Chapter 7.4 - Miscellaneous and Fastidious Gram-Negative Rods (HARR)

TCBS agar

TCBS agar

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.

Vibrio parahaemolyticus

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 test = Neg

TCBS agar = Green colonies

Campylobacter jejuni

A gram-negative S-shaped rod recovered from selective media for Campylobacter species gave the following results:

Catalase = +

Oxidase = +

Motility = +

Hippurate hydrolysis = +

Growth at 42°C = +

Nalidixic acid = Susceptible

Pigment = Neg

Grape odor = Neg

Cephalothin = Resistant

The most likely identification is:

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

Which atmospheric condition is needed to recover Campylobacter spp. from specimens inoculated onto a Campy-selective agar at 35°C–37°C and 42°C?

Urease, nitrate, and hippurate hydrolysis

Which group of tests best differentiates Helicobacter pylori from C. jejuni?

Oxidase

Which of the following tests should be done first in order to differentiate Aeromonas spp. from the Enterobacteriaceae?

Oxidase

Which is the best rapid test to differentiate Plesiomonas shigelloides from a Shigella species on selective enteric agar?

DNase and VP

Which are the best two tests to differentiate A. hydrophilia from P. shigelloides?

Actinobacillus

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, bacteremia, as well as wound and dental infections in humans?

Indole

Which of the following tests may be used to differentiate Cardiobacterium hominis from Actinobacillus spp.?

Eikenella corrodens

A mixture of slender gram-negative rods and coccobacilli with rounded ends was recovered from blood cultures following 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

Sheep blood agar

Kingella kingae can best be differentiated from Eikenella corrodens using which medium?

Endocarditis

Kingella kingae is usually associated with which type of infection?

Capnocytophaga spp.

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

Pasteurella spp.

Smooth gray colonies showing no hemolysis are recovered from an infected cat scratch on blood and chocolate agar but fail to grow on MacConkey agar. The organisms are gram-negative pleomorphic rods that are both catalase and oxidase positive and strongly indole positive. The most likely organism is:

Bordet–Gengou agar

Which media should be used to recover Bordetella pertussis from a nasopharyngeal specimen?

Biphasic Castenada bottles with Brucella broth

Which medium is recommended for the recovery of Brucella spp. from blood and bone marrow specimens?

Basic fuchsin and thionin

In addition to CO2 requirements and biochemical characteristics, Brucella melitensis and Brucella abortus are differentiated by growth on media containing which two dyes?

Cysteine and cystine

Which of the following amino acids are required for growth of Francisella tularensis?

Buffered charcoal–yeast extract (CYE) agar

Which medium is best for recovery of Legionella pneumophila from clinical specimens?

Indole and xylose

Haemophilus influenzae causes ocular infections (pinkeye) and requires X and V factors in the primary medium for growth. The subspecies Haemophilus influenza (biogroup) aegyptius can further be identified and differentiated by which two tests?

Chocolate agar

Haemophilus species that require the V factor (NAD) are easily recovered on which primary agar plate?

NAD

Which of the following products is responsible for satellite growth of Haemophilus spp. around colonies of Staphylococcus and Neisseria spp. on sheep blood agar?

Horse blood agar and Mueller–Hinton agar with X and V strips

Which of the following plates should be used in order to identify Haemophilus haemolyticus and Haemophilus parahaemolyticus?

b

The majority of Haemophilus influenzae infections are caused by which of the following capsular serotypes?

H. aphrophilus

Which Haemophilus species is generally associated with endocarditis?

H. ducreyi

Which Haemophilus species is difficult to isolate and recover from genital ulcers and swollen lymph nodes?

Production of β-lactamase enzymes

Which of the following is a characteristic of strains of Haemophilus influenzae that are resistant to ampicillin?

Haemophilus influenzae

A small, gram-negative coccobacillus recovered from the CSF of a 2-year-old 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?

X factor requirement

The δ-ALA test (for porphyrins) is a confirmatory procedure for which test used for identification of Haemophilus species?

Bartonella spp.

An elderly woman who cared for several domestic cats was hospitalized with suspected cat-scratch disease (CSD). Blood cultures appeared negative, but a small, slightly curved pleomorphic gram-negative bacillus grew on BHI agar (brain, heart infusion agar with 5% horse or rabbit blood). What is the most likely identification?

Bordetella pertussis

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–Genjou, and Regan–Lowe (with 10% charcoal) agars. All media grew a gram-negative coccobacillus. Carbohydrate and biochemical tests were negative. What is the most likely identification?

Endocarditis

The HACEK group of organisms (Haemophilus aphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella spp.) are all known for which type of infection?