In the present report we describe the characteristics of 189 antimicrobial-resistant Streptococcus agalactiae isolates from bovine (38 isolates) and human (151 isolates) sources. All the strains were resistant to tetracycline (TET), and 16 (8.5%) were also resistant to erythromycin, corresponding to 23.7% of the TET-resistant bovine isolates and 4.6% of the TET-resistant human isolates. The tet(O), erm(B), and mreA resistance-related genes, as well as the bca and scpB virulence-related genes, were the most frequent among the bovine isolates, while the tet(M), erm(A), mreA, bca, lmb, and scpB genes were the most prevalent among the isolates from humans. Although a few major clusters were observed, pulsed-field gel electrophoresis results revealed a variety of profiles, reflecting the substantial genetic diversity among strains of this species isolated from either humans or bovines.Streptococcus agalactiae (group B Streptococcus [GBS]) is an important bovine pathogen, especially as a cause of both clinical and subclinical mastitis in dairy cows (23). In humans, GBS has been described as one of the most common agents of invasive infections in neonates, but it also causes invasive and noninvasive infections in adults (29). ␤-Lactam agents constitute the drugs of choice for the prophylaxis and treatment of GBS infections, since GBS isolates with confirmed resistance to these antimicrobial agents have not been observed to date (23,29). Erythromycin and other macrolides are the recommended second-line agents and the first alternative in case of allergy to ␤-lactams. Several studies, however, have documented the emergence and spread of resistance of GBS to macrolides (2, 3, 9, 10), usually in association with resistance to tetracycline.In streptococci, the most frequent macrolide resistance mechanisms are ribosomal modification by a methylase encoded by an erm gene (37) and drug efflux by a membranebound protein encoded by a mef gene (24). The presence of the Erm methylase confers resistance to erythromycin and inducible or constitutive resistance to lincosamines and streptogramin B (the macrolide-lincosamine-streptogramin B [MLS B ] phenotype), while the presence of the Mef pump confers resistance to 14-and 15-membered macrolides (M phenotype). An additional efflux mechanism, encoded by the mreA gene, has been described in GBS (8). The linB gene, described in Enterococcus faecium (4), was recently detected in a GBS isolate (10).Although resistance to tetracycline among GBS isolates is frequently found at high rates and, therefore, tetracycline is no longer indicated for the treatment of GBS infections, tetracycline resistance genes are often found on the same motile unit as the erythromycin resistance genes (33), raising concern about the role of tetracycline-resistant strains in the spread of erythromycin-resistant strains. A variety of tetracycline resistance genes have been described to date, and most of them encode either a protein which pumps tetracycline out of the cell or a ribosomal protein which protects the r...

Information on the characteristics of Streptococcus agalactiae obtained from bovine sources in Brazil is still very limited. The aim of this study was to assess the phenotypic and genotypic diversity among S. agalactiae isolates from milk of dairy cows presenting clinical or subclinical mastitis in the southeast region of Brazil. Phenotypic characterization was based on physiological and serological tests. Antimicrobial susceptibility tests were carried out by the disk method. Genetic diversity was evaluated by using random amplified polymorphic DNA-PCR (RAPD-PCR) (by using the primer 1254) and pulsed-field gel electrophoresis (PFGE) (by using SmaI as the restriction enzyme) and by PCRs for detection of genes associated with resistance to erythromycin and tetracycline as well as PCRs for detection of genes coding for cell surface-associated proteins. According to the results of physiologic tests, 45 (52.9%) isolates showed beta-hemolysis and 44 (51.7%) were susceptible to bacitracin. Fourteen different biotypes were detected. The two most frequent biotypes comprised strains that were non-beta-hemolytic; fermented galactose, lactose, and salicin; produced protease; and were negative for DNase production. Serotype III was predominant (66 isolates [77.6%]), followed by serotypes II, Ia, Ib, and VI. Resistance to tetracycline and erythromycin was found in 38 (44.7%) and 9 (10.5%) isolates, respectively, with tet(O) (31.7%) and erm(B) (100%) being the most frequently occurring resistance genes. Three genes coding for surface proteins, bca, lmb, and scpB, were detected in 55 (64.7%), 7 (8.2%), and 43 (50.5%) isolates, respectively. In most cases, isolates from animals in the same herd presented closely related genetic profiles (determined by either RAPD-PCR or PFGE), which were distinct from those of isolates from different herds.Infectious mastitis is an important health problem affecting dairy cattle and constitutes a source of economic loss for the dairy industry due to the effects on milk quality and yield. Additionally, the impact of this disease extends to the financial cost of therapeutic strategies and laboratory and veterinary services involved in control programs (15,16). The availability of information about the prevalence and the biological and epidemiological characteristics of the etiologic agents is essential for developing appropriate prevention programs and successful therapy (16,20).Streptococcus agalactiae, or group B Streptococcus (GBS), is a well-recognized worldwide etiological agent of mastitis in bovines, causing both clinical and mild subclinical mastitis of long duration (10,20). Bacterial cells are shed in milk from infected quarters, and transmission to uninfected quarters and cows usually occurs during the milking period (15, 21).The prevalence of GBS in cattle has been investigated in many areas, and the highest frequencies have been found in regions where appropriate control measures have not been implemented (20). In Brazil, studies have been developed by Empresa Brasileira de Agropecuá...