Medical Microbiology

HaemophilusandPasteurella 301

Haemophilusinfluenzae..............................

Hemophilicbacteriaaresodesignatedbecausetheyrequiregrowthfactors

containedinblood.ThemostimportanthumanpathogeninthisgenusisH.

influenzae.OtherHaemophilusspecieseitherinfectonlyanimalsorarefound

inthenormalhumanmucosalflora.TheselatterincludeH.parainfluenzae,H.

hemolyticus,H.segnis,H.aphrophilus,andH.paraphrophilus.Thesespecies

cancauseinfectionsonoccasion.

Morphologyandculture.Haemophilusaresmall(length: 1 .0– 1 .5lm,width:

0.3lm),oftenencapsulated,nonmotile,Gram-negativerods(Fig.4. 21 a).The

encapsulatedstrainsaresubclassifiedinserovarsa-fbasedonthefinestruc-

tureoftheircapsulepolysaccharides.Serovarb(Hib)causesmostHaemophi-

lusinfectionsinhumans.

Haemophilusinfluenzae

Fig.4. 21 a Gram-stained cere-

brospinalfluidsedimentprepara-

tion.Fine,Gram-negativerodssur-

roundedbyacapsule(serovarb).

Clinicaldiagnosis:purulentmenin-

gitis.

bSatellitecoloniesofHaemophilus

influenzaesurroundingtheStaphylo-

coccusaureusstreak.S.aureuspro-

videssmallamountsofVfactor.The

bloodagarcontainsfreeXfactor.

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Kayser, Medical Microbiology © 2005 Thieme