Serotypes, antibiotic resistance, and molecular characterization of non-typhoidal salmonella isolated from diarrheic patients in Guangxi Zhuang Autonomous Region, China, 2014–2017

Genomic and resistome analysis of Salmonella enterica isolates from retail markets in Yichun city, China

Nontyphoidal Salmonella (NTS) causes global outbreaks of foodborne disease. The main source of Salmonella for humans is animal-borne foods; however, the monitoring of Salmonella in the food chain via genomic platforms was limited in China. This study evaluated the prevalence, resistome, and virulome diversity of Salmonella strains identified from pork, retail environment, aquatic products, and poultry eggs of retail markets in Yichun city, Jiangxi province. The overall incidence of Salmonella was 9.4 %, with a higher contamination rate observed in pork at 13.5 %, followed by the retail environment at 7.69 %. The genomic analysis of the isolates revealed a total of fifteen distinct serovars, with serovar Enteritidis being the most prevalent (64.3 %). The phenotypic resistance analysis conducted by the broth microdilution method, revealed that 81.12 % of the isolates exhibited multidrug resistance (MDR), with high resistance to trimethoprim/sulphonamides (100 %), followed by tetracycline (99.3 %) and streptomycin (99.3 %). Genotypic analysis of antimicrobial resistance identified 80 antimicrobial-resistant genes (ARGs), with mdf(A), aph(3')-Ib, tet(A), dfrA12, floR, bla TEM-1B , qnrS3, and sul2, conferring resistance to different antimicrobial classes, being the predominant ARGs. Additionally, forty ESBL genes, particularly critical genes such as bla CTX-M and bla NDM-1, were also identified in Salmonella isolates. The IncR, IncFIB (K), and IncX1 plasmid replicons were widely prevalent and served as significant reservoirs of horizontally acquired foreign genes. Moreover, key virulence genes such as cdtB, lpf and sef were also detected, in addition to Salmonella pathogenicity islands SPI-1 and SPI-2. This study reveals the prevalence of multidrug-resistant and virulent strains of Salmonella serovars in the markets of Yichuan city, posing a risk of human infections. The gained knowledge provided essential baseline information that may be utilized for regular tracking of MDR Salmonella transmission in the food chain to minimize potential future outbreaks.

Genomic characteristics and antibiotic resistance profiles of monophasic Salmonella Typhimurium in Shaanxi Province, China

Introduction

Monophasic Salmonella Typhimurium, characterized by the absence of phase II flagellar antigens, has become increasingly prevalent as a foodborne pathogen, raising significant public health concerns due to its multidrug resistance. This study investigated the genomic characteristics and antibiotic resistance profiles of the monophasic Salmonella Typhimurium strains isolated from patients and food sources in Shaanxi Province, China.

Methods

A total of 58 strains were collected between 2020 and 2021, with 4 strains isolated from food and 54 from patients. Whole genome sequencing was performed to assess genomic features. Antimicrobial susceptibility was tested against 17 antimicrobial agents using the broth dilution method, while pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing were employed for genetic characterization and epidemiological analysis. Phylogenetic analysis was conducted using single nucleotide polymorphism clustering.

Results and discussion

Our results revealed that all the strains belonged to the ST34 and did not carry virulence genes on pSLT (NC_003277). There were 12 strains carrying the STM2757 gene. The isolates exhibited a considerable diversity in PFGE subtypes. Phenotypic antimicrobial resistance showed that the strains were most resistant to tetracycline (94.34%; 50/53) and ampicillin (94.34%; 50/53), followed by streptomycin (88.68%; 47/53) and ampicillin/sulbactam (64.15%; 34/53). Resistance gene prediction highlighted the presence of 64 distinct genes, with aac(6')-Iaa found in all strains (100%) and tet(B) in 93.1% of strains. Notably, the floR gene, relevant for resistance to phenicols, was observed in 44.83% of isolates. Genomic analysis revealed that 96.55% of strains were positive for the sodC1 virulence gene, whereas only 10.34% carried the sopE gene. The most plasmid replicon was IncQ1 (84.48%; 49/58), followed by IncHI2 (32.76%; 19/58) and IncHI2A (32.76%; 19/58). Single nucleotide polymorphism analysis showed that 2 strains were clustered together with SRR17830210 (UK outbreak isolate) with a bootstrap value of 0.949. There were only 12 allelic differences between SNXiAn21SAL011 and the reference strain. Conclusively, the monophasic Salmonella Typhimurium ST34 strains in Shaanxi Province demonstrated unique genomic and antimicrobial resistance traits. This study may help to prevent outbreaks and rationalize salmonellosis antimicrobial therapeutics.

Tracing the evolution: the rise of Salmonella Thompson co-resistant to clinically important antibiotics in China, 1997-2020

As clinical Salmonella enterica serovar Thompson (S. Thompson) emerged among the top ten prevalent serovars in China, understanding the distribution and origin of its multidrug-resistant (MDR) strains becomes imperative. This study employed antimicrobial susceptibility testing, whole-genome sequencing, and bioinformatics analysis to investigate the prevalence and genomic profiles of clinically important S. Thompson ST26 across China from 1997 to 2020. Upon analyzing 141 isolates from various sources, we identified 29 isolates, derived from 25 diarrhea patients and four animal-derived foods, displayed co-resistance to ciprofloxacin, cefotaxime, and azithromycin (CIPRCTXRAZIR), all of which are considered the front-line and critically-important antimicrobial agents for treating Salmonella infections in humans. The IncC plasmid was the predominant mobile vector identified among the CIPRCTXRAZIR isolates, harboring four crucial resistance genes qnrS1, qepA4, blaCMY-2, and mph(A) that confer resistance to three critically important antimicrobials. However, the closely related and clustered IncC-harboring CIPRCTXRAZIR isolates (0-23 single nucleotide polymorphisms [SNPs]) indicated the clonal spreading of these clinically important isolates in different provinces of China. Notably, the CIPRCTXRAZIR isolates appeared in aquatic products of animal-derived food, highlighting the possibility of aquaculture practices in the emergence and transmission of important antimicrobial resistance. Our findings emphasize the critical public health implications of IncC-carrying clinically important S. Thompson ST26. The study calls for enhanced surveillance of the clinically important S. Thompson ST26 clone in clinical and aquaculture and implementation of targeted interventions to mitigate its spread, thereby protecting food safety and public health.IMPORTANCEWe highlighted the critical veterinary public health issue of clinically important Salmonella enterica serovar Thompson (S. Thompson) prevalence in animal-derived foods, particularly aquatic products, calling for urgent action. The ability of S. Thompson to resist critically important antimicrobials across diverse environments highlights the transmission and survival of resistant strains within the livestock and poultry industry, aquaculture, and food production chains. This study underscores the importance of continuous surveillance of clinically important S. Thompson, especially in aquaculture settings, and considers the global trade of aquatic products as a potential vector for international dissemination. Further investigation on the factors contributing to the clone spread of clinically important Salmonella strain and the development of intervention strategies to mitigate its public health impact.

Isolation and characterization of Salmonella Typhimurium monophasic variant phage and its application in foods

Salmonella Typhimurium monophasic variant (STm) is an emerging Salmonella serotype that causes food poisoning through the contamination of various foods, including animal products, vegetables, and fruits. In particular, the increasing prevalence of multidrug-resistant STm highlights the urgent need to develop effective strategies to control this pathogen. In this work, a novel and broad-spectrum Salmonella phage named vB_Sal_TmvP009 was isolated and characterized. Morphological and genomic analyses revealed that phage vB_Sal_TmvP009 belonged to the genus Jerseyvirus. Phage vB_Sal_TmvP009 was tolerant to a wide range of temperatures (-20°C∼60°C) and pH values (3∼12). The optimal multiplicity of phage infection was 0.0001, and it had a shorter latent period (8 min), longer lysis period (70 min), and a burst size of 292 PFU/cell. A total of 13 Salmonella serotypes could be lysed by phage vB_Sal_TmvP009. Furthermore, phage vB_Sal_TmvP009 inhibited the growth of multidrug-resistant Salmonella in lettuce or milk with the highest suppression of 3.4 and 3.7 log CFU/mL within 24 h, respectively. The genome of phage vB_Sal_TmvP009 contains lysin and spanin protein, but no tRNA, virulence factors, or drug resistance-related genes. These findings suggest that phage vB_Sal_TmvP009 is a promising antibacterial agent for controlling Salmonella in the food industry.

Characteristics of Nontyphoid Salmonella Isolated from Human, Environmental, Animal, and Food Samples in Burkina Faso: A Systematic Review and Meta-Analysis

Salmonella is one of the world's leading causes of zoonotic and foodborne illnesses. Recently, antimicrobial resistance (AMR) has become one of the most critical challenges to public health and food safety. Herein, we employed a meta-analysis to determine the pooled prevalence and spatiotemporal distribution of serovars and antimicrobial resistance in NTS in Burkina Faso. To find eligible articles, a comprehensive literature search of PubMed, African Journals Online, ScienceDirect, Google Scholar, and the gray literature (university libraries) in Burkina was conducted for the period from 2008 to 2020. Studies meeting the inclusion criteria were selected and assessed for risk of bias. To assess the temporal and spatial relationships between serotypes and resistant strains from humans, animals, food, and the environment, a random-effects statistical model meta-analysis was carried out using the Comprehensive Meta-Analysis Version 3.0 program. The NTS prevalence rates were 4.6% (95% CI: 3-7) and 20.1% (95% CI: 6.6-47.4) in humans and animals, respectively, and 16.8% (95% CI: 10.5-25.8) and 15.6% (95% CI: 8.2-27.5) in food and the environment, respectively. Most NTS serovars were S. Derby, reported both in food and animals, and S. Typhimurium, reported in humans, while S. Croft II, S. Jodpur II, and S. Kentucky were the most prevalent in the environment. NTS isolates were highly resistant to erythromycin, amoxicillin, cefixime, and cephalothin, with a pooled prevalence of multidrug resistance of 29% (95% CI: 14.5-49.5). The results of this review show a high diversity of Salmonella serotypes, as well as high antibiotic resistance in Salmonella isolates from animal, human, food, and environmental samples in Burkina, calling for a consolidated "One Health" approach to better understand the drivers of pathogen emergence, spread, and antimicrobial resistance, as well as the formulation of intervention measures needed to limit the risk associated with the disease.

Prevalence of antibiotic resistance in Salmonella Typhimurium isolates originating from Iran: a systematic review and meta-analysis

Objective

Antibiotic resistance in Salmonella represents a significant global public health concern. Among various serovars, Salmonella enterica serovar Typhimurium is prevalent in multiple countries. This study aims to conduct a systematic review and meta-analysis to evaluate the pattern of antibiotic resistance in S. Typhimurium isolates from diverse sources in Iran.

Methods

We conducted a comprehensive and systematic search for relevant articles until December 2023 in the following databases: PubMed, Scopus, Web of Science, and SID. The collected data were analyzed using Stata software version 17.

Results

Eighteen studies examined the pattern of antibiotic resistance in S. Typhimurium for various antibiotics in Iran. Piperacillin and tetracycline exhibited the highest resistance rates, at 79 and 60% respectively, while cefixime and ceftriaxone had the lowest resistance rates at 0%.

Conclusion

Our findings indicate a high level of antibiotic resistance among the studied antibiotics. This high level of antibiotic resistance raises concerns and underscores the necessity for monitoring the use of antibiotics. Moreover, resistance to these antibiotics was more prevalent in samples isolated from animals compared to other sources. This highlights the importance of animal screening to detect the presence of drug-resistant isolates, with the ultimate goal of reducing antibiotic resistance and preventing the transmission of resistant strains to humans.

Epidemiological, Genetic, and Phenotypic Characteristics of Non-Typhoidal Salmonella in Young Children, as Obtained from a Tertiary Hospital in Guangzhou, China

Gastroenteritis caused by non-typhoidal Salmonella (NTS) is a significant disease in childhood, ranking as the seventh-leading cause of diarrhea mortality in children aged < 5 years. To understand the epidemiological, genetic, and phenotypic characteristics of NTS, 465 anal swabs from children aged < 5 years in a tertiary hospital in Conghua District, Guangzhou, China, were collected from June to October 2021. An average prevalence of 35.27% (164/465) was observed, with whole genome sequencing identifying 11 serotypes, among which Salmonella 1,4,[5],12:i:- was the most prevalent (65.24%, 107/164). Meanwhile, ST34 was found to be the predominant subtype. Children who are breastfed, eat fresh food, and have good hygiene habits show a relatively low prevalence of NTS. Fever is a common symptom that may be caused by NTS infection. Antimicrobial resistance testing revealed that the majority of strains were resistant to tetracycline (83.5%) and ampicillin (82.3%), with multi-drug resistance (MDR) observed in 50.61% (83/164) of all strains tested. The predominant resistance spectrum presents as tetracycline-ampicillin-chloramphenicol-trimethoprim-sulfamethoxazole (30.49%, 50/164). The antimicrobial resistance rates (2.4%, 9.8%, 9.8%, 10.4%, 9.1%, and 3.7%, respectively) of cephalosporins (cefepime, cefuroxime, cefuroxime axetil, ceftriaxone, ceftazidime, and cefoxitin) were low. Therefore, continued surveillance of the prevalence and MDR profiles of NTS, along with the rational use antibiotics, is required. This protocol is significant for preventing further dissemination of NTS and formulating effective prevention and control strategies.

Exposure of Salmonella enterica serovar 1,4,[5],12:i:- to benzalkonium chloride leads to acquired resistance to this disinfectant and antibiotics

AIMS

Disinfectants such as benzalkonium chloride (BC), extensively used in animal farms and food-processing industries, contribute to the development of adaptive and cross-resistance in foodborne pathogens, posing a serious threat to food safety and human health. The purpose of this study is to explore whether continuous exposure of Salmonella enterica serovar 1,4,[5],12:i:- (S. 1,4,[5],12:i:-) to sublethal concentrations of BC could result in acquired resistance to this agent and other environmental stresses (e.g. antibiotics, heat, and acid).

METHODS AND RESULTS

BC tolerance increased in all tested strains after exposure to gradually increasing concentrations of BC, with increases in minimum inhibitory concentrations between two and sixfold. The survival rate of BC-adapted strains was significantly (P < 0.05) higher than that of their wild-type (non-adapted) counterparts in lethal concentrations of BC. In addition, significant reductions (P < 0.05) in zeta potential were observed in BC-adapted strains compared to wild-type ones, indicating that a reduction in cell surface charge was a cause of adaptative resistance. More importantly, two BC-adapted strains exhibited increased antibiotic resistance to levofloxacin, ceftazidime, and tigecycline, while gene mutations (gyrA, parC) and antibiotic efflux-related genes (acrB, mdsA, mdsB) were detected by genomic sequencing analysis. Moreover, the tolerance of BC-adapted strains to heat (50, 55, and 60°C) and acid (pH 2.0, 2.5) was strain-dependent and condition-dependent.

CONCLUSIONS

Repeated exposure to sublethal concentrations of BC could result in the emergence of BC- and antibiotic-resistant S. 1,4,[5],12:i:- strains.

The temporal dynamics of antimicrobial-resistant Salmonella enterica and predominant serovars in China

Salmonella enterica is one of the most common bacterial pathogens in humans and animals. Systematic studies on the trends and geographical distribution of antimicrobial-resistant Salmonella and dominant serovars have been well studied in European and American countries while not in China. Here, taking the One-Health strategy, we used >35 000 Salmonella enterica isolates to explore the temporal and spatial dynamics of dominant serovars in China. We found that Salmonella Typhimurium was the dominant serovar causing human infection in China, which was consistent with Australia but inconsistent with North American and European countries. The proportion of Salmonella serovars Typhimurium, London, Rissen, Corvallis, Meleagridis, Kentucky, and Goldcoast showed an increasing trend during 2006-2019. We randomly selected 1962 isolates for comparative genomics and antimicrobial resistance studies and found that the number of antibiotic resistance genes (ARGs) per isolate increased 1.84 and 2.69 times of human and non-human origins, respectively, spanning 14 years. The proportion of antimicrobial-resistant Salmonella isolates had an increasing trend during 2006-2019, especially beta-lactam, quinolone, tetracycline, and rifampicin resistance. Moreover, we found that higher diversity of sequence types (STs) in S. Typhimurium than in other serovars, ST34 from pig and ST19 from chicken origin, were mainly associated with isolates causing child and adult gastro-infection, respectively. Our results fill in the data gap on the trends of dominant serovars and antimicrobial resistance of Salmonella enterica in China. These data provide useful information for public health decision-makers prioritizing interventions for foodborne diseases and food safety.

Dynamics of Antimicrobial Resistance and Genomic Epidemiology of Multidrug-Resistant Salmonella enterica Serovar Indiana ST17 from 2006 to 2017 in China

The genetic features of foodborne Salmonella have changed in recent years as multidrug-resistant (MDR) strains have become prevalent among various serovars. The recent expansion of MDR Salmonella enterica serovar Indiana sequence type 17 (ST17) poses an increasing threat to global public health, as 24.3% (61/251) of S. Indiana isolates in this study exhibited resistance to three clinically important antimicrobial agents: fluoroquinolones (ciprofloxacin), extended-spectrum β-lactams (cephalosporin), and macrolides (azithromycin). Both the evolutionary histories and antimicrobial resistance (AMR) profiles of this serovar remain to be described. Bioinformatic analysis revealed multiple lineages have coexisted and spread throughout China. Specifically, emergence of a predominant lineage appears to be associated with accumulated various substitutions in the chromosomal quinolone resistance-determining regions (GyrA S83F D87N and ParC T57S S80R) (141 [56.2%]), as well as acquisition of an extended-spectrum β-lactamase (ESBL)-producing IncHI2 plasmid that has subsequently undergone extensive rearrangement and an IncX1 plasmid that contains mph(A), conferring resistance to azithromycin. Several other evolutionary events influencing the trajectory of this drug-resistant serovar were also identified, including sporadic acquisitions of bla_CTX-M-carrying plasmids, along with chromosomal integration of bla_CTX-M within subclusters. Most human isolates reside in clusters containing isolates from animals, mainly from chickens, indicating the close relationship of human isolates with those from food animals. These data demonstrate that MDR S. Indiana ST17 is already widespread and capable of acquiring resistance traits against the clinical important antimicrobial agents, suggesting it should be considered a high-risk global MDR pathogen. The complexity of its evolutionary history has implications for AMR surveillance, epidemiological analysis, and control of emerging clinical lineages.

IMPORTANCE The emergence and worldwide spread of AMR Salmonella constitute great public health concerns. S. enterica serovar Indiana is a typical MDR serovar characterized by sporadic reports. However, comprehensive population genomics studies have not been performed on this serovar. This study provides a detailed and comprehensive insight into the rapid evolution of AMR in this important Salmonella serovar in the past 15 years in eight provinces of China. We documented diverse contributory genetic processes, including stable chromosomal integrations of resistance genes, the persistence and evolution of mobile resistance elements within sublineages, and sporadic acquisition of different resistance determinants that occur at all genetic levels (genes, genetic contexts, plasmids, and host strains). There are different mechanisms of antimicrobial resistance in S. enterica serovar Indiana from those of other serovars. This study sheds light on the formation of MDR S. enterica serovar Indiana with chickens as its potential reservoirs and paves the way to curb its further expansion among food animals.

Molecular Characterization of Quinolone Resistance Determinants in Non-Typhoidal Salmonella Strains Isolated in Tehran, Iran

Background: Quinolone resistant Salmonella serotypes have been reported in recent years and have become increasingly widespread worldwide. Objectives: We evaluated the molecular mechanism of quinolone resistance in non-typhoidal Salmonella strains isolated from clinical samples in Tehran, Iran. Methods: The present study included the Salmonella isolates originated from hospitalized individuals and outpatients in Tehran, Iran. Serotyping of nalidixic acid-resistant Salmonella isolates was done by slide agglutination method. Then, the quinolone resistance-determining region (QRDR) of topoisomerase gene gyrA and the plasmid-mediated quinolone resistance (PMQR) determinants were detected using the polymerase chain reaction (PCR) method. Restriction fragment length polymorphism (RFLP) analysis was also employed to determine the possible mutation in the gyrA gene of those strains. Mutant strains were detected by enzymatic digestion, and their PCR products were sequenced immediately. Results: Amongst 141 isolates, 60% showed nalidixic acid resistance, whereas none of them were ciprofloxacin-resistant. The commonly prevalent serotypes were S. Enteritidis and S. Infantis. Of 85 nalidixic acid-resistant strains, 17 (20%) isolates harbored the qnrS gene. However, PCR analysis of the quinolone-resistant strains did not detect qnrA and qnrB genes. PCR-RFLP and sequencing analysis of the QRDRs of the gyrA gene indicated that 16 (18.8%) isolates had mutant patterns, and the most common point mutation was serine to phenylalanine at position 83. Conclusions: Our results demonstrated that point mutations in gyrA and the existence of plasmid-mediated gene qnrS were important mechanisms of quinolone resistance in non-typhoidal Salmonella strains isolated from human origin. Other alternative mechanisms of resistance, such as alterations in the expression of efflux pumps, should be studied to provide greater insight into the molecular mechanism of quinolone-resistant non-typhoidal Salmonella isolates.

Transcriptomic Responses of Salmonella enterica Serovars Enteritidis in Sodium Hypochlorite

Salmonella enterica serovars Enteritidis (S. Enteritidis) can survive extreme food processing environments including bactericidal sodium hypochlorite (NaClO) treatments generally recognized as safe. In order to reveal the molecular regulatory mechanisms underlying the phenotypes, the overall regulation of genes at the transcription level in S. Enteritidis after NaClO stimulation were investigated by RNA-sequencing. We identified 1399 differentially expressed genes (DEG) of S. Enteritidis strain CVCC 1806 following treatment in liquid culture with 100 mg/L NaClO for 20 min (915 upregulated and 484 downregulated). NaClO stress affects the transcription of genes related to a range of important biomolecular processes such as membrane damage, membrane transport function, energy metabolism, oxidative stress, DNA repair, and other important processes in Salmonella enterica. First, NaClO affects the structural stability of cell membranes, which induces the expression of a range of outer and inner membrane proteins. This may lead to changes in cell membrane permeability, accelerating the frequency of DNA conversion and contributing to the production of drug-resistant bacteria. In addition, the expression of exocytosis pump genes (emrB, yceE, ydhE, and ydhC) was able to expel NaClO from the cell, thereby increasing bacterial tolerance to NaClO. Secondly, downregulation of genes related to the Kdp-ATPase transporter system (kdpABC) and the amino acid transporter system (aroP, brnQ and livF) may to some extent reduce active transport by bacterial cells, thereby reducing their own metabolism and the entry of disinfectants. Downregulation of genes related to the tricarboxylic acid (TCA) cycle may drive bacterial cells into a viable but non-culturable (VBNC) state, resisting NaClO attack by reducing energy metabolism. In addition, significant upregulation of genes related to oxidative stress could mitigate damage caused by disinfectants by eliminating alkyl hydroperoxides, while upregulation of genes related to DNA repair could repair damage to bacterial cells caused by oxidative stress. Therefore, this study indicated that S. Enteritidis has genomic mechanisms to adapt to NaClO stress.

Antibiotic Resistance of Salmonella Typhimurium Monophasic Variant 1,4,[5],12:i:- in China: A Systematic Review and Meta-Analysis

Antibiotic resistance in Salmonella is a global public health problem. Salmonella enterica serovar 1,4,[5],12:i:- (S. 1,4,[5],12:i:-), a monophasic variant of Salmonella Typhmurium, is one of the leading Salmonella serovars in several countries. This study aimed to assess the prevalence of antibiotic resistance to this serovar in China through a systematic review and meta-analysis. Nineteen eligible studies during 2011–2021 were included. A total of 4514 isolates from humans, animals, foods, and the environment were reported, which mainly concerned isolates found in Guangdong, Guangxi, Jiangsu, and Shanghai. A random-effects model was used to estimate the pooled resistance rate of S. 1,4,[5],12:i:-. Rates were found to be very high (values ≥ 75%) for tetracycline, ampicillin, sulfisoxazole, and streptomycin; high (50–75%) for nalidixic acid, amoxicillin–clavulanic acid, and chloramphenicol; and moderate (25–50%) for trimethoprim–sulfamethoxazole, kanamycin, trimethoprim, and gentamicin. The rates of resistance to ciprofloxacin, cefotaxime, ceftriaxone, cefepime, ceftazidime, and colistin were low (values ≤ 25%), but of great concern in terms of their current clinical importance. Furthermore, a high multidrug resistance rate (86%, 95% CI: 78–92%) was present in S. 1,4,[5],12:i:-, with the ASSuT pattern largely dominating. Subgroup analysis results showed that the high heterogeneity of resistance rates was not entirely dependent on isolated sources. Taken together, the severity of antibiotic resistance in S. 1,4,[5],12:i:- urgently requires the rational use of antibiotics in future infection control and antibiotic stewardship programs.

Chlorine Tolerance and Cross-Resistance to Antibiotics in Poultry-Associated Salmonella Isolates in China

Chlorine disinfectants have been widely used in the poultry supply chain but this exposure can also result in the development of bacterial tolerance to chlorine and this is often linked to antibiotic cross-resistance. The objectives of this study were to investigate sodium hypochlorite (NaClO) tolerance of Salmonella isolated from poultry supply chains and evaluate cross-resistance. We collected 172 Salmonella isolates from poultry farms, slaughter houses and retail markets in China during 2019–2020. We found that S. Enteritidis, S. Kentucky, and S. Typhimurium constituted &gt; 80% of our Salmonella isolates. Overall, 68% of Salmonella isolates were resistant to &gt; 3 antibiotics and S. Kentucky displayed a significantly (p &gt; 0.05) higher frequency (93.2%) of multidrug resistance than the other serovars. Tolerance to chlorine at MIC &gt; 256 mg/L was detected in 93.6% of isolates (161/172) and tolerant isolates displayed higher decimal reduction times (D value) and less ultrastructural damage than did the suspectable strains under chlorine stress. Spearman analysis indicated significant positive correlations between chlorine tolerance (evaluated by the OD method) and antibiotic resistance (p &lt; 0.05) to ceftiofur, tetracycline, ciprofloxacin and florfenicol and this was most likely due to efflux pump over-expression. The most frequently detected chlorine resistance gene was qacEΔ1 (83.1%, n = 143) and we found a positive correlation between its presence and MIC levels (r = 0.66, p &lt; 0.0001). Besides, we found weak correlations between chlorine-tolerance and antibiotic resistance genes. Our study indicated that chlorine disinfectants most likely played an important role in the emergence of chlorine tolerance and spread of antibiotic resistance and therefore does not completely control the risk of food-borne disease. The issue of disinfectant resistance should be examined in more detail at the level of the poultry production chain.

Genetic Characterization of Salmonella Infantis with Multiple Drug Resistance Profiles Isolated from a Poultry-Farm in Chile

Salmonella comprises over 2500 serotypes and foodborne contamination associated with this pathogen remains an important health concern worldwide. During the last decade, a shift in serotype prevalence has occurred as traditionally less prevalent serotypes are increasing in frequency of infections, especially those related to poultry meat contamination. S. Infantis is one of the major emerging serotypes, and these strains commonly display antimicrobial resistance and can persist despite cleaning protocols. Thus, this work aimed to isolate S. Infantis strains from a poultry meat farm in Santiago, Chile and to characterize genetic variations present in them. We determined their genomic and phenotypic profiles at different points along the production line. The results indicate that the strains encompass 853 polymorphic sites (core-SNPs) with isolates differing from one another by 0-347 core SNPs, suggesting variation among them; however, we found discrete correlations with the source of the sample in the production line. Furthermore, the pan-genome was composed of 4854 total gene clusters of which 2618 (53.9%) corresponds to the core-genome and only 181 (3.7%) are unique genes (those present in one particular strain). This preliminary analysis will enrich the surveillance of Salmonella, yet further studies are required to assess their evolution and phylogeny.