Molecular epidemiology of methicillin-susceptible Staphylococcus aureus (MSSA) isolated from milk of cows with subclinical mastitis

Abstract

Bovine mastitis has been a concern for dairy herd for decades. The adaptation capacity of one of the main species responsible for this disease, Staphylococcus aureus (S. aureus), plays a pivotal role in this issue. The aim of this study was to establish a molecular and phenotypic profile of 285 S. aureus strains isolated from milk of subclinical mastitis cows from 18 different farms in São Paulo State using spa typing, multilocus sequence typing (MLST), pulsed field gel electrophoresis (PFGE), agr cluster (I, II, III and IV) typing, PCR for genes including enterotoxins (sea, seb, sec, sed, see, seg, seh, sei), toxic shock syndrome toxin (tsst-1), and Panton-Valentine leucocidin (pvl), as well as in vitro resistance assays for 12 antibiotics. The results showed a wide variety of strains with a high toxigenic potential; concomitantly, sec, seg and seh were prevalent. In addition, we observed a predominance of the spa types t605 (ST 126, CC126) and t127 (ST1, CC1) and the unusual presence of t321 causing bovine mastitis, which has been previously reported only in swine. The most frequent ST were ST126 (70.5%) and ST1 (10.5%). Regarding PFGE, we observed four major groups and six profile patterns. The highest resistance was observed for streptomycin (9.5%), followed by tetracycline (3.5%), clindamycin (9.3%), and erythromycin (2.8%). The tsst-1 gene was detected in 36.8% of isolates and pvl was not observed. One hundred and thirty-six (47.7%) isolates possessed agr type II, followed by types III (20%) and I (8.1%), with type IV not being detected. We observed that the same spa type could result in different PFGE profiles, so the exclusive use of spa type sequences can lead to incorrect interpretations regarding the spread of clones in an epidemiological context.

Presence of genes encoding enterotoxins in Staphylococcus aureus isolates recovered from food, food establishment surfaces and cases of foodborne diseases

“…A recent report from South America, performed in Sao Paulo, Brasil, examined more than 2,000 milk samples of bovine mastitis and 285 S. aureus strains, searching for the same enterotoxin genes than we did. The researchers found that the most frequently identified gene was seg, followed by seh 21 .These findings agree with reports on the presence of S. aureus enterotoxins in isolates from foods of different regions of the world. In Ethiopia, 51% of 160 S. aureus examined isolates from dairy products carried ET coding genes, being seg and sei the most frequently found, as in our series 22 .…”

Antimicrobial Resistance in Farm Animals in Brazil: An Update Overview

“…Susceptibility to the majority or all antimicrobial agents tested against S. aureus isolates from bovine mastitis has been observed in Brazilian herds [90][91][92][99][100][101]. However, resistance frequencies have increased for some antimicrobial agents compared to studies published in earlier periods [102][103][104][105].…”

“…Beta-lactam resistance, especially to penicillinase-labile penicillins (PSLP; for example, amoxicillin, ampicillin, penicillin G), has been widely observed among Staphylococcus isolates recovered from bovine mastitis [91,[97][98][99][100][106][107][108]. Penicillin G resistance frequencies have ranged from 30.4% to 100% in the studies published in the last ten years [100,101,109,110]. Some studies have also tested other PSLPs, sometimes with slightly higher resistance frequencies than penicillin G [106,[111][112][113].…”

“…MRSA isolation has been reported from mastitis cases in Brazilian herds, but the prevalence is low. In most studies, MRSA strains were not isolated [100,106,[109][110][111] or were isolated from few animals [101,114,117,118]. In 2012, Costa et al published a study with milk samples from 38 herds, in which 2% of S. aureus isolates from mastitis were MRSA [114].…”

“…A similar MRSA isolation prevalence (1.4%) was observed by Bonsaglia et al (2018), who analyzed 285 isolates recovered from 18 herds in São Paulo State (SE). They detected neither the mecA nor the mecC genes among the isolates [101]. Guimarães et al (2017) reported an outbreak of MRSA intramammary infections in Dutch cows from a dairy herd in São Paulo (SE).…”