Are the ASCP MLS, CSMLS, AIMS, AMT, or IBMS laboratory certification tests something you plan to study for? Gram-negative cocci and their related bacteria are the main subject of this practice exam.
Clinical microbiology diagnosis and effective patient care depend on the precise identification of gram-negative cocci, such as Neisseria gonorrhoeae, Neisseria meningitidis, Moraxella catarrhalis, and Kingella kingae. Serious illnesses linked to these species include endocarditis, otitis media, sepsis, meningitis, and gonorrhea.
This collection of 70 multiple-choice questions (MCQs) (Question IDs: 2071–2140) is designed to test your knowledge on:
- Culture media and growth requirements (Chocolate agar, Modified Thayer-Martin, CO₂ dependency)
- Biochemical differentiation tests (oxidase, carbohydrate utilization, ONPG, butyrate esterase)
- Virulence factors (capsule, endotoxin, IgA protease, beta-lactamase production)
- Key clinical scenarios (urethritis, meningitis, neonatal conjunctivitis, septic arthritis, endocarditis)
- Differentiation from look-alike organisms (Haemophilus, Acinetobacter, Kingella, Moraxella)
- Antibiotic resistance patterns (beta-lactamase, altered PBPs)
By practicing these MCQs, you will strengthen your ability to:
✔ Interpret Gram stain findings in different specimen types
✔ Identify organisms based on biochemical profiles
✔ Recall selective/differential media uses
✔ Apply knowledge to real-world clinical microbiology cases
Whether you are a student preparing for certification or a professional refreshing your knowledge, this mock test will sharpen your diagnostic skills in Gram-Negative Cocci Identification.
👉 Scroll down and attempt all 70 MCQs (2071–2140) to evaluate your preparation!
70 MCQs (2071-2140):
- A urethral swab from a male patient with discharge is plated on chocolate and modified Thayer-Martin agar. The Gram stain shows Gram-negative diplococci. After 48 hours of incubation in ambient air, there is no growth. The most likely reason for this is that the organism:
a) is a contaminant from skin flora.
b) was inhibited by the antibiotics in the Thayer-Martin agar.
c) requires an enhanced CO₂ atmosphere for growth.
d) only grows on blood agar at room temperature. - Which of the following is the most reliable method for the definitive identification of Neisseria gonorrhoeae from a pure culture?
a) Detection of beta-lactamase production
b) Carbohydrate utilization tests
c) Colony morphology on chocolate agar
d) A positive catalase test - A Gram stain of a cervical specimen shows many white blood cells and intracellular Gram-negative diplococci. This finding is considered diagnostic for gonorrhea in which of the following patients?
a) An asymptomatic female
b) A symptomatic male
c) A newborn infant
d) A post-menopausal female - An oxidase-positive, Gram-negative diplococcus is isolated from a sputum culture. It grows on blood and chocolate agars but not on modified Thayer-Martin agar. It does not ferment glucose, maltose, lactose, or sucrose. The most likely identification is:
a) Neisseria meningitidis
b) Neisseria lactamica
c) Moraxella catarrhalis
d) Acinetobacter lwoffii - Which test result is most useful for differentiating Neisseria lactamica from Neisseria meningitidis?
a) Growth on modified Thayer-Martin agar
b) A positive oxidase reaction
c) Rapid hydrolysis of ONPG (o-nitrophenyl-β-D-galactopyranoside)
d) Production of acid from glucose - A Gram-negative diplococcus is isolated from the cerebrospinal fluid of an adolescent. It is oxidase-positive and produces acid from both glucose and maltose. This organism is most likely:
a) Neisseria gonorrhoeae
b) Neisseria meningitidis
c) Moraxella catarrhalis
d) Haemophilus influenzae - Which characteristic is a key difference between Acinetobacter lwoffii and Neisseria gonorrhoeae?
a) Gram stain reaction
b) Ability to grow on MacConkey agar
c) Oxidase production
d) Cell shape - A positive satellite growth phenomenon around a Staphylococcus aureus streak on a blood agar plate is indicative of which organism’s requirement for V factor (NAD)?
a) Neisseria meningitidis
b) Haemophilus influenzae
c) Moraxella catarrhalis
d) Streptococcus pneumoniae - Which of the following organisms may be mistaken for Neisseria gonorrhoeae in Gram-stained smears of endocervical exudates due to its similar morphology?
a) Lactobacillus species
b) Streptococcus agalactiae
c) Moraxella osloensis
d) Pseudomonas aeruginosa - For which specimen type is a Gram stain considered an unreliable method for the diagnosis of Neisseria gonorrhoeae due to the presence of normal flora with similar morphology?
a) Male urethral exudate
b) Cerebrospinal fluid
c) Vaginal discharge
d) Synovial fluid - The HACEK group of bacteria, which can cause endocarditis, is characterized by which common growth requirement?
a) Incubation at 42°C
b) An anaerobic atmosphere
c) An enhanced CO₂ atmosphere
d) X and V factors - An organism isolated from a blood culture displays Gram-negative diplococci and is oxidase-positive. It grows on chocolate agar but not on MacConkey agar. Acid is produced from glucose but not from maltose. This organism is most likely:
a) Neisseria gonorrhoeae
b) Neisseria meningitidis
c) Moraxella catarrhalis
d) Kingella kingae - Which of the following is a characteristic feature of Moraxella catarrhalis colonies?
a) They exhibit a “hockey puck” consistency and can be pushed across the agar surface.
b) They are beta-hemolytic on sheep blood agar.
c) They produce a distinctive green pigment.
d) They require cysteine for growth. - A nasopharyngeal swab from a child with whooping cough is most appropriately cultured for Bordetella pertussis on which medium?
a) Thayer-Martin agar
b) Regan-Lowe agar
c) MacConkey agar
d) Buffered Charcoal Yeast Extract (BCYE) agar - All medically significant Neisseria species share which of the following enzymatic activities?
a) Beta-lactamase production
b) Oxidase production
c) DNase production
d) Hippurate hydrolysis - A Gram stain from a septic joint aspirate reveals numerous neutrophils and many Gram-negative diplococci. The chemistry results of the fluid would most likely show:
a) Decreased glucose, increased protein, increased white blood cells
b) Increased glucose, decreased protein, increased white blood cells
c) Normal glucose, normal protein, normal white blood cells
d) Decreased glucose, decreased protein, decreased white blood cells - Which non-culture method is considered best for the diagnosis of Neisseria gonorrhoeae in an adult female?
a) Gram stain of cervical secretions
b) Latex agglutination
c) Nucleic Acid Amplification Test (NAAT)
d) Catalase test - An oxidase-positive diplococcus is recovered from a genital culture. It ferments glucose but not maltose, lactose, or sucrose. This pattern is characteristic of:
a) Neisseria meningitidis
b) Neisseria lactamica
c) Neisseria gonorrhoeae
d) Moraxella catarrhalis - Kingella kingae, a member of the HACEK group, is best described as:
a) A fastidious Gram-negative rod that requires X and V factor
b) A Gram-negative diplococcus that is oxidase-positive and catalase-negative
c) A Gram-positive rod that is catalase-positive
d) A non-fermentative Gram-negative bacillus - Penicillin resistance in Neisseria gonorrhoeae is most commonly due to:
a) Alteration of penicillin-binding proteins (PBPs)
b) Production of beta-lactamase enzyme
c) Efflux pumps
d) Lack of a cell wall - The drug of choice for treating Neisseria meningitidis infections until susceptibility is known is:
a) Vancomycin
b) Penicillin G
c) Ceftriaxone
d) Azithromycin - Which of the following is a common cause of ophthalmia neonatorum (conjunctivitis in the newborn)?
a) Streptococcus agalactiae
b) Neisseria gonorrhoeae
c) Haemophilus influenzae
d) Staphylococcus aureus - The specimen of choice for the recovery of Neisseria gonorrhoeae from a symptomatic male is:
a) First-catch urine
b) Urethral swab of exudate
c) Clean-catch midstream urine
d) Rectal swab - Which additive in Thayer-Martin or Martin-Lewis agar makes them selective for pathogenic Neisseria?
a) Colistin and nalidixic acid
b) Vancomycin, colistin, and nystatin (or trimethoprim)
c) Cycloheximide
d) Sodium chloride - A positive “butyrate esterase” test is a key rapid test for identifying which organism?
a) Neisseria meningitidis
b) Haemophilus influenzae
c) Moraxella catarrhalis
d) Streptococcus pneumoniae - Neisseria meningitidis can be differentiated from Neisseria lactamica by its:
a) Positive oxidase reaction
b) Ability to grow on selective media
c) Failure to ferment lactose (negative ONPG test)
d) Gram stain morphology - Which of the following is NOT a virulence factor for Neisseria meningitidis?
a) Polysaccharide capsule
b) Endotoxin (LOS)
c) IgA protease
d) Coagulase - The most sensitive test for the initial diagnosis of cryptococcal disease is:
a) India ink prep of CSF
b) Gram stain
c) Cryptococcal antigen test
d) Culture on Sabouraud dextrose agar - A patient presents with recurrent purulent urethral discharge shortly after successful treatment for culture-proven gonorrhea. The most likely co-infecting etiology is:
a) Mycoplasma hominis
b) Chlamydia trachomatis
c) Trichomonas vaginalis
d) Ureaplasma urealyticum - For quality control of the oxidase test, which pair of organisms should be used?
a) Escherichia coli (negative) and Pseudomonas aeruginosa (positive)
b) Staphylococcus aureus (positive) and Staphylococcus epidermidis (positive)
c) Streptococcus pyogenes (negative) and Enterococcus faecalis (negative)
d) Klebsiella pneumoniae (negative) and Proteus mirabilis (negative) - A Gram-negative rod isolated from a urinary tract infection ferments lactose and produces pink colonies on MacConkey agar. The most likely organism is:
a) Escherichia coli
b) Pseudomonas aeruginosa
c) Proteus mirabilis
d) Salmonella enterica - Which test differentiates Klebsiella pneumoniae from Enterobacter cloacae?
a) Motility
b) Indole
c) Citrate
d) Lactose fermentation - A swarming growth pattern on blood agar is characteristic of:
a) Escherichia coli
b) Proteus mirabilis
c) Serratia marcescens
d) Klebsiella pneumoniae - Non-lactose fermenting colonies that produce H₂S on Hektoen enteric agar are suggestive of:
a) Shigella flexneri
b) Salmonella species
c) Escherichia coli
d) Klebsiella oxytoca - Which Gram-negative bacillus produces a red pigment at room temperature?
a) Serratia marcescens
b) Klebsiella pneumoniae
c) Proteus vulgaris
d) Enterobacter aerogenes - Which test is most useful in differentiating Shigella from Salmonella?
a) Indole
b) H₂S production
c) Oxidase
d) Urease - A non-fermentative, oxidase-positive, Gram-negative bacillus producing a fruity odor is most likely:
a) Escherichia coli
b) Pseudomonas aeruginosa
c) Proteus mirabilis
d) Klebsiella pneumoniae - Which test distinguishes Proteus vulgaris from Proteus mirabilis?
a) Indole
b) Citrate
c) Oxidase
d) Lactose fermentation - A Gram-negative bacillus isolated from a stool sample shows non-lactose fermentation, no H₂S, and is non-motile. The most likely organism is:
a) Shigella dysenteriae
b) Salmonella Typhi
c) Escherichia coli
d) Klebsiella pneumoniae - Which of the following organisms is oxidase-positive and non-fermentative?
a) Escherichia coli
b) Salmonella enterica
c) Pseudomonas aeruginosa
d) Shigella sonnei - On MacConkey agar, lactose fermenters appear pink due to:
a) Acid production
b) Alkaline reaction
c) Gas production
d) H₂S release - Which Gram-negative bacillus is associated with “rice water stools”?
a) Salmonella Typhi
b) Vibrio cholerae
c) Escherichia coli
d) Klebsiella pneumoniae - Which organism is best identified by the “string test” (viscous colonies on agar)?
a) Vibrio cholerae
b) Shigella dysenteriae
c) Escherichia coli
d) Proteus vulgaris - A non-lactose fermenting, urease-positive Gram-negative rod is most likely:
a) Klebsiella pneumoniae
b) Proteus mirabilis
c) Escherichia coli
d) Shigella flexneri - Which test differentiates Escherichia coli from Klebsiella pneumoniae?
a) Motility
b) Urease
c) Oxidase
d) Citrate - Which organism produces a characteristic “bull’s eye” colony on CIN agar?
a) Yersinia enterocolitica
b) Shigella sonnei
c) Salmonella Typhi
d) Klebsiella oxytoca - Which test is most useful in differentiating Vibrio cholerae from Aeromonas species?
a) Oxidase
b) Salt tolerance (growth in 6% NaCl)
c) Urease
d) Citrate - A Gram-negative bacillus producing mucoid colonies due to a polysaccharide capsule is most likely:
a) Escherichia coli
b) Klebsiella pneumoniae
c) Proteus mirabilis
d) Shigella flexneri - Which Gram-negative rod is associated with wound infections from seawater exposure?
a) Escherichia coli
b) Vibrio vulnificus
c) Salmonella enterica
d) Shigella sonnei - A triple sugar iron (TSI) slant showing alkaline slant, acid butt, and H₂S production suggests:
a) Escherichia coli
b) Salmonella species
c) Shigella species
d) Pseudomonas aeruginosa - Which test differentiates Enterobacter cloacae from Escherichia coli?
a) Indole
b) Oxidase
c) Lactose fermentation
d) Citrate - Which Gram-negative bacillus is characteristically positive for urease and causes urinary tract infections with struvite stones?
a) Proteus mirabilis
b) Escherichia coli
c) Salmonella Typhi
d) Shigella dysenteriae - Which organism is associated with red currant jelly sputum in pneumonia?
a) Escherichia coli
b) Klebsiella pneumoniae
c) Pseudomonas aeruginosa
d) Serratia marcescens - A Gram-negative bacillus isolated from the stool of a child with bloody diarrhea and hemolytic uremic syndrome is most likely:
a) Escherichia coli O157:H7
b) Shigella sonnei
c) Salmonella Typhi
d) Klebsiella oxytoca - Which organism shows “safety-pin” bipolar staining on Gram stain?
a) Yersinia pestis
b) Shigella dysenteriae
c) Escherichia coli
d) Vibrio cholerae - Which test differentiates Vibrio cholerae from Vibrio parahaemolyticus?
a) Indole
b) Oxidase
c) Growth in high salt concentration
d) Citrate - Which non-fermentative Gram-negative bacillus is a common cause of ventilator-associated pneumonia in hospitalized patients?
a) Pseudomonas aeruginosa
b) Klebsiella pneumoniae
c) Escherichia coli
d) Proteus vulgaris - A Gram-negative rod shows lactose fermentation with a slow, delayed reaction on MacConkey agar. This suggests:
a) Serratia marcescens
b) Escherichia coli
c) Salmonella Typhi
d) Shigella sonnei - Which test is most useful for differentiating Salmonella Typhi from other Salmonella species?
a) Urease
b) Citrate utilization
c) Vi antigen detection
d) Indole - Which Gram-negative bacillus is a common contaminant of disinfectants and associated with opportunistic infections in burns?
a) Escherichia coli
b) Pseudomonas aeruginosa
c) Klebsiella pneumoniae
d) Shigella flexneri - Which characteristic best differentiates Pseudomonas aeruginosa from other non-fermentative Gram-negative bacilli?
a) Lactose fermentation
b) Oxidase positivity and growth at 42°C
c) Production of indole
d) Absence of pigment production - Klebsiella pneumoniae can be distinguished from Escherichia coli by which feature?
a) Motility and indole production
b) Lactose fermentation
c) Beta-hemolysis on blood agar
d) Oxidase positivity - On Hektoen enteric agar, Shigella species typically produce colonies that are:
a) Green, non-H₂S producing
b) Black-centered, H₂S producing
c) Pink, lactose-fermenting
d) Yellow, sucrose-fermenting - Salmonella Typhi differs from other Salmonella species because it:
a) Produces abundant H₂S
b) Possesses a Vi antigen
c) Is indole positive
d) Ferments lactose - Which organism produces a red pigment at room temperature?
a) Serratia marcescens
b) Klebsiella pneumoniae
c) Proteus vulgaris
d) Enterobacter cloacae - A swarming growth pattern on blood agar is most characteristic of:
a) Escherichia coli
b) Proteus mirabilis
c) Salmonella enterica
d) Klebsiella oxytoca - The “string test” (formation of a mucoid string >5 mm) is used to identify:
a) Shigella sonnei
b) Vibrio cholerae
c) Yersinia pestis
d) Salmonella Paratyphi - Yersinia enterocolitica can be differentiated from Enterobacteriaceae by its ability to:
a) Ferment lactose
b) Grow at cold temperatures (4°C)
c) Produce pyocyanin
d) Swarm on blood agar - Which organism is commonly associated with hospital-acquired pneumonia in ventilated patients and produces a grape-like odor?
a) Escherichia coli
b) Pseudomonas aeruginosa
c) Klebsiella pneumoniae
d) Proteus mirabilis - Vibrio vulnificus infection is most often linked to:
a) Consumption of undercooked poultry
b) Exposure to seawater or raw oysters
c) Contact with contaminated soil
d) Transmission via respiratory droplets
Answer Key
Answer Key:
- c) requires an enhanced CO₂ atmosphere for growth
- b) Carbohydrate utilization tests
- b) A symptomatic male
- c) Moraxella catarrhalis
- c) Rapid hydrolysis of ONPG (o-nitrophenyl-β-D-galactopyranoside)
- b) Neisseria meningitidis
- b) Ability to grow on MacConkey agar
- b) Haemophilus influenzae
- c) Moraxella osloensis
- c) Vaginal discharge
- c) Ceftriaxone
- b) Neisseria gonorrhoeae
- b) Urethral swab of exudate
- b) Vancomycin, colistin, and nystatin (or trimethoprim)
- c) Moraxella catarrhalis
- c) Failure to ferment lactose (negative ONPG test)
- d) Coagulase
- c) Cryptococcal antigen test
- b) Chlamydia trachomatis
- a) Escherichia coli (negative) and Pseudomonas aeruginosa (positive)
- a) Acid production
- b) Vibrio cholerae
- a) Vibrio cholerae
- b) Proteus mirabilis
- a) Motility
- a) Yersinia enterocolitica
- b) Salt tolerance (growth in 6% NaCl)
- b) Klebsiella pneumoniae
- b) Vibrio vulnificus
- b) Salmonella species
- b) Oxidase positivity and growth at 42°C
- a) Motility and indole production
- a) Green, non-H₂S producing
- b) Possesses a Vi antigen
- a) Serratia marcescens
- b) Proteus mirabilis
- b) Vibrio cholerae
- b) Grow at cold temperatures (4°C)
- b) Pseudomonas aeruginosa
- b) Exposure to seawater or raw oysters
- c) An enhanced CO₂ atmosphere
- a) Neisseria gonorrhoeae
- a) They exhibit a “hockey puck” consistency and can be pushed across the agar surface.
- b) Regan-Lowe agar
- b) Oxidase production
- a) Decreased glucose, increased protein, increased white blood cells
- c) Nucleic Acid Amplification Test (NAAT)
- b) Neisseria lactamica
- b) A Gram-negative diplococcus that is oxidase-positive and catalase-negative
- b) Production of beta-lactamase enzyme
- a) Escherichia coli
- a) Motility
- b) Proteus mirabilis
- b) Salmonella species
- a) Serratia marcescens
- b) H₂S production
- b) Pseudomonas aeruginosa
- a) Indole
- a) Shigella dysenteriae
- c) Pseudomonas aeruginosa
- a) Indole
- a) Proteus mirabilis
- b) Klebsiella pneumoniae
- a) Escherichia coli O157:H7
- a) Yersinia pestis
- c) Growth in high salt concentration
- a) Pseudomonas aeruginosa
- a) Serratia marcescens
- c) Vi antigen detection
- b) Pseudomonas aeruginosa
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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