Deck 22: Nonfermenting Gram-Negative Rods

Question 1

Which of the following characteristics would lead you to suspect the presence of a nonfermenting gram-negative rod?

A) TSI reaction is K/A
B) Oxidase negative
C) Inability to grow on MacConkey agar
D) Susceptible to multiple antimicrobial agents

Answer 1

Inability to grow on MacConkey agar

Question 2

The deep or butt reaction of a TSI slant appears red-orange for non-fermenting gram-negative rods because the organisms

A) ferment the sugars present.
B) oxidize the sugars present.
C) cannot ferment the sugars present.
D) degrade the proteins present.

Answer 2

cannot ferment the sugars present.

Question 3

Commercial identification systems may have problems with the identification of non-fermenting gram-negative rods because

A) some of these organisms are slow growing.
B) their biochemical reactions tend to be weak.
C) they are not frequently isolated.
D) a and b.
E) b and c.

Answer 3

a and b.

Question 4

Respiratory cultures obtained from an individual with cystic fibrosis should include selective medium for the isolation of

A) Burkholderia pseudomallei.
B) Burkholderia cepacia complex.
C) Acinetobacter baumannii.
D) Stenotrophomonas maltophilia.

Question 5

The second- and third-degree burns of a firefighter become infected with Pseudomonas aeruginosa while she is hospitalized in the burn unit. What is the most likely environmental source for this organism?

A) Her gastrointestinal tract
B) The bathtub used to debride her wounds
C) Fresh flowers received from her family
D) Her blood pressure cuff

Question 6

A 69-year-old retired army general develops pneumonia after his diagnosis of chronic lymphocytic leukemia. The organism isolated in his sputum culture is an oxidase-positive, wrinkled, non-lactose fermenter with a musty odor that is arginine positive. He probably acquired this organism from

A) aerosols of soil and water while serving in Vietnam.
B) his pet horse.
C) the hospital environment.
D) his normal upper respiratory flora.

Question 7

The decarboxylase control tube inoculated with a suspected non-fermenting gram-negative rod is a turbid dirty gray color after incubation at 35°C in ambient air for 24 hours. This result

A) renders all decarboxylase results invalid.
B) is acceptable and the decarboxylase results can be read.
C) indicates the tube was probably not inoculated.
D) should be read at 48 hours not 24 hours.

Question 8

Hugh-Leifson oxidation-fermentation (OF) medium differs from carbohydrate medium used to identify Enterobacteriaceae by all of the following characteristics except

A) brom thymol blue is used as the pH indicator.
B) a control tube is not required for OF medium.
C) there is a higher percentage of carbohydrate present in OF medium.
D) there is a lower concentration of protein present in OF medium.

Question 9

An oxidase-positive, wrinkled, non-lactose fermenting colony is suspicious for

A) the organism that causes glanders.
B) an individual with cystic fibrosis.
C) a potential bioterrorism agent.
D) a common antibiotic-resistant nosocomial organism.

Question 10

The isolation of an extremely mucoid, oxidase-positive, non-lactose fermenter from the lower respiratory tract usually correlates with the clinical diagnosis of

A) melioidosis.
B) nothing-it is an environmental contaminant.
C) glanders.
D) cystic fibrosis.

Question 11

Which of the following gram-negative rods is associated with individuals who have cystic fibrosis?

A) An oxidase-positive, pyocyanin-producing, non-lactose fermenter.
B) An oxidase-negative, nonmotile, non-lactose fermenter that is K/NC on TSI.
C) An oxidase-positive, lysine-positive, non-lactose fermenter.
D) a and c.
E) All of the above.

Question 12

Two blood cultures of a premature infant grow a yellow-pigmented colony that is a non-lactose fermenter. The colony provides the following reactions:
$\begin{array}{lrr} \text { Oxidase: purple}& \text { Indole: pink}& \text { Motility: negative}\end{array}$
The organism is probably

A) Burkholderia cepacia complex.
B) Stenotrophomonas maltophilia.
C) Elizabethkingia meningosepticum.
D) none of the above.

Question 13

An anemic patient received a unit of blood. She develops fever and chills after infusion of the unit. Blood cultures of the patient and a sample of the blood unit grow the same organism. The non-lactose fermenter isolated displays the following reactions:
$\begin{array}{lrr}\text {Oxidase: purple}&\text {Growth at \( 42^{\circ} \mathrm{C} \) : negative}\\\text {Colony under UV light: yellow}&\text {Arginine: purple}\\\text {Motility: positive}&\text {Gelatin hydrolysis: liquified}\\\text {Acetamide: no color change}&\text {Nitrate after addition of zinc: red}\end{array}$
The organism is

A) Pseudomonas. putida
B) P. fluorescens.
C) P. aeruginosa.
D) P. stutzeri.

Question 14

Which of the following oxidase-negative, non-motile, non-fermenting, gram-negative rods can mimic a late lactose fermenter due to the oxidation of lactose rather than fermentation?

A) Acinetobacter baumannii
B) Burkholderia cepacia complex
C) Achromobacter xylosoxidans
D) Stenotrophomonas maltophilia

Question 15

A physician calls the microbiology department for the results of a lower respiratory culture of a 15-year-old female with cystic fibrosis. The culture grows an oxidase-negative, motile, lysine-positive, non-lactose fermenter that presents as K/NC on TSI and an oxidase-positive, lysine-positive, non-lactose fermenter. Based on these results, you tell the physician she can potentially treat both organisms with

A) imipenem.
B) an aminoglycoside.
C) polymyxin B.
D) trimethoprim-sulfamethoxazole.

Question 16

An oxidase-negative, non-motile, non-lactose fermenter demonstrates K/NC on TSI and is considered a significant nosocomial pathogen due to its multiresistance. Which of the following antibiotics remains a viable treatment option for this organism?

A) Imipenem
B) Piperacillin/tazobactam
C) Aztreonam
D) Ciprofloxacin

Question 17

A tracheal aspirate, obtained from a comatose patient on a ventilator, grew an oxidase-positive non-lactose fermenter that produced a distinctive odor of sliced apples. It proved to be:
Motile: positive
Nitrate: red after addition of reagents A, B, and zinc
OF medium:
Open tubes: glucose: blue, maltose: blue, lactose: blue, sucrose: blue
Closed tubes: glucose: green, maltose: green, lactose: green, sucrose: green
This organism is

A) Acinetobacter baumannii.
B) Alcaligenes faecalis.
C) Moraxella nonliquefaciens.
D) Elizabethkingia meningosepticum.

Question 18

A patient in the intensive care unit has developed pneumonia. A sputum culture grows an oxidase-negative, non-lactose fermenter. The organism is demonstrated in the Gram stain below. The microbiologist works up the organism as a member of the Enterobacteriaceae. The next day she realizes her error. The organism displays the following results:
Source: CDC and Dr. W. A. Clark
TSI: K/NC
Motility: negative
OF medium:
Open tubes: glucose: yellow, lactose: yellow, maltose: green
Closed tubes: glucose: green, lactose: green, maltose: green

A) Stenotrophomonas maltophilia.
B) Acinetobacter baumannii.
C) Moraxella lacunata.
D) Pseudomonas fluorescens.

Question 19

A yellow-pigmented gram-negative rod is isolated from the tracheal aspirate of a 76-year-old female. She is comatose due to meningitis and on a ventilator. The organism proved to be:
$\begin{array}{ll} \text {MacConkey agar: clear colonies}& \text {Oxidase: no color change}\\ \text {Motility: positive}& \text {TSI: \( \mathrm{K} / \mathrm{NC} \)}\end{array}$

OF medium:
Open tubes: glucose: yellow, lactose: yellow, maltose: yellow
Closed tubes: glucose: green, lactose: green, maltose: green
When assessing the organisms's clinical significance, it is probably

A) of limited pathogenicity
B) a colonizer.
C) a true nosocomial pathogen.
D) a and b.

Question 20

A 23-year-old male develops folliculitis after spending the afternoon in the hot tub at a ski resort. The ski resort physician submits a swab of the pustular discharge for culture. The organism isolated grew as an oxidase-positive, non-lactose fermenter. It is beta-hemolytic on sheep blood agar with a cyan-colored pigment in the surrounding medium and emits a fruity odor. These culture results

A) are adequate to presumptively identify the organism as Pseudomonas aeruginosa.
B) require additional biochemical testing to definitively identify the organism.
C) are not needed because the organism is an environmental contaminant.
D) also require viewing the organism under an ultraviolet light.