Phenotypic and Molecular Characteristics of Streptococcus agalactiae Isolates Recovered from Milk of Dairy Cows in Brazil

Abstract

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...

In vitro antimicrobial susceptibility and genetic resistance determinants of Streptococcus agalactiae isolated from mastitic cows in Brazilian dairy herds

“…Gao et al (2012), in a study of 55 S. agalactiae isolates collected from Chinese cows, reported that 29.4% were resistant to this antimicrobial. In contrast, all 85 strains of this bacterium recovered from Brazilian cattle in an investigation by Duarte et al (2004) were found to be resistant. In addition, Rato et al (2013) documented a resistance rate of 80.6% among 108 isolates collected from Portuguese cows.…”

“…Erythromycin resistance has been documented worldwide in studies concerning S. agalactiae strains of human and bovine origin. In the United States and Europe, resistance rates of approximately 4-50% have been reported (DIPERSIO; DIPERSIO, 2006;DOGAN et al, 2005;GUÉRIN-FAUBLÉE et al, 2002;SADOWY et al, 2010), while in Brazil, estimates have been lower than 10% (CORRÊA et al, 2011;DUARTE et al, 2004DUARTE et al, , 2005PALMEIRO et al, 2010). However, of the Brazilian bovine isolates examined by Pinto et al (2013), 27.6% were resistant to this antibiotic, a higher value than that recorded in the present work (19.5%).…”

“…High rates of tetracycline resistance (60-90%) have been reported among both human and bovine S. agalactiae isolates (DOGAN et al, 2005;DUARTE et al, 2004;GAO et al, 2012;PINTO et al, 2013;RATO et al, 2013). In the current work, resistance to this antimicrobial was found to be approximately 35.6%.…”

“…These are the most commonly identified tet genes among both bovine and human S. agalactiae isolates (DOGAN et al, 2005;DUARTE et al, 2005;DUTRA et al, 2014;PINTO et al, 2014), while others determinants such as tetS and tetK being observed less frequently (DUARTE et al, 2004;RATO et al, 2013). Four isolates exhibiting phenotypic tetracycline resistance harbored neither tetM nor tetO, suggesting the presence of a different tet gene, such as tetS or tetK.…”

“…In this study, ermB was found in 16.1% of strains and its presence was associated with resistance to these antibiotics, whereas ermA was not detected. Prior investigations have described ermB as the most common erm gene in bovine S. agalactiae isolates, while ermA is more frequent among human strains (DUARTE et al, 2004;DUTRA et al, 2014). Six isolates showed phenotypic resistance to erythromycin and clindamycin despite not carrying ermA or ermB.…”