Characterization and antibiotic susceptibility of Streptococcus agalactiae isolates causing urinary tract infections

Streptococcus agalactiae (GBS) has been implicated in urinary tract infections but the microbiological characteristics and antimicrobial susceptibility of these strains are poorly investigated. In this study, 87 isolates recovered from urine samples of patients who had attended the Spedali Civili of Brescia (Italy) and had single organism GBS cultured were submitted to antimicrobial susceptibility testing, molecular characterization of macrolide and levofloxacin resistance, PCR-based capsular typing and analysis of surface protein genes. By automated broth microdilution method, all isolates were susceptible to penicillin, cefuroxime, cefaclor, and ceftriaxone; 80%, 19.5% and 3.4% of isolates were non-susceptible to tetracycline, erythromycin, and levofloxacin, respectively. Macrolide resistance determinants were iMLSB (n = 1), cMLSB (n = 10) and M (n = 5), associated with ermTR, ermB and mefA/E. Levofloxacin resistance was linked to mutations in gyrA and parC genes. Predominant capsular types were III, Ia, V, Ib and IX. Type III was associated with tetracycline resistance, while type Ib was associated with levofloxacin resistance. Different capsular type-surface protein gene combinations (serotype V-alp2, 3; serotype III-rib; serotype Ia-epsilon) were detected. A variety of capsular types are involved in significant bacteriuria. The emergence of multidrug resistant GBS may become a significant public health concern and highlights the importance of careful surveillance to prevent the emergence of these virulent GBS.