Exam 3 - (CH 18) Haemophilus, HACEK, Legionella & Fastidious GNB Textbook Review Questions

Question 1

Which of the following describes Haemophilus influenzae Biotype II?
A. Primarily causes meningitis and is ornithine negative and indole positive.
B. Primarily causes ear infections and is ornithine negative and indole positive.
C. Primarily causes upper respiratory tract infection and is indole negative.
D. Primarily causes conjunctivitis and is urease negative.

Answer 1

B. Primarily causes ear infections and is ornithine negative and indole positive.

Question 2

Which species is the causative agent of chancroid?
A. Haemophilus influenzae biogroup aegyptius
B. Haemophilus parahaemolyticus
C. Haemophilus ducreyi
D. Haemophilus haemolyticus

Answer 2

C. Haemophilus ducreyi

Question 3

Carryover of X factor-containing medium to the agar plates used for X factor requirement testing or anaerobic incubation can cause Haemophilus influenzae to be incorrectly identified as
A. Haemophilus parainfluenzae.
B. Haemophilus ducreyi.
C. Haemophilus haemolyticus.
D. Haemophilus parahaemolyticus.

Answer 3

A. Haemophilus parainfluenzae.

Question 4

In the porphyrin test, porphobilinogen is detected by the addition of
A. Kovac reagent.
B. naphthylamine.
C. X and V factors.
D. sulfanilic acid.

Answer 4

A. Kovac reagent.

Question 5

Which of the following is oxidase negative and requires V factor?
A. Cardiobacterium hominis
B. Haemophilus influenzae
C. Aggregatibacter segnis
D. Eikenella corrodens

Answer 5

C. Aggregatibacter segnis

Question 6

Which of the following colony characteristics best describes colonies of Aggregatibacter actinomycetemcomitans?
A. Large, yellow colonies with a bleach-like odor
B. Pinpoint colony with opaque zone near the center after 18 hours
C. Star shape with four to six points in the center after 48 hours
D. Small red colonies that pit the agar

Answer 6

C. Star shape with four to six points in the center after 48 hours

Question 7

Which of the following statements is typically true of Eikenella corrodens?
A. They are oxidase and catalase positive and colonies “pit” the agar.
B. They are hemolytic on sheep blood agar (SBA) and sensitive to clindamycin.
C. Colonies have a fruity odor and produce a green pigment.
D. Isolates do not usually grow on MacConkey (MAC) or eosin-methylene blue (EMB) agar.

Answer 7

D. Isolates do not usually grow on MacConkey (MAC) or eosin-methylene blue (EMB) agar.

Question 8

Which of the following characteristics would indicate that an isolate is a Kingella spp. rather than Neisseria gonorrhoeae?
A. Acid production from glucose
B. Catalase negative
C. Spore-forming fusiform rod
D. No growth on Thayer-Martin media

Answer 8

B. Catalase negative

Question 9

Which of the following is oxidase positive?
A. Capnocytophaga gingivalis
B. Capnocytophaga granulosa
C. Capnocytophaga ochracea
D. Capnocytophaga canimorsus

Answer 9

D. Capnocytophaga canimorsus

Question 10

Which genus is most likely given the following description?
1. Nonmotile coccobacilli
2. Oxidase positive
3. Bipolar staining
4. No growth on MAC agar
A. Pasteurella
B. Francisella
C. Cardiobacterium
D. Kingella

Answer 10

A. Pasteurella

Question 11

Describe the appearance of H. influenzae with the X and V strip test.

Answer 11

H. influenzae will grow only where both X and V factors are present; therefore, the bacteria will grow between the two strips where the two factors have diffused and around the XV strip.

Question 12

The porphyrin test for H. influenzae would be __________ because the organism __________ biosynthesize heme. The fluorescence result of the test would be __________.
a. Negative; cannot; negative
b. Positive; cannot; positive
c. Negative; can; positive
d. Positive; can; negative

Answer 12

a. Negative; cannot; negative

Question 13

Infections caused by β-lactamase– positive H. influenzae should be treated with which of the following?
a. Ampicillin
b. Penicillin
c. Either of the above
d. None of the above

Answer 13

d. None of the above

Question 14

Describe the optimal growth conditions for the recovery of H. ducreyi.

Answer 14

H. ducreyi is fastidious and requires enriched media for growth. GC agar supplemented with 1% hemoglobin, 5% fetal calf serum, 1% IsoVitaleX, and 3 mg/ L of vancomycin is recommended. The plates need to be incubated in an atmosphere of increased humidity and CO2 (5% to 10%) and at a temperature of about 32 °

Question 15

Compare the pathogenesis of H. aegyptius with H. influenzae biogroup aegyptius.

Answer 15

Both H. aegyptius and H. influenzae biogroup aegyptius are noted for causing conjunctivitis. H. influenzae biogroup aegyptius, however, is associated with a more invasive disease known as Brazilian purpuric fever characterized by conjunctivitis, high fever, vomiting, petechiae, purpura, septicemia, and shock

Question 16

A cervical culture for possible gonococcal infection is sent to the microbiology laboratory. After 24 hours of incubation, the modified Thayer-Martin (MTM) plate has small opaque colonies that adhere slightly to the medium. Microscopic examination reveals gram-negative coccobacilli, many with square ends. The organism ferments glucose and is superoxol and catalase negative. The most likely identification is:
a. N. gonorrhoeae
b. K. denitrificans
c. M. catarrhalis
d. H. ducreyi

Answer 16

b. K. denitrificans

Question 17

A 52-year-old man who had recently received a kidney transplant was admitted to the hospital with a low-grade fever, a heart murmur, and neutropenia. He had a history of periodontal disease and recently had had two teeth extracted. Blood cultures were positive after 48 hours. The isolate grew on chocolate (CHOC) agar and sheep blood agar (SBA) in 5% CO2. The colonies were nonhemolytic, slightly adhered to the surface of the media, and had a slight yellow appearance when removed. The isolate was catalase, indole, and oxidase negative. Microscopic morphology indicated gram-negative fusiform bacilli. The most probable identification is:

a. A. aphrophilus
b. K. kingae
c. C. hominis
d. Capnocytophaga spp.

Answer 17

d. Capnocytophaga spp.

Question 18

An isolate from an infected cat bite is oxidase, catalase, ornithine decarboxylase, indole, and urease positive. After 48 hours of incubation at 35 ° C, growth on SBA was described as mucoid colonies exhibiting a greenish-brown halo. A MAC agar plate shows no growth. What organism is the mostly likely cause of the infection?

Answer 18

The most likely identification is Pasteurella multocida. This microorganism is noted for causing skin infections following cat and dog bites. P. multocida is the most common Pasteurella spp. isolated.

Question 19

Which microbiologic tests are most useful in differentiating B. melitensis from H. influenzae?

Answer 19

Brucella melitensis will grow on SBA and does not require X or V factor, whereas H. influenzae will not grow on SBA and does require X and V factors.

Question 20

A patient is complaining of a painful cervical lymph node following a case of pharyngitis. Further investigation reveals that the patient consumed a medium-cooked wild rabbit in a restaurant in Germany 2 months earlier. What is the most likely cause of the infection?

Answer 20

Francisella tularensis is the most likely causative agent. The primary reservoirs for F. tularensis are rabbits. Although some infections are acquired by ingestion, it is more common to find ulceroglandular infections following direct contact with rabbits.

Question 21

What risk factors contribute to the more severe form of legionellosis?

Answer 21

Travel, age (older adults), smoking, alcohol consumption, and an immunocompromised state are risk factors that contribute to severe infections caused by Legionella spp.

Question 22

What environmental factors contribute to infection caused by Legionella spp.?

Answer 22

Crowded conditions and warm, humid, environmental sources contribute to infections by Legionella

Question 23

What is the culture medium of choice for the recovery of Legionella spp.?

Answer 23

Buffered charcoal yeast extract (BCYE) agar is the preferred medium for the recovery of Legionella spp.

Question 24

What factors of Legionella can contribute to the colonization of human-made water supplies?

Answer 24

Chlorine tolerance below 2 to 3 mg/ L, ability to grow at 20 ° to 43 ° C and survive for varying periods at 40 ° to 60 ° C, capability to adhere to components of piped water systems, ability to survive in the presence of environmental bacteria and algae, and ability to multiply within free-living protozoa are factors contributing to human infections caused by Legionella spp.

Question 25

What is the best nonrespiratory specimen for rapid detection of Legionella?

Answer 25

Urine for the urine antigen test is the best nonrespiratory specimen for the detection of Legionella spp.

Question 26

What presumptive identification methods are currently used to identify Legionella spp. in culture?

Answer 26

Presumptive identification methods include Gram staining a suspicious colony growing only on BCYE medium and finding thin, faintly-staining gram-negative rods that may show size variation, from 2 to 20 µm in length. Also, a test for L-cysteine by subculturing to BCYE and SBA should be performed. Bacteria demonstrating a requirement for L-cysteine should be typed using anti-Legionella antisera.

Question 27

Besides respiratory tract specimens, what clinical specimen is useful for the sensitive detection of Legionella antigen?
a. Blood
b. Stool
c. Urine
d. Cerebrospinal fluid (CSF)

Answer 27

c. Urine

Question 28

Are adults immune to Bordetella pertussis infection? Explain.

Answer 28

No, adults are not immune; however, infections in adults are normally mild or asymptomatic. Adults serve as reservoirs for disease in children and adolescents.

Question 29

What are the clinical samples of choice for the diagnosis of B. pertussis infection?

Answer 29

Nasopharyngeal aspirates and Dacron swabs are the clinical samples of choice for the diagnosis of B. pertussis infection.

Question 30

What transport media are appropriate for maximum recovery of B. pertussis?

Answer 30

Amies, casamino acid, and Regan-Lowe with charcoal and cephalexin transport media are the most appropriate for the maximum recovery of B. pertussis.

Question 31

Which method is preferred for the detection of Bordetella in nasopharyngeal smears?

Answer 31

PCR testing is the most widely accepted method for the rapid detection of B. pertussis.

Question 32

Compare the diseases caused by B. pertussis and B. parapertussis.

Answer 32

Both species cause pertussis in children; however, pertussis caused by B. parapertussis tends to be milder.

Question 33

Is serology a good method to identify and respond to pertussis outbreaks in real time?

Answer 33

No, serologic testing is not widely available, but it can be used as a retrospective epidemiologic tool.

Question 34

The antimicrobial agent of choice for the treatment of pertussis is:
a. Ampicillin
b. Amoxicillin
c. Erythromycin
d. Penicillin

Answer 34

c. Erythromycin

Question 35

B. bronchiseptica is considered normal oral biota in:
a. Humans
b. Dogs
c. Cows
d. Rats

Answer 35

b. Dogs

Question 36

Points to Remember

Answer 36

■ The genus Haemophilus consists of gram-negative coccobacilli or bacilli. They are facultative anaerobes that are generally oxidase and catalase positive.
■ Haemophilus spp. require preformed growth factors, X and V factors, present in blood. Testing for these factors with X and V strips and the porphyrin test are important aspects of laboratory identification procedures.
■ The advent of the Hib vaccine has decreased infection by H. influenzae type b in children in the United States by 99%, but serotype b remains prevalent in developing countries.
■ H. ducreyi causes the STD chancroid. In contrast to many other Haemophilus spp., it is not considered part of the normal oral biota of humans.
■ HACEK is an acronym for Haemophilus spp., Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella spp. The HACEK group is an important cause of endocarditis, specifically related to poor oral hygiene or dental procedures.
■ Pasteurella, Brucella, and Francisella spp. are important causes of zoonotic infections.
■ The most common Pasteurella species isolated from humans, P. multocida, most frequently causes wound infections after cat or dog bites.
■ Brucella and Francisella spp. are fastidious gram-negative coccobacilli causing zoonoses and are considered potential bioterrorism agents.

Question 37

Points to Remember

Answer 37

■ Legionella spp. are pleomorphic, weakly staining gram-negative bacilli, which are ubiquitous in aquatic environments and infect humans through the respiratory route.
■ Legionella spp. are transmitted to humans primarily via aerosolized particles. Sources include contaminated potable water distribution systems, respiratory therapy equipment, and recreational waters. Transmission between humans has not been demonstrated.
■ Legionnaires’ disease is a febrile disease with pneumonia that is often associated with travel. Pontiac fever is a milder febrile disease resembling influenza that may be caused by inhalation of bacterial toxin.
■ On BCYE agar, colonies appear convex and glistening. The central portion of young colonies have a “ground glass” appearance, light gray and granular, whereas the periphery of the colony has pink or light blue or bottle-green bands.
■ Using a combination of nonselective and selective BCYE agar is the best strategy for isolation of Legionella organisms. Acid treatment of specimens contaminated with other bacteria before inoculation enhances isolation of Legionella spp.
■ Rapid assays useful for the detection of Legionella spp. are the urine antigen detection tests.
■ Infections caused by Bordetella spp. are acquired through the respiratory tract via respiratory droplets or direct contact with infectious secretions.
■ B. pertussis and B. parapertussis cause pertussis, or whooping cough, and are primary human pathogens of the respiratory tract. ■ Bordetella spp. are tiny, gram-negative coccobacilli and might become elongated if recovered from media containing cephalexin.
■ Nasopharyngeal aspirates or swab specimens should be plated directly onto culture media or transferred to an appropriate transport system (casamino acid or Amies transport medium) at the bedside. ■ Contemporary laboratory diagnosis of pertussis generally employs culture isolation with or without PCR testing.
■ B. bronchiseptica can be part of the normal oral biota of dogs and cats, and infections in humans typically follow bites by these animals.
■ Antimicrobial susceptibility testing is not normally performed on B. pertussis. The drug of choice in the treatment of pertussis is erythromycin.