Collection of GBS samples at 35-37 weeks of gestation and isolation

Remove each swab from the packaging and insert the swab 2 cm into the vagina, followed by the rectum, inserting the swab 1 cm through the anal sphincter. Three swabs were collected for each patient.

The First swab was inoculated on Todd-Hewitt broth supplemented with gentamicin 8 μg/ml and nalidixic acid 15 μg/ml (THB, Becton-Dickinson, NJ, USA). The second swab was inoculated into LIM enrichment broth (Todd-Hewitt broth with 1% yeast extract, 15 μg/ml nalidixic acid, and 10 μg/ml colistin, Becton-Dickinson, New Jersey, USA). Both swabs were incubated for 18-24 hours at 37° C in 5% CO 2 . The third swab was submerged into an appropriate transport medium (ESwab, Copan Diagnostics, Brescia, Italy). Finally, the three swabs were subcultured onto Petri dishes with Columbia agar (OXOID LTD, Basingstoke, Hampshire, England) with 5% sheep blood and incubated for 18-24 hours at 37° C to confirm GBS identification afterward.

Criteria for GBS identification

a) Gram-positive coccus.

b) Negative Catalase test.

c) CAMP test with wedge-shaped hemolysis in the presence of Staphylococcus

aureus ATCC 25923.

d) Positive hippurate hydrolysis.

e) Observation of growth with color change from white to orange pigment after

18-24 h incubation in the Strep B Carrot Broth® chromogenic medium (Hardy

Diagnostics®, Santa María, CA, USA).

f) Growth mauve colonies into CHROMagarTM StrepB base.