Aerobic Gram-Positive Rods, Spirochetes, Mycoplasmas and Ureaplasmas, and Chlamydia, Anaerobic Bacteria

Large gram-positive spore-forming rods growing on blood agar as large, raised, β-hemolytic colonies that spread and appear as frosted green-gray glass are most likely:

A. Pseudomonas spp.
B. Bacillus spp.
C. Corynebacterium spp.
D. Listeria spp.

B. Bacillus spp.

Bacillus anthracis and Bacillus cereus can best be differentiated by which tests?

A. Motility and β-hemolysis on a blood agar plate
B. Oxidase and β-hemolysis on a blood agar plate
C. Lecithinase and glucose
D. Lecithinase and catalase

A. Motility and β-hemolysis on a blood agar plate

(Both species of Bacillus are catalase and lecithinase positive and produce acid from glucose. B. cereus is β-hemolytic and motile, but B. anthracis is neither.)

Which is the specimen of choice for proof of food poisoning by Bacillus cereus?

A. Sputum
B. Blood
C. Stool
D. Food

D. Food

A suspected Bacillus anthracis culture obtained from a wound specimen produced colonies that had many outgrowths (Medusa-head appearance), but were not β-hemolytic on sheep blood agar. Which test should be performed next?

A. Penicillin (10-unit) susceptibility test
B. Lecithinase test
C. Glucose test
D. Motility test

A. Penicillin (10-unit) susceptibility test

Which of the following tests should be performed for initial differentiation of Listeria monocytogenes from group B streptococci?

A. Gram stain, motility at room temperature, catalase
B. Gram stain, CAMP test, H2S/TSI
C. Oxidase, CAMP test, glucose
D. Oxidase, bacitracin

A. Gram stain, motility at room temperature, catalase

Culture of a finger wound specimen from a meat packer produced short gram-positive bacilli on a blood agar plate with no hemolysis. Given the following test results at 48 hours, what is the most likely identification?

Catalase = Neg
H2S/TSI = +
Motility (wet prep) = Neg
Motility (media) = Neg (bottle-brush growth in stab culture)

A. Bacillus cereus
B. Listeria monocytogenes
C. Erysipelothrix rhusiopathiae
D. Bacillus subtilis

C. Erysipelothrix rhusiopathiae

(E. rhusiopathiae is catalase negative, whereas
the other three organisms are catalase positive.)

A non-spore-forming, slender gram-positive rod forming palisades and chains was recovered from a vaginal culture and grew well on tomato juice agar. The most likely identification is:

A. Lactobacillus spp.
B. Bacillus spp.
C. Neisseria spp.
D. Streptococcus spp.

A. Lactobacillus spp.

(Lactobacillus spp. are part of the normal flora of the vagina (are not considered a pathogen) and are sometimes confused with the streptococci.)

A Corynebacterium species recovered from a throat culture is considered a pathogen when it produces:

A. A pseudomembrane of the oropharynx
B. An exotoxin
C. Gray-black colonies with a brown halo on Tinsdale's agar
D. All of these options

D. All of these options

A presumptive diagnosis of Gardnerella vaginalis can be made using which of the following findings?

A. Oxidase and catalase tests
B. Pleomorphic bacilli heavily colonized on vaginal epithelium
C. Hippurate hydrolysis test
D. All of these options

D. All of these options

A gram-positive branching filamentous organism recovered from a sputum specimen was found to be positive with a modified acid-fast stain method. What is the most likely presumptive identification?

A. Bacillus spp.
B. Nocardia spp.
C. Corynebacterium spp.
D. Listeria spp.

B. Nocardia spp.

Routine laboratory testing for Treponema pallidum involves:

A. Culturing
B. Serological analysis
C. Acid-fast staining
D. Gram staining

B. Serological analysis

Spirochetes often detected in the hematology laboratory, even before the physician suspects the infection, are:

A. Borrelia spp.
B. Treponema spp.
C. Campylobacter spp.
D. Leptospira spp.

A. Borrelia spp.

(Borrelia spp. are often seen on Wright's-stained smears of peripheral blood as helical bacteria with 3-10 loose coils. They are gram negative but stain well with Giemsa's stain.)

Which of the following organisms is the cause of Lyme disease?

A. Treponema pallidum
B. Neisseria meningitidis
C. Babesia microti
D. Borrelia burgdorferi

D. Borrelia burgdorferi

The diagnostic method most commonly used for the identification of Lyme disease is:

A. Serology
B. Culture
C. Gram stain
D. Acid-fast stain

A. Serology

Primary atypical pneumonia is caused by:

A. Streptococcus pneumoniae
B. Mycoplasma pneumoniae
C. Klebsiella pneumoniae
D. Mycobacterium tuberculosis

B. Mycoplasma pneumoniae

Which organism typically produces "fried-egg" colonies on agar within 1-5 days of culture from a genital specimen?

A. Mycoplasma hominis
B. Borrelia burgdorferi
C. Leptospira interrogans
D. Treponema pallidum

A. Mycoplasma hominis

The manganous chloride-urea test is used for the identification of which organism?

A. Mycoplasma pneumoniae
B. Ureaplasma urealyticum
C. Bacillus cereus
D. Borrelia burgdorferi

B. Ureaplasma urealyticum

A gram-positive (gram-variable), beaded organism with delicate branching was recovered from the sputum of a 20-year-old patient with leukemia. The specimen produced orange, glabrous, waxy colonies on Middlebrook's agar that showed partial acid-fast staining with the modified Kinyoun stain. What is the most likely identification?

A. Rhodococcus spp.
B. Actinomadura spp.
C. Streptomyces spp.
D. Nocardia spp.

D. Nocardia spp.

(All of the listed organisms produce mycelium (aerial or substrate), causing them to appear branched when Gram stained, but only the Nocardia spp. are positive for modified acid-fast stain.)

A direct smear from a nasopharyngeal swab stained with Loeffler methylene blue stain showed various letter shapes and deep blue, metachromatic granules. The most likely identification is:

A. Corynebacterium spp.
B. Nocardia spp.
C. Listeria spp.
D. Gardnerella spp.

A. Corynebacterium spp.

Which of the following is the best, rapid, noncultural test to perform when Gardnerella vaginalis is suspected in a patient with vaginosis?

A. 10% KOH test
B. 3% H2O2 test
C. 30% H2O2 test
D. All of these options

A. 10% KOH test

(The "whiff" test is used for a presumptive diagnosis of an infection with G. vaginalis. A fishlike odor is noted after the addition of 1 drop of 10% KOH to the vaginal washings.)

Which is the test of choice for the confirmation of Chlamydia trachomatis infection in urine?

A. Enzyme immunoassay antigen testing
B. PCR molecular testing
C. Culture using McCoy and Hela cells
D. Microimmunofluorescence (MIF) test

B. PCR molecular testing

Which test is the most reliable for the detection of Mycoplasma pneumonia in serum and for the confirmation of diagnosis?

A. EIA testing and direct antigen testing
B. Cold agglutinin testing using Group O RBCs
C. Culture on SP4 glucose broth with arginine
D. Complement fixation

A. EIA testing and direct antigen testing

Identify the following bacterium and specimen pairing that is mismatched (specimen not appropriate for isolation).

A. Chlamydia (Chlamydophila) psittaci: fecal swab
B. Chlamydia trachomatis: first voided urine
C. Chlamydia trachomatis: endocervical swab
D. Chlamydia pneumonia: throat swab or sputum

A. Chlamydia (Chlamydophila) psittaci: fecal swab

Which of the following organisms are transmitted to animals and humans after a tick bite?

A. Leptospira.
B. Chlamydia and Mycoplasma spp.
C. Neisseria sicca
D. Ehrlichia and Anaplasma spp.

D. Ehrlichia and Anaplasma spp.

(Ehrlichia and Anaplasma spp. are intracellular
bacteria and are the causative agents of human monocytotropic ehrlichiosis (HME) and human granulocytotropic anaplasmosis (HGA). The organisms infect humans, dogs, and cattle through the bite of an infected Ixodes tick which also transmits Borrelia spp., causing Lyme disease.)

Following a hike in the woods, a young male noted a tick on his ankle. He removed the tick, but 2 weeks later noticed a circular, bull's eye rash at the site of the bite. Which specimen(s) should be obtained to establish a diagnosis of Lyme borreliosis?

A. Lymph node biopsy, skin scraping
B. Blood, CSF, and skin biopsy
C. Hair, fingernails
D. Saliva, sputum

B. Blood, CSF, and skin biopsy

Obligate anaerobes, facultative anaerobes, and microaerophiles are terms referring to bacteria that require:

A. Increased nitrogen
B. Decreased CO2
C. Increased O2
D. Decreased O2

D. Decreased O2

Which of the following most affects the oxidation-reduction potential (Eh or redox potential) of media for anaerobic bacteria?

A. O2
B. Nitrogen
C. pH
D. Glucose

C. pH

Which of the following is the medium of choice for the selective recovery of gram-negative anaerobes?

A. Kanamycin-vancomycin (KV) agar
B. Phenylethyl alcohol (PEA) agar
C. Cycloserine-cefoxitin-fructose agar (CCFA)
D. THIO broth

A. Kanamycin-vancomycin (KV) agar

Anaerobic bacteria are routinely isolated from all of the following types of infections except:

A. Lung abscesses
B. Brain abscesses
C. Dental infections
D. Urinary tract infections

D. Urinary tract infections

Methods other than packaged microsystems used to identify anaerobes include:

A. Antimicrobial susceptibility testing
B. Gas-liquid chromatography (GLC)
C. Special staining
D. Enzyme immunoassay

B. Gas-liquid chromatography (GLC)

Which broth is used for the cultivation of anaerobic bacteria in order to detect volatile fatty acids as an aid to identification?

A. Prereduced peptone-yeast extract-glucose (PYG)
B. THIO broth
C. Gram-negative (GN) broth
D. Selenite (SEL) broth

A. Prereduced peptone-yeast extract-glucose (PYG)

A gram-positive spore-forming bacillus growing on sheep-blood agar anaerobically produces a double zone of β-hemolysis and is positive for lecithinase. What is the presumptive identification?

A. Bacteroides ureolyticus
B. Bacteroides fragilis
C. Clostridium perfringens
D. Clostridium difficile

C. Clostridium perfringens

Egg yolk agar is used to detect which enzyme produced by Clostridium species?

A. Lecithinase
B. β-Lactamase
C. Catalase
D. Oxidase

A. Lecithinase

Which of the following organisms will display lipase activity on egg yolk agar?

A. Clostridium botulinum
B. Clostridium sporogenes
C. Clostridium novyi (A)
D. All of these options

D. All of these options

Which spore type and location is found on Clostridium tetani?

A. Round, terminal spores
B. Round, subterminal spores
C. Ovoid, subterminal spores
D. Ovoid, terminal spores

A. Round, terminal spores

Gram-positive bacilli recovered from two blood cultures from a 60-year-old diabetic patient gave the following results:

Spores seen = Neg
Motility = Neg
Volatile acids by GLC (PYG) = acetic acid (A) and butyric acid (B)
Hemolysis = + (double zone)
Lecithinase = +

What is the most likely identification?

A. Clostridium tetani
B. Clostridium perfringens
C. Clostridium novyi (B)
D. Clostridium sporogenes

B. Clostridium perfringens

Which mechanism is responsible for botulism in infants caused by Clostridium botulinum?

A. Ingestion of spores in food or liquid
B. Ingestion of preformed toxin in food
C. Virulence of the organism
D. Lipase activity of the organism

A. Ingestion of spores in food or liquid

The classic form of foodborne botulism is characterized by the ingestion of:

A. Spores in food
B. Preformed toxin in food
C. Toxin H
D. All of these options

B. Preformed toxin in food

Which test is performed in order to confirm an infection with Clostridium botulinum?

A. Toxin neutralization
B. Spore-forming test
C. Lipase test
D. Gelatin hydrolysis test

A. Toxin neutralization

Which Clostridium spp. causes pseudomembranous colitis or antibiotic-associated colitis?

A. C. ramosum
B. C. difficile
C. C. perfringens
D. C. sporogenes

B. C. difficile

Identification of Clostridium tetani is based upon:

A. Gram stain of the wound site
B. Anaerobic culture of the wound site
C. Blood culture results
D. Clinical findings

D. Clinical findings

Obligate anaerobic gram-negative bacilli that do not form spores grow well in 20% bile and are resistant to penicillin 2-unit disks are most likely:

A. Porphyromonas spp.
B. Bacteroides spp.
C. Fusobacterium spp.
D. Prevotella spp.

B. Bacteroides spp.

Which Bacteroides spp. is noted for "pitting" of the agar and is sensitive to penicillin 2-unit disks?

A. B. vulgatus
B. B. ovatus
C. B. thetaiotaomicron
D. B. ureolyticus

D. B. ureolyticus

Which gram-negative bacilli produce black pigment and brick red fluorescence when exposed to an ultraviolet light source?

A. Porphyromonas spp. and Prevotella spp.
B. Fusobacterium spp. and Actinomyces spp.
C. Bacteroides spp. and Fusobacterium spp.
D. All of these options

A. Porphyromonas spp. and Prevotella spp.

The following characteristics of an obligate anaerobic gram-negative bacilli best describe which of the listed genera?
Gram stain: long, slender rods with pointed ends Colonial appearance: dry bread crumbs or
"fried-egg" appearance
Penicillin 2-unit disk test: Susceptible

A. Bacteroides spp.
B. Fusobacterium spp.
C. Prevotella spp.
D. Porphyromonas spp.

B. Fusobacterium spp.

All of the following genera are anaerobic cocci that stain gram positive except:

A. Peptococcus spp.
B. Peptostreptococcus spp.
C. Streptococcus spp.
D. Veillonella spp.

D. Veillonella spp.

The gram-positive non-spore-forming anaerobic rods most frequently recovered from blood cultures as a contaminant are:

A. Propionibacterium acnes
B. Clostridium perfringens
C. Staphylococcus intermedius
D. Veillonella parvula

A. Propionibacterium acnes

Which Clostridium species is most often recovered from a wound infection with gas gangrene?

A. C. sporogenes
B. Clostridium sordellii
C. C. novyi
D. C. perfringens

D. C. perfringens

Gram stain of a smear taken from the periodontal pockets of a 30-year-old man with poor dental hygiene showed sulfur granules containing gram-positive rods (short diphtheroids and some unbranched filaments). Colonies on blood agar resembled "molar teeth" in formation. The most likely organism is:

A. Actinomyces israelii
B. Propionibacterium acnes
C. Staphylococcus intermedius
D. Peptostreptococcus anaerobius

A. Actinomyces israelii

Antimicrobial susceptibility testing of anaerobes is done by which of the following methods?

A. Broth disk elution
B. Disk agar diffusion
C. Microtube broth dilution
D. β-Lactamase testing

C. Microtube broth dilution