Investigation of the Serotype Distribution, Biofilm Production and Antibiotic Susceptibilities of Group B Streptococci Isolated From Urinary Samples

Abstract

Streptococcus agalactiae (Group B streptococcus, GBS), a member of normal flora of human gastrointestinal and genitourinary systems, is a leading cause of sepsis, meningitis, and pneumonia particularly in newborn. GBS can also cause severe infections in pregnant women and adults with underlying disease, as well as mild diseases, such as urinary tract infections (UTIs). GBS strains exhibit 10 different serotypes, and the identification of serotype distribution is important epidemiologically. The role of biofilm production is one of the virulence factors that has been discussed in the pathogenesis of GBS infections. Although resistance to penicillin and ampicillin has not been documented in GBS, different rates of resistance has been reported for the alternative antibiotics to penicillin. The aim of this study was to investigate the serotype distribution, the ability of biofilm formation and the antibiotic susceptibilities of S. agalactiae strains isolated from urine cultures. A total of 60 strains were included in the study, 40 of them were isolated from patients (38 female 2 male; mean age: 36.7 years) with urinary tract complaints whose cultures yielded single type of colonies in the number of >= 50.000 cfu/ml, whereas 20 of them were isolated from patients (19 female 1 male; mean age: 37.2 years) without urinary tract complaints whose cultures yielded mixed colonies in the number of <= 20.000 cfu/ml. Chromogenic media were used for the isolation and the isolates were identified by conventional methods. The isolates were then serotyped by latex agglutination method and their antibiotic susceptibilities were determined by disk diffusion method recommended by CLSI documents. Biofilm formation of the strains were investigated by microplate and Congo red agar (CRA) methods. In our study, the most frequently detected serotypes were V (n=18; 30%) and II (n=14; 23.3%), followed by serotype Ia (n=10; 16.7%), III (n=9; 15%), Ib (n=3; 5%), VI (n=1; 1.7%) and VII (n=1; 1.7%). Serotype IV, VIII and IX were not detected, while four (6.7%) isolates were untypeable. Serotype V (13/40; 32.5%) and serotip II (6/20; 30%) were in the first line among the strains isolated from patient and control groups, respectively. All of the GBS isolates were found susceptible to penicillin, vancomycin and cefotaxime. The rates of resistance against ofloxacin, erythromycin and clindamycin in patient group were found as 22.5%, %10 and 5%, respectively. In the control group resistance rates against erythromycin and clindamycin were both 10%, while no resistance was detected to the other antibiotics. The ofloxacin resistance in the patient group was found significantly higher than that of control group (p=0.02). By microplate method, the percentage of moderate/strong biofilm producers was found as 42.5%(17/40) in the patient group and 20% (4/20) in the control group, however the difference between the groups was not statistically significant (p=0.08). All GBS strains were detected as positive by the CRA method, and it has been suggested that this might have been