Comparison of rapid cultural methods for the detection of Salmonella species

Establishment of a Simple, Sensitive, and Specific Salmonella Detection Method Based on Recombinase-Aided Amplification Combined with dsDNA-Specific Nucleases

Salmonella is a common foodborne pathogen that can cause food poisoning, posing a serious threat to human health. Therefore, quickly, sensitively, and accurately detecting Salmonella is crucial to ensuring food safety. For the Salmonella hilA gene, we designed Recombinase-aided amplification (RAA) primers and dsDNA-specific nuclease (DNase) probes. The ideal primer and probe combination was found when conditions were optimized. Under UV light, a visual Salmonella detection technique (RAA-dsDNase) was developed. Additionally, the RAA-dsDNase was modified to further reduce pollution hazards and simplify operations. One-pot RAA-dsDNase-UV or one-pot RAA-dsDNase-LFD was developed as a Salmonella detection method, using UV or a lateral flow dipstick (LFD) for result observation. Among them, one-pot RAA-dsDNase and one-pot RAA-dsDNase-LFD had detection times of 50 min and 60 min, respectively, for detecting Salmonella genomic DNA. One-pot RAA-dsDNase-UV had a detection limit of 101 copies/μL and 101 CFU/mL, while one-pot RAA-dsDNase-LFD had a sensitivity of 102 copies/μL and 102 CFU/mL. One-pot RAA-dsDNase-UV and one-pot RAA-dsDNase-LFD assays may identify 17 specific Salmonella serovars witho ut causing a cross-reaction with the remaining 8 bacteria, which include E. coli. Furthermore, Salmonella in tissue and milk samples has been reliably detected using both approaches. Overall, the detection method developed in this study can quickly, sensitively, and accurately detect Salmonella, and it is expected to become an important detection tool for the prevention and control of Salmonella in the future.

Prevalence of Schistosoma mansoni-Salmonella coinfection among patients in southern Ethiopia

Concurrent infection with Schistosoma mansoni and Salmonella species is not uncommon in the endemic area of sub-Saharan Africa, although its prevalence may have regional variations. We discuss such coinfection and associated factors in an Ethiopian context. We assessed the prevalence of S. mansoni and Salmonella coinfections among patients attending two hospitals in southern Ethiopia. A facility-based cross-sectional study was carried out between 1 October and 30 November 2019. In total 271 participants with gastrointestinal complaints were selected through a systematic sampling technique. S. mansoni was detected using direct microscopy and formalin-ether concentration techniques, whereas Salmonella was identified by conventional culture methods and the Widal test. Antibiotic susceptibility test for Salmonella isolates was performed. The prevalence rates of S. mansoni and Salmonella infections were 17.30% and 7.70% respectively. The prevalence of S. mansoni-Salmonella coinfection was 7.7%. Of the factors analysed in connection with coinfection, male sex, age and frequency of exposure to contaminated water bodies were found to be statistically significant. S. mansoni-Salmonella coinfections pose a grave health problem in the study area, especially among children. Our conclusions can be used by the medical community to frame and implement intervention strategies for the management of S. mansoni-Salmonella coinfections.

Prevalence and Associated Risk Factors of Salmonella, Shigella, and Intestinal Parasites among Food Handlers in Motta Town, North West Ethiopia

Background

Intestinal parasite, Salmonella, and Shigella infections are the main public health concerns in the world, especially in developing countries due to inaccessibility of safe water and unhygienic food handling practices of food handlers.

Methods

A cross-sectional study was conducted in food handlers in Motta town, from February 2019 to April 2019. The study was undertaken to determine the prevalence and associated risk factors of Salmonella, Shigella, and intestinal parasites among 243 food handlers. Sociodemographic and risk factors were collected using pretested structured questionnaire. The stool sample was collected and examined with direct wet mount and concentration techniques. Culture was performed using xylose lysine deoxycholate agar and MacConkey agar and biochemical tests like Klinger iron agar (KIA), lysine iron agar (LIA), Simmons citrate agar, sulphide indole motility test, citrate utilization, and urease production test were conducted to isolate Salmonella species and Shigella species. An antibiotics susceptibility test was performed with Mueller-Hinton agar using the disk diffusion method. Data were entered using statistical package Epi-Data Version 3.1 and analysed with logistic regression using SPSS version 25 and Fisher's exact test. A p value < 0.05 at 95% CI was considered as statistically significant.

Results

The prevalence of intestinal parasite, Salmonella, and Shigella was 27.6%, 2.5%, and 1.6%, respectively, and hookworm was the predominant intestinal parasite detected in the stool. Antimicrobial resistance was observed in ampicillin and tetracycline (100%) in Salmonella species and Shigella species. Risk factors like fingernail status, fruit washing before eating, cleaning utensils, and regular shoe wearing habit were associated with intestinal parasite, whereas fingernail status and wearing kitchen gown during food service were significantly associated with Salmonella and Shigella infections.

Conclusion

The prevalence of intestinal parasitic infections, Salmonella, and Shigella infections in this study indicates the importance of food handlers as probable sources of enteropathogenic infections. Food handlers should have follow-up on the order of food safety rules and keep their personal hygiene. Hotel owners are responsible to control the health status and their created awareness by given food hygiene training for food handlers. Therefore, policy-makers and implementers should focus on the risk factors to reduce the prevalence below the level of public health importance.

A Single-Step Enrichment Medium for Nonchromogenic Isolation of Healthy and Cold-Injured Salmonella spp. from Fresh Vegetables

Culture-based detection of nontyphoidal Salmonella spp. in foods requires at least four working days; therefore, new detection methods that shorten the test time are needed. In this study, we developed a novel single-step Salmonella enrichment broth, SSE-1, and compared its detection capability with that of commercial single-step ONE broth-Salmonella (OBS) medium and a conventional two-step enrichment method using buffered peptone water and Rappaport-Vassiliadis soy broth (BPW-RVS). Minimally processed lettuce samples were artificially inoculated with low levels of healthy and cold-injured Salmonella Enteritidis (100 or 101 colony-forming unit/25 g), incubated in OBS, BPW-RVS, and SSE-1 broths, and streaked on xylose lysine deoxycholate (XLD) agar. Salmonella recoverability was significantly higher in BPW-RVS (79.2%) and SSE-1 (83.3%) compared to OBS (39.3%) (p < 0.05). Our data suggest that the SSE-1 single-step enrichment broth could completely replace two-step enrichment with reduced enrichment time from 48 to 24 h, performing better than commercial single-step enrichment medium in the conventional nonchromogenic Salmonella detection, thus saving time, labor, and cost.

Development of a rapid method to quantify Salmonella Typhimurium using a combination of MPN with qPCR and a shortened time incubation

A novel method was developed for the specific quantification of S. Typhimurium using a most-probable-number (MPN) combined with qPCR and a shortened incubation time (MPN-qPCR-SIT). For S. Typhimurium enumeration, dilutions of samples were transferred into three wells on a microtiter plate and the plate was incubated for 4 h. The S. Typhimurium presence in the wells was identified using a qPCR and populations were determined based on an MPN calculation. The R² between the MPN-qPCR-SIT and conventional MPN exhibited a high level of correlation (0.9335-0.9752), suggesting that the MPN-qPCR-SIT offers a reliable alternative method for S. Typhimurium quantification. Although plating and qPCR were limited in their ability to detect low levels of S. Typhimurium (e.g. 0.18 log MPN/ml), these levels could be successfully detected with the MPN-qPCR-SIT. Chicken breast samples inoculated with S. Typhimurium were incubated at 0, 4, and 24 h and incubated samples were subjected to microbiome analysis. Levels of Salmonella and Enterobacteriaceae increased significantly with incubation time. The obvious benefits of the MPN-qPCR-SIT are: 1) a further confirmation step is not required, 2) the detection limit is as low as conventional MPN, but 3) is more rapid, requiring approximately 7 h to simultaneously complete quantification.