Study on Heat Stress Response in Salmonella Typhimurium and Salmonella Enteritidis and its Impact on their Attachment to Dressed Broiler Skin Surface

Effectiveness Evaluation of a UV-C-Photoinactivator against Selected ESKAPE-E Pathogens

Healthcare-associated infections (HAI) worldwide includes infections by ESKAPE-E pathogens. Environmental surfaces and fomites are important components in HAI transmission dynamics, and shoe soles are vectors of HAI. Ultraviolet (UV) disinfection is an effective method to inactivate pathogenic microorganisms. In this study, we investigated whether the SANITECH UV-C shoe sole decontaminator equipment that provides germicidal UV-C radiation could effectively reduce this risk of different pathogens. Six standard strains and four clinical MDR strains in liquid and solid medium were exposed to a UV-C System at specific concentrations at other times. Bacterial inactivation (growth and cultivability) was investigated using colony counts and resazurin as metabolic indicators. SEM was performed to assess the membrane damage. Statistically significant reduction in cell viability for all ATCCs strains occurred after 10 s of exposure to the UV-C system, except for S. enterica, which only occurred at 20 s. The cell viability of P. aeruginosa (90.9%), E. faecalis and A. baumannii (85.3%), S. enterica (82.9%), E. coli (79.2%) and S. aureus (71.9%) was reduced considerably at 20 s. In colony count, after 12 s of UV-C exposure, all ATCC strains showed a 100% reduction in CFU counts, except for A. baumannii, which reduced by 97.7%. A substantial reduction of colonies above 3 log₁₀ was observed at 12 and 20 s in all bacterial strains tested, except for A. baumannii ATCC 19606 (12 s). The exposure of ATCCs bacterial strains to the UV-C system for only 2 s was able to reduce 100% in the colony forming units (CFU) count in all ATCCs strains, S. aureus, P. aeruginosa, E. coli, A. baumannii, E. faecalis, except the S. enterica strain which had a statistically significant reduction of 99.7%. In ATCC strains, there was a substantial decrease in colonies after 4 s (sec) of exposure to the UV-C system, with a reduction ranging from 3.78-4.15 log₁₀ CFU/mL. This reduction was observed in MDR/ESKAPE-E strains within 10 s, showing that UV-C could eliminate above 3.84 log₁₀ CFU/mL. SEM showed a reduction of pili-like appendages after UV-C treatment in all strains except for E. coli (ATCC 25922). The Sanitech UV-C shoe sole decontaminator equipment from Astech Serv. and Fabrication Ltd. (Petrópolis, Brazil), effectively killed in vitro a series of ATCCs and MDR/ESKAPE-E bacteria of sanitary interest, commonly found in the hospital environment.

Efficacy and Quality Attributes of Antimicrobial Agent Application via a Commercial Electrostatic Spray Cabinet To Inactivate Salmonella on Chicken Thigh Meat

ABSTRACT

Salmonella is a foodborne pathogen associated with poultry meat. This study aimed to determine the efficiency and quality attributes of two antimicrobial agents to reduce Salmonella on raw chicken meat when applied individually and in combination using an electrostatic spray cabinet. Thus, 5 log CFU/g of nonpathogenic, rifampin-resistant Salmonella Typhimurium was inoculated on skinless, boneless, raw chicken thigh meat and passed through an electrostatic spray cabinet while being sprayed with 5% lauric arginate (LAE), and 100, 1,000, 1,500, and 1,750 ppm of peracetic acid (PAA). Spraying of 5% LAE for 45 s significantly reduced Salmonella by 5 log (P < 0.05). The 1,500 ppm of PAA reduced Salmonella significantly within 45 s (1.157 log). Spraying of 1,500 ppm of PAA followed by LAE within 15 s reduced Salmonella significantly more than vice versa (P < 0.05). The color, water holding capacity, and texture did not differ significantly but resulted in significantly strong aroma and flavor. Both LAE and PAA efficiently reduced Salmonella when applied in an electrostatic spray cabinet on raw chicken thigh meat. The results suggest that the sequential order of application of antimicrobial agents is important to improve the safety and quality of raw chicken thigh meat.

HIGHLIGHTS

Successive exposure to Mentha piperita L. essential oil affects the culturability and induces membrane repair in a persister epidemic Salmonella Typhimurium PT4

This study had as aims to evaluate the effects of successive exposures to Mentha piperita L. essential oil (MPEO) on culturability and physiological functions of Salmonella Typhimurium PT4. S. Typhimurium PT4 cells (10⁸ log CFU/mL) were exposed to the same (1.25 μL/mL) or increasing MPEO concentrations (1.25-80 μL/mL) during 252 h. At each 36-h interval, the viable cell counts, and distinct cell functions were assessed using plate counting and flow cytometry, respectively. As the exposure time to the same MPEO concentration increased, the population of S. Typhimurium PT4 cells with damaged, permeabilized and depolarized membrane, and compromised efflux activity decreased. Otherwise, S. Typhimurium PT4 cells with damaged membrane physiological functions increased over the exposure to increasing concentrations of MPEO. Genomic analyses showed that the strain carries 17 genes associated with stress responses and the persistence of the tested strain among sources associated with poultry spanning more than 16 years and its virulence for humans. Therefore, successive exposure to a sublethal concentration of MPEO induced S. Typhimurium PT4 cells capable of maintaining the membrane integrity and its functions despite their non-culturable state.

Expression of DnaK and HtrA genes under high temperatures and their impact on thermotolerance of a Salmonella serotype isolated from tahini product

Background

Salmonella is considered to be the second largest source of infection in food-borne diseases. It is also considered one of the most important dangers particularly in the meat and dairy industry. Therefore, the main objective of our study was to determine the relationship between thermotolerance of a Salmonella serotype and the expression of DnaK and HtrA genes.

Results

In this study, expression of the two genes DnaK and HtrA was compared under four different temperatures 37 °C, 42 °C, 50 °C, and 55 °C in two serotypes of Salmonella enterica subsp. enterica. One of them was isolated from tahini product and identified as Salmonella enterica subsp. enterica serovar choleraesuis. This identified serotype was found to be more thermotolerant than the second serotype (Salmonella enterica subsp. enterica serovar typhimurium (ATCC 13311)), which was used as reference. This conclusion was based on D and Z values, which were used to compare thermoresistance ability of the two serotypes under four different temperatures 60 °C, 65 °C, 70 °C, and 75 °C. In addition, the results of qRT-PCR showed that after 43 °C (induction temperature), the relative expression (fold change) of DnaK and HtrA genes increased up to 5 and 47, respectively, comparing to their expression at 37 °C.

Conclusions

Thermotolerance of the identified S. choleraesuis serotype showed significantly high expression levels of DnaK and HtrA genes.

Response to Acid Adaptation in Salmonella enterica Serovar Enteritidis

Acid adaptation in Salmonella Enteritidis was characterized by phenotypic and gene-expression analyses. S. Enteritidis cells at log-phase and stationary-phase were kept at pH 4.5 to 6.0 for 1 to 4 hours. All treatments induced various levels of acid tolerance response that were dependent on pH, exposure time and growth phase. This acid adaptation resulted in tolerance to 50 °C and 8% NaCl regardless of the growth phase. However, the tolerance of log-phase and stationary-phase cells to low temperatures (4 and -20 °C) was increased and decreased, respectively. RT-qPCR analysis revealed that genes involved in tolerance to acid (SEN1564A and cfa), heat (rpoH, uspB, and htrA), salt (proP, proV, and osmW), and cold (cspA, cspC, and csdA) stress were generally upregulated after acid adaptation. These results provide an initial insight into mechanisms of acid adaptation and induced cross protection in S. Enteritidis. PRACTICAL APPLICATION: Stress tolerance acquisition resulting from acid adaptation in foodborne pathogens poses a great threat to food safety. The current work showed that acid adaptation induced direct tolerance and cross-tolerance to high temperature, low temperature, and salt in Salmonella Enteritidis, possibly due to the upregulation of stress tolerance-related genes. These results provide key insights into acid adaptation mechanisms and efficient control of S. Enteritidis.

Quantitative assessment of tolerance response to stress after exposure to oregano and rosemary essential oils, carvacrol and 1,8-cineole in Salmonella Enteritidis 86 and its isogenic deletion mutants ∆dps, ∆rpoS and ∆ompR

This study assessed the influence of rpoS, dps and ompR genes on the tolerance response of Salmonella Enteritidis 86 (SE86) to homologous and heterologous stressing agents after exposure to essential oils (EOs) from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) and their major constituents (ICs), carvacrol (CAR) and 1,8-cineole (CIN), respectively, by modelling the log reduction over time. Minimum inhibitory concentration values of OVEO (1.25 μL/mL), CAR (0.62 μL/mL), ROEO (20 μL/mL) and CIN (10 μL/mL) against SE86 were always one-fold higher than those against ∆dps, ∆rpoS and ∆ompR mutants. Exposure to the same concentration of OVEO, CAR, ROEO or CIN caused higher reductions (up to 2.5 log CFU/mL) in ∆dps, ∆rpoS and ∆ompR mutants than in SE86 in chicken broth. In assays with homologous stressing agents, ompR, dps and rpoS influenced the tolerance to OEs or ICs. After adaptation to OVEO, CAR, ROEO and CIN, osmotolerance and acid tolerance of SE86 were influenced by rpoS gene, while thermotolerance of SE86 was influenced by ompR. Tolerance of SE86 to sodium hypochlorite after adaptation to OEs or ICs was influenced by rpoS and dps. These findings quantitatively describe for the first time the influence of rpoS, dps and ompR genes on the tolerance of Salmonella Enteritidis to OVEO, CAR, ROEO and CIN.

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.