Medical Microbiology

242 4 BacteriaasHumanPathogens

sistanceextendstocephalosporinsaswell.However,certaincephalosporins

(e.g.,ceftriaxone)canbeusedagainstpenicillin-resistantpneumococcidueto

theirhigherlevelsofactivity.

Epidemiologyandprophylaxis.Pneumococcalinfectionsareendemicand

occurinallseasons,morefrequentlyintheelderly.Humansarethenatural

pathogenreservoir.

ThevaccineproductPneumovaxÒisavailableforimmunizationpurposes.

Itcontains 25 mgofthepurifiedcapsulepolysaccharidesofeachof 23 ofthe

mostfrequentserovars.Eightytoninetypercentofallisolatedpneumococci

haveantigenscontainedinthisvaccine,whichisprimarilyindicatedinper-

sonswithpredisposingprimarydiseases.Thereisalsoaseven-valentcon-

jugatevaccinethatiseffectiveinchildrenundertwoyearsofage(p. 3 3).Ex-

posureprophylaxisisnotnecessary.

Streptococcusagalactiae(BStreptococci).............

Bstreptococcioccasionallycauseinfectionsoftheskinandconnectivetissues,

sepsis,urinarytractinfections,pneumonia,andperitonitisinimmunocom-

promisedindividuals.Aboutonein 1000 neonatessuffersfromasepsiswith

orwithoutmeningitis.Theseinfectionsmanifestinthefirstdaysoflife(early

onsettype)orinthefirstweeksoflife(lateonsettype).Intheearlyonset

form,theinfectioniscausedintrapartumbyBstreptococcicolonizingthe

vagina.Potentialpredisposingfactorsincludebirthcomplications,premature

birth,andalackofantibodiestothecapsuleinmotherandneonate.

OralStreptococci......................................

Mostoftheoralstreptococciofthetypeoftenknownastheviridansgroup

havenogroupantigen.Theyusuallycausea-hemolysis,somec-hemolysisas

well.

Oralstreptococciareresponsiblefor 50 – 70 %ofallcasesofbacterialen-

docarditis,overallincidenceofwhichisonetotwocasesper 100000 an-

nually.Theoriginsofendocarditislieininvasionofthevascularsystem

throughlesionsintheoralmucosa.Atransitorybacteremiaresults.Theheart

valvesarecolonizedandabiofilmisformedbytheorganism.Predisposing

factorsincludecongenitalheartdefects,acuterheumaticfever,cardiacsur-

gery,andscarredheartvalves.Laboratorydiagnosisofendocarditisinvolves

isolationofthepathogenfrombloodcultures.Drugtherapyofendocarditisis

carriedoutwitheitherpenicillinGaloneorcombinedwithanaminoglyco-

side(mostlygentamicin).Bactericidalactivityisthedecisiveparameter.

4

Kayser, Medical Microbiology © 2005 Thieme