Presence of methicillin-resistant Staphylococcus aureus in raw cow’s milk: adhesive capacities and extracellular enzymes characterization

Abstract

Raw milk contamination by Methicillin-resistant S. aureus (MRSA) threatens food safety and leads to public health problems. Our study evaluates biofilm formation and virulence factors among 21 MRSA in raw cow’s milk. Methicillin resistance was confirmed by cefoxitin screening using the automated VITEK2 system, with a minimum inhibitory concentration greater than 8 mg/l. Qualitative characterization of biofilm-producing strains was performed on Congo red agar (CRA), with a semi-quantitative adhesion test on 96-well tissue culture plates (TCP). The ability to produce different enzymes was evaluated, such as caseinase, lipase, and phospholipase (lecithinase). The surface hydrophobicity of the bacteria was determined, and the autoaggregation test was used to predict the interactions between bacterial cells. Among the tested strains, 61.9% were biofilm producers in the CRA, developing a positive and variable phenotype. Furthermore, 19.05% and 80.95% of isolates were high and low biofilm formation on TCP. The enzymatic activity showed that lécithinase, caseinase, and lipase activities were detected in 100%, 80.95%, and 80.95% of cases. Highly hydrophilic (85.71%) and weakly hydrophobic (14.29%) were detected in MRSA isolates. The strains showed that 71.43% were moderate autoaggregation and 28.57% were low autoaggregation. No significant difference was found between the CRA method and TCP (P> 0.05). A significant association was found between adhesion capacity and bacterial autoaggregation in S. aureus strains (p>0.05). On the other hand, no statistical association between the hydrophobicity of microbial strains and adhesion capacity (p<0.05) was found. The same result was for the hydrophobicity of microbial strains and autoaggregation (p<0.05). This investigation could be beneficial for developing new control measures, prevention, and effective treatment against staphylococcal bacterial resistance.