부산대학교 도서관

Escherichia coliharboring a transmissible locusof stress tolerance (tLST) and the ability to form biofilms represent a serious risk in dairy production. Thus, we aimed to evaluate the microbiological quality of pasteurized milk from two dairy producers in Mato Grosso, Brazil, with a focus on determining the possible presence of E. coliwith heat resistance (60 °C/6 min), biofilm-forming potential phenotypes and genotypes, and antimicrobial susceptibility. For this, fifty pasteurized milk samples from producers named A and B were obtained for 5 weeks to investigate the presence of Enterobacteriaceaemembers,coliforms, and E. coli. For heat resistance, E. coliisolates were exposed to a water bath at 60 °C for 0 and 6 min. In antibiogram analysis, eight antibiotics belonging to six antimicrobial classes were analyzed. The potential to form biofilms was quantified at 570 nm, and curli expression by Congo Red was analyzed. To determine the genotypic profile, we performed PCR for the tLST and rpoSgenes, and pulsed-field gel electrophoresis (PFGE) was used to investigate the clonal profile of the isolates. Thus, producer A presented unsatisfactory microbiological conditions regarding Enterobacteriaceaeand coliforms for weeks 4 and 5, while all samples analyzed for producer B were contaminated at above-the-limit levels established by national and international legislation. These unsatisfactory conditions enabled us to isolate 31 E. colifrom both producers (7 isolates from producer A and 24 isolates from producer B). In this way, 6 E. coliisolates (5 from producer A and 1 from producer B) were highly heat resistant. However, although only 6 E. colishowed a highly heat-resistant profile, 97% (30/31) of all E. coliwere tLST-positive. In contrast, all isolates were sensitive to all antimicrobials tested. In addition, moderate or weak biofilm potential was verified in 51.6% (16/31), and the expression of curli and presence of rpoSwas not always related to this biofilm potential. Therefore, the results emphasize the spreading of heat-resistant E. coliwith tLST in both producers and indicate the biofilm as a possible source of contamination during milk pasteurization. However, the possibility of E. coliproducing biofilm and surviving pasteurization temperatures cannot be ruled out, and this should be investigated.