Caracterização de bactérias Gram positivas psicrotróficas aderidas em tanques de refrigeração de leite cru quanto a espécies, expressão de enzimas e perfis de resistência a antimicrobianos

Abstract

Milk can be contaminated by psychrotrophic bacteria in several points of the productive chain including during refrigerated storage in expansion tanks. Once contaminated by psychrotrophics milk can suffer alterations in its flavor, aroma and texture. The contaminant bacteria of milk may present resistance to several antibiotics. The genes of antibiotic resistance may be transferred via food to the pathogenic bacteria of humans rendering it difficult the treatment of infections. This work aimed to identify the Gram positive psychrotrophic bacteria present in refrigerated raw milk storage tanks, to evaluate the production capacity of extra-cellular enzymes (proteases, lipases and lecithinases) by these bacteria and to verify their antibiotic resistance profile. The samples belonged to the collection of the Laboratory of Food Microbiology of UFLA. These samples were previously collected in refrigeration expansion tanks for raw milk using sterile swab. Fifty three isolates were selected randomly and identified with the help of the identification kit BBL Crystal Gram-Positive. The production of extra-cellular enzymes using milk agar, tributyrin agar base and TSA supplemented with egg yolk emulsion was evaluated. For the antibiogram, 12 antibiotics for Gram positive bacteria were used. The results revealed the presence of Bacillus subtilis, Bacillus licheniformis, Corynebacterium spp., Corynebacterium jeikeium, Corynebacterium aquaticum, Corynebacterium bovis, Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, Staphylococcus spp., Staphylococcus simulans, Staphylococcus vitulus, Staphylococcus saccharolyticus, Lactococcus lactis ssp. lactis , Lactococcus garviae and Micrococcus sedentarius in the expansion tanks. The isolates were evaluated in relation to the production of extra cellular enzymes and 83% of the isolates produced proteases, 87%, lipases and 63%, lecithinases. When present in milk, these enzymes can cause its deterioration, including after it is thermally treated. Antibiotic resistance was also evaluated by means of agar diffusion test, classifying the microorganisms as resistant, intermediary and sensitive. The microorganisms were most sensitive to sulfazotrim and ciprofloxacin. All the isolates presented multiple resistance to the drugs tested.