Abstract
Staphylococcus aureus is one of the main agents isolated from bovine mastitis cases, characterized by lower cure rates compared to other pathogens causing this disease. This phenomenon is mainly explained by the multiresistance acquisition to antimicrobials and the ability of S. aureus to form biofilms on biotic and abiotic surfaces. In this work 15 samples of S. aureus isolated from the automated milking facility were analyzed regarding the resistance profile to antimicrobials, virulence factors (capsule production, hemolysin, and protease) and adhesion capacity under different temperatures (42±1°C, 36±1°C, 25±1°C, 9±1°C, and 3±1°C). All isolates showed methicillin-resistant (MRSA) characteristics and multidrug resistance profile to the antimicrobials tested (penicillin G, chloramphenicol, oxacillin, cephalexin, tetracycline, amoxicillin + clavulanic acid, sulfa + trimetropim, gentamicin, doxycycline, ceftiofur, neomycin, and vancomycin) with an IRMA index between 0.5 and 1.0. Five isolates were resistant to vancomycin (VRSA), two were resistant to all active principles, and the others to at least six of these drugs. Adhesion capacity and biofilm formation were found in 3 of the 5 evaluated temperatures, including the cooling conditions. Regarding the virulence factors, 86.7% of the isolates formed capsules, 60% revealed the presence of protease, 26.7% expressed the α-hemolysin factor, and 13.3% of them presented β-hemolysin. The fact that all isolates presented MRSA characteristics represents a potential risk to those exposed to this agent, and the formation of biofilm in liners even after the use of detergents and sanitization highlights the urgency of searching for alternatives for dispersion of the biofilm by S. aureusin the automated milking facility.
Highlights
Bovine mastitis is an inflammation of the mammary glands that negatively affects the dairy industry, with strong negative consequences for animal welfare, food safety, and productivity, leading to economic losses due to reduced milk production and increased costs of clinical treatment (SCHUKKEN et al, 2011; HEIKKILÄ et al, 2018)
For isolating S. aureus, 25 mL of the samples were homogenized in 225 mL of Buffered Peptone Water (BPW, Laborclin®1) and, after a series of decimal dilutions, a 0.1 mL aliquot of each sample was seeded on plates containing Agar Baird-Parker (ABP, Laborclin®1), which were incubated at 36±1°C for 48 h (EVANCHO et al, 2001)
In the disc-diffusion antimicrobial sensitivity test, all analyzed S. aureus isolates showed a pattern of multidrug resistance to antimicrobials tested with Multiple Antimicrobial Resistance (MAR) Index ≥ 0.5, being resistant to three or more classes of antimicrobials (Table 2)
Summary
Bovine mastitis is an inflammation of the mammary glands that negatively affects the dairy industry, with strong negative consequences for animal welfare, food safety, and productivity, leading to economic losses due to reduced milk production and increased costs of clinical treatment (SCHUKKEN et al, 2011; HEIKKILÄ et al, 2018). Staphylococcus aureus is one of the main agents causing subclinical and clinical mastitis in dairy cattle (RALL et al, 2014; BONSAGLIA et al, 2018). The prevention and control of staphylococcal mastitis are vital for the entire milk production chain, since this disease requires an increased use of antimicrobials in dairy herds (STEVENS et al, 2018). In this context, 15 samples of S. aureus isolated from the automated milking environment were analyzed regarding the antimicrobial resistance profile, virulence factors, and adhesion ability under different temperatures
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