8.4 Miscellaneous and Fastidious Gram-Negative Rods

Question 1

A visitor to South America who returned with diarrhea is suspected of being infected with V. cholerae. Select the best medium for recovery and identification of this organism.
A. MacConkey agar
B. Blood agar
C. TCBS agar
D. XLD agar

Answer 1

C. TCBS agar

Question 2

A curved gram-negative, rod-producing, oxidase-positive colonies on blood agar was recovered from a stool culture. Given the following results, what is the most likely identification?

Lysine decarboxylase = +
Arginine decarboxylase = Neg
Indole = +
KIA = Alk/Acid
VP = Neg
Lactose = Neg
Urease = +/-
String = Neg
TCBS agar = Green colonies

A. Vibrio cholerae
B. Vibrio parahaemolyticus
C. Shigella spp.
D. Salmonella spp.

Answer 2

B. Vibrio parahaemolyticus

Question 3

A gram-negative S-shaped rod recovered from selective media for Campylobacter species gave the following results:
Catalase = +
Oxidase = +
Nitrate Reduction = +
Motility = +
Hippurate hydrolysis = +
Growth at 42 C = +
Nalidixic acid = Susceptible
Pigment = Neg
Grape odor = Neg
Cephalothin = Resistant

The most likely identification is:
A. Pseudomonas aeruginosa
B. Campylobacter jejuni
C. Campylobacter fetus
D. Pseudomonas putida

Answer 3

B. Campylobacter jejuni

Question 4

Which atmospheric condition is needed to recover Campylobacter spp. from specimens inoculated onto a Campy-selective agar at 35C to 37C and 42C?
A. 5% O2, 10% CO2, and 85% N2
B. 20% O2, 10% CO2, and 70% N2
C. 20% O2, 20% CO2, and 60% N2
D. 20% O2, 5% CO2, and 75% N2

Answer 4

A. 5% O2, 10% CO2, and 85% N2

Question 5

Which group of tests best differentiates Helicobacter from C.jejuni?
A. Catalase, oxidase, and Gram stain
B. Catalase, oxidase, and nalidixic acid sensitivity
C. Catalase, oxidase, and cephalothin sensitivity
D. Urease, nitrate, and hippurate hydrolysis.

Answer 5

D. Urease, nitrate, and hippurate hydrolysis.

H.pylori is found in specimens from gastric secretions and biopsies and has been implicated as a cause of gastric ulcers. It is found only in the mucous-secreting epithelial cells of the stomach. Both H. pylori and C. jejuni are catalase and oxidase postive. However, Helicobacter spp. are urease positive, which differentiates them from Campylobacter spp.

Question 6

Which of the following tests should be done first to differentiate Aeromonas spp. from the Enterobacteriaceae?
A. Urease
B. OF glucose
C. Oxidase
D. Catalase

Answer 6

C. Oxidase

Question 7

Which of the best rapid test to differentiate P. shigelloides from a Shigella species on selective enteric agar?
A. Oxidase
B. Indole
C. Triple-sugar iron agar
D. Urease

Answer 7

A. Oxidase

Question 8

Which are the best two tests to differentiate A. hydrophila from P. shigelloides?
A. Oxidase and motility
B. DNase and Voges-Proskauer test
C. Indole and lysine decarboxylase
D. Growth on MacConkey and blood agar

Answer 8

B. DNase and Voges-Proskauer test

Question 9

Which genus (in which most species are oxidase and catalase positive) of small gram-negative coccobacilli is associated mainly with animals but may cause endocarditis and bacteremia, as well as wound and dental infections in humans?
A. Aggregatibacter (formerly Actinobacillus spp.)
B. Pseudomonas
C. Campylobacter
D. Vibrio

Answer 9

A. Aggregatibacter (formerly Actinobacillus spp.)

Question 10

Which of the following tests may be used to differentiate Cardiobacterium hominis from Aggregatibacter spp. (formerly Actinobacillus spp.)?
A. Gram stain
B. Indole
C. Anaerobic incubation
D. Oxidase

Answer 10

B. Indole

Question 11

A mixture of slender gram-negative rods and coccobacilli with rounded ends was recovered from blood cultures after a patient’s root canal surgery. Given the following results after 48 hours, what is the most likely organism?
Catalase = Neg
Ornithine decarboxylase = +
Urease = Neg
Lysine decarboxylase = +
Oxidase = +
X and V requirement = Neg
Indole = Neg
Carbohydrates = Neg (no acid produced)
Growth on blood and chocolate agar = + (with pitting of agar)
Growth on MacConkey agar = Neg

A. Eikenella corrodens
B. Aggregatibacter (formerly Actinobacillus) spp.
C. Cardiobacterium hominis
D. Proteus spp.

Answer 11

A. Eikenella corrodens

Question 12

** Kingella kingae can best be differentiated from E.corrodens by using which medium?**
A. Sheep blood agar
B. Chocolate agar
C. MacConkey agar
D. Xylose lysine deoxycholate agar

Answer 12

A. Sheep blood agar

Question 13

** K.kingae is usually associated with which type of infection?**
A. Middle ear infection
B. Endocarditis
C. Meningitis
D. Urogenital infection

Answer 13

B. Endocarditis

Question 14

**Cultures obtained from a dog bite wound produced yellow, tan, and slightly pink colonies on blood and chocolate agar, with a margin of fingerlike projections appearing as a film around the colonies. Given the following results at 24 hours, which is the most likely organism?
Oxidase = +
Catalase = +
Growth on MacConkey agar = Neg
Motility = Neg

A. Aggregatibacter (formerly Actinobacillus) spp.
B. Eikenella spp.
C. Capnocytophaga spp.
D. Pseudomonas spp.

Answer 14

C. Capnocytophaga spp.

Question 15

**Smooth gray colonies showing no hemolytic activity were recovered from an infected cat scratch wound culture; the colonies grew on blood and chocolate agar (a musty odor was noted) but failed to grow on MacConkey agar. The organisms were gram-negative pleomorphic rods that were both catalase and oxidase positive and strongly indole positive. The most likely organism is:
A. Haemophilus spp.
B. Pasteurella spp.
C. Proteus spp.
D. Pseudomonas spp.

Answer 15

B. Pasteurella spp.

Question 16

Which media should be used to recover B. pertussis from a nasopharyngeal specimen?
A. Chocolate agar
B. Blood agar
C. MacConkey agar
D. Bordet-Gengou agar

Answer 16

D. Bordet-Gengou agar

Question 17

Which medium is recommended for the recovery of Brucella spp. from blood and bone marrow specimens?
A. Biphasic Castenada bottles with Brucella broth
B. Blood culture bottles with Brucella broth
C. Bordet-Gengou agar plates and THIO broth
D. Blood culture bottles with THIO broth

Answer 17

A. Biphasic Castenada bottles with Brucella broth

Question 18

In addition to CO2 requirements and biochemical characteristics, B. melitensis and Brucella abortus are differentiated by growth on media containing which two dyes?
A. Basic fuchsin and thionin
B. Methylene blue and crystal violet
C. Carbol fuchsin and iodine
D. Safranin and methylene blue

Answer 18

A. Basic fuchsin and thionin

Question 19

**Which of the following amino acids are required for growth of Francisella tularensis? **
A. Leucine and ornithine
B. Arginine and lysine
C. Cysteine and cystine
D. Histidine and tryptophan

Answer 19

C. Cysteine and cystine

Question 20

Which medium is best for recovery of Legionella pneumophila from clinical specimens?
A. Chocolate agar
B. Bordet-Gengou agar
C. New yeast extract agar
D. Buffered charcoal-yeast extract (CYE) agar

Answer 20

D. Buffered charcoal-yeast extract (CYE) agar

Question 21

** Haemophilus aegyptius (formerly H.influenzae biogroup aegyptius) causes ocular infections (“pink eye”) and requires X and V factors in the primary medium for growth. H. aegyptius and H. influenzae can further be identified and differentiated by which two tests?**
A. Indole and xylose
B. Glucose and urease
C. Oxidase and catalase
D. Aminolevulinic acid (ALA) test and oxidase

Answer 21

A. Indole and xylose

Question 22

** Haemophilus species that require the V factor (NAD) are easily recovered on which primary agar plate?**
A. Blood agar made with sheep RBCs
B. Blood agar made with horse RBCs
C. Chocolate agar
D. Xylose agar

Answer 22

C. Chocolate agar

Question 23

Which of the following products is responsible for satellite growth of Haemophilus spp. around colonies of Staphylococcus growing on sheep blood agar?
A. NAD and Hemin
B. Lactose
C. Indole
D. Oxidase

Answer 23

A. NAD and Hemin

Question 24

Which of the following plates should be used to identify H. haemolyticus and *H. parahaemolyticus?
A. Sheep blood agar and chocolate agar
B. Horse blood agar and Mueller-Hinton agar with X and V strips
C. Brain-heart infusion (BHI) agar with sheep red cells added
D. Chocolate agar and Mueller-Hinton agar with X factor added

Answer 24

B. Horse blood agar and Mueller-Hinton agar with X and V strips

Question 25

The majority of H.influenzae infections are caused by which of the following capsular serotypes?
A. a
B. b
C. c
D. d

Answer 25

B. b

Question 26

Which of the following, usually recovered from blood cultures, is generally associated with subacute bacterial endocarditis?
A. Haemophilus influenzae
B. Haemophilus ducreyi
C. Aggregatibacter (Haemophilus) aphrophilus
D. Haemophilus haemolyticus

Answer 26

C. Aggregatibacter (Haemophilus) aphrophilus

Question 27

Which Haemophilus species is difficult to isolate and recover from genital ulcers and swollen lymph nodes?
A. Haemophilus aegyptius
B. Haemophilus ducreyi
C. Haemophilus haemolyticus
D. Haemophilus parahaemolyticus

Answer 27

B. Haemophilus ducreyi

Question 28

Which of the following is a characteristic of strains of H.influenzae that are resistant to ampicillin?
A. Production of Beta-lactamase enzymes
B. Hydrolysis of chloramphenicol
C. Hydrolysis of urea
D. All of the options

Answer 28

A. Production of Beta-lactamase enzymes

Question 29

A small, gram-negative coccusbacillus recovered from the CSF of a 2-year-old unvaccinated child gave the following results:

Indole = +
Glucose = + (acid)
X requirement = +
V requirement = +
Urease = +
Lactose = Neg
Sucrose = Neg
Hemolysis = Neg
Which is the most likely identification?
A. Haemophilus parainfluenzae
B. Haemophilus influenzae
C. Haemophilus ducreyi
D. Aggregatibacter (formerly Haemophilus) aphrophilus

Answer 29

B. Haemophilus influenzae

Question 30

The ALA test (for porphyrins) is a confirmatory procedure for which test used for identification of Haemophilus species?
A. X factor requirement
B. V factor requirement
C. Urease production
D. Indole production

Answer 30

A. X factor requirement

Question 31

An older woman who cared for several domestic cats was hospitalized with suspected cat scratch disease (CSD). Blood cultures appeared negative, but after several days, a small, slightly curved pleomorphic gram-negative bacillus grew on BHI agar (with 5% horse or rabbit blood). Other biochemical testing gave negative results. What is the most likely identification?
A. Bartonella spp.
B. Brucella spp.
C. Kingella spp.
D. Haemophilus spp.

Answer 31

A. Bartonella spp.

Question 32

**A 5-year-old nonimmunized male with a persistent cough, fever, and flulike symptoms was admitted to the hospital. Nasopharyngeal swabs were cultured on 15% blood, chocolate, Bordet-Gengou, and Regan-Lowe (with 10% charcoal) agars. All media grew a gram-negative coccobacillus after 3 days incubation. Carbohydrate and biochemical tests gave negative results. What is the most likely identification?
A. Haemophilus influenza
B. Bordetella pertussis
C. Haemophilus parainfluenzae
D. Bordetella bronchiseptica

Answer 32

B. Bordetella pertussis

Question 33

** A 29-year-old male who often hunted rabbits and spent a lot of time in the woods was admitted to the hospital with skin ulcers on his upper extremities. At 48 hours, a small coccobacillus was recovered only from the aerobic blood culture bottle. The organism stained poorly with Gram stain but did stain with a riding orange. Cultures taken from the ulcers did not grow on primary media. What is the most likely identification?**
A. Pseudomonas aeruginosa
B. Pseudomonas fluorescens
C. Chryseobacterium spp.
D. Francisella tularensis

Answer 33

D. Francisella tularensis

Question 34

**A neonate was readmitted to the hospital with a diagnosis of meningitis. CSF revealed gram-negative straight rods. At 24 hours, the organism grew on 5% sheep blood and chocolate agars displaying a yellow pigment. On MacConkey agar, it appeared as an NLF. Colonies were oxidase, DNase, and gelatinase positive, and oxidized glucose and mannitol. What is the most likely identification?
A. Haemophilus influenza
B. Elizabethkingia (formerly Chryseobacterium) meningosepticum
C. Stenotrophomonas maltophilia
D. Acinetobacter spp.

Answer 34

B. Elizabethkingia (formerly Chryseobacterium) meningosepticum

Question 35

**A 46-year-old dog warden was admitted to the hospital with several puncture bite wounds encountered while wrangling a stray dog. Culture at 48 hours produced small yellow colonies on 5% sheep blood and chocolate agars in 10% CO2, but no growth on MacConkey agar. Gram staining showed gram-negative curved, fusiform rods. Colonies were oxidase and catalase positive. What is the most likely identification?
A. Capnocytophaga canimorsus
B. Francisella tularensis
C. Legionella pneumophila
D. Pseudomonas aeruginosa

Answer 35

A. Capnocytophaga canimorsus

Question 36

The AACEK (formerly HACEK) group of organisms consisting of Aggregatibacter (Haemophilus) aphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella spp.) are known by this acronym to denote which type of infection?
A. Urinary tract infection
B. Subacute bacterial endocarditis
C. Pharyngitis
D. Tonsillitis

Answer 36

B. Subacute bacterial endocarditis

Question 37

A suspected case of Legionnaires disease was noted on the request form for a culture and sensitivity ordered on a sputum sample. The patient was a 70-year-old male, who presented with a positive serological test result for Legionella spp. What is the most efficient way to confirm the infection using the submitted sample?

A. Culture the sputum on MacConkey agar
B. Gram stain of the sputum
C. Acid-fast staining
D. Direct immunofluorescent microscopy

Answer 37

D. Direct immunofluorescent microscopy

Question 38

Gastric biopsy material was obtained from a 35-year-old male. A suspected case of H.pylori could presumptively be identified and then ultimately confirmed by which of the following methods?
A. Urea broth test and polymerase chain reaction
B. Gram staining and culture
C. Acid-fast staining and culture
D. Giemsa staining and culture

Answer 38

A. Urea broth test and polymerase chain reaction

Question 39

Which acronym is used in reference to the slow-growing group of gram-negative bacteria indicated in subacute bacterial endocarditis?
A. HLACK
B. AACEK
C. ANBBC
D. NBCCBS

Answer 39

B. AACEK

Question 40

A 20-year-old male presented with soft chancres in the genital area and swollen lymph nodes. A culture specimen was taken but failed to grow after 4 days on chocolate agar, sheep blood agar, and MTM agar. Gram staining showed small, pleomorphic gram-negative rods. What is the most likely presumptive identification?
A. Neisseria gonorrheae
B. Haemophilus ducreyi
C. Haemophilus influenzae
D. Moraxella spp.

Answer 40

B. Haemophilus ducreyi

H.ducreyi may take up to 7 days to grow on chocolate agar (requiring X factor for growth) and preferably at 33 C with high humidity. Testing for chancroid disease requires specialized media.

Question 41

A 7-year-old female became ill after eating a chicken sandwich from a fast-food restaurant. After 24 hours of gastroenteritis, a stool swab was obtained for culture, with normal fecal flora growing on Mac and XLD agars at 18 hours. Furthermore, growth was observed on Camp-BA at 48 hours (at both 42 C and 37 C incubation). Which test(s) differentiate C. jejuni subsp. doylei from C. jejuni subsp. jejuni because both grow at 37C and 42C.

A. Urease
B. Hippurate hydrolysis
C. Cephalothin and nalidixic acid antibiotic disks
D. Growth at 25 C

Answer 41

C. Cephalothin and nalidixic acid antibiotic disks

To separate C. jejuni subspecies. jejuni from C. jejuni subspecies. doylei ( both are positive for hippurate hydrolysis and grow at 37 C and 42). It is best to use cephalothin (30 ug disk) and nalidixic acid ( 30–ug) antibiotic testing. jejuni are resistant to cephalothin and do

Question 42

A suspected B. pertussis diagnosis relies on symptoms and growth of the organism on Regan-Lowe agar or Bordet-Gengou agar (displaying small, shiny colonies resembling mercury droplets), and the colonies take several days to grow. The most reliable serologic identification is with which method?
A. Enzyme-linked immunosorbent assay (ELISA) using paired samples
B. Agglutination
C. Complement fixation
D. Enzyme immunoassay

Answer 42

A. Enzyme-linked immunosorbent assay (ELISA) using paired samples