Behavior variability of Salmonella enterica isolates from meat-related sources

Antibiotic resistance and biofilm formation ability of Salmonella serotypes isolated from beef, mutton, and meat contact surfaces at retail

In this study, Salmonella isolates recovered from meat (beef and mutton) and meat contact surfaces at retail were investigated to determine their serotype, antibiotic resistance, and biofilm formation ability. Salmonella was found in 29 (24.17%) samples out of 120 samples including 14/50 (28%) of beef, 10/40 (25%) of mutton, and 5/30 (16.67%) of meat contact surfaces. Seven isolates were identified as S. Enteritidis, three as S. Typhimurium, and two as S. Typhi, while the rest of the isolates were considered as other Salmonella spp. All of the isolates were resistant to at least one antimicrobial agent and 48.27% of them were identified as multidrug-resistant (MDR) Salmonella. All (100%) of meat contact surfaces isolates, 42.8% of beef isolates, and 30% of mutton isolates were found to be MDR Salmonella. Resistance to nalidixic acid (100%), tetracycline (79.3%), and sulphamethoxazole/trimethoprim (44.8%) were observed. The gyrA gene was detected in 19 of 29 isolates, but tetA was found in one isolate. All of the serotypes were able to form biofilm (75.86 % moderate and 24.14 % strong) and S. Enteritidis was the strongest biofilm producer. The findings indicated that the majority of Salmonella isolates in this study were MDR and biofilm producer. Then, safety measures such as cleaning and disinfection must be taken to control Salmonella and promote public health. PRACTICAL APPLICATION: The present study provides useful information on the prevalence of Salmonella serotypes in meat and meat contact surfaces and their antibiotic resistance patterns as well as biofilm formation capacities. Improving hygiene practices in livestock, slaughterhouses, and at retails may reduce the risk of meat contamination to Salmonella. Meanwhile, high levels of antibiotic resistance in Salmonella isolates emphasized on the improper use of antibiotics.

Validation of Droplet Digital Polymerase Chain Reaction for Salmonella spp. Quantification

Salmonellosis is a foodborne disease caused by Salmonella spp. Although cell culture is the gold standard for its identification, validated molecular methods are becoming an alternative, because of their rapidity, selectivity, and specificity. A simplex and duplex droplet digital polymerase chain reaction (ddPCR)-based method for the identification and quantification of Salmonella using ttr, invA, hilA, spaQ, and siiA gene sequences was validated. The method has high specificity, working interval between 8 and 8,000 cp/μL in ddPCR reaction, a limit of detection of 0.5 copies/μL, and precision ranging between 5 and 10% measured as a repeatability standard deviation. The relative standard measurement uncertainty was between 2 and 12%. This tool will improve food safety in national consumption products and will increase the competitiveness in agricultural product trade.

Strain variability in biofilm formation: A food safety and quality perspective

The inherent differences in microbial behavior among identically treated strains of the same microbial species, referred to as "strain variability", are regarded as an important source of variability in microbiological studies. Biofilms are defined as the structured multicellular communities with complex architecture that enable microorganisms to grow adhered to abiotic or living surfaces and constitute a fundamental aspect of microbial ecology. The research studies assessing the strain variability in biofilm formation are relatively few compared to the ones evaluating other aspects of microbial behavior such as virulence, growth and stress resistance. Among the available research data on intra-species variability in biofilm formation, compiled and discussed in the present review, most of them refer to foodborne pathogens as compared to spoilage microorganisms. Molecular and physiological aspects of biofilm formation potentially related to strain-specific responses, as well as information on the characterization and quantitative description of this type of biological variability are presented and discussed. Despite the considerable amount of available information on the strain variability in biofilm formation, there are certain data gaps and still-existing challenges that future research should cover and address. Current and future advances in systems biology and omics technologies are expected to aid significantly in the explanation of phenotypic strain variability, including biofilm formation variability, allowing for its integration in microbiological risk assessment.

Short Chain Fatty Acids Commonly Produced by Gut Microbiota Influence Salmonella enterica Motility, Biofilm Formation, and Gene Expression

Short chain fatty acids (SCFAs) are commonly produced by healthy gut microbiota and they have a protective role against enteric pathogens. SCFAs also have direct antimicrobial activity against bacterial pathogens by diffusion across the bacterial membrane and reduction of intracellular pH. Due to this antimicrobial activity, SCFAs have promising applications in human health and food safety. In this study, the minimum inhibitory concentrations (MICs) of four SCFAs (acetic acid, butyric acid, propionic acid, and valeric acid) in Salmonella strains isolated from poultry were determined. The effect of subinhibitory concentrations of SCFAs in Salmonella biofilm formation, motility, and gene expression was also evaluated. Butyric acid, propionic acid, and valeric acid showed a MIC of 3750 µg/mL in all strains tested, while the MIC of acetic acid was between 1875 and 3750 µg/mL. Subinhibitory concentrations of SCFAs significantly (p < 0.05) reduced the motility of all Salmonella strains, especially in the presence of acetic acid. Biofilm formation was also significantly (p < 0.05) lower in the presence of SCFAs in some of the Salmonella strains. Salmonella strain. Salmonella Typhimurium T7 showed significant (p < 0.05) upregulation of important virulence genes, such as invA and hilA, especially in the presence of butyric acid. Therefore, SCFAs are promising substances for the inhibition of the growth of foodborne pathogens. However, it is important to avoid the use of subinhibitory concentrations that could increase the virulence of foodborne pathogen Salmonella.

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.

High Phenotypic Variability among Representative Strains of Common Salmonella enterica Serovars with Possible Implications for Food Safety

Salmonella is an important foodborne pathogen, whose ability to resist stress and survive can vary among strains. This variability is normally not taken into account when predictions are made about survival in foods with negative consequences. Therefore, we examined the contribution of variable phenotypic properties to survival under stress in 10 Salmonella serovars. One strain (Typhimurium 10) was intentionally RpoS-negative; however, another strain (Heidelberg) showed an rpoS mutation, rendering it inactive. We assessed an array of characteristics (motility, biofilm formation, bile resistance, acid resistance, and colony morphology) that show major variability among strains associated with a 10- to 19-fold difference between the highest and the lowest strain for most characteristics. The RpoS status of isolates did not affect variability in the characteristics, with the exception of resistance to NaCl, acetic acid, lactic acid, and the combination of acetic acid and salt, where the variability between the highest and the lowest strain was reduced to 3.1-fold, 1.7-fold, 2-fold, and 1.7-fold, respectively, showing that variability was significant among RpoS-positive strains. Furthermore, we also found a good correlation between acid resistance and lysine decarboxylase activity, showing its importance for acid resistance, and demonstrated a possible role of RpoS in the lysine decarboxylase activity in Salmonella.