Enterica Serovar Research Articles

Active Quantum Biomaterials-Enhanced Microrobots for Food Safety.

Timely disruptive tools for the detection of pathogens in foods are needed to face global health and economic challenges. Herein, the utilization of quantum biomaterials-enhanced microrobots (QBEMRs) as autonomous mobile sensors designed for the precise detection of endotoxins originating from Salmonella enterica (S. enterica) as an indicator species for food-borne contamination globally is presented. A fluorescent molecule-labeled affinity peptide functions as a specific probe, is quenched upon binding to the surface of QBEMRs. Owing to its selective affinity for endotoxin, in the presence of S. enterica the fluorescence is restored and easy to observe and quantifies optical color change to indicate the presence of Salmonella. The devised approach is designed to achieve highly sensitive detection of the S. enterica serovar Typhimurium endotoxin with exquisite selectivity through the utilization of QBEMRs. Notably, no fluorescence signal is observed in the presence of endotoxins bearing similar structural characteristics, highlighting the selectivity of the approach during food sample analysis. Technically, the strategy is implemented in microplate readers to extend microrobots-based approaches to the routine laboratory. This new platform can providefast and anticipated results in food safety.

Fresh produce-associated foodborne disease outbreaks in Australia, 2001 to 2017.

Fresh produce is an important source of foodborne outbreaks in Australia. Using descriptive analysis, we examined confirmed and suspected foodborne outbreaks associated with fresh produce in Australia recorded in the OzFoodNet outbreak register from 2001 to 2017. The outbreak register contains reports of foodborne disease outbreaks collected by OzFoodNet epidemiologists and public health officials. A fresh produce outbreak was defined as the occurrence of two or more cases of the same illness in which the investigation had implicated a common food and this food contained fresh produce. A total of 92 fresh produce outbreaks were reported, encompassing 3,422 reported illnesses, 446 hospitalisations and four deaths. Of these outbreaks, 76.1% (70/92) were caused by a known pathogen, with the majority caused by either Salmonella enterica (n = 30) or Norovirus (n = 29). Most outbreaks (77.2%; 71/92) were associated with consumption of foods containing multiple ingredients, some of which were not fresh produce. The largest outbreaks associated with a single fresh produce item included bean sprouts contaminated with S. enterica serovar Saintpaul (419 illnesses and 76 hospitalisations) and semi-dried tomatoes contaminated with Hepatitis A (372 illnesses and 169 hospitalisations). Restaurants (45.7%; n = 42/92) and commercial catering (15.2%: n = 14/92) were common settings for fresh produce outbreaks. Outbreaks occurred in all states and territories of Australia and in all seasons, with an increased frequency in the warmer months (September-May). Although the number of fresh produce-associated outbreaks did not seem to be increasing in Australia, integrated surveillance is needed to rapidly identify sources of infection due to the propensity of these outbreaks to be large and widespread.

Molecular Patterns and Antimicrobial Resistance Characterization of Salmonella enterica Non-Typhoidal from Human, Food, and Environment Samples Isolated in Luanda, Angola

The aim of this study was to characterize the antimicrobial resistance phenotype and genotype of non-typhoidal Salmonella spp. isolated in Luanda, Angola. Between 2013 and 2015, human clinical samples, food, and environmental samples (n = 290) were collected at different regions of Luanda city and screened for the presence of Salmonella spp. Bacterial isolates were preliminarily identified using the API 20E Kit, and their identification was confirmed using PCR and serotyping. All Salmonella spp. isolates were tested by minimum inhibitory concentration against 19 antimicrobials. The isolates were also screened using PCR for the presence of resistance genes (blaOXA-1, blaSHV, blaTEM, sul1, sul2, sul3, qnrA, qnrB, qnrS, qnrC, qnrD, aac(6′)-Ib, dfrIa [targeting dfrA1, dfrA5, dfrA15, dfrA15b, dfrA16, dfrA16b] and dfrA12, cmlA, and floR) and typed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Salmonella enterica non-typhoidal was detected in 21.3% of the clinical samples (n = 32/150), 11.1% of the food samples (n = 10/90), and 26% of the environmental samples (n = 13/50). Serotyping revealed that the monophasic variant of Salmonella Typhimurium (Salmonella enterica serovar 4,[5],12:i:-) was detected in 38.1% of the samples. Moreover, serovar Salmonella Enteritidis was the second most frequent. Only 7.3% of the isolates were resistant to at least one antimicrobial. Furthermore, isolates from different origins (clinical, environmental, and food) were associated with the same lineages, Salmonella Enteritidis ST11 and S. enterica ser. Typhimurium ST313. The detection of S. enterica serovar 4,[5],12:i:- in different settings reinforces the need for a One Health approach to control this zoonosis in Angola.

First report on whole genome sequencing and comparative genomics of Salmonella enterica serovar Abortusequi isolated from Donkey in India.

Salmonella enterica subspecies enterica serovar Abortusequi (S. Abortusequi) is a leading cause of abortion in equines that hinders the rapid growth of equine industry. S. Abortusequi infection in equids has re-emerged over last ten years. In the present study, S. Abortusequi was isolated and characterized from donkeys during an abortion storm in the southern peninsular region of India. Further, whole genome sequencing and phylogenomic analysis revealed that the present isolate was clustered among S. Abortusequi clade. The core genome MLST (cgMLST) analysis based on hierarchical clustering and single nucleotide polymorphism (SNP) core-genome dendrogram of the present isolate against 10S. Abortusequi isolates revealed that the present isolate established a distinct clade compared to all previously reported isolates. A comparison of cgMLST and SNP analyses revealed the same clustering concordance between isolates. In addition, comparative genomics and phylogenetic analysis was carried out with six S. Abortusequi serovars showed a higher number of core genes than accessory genes. Further, comparative analysis of phenotype and genotype antimicrobial resistance revealed a concordance of 32% and discordance of 68% respectively.

Genome-wide fitness analysis of Salmonella enterica reveals aroA mutants are attenuated due to iron restriction in vitro.

Salmonella enterica is a globally disseminated pathogen that is the cause of over 100 million infections per year. The resulting diseases are dependent upon host susceptibility and the infecting serovar. As S. enterica serovar Typhimurium induces a typhoid-like disease in mice, this model has been used extensively to illuminate various aspects of Salmonella infection and host responses. Due to the severity of infection in this model, researchers often use strains of mice resistant to infection or attenuated Salmonella. Despite decades of research, many aspects of Salmonella infection and fundamental biology remain poorly understood. Here, we use a transposon insertion sequencing technique to interrogate the essential genomes of widely used isogenic wild-type and attenuated S. Typhimurium strains. We reveal differential essential pathways between strains in vitro and provide a direct link between iron starvation, DNA synthesis, and bacterial membrane integrity.IMPORTANCESalmonella enterica is an important clinical pathogen that causes a high number of deaths and is increasingly resistant to antibiotics. Importantly, S. enterica is used widely as a model to understand host responses to infection. Understanding how Salmonella survives in vivo is important for the design of new vaccines to combat this pathogen. Live attenuated vaccines have been used clinically for decades. A widely used mutation, aroA, is thought to attenuate Salmonella by restricting the ability of the bacterium to access particular amino acids. Here we show that this mutation limits the ability of Salmonella to acquire iron. These observations have implications for the interpretation of many previous studies and for the use of aroA in vaccine development.

Identification and Antimicrobial Susceptibility of Serovar Choleraesuis in a Salmonella Outbreak in Central-Western Albania

Abstract Swine paratyphoid infection is caused by the swine-adapted Salmonella enterica serovar Choleraesuis. Infected individuals remain healthy carriers, and if the infection occurs at the end of the fattening period, it could pose a threat to human health. The present work aimed to assess antimicrobial susceptibility of S. enterica serovar Choleraesuis serotypes isolated from domestic pigs in central-western Albania, and to assess the presence and circulation of antibiotic-resistant paratyphoid Salmonella in Albania. Increasing mortality was reported in 6 farrow-to-finish pig farms located in the western and central parts of the country from December 2022 to April 2023. Post-mortem examination revealed macroscopic lesions in different organs indicating Salmonella infection. Four serovars Choleraesuis were isolated out of 24 different Salmonella spp. Multi-drug resistance (MDR), extensively drug-resistant (XDR), and Pan Drug Resistance (PDR) was calculated. Three out of four isolates showed MDR, and one out of four showed XDR. All S. enterica serovar Choleraesuis isolates showed resistance to at least two antimicrobials. Three isolates were observed to display MAR index values >0.2 indicating high-risk contaminated sources with frequent use of antibiotics. The predominant antimicrobial resistance was observed for amoxicillin, oxytetracycline, sulfamethoxazole, trimethoprim, spiramycin, colistin sulpha, and doxycycline. The findings emphasize the importance of strict biosecurity measures in affected pig farms, and prevention and control of S. enterica serovar Choleraesuis in the farm sanitary programs in Albania.

Transcriptional regulator MarT negatively regulates MarT-regulated motility gene I, a new gene involved in invasion and virulence of Salmonella enterica.

The speciation of Salmonella occurred by acquisition of genomic islands from other bacterial species and continued to diverge into subspecies and serovars with diferent range of host. S. enterica serovar Typhimurium (STM) is a generalist pathogen infecting hosts that include birds, mice, and humans, whilst S. enterica serovar Typhi (STY) is a restricted-host pathogen, infecting only humans. Despite their ranges of hosts, STM and STY possess 97-98% identity. Gain of genes by horizontal transference and loss of genes by mutations, are believed essential for differentiation of Salmonella. Salmonella pathogenicity island 3 (SPI-3) is an example combining these two processes. SPI-3 encodes misL and marT, among other genes. In STM, misL is required for gut colonization. Furthermore, protein MarT, positively regulates expression of misL by binding to misL-promoter. On the other hand, in SPI-3 of STY, marT and misL are pseudogenes. Interestingly, the gene t3766 (gene involved in resistance to H2O2) is present only in STY and is negatively regulated when marT STM is heterologously expressed in STY. Based on the view that MarT might regulate genes implicated in virulence, this work searched for new genes regulated by MarT. In silico searches for possible MarT target genes were performed, and 4 genes were selected for further analysis as they contained at least 2 copies of the consensus MarT-binding sequence in their promoters. Mutating marT in STM or heterologously expressing marT STM in STY confirmed that MarT negatively regulates ORF STY1408 or STM14_2003, its homologue in STM. STY1408 encodes for a putative protein with homology to methyl accepting chemotaxis proteins, which participate in chemotaxis and motility. Therefore, STY1408 was named mrmI (MarT-regulated motility gene I). Motility assays confirmed that the product of mrmI modulates motility. In addition, in vitro infection of cells with STM and STY mutants in mrmI reduces association with cells at 1, 3 and 24 h post-infection. Oral infection of mice showed that a mrmI null mutant was defective in producing systemic disease. Therefore, we conclude that MarT regulated mrmI, is involved in virulence of Salmonella. While pseudogenization of marT might modulate the fitness of narrow host range STY.

Design and Synthesis of 6-amido-3-carboxypyridazine Derivatives as Potent T3SS Inhibitors of Salmonella enterica Serovar Typhimurium.

Salmonella enterica (S. enterica) serovar Typhimurium, an anaerobic enteric pathogene, could cause human and animal diseases ranging from mild gastroenteritis to whole body serious infections. The goal of this paper was to synthesize new 6-amido-3-carboxypyridazine derivatives with different lengths of side chains with the aim of getting potent antibacterial agents. Synthesized compounds were analyzed by analytical techniques, such as 1H NMR, 13C NMR spectra, and mass spectrometry. We designed a series of novel 6-amido-3-carboxypyridazines using FA as the lead compound with the scaffold hopping strategy and their inhibitory activity against the effectors of type III secretion system (T3SS) using SDS-PAGE and western blot analysis for two rounds. Also, the preliminary mechanism of action of this series of compounds on T3SS was performed using real-time qPCR. Nine 6-amido-3-carboxypyridazines was synthesized. The inhibitory activities evaluated showed that compound 2i was the most potent T3SS inhibitor, which demonstrated potent inhibitory activities on the secretion of the T3SS SPI-1 effectors in a dose-dependent manner. The transcription of SPI-1 may be affected by compound 2i through the SicA/InvF regulatory pathway. The novel synthetic 6-amido-3-carboxypyridazines could act as potent leads for the development of novel antibacterial agents.

Establishing a surveillance programme for Salmonella Dublin in Austrian dairy herds by comparing herd-level vs. individual animal detection methods

Due to its increasing occurrence in cattle farms in various countries, leading to significant economic losses in affected livestock, Salmonella enterica subspecies enterica serovar Dublin (S. Dublin) has become a highly investigated pathogen in cattle production. In Austria, there have been occasional human cases of S. Dublin as well as an increase in laboratory-confirmed cases in cattle, indicating the need for a screening programme to determine the current status in Austria. The aims of this study were, firstly, to determine the seroprevalence of S. Dublin in dairy herds through bulk milk screenings in two federal states (Salzburg, Tyrol) of Austria. Secondly, the study aimed to identify the infection status of the herds through individual animal and herd level detection, comparing microbiological, molecular and serological detection methods. The results of the study will allow the development of a sampling strategy for a surveillance programme in Austria.A total of 6973 dairy farms were tested through serological bulk milk screening. The seroprevalence for the federal state of Tyrol was 14.8 % and for Salzburg it was 18.2 %, resulting in an average seroprevalence of 16.5 %. At an individual animal level, 205 (11.3 %) animals tested positive for shedding of S. Dublin in the faeces through microbiological detection, and 268 (17.0 %) animals had positive values (ct value ≤ 38) by qPCR. The association between microbiological and molecular detection was statistically significant (p < 0.001), with a calculated kappa value of 0.65 ± 0.27 (p ≤ 0.001), assuming a substantial level of agreement. In 17 herds, where an individual animal tested positive for shedding of S. Dublin, environmental sampling and testing were carried out. At a herd level 16 (94.1 %) out of the 17 participating herds, tested positive for S. Dublin either microbiologically or by molecular assay in boot swab samples. Bulk milk samples from 14 out of the 17 participating herds were analysed for antibodies to S. Dublin and 12 samples (85.7 %) were positive. In total 111 (18.9 %) out of 587 blood samples tested positive for S. Dublin antibodies, demonstrating a statistically significant correlation (p < 0.001) both with microbiological (κ = 0.32 ± 0.49; p ≤ 0.001) and molecular (κ=0.23 ± 0.06; p ≤ 0.001) findings.It was possible to identify S. Dublin by culture from boot swabs in 14 (82.4 %) out of 17 herds and by molecular assay using qPCR in 15 (88.2 %) out of 17 herds, indicating a suitable sample type for screening on a herd level-basis for acute infections, but not for identifying chronic infections or asymptomatic carriers. Other environmental samples, such as sponge-sticks, are only suitable to a limited extent for the detection of S. Dublin. The results of this study demonstrate a moderate S. Dublin prevalence in dairy herds in the selected Austrian regions, signalling further screening and management programmes for the future.

The transcriptional regulation of the horizontally acquired iron uptake system, yersiniabactin and its contribution to oxidative stress tolerance and pathogenicity of globally emerging salmonella strains

ABSTRACT The bacterial species Salmonella enterica (S. enterica) is a highly diverse pathogen containing more than 2600 distinct serovars, which can infect a wide range of animal and human hosts. Recent global emergence of multidrug resistant strains, from serovars Infantis and Muenchen is associated with acquisition of the epidemic megaplasmid, pESI that augments antimicrobial resistance and pathogenicity. One of the main pESI’s virulence factors is the potent iron uptake system, yersiniabactin encoded by fyuA, irp2-irp1-ybtUTE, ybtA, and ybtPQXS gene cluster. Here we show that yersiniabactin, has an underappreciated distribution among different S. enterica serovars and subspecies, integrated in their chromosome or carried by different conjugative plasmids, including pESI. While the genetic organization and the coding sequence of the yersiniabactin genes are generally conserved, a 201-bp insertion sequence upstream to ybtA, was identified in pESI. Despite this insertion, pESI-encoded yersiniabactin is regulated by YbtA and the ancestral Ferric Uptake Regulator (Fur), which binds directly to the ybtA and irp2 promoters. Furthermore, we show that yersiniabactin genes are specifically induced during the mid-late logarithmic growth phase and in response to iron-starvation or hydrogen peroxide. Concurring, yersiniabactin was found to play a previously unknown role in oxidative stress tolerance and to enhance intestinal colonization of S. Infantis in mice. These results indicate that yersiniabactin contributes to Salmonella fitness and pathogenicity in vivo and is likely to play a role in the rapid dissemination of pESI among globally emerging Salmonella lineages.

Genetic characterization of blaCTX-M-65 in Salmonella Infantis and blaCMY-2 in Salmonella Heidelberg isolated from fresh ground turkey meat sold in supermarkets in Los Andes and San Felipe, Chile

Annually, food poisoning caused by non-typhoidal Salmonella (NTS) accounts for 40 million foodborne infections worldwide. Outbreaks due to multidrug-resistant NTS strains are associated with the consumption of poultry products. We aimed to determine the proportion of NTS in ground turkey meat available at supermarkets in two locations in Chile, characterizing their serovars, virulence traits, and antimicrobial resistance profiles. Between September and December 2018, we analyzed 47 samples of packed ground turkey meat purchased at 13 supermarkets. NTS were identified by MALDI-TOF, and antimicrobial susceptibility was determined by the disk-diffusion agar method. Whole genome sequencing was performed with MiSeq (Illumina) followed by Nullarbor analysis. NTS was detected in 6 out of 47 samples (12.8 %, 95 %CI: 6.0–25.1 %), identifying S. enterica serovar Infantis (n=4 isolates), serovar Agona (n=1 isolate), and serovar Heidelberg (n=1 isolate), respectively. S. Infantis belonged to sequence type (ST)32, differentiating two clones, whereas the S. Agona was ST13 and S. Heidelberg was ST15. S. Infantis strains were multidrug antibiotic resistant, harboring blaCTX-M-65, tetA, and mutations that confer fosfomycin resistance. Serovars Agona and Heidelberg showed tetracycline (tetB) and fosfomycin resistance (fosA7). Additionally, serovar Heidelberg showed resistance to sulfamethoxazole-trimethoprim, aminoglycosides, and carried the blaCMY-2 gene. This is the first report in Chile about NTS detected in raw ground turkey meat available in supermarkets. S. Infantis and S. Agona strains showed a phylogenetic relationship with strains of the same serovars isolated from the environment in our country. This situation would impact food poisoning and the dissemination of bacterial resistance between animals, humans, and the environment.

Chemical composition, antioxidant and antimicrobial activities of Rumex obtusifolius L. essential oil from the highlands of Ecuador

The chemical composition, antioxidant and antimicrobial activities of the essential oil from the aerial parts of Rumex obtusifolius L. were studied. To the best of the authors’ knowledge, this essential oil has never been fully characterized. The component analysis of the essential oil was done by gas chromatography with flame ionization detector (GC-FID) and mass selective detector (GC-MS). A total of 104 compounds, representing 97.8% of the essential oil, were identified. Aliphatic compounds, mainly methyl ketones (74.2%) and monoterpene hydrocarbons (13.7%) were found to be the most abundant compounds. The major compounds were undecan-2-one (47.6%) and nonan-2-one (13.4%). The antioxidant activity of the essential oil, evaluated by DPPH (IC50 9.11 mg/mL) and ABTS (IC50 36.72 mg/mL) assays, exhibited a weak ability in scavenging radicals. The essential oil also showed a low ferric reducing activity. The essential oil exhibited very good activity against E. coli and S. aureus, but low activities against S. enterica serovar, P. aeruginosa and C. albicans. MIC values of the essential oil varied from 0.38-27.04 μL/mL, with the lowest for E. coli.

Clustered Regularly Interspaced Short Palindromic Repeat-1 (CRISPR-1) Locus as a Tool for Tracing the Zoonotic History of Salmonella enterica Strains.

Background Salmonella enterica is a significant foodborne pathogen that causes considerable illness and death in humans and animals. The clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein (Cas) system in bacteria acts as an adaptive immune defense against invasive genetic elements by incorporating short intergenic spacers (IGSs) into CRISPR loci. These loci serve as molecular records of past interactions with phages and plasmids, providing insights into the transmission and evolution of bacterial strains across different hosts. Aim This study aimed to investigate the diversity of IGSs in the CRISPR-1 locus of S. enterica isolates from humans and camels. The objective was to assess the potential of IGSs to distinguish strains, track sources, and understand patterns of zoonotic transmission. Materials and methods Genomic DNA was extracted from multiple strains of S. enterica, and the CRISPR-1 locus was polymerase chain reaction (PCR) amplified and sequenced. The sequences were compared to identify distinct patterns of IGSs and potential host-specific characteristics. Sanger sequencing and bioinformatics tools were used to classify the IGSs and determine their similarity to known sequences in the National Center for Biotechnology Information (NCBI) database. Results Sequence analysis revealed five distinct CRISPR-1 types among S. enterica isolates from humans and three among camel isolates. The presence of shared IGSs between human and camel S. entericaisolates suggested zoonotic or reverse-zoonotic transmission events. Additionally, host-specific unknown IGSs (UIGS) were identified. Importantly, camel isolates initially identified as S. enterica subspeciesenterica serovar Enteritidis based on rrnH gene sequencing were reclassified as S. enterica serovar Enteritidis based on CRISPR-1 profiling, demonstrating the higher resolution of CRISPR-based genotyping. Conclusion The diversity of IGSs in the CRISPR-1 locus effectively differentiated S. enterica strains and provided insights into their evolutionary origins and transmission dynamics. CRISPR-based genotyping proves to be a promising tool to complement traditional serotyping methods, enhancing the molecular epidemiology of salmonellosis and potentially leading to better management and control strategies for this pathogen.

Salmonella enterica subsp. enterica serovar Paratyphi B from mute swan (Cygnus olor): complete genome sequence features point towards invasive variant potential.

A subgroup of Salmonella (S.) enterica subsp. enterica serovar Paratyphi B is significantly associated with invasive infections in humans. We report the complete genome sequence of a potentially invasive. S. Paratyphi B isolated from a mute swan (Cygnus olor) found dead at an urban recreation park in Berlin, Germany.

The Salmonella virulence protein PagN contributes to the advent of a hyper-replicating cytosolic bacterial population

ABSTRACT Salmonella enterica subspecies enterica serovar Typhimurium is an intracellular pathogen that invades and colonizes the intestinal epithelium. Following bacterial invasion, Salmonella is enclosed within a membrane-bound vacuole known as a Salmonella-containing vacuole (SCV). However, a subset of Salmonella has the capability to prematurely rupture the SCV and escape, resulting in Salmonella hyper-replication within the cytosol of epithelial cells. A recently published RNA-seq study provides an overview of cytosolic and vacuolar upregulated genes and highlights pagN vacuolar upregulation. Here, using transcription kinetics, protein production profile, and immunofluorescence microscopy, we showed that PagN is exclusively produced by Salmonella in SCV. Gentamicin protection and chloroquine resistance assays were performed to demonstrate that deletion of pagN affects Salmonella replication by affecting the cytosolic bacterial population. This study presents the first example of a Salmonella virulence factor expressed within the endocytic compartment, which has a significant impact on the dynamics of Salmonella cytosolic hyper-replication.

Comprehensive Investigation of Salmonella spp.: Isolation, Characterization and PCR Primer Set Evaluation for Enhanced Detection and Identification

Background: Salmonellosis is a serious health concern for both animals and humans. According to a report of the Centers for Disease Control and Prevention, 40,000 human infections occur annually; however, the number of unconfirmed cases is as high as approximately 800,000-4000,000. These organisms gain entry into the gastrointestinal cells and cause serious diseases, resulting in intestinal damage and even death. Methods: In this research, 115 Salmonella isolates from different sources were tested. Using morphological, cultural, and biochemical methods, they were classified into 30 serovars. Plasmid profiling was used for quick identification, which showed similarities among the isolates.PCR primer sets targeting specific genes, such as invA, hilA, iroB, oriC, fimA, hitJ and stn, demonstrated reliability, accuracy and specificity for identifying S. enterica serovars. Result: This study recommends the use of specific primer sets in PCR-based methods for rapid and reliable identification and detection of locally isolated Salmonella serovars/strains. This research adds to the continuing efforts for improving the diagnostic techniques to tackle the challenges presented by Salmonella spp.

Utilization of Whey for Eco-Friendly Bio-Preservation of Mexican-Style Fresh Cheeses: Antimicrobial Activity of Lactobacillus casei 21/1 Cell-Free Supernatants (CFS).

Using whey, a by-product of the cheese-making process, is important for maximizing resource efficiency and promoting sustainable practices in the food industry. Reusing whey can help minimize environmental impact and produce bio-preservatives for foods with high bacterial loads, such as Mexican-style fresh cheeses. This research aims to evaluate the antimicrobial and physicochemical effect of CFS from Lactobacillus casei 21/1 produced in a conventional culture medium (MRS broth) and another medium using whey (WB medium) when applied in Mexican-style fresh cheese inoculated with several indicator bacteria (Escherichia coli, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, and Listeria monocytogenes). The CFSs (MRS or WB) were characterized for organic acids concentration, pH, and titratable acidity. By surface spreading, CFSs were tested on indicator bacteria inoculated in fresh cheese. Microbial counts were performed on inoculated cheeses during and after seven days of storage at 4 ± 1.0 °C. Moreover, pH and color were determined in cheeses with CFS treatment. Lactic and acetic acid were identified as the primary antimicrobial metabolites produced by the Lb. casei 21/1 fermentation in the food application. A longer storage time (7 days) led to significant reductions (p < 0.05) in the microbial population of the indicator bacteria inoculated in the cheese when it was treated with the CFSs (MRS or WB). S. enterica serovar Typhimurium was the most sensitive bacteria, decreasing 1.60 ± 0.04 log10 CFU/g with MRS-CFS, whereas WB-CFS reduced the microbial population of L. monocytogenes to 1.67 log10 CFU/g. E. coli and S. aureus were the most resistant at the end of storage. The cheese's pH with CFSs (MRS or WB) showed a significant reduction (p < 0.05) after CFS treatment, while the application of WB-CFS did not show greater differences in color (ΔE) compared with MRS-CFS. This study highlights the potential of CFS from Lb. casei 21/1 in the WB medium as an ecological bio-preservative for Mexican-style fresh cheese, aligning with the objectives of sustainable food production and guaranteeing food safety.

Antimicrobial activity of chitosan- edible films containing a combination of carvacrol and rosemary nano-emulsion against Salmonella enterica serovar Typhimurium and Listeria monocytogenes for ground meat

This research aimed to assess the potential of active food packaging as an innovative approach to enhance the quality of fresh food products. Specifically, our focus was on developing chitosan edible films combined with rosemary nanoemulsion (Ch-RNE) and carvacrol nano-emulsion (Ch-CNE) as effective antibacterial food packaging solutions. The efficacy of these films against artificially inoculated L. monocytogenes (NCTC 13372\\ ATCC® 7644) as a Gram-positive bacterium, and S. enterica serovar Typhimurium (ATCC 14028) as a Gram-negative bacterium, in ground meat was investigated. The size of the prepared nano-emulsions was characterized using zeta sizer, FTIR and HRTEM. The MIC of both nano-emulsions against both pathogens was found to be 0.78 % and 1.56 %. Filmogenic mixtures were casted using these concentrations, which were then dried and evaluated for their physical and mechanical properties.

Occurrence and characterization of rmtB-harbouring Salmonella and Escherichia coli isolates from a pig farm in the UK.

To characterize and elucidate the spread of amikacin-resistant Enterobacteriaceae isolates from environmental samples on a pig farm in the UK, following the previous identification of index Salmonella isolates harbouring the rmtB gene, a 16S rRNA methylase. Environmental samples were collected during two visits to a pig farm in the UK. Isolates were recovered using selective media (amikacin 128 mg/L) followed by real-time PCR and WGS to analyse rmtB-carrying Salmonella and Escherichia coli isolates. Salmonella and E. coli isolates harbouring the rmtB gene were detected at both farm visits. All Salmonella isolates were found to be monophasic S. enterica serovar Typhimurium variant Copenhagen of ST34. rmtB-harbouring E. coli isolates were found to be one of three STs: ST4089, ST1684 and ST34. Long-read sequencing identified the rmtB gene to be chromosomally located in Salmonella isolates and on IncFII-type plasmids in E. coli isolates. The results showed the rmtB gene to be flanked by IS26 elements and several resistance genes. We report on the occurrence of rmtB-harbouring Enterobacteriaceae on a pig farm in the UK. rmtB confers resistance to multiple aminoglycosides and this work highlights the need for surveillance to assess dissemination and risk.

Rapid discrimination of four Salmonella enterica serovars: A performance comparison between benchtop and handheld Raman spectrometers.

Foodborne illnesses, particularly those caused by Salmonella enterica with its extensive array of over 2600 serovars, present a significant public health challenge. Therefore, prompt and precise identification of S. enterica serovars is essential for clinical relevance, which facilitates the understanding of S. enterica transmission routes and the determination of outbreak sources. Classical serotyping methods via molecular subtyping and genomic markers currently suffer from various limitations, such as labour intensiveness, time consumption, etc. Therefore, there is a pressing need to develop new diagnostic techniques. Surface-enhanced Raman spectroscopy (SERS) is a non-invasive diagnostic technique that can generate Raman spectra, based on which rapid and accurate discrimination of bacterial pathogens could be achieved. To generate SERS spectra, a Raman spectrometer is needed to detect and collect signals, which are divided into two types: the expensive benchtop spectrometer and the inexpensive handheld spectrometer. In this study, we compared the performance of two Raman spectrometers to discriminate four closely associated S. enterica serovars, that is, S. enterica subsp. enterica serovar dublin, enteritidis, typhi and typhimurium. Six machine learning algorithms were applied to analyse these SERS spectra. The support vector machine (SVM) model showed the highest accuracy for both handheld (99.97%) and benchtop (99.38%) Raman spectrometers. This study demonstrated that handheld Raman spectrometers achieved similar prediction accuracy as benchtop spectrometers when combined with machine learning models, providing an effective solution for rapid, accurate and cost-effective identification of closely associated S. enterica serovars.