Negative staining to visualize capsules
- b) Treponema pallidum
- b) Non-traditional identification techniques
- b) Bubble formation
- b) Identification of plasmids, toxins, or serotypes
- b) Sequence types using several conserved genes
- b) Observing utilization of various substrates visually
- b) Confirming species based on genetic relationships
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.
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