Streptococcus agalactiae: Sensitivity profile in pregnant women attending health units in northeastern Brazil

ARTICLE HIGHLIGHTS

Research background

Streptococcus agalactiae (Group B Streptococcus, GBS) is a bacterium known to be a causative agent of maternal and neonatal infections. The colonization of pregnant women by GBS, although most patients are asymptomatic, represents a risk for several pathologies, from chorioamnionitis, endometritis, cystitis, and pyelonephritis to febrile bacteremia. In addition, this infection can trigger pneumonia, meningitis and sepsis in neonates. To prevent this vertical transmission, prophylaxis with crystalline penicillin G or macrolides is recommended. However, with increasing levels of resistance, it is necessary to know the local resistance profile regarding adequate antimicrobial use.

Research motivation

It is important to identify and prophylactically treat pregnant women to avoid puerperal problems, especially early neonatal infection. In this sense, knowledge on GBS colonization detection and resistance rates to standard treatments is essential for clinical practice on GBS disease.

Research objectives

To verify the sensitivity profile of Streptococcus agalactiae isolated in pregnant women attending health units in the urban area of Vitória da Conquista, in Bahia State, Brazil.

Research methods

This is a cross-sectional study with a quantitative approach where 210 vaginorectal swabs collected from pregnant women attending health units in the county of Vitória da Conquista, in Bahia State, Brazil were analyzed. Pregnant women with gestational ages from 32 wk to 40 wk were eligible for this study. A single vaginal/rectal swab was collected from the women without a speculum, inoculated into Stuart transport medium, and placed in a chromogenic medium (Biomérieux^®) for streptococci by the depletion technique. Subsequently, the samples were added to blood agar (Isofar^®) 5% (sheep blood) incubated for 18 h to 24 h at 35°C to 37°C in an atmosphere of 5% CO_2. The swabs were then inoculated into tubes containing Todd-Hewitt medium (Biomérieux^®) at 35°C to 37°C from 18 h to 24h and then into chromogenic medium (Biomérieux^®) for streptococci and blood agar (Isofar^®) 5% (lamb).

All small colony growth with a grayish pattern, surrounded by a discrete halo of β-hemolysis, or without hemolysis (characteristics for GBS identification) underwent the catalase test and conventional Gram staining followed by microscopic analysis. For Gram-positive, catalase-negative colonies, obtained from blood agar and pink or red colonies obtained from chromogenic medium, a CAMP test (Christie, Atkins and Munch-Petersen) was performed using the kit composed of Todd-Hewitt and Hemolisinabac^® (Probac do Brasil) and latex agglutination (serogroupage) using the Slidex^® Strepto Plus B kit (Biomeriéux), to confirm the species. The antimicrobial sensitivity profile of positive GBS samples was determined by the disk diffusion technique, according to the CLSI12 manual, in Mueller Hinton medium (Isofar^®) supplemented with 5% sheep blood.

Research results

Among the 210 pregnant women participating in the study, 38 (18.1%) had a positive GBS culture. All GBS strains isolated were sensitive to 10 U penicillin, 10 µg ampicillin, 30 µg cefotaxime and 30 µg vancomycin. Seven strains (18.4%) resistant to clindamycin 2 µg and eight (21.1%) resistant to erythromycin 15 µg were observed. Of these, six were concomitantly resistant to erythromycin and clindamycin, two resistant only to erythromycin and one resistant only to clindamycin. All nine GBS isolates that showed resistance to erythromycin and/or clindamycin showed negative results on the D-test. Two thirds of the isolates showed cMLSB phenotype and resistance only to erythromycin in specimens in this study (02), refers to strains with phenotype M and resistance to clindamycin (01) only with phenotype L.

Research conclusions

Chemoprophylaxis for GBS in pregnant women, especially for those allergic to penicillin, should be guided by an antimicrobial susceptibility test as resistant GBS strains were reported in this study.

Research perspectives

The information provided by this study is applicable for the elaboration of GBS guidelines for adequate prophylaxis in different populations.