Phentotypic, gentotypic antimicrobial resistance and pathogenicity of Salmonella enterica serovars Typimurium and Enteriditis in poultry and poultry products

Genomics Revealed Novel Chromosomal Integration of Antimicrobial Resistance Cluster tet(B), sul2, blaTEM-1B, aph(3″)-Ib, and aph(6)-Id in Salmonella Typhimurium

Antimicrobial-resistant Salmonella has posed a huge threat to food safety and public health, and tetracycline is the commonly used antibiotic for treating salmonellosis. In this study, eight Salmonella Typhimurium isolates from diarrhea patients (n = 7) and clam (n = 1) exhibited high-level tetracycline resistance (minimum inhibitory concentration = 128 μg/mL), and these isolates were further resistant to ampicillin and sulfonamides, formatting the R-type ASuT (ampicillin, sulfonamides, and tetracycline). Then, these eight isolates were sequenced using PacBio platform, revealing the presence of tetracycline resistance gene tet(B), along with sulfonamide-resistance gene sul2, extended-spectrum-β-lactamase gene blaTEM-1B, and aminoglycoside resistance genes aph(3″)-Ib and aph(6)-Id on the chromosome, which was associated with R-type ASuT. Four types (A, B1, B2, and C) of genetic arrangement for chromosomally encoding tet(B) were found, inserted into fljBA operon. Type C (fljBA operon-tet(B)-sul2-blaTEM-1B-aph(3″)-Ib-aph(6)-Id-merACDEPTR) was the most common type and was accompanied by various insertion sequences (ISs) (IS26, IS1, and ISVsa5) and recombinases. Pairwise sequence alignment showed that type C arrangement likely resulted from stepwise acquisitions and rearrangements facilitated by the actions of ISs, followed by integration into the chromosome by prophages. Phylogenomic analysis showed that all eight Salmonella Typhimurium isolates from China in this study, along with a human-borne Salmonella Typhimurium isolate (DA34821) from Germany and a foodborne Salmonella Typhimurium isolate (CFSA629) from China, clustered into a single clade, sharing ≤67 SNPs, which suggested that clone spread occurred. These findings underline the emergence of R-type ASuT in Salmonella Typhimurium, which is attributed to the presence of an antimicrobial resistance gene cluster (tet(B), sul2, blaTEM-1B, aph(3″)-Ib, and aph(6)-Id) encoded on the chromosome.

Ecological prevalence and genomic characterization of Salmonella isolated from selected poultry farms in Jiangxi province, China

Non-typhoidal Salmonella (NTS), particularly antimicrobial-resistant serovars, remains the major source of foodborne bacterial illnesses. Raw chicken is the leading cause of human salmonellosis. In this study, we evaluated the prevalence, antimicrobial resistance profiles, and genomic features of 143/1,800 (7.94%) Salmonella strains isolated from poultry farms in five major regions of Jiangxi province, China, between 2022 and 2023 using Whole genome sequencing (WGS). Among Salmonella isolates, the most common serovars were Infantis (ST32) and Enteritidis (ST11). Resistance to amoxicillin and tetracycline was the most prevalent, with 60.84% of Salmonella isolates exhibiting a multi-drug resistance (MDR) pattern. The detection of antimicrobial-resistant genes (ARGs) examined was aligned with the resistant phenotypes found. A total of 61 ARGs were identified, with aph(3')-Ia, qnrS1, aph(3'')-Ib, and tetA being the prominent ARGs. Furthermore, 24 beta-lactam genes were also identified, including blaTEM, blaSHV, and blaCTX-M. The number of ARGs and the distribution of serovars varied according to the year, farms, and cities. Salmonella isolates carried 13 heavy metal resistance genes (HMRGs) and two biocide resistance genes, with pcoS being the most prevalent. A total of 145 virulence genes and 19 plasmids were found, with serovars Infantis and Enteritidis having the most virulence genes. The high occurrence of MDR Salmonella in this study, particularly carrying numerous mobile genetic elements (MGEs), posed a serious threat to food safety and public health, emphasizing the need to improve poultry farm hygiene to decrease contamination and transmission.

Colistin-, cefepime-, and levofloxacin-resistant Salmonella enterica serovars isolated from Egyptian chicken carcasses

OBJECTIVES

The emergence of multidrug-resistant (MDR) Salmonella strains, especially resistant ones toward critically important antimicrobial classes such as fluoroquinolones and third- and fourth-generation cephalosporins, is a growing public health concern. The current study, therefore, aimed to determine the prevalence, and existence of virulence genes (invA, stn, and spvC genes), antimicrobial resistance profiles, and the presence of β-lactamase resistance genes (blaOXA, blaCTX-M1, blaSHV, and blaTEM) in Salmonella strains isolated from native chicken carcasses in Egypt marketed in Mansoura, Egypt, as well as spotlight the risk of isolated MDR, colistin-, cefepime-, and levofloxacin-resistant Salmonella enterica serovars to public health.

METHODS

One hundred fifty freshly dressed native chicken carcasses were collected from different poultry shops in Mansoura City, Egypt between July 2022 and November 2022. Salmonella isolation was performed using standard bacteriological techniques, including pre-enrichment in buffered peptone water (BPW), selective enrichment in Rappaport Vassiliadis broth (RVS), and cultivating on the surface of xylose-lysine-desoxycholate (XLD) agar. All suspected Salmonella colonies were subjected to biochemical tests, serological identification using slide agglutination test, and Polymerase Chain Reaction (PCR) targeting the invasion A gene (invA; Salmonella marker gene). Afterward, all molecularly verified isolates were screened for the presence of virulence genes (stn and spvC). The antimicrobial susceptibility testing for isolated Salmonella strains towards the 16 antimicrobial agents tested was analyzed by Kirby-Bauer disc diffusion method, except for colistin, in which the minimum inhibition concentration (MIC) was determined by broth microdilution technique. Furthermore, 82 cefotaxime-resistant Salmonella isolates were tested using multiplex PCR targeting the β-lactamase resistance genes, including blaOXA, blaCTX-M1, blaSHV, and blaTEM genes.

RESULTS

Salmonella enterica species were molecularly confirmed via the invA Salmonella marker gene in 18% (27/150) of the freshly dressed native chicken carcasses. Twelve Salmonella serotypes were identified among 129 confirmed Salmonella isolates with the most predominant serotypes were S. Kentucky, S. Enteritidis, S. Typhimurium, and S. Molade with an incidence of 19.4% (25/129), 17.1% (22/129), 17.1% (22/129), and 10.9% (14/129), respectively. All the identified Salmonella isolates (n = 129) were positive for both invA and stn genes, while only 31.8% (41/129) of isolates were positive for the spvC gene. One hundred twenty-one (93.8%) of the 129 Salmonella-verified isolates were resistant to at least three antibiotics. Interestingly, 3.9%, 14.7%, and 75.2% of isolates were categorized into pan-drug-resistant, extensively drug-resistant, and multidrug-resistant, respectively. The average MAR index for the 129 isolates tested was 0.505. Exactly, 82.2%, 82.2%, 63.6%, 51.9%, 50.4%, 48.8%, 11.6%, and 10.1% of isolated Salmonella strains were resistant to cefepime, colistin, cefotaxime, ceftazidime/clavulanic acid, levofloxacin, ciprofloxacin, azithromycin, and meropenem, respectively. Thirty-one out (37.8%) of the 82 cefotaxime-resistant Salmonella isolates were β-lactamase producers with the blaTEM as the most predominant β-lactamase resistance gene, followed by blaCTX-M1 and blaOXA genes, which were detected in 21, 16, and 14 isolates respectively).

CONCLUSION

The high prevalence of MDR-, colistin-, cefepime-, and levofloxacin-resistant Salmonella serovars among Salmonella isolates from native chicken is alarming as these antimicrobials are critically important in treating severe salmonellosis cases and boost the urgent need for controlling antibiotic usage in veterinary and human medicine to protect public health.

Distribution of bacteria and antimicrobial resistance in retail Nile tilapia (Oreochromis spp.) as potential sources of foodborne illness

This study aimed to investigate AMR profiles of Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae isolated from Nile tilapia (Oreochromis spp.) (n = 276) purchased from fresh markets and supermarkets in Bangkok, Thailand. A sample of tilapia was divided into three parts: fish intestine (n = 276), fish meat (n = 276), and liver and kidney (n = 276). The occurrence of A. hydrophila, Salmonella, and V. cholerae was 3.1%, 7.4%, and 8.5%, respectively. A high prevalence of these pathogenic bacteria was observed in fresh market tilapia compared to those from supermarkets (p < 0.05). The predominant Salmonella serovars were Paratyphi B (6.4%), followed by Escanaba (5.7%), and Saintpaul (5.7%). All isolates tested positive for the virulence genes of A. hydrophila (aero and hly), Salmonella (invA), and V. cholerae (hlyA). A. hydrophila (65.4%), Salmonella (31.2%), and V. cholerae (2.9%) showed multidrug resistant isolates. All A. hydrophila isolates (n = 26) exhibited resistant to ampicillin (100.0%) and florfenicol (100.0%), and often carried sul1 (53.8%) and tetA (50.0%). Salmonella isolates were primarily resistant to ampicillin (36.9%), with a high incidence of blaTEM (26.2%) and qnrS (25.5%). For V. cholerae isolates, resistance was observed against ampicillin (48.6%), and they commonly carried qnrS (24.3%) and tetA (22.9%). To identify mutations in the quinolone resistance determining regions (QRDRs), a single C248A point mutation of C248A (Ser-83-Tyr) in the gyrA region was identified in six out of seven isolates of Salmonella isolates. This study highlighted the presence of antimicrobial-resistant pathogenic bacteria in Nile tilapia at a selling point. It is important to rigorously implement strategies for AMR control and prevention.

Occurrence and molecular characteristics of antimicrobial resistance, virulence factors, and extended-spectrum β-lactamase (ESBL) producing Salmonella enterica and Escherichia coli isolated from the retail produce commodities in Bangkok, Thailand

The incidence of antimicrobial resistance (AMR) in the environment is often overlooked and leads to serious health threats under the One Health paradigm. Infection with extended-spectrum β-lactamase (ESBL) producing bacteria in humans and animals has been widely examined, with the mode of transmission routes such as food, water, and contact with a contaminated environment. The purpose of this study was to determine the occurrence and molecular characteristics of resistant Salmonella enterica (S. enterica) (n = 59) and Escherichia coli (E. coli) (n = 392) isolated from produce commodities collected from fresh markets and supermarkets in Bangkok, Thailand. In this study, the S. enterica isolates exhibited the highest prevalence of resistance to tetracycline (11.9%) and streptomycin (8.5%), while the E. coli isolates were predominantly resistant to tetracycline (22.5%), ampicillin (21.4%), and sulfamethoxazole (11.5%). Among isolates of S. enterica (6.8%) and E. coli (15.3%) were determined as multidrug resistant (MDR). The prevalence of ESBL-producing isolates was 5.1% and 1.0% in S. enterica and E. coli, respectively. A minority of S. enterica isolates, where a single isolate exclusively carried blaCTX-M-55 (n = 1), and another isolate harbored both blaCTX-M-55 and blaTEM-1 (n = 1); similarly, a minority of E. coli isolates contained blaCTX-M-55 (n = 2) and blaCTX-M-15 (n = 1). QnrS (11.9%) and blaTEM (20.2%) were the most common resistant genes found in S. enterica and E. coli, respectively. Nine isolates resistant to ciprofloxacin contained point mutations in gyrA and parC. In addition, the odds of resistance to tetracycline among isolates of S. enterica were positively associated with the co-occurrence of ampicillin resistance and the presence of tetB (P = 0.001), while the E. coli isolates were positively associated with ampicillin resistance, streptomycin resistance, and the presence of tetA (P < 0.0001) in this study. In summary, these findings demonstrate that fresh vegetables and fruits, such as cucumbers and tomatoes, can serve as an important source of foodborne AMR S. enterica and E. coli in the greater Bangkok area, especially given the popularity of these fresh commodities in Thai cuisine.

Prevalence and antibiotics resistance status of Salmonella in raw meat consumed in various areas of Lahore, Pakistan

This study reports the prevalence and antibiotics resistance status of Salmonella detected in raw meat from Lahore, Pakistan. Overall, N = 111 meat samples, were collected from local markets. Salmonella was recovered from 57 (51.35%) samples, including 45.83% of poultry, 60% of buffalo, 64.28% of cow, and 60% of goat meat samples. The predominant Salmonella strains were Salmonella enterica serovars; Typhimurium (45.4%), Typhi (27.2%), and Enteritidis (18.1%), identified by VITEK system and 16S rRNA gene sequencing. The isolates exhibited high resistance to Erythromycin (100%), Cefepime (98.24%), Colistin (94.73%), Azithromycin (92.98%), Tetracycline (87.71%), Polymyxin B (84.21%), Ciprofloxacin (84.21%), Trimethoprim-Sulfamethoxazole (80.70%), Nalidixic Acid (80.70%), Kanamycin (78.94%), Chloramphenicol (77.19%), Streptomycin (71.92%) and Ampicillin (64.91%). While the isolates exhibited more susceptibility to Meropenem (75.43%) and Amikacin (73.68%). N = 8 strains were designated as Multidrug Resistant (MDR) and N = 3 as Extensively Drug-Resistant (XDR) Salmonella. The PCR-based detection of resistance genes revealed the presence of blaTEM-1 gene (100%), catA1 gene (64%), and gyrA gene (18%). The whole genome sequencing (WGS) of two selected strains and subsequent downstream analysis confirmed the strains as MDR and XDR Salmonella enterica serovar Typhi. The study showed that raw meat consumed in Lahore carries a significantly high number of drug-resistant Salmonella.

Bioprotective potential of lactic acid bacteria for Salmonella biocontrol in vitro

Lactic acid bacteria (LAB) are an important option for Salmonella control in animal production, resulting in lower antibiotic use. The objective of this research was to isolate LAB from meat products and from commercial probiotics sold as nutritional supplements for in vitro verification of their bioprotective potential. Eleven bacteria were identified as Pediococcus acidilactici, two as Lacticaseibacillus rhamnosus, one as Lacticaseibacillus paracasei paracasei, one as Limosilactobacillus fermentum, and one as a consortium of Lactobacillus delbrueckii bulgaricus and L. fermentum. All bacteria showed inhibitory activity against Salmonella, with emphasis on the inhibition of P. acidilactici PUCPR 011 against Salmonella Enteritidis 33SUSUP, S. Enteritidis 9SUSP, S. Enteritidis 56301, S. Enteritidis CRIFS 1016, Salmonella Typhimurium ATCC™ 14,028®, and Salmonella Gallinarum AL 1138, with inhibition halos of 7.3 ± 0.5 mm, 7.7 ± 1.0 mm, 9.0 ± 1.8 mm, 7.3 ± 0.5 mm, 7.7 ± 1.0 mm, and 7.3 ± 0.5, respectively. The isolates P. acidilactici PUCPR 011, P. acidilactici PUCPR 012, P. acidilactici PUCPR 014, L. fermentum PUCPR 005, L. paracasei paracasei PUCPR 013, and L. rhamnosus PUCPR 010 showed inhibition greater than 2 mm against at least 3 Salmonella and were used for encapsulation and in vitro digestion. The encapsulation efficiency ranged from 76.89 ± 1.54 to 116.48 ± 2.23%, and the population after 12 months of storage was from 5.31 ± 0.17 to 9.46 ± 0.09 log CFU/g. When simulating swine and chicken digestion, there was a large reduction in bacterial viability, stabilizing at concentrations close to 2.5 log CFU/mL after the analyses. The analyzed bacteria showed strong in vitro bioprotective potential; further analyses are required to determine in vivo effectiveness.

Emergence of colistin resistance and characterization of antimicrobial resistance and virulence factors of Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae isolated from hybrid red tilapia cage culture

Background

Tilapia is a primary aquaculture fish in Thailand, but little is known about the occurrence of antimicrobial resistance (AMR) in Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae colonizing healthy tilapia intended for human consumption and the co-occurrence of these AMR bacteria in the cultivation water.

Methods

This study determined the phenotype and genotype of AMR, extended-spectrum β-lactamase (ESBL) production, and virulence factors of A. hydrophila, Salmonella spp., and V. cholerae isolated from hybrid red tilapia and cultivation water in Thailand. Standard culture methods such as USFDA's BAM or ISO procedures were used for the original isolation, with all isolates confirmed by biochemical tests, serotyping, and species-specific gene detection based on PCR.

Results

A total of 278 isolates consisting of 15 A. hydrophila, 188 Salmonella spp., and 75 V. cholerae isolates were retrieved from a previous study. All isolates of A. hydrophila and Salmonella isolates were resistance to at least one antimicrobial, with 26.7% and 72.3% of the isolates being multidrug resistant (MDR), respectively. All A. hydrophila isolates were resistant to ampicillin (100%), followed by oxytetracycline (26.7%), tetracycline (26.7%), trimethoprim (26.7%), and oxolinic acid (20.0%). The predominant resistance genes in A. hydrophila were mcr-3 (20.0%), followed by 13.3% of isolates having floR, qnrS, sul1, sul2, and dfrA1. Salmonella isolates also exhibited a high prevalence of resistance to ampicillin (79.3%), oxolinic acid (75.5%), oxytetracycline (71.8%), chloramphenicol (62.8%), and florfenicol (55.3%). The most common resistance genes in these Salmonella isolates were qnrS (65.4%), tetA (64.9%), bla _TEM (63.8%), and floR (55.9%). All V. cholerae isolates were susceptible to all antimicrobials tested, while the most common resistance gene was sul1 (12.0%). One isolate of A. hydrophila was positive for int1, while all isolates of Salmonella and V. cholerae isolates were negative for integrons and int _SXT. None of the bacterial isolates in this study were producing ESBL. The occurrence of mcr-3 (20.0%) in these isolates from tilapia aquaculture may signify a serious occupational and consumer health risk given that colistin is a last resort antimicrobial for treatment of Gram-negative bacteria infections.

Conclusions

Findings from this study on AMR bacteria in hybrid red tilapia suggest that aquaculture as practiced in Thailand can select for ubiquitous AMR pathogens, mobile genetic elements, and an emerging reservoir of mcr and colistin-resistant bacteria. Resistant and pathogenic bacteria, such as resistance to ampicillin and tetracycline, or MDR Salmonella circulating in aquaculture, together highlight the public health concerns and foodborne risks of zoonotic pathogens in humans from cultured freshwater fish.

Antimicrobial resistance, Extended-Spectrum β-Lactamase production and virulence genes in Salmonella enterica and Escherichia coli isolates from estuarine environment

The impact of antimicrobial resistance (AMR) on global public health has been widely documented. AMR in the environment poses a serious threat to both human and animal health but is frequently overlooked. This study aimed to characterize the association between phenotype and genotype of AMR, virulence genes and Extended-Spectrum β-Lactamase (ESBL) production from estuarine environment. The Salmonella (n = 126) and E. coli (n = 409) were isolated from oysters and estuarine water in Thailand. The isolates of Salmonella (96.9%) and E. coli (91.4%) showed resistance to at least one antimicrobial agent. Multidrug resistance (MDR) was 40.1% of Salmonella and 23.0% of E. coli. Resistance to sulfamethoxazole was most common in Salmonella (95.2%) and E. coli (77.8%). The common resistance genes found in Salmonella were sul3 (14.3%), followed by blaTEM (11.9%), and cmlA (11.9%), while most E. coli were blaTEM (31.5%) and tetA (25.4%). The ESBL production was detected in Salmonella (1.6%, n = 2) of which one isolate was positive to blaTEM-1. Eight E. coli isolates (2.0%) were ESBL producers, of which three isolates carried blaCTX-M-55 and one isolate was blaTEM-1. Predominant virulence genes identified in Salmonella were invA (77.0%), stn (77.0%), and fimA (69.0%), while those in E. coli isolates were stx1 (17.8%), lt (11.7%), and stx2 (1.2%). Logistic regression models showed the statistical association between resistance phenotype, virulence genes and ESBL production (p < 0.05). The findings highlighted that estuarine environment were potential hotspots of resistance. One Health should be implemented to prevent AMR bacteria spreading.

Molecular Epidemiology of Antimicrobial Resistance and Virulence Profiles of Escherichia coli, Salmonella spp., and Vibrio spp. Isolated from Coastal Seawater for Aquaculture

The occurrence of waterborne antimicrobial-resistant (AMR) bacteria in areas of high-density oyster cultivation is an ongoing environmental and public health threat given the popularity of shellfish consumption, water-related human recreation throughout coastal Thailand, and the geographical expansion of Thailand's shellfish industry. This study characterized the association of phenotypic and genotypic AMR, including extended-spectrum β-lactamase (ESBL) production, and virulence genes isolated from waterborne Escherichia coli (E. coli) (n = 84), Salmonella enterica (S. enterica) subsp. enterica (n = 12), Vibrio parahaemolyticus (V. parahaemolyticus) (n = 249), and Vibrio cholerae (V. cholerae) (n = 39) from Thailand's coastal aquaculture regions. All Salmonella (100.0%) and half of V. cholerae (51.3%) isolates harbored their unique virulence gene, invA and ompW, respectively. The majority of isolates of V. parahaemolyticus and E. coli, ~25% of S. enterica subsp. enterica, and ~12% of V. cholerae, exhibited phenotypic AMR to multiple antimicrobials, with 8.9% of all coastal water isolates exhibiting multidrug resistance (MDR). Taken together, we recommend that coastal water quality surveillance programs include monitoring for bacterial AMR for food safety and recreational water exposure to water for Thailand's coastal water resources.

Bacterial Pathogens in the Food Industry: Antibiotic Resistance and Virulence Factors of Salmonella enterica Strains Isolated from Food Chain Links

Salmonella is one of the most important foodborne pathogens. Fifty-three strains of Salmonella deposited in the Culture Collection of Industrial Microorganisms-Microbiological Resources Center (IAFB) were identified using molecular and proteomic analyses. Moreover, the genetic similarity of the tested strains was determined using the PFGE method. Main virulence genes were identified, and phenotypical antibiotic susceptibility profiles and prevalence of resistance genes were analyzed. Subsequently, the occurrence of the main mechanisms of β-lactam resistance was determined. Virulence genes, invA, fimA, and stn were identified in all tested strains. Phenotypic tests, including 28 antibiotics, showed that 50.9% of the strains were MDR. The tet genes associated with tetracyclines resistance were the most frequently identified genes. Concerning the genes associated with ESBL-producing Salmonella, no resistance to the TEM and CTX-M type was identified, and only two strains (KKP 1597 and KKP 1610) showed resistance to SHV. No strains exhibited AmpC-type resistance but for six Salmonella strains, the efflux-related resistance of PSE-1 was presented. The high number of resistant strains in combination with multiple ARGs in Salmonella indicates the possible overuse of antibiotics. Our results showed that it is necessary to monitor antimicrobial resistance profiles in all food chain links constantly and to implement a policy of proper antibiotic stewardship to contain or at least significantly limit the further acquisition of antibiotic resistance among Salmonella strains.

Antimicrobial resistance analysis and whole-genome sequencing of Salmonella enterica serovar Indiana isolate from ducks

OBJECTIVES

Salmonella is one of the most important genera of enteric pathogenic bacteria that threatened duck farms. The aim of this study was to increase the understanding of antimicrobial resistance mechanisms in duck-origin S. enterica serovar Indiana isolate.

METHODS

Salmonella was isolated from duck cloacal swabs collected from the duck farms located in Zhejiang and Henan province of China. All of the isolates were identified after a series of confirmation tests including selective culture method, biochemical tests, serotyping and PCR targeting invA gene, and then subjected to antimicrobial susceptibility testing using the standard Kirby-Bauer disk diffusion method. Subsequently, whole-genome analysis of a representative multi-drug resistant Salmonella enterica serovar Indiana isolate SAP was performed using a combination of Nanopore and Illumina sequencing platforms.

RESULTS

A total of 18 Salmonella isolates were identified. The predominant serotype was S. enterica serovar Indiana (14 out of 18 isolates). The MDR pattern AMP-CFP-GEN-KAN-NEO-TET-NOR-CIP-CLB-SXT was observed in all 14 S. enterica serovar Indiana isolates. The genome of S. enterica serovar Indiana isolate SAP carried 65 antimicrobial resistance genes belonging to different antimicrobial resistance gene family including antibiotic efflux pump, rpsL, kdpDE, AAC(6'), general bacterial porin with reduced permeability to beta-lactams, ampC-type beta-lactamase, mutant Lpx gene conferring resistance to colistin, sulfonamide resistant dihydropteroate synthase folP, and trimethoprim resistant dihydrofolate reductase dfr.

CONCLUSION

S. enterica serovar Indiana strain isolated in this study carried multiple antimicrobial-resistant genes and exhibited resistance to multiple antibiotics.

Cell-free supernatants produced by lactic acid bacteria reduce Salmonella population in vitro

The genus Salmonella is closely associated with foodborne outbreaks and animal diseases, and reports of antimicrobial resistance in Salmonella species are frequent. Several alternatives have been developed to control this pathogen, such as cell-free supernatants (CFS). Our objective here was to evaluate the use of lactic acid bacteria (LAB) CFS against Salmonella in vitro. Seventeen strains of LAB were used to produce CFS, and their antimicrobial activity was screened towards six strains of Salmonella. In addition, CFS were also pH-neutralized and/or boiled. Those with the best results were lyophilized. MICs of lyophilized CFS were 11.25-22.5 g l^-1. Freeze-dried CFS were also used to supplement swine and poultry feed (11.25 g kg^-1) and in vitro simulated digestion of both species was performed, with Salmonella contamination of 5×10⁶ and 2×10⁵ c.f.u. g^-1 of swine and poultry feed, respectively. In the antimicrobial screening, all acidic CFS were able to inhibit the growth of Salmonella. After pH neutralization, Lactobacillus acidophilus Llorente, Limosilactobacillus fermentum CCT 1629, Lactiplantibacillus plantarum PUCPR44, Limosilactobacillus reuteri BioGaia, Lacticaseibacillus rhamnosus ATCC 7469 and Pediococcus pentosaceus UM116 CFS were the only strains that partially maintained their antimicrobial activity and, therefore, were chosen for lyophilization. In the simulated swine digestion, Salmonella counts were reduced ≥1.78 log c.f.u. g^-1 in the digesta containing either of the CFS. In the chicken simulation, a significant reduction was obtained with all CFS used (average reduction of 0.59±0.01 log c.f.u. ml^-1). In general, the lyophilized CFS of L. fermentum CCT 1629, L. rhamnosus ATCC 7469 and L. acidophilus Llorente presented better antimicrobial activity. In conclusion, CFS show potential as feed additives to control Salmonella in animal production and may be an alternative to the use of antibiotics, minimizing problems related to antimicrobial resistance.

Incidence of Multidrug-Resistant Escherichia coli Harbouring blaTEM and tetA Genes Isolated from Seafoods in Lagos Nigeria

The presence of multidrug-resistant Escherichia coli of fecal origin in seafood is a serious concern. Seafood containing MDR E. coli can serve as a medium for the transfer of resistant bacteria to consumers. The aim of the present study is to isolate and identify multidrug-resistant E. coli and associated resistant genes from selected seafood (catfish, crabs and tilapia fish) purchased from wholesalers and retailers at sea landing areas in Lagos state, Nigeria. A total of two hundred and thirty-eight (238) samples consisting of catfish (52), tilapia fish (78) and crab (108) were collected and investigated for the presence of E. coli from the period of June 2018-April 2019. Colonies that showed metallic sheen were considered presumptive E. coli isolates, and positive isolates were chosen for further confirmed by biochemical methods using IMViC tests, Oxidase test, triple sugar iron agar test and sugar fermentation test. Antimicrobial susceptibility of the isolates to eight classes of antibiotics was determined by disc diffusion methods while amplification of suspected antibiotic resistance genes were done by the polymerase chain reaction (PCR) using specific primers. A total of 105 (44.1%) E. coli were isolated from selected samples by standard microbiological procedures. The grand total of 59 (56.2%) isolates showed multiple antibiotic-resistant patterns. The overall result showed high-level resistance to tetracycline 101/105 (96.1%) and trimethoprim 90/105 (85.7%), cefotaxime 67/105 (42.9%) while the highest susceptibility of 101/105 (96.2%) was recorded for amikacin followed by gentamicin 84/105 (80%), meropenem 75/105 (71.4%), ceftazidime (69.5). The presence of tetA and blaTEM was prevalent among the isolates. Our results indicate that seafood may be a reservoir of β-lactam and tetracycline-resistance determinants.

Investigation of a Salmonellosis Outbreak Caused by Multidrug Resistant Salmonella Typhimurium in China

The rapid emergence of multidrug resistant Salmonella is a global public-health concern as outbreaks in recent years have mostly been caused by multidrug resistant strains. Here, we evaluated an outbreak in China caused by multidrug resistant Salmonella enterica serovar Typhimurium (S. Typhimurium) by employing an epidemiological and laboratory investigation using conventional methods and whole genome sequencing (WGS). Eleven of the 12 people who participated in a banquet showed gastrointestinal symptoms, and 8S. Typhimurium strains were recovered. Isolated outbreak strains showed multidrug resistance (MDR), and decreased susceptibility to ciprofloxacin, a first-line drug recommended by WHO for clinical treatment of intestinal infections. Antimicrobial resistance (AMR) gene analysis indicated that the MDR phenotype of these outbreak strains may be due to the presence of a number of AMR genes, including the blaOXA-1 and blaTEM-1 β-lactamase genes, which are often plasmid-borne and easily transferred. Further virulence gene analysis indicated that these outbreak strains also carried a large number of virulence genes, including 2 types of Salmonella pathogenicity islands (SPI-1 and SPI-2) and many adhesion-related virulence genes. Cluster analysis based on pulse-field gel electrophoresis data and phylogenetic analysis based on WGS revealed that the outbreak clone was closely related to and thus probably derived from local strains. This outbreak caused by multidrug resistant S. Typhimurium highlights the need for government improved strategies for the prevention and control of Salmonella infections.

Salmonella Enteritidis Effector AvrA Suppresses Autophagy by Reducing Beclin-1 Protein

Autophagy is a cellular process to clear pathogens. Salmonella enterica serovar Enteritidis (S.E) has emerged as one of the most important food-borne pathogens. However, major studies still focus on Salmonella enterica serovar Typhimurium. Here, we reported that AvrA, a S. Enteritidis effector, inhibited autophagy to promote bacterial survival in the host. We found that AvrA regulates the conversion of LC3 I into LC3 II and the enrichment of lysosomes. Beclin-1, a key molecular regulator of autophagy, was decreased after AvrA expressed strain colonization. In S.E-AvrA--infected cells, we found the increases of protein levels of p-JNK and p-c-Jun and the transcription level of AP-1. AvrA-reduction of Beclin-1 protein expression is through the JNK pathway. The JNK inhibitor abolished the AvrA-reduced Beclin-1 protein expression. Moreover, we identified that the AvrA mutation C186A abolished its regulation of Beclin-1 expression. In addition AvrA protein was found interacted with Beclin-1. In organoids and infected mice, we explored the physiologically related effects and mechanism of AvrA in reducing Beclin-1 through the JNK pathway, thus attenuating autophagic responses. This finding not only indicates an important role of S. Enteritidis effector in reducing host protein as a strategy to suppress autophagy, but also suggests manipulating autophagy as a new strategy to treat infectious diseases.

Environmental persistence and virulence of Salmonella spp. Isolated from a poultry slaughterhouse

Salmonella spp. is responsible for severe foodborne disease, and is one of the main agents involved in foodborne outbreaks worldwide. Contamination occurs mainly as a result of poultry and egg consumption since they can carry some serotypes pathogenic to humans. The aim of the study was to evaluate the persistence and pathogenic potential of Salmonella spp. (n = 40) isolated from poultry slaughterhouse mats, using adhesion and invasion assays, antimicrobial susceptibility by disc diffusion, and biofilm production as phenotypic tests and genotypic analyses. Polystyrene mats presented 3.2 times greater chance of isolating Salmonella than canvas mats. Besides, we observed resistance to tetracycline (17.5%), ampicillin (10%), cefotaxime (7.5%), trimethoprim-sulfamethoxazole (5%), and chloramphenicol (2.5%). All strains possessed the invA, sipB, sipD, ssaR, sifA, sitC, iroN, tolC, flgK, fljB, and flgL genes. The genes sopB and sipA were both present in 92.5% of the isolates, while sopD and spvB were observed in 90% and 32.5% of strains, respectively. All strains adhered to and invaded HeLa cells. Regarding biofilm production, 31 (77.5%) strains were able to produce biofilm on polystyrene microplates. Using PFGE, we detected the persistence of clones in the environment for up to 18 fromthe 20 weeks. The ability of these strains to produce a biofilm and thus persist in the environment and disperse through contact surfaces in the processing plant favors the contamination of food, aggravated by the pathogenic potential of these isolates demonstrated by their adhesion capacity, invasion and resistance to various antibiotic agents.