Braz J Infect Dis. 2013 Mar-Apr;17(2):131-6.

Distribution of serotypes and evaluation of antimicrobial susceptibility among human and bovine Streptococcus agalactiae strains isolated in Brazil between 1980 and 2006.

Pinto TC, Costa NS, Vianna Souza AR, Silva LG, Corrêa AB, Fernandes FG, Oliveira IC, Mattos MC, Rosado AS, Benchetrit LC.

Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.



Streptococcus agalactiae is a common agent of clinical and subclinical bovine mastitis and an important cause of human infections, mainly among pregnant women, neonates and nonpregnant adults with underlying diseases. The present study describes the genetic and phenotypic diversity among 392 S. agalactiae human and bovine strains isolated between 1980 and 2006 in Brazil. The most prevalent serotypes were Ia, II, III and V and all the strains were susceptible to penicillin, vancomycin and levofloxacin. Resistance to clindamycin, chloramphenicol, erythromycin, rifampicin and tetracycline was observed. Among the erythromycin resistant strains, mefA/E, ermA and, mainly, ermB gene were detected, and a shift of prevalence from the macrolide resistance phenotype to the macrolide-lincosamide-streptogramin B resistance phenotype over the years was observed. The 23 macrolide-resistant strains showed 19 different pulsed-field gel electrophoresis profiles. Regarding macrolide resistance, a major concern in S. agalactiae epidemiology, the present study describes an increase in erythromycin resistance from the 80s to the 90s followed by a decrease in the 2000-2006 period. Also, the genetic heterogeneity described points out that erythromycin resistance in Brazil is rather due to horizontal gene transmission than to spreading of specific macrolide-resistant clones. Copyright © 2013 Elsevier Editora Ltda.

PMID: 23453948



Streptococcus agalactiae, also known as group B Streptococcus (GBS), was first identified as a major cause of bovine mastitis during the late 19th century. Only in the mid 20th century this microorganism was also recognized as a frequent cause of invasive diseases among human newborns, and the epidemiological linkage between such different hosts has been the target of exhaustive studies for many years.

GBS epidemiology is still largely unknown in Brazil, and therefore we aimed to gather valuable information on this subject, by analyzing serotype distribution and antimicrobial susceptibility profiles of a large and diverse collection of GBS isolates, representing different periods of time and different isolation sources, which also enabled a comparison between human and bovine isolates.

Our results showed that serotype distribution was mainly stable along time, highlighting the prevalence of serotypes Ia, II, III and V (Figure 1). However, differences on serotype distribution were seen between human and bovine isolates, with serotype III prevailing among the former and serotype V among the last.

The most striking difference between GBS recovered from different hosts regarded erythromycin and clindamycin resistance. While around 4% and 2% of human isolates were resistant to erythromycin and clindamycin respectively, those numbers were around 30% and 20% for bovine isolates. Moreover, while erythromycin resistance levels showed a decreasing tendency along time among human isolates, an increasing trend was observed among bovine strains (Figure 2).

The emergence of erythromycin resistance has been linked to the vertical dissemination of specific GBS clones in some places of the world. In the present study, a great genetic diversity was seen among erythromycin-resistant isolates (Figure 3), suggesting that lateral gene transfer of resistance determinants might also play an important role in our setting. Still, some major clusters were observed, including cluster A, which was the most predominant and has been circulating since 1990. It is also worthy to highlight that closely related and even indistinguishable erythromycin-resistant clones were isolated from both human and bovine sources.

Preventive measures against GBS neonatal infections are usually based on the use of antibiotics. Although GBS is still largely susceptible to the first-line therapy which is represented by the beta-lactams, increasing rates of resistance to the alternative drugs erythromycin and clindamycin are being detected among isolates recovered from human sources in the last decades. Nevertheless, according to our results, erythromycin resistance has not fully emerged among GBS isolates recovered from humans in Brazil. The observation that it has, however, considerably increased among those recovered from cattle, especially in the last years, raises the question of how long this scenario will last among human GBS strains.



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Fig-1-Pinto-et-al-2013Figure 1. Distribution of serotypes among Streptococcus agalactiae strains according to the period of isolation. Isolates from human and bovine sources were included, and nontypeable isolates were excluded.

Fig-2-Pinto-et-al-2013Figure 2. Distribution of erythromycin-resistant Streptococcus agalactiae (group B Streptococcus; GBS) isolates according to the period of isolation. An increasing trend of erythromycin-resistance occurrence was observed when all GBS isolates (in red) and those from bovine sources (in green) were considered, while human GBS strains (in blue) showed a decreasing tendency.


Figure 3. Genetic diversity among erythromycin-resistant Streptococcus agalactiae isolates by Pulsed-field gel electrophoresis (PFGE). Five major clusters were observed, three of which comprised both human and bovine isolates. Indistinguishable PFGE profiles were observed for both human and bovine isolates belonging to cluster E. cMLSB: constitutive macrolide, lincosamide and streptogramin B-type resistance; M: macrolide resistance; NT: nontypeable.


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