Bacteriological Quality and Public Health Risk of Ready-to-Eat Foods in Developing Countries: Systematic Review and Meta Analysis

Occurrence & characterization of Staphylococcus aureus from ready-to-eat (RTE), and cooked food in Singapore: A retrospective analysis

Staphylococcus aureus is one of the major foodborne pathogens that poses significant public health risk, particularly in ready-to-eat (RTE) food prepared under inadequate hygiene conditions. Staphylococcal food poisoning (SFP) is increasingly prevalent worldwide, yet it is not reportable in Singapore, leaving a knowledge gap regarding the clinical incidence and virulence of local strains. This study examined the genetic diversity, antimicrobial resistance (AMR), and virulence determinants of S. aureus in RTE, and cooked food using both conventional testing and whole-genome sequencing (WGS) tools. We retrospectively analyzed 12178 RTE, and cooked food samples collected in Singapore from 2020 to 2023, detecting S. aureus in 0.19 % (23/12178) of samples. Genotype t4171_ST1155 was most common (4/23), followed by t91_ST2990 (3/23). Immunoassays detected the production of classical staphylococcal enterotoxin (SE) A, B, and C types in 43.5 % (10/23) of the isolates. Additionally, genomic analysis identified three more isolates that contained only non-classical SE genes, which were not detectable through immunoassays. AMR occurrence was highest for tetracycline (21.7 %, 5/23), followed by erythromycin (8.7 %, 2/23), clindamycin, gentamicin, and sulfamethoxazole-trimethoprim (4.3 %, 1/23 each). A minority (30.4 %, 7/23) of isolates possessed the complete icaADBC operon, which is associated with the well-studied matrix component involved in biofilm formation. Our findings indicate a low occurrence of S. aureus in RTE, and cooked foods in Singapore, with a minority carrying AMR and biofilm formation features, though about half are enterotoxigenic. This investigation plays a crucial role in comprehending the food safety landscape in Singapore, enabling the development of effective risk mitigation strategies aimed at improving community food safety.

Prevalence, Antibiotic Resistance, and Molecular Typing of Staphylococcus aureus Isolated from Ready-to-Eat Foods in Guangdong, South China

The increasing global popularity of ready-to-eat (RTE) foods for their convenience simultaneously brings along a risk, as these products can be contaminated with various microorganisms, including potentially harmful pathogens. We aimed to investigate the food contamination of Staphylococcus aureus (S. aureus) in RTE foods in Guangdong, South China. All S. aureus isolates were subjected to characterization through antimicrobial susceptibility tests, multilocus sequence typing (MLST), and PCR analysis for detecting mec and blaZ genes. A total of 824 RTE food samples were collected from 2017 to 2022, of which 73 (8.9%) were found to be contaminated with S. aureus. Contamination levels were mostly in the range of 0.3-1.0 most probable number (MPN)/g, with 10 samples exceeding 110 MPN/g. Of the 73 S. aureus isolates, 10 were identified as methicillin-resistant S. aureus (MRSA). In MRSA, resistance was most frequently observed to penicillin (100%, 10/10), followed by erythromycin (80.0%, 8/10) and tetracycline (70%, 7/10). And in methicillin-sensitive S. aureus (MSSA), resistance was most frequently observed to penicillin (98.4%, 62/63), followed by tetracycline (30.2%, 19/63) and erythromycin (23.8%, 15/63). Overall, 98.6% (72/73) of the isolates demonstrated resistance to at least one antimicrobial agent, whereas 31.5% (23/73) were resistant to three or more antimicrobials. Fifty-seven S. aureus isolates harbored the penicillin-resistant gene blaZ, and 10 isolates carried the mec gene. In addition, 30.1% of the isolates harbored genes for classical staphylococcal enterotoxins (SEs), with seb being the most frequently detected SE gene. MLST revealed that the 73 isolates belonged to 14 different sequence types (STs), the most prevalent of which was ST7. In MRSA, the most common prevalent clone is ST6, and in MSSA, ST7 was the most common isolates. The prevalent multidrug resistance indicates that the resistance situation of foodborne S. aureus in Guangdong is severe, posing a potential threat to consumer safety and health.

Propidium monoazide (PMA) qPCR assay compared to the plate count method for quantifying the growth of Salmonella enterica serotypes in vacuum-packaged turkey breast combined with a mathematical modeling approach

This study compares the plate count (PC) and the Propidium Monoazide-quantitative Polymerase Chain Reaction (PMA-qPCR) methods to assess the growth of a cocktail of three serotypes of Salmonella enterica (Heidelberg, Typhimurium, and Enteritidis) in cooked, sliced, and vacuum-packaged turkey breast (STB) under isothermal storage temperatures (8 °C-20 °C), using predictive models. Standard curves were developed for PMA-qPCR, demonstrating high efficiency (101%) and sensitivity, with quantification limits ranging from 1 to 2 log10 CFU/g for all temperatures studied. Comparative analysis revealed a significant correlation (R2 = 0.99; 95% CI) between the PC and PMA-qPCR methods; however, the agreement analysis indicated a mean difference (Bias) of -0.11 log10 CFU/g (p < 0.05), suggesting underestimation by the PC method. This indicates the presence of stressed or viable but nonculturable (VBNC) cells, detectable by PMA-qPCR but not by PC. The Baranyi and Roberts model showed a good ability to describe the behavior of S. enterica cocktail in STB for PC and PMA-qPCR data under all isothermal conditions. The exponential secondary model more accurately represented the temperature dependence of the maximum specific growth rate compared to the Ratkowsky square root model, with R2 values ≥ 0.984 and RMSE values ≤ 0.011 for both methods. These results suggest that combining PMA-qPCR with predictive modeling allows for a more accurate prediction of S. enterica growth, compared to PC method. In the event of cold chain disruptions of meat products, the use of PMA-qPCR method allow the quantification of VBNC cells, that can still pose a health risk to consumers, especially in ready-to-eat products.

Prevalence Trends of Foodborne Pathogens Bacillus cereus, Non-STEC Escherichia coli and Staphylococcus aureus in Ready-to-Eat Foods Sourced from Restaurants, Cafés, Catering and Takeaway Food Premises

Foodborne pathogens of Bacillus cereus (B. cereus), non-STEC Escherichia coli (non-STEC E. coli) and Staphylococcus aureus (S. aureus) are currently non-notifiable in Australia unless attributed to a food poisoning outbreak. Due to the lack of data around individual cases and isolations in foods, any changes in prevalence may go undetected. The aim of this study was to determine any changes in the prevalence of B. cereus, non-STEC E. coli and S. aureus in ready-to-eat (RTE) foods sampled from Western Australian restaurants, cafés, catering facilities and takeaway food premises from July 2009 to June 2022. A total of 21,822 microbiological test results from 7329 food samples analysed over this 13-year period were reviewed and analysed. Linear trend graphs derived from the annual prevalence and binary logistic regression models were used to analyse the sample results, which indicated an increase in prevalence for B. cereus. In contrast, a decrease in prevalence for both S. aureus and non-STEC E. coli was determined. Additionally, there were changes in prevalence for the three bacteria in specific months, seasons, specific RTE foods and food premises types. Further research is needed to gain a better understanding of the potential drivers behind these changes in prevalence, including the potential impacts of climate change, COVID-19, legislation and guidelines targeting specific RTE foods, and the difficulty of differentiating B. cereus from B. thuringeniesis using standard testing methods.

Advances in the applications of Bacteriophages and phage products against food-contaminating bacteria

Food-contaminating bacteria pose a threat to food safety and the economy by causing foodborne illnesses and spoilage. Bacteriophages, a group of viruses that infect only bacteria, have the potential to control bacteria throughout the "farm-to-fork continuum". Phage application offers several advantages, including targeted action against specific bacterial strains and minimal impact on the natural microflora of food. This review covers multiple aspects of bacteriophages applications in the food industry, including their use as biocontrol and biopreservation agents to fight over 20 different genera of food-contaminating bacteria, reduce cross-contamination and the risk of foodborne diseases, and also to prolong shelf life and preserve freshness. The review also highlights the benefits of using bacteriophages in bioprocesses to selectively inhibit undesirable bacteria, such as substrate competitors and toxin producers, which is particularly valuable in complex microbial bioprocesses where physical or chemical methods become inadequate. Furthermore, the review briefly discusses other uses of bacteriophages in the food industry, such as sanitizing food processing environments and detecting specific bacteria in food products. The review also explores strategies to enhance the effectiveness of phages, such as employing multi-phage cocktails, encapsulated phages, phage products, and synergistic hurdle approaches by combining them with antimicrobials.

Impact of packaging atmosphere, oregano essential oil, and storage temperature on cold-adapted Salmonella Enteritidis and Salmonella Typhimurium on ready-to-eat smoked turkey

The hazard of diseases created by S. Enteritidis and S. Typhimurium is relatively high in turkey meat products. Combinations of preservation methods are utilized in many strategies, such as mild heat with decreased water activity, a changed atmosphere, refrigerated storage, and decreased heat treatment with some acidification. Within the domain of ready-to-eat food technology, a range of preservation methods are typically utilized to enhance shelf life, such as applying mild heat in tandem with reduced water activity, employing modified atmosphere packaging, utilizing refrigerated storage, and utilizing reduced heat treatment combined with acidification. This investigation aimed to determine how S. Enteritidis and S. Typhimurium grew when sliced ready-to-eat smoked turkey (RTE-SM) was stored at 0, 5, 10, and 15°C for various periods. The study also examined the effects of modified atmosphere packaging (MAP) (40% CO2 and 60% N2) and VP on these growth patterns. Total viable count (TVC), lactic acid bacteria (LAB), pH, and redox potential levels were determined. The control experiment on RTE-SM showed no Salmonella growth within 30 d of storage at any temperature. This indicated that the RTE-SM in use did not initially contain S. Typhimurium and S. Enteritidis. Results indicated that the storage of RTE-SM using a combination of VP, MAP, and MAPEO with storage at 0 and 5°C did not allow for the pathogen to grow throughout storage. In comparison, at 10 and 15°C after one day, which allowed for minor growth (0.17-0.5 log CFU/g)? In contrast, at 0 and 5°C, Salmonella survives until the end of storage (173 d). However, the combination of MAPEO with the same storage temperatures achieved the elimination of the pathogen in the meat after 80 d. The combination of both packaging systems with high temperatures (10 or 15°C) allowed for the multiplication and growth of the bacterium through the product's shelf life of more than 1 log CFU/g. Thus, a combination of MAP or MAPEO with low storage temperatures (0 or 5°C) inhibited the growth of the pathogen.

Microbiological assessment of ready-to-eat foods and drinking water sources as a potential vehicle of bacterial pathogens in northern India

Foodborne illnesses caused by the consumption of contaminated foods have frequent occurrences in developing countries. The incorporation of contaminated water in food processes, preparation, and serving is directly linked to several gastrointestinal infections. Keeping in view, this study was conducted to assess the microbial quality of both drinking water sources and commonly consumed fresh ready-to-eat (RTE) foods in the region. The drinking water samples from water sources and consumer points, as well as food samples from canteens, cafes, hotels, and restaurants, were collected for the microbiological analysis. Fifty-five percent (n = 286) of water samples were found to be positive for total coliforms with MPN counts ranging from 3 to 2600 (100 ml) -1. E. coli was detected in nearly 30% of the total water samples. Overall, 65% tap water samples were found unsatisfactory, followed by submersible (53%), filter (40%), and WTP (30%) sources. Furthermore, the examination of RTE foods (n = 80) found that 60% were of unsatisfactory microbial quality with high aerobic plate counts. The salads were the most contaminated category with highest mean APC 8.3 log CFU/g followed by pani puri, chats, and chutneys. Presence of coliforms and common enteropathogens was observed in both water and food samples. The detected isolates from the samples were identified as Enterobacter spp., Klebsiella spp., Pseudomonas aeruginosa, Salmonella spp., Shigella spp., and Staphylococcus spp. Based on these findings, microbiological quality was found compromised and this may pose hazard to public health. This exploratory study in the Punjab region also suggests that poor microbiological quality of water sources can be an important source of contamination for fresh uncooked RTE foods, thus transferring pathogens to the food chain. Therefore, only safe potable drinking water post-treatment should be used at all stages.

Analysis of Antimicrobial Resistance in Bacterial Pathogens Recovered from Food and Human Sources: Insights from 639,087 Bacterial Whole-Genome Sequences in the NCBI Pathogen Detection Database

Understanding the role of foods in the emergence and spread of antimicrobial resistance necessitates the initial documentation of antibiotic resistance genes within bacterial species found in foods. Here, the NCBI Pathogen Detection database was used to query antimicrobial resistance gene prevalence in foodborne and human clinical bacterial isolates. Of the 1,843,630 sequence entries, 639,087 (34.7%) were assigned to foodborne or human clinical sources with 147,788 (23.14%) from food and 427,614 (76.88%) from humans. The majority of foodborne isolates were either Salmonella (47.88%), Campylobacter (23.03%), Escherichia (11.79%), or Listeria (11.3%), and the remaining 6% belonged to 20 other genera. Most foodborne isolates were from meat/poultry (95,251 or 64.45%), followed by multi-product mixed food sources (29,892 or 20.23%) and fish/seafood (6503 or 4.4%); however, the most prominent isolation source varied depending on the genus/species. Resistance gene carriage also varied depending on isolation source and genus/species. Of note, Klebsiella pneumoniae and Enterobacter spp. carried larger proportions of the quinolone resistance gene qnrS and some clinically relevant beta-lactam resistance genes in comparison to Salmonella and Escherichia coli. The prevalence of mec in S. aureus did not significantly differ between meat/poultry and multi-product sources relative to clinical sources, whereas this resistance was rare in isolates from dairy sources. The proportion of biocide resistance in Bacillus and Escherichia was significantly higher in clinical isolates compared to many foodborne sources but significantly lower in clinical Listeria compared to foodborne Listeria. This work exposes the gaps in current publicly available sequence data repositories, which are largely composed of clinical isolates and are biased towards specific highly abundant pathogenic species. We also highlight the importance of requiring and curating metadata on sequence submission to not only ensure correct information and data interpretation but also foster efficient analysis, sharing, and collaboration. To effectively monitor resistance carriage in food production, additional work on sequencing and characterizing AMR carriage in common commensal foodborne bacteria is critical.

Assessment of consumer demographics and food safety risks associated with ready-to-eat (RTE) homemade foods purchased online in the UAE

In the UAE, female entrepreneurs, termed "Tajrat", sell a variety of homemade food products over online social media (OSM) platforms. Some of these food products are prepared and sold outside regulatory channels, with serious public health consequences. The study aimed to identify consumer demographics associated with purchasing of RTE, homemade food sold over in OSM platforms in the UAE and to assess the food quality by evaluating microbiological quality and fat percentage in RTE foods. A representative survey of the population of the UAE (n = 1303) was conducted, covering consumer demographics, frequency of purchase, and respondents' perception towards safety and nutritional value. 66 % of respondents were Emiratis, fifty percent of whom purchased RTE foods online. Moreover, 61 % of participants purchased from "Tajrat" via OSM as opposed to other sources. Convenience (47 %) and taste (41 %) were the main drivers for purchasing RTE homemade foods. Although 76 % of respondents have at least one member of their family considered vulnerable, the safety levels, quality, and nutritional value of such products did not carry the same significance. Microbiological analysis of 35 food samples purchased online from "Tajrat" was conducted. Listeria spp. was isolated from 22 % of the samples, 43 % showed positive Staphylococcus aureus, and 31 % of the samples had coliform bacteria. Total Fat Content of RTE homemade food samples ranged between 2.6 and 30 g/100 g which is considered high and can cause serious health issues if consumed frequently. Recommendations from this study will help policy makers and regulators in the UAE to develop and implement education strategies targeting homemade food handlers.

An Outbreak of Salmonella Typhimurium Infections Linked to Ready-To-Eat Tofu in Multiple Health Districts - Ontario, Canada, May-July 2021

From May to mid-August 2021, the Ontario, Canada provincial public health agency, Public Health Ontario, in collaboration with local public health authorities and federal food safety partners, investigated a spatiotemporal cluster of 38 patients with Salmonella Typhimurium infections across multiple public health districts in Ontario. Five (13%) patients were hospitalized; no deaths were reported. The outbreak was linked to consumption of ready-to-eat seasoned tofu from one manufacturer that was distributed to multiple Ontario restaurants. Isolates from the seasoned tofu were within one or fewer allele differences to the outbreak strain by whole genome sequencing. Evidence from food safety investigations conducted by local public health authorities and the Canadian Food Inspection Agency (CFIA) revealed that unsanitary conditions could have led to cross-contamination of the tofu, and insufficient heating of the tofu at the production level likely resulted in failure to eliminate the pathogen. The CFIA issued a food recall for the tofu at hotel, restaurant, and institution levels. Tofu was identified as a novel outbreak-associated food vehicle for S. Typhimurium in this outbreak. Interventions that target the production level and all parts of the supply chain and include additional safeguarding steps that minimize microbial growth are important.

An Outbreak of Salmonella Typhimurium Infections Linked to Ready-To-Eat Tofu in Multiple Health Districts - Ontario, Canada, May-July 2021

From May to mid-August 2021, the Ontario, Canada provincial public health agency, Public Health Ontario, in collaboration with local public health authorities and federal food safety partners, investigated a spatiotemporal cluster of 38 patients with Salmonella Typhimurium infections across multiple public health districts in Ontario. Five (13%) patients were hospitalized; no deaths were reported. The outbreak was linked to consumption of ready-to-eat seasoned tofu from one manufacturer that was distributed to multiple Ontario restaurants. Isolates from the seasoned tofu were within one or fewer allele differences to the outbreak strain by whole genome sequencing. Evidence from food safety investigations conducted by local public health authorities and the Canadian Food Inspection Agency (CFIA), revealed that unsanitary conditions could have led to cross-contamination of the tofu, and insufficient heating of the tofu at the production level likely resulted in failure to eliminate the pathogen. The CFIA issued a food recall for the tofu at hotel, restaurant, and institution levels. Tofu was identified as a novel outbreak-associated food vehicle for S. Typhimurium in this outbreak. Interventions that target the production level and all parts of the supply chain and include additional safeguarding steps that minimize microbial growth are important.