CALIFORNIA PUBLIC HEALTH MICROBIOLOGIST (PHM)
CERTIFICATION EXAMINATION
PRACTICE TEST NEWEST EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS WITH RATIONALES LATEST UPDATES 2026-
2027 (VERIFIED ANSWERS) ALREADY GRADED A+
1. Which selective and differential medium is used to isolate Salmonella from stool specimens
and produces colonies with black centers due to H₂S production?
A) MacConkey agar
B) Hektoen enteric agar
C) Xylose lysine deoxycholate (XLD) agar
D) Thiosulfate citrate bile salts sucrose (TCBS) agar
Correct Answer: B
Rationale: Hektoen enteric agar contains ferric ammonium citrate and sodium thiosulfate,
allowing detection of H₂S production. Salmonella produces black-centered colonies on this
medium due to H₂S. XLD agar also yields black colonies, but HE is more selective for
Salmonella; MacConkey agar is not selective enough; TCBS is for Vibrio.
2. In a water testing laboratory, the Most Probable Number (MPN) method for coliforms uses
a series of tubes containing lauryl tryptose broth. A positive tube shows:
A) Purple color change
B) Gas production in the Durham tube and/or turbidity
C) Black precipitate
D) Fluorescence under UV light
Correct Answer: B
Rationale: Coliforms ferment lactose in lauryl tryptose broth, producing gas and acid. Gas is
trapped in the Durham tube, and turbidity indicates growth. Fluorescence indicates fecal
coliforms in MUG tests, black precipitate is for H₂S production, and purple color change is
typical for other indicators.
,3. According to the California Code of Regulations, Title 17, which of the following diseases
must be immediately reported by telephone to the local health officer upon laboratory
confirmation?
A) Influenza
B) Bacillus anthracis (anthrax)
C) Hepatitis C
D) Lyme disease
Correct Answer: B
Rationale: Anthrax is a Category A bioterrorism agent and requires immediate telephone
reporting under Title 17, Section 2500. Influenza deaths are reportable, but not every case.
Hepatitis C and Lyme disease are routine reportable diseases, not immediate telephone.
4. The molecular method that uses a target-specific probe with a reporter and quencher, and
relies on the 5′ exonuclease activity of Taq polymerase, is called:
A) SYBR Green qPCR
B) TaqMan assay
C) Loop-mediated isothermal amplification (LAMP)
D) Nucleic acid sequence-based amplification (NASBA)
Correct Answer: B
Rationale: TaqMan probes are hydrolyzed by Taq polymerase during amplification, separating
reporter from quencher and generating fluorescence. SYBR Green binds double-stranded DNA
but is not a hydrolysis probe. LAMP and NASBA are isothermal methods not involving 5′
exonuclease.
5. A food sample is tested for Staphylococcus aureus enterotoxin. The most appropriate
confirmatory test after isolating the organism is:
A) Catalase test
B) Coagulase test and thermonuclease detection
C) Gram stain
D) Oxidase test
Correct Answer: B
Rationale: S. aureus is coagulase-positive and produces thermostable nuclease
(thermonuclease), which correlates with enterotoxin production. Catalase is positive but not
confirmatory; Gram stain only shows morphology, and oxidase is negative for staphylococci.
6. Which biosafety level (BSL) is required for culturing Mycobacterium tuberculosis in a public
health laboratory?
A) BSL-1
,B) BSL-2
C) BSL-3
D) BSL-4
Correct Answer: C
Rationale: M. tuberculosis is transmitted by aerosol and requires BSL-3 containment, including
negative pressure, HEPA filtration, and respiratory protection. BSL-2 is for bloodborne
pathogens, BSL-1 for non-infectious agents, BSL-4 for exotic viruses.
7. In a water sample, the presence of Escherichia coli is confirmed by a positive indole test
and fluorescence in MUG (4-methylumbelliferyl-β-D-glucuronide) agar. What enzyme does E.
coli produce to cleave MUG?
A) β-galactosidase
B) β-glucuronidase
C) Urease
D) Phenylalanine deaminase
Correct Answer: B
Rationale: E. coli produces β-glucuronidase, which hydrolyzes MUG to release fluorescent 4-
methylumbelliferone. β-galactosidase acts on ONPG, not MUG. Urease is for urea, and
phenylalanine deaminase is for Proteus.
8. The California Public Health Microbiologist (PHM) certification is issued by:
A) American Society for Microbiology
B) California Department of Public Health, Laboratory Field Services
C) Centers for Disease Control and Prevention
D) Clinical Laboratory Improvement Amendments program
Correct Answer: B
Rationale: The PHM certification in California is administered by the California Department of
Public Health, Laboratory Field Services, under Title 17. ASM provides national certification
(e.g., SM), CDC does not certify, and CLIA is federal regulation.
9. An environmental water sample is collected for Legionella testing. What is the preferred
method for concentration of large-volume water samples (e.g., 1 L) prior to culture?
A) Centrifugation at 5000 × g
B) Membrane filtration (0.2 µm pore size)
C) Precipitation with alum
D) Boiling for 10 minutes
Correct Answer: B
Rationale: Membrane filtration concentrates bacteria onto a filter, which is then placed on
, selective media (BCYE agar). Centrifugation is not practical for large volumes; precipitation is
not used; boiling would kill the bacteria.
10. A clinical specimen from a skin ulcer shows gram-negative coccobacilli with bipolar
staining ("safety pin" appearance). The organism grows on sheep blood agar but not on
MacConkey agar. It is catalase-positive and oxidase-negative. The most likely agent is:
A) Yersinia pestis
B) Francisella tularensis
C) Brucella melitensis
D) Pasteurella multocida
Correct Answer: A
Rationale: Y. pestis is a bipolar-staining gram-negative coccobacillus, catalase-positive,
oxidase-negative, and does not grow on MacConkey agar. F. tularensis requires cysteine and
does not grow on blood agar easily; Brucella grows on MacConkey and is oxidase-positive;
Pasteurella is oxidase-positive.
11. A public health laboratory uses pulse-field gel electrophoresis (PFGE) for outbreak
investigation. PFGE separates DNA fragments based on:
A) Size under alternating electric field directions
B) Sequence homology
C) Isoelectric point
D) Fluorescent labeling intensity
Correct Answer: A
Rationale: PFGE uses alternating electric fields to separate large DNA molecules (after
restriction digestion) by size in an agarose gel. It does not rely on sequence, charge, or
fluorescence for separation.
12. According to CLIA, moderate-complexity testing may be performed in a public health
laboratory by:
A) Any laboratory professional with a high school diploma
B) A certified PHM or other qualified personnel with documented training and competency
C) Only a medical doctor
D) No personnel requirements exist
Correct Answer: B
Rationale: CLIA requires moderate-complexity testing personnel to have at least an associate
degree and training, but in California, the PHM certification fulfills this for public health
laboratories. High school diploma alone is insufficient; MD is not required.
CERTIFICATION EXAMINATION
PRACTICE TEST NEWEST EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS WITH RATIONALES LATEST UPDATES 2026-
2027 (VERIFIED ANSWERS) ALREADY GRADED A+
1. Which selective and differential medium is used to isolate Salmonella from stool specimens
and produces colonies with black centers due to H₂S production?
A) MacConkey agar
B) Hektoen enteric agar
C) Xylose lysine deoxycholate (XLD) agar
D) Thiosulfate citrate bile salts sucrose (TCBS) agar
Correct Answer: B
Rationale: Hektoen enteric agar contains ferric ammonium citrate and sodium thiosulfate,
allowing detection of H₂S production. Salmonella produces black-centered colonies on this
medium due to H₂S. XLD agar also yields black colonies, but HE is more selective for
Salmonella; MacConkey agar is not selective enough; TCBS is for Vibrio.
2. In a water testing laboratory, the Most Probable Number (MPN) method for coliforms uses
a series of tubes containing lauryl tryptose broth. A positive tube shows:
A) Purple color change
B) Gas production in the Durham tube and/or turbidity
C) Black precipitate
D) Fluorescence under UV light
Correct Answer: B
Rationale: Coliforms ferment lactose in lauryl tryptose broth, producing gas and acid. Gas is
trapped in the Durham tube, and turbidity indicates growth. Fluorescence indicates fecal
coliforms in MUG tests, black precipitate is for H₂S production, and purple color change is
typical for other indicators.
,3. According to the California Code of Regulations, Title 17, which of the following diseases
must be immediately reported by telephone to the local health officer upon laboratory
confirmation?
A) Influenza
B) Bacillus anthracis (anthrax)
C) Hepatitis C
D) Lyme disease
Correct Answer: B
Rationale: Anthrax is a Category A bioterrorism agent and requires immediate telephone
reporting under Title 17, Section 2500. Influenza deaths are reportable, but not every case.
Hepatitis C and Lyme disease are routine reportable diseases, not immediate telephone.
4. The molecular method that uses a target-specific probe with a reporter and quencher, and
relies on the 5′ exonuclease activity of Taq polymerase, is called:
A) SYBR Green qPCR
B) TaqMan assay
C) Loop-mediated isothermal amplification (LAMP)
D) Nucleic acid sequence-based amplification (NASBA)
Correct Answer: B
Rationale: TaqMan probes are hydrolyzed by Taq polymerase during amplification, separating
reporter from quencher and generating fluorescence. SYBR Green binds double-stranded DNA
but is not a hydrolysis probe. LAMP and NASBA are isothermal methods not involving 5′
exonuclease.
5. A food sample is tested for Staphylococcus aureus enterotoxin. The most appropriate
confirmatory test after isolating the organism is:
A) Catalase test
B) Coagulase test and thermonuclease detection
C) Gram stain
D) Oxidase test
Correct Answer: B
Rationale: S. aureus is coagulase-positive and produces thermostable nuclease
(thermonuclease), which correlates with enterotoxin production. Catalase is positive but not
confirmatory; Gram stain only shows morphology, and oxidase is negative for staphylococci.
6. Which biosafety level (BSL) is required for culturing Mycobacterium tuberculosis in a public
health laboratory?
A) BSL-1
,B) BSL-2
C) BSL-3
D) BSL-4
Correct Answer: C
Rationale: M. tuberculosis is transmitted by aerosol and requires BSL-3 containment, including
negative pressure, HEPA filtration, and respiratory protection. BSL-2 is for bloodborne
pathogens, BSL-1 for non-infectious agents, BSL-4 for exotic viruses.
7. In a water sample, the presence of Escherichia coli is confirmed by a positive indole test
and fluorescence in MUG (4-methylumbelliferyl-β-D-glucuronide) agar. What enzyme does E.
coli produce to cleave MUG?
A) β-galactosidase
B) β-glucuronidase
C) Urease
D) Phenylalanine deaminase
Correct Answer: B
Rationale: E. coli produces β-glucuronidase, which hydrolyzes MUG to release fluorescent 4-
methylumbelliferone. β-galactosidase acts on ONPG, not MUG. Urease is for urea, and
phenylalanine deaminase is for Proteus.
8. The California Public Health Microbiologist (PHM) certification is issued by:
A) American Society for Microbiology
B) California Department of Public Health, Laboratory Field Services
C) Centers for Disease Control and Prevention
D) Clinical Laboratory Improvement Amendments program
Correct Answer: B
Rationale: The PHM certification in California is administered by the California Department of
Public Health, Laboratory Field Services, under Title 17. ASM provides national certification
(e.g., SM), CDC does not certify, and CLIA is federal regulation.
9. An environmental water sample is collected for Legionella testing. What is the preferred
method for concentration of large-volume water samples (e.g., 1 L) prior to culture?
A) Centrifugation at 5000 × g
B) Membrane filtration (0.2 µm pore size)
C) Precipitation with alum
D) Boiling for 10 minutes
Correct Answer: B
Rationale: Membrane filtration concentrates bacteria onto a filter, which is then placed on
, selective media (BCYE agar). Centrifugation is not practical for large volumes; precipitation is
not used; boiling would kill the bacteria.
10. A clinical specimen from a skin ulcer shows gram-negative coccobacilli with bipolar
staining ("safety pin" appearance). The organism grows on sheep blood agar but not on
MacConkey agar. It is catalase-positive and oxidase-negative. The most likely agent is:
A) Yersinia pestis
B) Francisella tularensis
C) Brucella melitensis
D) Pasteurella multocida
Correct Answer: A
Rationale: Y. pestis is a bipolar-staining gram-negative coccobacillus, catalase-positive,
oxidase-negative, and does not grow on MacConkey agar. F. tularensis requires cysteine and
does not grow on blood agar easily; Brucella grows on MacConkey and is oxidase-positive;
Pasteurella is oxidase-positive.
11. A public health laboratory uses pulse-field gel electrophoresis (PFGE) for outbreak
investigation. PFGE separates DNA fragments based on:
A) Size under alternating electric field directions
B) Sequence homology
C) Isoelectric point
D) Fluorescent labeling intensity
Correct Answer: A
Rationale: PFGE uses alternating electric fields to separate large DNA molecules (after
restriction digestion) by size in an agarose gel. It does not rely on sequence, charge, or
fluorescence for separation.
12. According to CLIA, moderate-complexity testing may be performed in a public health
laboratory by:
A) Any laboratory professional with a high school diploma
B) A certified PHM or other qualified personnel with documented training and competency
C) Only a medical doctor
D) No personnel requirements exist
Correct Answer: B
Rationale: CLIA requires moderate-complexity testing personnel to have at least an associate
degree and training, but in California, the PHM certification fulfills this for public health
laboratories. High school diploma alone is insufficient; MD is not required.
