Prevalence and antimicrobial susceptibility of Salmonella enteritidis and Salmonella typhimurium isolated from hen eggs and quail eggs in Karaj, Iran.

BACKGROUND AND AIM: Different Salmonella serotypes are considered one of the most important food pathogens in the world. Poultry meat and eggs are the primary carriers of Salmonella in human populations. This study aimed to estimate the Salmonella enteritidis and Salmonella typhimurium contamination rates of retail hen and quail eggs in Karaj, Iran. Moreover, the antimicrobial resistance patterns of the strains were evaluated, and the efficiency of the standard culture method and multiplex polymerase chain reaction (m-PCR) were compared. MATERIALS AND METHODS: In this descriptive cross-sectional study over 1 year (Jan-Dec 2022), 150 commercial and 150 backyard hen eggs and 300 commercial quail eggs, without cracks and fractures, were collected randomly from best selling groceries in Karaj city. All samples were examined for Salmonella contamination independently by standard culture and m-PCR approaches. A standard disc diffusion method was employed to assess the antimicrobial susceptibility of the strains against 18 antimicrobial agents. RESULTS: Out of 300 examined eggs, 2 S. enteritidis strains were isolated from the shell of backyard hen eggs. The same serotype was also detected in the contents of one of these two eggs. One S. typhimurium was isolated from the shell of a commercial hen egg. Overall, the Salmonella contamination of the shell and contents was 1% and 0.3%, respectively. Salmonella was not isolated from the eggshells or the contents of the quail eggs. There was complete agreement between the results of m-PCR and the standard culture methods. Among the 18 tested antibiotics, the highest resistance was recorded for colistin (100%), followed by nalidixic acid (75%). CONCLUSION: As most Salmonella spp. are associated with human food poisoning, continuous surveillance is required to effectively reduce the risk posed by contaminated poultry eggs. Furthermore, mandatory monitoring of antimicrobial use on Iranian poultry farms is recommended.

A highly sensitive point-of-care detection platform for Salmonella typhimurium by integrating magnetic enrichment and fluorescent CsPbBr3@SiO2.

A platform was designed based on Fe3O4 and CsPbBr3@SiO2 for integrated magnetic enrichment-fluorescence detection of Salmonella typhimurium, which significantly simplifies the detection process and enhances the working efficiency. Fe3O4 served as a magnetic enrichment unit for the capture of S. typhimurium. CsPbBr3@SiO2 was employed as a fluorescence-sensing unit for quantitative signal output, where SiO2 was introduced to strengthen the stability of CsPbBr3, improve its biomodificability, and prevent lead leakage. More importantly, the SiO2 shell shows neglectable absorption or scattering towards fluorescence, making the CsPbBr3@SiO2 exhibit a high quantum yield of 74.4%. After magnetic enrichment, the decreasing rate of the fluorescence emission intensity of the CsPbBr3@SiO2 supernatant at 527 nm under excitation light at UV 365 nm showed a strong linear correlation with S. typhimurium concentration of 1 × 102~1 × 108 CFU∙mL-1, and the limit of detection (LOD) reached 12.72 CFU∙mL-1. This platform has demonstrated outstanding stability, reproducibility, and resistance to interference, which provides an alternative for convenient and quantitative detection of S. typhimurium.

In silico and PCR Screening for a Live Attenuated Salmonella Typhimurium Vaccine Strain.

The application of live attenuated Salmonella Typhimurium vaccines has significantly helped control Salmonella in poultry products. Because the U.S. Department of Agriculture-Food Safety Inspection Service (USDA-FSIS) scores all Salmonella as positive, regardless of serovar, attenuated vaccine strains that are identified at processing contribute negatively toward Salmonella performance standards. This study was designed to determine the incidence of a live attenuated Salmonella serovar Typhimurium vaccine identified in broiler products by FSIS and to develop a PCR assay for screening of isolates. Salmonella Typhimurium short-read sequences from broiler samples uploaded to the National Center for Biotechnology Information (NCBI) Pathogen Detection database by the USDA-FSIS from 2016 to 2022 were downloaded and assembled. These were analyzed using the Basic Local Alignment Search Tool (BLAST) with a sequence unique to field strains, followed by a sequence unique to the vaccine strain. The PCR assays were developed against field and vaccine strains by targeting transposition events in the crp and cya genes and validated by screening Salmonella serovar Typhimurium isolates. Between 2016 and 2022, 1708 Salmonella Typhimurium isolates of chicken origin were found in the NCBI Pathogen Detection database, corresponding to 7.99% of all Salmonella identified. Of these, 104 (5.97%) were identified as the vaccine strain. The PCR assay differentiated field strains from the vaccine strain when applied to isolates and was also able to detect the vaccine strain from DNA isolated from mixed serovar overnight Salmonella enrichment cultures. Live attenuated Salmonella vaccines are a critical preharvest tool for Salmonella control and are widely used in industry. With forthcoming regulations that will likely focus on Salmonella Typhimurium, along with other serovars, there is a need to distinguish between isolates belonging to the vaccine strain and those that are responsible for causing human illness.

Detección in silico y por PCR de una cepa vacunal viva atenuada de Salmonella Typhimurium. La aplicación de vacunas vivas atenuadas contra Salmonella Typhimurium ha ayudado significativamente a controlar Salmonella en productos avícolas. Debido a que el Servicio de Inspección de Seguridad Alimentaria del Departamento de Agricultura de los Estados Unidos. (USDA-FSIS) califica todas las Salmonella como positivas, independientemente del serovar. Las cepas atenuadas de la vacuna que se identifican en el procesamiento contribuyen negativamente a los estándares de desempeño de Salmonella. Este estudio fue diseñado para determinar la incidencia de una vacuna viva atenuada de Salmonella serovar Typhimurium identificada en productos de pollo de engorde por el FSIS y para desarrollar un ensayo de PCR para la detección de aislados. Se recolectaron y ensamblaron secuencias de lectura corta de Salmonella Typhimurium de muestras de pollos de engorde introducidas en la plataforma de detección de patógenos del Centro Nacional de Información Biotecnológica (NCBI) por el USDA-FSIS entre los años 2016 al 2022. Estos se analizaron utilizando la herramienta de búsqueda de alineación local básica con una secuencia exclusiva para las cepas de campo, seguida de una secuencia exclusiva para la cepa vacunal. Los ensayos de PCR se desarrollaron contra cepas de campo y vacunales centrándose en eventos de transposición en los genes crp y cya y se validaron mediante la detección de aislados de Salmonella serovar Typhimurium. Entre 2016 y 2022, se encontraron 1708 aislados de Salmonella Typhimurium de origen avícola en el sistema de detección de patógenos del NCBI, lo que corresponde al 7.99 % de todas las Salmonellas identificadas. De ellas, 104 (5.97%) fueron identificadas como cepa vacunal. El ensayo de PCR diferenció las cepas de campo de la cepa de la vacuna cuando se aplicó a los aislados y también fue capaz de detectar la cepa de la vacuna a partir del ADN aislado de cultivos de enriquecimiento por toda la noche de Salmonella con serovares mixtos. Las vacunas vivas atenuadas contra Salmonella son una herramienta fundamental para el control de Salmonella y se utilizan ampliamente en la industria. Con las próximas regulaciones que probablemente se centrarán en Salmonella Typhimurium, junto con otros serovares, es necesario distinguir entre los aislados que pertenecen a la cepa vacunal y los que son responsables de causar enfermedades humanas.

UIO66 low background signal and fluorescence synergism strategy for highly sensitive detection of Salmonella typhimurium.

Successful construction of a detection method for Salmonella typhimurium (S. typhimurium) based on the synergy of hybridization chain reaction (HCR) and fluorescence was realized in this paper. First, the aptamer modified with the quenching group Black Hole Quencher-1 acid (BHQ1) was immobilized on the magnetic beads in combination with the complementary chain of the aptamer modified with 6-carboxyfluorescein (6-FAM). Second, S. typhimurium and cDNA-6-FAM immobilized on magnetic beads competitively bound to the aptamer. Finally, the cDNA-6-FAM was released after magnetic separation acted as a promoter to trigger HCR amplification when the target presented. The fluorescence signal could be significantly improved by the combination of green SYBR Green I (SGI) and HCR long double-stranded DNA and the fluorescent synergy of 6-FAM and SGI. Because of the separation of target and its aptamer, the trigger strand was abstracted by magnetic separation. There was no HCR to generate long double-stranded DNA, and the fluorescence of excess hairpin/SGI could be adsorbed through UIO66 so that only a very low background signal was detected. This fluorescent sensor was capable of monitoring S. typhimurium in the range of 10-3.2 × 107 CFU mL-1 with a limit of detection as low as 1.5 CFU mL-1. Because of the excellent properties of the aptasensor and the validity of SGI fluorescence synergy, this HCR enzyme-free amplification strategy could be generalized to other areas.

Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on a "three-in-one" nanohybrid with high oxidase-like activity for AIEgen.

A colorimetry/fluorescence dual-mode assay based on the aptamer-functionalized magnetic covalent organic framework-supported CuO and Au NPs (MCOF-CuO/Au@apt) was developed for Salmonella typhimurium (S. typhimurium) biosensing. The nanohybrid combined three functions in one: good magnetic separation characteristic, excellent oxidase-mimic activity for tetrap-aminophenylethylene (TPE-4A), and target recognition capability. The attachment of MCOF-CuO/Au@apt onto the surface of S. typhimurium resulted in a significant reduction in the oxidase-mimicking activity of the nanohybrid, which could generate dual-signal of colorimetry and fluorescence through the catalytic oxidation of TPE-4A. Based on this, S. typhimurium could be specifically detected in the linear ranges of 102- 106 CFU·mL-1 and 101- 106 CFU·mL-1, with LODs of 7.6 and 2.1 CFU·mL-1, respectively in colorimetry/fluorescence modes. Moreover, the smartphone and linear discrimination analysis-based system could be used for on-site and portable testing. In addition, this platform showed applicability in detecting S. typhimurium in milk, egg liquid and chicken samples.

Unveiling the genomic landscape of Salmonella enterica serotypes Typhimurium, Newport, and Infantis in Latin American surface waters: a comparative analysis.

Surface waters are considered ecological habitats where Salmonella enterica can persist and disseminate to fresh produce production systems. This study aimed to explore the genomic profiles of S. enterica serotypes Typhimurium, Newport, and Infantis from surface waters in Chile, Mexico, and Brazil collected between 2019 and 2022. We analyzed the whole genomes of 106 S. Typhimurium, 161 S. Newport, and 113 S. Infantis isolates. Our phylogenetic analysis exhibited distinct groupings of isolates by their respective countries except for a notable case involving a Chilean S. Newport isolate closely related to two Mexican isolates, showing 4 and 13 single nucleotide polymorphisms of difference, respectively. The patterns of the most frequently detected antimicrobial resistance genes varied across countries and serotypes. A strong correlation existed between integron carriage and genotypic multidrug resistance (MDR) across serotypes in Chile and Mexico (R > 0.90, P < 0.01), while integron(s) were not detected in any of the Brazilian isolates. By contrast, we did not identify any strong correlation between plasmid carriage and genotypic MDR across diverse countries and serotypes.IMPORTANCEUnveiling the genomic landscape of S. enterica in Latin American surface waters is pivotal for ensuring public health. This investigation sheds light on the intricate genomic diversity of S. enterica in surface waters across Chile, Mexico, and Brazil. Our research also addresses critical knowledge gaps, pioneering a comprehensive understanding of surface waters as a reservoir for multidrug-resistant S. enterica. By integrating our understanding of integron carriage as biomarkers into broader MDR control strategies, we can also work toward targeted interventions that mitigate the emergence and dissemination of MDR in S. enterica in surface waters. Given its potential implications for food safety, this study emphasizes the critical need for informed policies and collaborative initiatives to address the risks associated with S. enterica in surface waters.

Sucrose-fermenting Salmonella Typhimurium N23-2364: a challenge for the diagnostic laboratory.

We describe a case of Salmonella infection caused by a sucrose-fermenting Salmonella enterica Typhimurium sequence type 12 which acquired transposon CTnscr94 carrying the sucrose operon scrKYABR. Sucrose-fermenting Salmonella are particularly challenging for culture-based detection and may lead to failure to detect Salmonella in clinical samples.

Colorimetric biosensor based on aptamer recognition-induced multi-DNA release and peroxidase-mimicking three-way junction DNA-Ag/PtNCs for the detection of Salmonella typhimurium.

Salmonella typhimurium, as a major foodborne pathogen, poses a serious threat to public health safety worldwide. Here, we present a colorimetric biosensor based on aptamer recognition-induced multi-DNA release and peroxidase-mimicking three-way junction DNA-silver/platinum bimetallic nanoclusters (3WJ/DNA-Ag/PtNCs) for the detection of S. typhimurium. In this method, S. typhimurium specifically binds to the aptamer and releases multiple cDNAs to form the three-way junction DNA structure and synthesize silver/platinum bimetallic nanoclusters, which induces signaling changes. Interestingly and importantly, the use of 3WJ/DNA as the template for synthesizing Ag/PtNCs gives the method an extremely low background signal. Under the optimal conditions, the constructed biosensor had a linear response range of 2.6 × 102-2.6 × 106 CFU/mL and a detection limit of 2.6 × 102 CFU/mL for the detection of S. typhimurium. In addition, the proposed method can effectively detect S. typhimurium in milk.

Development and application of a multiplex PCR method to differentiate Salmonella enterica serovar Typhimurium from its monophasic variants in pig farms.

Salmonella enterica serovar Typhimurium monophasic variants (Salmonella 4,[5],12:i:-) has increased dramatically, causing human salmonellosis and colonization in pigs. With a difference to S. Typhimurium, the monophasic variants of S. Typhimurium lose the gene cassettes encoding the second phase flagellin. To establish a rapid method to detect and differentiate the two serotypes, we analyzed the published 679 genomes of S. Typhimurium and its monophasic variants and found that no Salmonella 4,[5],12:i:- strains carry both fljB and hin genes. Therefore, we established a novel multiplex PCR method using the fljB-hin region and mdh gene as target sequences to detect and differentiate both serotypes. This method can be used to specifically detect both serotypes with a detection limit for DNA concentration at 10 pg/µL. In addition, the PCR assay successfully differentiated 36 S. Typhimurium isolates from 62 isolates of monophasic variants preserved in our laboratory from 2009 to 2017, which corresponds to the whole-genome-based serotyping results. Application of the multiplex PCR method to 60 fecal samples from a pig farm identified 11.7% (7/60) of S. Typhimurium monophasic variants, which is consistent with the whole-genome-based serotyping results. The multiplex PCR assay is a rapid and precise method for the detection of S. Typhimurium monophasic variants from samples across food production chains.

A Salmonella Microfluidic Chip Combining Non-Contact Eddy Heater and 3D Fan-Shaped Mixer with Recombinase Aided Amplification.

Foodborne pathogenic bacteria have become a worldwide threat to human health, and rapid and sensitive bacterial detection methods are urgently needed. In this study, a facile microfluidic chip was developed and combined with recombinase-aided amplification (RAA) for rapid and sensitive detection of Salmonella typhimurium using a non-contact eddy heater for dynamic lysis of bacterial cells and a 3D-printed fan-shaped active mixer for continuous-flow mixing. First, the bacterial sample was injected into the chip to flow through the spiral channel coiling around an iron rod under an alternating electromagnetic field, resulting in the dynamic lysis of bacterial cells by this non-contact eddy heater to release their nucleic acids. After cooling to ~75 °C, these nucleic acids were continuous-flow mixed with magnetic silica beads using the fan-shaped mixer and captured in the separation chamber using a magnet. Finally, the captured nucleic acids were eluted by the eluent from the beads to flow into the detection chamber, followed by RAA detection of nucleic acids to determine the bacterial amount. Under the optimal conditions, this microfluidic chip was able to quantitatively detect Salmonella typhimurium from 1.1 × 102 to 1.1 × 105 CFU/mL in 40 min with a detection limit of 89 CFU/mL and might be prospective to offer a simple, low-cost, fast and specific bacterial detection technique for ensuring food safety.

Public Health Response to Multistate Salmonella Typhimurium Outbreak Associated with Prepackaged Chicken Salad, United States, 2018.

Quantifying the effect of public health actions on population health is essential when justifying sustained public health investment. Using modeling, we conservatively estimated that rapid response to a multistate foodborne outbreak of Salmonella Typhimurium in the United States in 2018 potentially averted 94 reported cases and $633,181 in medical costs and productivity losses.

Genome Analysis and Therapeutic Evaluation of a Novel Lytic Bacteriophage of Salmonella Typhimurium: Suggestive of a New Genus in the Subfamily Vequintavirinae.

Salmonella Typhimurium, a foodborne pathogen, is a major concern for food safety. Its MDR serovars of animal origin pose a serious threat to the human population. Phage therapy can be an alternative for the treatment of such MDR Salmonella serovars. In this study, we report on detailed genome analyses of a novel Salmonella phage (Salmonella-Phage-SSBI34) and evaluate its therapeutic potential. The phage was evaluated for latent time, burst size, host range, and bacterial growth reduction in liquid cultures. The phage stability was examined at various pH levels and temperatures. The genome analysis (141.095 Kb) indicated that its nucleotide sequence is novel, as it exhibited only 1-7% DNA coverage. The phage genome features 44% GC content, and 234 putative open reading frames were predicted. The genome was predicted to encode for 28 structural proteins and 40 enzymes related to nucleotide metabolism, DNA modification, and protein synthesis. Further, the genome features 11 tRNA genes for 10 different amino acids, indicating alternate codon usage, and hosts a unique hydrolase for bacterial lysis. This study provides new insights into the subfamily Vequintavirinae, of which SSBI34 may represent a new genus.

Electrochemical biosensor for detecting pathogenic bacteria based on a hybridization chain reaction and CRISPR-Cas12a.

In this study, Lba Cas12a (Cpf1) as one of the CRISPR systems from Lachnospiraceae bacterium was coupled with a hybridization chain reaction (HCR) to develop an electrochemical biosensor for detecting the pathogenic bacterium, Salmonella typhimurium. Autonomous cross-opening of functional DNA hairpin structures of HCR yielded polymer double-stranded DNA wires consisting of numerous single-stranded DNAs, which initiated the trans-cleavage activity of CRISPR-Cas12a to indiscriminately cleave random single-stranded DNA labeling electrochemical tags on the surface of the electrode. It led to a variation in the electron transfer of electrochemical tags. The polymer double-stranded DNA of HCR was immobilized on dynabeads (DBs) via the S. typhimurium aptamer and released from DBs. The established method could selectively and sensitively quantify S. typhimurium in samples with detection limits of 20 CFU/mL. Our study provides a novel insight for exploring universal analytical methods for pathogenic bacteria based on CRISPR-Cas12a coupled with HCR.

Isolates of Salmonella typhimurium circumvent NLRP3 inflammasome recognition in macrophages during the chronic phase of infection.

Inflammasome signaling results in cell death and release of cytokines from the IL-1 family, which facilitates control over an infection. However, some pathogens such as Salmonella typhimurium (ST) activate various innate immune signaling pathways, including inflammasomes, yet evade these cell death mechanisms, resulting in a chronic infection. Here we investigated inflammasome signaling induced by acute and chronic isolates of ST obtained from different organs. We show that ST isolated from infected mice during the acute phase displays an increased potential to activate inflammasome signaling, which then undergoes a protracted decline during the chronic phase of infection. This decline in inflammasome signaling was associated with reduced expression of virulence factors, including flagella and the Salmonella pathogenicity island I genes. This reduction in cell death of macrophages induced by chronic isolates had the greatest impact on the NLRP3 inflammasome, which correlated with a reduction in caspase-1 activation. Furthermore, rapid cell death induced by Casp-1/11 by ST in macrophages limited the subsequent activation of cell death cascade proteins Casp-8, RipK1, RipK3, and MLKL to prevent the activation of alternative forms of cell death. We observed that the lack of the ability to induce cell death conferred a competitive fitness advantage to ST only during the acute phase of infection. Finally, we show that the chronic isolates displayed a significant attenuation in their ability to infect mice through the oral route. These results reveal that ST adapts during chronic infection by circumventing inflammasome recognition to promote the survival of both the host and the pathogen.

A Fluorescent Biosensor for Sensitive Detection of Salmonella Typhimurium Using Low-Gradient Magnetic Field and Deep Learning via Faster Region-Based Convolutional Neural Network.

In this study, a fluorescent biosensor was developed for the sensitive detection of Salmonella typhimurium using a low-gradient magnetic field and deep learning via faster region-based convolutional neural networks (R-CNN) to recognize the fluorescent spots on the bacterial cells. First, magnetic nanobeads (MNBs) coated with capture antibodies were used to separate target bacteria from the sample background, resulting in the formation of magnetic bacteria. Then, fluorescein isothiocyanate fluorescent microspheres (FITC-FMs) modified with detection antibodies were used to label the magnetic bacteria, resulting in the formation of fluorescent bacteria. After the fluorescent bacteria were attracted against the bottom of an ELISA well using a low-gradient magnetic field, resulting in the conversion from a three-dimensional (spatial) distribution of the fluorescent bacteria to a two-dimensional (planar) distribution, the images of the fluorescent bacteria were finally collected using a high-resolution fluorescence microscope and processed using the faster R-CNN algorithm to calculate the number of the fluorescent spots for the determination of target bacteria. Under the optimal conditions, this biosensor was able to quantitatively detect Salmonella typhimurium from 6.9 × 101 to 1.1 × 103 CFU/mL within 2.5 h with the lower detection limit of 55 CFU/mL. The fluorescent biosensor has the potential to simultaneously detect multiple types of foodborne bacteria using MNBs coated with their capture antibodies and different fluorescent microspheres modified with their detection antibodies.

Evaluation of antimicrobial activities of plant aqueous extracts against Salmonella Typhimurium and their application to improve safety of pork meat.

Nine odorless laboratory-collected hydro-distilled aqueous extracts (basil, calendula, centrifuged oregano, corn silk, laurel, oregano, rosemary, spearmint, thyme) and one industrial steam-distilled oregano hydrolate acquired as by-products of essential oils purification were screened for their in vitro antimicrobial activity against three Salmonella Typhimurium strains (4/74, FS8, FS115) at 4 and 37 °C. Susceptibility to the extracts was mainly plant- and temperature-dependent, though strain dependent effects were also observed. Industrial oregano hydrolate eliminated strains immediately after inoculation, exhibiting the highest antimicrobial potential. Hydro-distilled extracts eliminated/reduced Salmonella levels during incubation at 4 °C. At 37 °C, oregano, centrifuged oregano, thyme, calendula and basil were bactericidal while spearmint, rosemary and corn silk bacteriostatic. A strain-dependent effect was observed for laurel. The individual or combined effect of marinades and edible coatings prepared of industrial hydrolate and hydro-distilled oregano extracts with or without oregano essential oil (OEO) was tested in pork meat at 4 °C inoculated with FS8 strain. Lower in situ activity was observed compared to in vitro assays. Marinades and edible coatings prepared of industrial oregano hydrolate + OEO were the most efficient in inhibiting pathogen. Marination in oregano extract and subsequent coating with either 50% oregano extract + OEO or water + OEO enhanced the performance of oregano extract. In conclusion, by-products of oregano essential oil purification may be promising alternative antimicrobials to pork meat stored under refrigeration when applied in the context of multiple hurdle approach.

Direct association between rainfall and non-typhoidal Salmonella bloodstream infections in hospital-admitted children in the Democratic Republic of Congo.

Non-typhoidal Salmonella (NTS) ranks first among causes of bloodstream infection in children under five years old in the Democratic Republic of Congo and has a case fatality rate of 15%. Main host-associated risk factors are Plasmodium falciparum malaria, anemia and malnutrition. NTS transmission in sub-Saharan Africa is poorly understood. NTS bloodstream infections mostly occur during the rainy season, which may reflect seasonal variation in either environmental transmission or host susceptibility. We hypothesized that environment- and host-associated factors contribute independently to the seasonal variation in NTS bloodstream infections in children under five years old admitted to Kisantu referral hospital in 2013-2019. We used remotely sensed rainfall and temperature data as proxies for environmental factors and hospital data for host-associated factors. We used principal component analysis to disentangle the interrelated environment- and host-associated factors. With timeseries regression, we demonstrated a direct association between rainfall and NTS variation, independent of host-associated factors. While the latter explained 17.5% of NTS variation, rainfall explained an additional 9%. The direct association with rainfall points to environmental NTS transmission, which should be explored by environmental sampling studies. Environmental and climate change may increase NTS transmission directly or via host susceptibility, which highlights the importance of preventive public health interventions.

Evaluation of the Stress Tolerance of Salmonella with Different Antibiotic Resistance Profiles.

Disease caused by antibiotic-resistant Salmonella is a serious clinical problem that poses a great threat to public health. The present study is aimed at assessing differences in bacterial kinetics with different antibiotic resistance profiles under environmental stress and at developing microbial tolerance models in lettuce during storage from 4 to 36°C. The drug-resistance phenotypes of 10 Salmonella Typhimurium (S. Typhimurium) isolates were examined using the broth microdilution method. The results of 10 S. Typhimurium isolates in the suspensions showed that a slow trend towards reduction of drug-sensitive (DS) isolates in relation to the others though without statistical difference. Compared to DS S. Typhimurium SA62, greater bacterial reduction was observed in multidrug-resistant (MDR) S. Typhimurium HZC3 during lettuce storage at 4°C (P < 0.05). It was likely that a cross-response between antibiotic resistance and food-associated stress tolerance. The greater growth in lettuce at 12°C was observed for DS S. Typhimurium SA62 compared to MDR S. Typhimurium HZC3 and was even statistically different (P < 0.05), while no significant difference was observed for bacterial growth between MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 strains in lettuce storage from 16 to 36°C (P > 0.05). The goodness-of-fit indices indicated the Log-linear primary model provided a satisfactory fit to describe the MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 survival at 4°C. A square root secondary model could be used to describe the effect of temperature (12, 16, 28, and 36°C) on the growth rates of S. Typhimurium HZC3 (adj - R 2 = 0.91, RMSE = 0.06) and S. Typhimurium SA62 (adj - R 2 = 0.99, RMSE = 0.01) derived from the Huang primary model. It was necessary to pay attention to the tolerance of antibiotic resistant bacteria under environmental stress, and the generated models could provide parts of the input data for microbial risk assessment of Salmonella with different antibiotic resistance profile in lettuce.