Biofilm production and beta-lactamic resistance in Brazilian Staphylococcus aureus isolates from bovine mastitis

Abstract

Staphylococcus spp. play an important role in the etiology of bovine mastitis. Staphylococcus aureus is considered the most relevant species due to the production of virulence factors such as slime, which is required for biofilm formation. This study aimed to evaluate biofilm production and its possible relation to beta-lactamic resistance in 20 S. aureus isolates from bovine mastitic milk. The isolates were characterized by pheno-genotypic and MALDI TOF-MS assays and tested for genes such as icaA, icaD, bap, agr RNAIII, agr I, agr II, agr III, and agr IV, which are related to slime production and its regulation. Biofilm production in microplates was evaluated considering the intervals determined along the bacterial growth curve. In addition, to determine the most suitable time interval for biofilm analysis, scanning electron microscopy was performed. Furthermore, genes such as mecA and blaZ that are related to beta-lactamic resistance and oxacillin susceptibility were tested. All the studied isolates were biofilm producers and mostly presented icaA and icaD. The Agr type II genes were significantly prevalent. According to the SEM, gradual changes in the bacterial arrangement were observed during biofilm formation along the growth curve phases, and the peak was reached at the stationary phase. In this study, the penicillin resistance was related to the production of beta-lactamase, and the high minimal bactericidal concentration for cefoxitin was possibly associated with biofilm protection. Therefore, further studies are warranted to better understand biofilm formation, possibly contributing to our knowledge about bacterial resistance in vivo.

Antimicrobial Resistance in Farm Animals in Brazil: An Update Overview

“…Sulfonamide resistance frequency (65%) was the highest among the drugs tested [112]. Low tetracycline resistance frequencies (<10%) have also been reported among S. aureus isolates [101,109,110,117]. In most of these studies, the resistance frequencies to other antimicrobial agents tested were low as well [101,117].…”

“…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].…”

“…Marques et al (2017) detected the blaZ gene in 14 of 20 isolates considered resistant to penicillin G by the edge zone, and among them, only five isolates had the phenotype confirmed by disk diffusion test [110]. High PSLP resistance frequencies (>80%) were observed in isolates obtained between 2004 and 2008 from cows with clinical (59 isolates) and subclinical (293 isolates) mastitis belonging to 38 herds [114].…”

“…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].…”

“…Erythromycin and clindamycin are often tested for S. aureus isolates recovered from bovine mastitis. Although macrolide resistance frequencies have also varied in different studies, in most of them, the frequencies were 0%-10% [101,110,117]. The highest erythromycin resistance frequency was 58.7% [106].…”