Question 1

Among Haemophilus influenzae strains,group designations (e.g. ,type b)are based on:

Accepted Answer

Among H.influenzae strains,two broad categories exist: typeable and nontypeable.Strains are typed on the basis of capsular characteristics.The capsule is made up of a sugar-alcohol phosphate (e.g. ,polyribitol phosphate)complex.Differences in this complex are the basis for separating encapsulated strains into one of six groups: type a,b,c,d,e,or f.

Question 2

To increase the sensitivity of direct Gram-stain examination of body fluid specimens,the specimens are usually:

Accepted Answer

To increase the sensitivity of direct Gram-stain examination of body fluid specimens,especially CSF,the specimens are usually centrifuged (2000 rpm for 10 minutes),and the smear is prepared from the resulting pellet.This concentration step can increase the sensitivity of direct microscopic examination by fivefold to tenfold.

Question 3

Isolates from cerebrospinal fluid (CSF)or respiratory tract specimens that are gram-negative coccobacilli grow on chocolate agar in CO₂ but not on blood agar,and are porphyrin-negative and nonhemolytic on rabbit or horse blood may be identified as:

Accepted Answer

All characteristics listed are those that describe H.influenzae.

Question 4

A 6-year-old boy was diagnosed with purulent conjunctivitis caused by a species of Haemophilus.What would the biochemical profile of the organism be?

Accepted Answer

The organism responsible for causing purulent conjunctivitis is H.aegyptius.Biochemically,it requires both X and V factors for growth and is hemolytic on rabbit blood.

Question 5

Of the following media,which provides the NAD necessary for the growth of Haemophilus spp.?

Accepted Answer

Five percent sheep blood agar provides one of the factors,hemin or X factor,necessary for the growth of Haemophilus spp.Most strains will not grow on 5% sheep blood agar because it contains hemin but not NAD.Chocolate,however,contains both necessary nutrients.

Question 6

The virulence of this organism,which causes chancroid,is most likely attributed to:

Accepted Answer

The organism that causes chancroid is H.ducreyi.Although the virulence is uncertain,capsular factors,pili,and certain toxins are probably involved in the attachment and penetration of host epithelial cells.

Question 7

H.influenzae can be distinguished from H.aegyptius by its _____ test for _____.

Accepted Answer

H.influenzae and H.aegyptius are biochemically quite similar;however,H.influenzae is positive for xylose fermentation,whereas H.aegyptius is negative.H.influenzae is also nonhemolytic on rabbit blood,and H.aegyptius is β-hemolytic.

Question 8

Isolates from an ear swab that are gram-negative coccobacilli grow on chocolate agar in CO₂ but not blood agar,require both X and V factors for growth,and are nonhemolytic on rabbit or horse blood may be identified as:

Accepted Answer

All characteristics listed are those that describe H.influenzae,which is commonly implicated in otitis media.

Question 9

The sputum of a 75-year-old man with chronic lung infections yields the following:
·Many gram-negative coccobacilli in Gram stain
·X and V factors required for growth
·Nonhemolytic on rabbit blood agar
The organism can be identified as:

Accepted Answer

H.influenzae is nonhemolytic on rabbit blood and requires both X and V factors to grow.Although H.aegyptius and H.haemolyticus both require X and V factors for growth,they are hemolytic on rabbit blood.H.parainfluenzae requires only V factor and is variable for β-hemolysis.

Question 10

Isolates from CSF that are gram-negative coccobacilli,grow on chocolate agar in CO₂ but not blood agar,require factor V but not X,and are nonhemolytic on rabbit or horse blood may be identified as:

Accepted Answer

All characteristics listed are those that describe H.parainfluenzae.

Question 11

Performance of the "factor requirement test" for Haemophilus involves the:

Accepted Answer

Traditional identification criteria include the requirement for X and/or V factors for growth.To establish X and V factor requirements,disks impregnated with each factor are placed on unsupplemented media,usually Mueller-Hinton agar or trypticase soy agar,that has been inoculated with a light suspension of the organism.After overnight incubation at 35°C in ambient air,the plate is then examined for growth around each disk.Many X factor-requiring organisms are able to carry over enough factor from the primary medium to give false-negative results (i.e. ,growth occurs at such a distance from the X disk as to falsely indicate that the organism does not require the X factor).

Question 12

Which of the following media provides the factors necessary for the growth of Haemophilus spp.?

Accepted Answer

Chocolate agar provides the factors (i.e. ,hemin [X factor] and NAD [V factor])that are necessary for the growth of Haemophilus spp.Most strains will not grow on 5% sheep blood agar,which contains hemin but not NAD.

Question 13

In a phenomenon known as satelliting,tiny colonies of Haemophilus spp.may be observed growing on sheep blood agar close to colonies of:

Accepted Answer

Five percent sheep blood agar contains hemin but not NAD.Several bacterial species,including S.aureus,produce NAD as a metabolic byproduct.Therefore,tiny colonies of Haemophilus spp.may be observed growing on sheep blood agar close to colonies of bacteria that can produce V factor.This phenomenon is known as satelliting.

Question 14

With one exception,species of the genus Haemophilus require which of the following media ingredients for in vitro growth?

Accepted Answer

Species of the genus Haemophilus,except for Haemophilus aphrophilus,require hemin and NAD for in vitro growth.

Question 15

In a phenomenon known as satelliting,tiny colonies of Haemophilus spp.may be observed growing on sheep blood agar close to colonies of bacteria that can produce:

Accepted Answer

Five percent sheep blood agar contains hemin but not NAD.Several bacterial species,including S.aureus,produce NAD as a metabolic byproduct.Therefore,tiny colonies of Haemophilus spp.may be observed growing on sheep blood agar close to colonies of bacteria that can produce V factor.This phenomenon is known as satelliting.

Question 16

Although a useful test in the past,the particle agglutination assay for the detection of H.influenzae,type b,capsular polysaccharide antigen is no longer reliable because of:

Accepted Answer

The detection of H.influenzae,type b,capsular polysaccharide directly in clinical specimens,such as CSF and urine,can be performed using commercially available particle agglutination assays.Historically,the latex tests have been sensitive and specific for the detection of H.influenzae,type b,especially in patients who have been on antimicrobial therapy before the collection of the specimen.Unfortunately,these tests have been reported as positive in the CSF and urine of patients who have recently received an H.influenzae,type b,vaccination;therefore positive results of agglutination assays must be interpreted with caution.

Question 17

Which of the following opportunistic organisms is associated with slowly progressive subacute bacterial endocarditis?

Accepted Answer

A.aphrophilus is opportunistic in nature and is a member of the H.aphrophilus,Aggregatibacter actinomycetemcomitans,Cardiobacterium hominis,Eikenella corrodens,and Kingella spp.(HACEK)group of bacteria associated with slowly progressive (subacute)bacterial endocarditis.

Question 18

Growth of most Haemophilus species in culture is enhanced by:

Accepted Answer

All of the choices describe conditions necessary for the cultivation of H.ducreyi.Other Haemophilus species do not have these requirements but are enhanced by increased (5% to 10%)CO₂.

Question 19

Chancroid is the sexually transmitted disease caused by:

Accepted Answer

Chancroid is the sexually transmitted disease caused by H.ducreyi.Although small outbreaks of this disease have occurred in the United States,this disease is more commonly recognized among socioeconomically disadvantaged populations that inhabit tropical environments.

Question 20

H.ducreyi requires what special media to grow?

Accepted Answer

H.ducreyi requires special media to grow.Mueller-Hinton-based chocolate agar,supplemented with 1% IsoVitaleX and vancomycin,and heart infusion-based agar,supplemented with 10% fetal bovine serum,are two such media.

Quiz 30: Haemophilus

Among Haemophilus influenzae strains,group designations (e.g. ,type b) are based on: