Isolation and molecular characterization of multidrug-resistant Salmonella enterica serovars

Detection and antibiotic resistance of Salmonella isolates from selected poultry farms in Dar es Salaam, Tanzania

Introduction. Salmonella is one of the most prevalent foodborne bacteria, posing a significant global health concern and responsible for ~155,000 deaths and 93.8 million human foodborne illnesses annually. The rampant use of antibiotic agents to combat salmonellosis in poultry has contributed to the emergence of resistance against commonly used antibiotics. Methodology. The cross-sectional study was conducted between January and June 2023 across three districts in the Dar es Salaam region, Tanzania. Salmonella isolates were detected and confirmed by using standard microbiological conventional methods and molecular methods such as PCR and genomic sequencing. PCR was used for detecting the presence of the invA gene, and partial DNA sequencing was performed to identify species and their close relatedness. A Kirby-Bauer disc diffusion method was employed to evaluate Salmonella sensitivity to seven different commonly used antibiotics, namely ampicillin, azithromycin, chloramphenicol, ciprofloxacin, gentamycin, trimethoprim/sulfamethoxazole and tetracycline. Salmonella strain with reference number ATCC 8739 was used as a control. Results. The overall Salmonella isolates from faecal droppings were 6.04% (n=796). Of the PCR-confirmed isolates, 64.3% (n=28) were resistant to more than two classes of antibiotics and hence considered multidrug resistant. The highest resistance was observed with ampicillin (92.9%, n=26), followed by tetracycline (71.43%, n=20), ciprofloxacin (42.9%, n=12), sulphonamide (42.85%, n=12), gentamicin (35.7%, n=10) and azithromycin (28.9%, n=8). All the isolates were susceptible to chloramphenicol (100%, n=28). Twenty-eight isolates were sent for sequencing, out of which 16 sequences (OR021717-OR021739) met the criteria for phylogenetic analysis. All 16 sequences had a per cent identity to EU348369 strains Senftenberg isolated from China, OL581594 Salmonella Newport isolated from China and EU348368 Salmonella Pullorum isolates from China. Other sequences diverged more distantly; these are Salmonella Abony with accession number CP007541 and Salmonella Kentucky with accession number OL581592. The tree also included an outgroup species, Salmonella bongori, which was downloaded from GenBank with accession numbers NC015761 and NC021870 S. bongori. Conclusion. The high level of antibiotic resistance found in this study could be due to the misuse of antibiotics in poultry management, and/or, probably, there were circulating resistant Salmonella strains in the environment. To reverse the trend observed, immediate interventions such as advocating for the prudent use of antibiotics in poultry production systems by strengthening extension services to poultry farmers and the use of a farmer field school model to improve poultry management through improved farm biosecurity are required.

Limitation of the Lytic Effect of Bacteriophages on Salmonella and Other Enteric Bacterial Pathogens and Approaches to Overcome

Bacteriophages (phages) have emerged as promising agents for combating bacterial pathogens, including nontyphoidal Salmonella enterica (S. enterica), the most common foodborne pathogen worldwide. The emergence of antimicrobial-resistant (AMR) S. enterica poses a severe healthcare issue. Nowadays, many countries worldwide have banned antibiotics for animal feeds or additives, and various strategies have been developed and gained popularity for their potential to address S. enterica infection. Among these strategies, phage therapy shows more promise because of its ability to specifically target bacterial pathogens without disrupting the beneficial microbiota or animal/human cells. Phages are viruses that rupture host cells through the lysis of phage-encoded endolysin proteins. Nonetheless, phages also face various challenges, including phage resistance, gene transduction, serovar diversity, and the immune response of animal/human organisms, which limit the efficacy of S. enterica. Due to this limitation of phages, endolysin, as a lytic protein for bacterial cells derived from phages, has been demonstrated as another promising solution against various bacterial pathogens, including AMR. This review is aimed at discussing the benefits and limitations of phage therapies and exploring the promising potential of phage-encoded endolysins in controlling S. enterica.

Multiplex PCR-based genotyping of Salmonella Enteritidis and Salmonella Typhimurium from food sources and assessment of their antimicrobial resistance profiles in Egypt

BACKGROUND

Salmonellosis is a widespread zoonotic disease that poses a significant threat to livestock and public health. This study aimed to serotype 20 Salmonella isolates obtained from sixty retail chicken meats, assess Salmonella contamination from eggs, and evaluate antibiotic resistance profiles.

METHODS AND RESULTS

Twenty eggs were randomly collected in the new Borg El Arab market. Bacterial isolation was carried out utilizing both traditional culture, biochemical, and PCR methods. Among the twenty eggs analyzed, three (15%) tested positive for Salmonella, while the remaining seventeen (85%) were confirmed as negative. Genotyping through multiplex PCR revealed the presence of two S. Enteritidis and other serovar, with the use of three specific gene sets: a random sequence for Salmonella spp., sdfI gene for S. Enteritidis, and flagellin (fliC gene) for S. Typhimurium. Out of the 20 isolates obtained from chicken meat, five (25%) were identified as S. Typhimurium, and three (15%) were classified as S. Enteritidis. All isolates sourced from chicken meat exhibited resistance to Rifampicin and Amoxicillin, with 90% displaying sensitivity to cefotaxime, gemifloxacin, and Erythromycin. Importantly, S. Blegdam, identified via serological methods, displayed resistance to all tested antibiotics. For the three isolates obtained from eggs, 66.6% showed sensitivity to cefotaxime, erythromycin, cefuraxime, and cefaclor, while displaying complete resistance (100%) to Amoxicillin, rifampicin, clarithromycin, and cefadroxil. Notably, one serovar exhibited absolute resistance to all tested drugs.

CONCLUSION

Stakeholders must implement strict control measures and rationalize antibiotic use in veterinary and human medicine due to the rise of antibiotic-resistant strains.

Whole-genome sequencing of multidrug resistance Salmonella Typhi clinical strains isolated from Balochistan, Pakistan

Introduction

Salmonella enterica serovar Typhi (S. Typhi) is a major cause of morbidity and mortality in developing countries, contributing significantly to the global disease burden.

Methods

In this study, S. Typhi strains were isolated from 100 patients exhibiting symptoms of typhoid fever at a tertiary care hospital in Pakistan. Antimicrobial testing of all isolates was performed to determine the sensitivity and resistance pattern. Three MDR strains, namely QS194, QS430, and QS468, were subjected to whole genome sequencing for genomic characterization.

Results and Discussion

MLST analysis showed that QS194, belonged to ST19, which is commonly associated with Salmonella enterica serovar typhimurium. In contrast, QS430 and QS468, belonged to ST1, a sequence type frequently associated with S. Typhi. PlasmidFinder identified the presence of IncFIB(S) and IncFII(S) plasmids in QS194, while IncQ1 was found in QS468. No plasmid was detected in QS430. CARD-based analysis showed that the strains were largely resistant to a variety of antibiotics and disinfecting agents/antiseptics, including fluoroquinolones, cephalosporins, monobactams, cephamycins, penams, phenicols, tetracyclines, rifamycins, aminoglycosides, etc. The S. Typhi strains possessed various virulence factors, such as Vi antigen, Agf/Csg, Bcf, Fim, Pef, etc. The sequencing data indicated that the strains had antibiotic resistance determinants and shared common virulence factors. Pangenome analysis of the selected S. Typhi strains identified 13,237 genes, with 3,611 being core genes, 2,093 shell genes, and 7,533 cloud genes. Genome-based typing and horizontal gene transfer analysis revealed that the strains had different evolutionary origins and may have adapted to distinct environments or host organisms. These findings provide important insights into the genetic characteristics of S. Typhi strains and their potential association with various ecological niches and host organisms.

Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals' contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.