Streptococcus agalactiae in a Large Portuguese Teaching Hospital: Antimicrobial Susceptibility, Serotype Distribution, and Clonal Analysis of Macrolide-Resistant Isolates

Group B streptococci are emerging as a cause of serious infection worldwide. The capsular polysaccharides are not only important virulence factors but also the target of vaccine development efforts. Serotypes III (24.6%), V (23.4%), Ia (17.8%), and II (16.3%) were the most prevalent among 252 Streptococcus agalactiae isolates collected during 1999-2002 in the largest hospital of Lisbon, Portugal. The substantial proportion of bacteremic patients (17 neonates and 21 adults) in this period illustrates the present importance of S. agalactiae as a cause of invasive disease. All isolates were fully susceptible to penicillin (MIC50 = 0.064 μg/ml; MIC90 = 0.094 μg/ml, range 0.008-0.094), cefotaxime, chloramphenicol, ofloxacin, and vancomycin. Resistance was found to tetracycline (75.4%), erythromycin (10.7%), and clindamycin (9.9%). Of the 27 erythromycin-resistant isolates, 70.4% had the cMLSB, 22.2% the iMLSB, and 7.4% the M phenotype. All isolates presenting the M phenotype carried the mef(A) gene, whereas th...