A new 7-plex PCR assay for simultaneous detection of shiga toxin-producing Escherichia coli O157 and Salmonella Enteritidis in meat products

Evaluation of Simultaneous Growth of Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes in Ground Beef Samples in Different Growth Media

Several multiplex approaches for the simultaneous detection of pathogens in food have been developed in recent years, but the use of a single enrichment medium remains a problem. In this study, six enrichment broths (five non-selective media, tryptic soy broth (TSB), brain heart infusion broth (BHI), buffered peptone water (BPW), universal pre-enrichment broth (UPB), no. 17 broth, and a selective, Salmonella Escherichia Listeria broth (SEL)), were studied for the simultaneous detection of E. coli O157:H7, Salmonella spp., and L. monocytogenes, to validate the suitable enrichment broth to be used for the detection methods. Different ratios of E. coli O157:H7, Salmonella spp., and L. monocytogenes were used. Almost all non-selective broths evaluated in this study showed similar growth parameters and profiles among each other. The only selective enrichment broth under analysis (SEL) showed distinct growth features compared to the non-selective media, allowing for a slower but balanced growth of the three pathogens, which could be beneficial in preventing the overgrowth of fast-growing bacteria. In addition, when tested in ground beef samples, SEL broth seems to be the most distinctive medium with a balanced growth pattern observed for the three pathogens. Overall, this study is intended to provide the basis for the selection of suitable enrichment broths according to the technology detection to be used, the desired time of enrichment, and the expected balanced concentration of pathogens.

Phenotypic and genotypic characterization of antibiotic-resistant Salmonella isolated from humans, aquaculture, and poultry in Sri Lanka: A retrospective study

BACKGROUND

In Sri Lanka, foodborne diseases caused by nontyphoidal Salmonella are of increasing concern. We therefore aimed to characterize the dominant Salmonella serovars in humans, poultry, and aquaculture through a One Health approach.

METHODS

We collected isolates from different sectors, confirmed their identities using PCR, screened their antibiotic resistance profiles, and determined their antibiotic resistance genes based on whole-genome sequencing.

RESULTS

Of the 75 Salmonella isolates identified, the majority of serotypes were unidentified. Both Salmonella enterica serovar Enteritidis (S. Enteritidis) and Salmonella enterica serovar Typhimurium (S. Typhimurium) could be isolated from human sources and were also found prevalent in the poultry sector. ST36, ST11 and ST1541 were the dominant serotypes of S. Typhimurium and S. Enteritidis, respectively. Alarmingly, 4% (1/25) of poultry Salmonella isolates were resistant to ciprofloxacin, suggesting an emergence of this phenotype. Moreover, virulence genes were very diverse among S. Enteritidis and S. Typhimurium isolates.

CONCLUSIONS

With the diversity of unidentified serotypes found and the detection of emerging resistances, our study highlights the importance of a One Health approach to monitoring antibiotic resistance. For public health initiatives in Sri Lanka to be successful in mitigating salmonellosis, all three sectors - humans, aquaculture, and poultry - must be tackled concomitantly in a coordinated manner under the One Health approach because antibiotic resistance genes, and even specific sequence types, may be able to spread across the aforementioned sectors. We anticipate that our results will inform public health policies in Sri Lanka to tackle foodborne illnesses.

Simultaneous Detection of Four Main Foodborne Pathogens in Ready-to-Eat Food by Using a Simple and Rapid Multiplex PCR (mPCR) Assay

The increasing consumption of organic or ready-to-eat food may cause serious foodborne disease outbreaks. Developing microbiological culture for detection of food-borne pathogens is time-consuming, expensive, and laborious. Thus, alternative methods such as polymerase chain reaction (PCR) are usually employed for outbreaks investigation. In this work, we aimed to develop a rapid and simple protocol for the simultaneous detection of Escherichia coli (E coli), Listeria monocytogenes (L. monocytogenes), Staphylococcus aureus (S. aureus) and Salmonella enterica (S. enterica), by the combination of an enrichment step in a single culture broth and a multiplex PCR (mPCR) assay. The effectiveness of several enrichment media was assessed by culture and PCR. Buffered peptone water (BPW) was selected as the optimum one. Then, mPCR conditions were optimized and applied both to pure co-cultures and artificially inoculated food samples (organic lettuce and minced meat). In the culture medium inoculated at 10⁰ CFU/mL, mPCR was able to detect the four microorganisms. When performed on artificially food samples, the mPCR assy was able to detect E. coli, S. enterica, and L. monocytogenes. In conclusion, BPW broth can effectively support the simultaneous growth of E. coli, S. aureus, L. monocytogenes, and S. enterica and could be, thus, used prior to a mPCR detection assay in ready-to-eat food, thereby considerably reducing the time, efforts and costs of analyzes.

Simultaneous detection of Salmonella pathogenicity island 2 and its antibiotic resistance genes from seafood

Salmonella enterica serovars are virulent pathogens of humans and animals with many strains possessing multiple drug resistance traits. They have been found to carry resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracycline (ACSSuT-resistant). A rapid and sensitive multiplex PCR (mPCR)-based assay was developed for the detection of Salmonella serovars from seafood. Six sets of primers which are one primer pair targeting Salmonella specific gene invA (284 bp), two Salmonella pathogenicity island 2 (SPI-2) genes ssaT (780 bp) and sseF (888 bp) and three antibiotic resistance genes floR (198 bp), sul1 (425 bp), tetG (550 bp) were used for the study. The specificity and sensitivity of the assay were tested by spiking shrimp/fish/clam homogenate with viable cells of Salmonella. This assay allows for the cost effective and reliable detection of pathogenic Salmonella enterica from seafood. The mPCR developed in the present study proved to be a potent analytical tool for the rapid identification of multidrug-resistant Salmonella serovars from seafood.