Characterization of Salmonella Typhimurium and its monophasic variant 1,4, [5],12:i:- isolated from different sources

Serovar and sequence type distribution and phenotypic and genotypic antimicrobial resistance of Salmonella originating from pet animals in Chongqing, China

A total of 334 Salmonella isolates were recovered from 6,223 pet rectal samples collected at 50 pet clinics, 42 pet shops, 7 residential areas, and 4 plazas. Forty serovars were identified that included all strains except for one isolate that did not cluster via self-agglutination, with Salmonella Typhimurium monophasic variant, Salmonella Kentucky, Salmonella Enteritidis, Salmonella Pomona, and Salmonella Give being the predominant serovars. Fifty-one sequence types were identified among the isolates, and ST198, ST11, ST19, ST451, ST34, and ST155 were the most common. The top four dominant antimicrobials to which isolates were resistant were sulfisoxazole, ampicillin, doxycycline, and tetracycline, and 217 isolates exhibited multidrug resistance. The prevalence of β-lactamase genes in Salmonella isolates was 59.6%, and among these isolates, 185 harbored blaTEM, followed by blaCTX-M (66) and blaOXA (10). Moreover, six PMQR genes, namely, including qnrA (4.8%), qnrB (4.2%), qnrD (0.9%), qnrS (18.9%), aac(6')-Ib-cr (16.5%), and oqxB (1.5%), were detected. QRDR mutations (76.6%) were very common in Salmonella isolates, with the most frequent mutation in parC (T57S) (47.3%). Furthermore, we detected six tetracycline resistance genes in 176 isolates, namely, tet(A) (39.5%), tet(B) (8.1%), tet(M) (7.7%), tet(D) (5.4%), tet(J) (3.3%), and tet(C) (1.8%), and three sulfonamide resistance genes in 303 isolates, namely, sul1 (84.4%), sul2 (31.1%), and sul3 (4.2%). Finally, we found 86 isolates simultaneously harboring four types of resistance genes that cotransferred 2-7 resistance genes to recipient bacteria. The frequent occurrence of antimicrobial resistance, particularly in dogs and cats, suggests that antibiotic misuse may be driving multidrug-resistant Salmonella among pets.IMPORTANCEPet-associated human salmonellosis has been reported for many years, and antimicrobial resistance in pet-associated Salmonella has become a serious public health problem and has attracted increasing attention. There are no reports of Salmonella from pets and their antimicrobial resistance in Chongqing, China. In this study, we investigated the prevalence, serovar diversity, sequence types, and antimicrobial resistance of Salmonella strains isolated from pet fecal samples in Chongqing. In addition, β-lactamase, QRDR, PMQR, tetracycline and sulfonamide resistance genes, and mutations in QRDRs in Salmonella isolates were examined. Our findings demonstrated the diversity of serovars and sequence types of Salmonella isolates. The isolates were widely resistant to antimicrobials, notably with a high proportion of multidrug-resistant strains, which highlights the potential direct or indirect transmission of multidrug-resistant Salmonella from pets to humans. Furthermore, resistance genes were widely prevalent in the isolates, and most of the resistance genes were spread horizontally between strains.

Antimicrobial Resistance of Listeria monocytogenes Strains Isolated in Food and Food-Processing Environments in Italy

Listeria monocytogenes, along with various other pathogenic bacteria, may show resistance against a broad spectrum of antibiotics. Evaluating the extent of resistance in harmful microorganisms like Listeria monocytogenes holds significant importance in crafting novel therapeutic strategies to mitigate or combat the rise of infections stemming from antibiotic-resistant bacteria. The present work aims to investigate the occurrence of antimicrobial resistance among Listeria monocytogenes strains in meat products (n = 173), seafood (n = 54), dairy products (n = 19), sauces (n = 2), confectionary products (n = 1), ready-to-eat rice dishes (n = 1), and food-processing environments (n = 19). A total of 269 Listeria monocytogenes strains belonging to eight different serovars were tested against 10 antimicrobials. In the classes of antibiotics, most of the strains were resistant antibiotics belonging to the family of β-lactams (92.94%). High proportions of L. monocytogenes isolates were resistant to oxacillin (88.48%), followed by fosfomycin (85.87%) and flumenique (78.44%). The lowest level of resistance was observed against gentamycin (1.49%). A total of 235 strains (n = 87.36%) showed a profile of multidrug resistance. In conclusion, a high occurrence of resistant and multidrug-resistant strains of Listeria monocytogenes was observed among the examined serotypes isolated from different food sources. This understanding enables the adoption of suitable measures to avert contamination and the spread of resistant bacteria via food.

Salmonella enterica serovars linked with poultry in India: antibiotic resistance profiles and carriage of virulence genes

Salmonella is an important poultry pathogen with zoonotic potential. Being a foodborne pathogen, Salmonella-contaminated poultry products can act as the major source of infection in humans. In India, limited studies have addressed the diversity of Salmonella strains of poultry origin. This study represented 26 strains belonging to Salmonella serovars Typhimurium, Infantis, Virchow, Kentucky, and Agona. The strains were tested for resistance to 14 different antimicrobial agents using the Kirby-Bauer disk-diffusion assay. The presence of the invA, hilA, agfA, lpfA, sopE, and spvC virulence genes was assessed by polymerase chain reaction (PCR), and the genetic diversity was assessed by Enterobacterial Repetitive Intergenic Consensus Polymerase Chain Reaction (ERIC-PCR). The highest resistance to tetracycline (n = 17; 65.38%) followed by nalidixic acid (n = 16; 61.53%) was detected among the strains. Among the strains (n = 17) phenotypically resistant to tetracycline, 94% (n = 16) were also positive for the tetA gene. Based on the presence of virulence genes, the strains were characterized into three virulence profiles (PI, P2, and P3). Among the investigated virulence genes, invA, hilA, agfA, and lpfA were present in all strains. The sopE gene was mostly associated with serovars Virchow (n = 3; 100%) and Typhimurium (n = 8; 80%), whereas spvC gene was exclusive for two Typhimurium strains that lacked sopE gene. ERIC-PCR profiling indicated clusters correlating their serovar, geographical, and farm origins. These results demonstrate that Salmonella isolates with a wide genetic range, antibiotic resistance, and virulence characteristics can colonize poultry. The presence of such strains is crucial for both food safety and public health.

Diversity of evolution in MDR monophasic S. Typhimurium among food animals and food products in Southern China from 2011 to 2018

The monophasic variant of Salmonella enterica serovar Typhimurium with the antigenic formula 1,4,[5],12:i:- is one of the most common pathogenic bacteria causing global food-borne outbreaks. However, the research on molecular characteristics and evolution of monophasic S. typhimurium in China is still lacking. In the current study, 59 monophasic S. typhimurium strains were isolated from food animals and food products in South China between 2011 and 2018. A total of 87.5 % of monophasic S. typhimurium isolates were grouped into one independent clade with other monophasic S. typhimurium strains in China distinct from other countries by phylogenomic analysis. These isolates possess variable genotypes, including multiple ARGs on plasmid IncHI2, diverse evolutions at the fljAB locus, and virulence factors. Our results suggest that the monophasic S. typhimurium isolates currently circulating in China might be an independent epidemic subtype.

High levels of multidrug-resistant isolates of genetically similar Salmonella 1,4, [5],12:I:- from Brazil between 1983 and 2020

Introduction. Salmonella 1,4, [5],12:i:- strains with different antimicrobial resistance profiles have been associated with foodborne disease outbreaks in several countries. In Brazil, S. 1,4, [5],12:i:- was identified as one of the most prevalent serovars in São Paulo State during 2004-2020.Gap Statement. However, few studies have characterized this serovar in Brazil.Aim. This study aimed to determine the antimicrobial resistance profiles of S. 1,4, [5],12:i:- strains isolated from different sources in Southeast Brazil and compare their genetic diversity.Methodology. We analysed 113 S. 1,4, [5],12:i:- strains isolated from humans (n=99), animals (n=7), food (n=5) and the environment (n=2) between 1983 and 2020. Susceptibility testing against 13 antimicrobials was performed using the disc diffusion method for all the strains. Plasmid resistance genes and mutations in the quinolone resistance-determining regions were identified in phenotypically fluoroquinolone-resistant strains. Molecular typing was performed using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) for all strains and multilocus sequence typing (MLST) for 40 selected strains.Results. Of the 113 strains, 54.87 % were resistant to at least one antimicrobial. The highest resistance rates were observed against ampicillin (51.33 %), nalidixic acid (39.82 %) and tetracycline (38.05 %). Additionally, 39 (34.51 %) strains were classified as multidrug-resistant (MDR). Nine fluoroquinolone-resistant strains exhibited the gyrA mutation (Ser96→Tyr96) and contained the qnrB gene. The 113 strains were grouped into two clusters using ERIC-PCR, and most of strains were present in one cluster, with a genetic similarity of ≥80 %. Finally, 40 strains were typed as ST19 using MLST.Conclusion. The prevalence of MDR strains is alarming because antimicrobial treatment against these strains may lead to therapeutic failure. Furthermore, the ERIC-PCR and MLST results suggested that most strains belonged to one main cluster. Thus, a prevalent subtype of Salmonella 1,4, [5],12:i:- strains has probably been circulating among different sources in São Paulo, Brazil, over decades.

Prevalence of Salmonella Typhimurium and Salmonella Enteritidis isolated from poultry meat: virulence and antimicrobial-resistant genes

Salmonellosis, a zoonotic disease, is one of the leading causes of foodborne illness worldwide. It is responsible for most infections caused by consumption of contaminated food. In recent years, a significant increase in the resistance of these bacteria to common antibiotics has been observed, posing a serious threat to global public health. The aim of this study was to investigate the prevalence of virulent antibiotic-resistant Salmonella spp. strains in Iranian poultry markets. A total of 440 chicken meat samples were randomly selected from meat supply and distribution facilities in Shahrekord and tested for bacteriological contamination. After culturing and isolating the strains, identification was performed using the classical bacteriological method and PCR. To determine antibiotic resistance, a disc diffusion test was performed according to the recommendations of the French Society of Microbiology. PCR was used to detect resistance and virulence genes. Only 9% of the samples were positive for Salmonella. These were Salmonella typhimurium isolates. All Salmonella typhimurium serotypes tested positive for the rfbJ, fljB, invA and fliC genes. Resistance to TET, cotrimoxazole, NA, NIT, piperacillin/tazobactam and other antibiotics was found in 26 (72.2%), 24 (66.7%), 22 (61.1%) and 21 (58.3%) isolates, respectively. The sul1, sul2 and sul3 genes were present in 20, 12 and 4 of 24 cotrimoxazole-resistant bacteria, respectively. Chloramphenicol resistance was found in six isolates, but more isolates tested positive for the floR and cat two genes. In contrast, 2 (33%) of the cat three genes, 3 (50%) of the cmlA genes and 2 (34%) of the cmlB genes were all positive. The results of this investigation showed that Salmonella typhimurium is the most common serotype of the bacterium. This means that most of the antibiotics commonly used in the livestock and poultry industries are ineffective against most Salmonella isolates, which is important for public health.

Antimicrobial Resistance and Genomic Characterization of Salmonella Infantis from Different Sources

The epidemiology of Salmonella Infantis is complex in terms of its distribution and transmission. The continuous collection and analysis of updated data on the prevalence and antimicrobic resistance are essential. The present work aimed to investigate the antimicrobial resistance and the correlation among S. Infantis isolates from different sources through the multiple-locus variable-number of tandem repeat (VNTR) analysis (MLVA). A total of 562 Salmonella strains isolated from 2018 to 2020 from poultry, humans, swine, water buffalo, mussels, cattle, and wild boar were serotyped, and 185 S. Infantis strains (32.92%) were identified. S. Infantis was commonly isolated in poultry and, to a lesser extent, in other sources. The isolates were tested against 12 antimicrobials, and a high prevalence of resistant strains was recorded. S. Infantis showed high resistance against fluoroquinolones, ampicillin, and tetracycline, which are commonly used in human and veterinary medicine. From all S. Infantis isolates, five VNTR loci were amplified. The use of MLVA was not sufficient to understand the complexity of the epidemiological relationships between S. Infantis strains. In conclusion, an alternative methodology to investigate genetic similarities and differences among S. Infantis strains is needed.

Highly prevalent MDR, frequently carrying virulence genes and antimicrobial resistance genes in Salmonella enterica serovar 4,[5],12:i:- isolates from Guizhou Province, China

Salmonella enterica serovar 4,[5],12:i:-, a monophasic variant of Salmonella Typhimurium lacking the phase 2 flagellin, is one of the common serotypes causing Salmonellosis worldwide. However, information on Salmonella serovar 4,[5],12:i:- from Guizhou Province has lacked so far. This study aimed to investigate the antimicrobial resistance, the presence of antimicrobial resistance genes and virulence genes, and characterize the MLST genotypes of Salmonella serovar 4,[5],12:i:- isolates from Guizhou province, China. We collected 363 non-typhoid Salmonella (NTS) isolates of Guizhou from 2013 to 2018. Biochemical identification, serogroups testing, and specific multiplex polymerase chain reaction (mPCR) assay were conducted to identify Salmonella 4,[5],12:i:- isolates. Isolates were determined the antimicrobial resistance by the micro broth dilution method, detected the presence of antimicrobial resistance genes and virulence genes by PCR, and examined the molecular genotyping by Multilocus sequence typing (MLST). Eighty-seven Salmonella 4,[5],12:i:- isolates were detected, accounting for 23.9% (87/363) of the total NTS isolates. All Salmonella 4,[5],12:i:- isolates showed highly resistant to sulfaoxazole (93.1%), streptomycin (90.8%), ampicillin (88.5%), tetracycline (86.2%) and doxycycline (86.2%). A high proportion (94.2%) of multi-drug resistance (MDR) isolates were found. Most (83.9%) Salmonella 4,[5],12:i:- isolates carried four antimicrobial resistance genes, especially blaTEM-1, strA-strB, sul2, and tetB genes. Salmonella 4,[5],12:i:- isolates showed a high rate of invA, sseL, mgtC, siiE, sopB, gipA, gtgB, sspH1, and sspH2 (72.4%~98.9%). On the contrary, none of the isolates were detected the spvC and pefA genes. MLST analysis revealed three sequence types (STs), and ST34 (97.7%) was the dominant sequence type. This study is the first report of Salmonella 4,[5],12:i:- in humans from Guizhou province, China. The data might be useful for rational antimicrobial usage against Salmonella 4,[5],12:i:- infections, risk management, and public health strategies in Guizhou.

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.

Genomic and phenotypic analysis of SspH1 identifies a new Salmonella effector, SspH3

Salmonella is a major foodborne pathogen and is responsible for a range of diseases. Not all Salmonella contribute to severe health outcomes as there is a large degree of genetic heterogeneity among the 2600 serovars within the genus. This variability across Salmonella serovars is linked to numerous genetic elements that dictate virulence. While several genetic elements encode virulence factors with well documented contributions to pathogenesis, many genetic elements implicated in Salmonella virulence remain uncharacterized. Many pathogens encode a family of E3 ubiquitin ligases that are delivered into the cells that they infect using a Type 3 Secretion System (T3SS). These effectors, known as NEL-domain E3s, were first characterized in Salmonella. Most Salmonella encode the NEL-effectors sspH2 and slrP, whereas only a subset of Salmonella encode sspH1. SspH1 has been shown to ubiquitinate the mammalian protein kinase PKN1, which has been reported to negatively regulate the pro-survival program Akt. We discovered that SspH1 mediates the degradation of PKN1 during infection of a macrophage cell line but that this degradation does not impact Akt signaling. Genomic analysis of a large collection of Salmonella genomes identified a putative new gene, sspH3, with homology to sspH1. SspH3 is a novel NEL-domain effector.

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.

Serotyping and Evaluation of Antimicrobial Resistance of Salmonella Strains Detected in Wildlife and Natural Environments in Southern Italy

Wild animals are potential vectors of antibiotic-resistant bacteria in the environment. The present study aimed to investigate the occurrence of antimicrobial resistance among Salmonella serovars isolated from wildlife and the environment in Italy. A total of 164 Salmonella isolates were analyzed, and six different subspecies and 64 serovars were detected. High proportions of Salmonella isolates proved resistant to streptomycin (34.1%), followed by trimethoprim-sulfamethoxazole (23.2%), tetracycline (17.7%), ciprofloxacin (14.63%) and ampicillin (11.59%). By source, the lowest level of resistance was observed in Salmonella serovars isolated from a water environment, while antimicrobial resistance was frequent in strains collected from shellfish, reptiles and birds. Multidrug-resistant strains were recovered from seafood (n = 11), mammals (n = 3) and water (n = 1). Three S. Typhimurium monophasic variant strains showed asimultaneous resistance to ampicillin, streptomycin, tetracycline and trimethoprim-sulfamethoxazole, which represents a recognized alert resistance profile for this serovar. These data indicate the environmental dissemination of resistant strains due to anthropogenic activities, which, in southern Italy, probably have a higher impact on marine ecosystems than on terrestrial ones. Moreover, as most of the animals considered in the present study are usually consumed by humans, the presence of resistant bacteria in them is a matter of great concern.

Prevalence, Virulence and Antimicrobial Susceptibility of Salmonella spp., Yersinia enterocolitica and Listeria monocytogenes in European Wild Boar (Sus scrofa) Hunted in Tuscany (Central Italy)

Wild boar is an animal the population of which constantly increases in Europe. This animal plays an important role as a reservoir for several pathogens, including three of the most important zoonoses: salmonellosis, yersiniosis and listeriosis. The aim of this investigation was to evaluate the occurrence of antimicrobial-resistant and virulence factor genes of Salmonella spp., Yersinia enterocolitica and Listeria monocytogenes isolated from wild boar in Tuscany (Central Italy). During two consequent hunting seasons (2018/2019 and 2019/2020), rectal swabs, spleens and livers were collected from 287 hunted wild boar to isolate strains. Each isolate was tested to investigate its antimicrobial resistance and to detect virulence factor genes by PCR. Eighteen Salmonella strains (6.27%) were isolated. Of these, 66.7% were resistant to streptomycin, 13.4% to cephalothin, 6.67% to imipenem and one isolate (6.67%) was resistant simultaneously to five antimicrobials. Moreover, the most detected genes were sopE (73.4%), pipB (66.7%), sodCI (53.3%), spvR and spvC (46.7%). In total, 54 (17.8%) Yersinia enterocolitica were isolated; of them, 26 (48.1%), 9 (16.7%), 17 (31.5%), 1 (1.85%) and 1 (1.85%) belonged to biotypes 1, 2, 3, 4 and 5, respectively. All strains (100%) demonstrated resistance to cephalothin and 70.4% to amoxicillin-clavulanic acid, 55.6% to ampicillin, and 37.0% to cefoxitin. Additionally, the most detected genes were ystA (25.9%), inv (24.1%), ail (22.2%), ystB (18.5%) and virF (14.8%). Finally, only one Listeriamonocytogenes isolate (0.35%) was obtained, belonging to serogroup IVb, serovar 4b, and it was found to be resistant to cefoxitin, cefotaxime and nalidixic acid. The results highlighted the role of wild boar as a carrier for pathogenic and antimicrobial-resistant Salmonella spp., Yersinia enterocolitica and Listeria monocytogens, representing a possible reservoir for domestic animals and human pathogens.

Serotypes and antimicrobial resistance profiles of Salmonella enterica recovered from clinical swine samples

Background and Aim:

Salmonella enterica is an important foodborne pathogen and is recognized as a major public health issue. The emergence of multidrug-resistant (MDR) S. enterica represents a major challenge for national public health authorities. We investigated the distribution of serovars and antimicrobial resistance of S. enterica isolates from clinical swine samples stored at the Veterinary Diagnostic Laboratory, Faculty of Veterinary Medicine, Kasetsart University from 2016 to 2017.

Materials and Methods:

Clinical samples were collected and subjected to standard microbiological techniques outlined in the Manual of Clinical Microbiology to identify Salmonella serovars. Susceptibility to antimicrobials was tested by the Kirby–Bauer disk diffusion method using a panel of 14 antimicrobials.

Results:

A total of 144 Salmonella isolates were identified and the dominant serovar was Salmonella Choleraesuis (66.67%), followed by monophasic Salmonella Typhimurium (18.75%), S. Typhimurium (9.03%), and Rissen (5.56%). The isolates displayed high resistance rates to ampicillin (AMP [100%]), amoxicillin (AX [100%]), tetracycline (TE [100%]), cefotaxime (CTX [89.58%]), ceftriaxone (CRO [87.50%]), chloramphenicol (C [82.64%]), gentamicin (CN [79.17%]), nalidixic acid (NA [72.92%]), and ceftazidime (CAZ [71.53%]). All isolates were MDR, with 29 distinct resistance patterns. The dominant MDR pattern among serovars Choleraesuis and Rissen exhibited resistance to 9 antimicrobials: (R7-14 AMP-AX-CAZ-CRO-CTX-NA-C-CN-TE). However, all tested isolates were susceptible to AX/clavulanic acid and fosfomycin.

Conclusion:

High resistance levels to the third generation of cephalosporins such as CAZ, CRO, and CTX highlight the need for careful and reasonable usage of antimicrobials in animals and humans, especially for S. Choleraesuis infections.

Identification and Antimicrobial Activity of Medium-Sized and Short Peptides from Yellowfin Tuna (Thunnus albacares) Simulated Gastrointestinal Digestion

Due to the rapidly increasing resistance to conventional antibiotics, antimicrobial peptides are emerging as promising novel drug candidates. In this study, peptide fragments were obtained from yellowfin tuna muscle by simulated gastrointestinal digestion, and their antimicrobial activity towards Gram-positive and Gram-negative bacteria was investigated. In particular, the antimicrobial activity of both medium- and short-sized peptides was investigated by using two dedicated approaches. Medium-sized peptides were purified by solid phase extraction on C18, while short peptides were purified thanks to a graphitized carbon black sorbent. For medium-sized peptide characterization, a peptidomic strategy based on shotgun proteomics analysis was employed, and identification was achieved by matching protein sequence database by homology, as yellowfin tuna is a non-model organism, leading to the identification of 403 peptides. As for short peptide sequences, an untargeted suspect screening approach was carried out by means of an inclusion list presenting the exact mass to charge ratios (m/z) values for all di-, tri- and tetrapeptides. In total, 572 short sequences were identified thanks to a customized workflow dedicated to short peptide analysis implemented on Compound Discoverer software.

Antimicrobial Susceptibility Testing for Salmonella Serovars Isolated from Food Samples: Five-Year Monitoring (2015-2019)

The continuous collection and analysis of updated data on the antimicrobic resistance among bacterial strains represent the essential core for the surveillance of this problem. The present work aimed to investigate the occurrence of antimicrobial resistance among Salmonella serovars isolated in foods in 2015-2019. A total of 178 Salmonella strains belonging to 39 serovars were tested against 10 antimicrobials. High proportions of Salmonella isolates were resistant to tetracycline (n = 53.9%), ciprofloxacin (n = 47.2%), ampicillin (n = 44.4%), nalidixic acid (n = 42.7%), and trimethoprim-sulfamethoxazole (n = 38.8%). Different resistance rates were recorded among the different serotypes of Salmonella, and S. Infantis, exhibited the highest resistance to antibiotics. A high percentage of strains isolated from poultry, pork, and bovine were resistant to at least one or two antimicrobials. Resistant and multidrug-resistant (MDR) strains were also recorded among the isolates from molluscan shellfish; however, the occurrence of resistant Salmonella strains isolated from this source was significantly lower compared with those reported for poultry, pork, and bovine. The high levels of resistance reported in the present study indicate a potential public health risk. Consequently, additional hygiene and antibiotic stewardship practices should be considered for the food industry to prevent the prevalence of Salmonella in foods.