Characterization of class 1 integrons and antibiotic resistance genes in multidrug-resistant Salmonella enterica isolates from foodstuff and related sources

In recent years, an increase in the occurrence of antimicrobial resistance among Salmonella enterica has been observed in several countries, which is worrisome because S. enterica is one of the most common causes of human gastroenteritis worldwide. The aim of this study was to characterize class 1 integrons and antibiotic resistance genotypes in Salmonella enterica isolates recovered from foodstuff and related sources. Nineteen multidrug-resistant (MDR) Salmonella enterica isolates were recovered. Higher resistance rates to tetracycline (90 percent), streptomycin (80 percent), sulfamethoxazole-trimethoprim (80 percent), ampicillin (60 percent) and nalidixic acid (70 percent) were related to the presence of the tetA, aadA, sul1/sul2, blaTEM-1 genes, and a codon mutation at position 83 of the gyrA gene, respectively. Class 1 integrons harboring aadA, blaTEM-1, sul1 or dhfr1 genes were detected in nine (45 percent) Salmonella enterica strains belonging to serotypes Brandenburg, Panama, Agona, Mbandaka and Alachua. Finally, clonal dissemination of S. Panama, S. Derby and S. Mbandaka was confirmed by PFGE. Detection of clonally related MDR Salmonella enterica suggests that endemic serotypes can be supported by class 1 integron-borne gene cassettes and/or mutations in drug targets. Emergence and dissemination of multidrug-resistant Salmonella enterica can have a major public health impact in an environment where large-scale suppliers ship their products.

Frequency of 2, 3, 5-triphenyltetrazolium chloride (TTC) non-reducing bacteria in pasteurized milk

2, 3, 5-triphenyltetrazolium chloride (TTC) is a dye largely used for enumeration of microbial colonies in solid culture media, being a key component of the dry rehydratable film system used for microbiological analysis of food. This dye is colorless in the oxidized form and red when reduced by microorganisms, due to formation of formazan. In this study, TTC was added to Plate Count Agar (PCA) for enumeration of microorganisms in thirty four pasteurized milk samples, with the aim to verify the frequency of microorganisms that are unable to reduce TTC. Milk samples were decimally diluted in saline and pour-plated in PCA plus 0.015(per cent) TTC. Colonies were counted after 24h and 48 h of incubation at 35(degree)C. From a total of 50,574 colonies 19,665(38.88 per cent) did not reduce TTC in 48h. It was observed that 571(6.36 per cent) colonies that were colorless in 24h became red in 48h. From those that didn't reduce TTC in 48h, 233 were purified and Gram stained. 229(98.71 per cent) of them were Gram positive cocci and bacilli. The results show that there is a high percentage of microorganisms unable to reduce TTC in pasteurized milk, which cannot be detected by laboratory procedures based on the formation of red colonies.

Inhibition of fooborne pathogens by bacteriocin-producing leuconostocs and lactobacillus sake isolated from "lingüiça frescal"

Two strains of lactic acid bacteria, isolated from "lingüiça" (a typical Brazilian meat product) stored under refrigeration, produced antagonistic substances active against selected foodborne pathogens. The proteinaceous nature of the inhibitors was demonstrated and so they were classified as bacteriocins. The inhibition due to acid production and phages was ruled out. The bacteriocin produced by Leuconostoc sp was active against Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus. The bacteriocin produced by Lactobacillus sake was active against Listeria monocytogenes and Staphylococcus aureus. Gram negative were bacteria not inhibited by the bacteriocins produced.