Caracterização fenotípica de Staphylococcus aureus isolados de alimentos de origem animal e de outras fontes relacionadas

Abstract

Bacteria grouped in biofilms are generally more resistant to different environmental conditions. The permanence and behavior of a microorganism in a food are determined by intrinsic and extrinsic factors related to food, which can also influence biofilm formation. In addition, S. aureus isolates may be resistant to antibiotics, including methicillin. The objective of the present study was to characterize phenotypically isolates of S. aureus from bovine raw milk and from different points of the swine slaughterhouse flowchart in order to evaluate the capacity of biofilm formation and factors that may influence this ability, bacterial behavior in the food environment and its antimicrobial susceptibility to methicillin. Twenty-eight S. aureus isolates were used, seven of which were derived from bovine raw milk and 21 from swine. The isolates were evaluated for biofilm production capacity in microtiter plates. The biofilm production capacity was also verified by some non-forming isolates and strong biofilm builders after subjecting them to different types of sublethal stress (42ºC, 4ºC, pH 5,0 and 5% NaCl). The behavior of S. aureus in food was tested through experimental contamination in pork loin and UHT whole milk. Furthermore, the sensitivity of the isolates to methicillin was assessed by the disc-diffusion test. Of the isolates tested, 57,1% (16/28) were able to form biofilm, 85,7% (6/7) from milk and 47,6% (10/21) from pigs. Of the three isolates previously classified as strong biofilm builders, most maintained this ability after being submitted to different types of sublethal stress. Concerning the three non-biofilm-forming isolates tested, only one remained unchanged and the others became weak formers in most of the stresses, except one of the isolates, which became a moderate biofilm-forming agent when exposed to stress by heat and salinity. The verification of the survival and multiplication capacity of S. aureus in food showed that both isolates from bovine and porcine raw milk were able to survive for five days in UHT milk and pork under refrigeration. have multiplied. Regarding the sensitivity to methicillin, 42,9% (12/28) of the isolates were classified as resistant, and of these, 85,7% (6/7) were isolated from milk and 28,6% (6/21) from swine. The results obtained increase the knowledge about the characteristics of S. aureus, thus, it is possible to adopt the appropriate procedures to avoid the multiplication of S. aureus in foods.