Clonal Expansion of Biofilm-Forming Salmonella Typhimurium ST34 with Multidrug-Resistance Phenotype in the Southern Coastal Region of China

Clonal spread of blaNDM-1-carrying Salmonella enterica serovar Typhimurium clone ST34 and wide spread of IncHI2/ST3-blaNDM-5 plasmid in China

OBJECTIVES

To characterize blaNDM-carrying Salmonella recovered from a pig slaughterhouse.

METHODS

In this study, 46 environment samples were collected from a slaughterhouse in China, and screened for carbapenem-resistant Enterobacterales. WGS, antimicrobial susceptibility testing and conjugation experiments were carried out to identify the isolates' resistance phenotypes and genetic characteristics. The phylogenetic relatedness of the Salmonella isolates obtained in this study and Salmonella (ST34 and ST29) in GenBank was determined.

RESULTS

Two ST34 Salmonella Typhimurium and one ST29 Salmonella Stanley, recovered from three environmental samples (6.52%), were positive for blaNDM-1 and blaNDM-5, respectively. The two ST34 S. Typhimurium strains exhibited a close relationship (10-36 SNPs) with two human-derived blaNDM-1-bearing isolates from China (Hong Kong and Guangxi Province) and two blaNDM-negative ST34 Salmonella strains from the UK. The blaNDM-1 genes were located on IncHI2/ST3 plasmids. The capture of blaNDM-1 by the IncHI2/ST3 plasmid seems to be due to homologous recombination mediated by circular structures, as the genetic arrangements of the blaNDM-1 gene contain two IS26 elements of the same orientation. The blaNDM-5 gene was also carried by the IncHI2/ST3 plasmid, which shares highly similar structures with other blaNDM-5-bearing IncHI2/ST3 plasmids from other sources (fish, chicken, duck, human).

CONCLUSIONS

This is the first report of a blaNDM-5-carrying IncHI2/ST3 plasmid in Salmonella. The clonal spread of NDM-1-producing ST34 S. Typhimurium across human and animal-associated environments, and the widespread dissemination of epidemic blaNDM-5-carrying IncHI2/ST3 plasmids among Enterobacteriaceae in China indicate the potential of further dissemination of blaNDM among Salmonella, which poses a threat to public health.

High Biofilm-Forming Multidrug-Resistant Salmonella Infantis Strains from the Poultry Production Chain

The ability of Salmonella species to adhere to surfaces and form biofilms, leading to persistent environmental reservoirs, might represent a direct link between environmental contamination and food processing contamination. The purpose of this study was to investigate the biofilm-forming ability of 80 multidrug-resistant (MDR) and extended-spectrum beta-lactamase (ESBL) producing Salmonella enterica serovar Infantis strains isolated from the broiler food chain production through whole genome sequencing (WGS), PCR, and morphotype association assays. Biofilm formation was quantified by testing the strains at two different temperatures, using 96-well polystyrene plates. The rough and dry colony (rdar) morphotype was assessed visually on Congo red agar (CRA) plates. Based on our results, all tested S. Infantis strains produced biofilm at 22 °C with an rdar morphotype, while at 37 °C, all the isolates tested negative, except one positive. Most isolates (58.75%) exhibited strong biofilm production, while 36.25% showed moderate production. Only 5 out of 80 (6.25%) were weak biofilm producers. WGS analysis showed the presence of the fim cluster (fimADF) and the csg cluster (csgBAC and csgDEFG), also described in S. Typhimurium, which are responsible for fimbriae production. PCR demonstrated the presence of csgD, csgB, and fimA in all 80 S. Infantis strains. To our knowledge, this is the first study comparing the effects of two different temperatures on the biofilm formation capacity of ESBL producing S. Infantis from the broiler production chain. This study highlights that the initial biofilm components, such as curli and cellulose, are specifically expressed at lower temperatures. It is important to emphasize that within the broiler farm, the environmental temperature ranges between 18-22 °C, which is the optimum temperature for in vitro biofilm formation by Salmonella spp. This temperature range facilitates the expression of biofilm-associated genes, contributing to the persistence of S. Infantis in the environment. This complicates biosecurity measures and makes disinfection protocols on the farm and in the production chain more difficult, posing serious public health concerns.

Genomic epidemiology of mcr carrying multidrug-resistant ST34 Salmonella enterica serovar Typhimurium in a one health context: The evolution of a global menace

The rapid global dissemination of Salmonella enterica sequence type 34 (ST34) has sparked significant concern due to its resistance to critical antimicrobials and its ability to spread across various sectors. In order to investigate the evolution and transmission dynamics of this epidemic clonal lineage, as well as the horizontal transfer of mcr-carrying plasmids within the One Health framework, we conducted a comprehensive genomic epidemiological study. This study focused on the 11 mcr-carrying S. enterica isolates obtained from clinical settings in China, while also considering 2337 publicly available genomes of mcr-carrying S. enterica collected from 20 countries and diverse sources spanning over a 22-year period. Among the mcr-positive Salmonella isolates, ST34 was found to be the predominant lineage, comprising 30.12 % (704/2337) of the total collection. These isolates were identified as either serovar Typhimurium or its monophasic variant, which were obtained from both clinical and non-clinical sources. Phylogeographic analyses traced the global spread of the mcr-carrying ST34 lineage, which was divided into three distinct clusters, with 83.10 % of them carrying mcr-1 or/and mcr-9 genes. Notably, the mcr-1 positive ST34 isolates were primarily found in China (190/298, 63.76 %), with only four from the United States. Conversely, mcr-9 positive ST34 isolates were predominantly identified in the United States (261/293, 89.08 %), while none were observed in China. The mcr-1 positive ST34 isolates was predicted to have originated from clinical sources in United Kingdom, whereas mcr-9 positive ST34 isolates was likely derived from environmental sources in Germany. The most recent common ancestor for mcr-1 and mcr-9 carrying ST34 S. enterica was estimated to have emerged around 1983 and 1951. These findings provided thorough and intuitive insights into the intercontinental spread of mcr-carrying S. enterica ST34 lineage in a One Health context. Ongoing surveillance is crucial for effectively monitoring the worldwide dissemination of this multidrug-resistant high-risk clone.

Clinical Characteristics, Antimicrobial Resistance, Virulence Genes and Multi-Locus Sequence Typing of Non-Typhoidal Salmonella Serovar Typhimurium and Enteritidis Strains Isolated from Patients in Chiang Mai, Thailand

Non-typhoidal salmonellosis (NTS) caused by ingesting Salmonella enterica contaminated food or drink remains a major bacterial foodborne disease. Clinical outcomes of NTS range from self-limited gastroenteritis to life-threatening invasive NTS (iNTS). In this study, we isolated Salmonella spp. from the stool and blood of patients hospitalized at Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand, between 2016-2021 (a total of 395 cases). Then, serovar Typhimurium and Enteritidis were identified and further characterized by multiplex PCR, and multi-locus sequence typing. Our data show that multidrug resistance (MDR) sequence type 34 (ST34) and ST11 are the predominant sequence types for serovars Typhimurium and Enteritidis, respectively. Most S. Typhimurium ST34 lacks spvB, and most S. Enteritidis ST11 harbor sseI, sodCI, rpoS and spvB genes. NTS can be found in a wide range of ages, and anemia could be a significant factor for S. Typhimurium infection (86.3%). Both S. Typhimurium (6.7%) and S. Enteritidis (25.0%) can cause iNTS in immunocompromised patients. S. Typhimurium conferred MDR phenotype higher than S. Enteritidis with multiple antibiotic resistance indexes of 0.22 and 0.04, respectively. Here, we characterized the important S. Typhimurium, S. Enteritidis, and human clinical factors of NTS within the region.

High Levels of Antibiotic Resistance in MDR-Strong Biofilm-Forming Salmonella Typhimurium ST34 in Southern China

Salmonella enterica subsp. enterica serovar Typhimurium (S. typhimurium) is an important zoonotic pathogen with important public health significance. To understand S. typhimurium's epidemiological characteristics in China, multi-locus sequence typing, biofilm-forming ability, antimicrobial susceptibility testing, and resistant genes of isolates from different regions and sources (human, food) were investigated. Among them, ST34 accounted for 82.4% (243/295), with ST19 ranking second (15.9%; 47/295). ST34 exhibited higher resistance levels than ST19 (p < 0.05). All colistin, carbapenem, and ciprofloxacin-resistant strains were ST34, as were most cephalosporin-resistant strains (88.9%; 32/36). Overall, 91.4% (222/243) ST34 isolates were shown to have multidrug resistance (MDR), while 53.2% (25/47) ST19 isolates were (p < 0.05). Notably, 97.8% (45/46) of the MDR-ACSSuT (resistance to Ampicillin, Chloramphenicol, Streptomycin, Sulfamethoxazole, and Tetracycline) isolates were ST34, among which 69.6% (32/46) of ST34 isolates were of human origin, while 30.4% (14/46) were derived from food (p < 0.05). Moreover, 88.48% (215/243) ST34 showed moderate to strong biofilm-forming ability compared with 10.9% (5/46) ST19 isolates (p < 0.01). This study revealed the emergence of high-level antibiotic resistance S. typhimurium ST34 with strong biofilm-forming ability, posing concerns for public health safety.

BolA affects the biofilm formation ability, outer membrane permeability and virulence, thus is required for the adaptability of Salmonella enterica serotype Typhimurium to the harsh survival environment

Salmonella enterica serotype Typhimurium, an important foodborne pathogen with high adaptability to the host's internal and external survival environment, seriously threatens public health. Therefore, to understand the mechanism underlying the high adaptability, this study investigated the transcription factor BolA by constructing BolA deletion strain 269△BolA, complemented strain 269BolAR and overexpression strain 269BolA+ based on WT269. BolA significantly inhibited motility; at 6 h, the BolA overexpression strain (269BolA+) showed 91.2% and 90.7% lower motility than the wild type (WT269) and BolA deletion strain (269△BolA), respectively, by downregulating motility-related flagellar genes. BolA promoted biofilm formation; 269BolA+ showed 3.6-fold and 5.2-fold higher biofilm formation ability than WT269 and 269ΔBolA, respectively, by upregulation biofilm formation-related genes. BolA overexpression downregulated the outer membrane gene OmpF and upregulated OmpC, thereby regulating cell permeability, and reducing the antibacterial effect of vancomycin, which can destruct the outer membrane. BolA improved adaptability; 269△BolA showed higher susceptibility to eight antibiotics and 2.5- and 4-fold lower acid and oxidative stress tolerance, respectively, than WT269. In Caco-2 and HeLa cells, 269△BolA showed 2.8- and 3-fold lower cell adhesion ability, respectively, and 4- and 2-fold lower cell invasion ability, respectively, than WT269, through downregulation of the virulence genes. Thus, BolA expression promotes biofilm formation and balances the membrane permeability, thereby improving the resistance of the strains, and enhances its host cell invasion ability by upregulating bacterial virulence factors. Results of this study suggest that the BolA gene may serve as a potential target of therapeutic or preventative strategies to control Salmonella Typhimurium infections.

Prevalence of Chromosomally Located blaCTX-M-55 in Salmonella Typhimurium ST34 Isolates Recovered from a Tertiary Hospital in Guangzhou, China

Nontyphoidal Salmonella (NTS) is one of the most prevalent bacterial causes of gastrointestinal infections worldwide. Meanwhile, the detection rate of CTX-M-55 ESBL-positive has increased gradually in China. To identify the molecular epidemiological and genomic characteristics of blaCTX-M-55-carrying nontyphoidal Salmonella (NTS) clinical isolates, a total of 105 NTS isolates were collected from a Chinese tertiary hospital. Antimicrobial susceptibility testing was performed to determine the resistance phenotype. Whole-genome sequencing and bioinformatics analysis were used to determine the antimicrobial resistance genes, serotypes, phylogenetic relationships, and the genetic environment of the blaCTX-M-55 gene. The results showed that among the 22 ceftriaxone resistant isolates, the blaCTX-M-55 was the most common β-Lactamase gene carried by 14 isolates, including serotypes S. Typhimurium (10/14), S. Muenster (2/14), S. Rissen (1/14), and S. Saintpaul (1/14). Phylogenetic analysis shows that 10 blaCTX-M-55-positive S. Typhimurium ST34 isolates were divided into two clusters. The genetic relationship of isolates in each cluster was very close (≤10 cgMLST loci). The blaCTX-M-55 gene was located on the chromosome in 10 isolates, on IncI1 plasmid in three isolates, and IncHI2 plasmid in one isolate. In conclusion, the blaCTX-M-55 gene, mainly located on the chromosome of S. Typhimurium ST34 isolates, was the main driving force associated with the resistance of NTS to cephalosporins. Therefore, close attention to the clonal dissemination of blaCTX-M-55-carrying S. Typhimurium ST34 in clinical settings must be monitored carefully. IMPORTANCE ESCs are the first choice for treating NTS infections. However, ESBLs and AmpC β-lactamases are the most typical cause for ESCs resistance. The CTX-M-55 ESBL-positive rate has gradually increased in the clinic in recent years. At present, the research about blaCTX-M-55-positive Salmonella mainly focuses on the foodborne animals or the environment while less on clinical patients. Thus, this study was carried out for identifying molecular epidemiological and genomic characteristics of blaCTX-M-55-carrying NTS clinical isolates. The results showed that the blaCTX-M-55 gene, mainly located on the chromosome of S. Typhimurium ST34 isolates from Conghua District, was the main driving force associated with the resistance of NTS to cephalosporins. Therefore, our work highlights the importance of monitoring the clonal dissemination of blaCTX-M-55-carrying S. Typhimurium ST34 in clinical settings.

Increased Drug Resistance and Biofilm Formation Ability in ST34-Type Salmonella Typhimurium Exhibiting Multicellular Behavior in China

Salmonella Typhimurium is an important food-borne pathogen. In this paper, multicellular behavior and associated characteristics of S. Typhimurium isolated from human and animal source food were studied. All the S. Typhimurium strains exhibiting multicellular behavior (100%) belonged to the ST34 type. In addition, most of the ST34-type multicellular behavior S. Typhimurium strains had a human origin (69.11%) and 98% of the ST34-type multicellular behavior strains exhibited strong biofilm formation capacity, which was much higher than that of non-multicellular behavior strains (7%, P < 0.01). Antibiotic resistance in ST34-type multicellular behavior strains was significantly higher than in strains with non-multicellular behavior for most conventional drugs (P < 0.05); notably, Polymyxin B (8%) and Imipenem (1%) resistances were also observed in the ST34-type strains. Furthermore, all the ST34-type multicellular behavior strains (100%) exhibited Multiple Drug Resistance (resistance to ≥3antibiotics), which was much higher than that of the non-multicellular behavior strains (P < 0.05). Consistent with the drug-resistant phenotype, the carrying rates of most drug-resistant genes in ST34-type multicellular behavior strains were higher than that those in non-multicellular behavior strains (P < 0.05). Therefore, this study revealed the emergence of a prevalent ST34-type multicellular behavior S. Typhimurium strains with increased biofilm formation ability and drug resistance rate, which poses a threat to public health safety, and highlights the need for comprehensive monitoring of the strains.

Global Spread and Molecular Characterization of CTX-M-Producing Salmonella Typhimurium Isolates

This study aimed to determine the global prevalence and molecular characterization of CTX-M-producing Salmonella Typhimurium isolates. A total of 330 (15.2%, 330/21779) bla_CTX-M-positive S. Typhimurium were obtained from the public databases in July 2021. Thirteen variants were found in the 330 members of the bla_CTX-M group, and bla_CTX-M-9 (26.4%, 88/330) was the most prevalent. The majority of bla_CTX-M-positive S. Typhimurium were obtained from humans (59.7%, 197/330) and animals (31.5%, 104/330). The number of bla_CTX-M-positive S. Typhimurium increased annually (p < 0.0001). These isolates were primarily found from China, the United Kingdom, Australia, the USA, and Germany. In addition, these isolates possessed 14 distinct sequence types (ST), and three predominated: ST34 (42.7%, 141/330), ST19 (37.0%, 122/330), and ST313 (10.3%, 34/330). The majority of ST34 S. Typhimurium isolates were distributed in China and mainly from swine. However, the majority of ST19 were distributed in the United Kingdom and Australia. Analysis of contigs showed that the major type of bla_CTX-M-carrying plasmid was identified as IncI plasmid (52.9%, 27/51) and IncHI2 plasmid (17.6%, 9/51) in 51 bla_CTX-M-positive S. Typhimurium isolates. In addition, WGS analysis further revealed that bla_CTX-M co-existed with nine antibiotic-resistant genes with a detection rate over 50%, conferring resistance to five classes of antimicrobials. The 154 virulence genes were detected among these isolates, of which 107 virulence genes were highly common. This study revealed that China has been severely contaminated by bla_CTX-M-positive S. Typhimurium isolates, these isolates possessed numerous ARGs and virulence genes, and highlighted that continued vigilance for bla_CTX-M-positive S. Typhimurium in animals and humans is urgently needed.

Salmonella Typhimurium ST34 Isolate Was More Resistant than the ST19 Isolate in China, 2007 - 2019

To disclose the antimicrobial susceptibility and wide adaptability of commonly occurring genotypes of Salmonella enterica serovar Typhimurium, the antimicrobial resistance and multilocus sequence typing (MLST) profiles of 196 Salmonella Typhimurium isolates (136 from food-producing animals, 19 from environments, 15 from markets, and 26 from humans) in China between 2007 and 2019 were analyzed. Tests of susceptibility to 19 antimicrobial agents using the broth microdilution method showed that 84.7% of the isolates were resistant to at least one antimicrobial. Antimicrobial susceptibility analysis demonstrated that 66.8% of the isolates were multidrug-resistant (MDR) strains, with resistance to three or more antimicrobials. The highest antidrug resistance was to ampicillin, amoxicillin/clavulanic acid, and tetracycline. Three MLST types were detected, and sequence type (ST) 19 was the most common ST. However, ST34 was associated with a higher MDR rate and more complex MDR patterns, than ST19 and ST99, although the exact mechanism has not been reported. Our study highlights the variation of drug resistance and STs from different sources and the association between STs and drug resistance, providing useful information for epidemiological research and developing a public health strategy.

Heavy Metal Resistance in Salmonella Typhimurium and Its Association With Disinfectant and Antibiotic Resistance

Metals are widely used in animal feed for their growth-stimulating and antimicrobial effects, yet their use may potentially promote the proliferation of antibiotic resistance through co-selection. We studied the prevalence and associations of metal, antibiotic, and disinfectant resistances of 300 Salmonella Typhimurium isolates from pig meat, pig manure, chicken meat, poultry manure, and human stool from Sichuan, China. Seventy four percent of the 300 Salmonella Typhimurium isolates were considered resistant to Cu, almost 50% to Zn and Cr, over 25% to Mn and Cd, and almost 10% to Co. Most of the isolates carried at least one heavy metal resistance gene (HMRG). The Cr-Zn-Cd-resistance gene czcD was carried by 254 isolates and the Cu-resistance genes pcoR and pcoC by 196 and 179 isolates, respectively. Most of the isolates were resistant to at least one antibiotic and almost 80% were multidrug-resistant. The prevalence of resistance to six antibiotics was higher among the pig meat and manure isolates than among other isolates, and that of streptomycin and ampicillin were highest among the pig meat isolates and that of ciprofloxacin and ofloxacin among the pig manure isolates. From 55 to 79% of the isolates were considered resistant to disinfectants triclosan, trichloroisocyanuric acid, or benzalkonium chloride. The metal resistances and HMRGs were associated with resistance to antibiotics and disinfectants. Especially, Cu-resistance genes were associated with resistance to several antibiotics and disinfectants. The transfer of the Cr-Zn-Cd-resistance gene czcD, Cu-resistance gene pcoC, and Co-Ni-resistance gene cnrA into Escherichia coli and the increased Cu-resistance of the transconjugants implied that the resistance genes were located on conjugative plasmids. Thus, the excessive use of metals and disinfectants as feed additives and in animal care may have the potential to promote antibiotic resistance through co-selection and maintain and promote antibiotic resistance even in the absence of antibiotics.

Characterization of Human Origin Salmonella Serovar 1,4,[5],12:i:- in Eastern China, 2014 to 2018

The prevalence of Salmonella serovar 1,4,[5],12:i:- among diarrhea patients has increased considerably in many countries around the world, including China. However, the characterization of this serovar of human origin has been less reported from China. We characterized 76 isolates of Salmonella 1,4,[5],12:i:- gained from diarrhea patients from 2014 to 2018 in the Jiangsu Province of eastern China. These isolates fell into a single-sequence type (ST34) determined by multilocus sequence typing (MLST), and into 44 pulsed-field gel electrophoresis band patterns, with 1 pattern (JSSMM015) comprising 12 isolates (15.9%). By means of PCR-based assays, the seven prophage located virulence genes were detected in our Salmonella 1,4,[5],12:i:- isolates with a high rate of gipA, gtgB, sspH1, sspH2, sodC1, and gtgE (93.4-97.4%), and with a moderate rate of sopE (42.1%). In contrast, none of the five plasmid-borne virulence genes (spvC, pefA, mig5, rck, and srgA) was identified. We tested the isolates' susceptibility to 18 antibiotics of 9 categories using the VITEK 2 system. A high proportion (89.5%) of the isolates were multidrug resistant (MDR) strains with full resistance to cefazolin, cefotetan, amikacin, gentamycin, and tobramycin, followed by resistance to ampicillin (88.2%) and ampicillin/sulbactam (80.3%). The resistance to piperacillin/tazobactam, ceftazidime, cefepime, and levofloxacin was scarce (2.6-9.2%). Notably, an isolate from 2018 was resistant to carbapenems. blaTEM-1B and aac(6')-Ib-cr were the most common drug resistance genes presented in cephalosporin- and fluoroquinolone-resistant strains. All Salmonella 1,4,[5],12:i:- isolates were capable of forming biofilm, with 13.2% of them having strong ability. However, no association was indicated between the scale of biofilm formation ability and MDR. Our results indicate that the combination of these characteristics may together provide a selective and competitive advantage to those Salmonella 1,4,[5],12:i:- isolates, contributing to their increasing prevalence observed worldwide.

Characterization of a novel class 1 integron InSW39 and a novel transposon Tn5393k identified in an imipenem-nonsusceptible Salmonella Typhimurium strain in Sichuan, China

This study aimed to characterize molecular mechanism of 3 Salmonella enterica strains and novel mobile genetic elements identified in them. The strains, designated SW1, SW39, and SW109084, were obtained from diarrhea patients. The results of susceptibility testing showed SW39 was nonsusceptible to imipenem and cefotaxime. Whole genome sequencing was performed on Illumina HiSeq platform. Multilocus-sequence typing revealed SW1 belonged to ST2529 which was first confirmed in S. enterica, SW109084 was ST34 which was first reported in Enteritidis and SW39 was ST19. Resistome analysis showed SW1, SW109084, and SW39 carried 14, 19, and 17 antibiotic resistance genes. Seven transposons and 4 integrons were confirmed in these strains. Notably, a novel In6- and In7-like class 1 integron designated InSW39 and a novel transposon Tn5393k were identified in plasmid pSW39. The study of genomics and resistance in S. enterica plays a significant role in prevention and treatment of Salmonella infections.

Pathogenicity of clinical Salmonella enterica serovar Typhimurium isolates from Thailand in a mouse colitis model

Salmonella enterica serovar Typhimurium (S. Typhimurium [STM]) is a leading cause of nontyphoidal salmonellosis (NTS) worldwide. The pathogenesis of NTS has been studied extensively using a streptomycin-pretreated mouse colitis model with the limited numbers of laboratory STM strains. However, the pathogenicity of the clinically isolated STM (STMC) strains endemic in Thailand in mice has not been explored. The aim of this study was to compare the pathogenicity of STMC strains collected from Northern Thailand with the laboratory STM (IR715) in mice. Five STMC isolates were obtained from the stool cultures of patients with acute NTS admitted to Maharaj Nakorn Chiang Mai Hospital in 2016 and 2017. Detection of virulence genes and sequence type (ST) of the strains was performed. Female C57BL/6 mice were pretreated with streptomycin sulfate 1 day prior to oral infection with STM. On Day 4 postinfection, mice were euthanized, and tissues were collected to analyze the bacterial numbers, tissue inflammation, and cecal histopathological score. We found that all five STMC strains are ST34 and conferred the same or reduced pathogenicity compared with that of IR715 in mice. A strain-specific effect of ST34 on mouse gut colonization was also observed. Thailand STM ST34 exhibited a significant attenuated systemic infection in mice possibly due to the lack of spvABC-containing virulence plasmid.

Molecular Relatedness of Salmonella enterica Typhimurium Isolates from Feces and an Infected Surgical Wound

Purpose

Salmonella enterica serovar Typhimurium infection is common in foodborne diseases, but its isolation from surgical incisions is rare. Our aim in this study was to trace the transmission source of a surgical incision infected with S. Typhimurium in a Yunnan Province hospital patient and elucidate the underlying molecular mechanisms of antibiotic resistance.

Methods

Primers were designed to amplify the drug-resistance genes using polymerase chain reaction (PCR). Susceptibility to antibiotics was determined using Etest strips. Macrorestriction profiles were analyzed using pulsed-field gel electrophoresis (PFGE) and XbaI. The two isolates were characterized using agglutination tests and multilocus sequence typing (MLST).

Results

MLST analysis revealed that S. Typhimurium isolates SM043 and SM080 belonged to the same genotype, ST34, and PFGE revealed that SM043 and SM080 had high similarity. The isolates were both resistant to third-generation cephalosporins. SM043 harbored the antibiotic resistance genes blaCTX-M-15, blaTEM-1, qnrS-1, qnrB, and acc-3, whereas blaCTX-M-15, blaTEM-1, blaCMY-2, qnrS-1, and acc-3 were detected in SM080.

Conclusion

The surgical incision infection by S. Typhimurium may have been hospital-acquired. Thus, it is critical to strengthen hospital sanitation by addressing hand hygiene and sterilization of the operational environment to avoid outbreaks of nosocomial Salmonella infections.

Biofilm Eradication by Symmetrical Selenoesters for Food-Borne Pathogens

Infections caused by Salmonella species and Staphylococcus aureus represent major health and food industry problems. Bacteria have developed many strategies to resist the antibacterial activity of antibiotics, leading to multidrug resistance (MDR). The over-expression of drug efflux pumps and the formation of biofilms based on quorum sensing (QS) can contribute the emergence of MDR. For this reason, the development of novel effective compounds to overcome resistance is urgently needed. This study focused on the antibacterial activity of nine symmetrical selenoesters (Se-esters) containing additional functional groups including oxygen esters, ketones, and nitriles against Gram-positive and Gram-negative bacteria. Firstly, the minimum inhibitory concentrations of the compounds were determined. Secondly, the interaction of compounds with reference antibiotics was examined. The efflux pump (EP) inhibitory properties of the compounds were assessed using real-time fluorimetry. Finally, the anti-biofilm and quorum sensing inhibiting effects of selenocompounds were determined. The methylketone and methyloxycarbonyl selenoesters were the more effective antibacterials compared to cyano selenoesters. The methyloxycarbonyl selenoesters (Se-E2 and Se-E3) showed significant biofilm and efflux pump inhibition, and a methyloxycarbonyl selenoester (Se-E1) exerted strong QS inhibiting effect. Based on results selenoesters could be promising compounds to overcome bacterial MDR.

Salmonella enterica mcr-1 Positive from Food in Brazil: Detection and Characterization

The mcr-1 gene has been identified in bacterial isolates obtained from humans, animals, environment, and food, including Salmonella spp., which is one of the major foodborne pathogens worldwide. The aim of this study was to evaluate the presence of mcr-1 gene in Salmonella spp. from food produced in Brazil and to characterize the isolates harboring this gene. A total of 490 Salmonella spp. isolates from the Brazilian National Program for the Control of Foodborne Pathogens were screened for the presence of mcr-1 gene by polymerase chain reaction (PCR). Whole genome sequencing (WGS) was performed in positive isolates to characterize the sequence type (ST), plasmid families and resistance genes. Antimicrobial susceptibility tests were performed by broth microdilution. Selected isolates were submitted to conjugation experiments using the Escherichia coli J53 as a receptor. We detected eight isolates harboring the mcr-1 gene; seven belonged to Salmonella enterica serovar Typhimurium and its monophasic variant 4,[5],12:i:-, and one belonged to serovar Saintpaul. Seven of the mcr-1 positive isolates displayed a high rate of resistance to other antibiotics in addition to colistin. Analysis of the WGS indicated that the ST 19 was the most common ST among the mcr-1 positive isolates. The mcr-1 gene was located in an IncX4 plasmid of ∼33 kb, with no additional resistance genes and with high identity with a plasmid obtained from a clinical isolate of E. coli mcr-1 positive in Brazil. All plasmids harboring the mcr-1 gene were able to conjugate. Our results suggest the spread of a single plasmid type in Brazil harboring the mcr-1 among Salmonella spp. The horizontal transfer of this mobile element has been contributing to the spread of the colistin resistance in the country.

Emergence and Dissemination of mcr-Carrying Clinically Relevant Salmonella Typhimurium Monophasic Clone ST34

Antibiotic resistance in bacteria is one of the urgent threats to both public and global health. The Salmonella Typhimurium monophasic sequence type 34 (ST34) clone, with its rapid dissemination and resistance to numerous critical antimicrobials, has raised global concerns. Here, we present an updated overview on the emerging infections caused by mobile colistin resistance (mcr)-carrying colistin-resistant ST34 isolates, covering their global dissemination and virulence-associated efficacy. The higher rates of mcr-1-positive ST34 in children in China highlights the increasing threat caused by this pathogen. Most of the ST34 isolates carrying the mcr-1 gene were isolated from animals and food products, indicating the role of foodborne transmission of mcr-1. The emergence of multidrug resistance genes along with various virulence factors and many heavy metal resistance genes on the chromosome and plasmid from ST34 isolates will challenge available therapeutic options. The presence of the colistin resistance gene (mcr-1, mcr-3, and mcr-5) with the multidrug-resistant phenotype in ST34 has spread across different countries, and most of the mcr-1 genes in ST34 isolates were detected in plasmid type IncHI2 followed by IncI2, and IncX4. Together, mcr-carrying S. Typhimurium ST34 may become a new pandemic clone. The fast detection and active surveillance in community, hospital, animal herds, food products and environment are urgently warranted.