In Vitro Activity of Telithromycin against Viridans Group Streptococci and Streptococcus bovis Isolated from Blood: Antimicrobial Susceptibility Patterns in Different Groups of Species

Abstract

The in vitro activities of penicillin, erythromycin, clindamycin, and telithromycin were determined against 155 viridans group streptococci (VGS) and 18 Streptococcus bovis blood isolates. Heterogeneity in the susceptibility patterns and macrolide resistance phenotypes and genotypes in the different groups of VGS was detected. We found seven telithromycin-resistant S. bovis isolates all harboring the erm(B) gene.Viridans group streptococci (VGS) are the main commensals of the oropharyngeal cavity in humans. They are the leading cause of subacute bacterial endocarditis and have also emerged as important pathogens causing sepsis in neutropenic cancer patients. Streptococcus bovis is frequently found as part of the commensal bowel flora. These organisms are also agents of endocarditis. Bacteremia caused by S. bovis isolates is associated with malignancies of the gastrointestinal tract.Recent studies have shown that VGS are becoming increasingly resistant to many antibiotics, and it seems that antimicrobial resistance is not homogeneous among the different members of the group (1,7,8,20). Most studies of VGS report that Streptococcus mitis, in addition to being the most frequently isolated group, is also the group that shows the highest rates of penicillin resistance (1,7,8,10,17). However, reports about the susceptibility of other VGS and S. bovis are scarce. The aim of our study was to determine overall rates of VGS susceptibility to penicillin, macrolides, and telithromycin and also to determine whether there are any differences in the susceptibility patterns and erythromycin resistance mechanisms of the different species that make up this group.A total of 155 VGS and 18 S. bovis strains isolated from blood were collected between 1998 and 2003. Of the 173 isolates, 111 were isolated from 1998 to 2002 and were previously characterized in terms of their macrolide resistance (15). All strains were identified by standard methods (16) and by the Rapid ID32 Strep system (bioMérieux, Marcy l'Étoile, France) and then classified according to the review of Coykendall (4).Susceptibility to penicillin, erythromycin, clindamycin, and telithromycin was determined by the agar dilution method. MICs were interpreted using NCCLS criteria for Streptococcus other than Streptococcus pneumoniae. For telithromycin, since no NCCLS breakpoints have been established, we used those defined for S. pneumoniae (12). Macrolide resistance phenotypes were determined using a double-disk diffusion method (18). The presence of erm and mef genes was determined by PCR amplification with previously described primers specific for erm(A), erm(B), erm(C), and mef(A) (18,19). Of the 155 VGS, 72 isolates belonged to the S. mitis group; other groups included Streptococcus anginosus (49 isolates), Streptococcus sanguis (21 isolates), Streptococcus salivarius (11 isolates), and Streptococcus mutans (2 isolates).The in vitro activities of the antibiotics tested for the different streptococci, except for the two S. mutans group isolates, which were susceptible ...

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Genomics, evolution, and molecular epidemiology of the Streptococcus bovis / Streptococcus equinus complex (SBSEC)

“…The susceptibility levels of Israeli S. bovis isolates to beta-lactams were in the same range as found previously (Siegman-Igra and Schwartz, 2003). However, erm susceptibility was higher, with only 22% in 18 blood isolates from Spain (Rodríguez-Avial et al, 2005), 35% in 48 isolates from patients' blood cultures in Hongkong, China (Lee et al, 2003) and 40% in 128 clinical Sgg and Sgp isolates from France (Leclercq et al, 2005). According to that French study the erm resistance was mainly based on the presence of ermB and rarely on mefA gene.…”

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