Antibiotic Resistance and Biofilm Production in Catalase-Positive Gram-Positive Cocci Isolated from Brazilian Pasteurized Milk

Background: Milk is a reservoir for several groups of microorganisms, which may pose health risks. The aim of this work was to assess the antibiotic resistance and biofilm pro-duction in catalase-positive Gram-positive cocci isolated from Brazilian pasteurized milk. Methods: The bacteria were isolated using Baird-Parker agar and identified by Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight (MALDI-TOF) mass spectrometer. Disk diffusion technique was used to evaluate antimicrobial susceptibility. For qualitative evaluation of biofilm production, the growth technique was used on Congo Red Agar. Results: Totally, 33 out of 64 isolates were identified, including Staphylococcus epidermidis (n=3; 4.7%), Macrococcus caseolyticus (n=14; 21.9%), and Kocuria varians (n=16; 25%). Twenty-two isolates were resistant to at least one antibiotic. Biofilm production was detected in only 5 isolates of K. varians and 1 isolate of S. epidermidis. All 14 M. caseolyticus isolates were resistant to at least one antibiotic; but, multidrug re-sistant (MDR) isolates were not detected. Among all K. varians isolates, 4 were resistant to at least one antibiotic from three different classes and were considered to be MDR. Conclusion: The presence of antibiotic-resistant M. caseolyticus, S. epidermidis, and K. varians isolates, especially MDRs, in milk samples highlights the possible role of milk as a reservoir of resistance genes.