Module 11: Streptococcus (Group B) Flashcards
Streptococcus agalactiae characteristics
Group B strep
Identifcal cellular morphology and growth requirement to S. pyogenes
Cultural Characteristics: 1mm, semitransparent, gray, butter or matt consistency, small zone of beta hemolysis
Genus ID:
catalase neg, nitrate neg
Streptococcus agalactiae Presumptive ID
Camp and Hippurate hydrolysis test for presumptive ID
Streptococcus agalactiae Definitive ID
identifying the group B cell wall antigen
May be done with latex or co-agglutination group B antisera
Listeria monocytogenes may cross agglutinate with group B antisera
Colonies on agar may be similar but Gram slide should differentiate the two as Listeria is a gram pos ROD
Direct ID of Group B antigen from clinical specimens
Group b strep may cause a serous general infection of the neonate
Requires rapid diagnosis
Both latex and co-agglutination reagents are avaliable for use with specimens
Spinal fluid: suitable specimen when available
Urine: good results reported
Serum: has been used but results not reliable
neonate is infected from birth canal
Antimicrobial susceptibility for Group B Streptococci
susceptible to penicillin
Pen G or ampicillin
Some strains may require combination of ampicillin and gentamicin
Erythromycin and vancomycin used for patients with penicillin allergy
Clinical significance (Pathogenicity) of Streptococcus agalactiae
Group B strep tends to be opportunistic causing infections in immunocompromised patients
May involve eye, ear, upper respiratory tract, surgical incisions, other body parts
Most serious neonatal sepsis rapid onset = born with it late onset = 1-4wks post partum Due to bacteria colonizing in vagina of mother High mortality rate
Pregnant people screen at 34-36wks gestation with group B strep broth
If they are heavily colonized, antibiotics may be given before delivery to reduce the chance of neonatal sepsis
Treatment: penicillin and ampicillin
