Module 11: Streptococcus (Group B)

Question 1

Streptococcus agalactiae characteristics

Answer 1

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

Question 2

Streptococcus agalactiae Presumptive ID

Answer 2

Camp and Hippurate hydrolysis test for presumptive ID

Question 3

Streptococcus agalactiae Definitive ID

Answer 3

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

Question 4

Direct ID of Group B antigen from clinical specimens

Answer 4

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

Question 5

Antimicrobial susceptibility for Group B Streptococci

Answer 5

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

Question 6

Clinical significance (Pathogenicity) of Streptococcus agalactiae

Answer 6

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