Intrinsic Parameters and Bacterial Growth Prediction in a Brazilian Minimally Ripened Cheese (Coalho) during Refrigerated Storage

This study evaluated the microbiological and physicochemical characteristics in different commercial brands of a Brazilian minimally ripened (coalho) cheese during 60 days of storage under refrigeration. Combinations of maximum and minimum values of water activity and pH determined in cheese samples at refrigeration temperature (7°C) were used in a bacterial growth prediction analysis. Maximum growth rate (Grmax) was estimated for different pathogenic and/or spoilage bacteria using the ComBase Predictor. Results of microbiological characterization analyses showed persistent high counts for all monitored microbial groups ( Lactobacillus spp., Lactococcus spp., Enterococcus spp., Staphylococcus spp., Enterobacteriaceae, proteolytic and lipolytic microorganisms, and fungi) in cheese samples; no dominant microbial group was observed over time. Values of pH (6.03 ± 0.16 to 7.28 ± 0.55), acidity (0.15% ± 0.09% to 0.66% ± 0.26%), sodium chloride (1.05% ± 0.19% to 1.97% ± 0.75%), and water activity (0.948 ± 0.020 to 0.974 ± 0.012) did not vary in cheese samples during storage. Estimated Grmax values for the tested bacteria were in the range of 0.004 to 0.044 log CFU/h. Highest Grmax values (0.005 to 0.044 log CFU/h) were predicted for the psychrotrophic Aeromonas hydrophila, Listeria monocytogenes, Pseudomonas spp., and Yersinia enterocolitica. Grmax values predicted for Escherichia coli, Salmonella spp., and Staphylococcus aureus were in the range of 0.004 to 0.016 log CFU/h. These results indicate unsatisfactory microbiological characteristics of commercially available coalho cheese. Physicochemical characteristics of commercial coalho cheese stored under refrigeration allow bacterial growth to occur, indicating higher risk for fast growth of contaminant bacteria in this product.

Changes of Antibiotic Resistance Phenotype in Outbreak-Linked Salmonella enterica Strains after Exposure to Human Simulated Gastrointestinal Conditions in Chicken Meat

Fifteen outbreak-linked Salmonella enterica strains in chicken meat were evaluated under simulated human gastrointestinal conditions for their resistance and susceptibility to 11 antibiotics from seven antibiotic classes. The MIC of each antibiotic was determined by microdilution in broth before and after the exposure of each strain to a continuous system simulating the conditions in the human mouth, esophagus-stomach, duodenum, and ileum. Strains were inoculated onto chicken breast (9 g; inoculated at 5 log CFU/g) prior to exposure. Data were interpreted according Clinical and Laboratory Standards Institute breakpoints. After the in vitro digestion, 12 Salmonella strains with reduced susceptibility to ciprofloxacin (CIP) changed to CIP resistant. The ceftriaxone (CTX)-intermediate Salmonella Newport strain changed to CTX resistant. The ampicillin (AMP)-susceptible Salmonella Heidelberg strain changed to AMP resistant, and the sulfamethoxazole-trimethoprim (SXT)-susceptible strains of Salmonella serovars Typhimurium, Agona, Newport, Albany, and Corvallis changed to SXT resistant. The Salmonella Heidelberg, Salmonella Newport, Salmonella Albany, and Salmonella Corvallis strains had the highest frequency of changes in antibiotic susceptibility with new resistant phenotypes to AMP and CIP, CTX and SXT, CIP and SXT, and CIP and SXT, respectively. Conditions imposed by a simulated gastrointestinal environment changed the susceptibility of S. enterica strains to clinically relevant antibiotics and should be considered in the selection of therapies for human salmonellosis.