NONFERMENTATIVE BACILLI

Question 1

What are the most appropriate screening tests to presumptively differentiate and identify the nonfermentative gram-negative bacilli (NFB) from the Enterobacteriaceae species?

Answer 1

Oxidase, TSI, nitrate reduction, growth on MacConkey agar

Question 2

Presumptive tests used for identification of the Pseudomonas spp. are:

Answer 2

Oxidase, oxidation–fermentation (OF) glucose (open), OF glucose (sealed), motility,
pigment production

Question 3

Which tests are most appropriate to differentiate between Pseudomonas aeruginosa and Pseudomonas putida?

Answer 3

Mannitol, nitrate reduction, growth at 42°C

Question 4

Which test group best differentiates Acinetobacter spp. from P. aeruginosa?

Answer 4

Oxidase, motility, nitrate reduction

Question 5

In addition to motility, which test best differentiates Acinetobacter spp. and Alcaligenes faecalis?

Answer 5

Oxidase

Question 6

The most noted differences between P. aeruginosa and Stenotrophomonas maltophilia are:

Answer 6

Oxidase, 42°C growth, and polar tuft of flagella

Question 7

Which nonfermentative bacillus is usually associated with a lung infection related to cystic fibrosis (CF)?

Answer 7

Pseudomonas aeruginosa

Question 8

A nonfermenter recovered from an eye wound is oxidase positive, motile with polar monotrichous flagella, and grows at 42°C. Colonies are dry, wrinkled or smooth, buff to light brown, and are difficult to remove from the agar. In which DNA homology group

Answer 8

Pseudomonas stutzeri

Question 9

Which organism is associated with immunodeficiency syndromes and melioidosis (a glanders-like disease prevalent in Southeast Asia and northern Australia)?

Answer 9

Burkholderia pseudomallei

Question 10

Which characteristics/biochemical tests are used to differentiate Burkholderia cepacia from S. maltophilia?

Answer 10

Pigment on blood agar, oxidase, DNase

Question 11

The following results were obtained from a pure culture of gram-negative rods recovered from the pulmonary secretions of a 10-year-old cystic fibrosis patient with pneumonia:

Oxidase = +
Motility = +
Glucose OF (open) = +
Gelatin hydrolysis = +
Pigment = Red
Arginine dihydrolase = + (nonfluorescent)
Growth at 42°C = +
Flagella = + (polar, monotrichous)

Answer 11

Pseudomonas aeruginosa

Question 12

Alcaligenes faecalis (formerly A. odorans) is distinguished from Bordetella bronchiseptica with which test?

Answer 12

Urease (rapid)

Question 13

Chryseobacterium spp. are easily distinguished from Acinetobacter spp. by which of the following two tests?

Answer 13

Oxidase, growth on MacConkey agar

Question 14

A gram-negative coccobacillus was recovered on chocolate agar from the CSF of an immunosuppressed patient. The organism was nonmotile and positive for indophenol oxidase but failed to grow on MacConkey agar. The organism was highly susceptible to penicillin. The most probable identification is:

Answer 14

Moraxella lacunata

Question 15

Cetrimide agar is used as a selective isolation agar for which organism?

Answer 15

Pseudomonas aeruginosa

Question 16

A specimen from a 15-year-old female burn patient was cultured after débridement, and the following results were obtained:
Oxidase = +
Catalase = +
Ornithine decarboxylase = Neg
Lysine decarboxylase = Neg
Motility = +
Glucose = + for oxidation (open tube)
Arginine dihydrolase = +
Maltose = Neg for oxidation (open tube)
Penicillin = Resistant
Aminoglycosides = Susceptible
Colistin (Polymixin B) = Susceptible

Answer 16

Pseudomonas aeruginosa

Question 17

A yellow pigment–producing organism, growing on chocolate agar, testing oxidase positive, nonmotile and does not grow on MacConkey agar was recovered from the blood of a neonate. What is the most likely organism?

Answer 17

Elizabethkingia (formerly Chryseobacterium) meningosepticum

Question 18

Which reagent(s) is (are) used to develop the red color indicative of a positive reaction in the nitrate reduction test?

Answer 18

Sulfanilic acid and α-naphthylamine

Question 19

A culture from an intra-abdominal abscess produced orange-tan colonies on blood agar that gave the following results:
Oxidase = +
KIA = Alk/Alk (H2S)+
DNase = +
Growth at 42°C = Neg
Nitrate reduction = +
Motility = + (single polar flagellum)
Ornithine decarboxylase = +
MacConkey agar = NLF (non–lactose fermenter)

Answer 19

Shewanella putrefaciens

Question 20

Chryseobacterium spp. and B. cepacia are easily differentiated by which test?

Answer 20

Motility

Question 21

A 15-year-old female complained of a severe eye irritation after removing her soft contact lenses. A swab specimen of the infected right eye was obtained by an ophthalmologist, who ordered culture and sensitivity testing. The culture was plated on blood agar and MacConkey agar. At 24 hours, growth of a gram-negative rod that tested positive for cytochrome oxidase was noted. The Mueller-Hinton sensitivity plate showed a bluish-green “lawn” of growth that proved highly resistant to most of the antibiotics tested except amikacin, tobramycin, and ciprofloxacin. What is the most likely identification?

Answer 21

Pseudomonas aeruginosa

Question 22

Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes, antimicrobial resistance, and production of alginate?

Answer 22

Pseudomonas aeruginosa

Question 23

A 20-year-old horse groomer exhibited a “glanders-like” infection. His history indicated he had suffered several open wounds on his hands 2 weeks before the swelling of his lymph nodes. A gram-negative rod was recovered from a blood culture that grew well on blood and MacConkey agars. Most of the biochemical tests were negative, including the cytochrome oxidase test. What is the most likely identification?

Answer 23

Burkholderia mallei

Question 24

A Vietnam War veteran presented with a “glanders-like” infection (melioidosis). Several blood cultures produced gram-negative rods that were positive for cytochrome oxidase, oxidized glucose and xylose, and grew at 42°C. What is the most likely organism?

Answer 24

Burkholderia pseudomallei

Question 25

Cytochrome oxidase-positive, nonfermentative gram-negative bacilli were recovered from the stool of a patient with CF. The isolates produced wet (mucoidy) light blue colonies on tryptic soy agar. Which identification is most likely?

Answer 25

Pseudomonas aeruginosa

Question 26

Several postoperative hospitalized patients were colonized with gram-negative coccobacilli growing on MacConkey agar. Specimens were obtained from blood, urine, and wound sites. Testing revealed oxidase negative, nonmotile organisms. Which of the following is the most likely cause of the nosocomial infections?

Answer 26

Acinetobacter spp.

Question 27

A nosocomial infection involving an 80-year-old female patient, recovering from pneumonia, produced many oxidase-negative colonies on MacConkey agar. Further testing results are:
Motility = +
Maltose = +
Resistant to most beta-lactams
Glucose = +
Resistant to most aminoglycosides

Answer 27

Stenotrophomonas maltophilia