Antimicrobial resistance of Salmonella isolated from food animals: A review

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

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

Phenotypic and genotypic survey of antibiotic resistance in Salmonella enterica isolates from dairy farms in Uruguay

Salmonella enterica is an important zoonotic pathogen that is frequently identified in dairy farming systems. An increase in antibiotic resistance has led to inadequate results of treatments, with impacts on animal and human health. Here, the phenotypic and genotypic susceptibility patterns of Salmonella isolates from dairy cattle and dairy farm environments were evaluated and compared. A collection of 75 S. enterica isolates were evaluated, and their phenotypic susceptibility was determined. For genotypic characterization, the whole genomes of the isolates were sequenced, and geno-serotypes, sequence types (STs) and core-genome-sequence types were determined using the EnteroBase pipeline. To characterize antibiotic resistance genes and gene mutations, tools from the Center for Genomic Epidemiology were used. Salmonella Dublin (SDu), S. Typhimurium (STy), S. Anatum (SAn), S. Newport (SNe), S. Agona (Sag), S. Montevideo (SMo) and IIIb 61:i:z53 were included in the collection. A single sequence type was detected per serovar. Phenotypic non-susceptibility to streptomycin and tetracycline was very frequent in the collection, and high non-susceptibility to ciprofloxacin was also observed. Multidrug resistance (MDR) was observed in 42 isolates (56.0%), with SAn and STy presenting higher MDR than the other serovars, showing non-susceptibility to up to 6 groups of antibiotics. Genomic analysis revealed the presence of 21 genes associated with antimicrobial resistance (AMR) in Salmonella isolates. More than 60% of the isolates carried some gene associated with resistance to aminoglycosides and tetracyclines. Only one gene associated with beta-lactam resistance was found, in seven isolates. Two different mutations were identified, parC_T57S and acrB_R717Q, which confer resistance to quinolones and azithromycin, respectively. The accuracy of predicting antimicrobial resistance phenotypes based on AMR genotypes was 83.7%. The genomic approach does not replace the phenotypic assay but offers valuable information for the survey of circulating antimicrobial resistance. This work represents one of the first studies evaluating phenotypic and genotypic AMR in Salmonella from dairy cattle in South America.

Antimicrobial Susceptibility of Salmonella Isolated from Chickens and Humans in Wau, South Sudan

Background. Salmonella infections are a public health problem across the globe. In South Sudan, there is little information regarding the prevalence and antibiotic resistance patterns of Salmonella. Therefore, this study assessed the prevalence and antimicrobial susceptibility of Salmonella isolates from chickens and humans in South Sudan. Fecal samples were collected and cultured on Xylose Lysine Deoxycholate Agar for the isolation of Salmonella and confirmed using biochemical tests and PCR through the amplification of the invA gene. A total of 417 fecal samples were examined, of which 270 (64.7%) were chicken cloacal swabs while 147 (35.3%) were humans’ stool specimens. Results. Eleven (11) Salmonella isolates were isolated from humans while nine were from chickens. All 11 isolates from humans were susceptible to sulfamethoxazole-trimethoprim, chloramphenicol, streptomycin, cefotaxime, nalidixic acid, and gentamicin. However, 4 (36.7%) isolates showed resistance to ciprofloxacin, 2 (18.9%) to ampicillin, and 1 (9.1%) to tetracycline. All chicken isolates were susceptible to chloramphenicol, streptomycin, sulfamethoxazole-trimethoprim, ciprofloxacin, cefotaxime, nalidixic acid, and gentamicin but showed resistance to tetracycline 2 (22.2%) and ampicillin 1 (11.1%). Conclusion. Antimicrobial resistant isolates were isolated in both chickens and humans. Further, MDR isolates were found in both chicken and human samples, and this is a public health concern. This, therefore, calls for concerted efforts to educate producers and consumers on public health, food safety, food hygiene in food production, and enhancement of surveillance programmes on zoonotic bacteria and antimicrobial susceptibility.

Association between antimicrobial resistance and biofilm forming ability of Salmonella enterica serotypes from commercial broiler farms in Brazil

1. This study determined the antimicrobial resistance profile and the biofilm-forming ability of Salmonella enterica strains isolated from commercial broiler houses over a three-year period in southern Brazil.

2. Of the 720 drag swabs analysed, 37 (5.1%) tested positive for non-typhoidal Salmonella spp. and S. Heidelberg was the most frequent serovar.

3. Among the antimicrobial resistant strains (83.8%; 31/37), resistance was most common to tetracycline, ampicillin and nalidixic acid. Multidrug resistance was found in 65% (24/37) of the isolates, with a large proportion of multidrug resistant S. Heidelberg strains (81%; 13/16).

4. In total, 65% (24/37) of the isolates showed the ability to produce biofilm and multiple antimicrobial resistance was negatively correlated with biofilm formation.

5. Strains susceptible to all tested antimicrobials tended to form stronger biofilms than multidrug resistant ones. This suggested that Salmonella spp. with less antimicrobial resistance depend more on the protection provided by biofilm to survive in the farm environment.

Impact of hygiene and sanitation in ruminant slaughterhouses on the bacterial contamination of meat in Central Java Province, Indonesia

Background and Aim: Ruminant slaughterhouse is one of the food-producing units to meet the protein demand of the people in Central Java. This study aimed to evaluate the implementation of sanitation and hygiene in ruminant slaughterhouses in Central Java based on their veterinary control number (NKV) certification and the microbiological quality of the meat produced. Materials and Methods: This study was conducted from September 2021 to December 2021. Thirty-three priority slaughterhouses, representing 33 districts/cities in Central Java Province, were assessed for their hygiene and sanitation practices according to the NKV criteria mandated by The Minister of Agriculture Regulation No. 11/2020 on NKV Certification for Animal Production Unit. Sixty-six meat samples from these slaughterhouses were obtained for microbiological analysis. The total plate count (TPC), counts of Escherichia coli and Staphylococcus aureus, and the presence of Salmonella spp. were determined. The microbiological tests followed the standard national testing procedure according to the Indonesian National Standard 2897:2008 on Method of Analysis for Microbiological Contaminants in Meat, Eggs, Milk, and its derived products. Results: The sanitation hygiene assessment of the 33 slaughterhouses showed that seven (21.2%) met the NKV criteria level 3, while the others did not. The average TPC of the meat samples was 1.57 × 105 CFU/g (4.93 log10), the S. aureus count was 7.6 CFU/g, and the E. coli count was 9.2 most probable number/g. Only one sample (1.50%) tested positive for Salmonella spp. A comprehensive assessment comparing the NKV criteria with the level of meat contamination showed that the ruminant slaughterhouses that satisfied the NKV criteria had more meat samples (85.71%), on average, that complied with the Indonesian National Standard for microbial contamination compared with those that did not satisfy the NKV criteria (69.23%). The odds ratio was 2.67. Conclusion: Most of the priority ruminant slaughterhouses in Central Java did not meet the NKV standards. The research only looks at the level of hygiene sanitation according to NKV standards in slaughterhouses, the level of contamination produced does not reflect the level of the consumer; therefore, the level of contamination should continue to be investigated at the post-production stage.

Prevalence of Multidrug-Resistant Salmonella enterica Serovars in Buffalo Meat in Egypt

The current study aimed to investigate the presence of Salmonella spp. prevalence in buffalo meat in Egypt, along with studying the antimicrobial susceptibility of the recovered isolates. Salmonella spp. was detected in 25% of tested buffalo meat. A total of 53 (100%) isolates were genetically verified by PCR as Salmonella, based on the detection of the invA gene. The stn and hilA genes were detected in 71.7% (38/53), and 83.0% (44/53) of the recovered isolates, respectively. Salmonella Enteritidis (11/53; 20.7%) was the most commonly isolated serovar, followed by S. Typhimurium (9/53; 17%), S. Montevideo (6/53; 11.3%), meanwhile, S. Chester, S. Derby, S. Papuana, and S. Saintpaul were the least commonly identified serovars (a single strain for each; 1.9%). Among the 16 antimicrobials tested, amikacin, imipenem, gentamicin, cefotaxime, meropenem, ciprofloxacin, and enrofloxacin were the most effective drugs, with bacterial susceptibility percentages of 98.1%, 94.3%, 92.5%, 86.8%, 83.0%, 73.6%, and 69.8%, respectively. Meanwhile, the least effective ones were erythromycin, streptomycin, clindamycin, cefepime, and nalidixic acid, with bacterial resistance percentages of 100%, 98.1%, 88.7%, 77.4%, and 66%, respectively. Interestingly, the high contamination level of Egyptian buffalo meat with multidrug-resistant Salmonella (79.2%; 42/53) can constitute a problem for public health. Therefore, programs to control Salmonella contamination are needed in Egypt.

Patterns of antimicrobial resistance in Salmonella isolates from fattening pigs in Spain

Background

Swine are considered a major source of foodborne salmonellosis, a public health issue further complicated by the circulation of multidrug-resistant Salmonella strains that threaten the safety of the food chain. The current study aimed to identify patterns that can help to understand the epidemiology of antimicrobial resistance (AMR) in Salmonella in pigs in Spain through the application of several multivariate statistical methods to data from the AMR national surveillance programs from 2001 to 2017.

Results

A total of 1,318 pig Salmonella isolates belonging to 63 different serotypes were isolated and their AMR profiles were determined. Tetracycline resistance across provinces in Spain was the highest among all antimicrobials and ranged from 66.7% to 95.8%, followed by sulfamethoxazole resistance (range: 42.5% − 77.8%), streptomycin resistance (range: 45.7% − 76.7%), ampicillin resistance (range: 24.3% − 66.7%, with a lower percentage of resistance in the South-East of Spain), and chloramphenicol resistance (range: 8.5% − 41.1%). A significant increase in the percentage of resistant isolates to chloramphenicol, sulfamethoxazole, ampicillin and trimethoprim from 2013 to 2017 was observed. Bayesian network analysis showed the existence of dependencies between resistance to antimicrobials of the same but also different families, with chloramphenicol and sulfamethoxazole in the centre of the networks. In the networks, the conditional probability for an isolate susceptible to ciprofloxacin that was also susceptible to nalidixic acid was 0.999 but for an isolate resistant to ciprofloxacin that was also resistant to nalidixic acid was only 0.779. An isolate susceptible to florfenicol would be expected to be susceptible to chloramphenicol, whereas an isolate resistant to chloramphenicol had a conditional probability of being resistant to florfenicol at only 0.221. Hierarchical clustering further demonstrated the linkage between certain resistances (and serotypes). For example, a higher likelihood of multidrug-resistance in isolates belonging to 1,4,[5],12:i:- serotype was found, and in the cluster where all isolates were resistant to tetracycline, chloramphenicol and florfenicol, 86.9% (n = 53) of the isolates were Typhimurium.

Conclusion

Our study demonstrated the power of multivariate statistical methods in discovering trends and patterns of AMR and found the existence of serotype-specific AMR patterns for serotypes of public health concern in Salmonella isolates in pigs in Spain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03377-3.

Sensitive Detection of a Single-Nucleotide Polymorphism in Foodborne Pathogens Using CRISPR/Cas12a-Signaling ARMS-PCR

Salmonella infection, particularly that caused by drug-resistant strain, has become a worldwide public health issue. Herein, we presented a CRISPR/Cas12a-signaling ARMS-PCR assay, termed cARMS, capable of sensitively detecting drug-resistant Salmonella enterica (S. enterica) involving single-nucleotide polymorphism (SNP). Owing to the dual-recognition processes, i.e., allele-specific primed polymerization and CRISPR/Cas12 binding, the cARMS assay yielded a high sensitivity for detecting SNP down to ∼0.5%. We used the cARMS assay to investigate the adaptation of SNP-involved drug-resistant S. enterica to salt stress. It was found that the mutants exhibited stronger adaptation to salt stress, indicating the potential risk of using high salt content as a sterilization strategy. The results verified the feasibility of the cARMS assay in controlling SNP-involved bacteria-associated biosafety.

Prevalence and antimicrobial resistance profile in <em>Salmonella</em> spp. isolates from swine food chain

The aim of this survey was to examine the prevalence and the antimicrobial resistance (AMR) of Salmonella spp. isolated from swine food chain. A total of 435 samples were collected: 360 from slaughterhouse (150 carcasses, 30 cecal samples, 180 environmental samples) and 75 from Italian traditional pork dry sausages. Thirty-six Salmonella were isolated and identified by Polymerase Chain Reaction (PCR): 13,3% (4/30) in fecal samples, 5,5% (10/180) in environmental samples, 7,3% (11/150) in carcasses, and 14,6% (11/75) in Italian traditional dry sausages. Salmonella serotypes were: S. Typhimurium (44,4%), S. Typhimurium monophasic variant (8,3%), S. Typhi (2,8%), S. Enteritidis (22,2%), S. Rissen (16,6%) and S. Derby (5,5%). Phenotypic and genotypic characterization of AMR Salmonella spp. isolates was executed through automatic system (VITEK 2, bioMèrieux) and PCR assays. Salmonella spp. showed phonotypical and genotypical resistance to at least one or more classes of antibiotic. All Salmonella spp. were resistant to aminoglycoside (amikacin and tobramycin) and gentamicin, 86,1% strains were resistant to tetracycline, 55,5% strains were resistant to ampicillin and piperacillin, 25% strains to trimethoprim, 5,5% strains to chloramphenicol, 2,8% strains to amoxicillin/ clavulanic acid, and nitrofurantoin. Among Salmonella isolates, the most detected AMR genes were catA for chloramphenicol (94,4%), nitrofuran nfsA (77.7%), nfsB (86,1%) and, for fluoroquinolone par C (100%) and gyrA (94,4%). This study reported epidemiological data regarding Salmonella spp. and AMR’s circulation in the swine food chain. This phenomenon (AMR) has critical repercussions on the final consumer health; therefore, it represents a crucial One-Health issue.

Development of Geraniol-Loaded Liposomal Nanoformulations against Salmonella Colonization in the Pig Gut

Salmonella is a global health threat, with pig production being one of the main sources of human salmonellosis. The current study investigated the antivirulence properties of geraniol for inhibiting the in vitro colonization of Salmonella. The minimum inhibitory (MIC) and bactericidal concentrations (MBC) of geraniol against Salmonella typhimurium followed by the sub-MIC of geraniol were determined. Results provided clear evidence that geraniol at 1/8 MIC can be used as an effective, non-toxic antivirulence compound to inhibit virulence factors (motility, adhesion, and invasiveness) affecting the colonization of S. typhimurium on IPEC-J2 cells. Additionally, the findings signified that microfluidics is an emerging technology suitable for the preparation of stable liposomes with a small size (<200 nm) and high encapsulation efficiency (EE) of up to 92.53%, which can act as effective carriers of geraniol into the pig gastrointestinal tract (GIT), targeting Salmonella, preventing colonization, and thus increasing the safety of the food supply chain.

Review and Comparison of Antimicrobial Resistance Gene Databases

As the prevalence of antimicrobial resistance genes is increasing in microbes, we are facing the return of the pre-antibiotic era. Consecutively, the number of studies concerning antibiotic resistance and its spread in the environment is rapidly growing. Next generation sequencing technologies are widespread used in many areas of biological research and antibiotic resistance is no exception. For the rapid annotation of whole genome sequencing and metagenomic results considering antibiotic resistance, several tools and data resources were developed. These databases, however, can differ fundamentally in the number and type of genes and resistance determinants they comprise. Furthermore, the annotation structure and metadata stored in these resources can also contribute to their differences. Several previous reviews were published on the tools and databases of resistance gene annotation; however, to our knowledge, no previous review focused solely and in depth on the differences in the databases. In this review, we compare the most well-known and widely used antibiotic resistance gene databases based on their structure and content. We believe that this knowledge is fundamental for selecting the most appropriate database for a research question and for the development of new tools and resources of resistance gene annotation.

Copper/Zinc-Modified Palygorskite Protects Against Salmonella Typhimurium Infection and Modulates the Intestinal Microbiota in Chickens

Palygorskite (Pal), a clay nanoparticle, has been demonstrated to be a vehicle for drug delivery. Copper has antibacterial properties, and zinc is an essential micronutrient for intestinal health in animals and humans. However, whether copper/zinc-modified Pal (Cu/Zn-Pal) can protect chickens from Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) infection remains unclear. In this study, three complexes (Cu/Zn-Pal-1, Cu/Zn-Pal-2, and Cu/Zn-Pal-3) were prepared, and Cu/Zn-Pal-1 was shown to be the most effective at inhibiting the growth of S. Typhimurium in vitro, whereas natural Pal alone had no inhibitory effect. In vivo, Cu/Zn-Pal-1 reduced S. Typhimurium colonization in the intestine of infected chickens and relieved S. Typhimurium-induced organ and intestinal mucosal barrier damage. Moreover, this reduction in Salmonella load attenuated intestinal inflammation and the oxidative stress response in challenged chickens. Additionally, Cu/Zn-Pal-1 modulated the intestinal microbiota in infected chickens, which was characterized by the reduced abundance of Firmicutes and the increased abundance of Proteobacteria and Bacteroidetes. Our results indicated that the Cu/Zn-Pal-1 complex may be an effective feed supplement for reducing S. Typhimurium colonization of the gut.

Lactobacillus reuteri and Enterococcus faecium from Poultry Gut Reduce Mucin Adhesion and Biofilm Formation of Cephalosporin and Fluoroquinolone-Resistant Salmonella enterica

Non-typhoidal Salmonella (NTS) can cause infection in poultry, livestock, and humans. Although the use of antimicrobials as feed additives is prohibited, the previous indiscriminate use and poor regulatory oversight in some parts of the world have resulted in increased bacterial resistance to antimicrobials, including cephalosporins and fluoroquinolones, which are among the limited treatment options available against NTS. This study aimed to isolate potential probiotic lactic acid bacteria (LAB) strains from the poultry gut to inhibit fluoroquinolone and cephalosporin resistant MDR Salmonella Typhimurium and S. Enteritidis. The safety profile of the LAB isolates was evaluated for the hemolytic activity, DNase activity, and antibiotic resistance. Based on the safety results, three possible probiotic LAB candidates for in vitro Salmonella control were chosen. Candidate LAB isolates were identified by 16S rDNA sequencing as Lactobacillus reuteri PFS4, Enterococcus faecium PFS13, and Enterococcus faecium PFS14. These strains demonstrated a good tolerance to gastrointestinal-related stresses, including gastric acid, bile, lysozyme, and phenol. In addition, the isolates that were able to auto aggregate had the ability to co-aggregate with MDR S. Typhimurium and S. Enteritidis. Furthermore, LAB strains competitively reduced the adhesion of pathogens to porcine mucin Type III in co-culture studies. The probiotic combination of the selected LAB isolates inhibited the biofilm formation of S. Typhimurium FML15 and S. Enteritidis FML18 by 90% and 92%, respectively. In addition, the cell-free supernatant (CFS) of the LAB culture significantly reduced the growth of Salmonella in vitro. Thus, L. reuteri PFS4, E. faecium PFS13, and E. faecium PFS 14 are potential probiotics that could be used to control MDR S. Typhimurium and S. Enteritidis in poultry. Future investigations are required to elucidate the in vivo potential of these probiotic candidates as Salmonella control agents in poultry and animal feed.

Multidrug-Resistant and Extended-Spectrum β-Lactamase-Producing Salmonella enterica Serotype Heidelberg Is Widespread in a Poultry Processing Facility in Southern Brazil

ABSTRACT

This study was conducted to characterize the distribution of Salmonella isolates in a poultry processing facility and to identify their antibiotic resistance profiles. Salmonella enterica was detected in 146 samples (66.7%), and 125 isolates were identified as Salmonella Heidelberg (n = 123), Salmonella Abony (n = 1), and Salmonella O:4,5 (n = 1). Salmonella Heidelberg isolates were subjected to XbaI macrorestriction analysis and pulsed-field gel electrophoresis. The 66 pulsotypes obtained were grouped into four major clusters, indicating cross-contamination and persistence of this serotype in the processing facility. Selected S. enterica isolates were characterized by their antibiotic resistance, and most (n = 122, 97.6%) were multidrug resistant. Resistance to third-generation cephalosporins ceftazidime (84 isolates, 67.2%) and cefotaxime and ceftriaxone (91 isolates, 72.8%) was particularly prevalent. Production of extended-spectrum β-lactamases (ESBL) was identified in 24 isolates (19.2%), and ESBL-producing isolates were resistant to at least eight antibiotics. This study revealed the high prevalence of Salmonella Heidelberg in the poultry chain, providing insight into the ecology of this pathogen in this facility. The high prevalence of multidrug-resistant S. enterica is a concern due to the potential consequences for public health.

HIGHLIGHTS

A Bayesian latent class mixture model with censoring for correlation analysis in antimicrobial resistance across populations

Background

The emergence of antimicrobial resistance across populations is a global threat to public health. Surveillance programs often monitor human and animal populations to evaluate trends of emergence in these populations. Many national level antibiotic resistance surveillance programs quantify the proportion of resistant bacteria as a means of monitoring emergence and control measures. The reason for monitoring these different populations are many, including interest in similar changes in resistance which might provide insight into emergence and control options.

Methods

In this research, we developed a method to quantify the correlation in antimicrobial resistance across populations, for the conventionally unnoticed mean shift of the susceptible bacteria. With the proposed Bayesian latent class mixture model with censoring and multivariate normal hierarchy, we address several challenges associated with analyzing the minimum inhibitory concentration data.

Results

Application of this approach to the surveillance data from National Antimicrobial Resistance Monitoring System led to a detection of positive correlation in the central tendency of azithromycin resistance of the susceptible populations from Salmonella serotype Typhimurium across food animal and human populations.

Conclusions

Our proposed approach has been shown to be accurate and superior to the commonly used naïve estimation by simulation studies. Further implementation of this Bayesian model could serve as a useful tool to indicate the co-existence of antimicrobial resistance, and potentially a need of clinical intervention.

High rates of Salmonella contamination in raw kibbe from commercial establishments: predominance of Salmonella Give

Salmonella is one of the major causes of gastroenteritis worldwide in both humans and animals and one of the main agents involved in foodborne disease outbreaks. In this study, 70 raw kibbe samples from different commercial establishments were analyzed for Salmonella spp. The isolates were seroyped and tested for susceptibility to antimicrobial agents. Pulsed-field Gel Electrophoresis was carried out following the standard protocol of the PulseNet network. Fifteen (21.4%) samples were contaminated with Salmonella and S. Give was the prevalent serotype (46.7%). Similarity of 96.3% was observed among the S. Give isolates (n = 7), which indicates the possible spread of the same clone in the analyzed commercial establishments. S. Rissen and S. Typhimurium showed antimicrobial resistance. The detection of a significant percentage of contamination in raw kibbe and of the resistant strains indicates the risk that the consumption of this dish may represent.

RETRACTED ARTICLE: Molecular detection of pathogenic Escherichia coli strains and their antibiogram associated with risk factors from diarrheic calves in Jimma Ethiopia

Diarrheagenic Escherichia coli are a number of pathogenic E. coli strains that cause diarrheal infection both in animal and human hosts due to their virulence factors. A cross sectional study was conducted between November, 2016 and April, 2017 to isolate and molecularly detect pathogenic E. coli from diarrheic calves to determine the pathogenic strains, antibiogram and associated risk factors in Jimma town. Purposive sampling technique was used to collect 112 fecal samples from diarrheic calves. Conventional culture and biochemical methods were conducted to isolate E. coli isolates. Molecular method was followed to identify virulence factors of pathogenic E. coli strains. Antimicrobial sensitivity patterns of the isolates were tested using the Kirby-Bauer disk diffusion method. A structured questionnaire was also used to collect information from dairy farms and socio-demographic data. The overall isolation rate of E. coli in calves was 51.8% (58/112) (95% CI 42.0-61.0). The occurrence of the bacterium differed significantly by age, colostrum feeding time, amount of milk given per time and navel treatment (P < 0.05). Multivariable analysis revealed that the odds of being infected was significantly highest in calves which fed 1-1.5 L amount of milk per a time (OR 5.38, 95% CI 1.66-17.45, P = 0.005). The overall virulence genes detection rate was 53.5% (95% CI 40.0-67.0). Eleven (19.6%) of eaeA, 6 (10.7%) of Stx1 and 13 (23.2%) of Stx2 genes were detected from calves isolates. Except ciprofloxacillin, all isolates were resistant to at least one drug. Multi drug resistance was recorded in 68.0% (38/56) of calves isolates. Neomycin, 83.3% (25/30), followed by amoxicillin, 53.3% (16/30) were the highest resisted virulence genes. The study demonstrated considerable isolation rate, multiple antimicrobial resistant isolates and high resistant virulent genes in diarrheic calves. It also indicated that the potential importance of calves as source of pathogenic E. coli strains and resistant genes for human diarrhea infection. Improving the hygienic practice of farms and wise use of antimicrobials could help to reduce the occurrence of pathogenic E. coli in farms. Hence, further studies are needed to describe all virulent factors and serotypes associated with the emergence of drug resistant pathogenic E. coli strains in calves.

A Study on the Antimicrobial and Antibiofilm Peptide 1018-K6 as Potential Alternative to Antibiotics against Food-Pathogen Salmonella enterica

Antimicrobial resistance has become one of the major global public health concerns, and it is indispensable to search for alternatives to conventional antibiotics. Recently, antimicrobial peptides have received great attention because of their broad-spectrum antimicrobial activity at relatively low concentrations, even against pathogens such as Salmonella enterica, which is responsible for most food-borne illnesses. This work aimed at evaluating the antimicrobial and antibiofilm activity of the innate defense peptide, named 1018-K6, against S. enterica. A total of 42 strains, belonging to three different subspecies and 32 serotypes, were included in this study. The antibiotic resistance profile of all the strains and the cytotoxic effects of 1018-K6 on mammalian fibroblast cells were also investigated. Results revealed that MIC (minimum inhibitory concentrations) and MBC (minimum bactericidal concentrations) values were in the ranges of 8-64 μg/mL and 16-128 μg/mL, respectively, although most strains (97%) showed MICs between 16 and 32 μg/mL. Moreover, sub-inhibitory concentrations of 1018-K6 strongly reduced the biofilm formation in several S. enterica strains, whatever the initial inoculum size. Our results demonstrated that 1018-K6 is able to control and manage S. enterica growth with a large potential for applications in the fields of active packaging and water disinfectants.

Virulence and Antimicrobial Resistance Profiles of Salmonella enterica Serovars Isolated from Chicken at Wet Markets in Dhaka, Bangladesh

Virulent and multi drug resistant (MDR) Salmonellaenterica is a foremost cause of foodborne diseases and had serious public health concern globally. The present study was undertaken to identify the pathogenicity and antimicrobial resistance (AMR) profiles of Salmonellaenterica serovars recovered from chicken at wet markets in Dhaka, Bangladesh. A total of 870 cecal contents of broiler, sonali, and native chickens were collected from 29 wet markets. The overall prevalence of S. Typhimurium, S. Enteritidis, and untyped Salmonella spp., were found to be 3.67%, 0.57%, and 1.95% respectively. All isolates were screened by polymerase chain reaction (PCR) for eight virulence genes, namely invA, agfA, IpfA, hilA, sivH, sefA, sopE, and spvC. S. Enteritidis isolates carried all virulence genes whilst S. Typhimurium isolates carried six virulence genes except sefA and spvC. A diverse phenotypic and genotypic AMR pattern was found. Harmonic descending trends of resistance patterns were observed among the broiler, sonali, and native chickens. Interestingly, virulent and MDR Salmonella enterica serovars were found in native chicken, although antimicrobials were not used in their production cycle. The research findings anticipate that virulent and MDR Salmonella enterica are roaming in the wet markets which can easily anchor to the vendor, consumers, and in the food chain.

Prevalence, Antimicrobial Resistance, and Molecular Characterization of Salmonella in Cattle, Beef, and Diarrheic Patients in Bishoftu, Ethiopia

Within Ethiopia, there is a lack of information on the genetic relatedness of Salmonella from cattle, beef, and diarrheic patients and its potential transmission from cattle to humans through consumption of contaminated beef. The objective of this study was to assess the prevalence and determine the serotypes, genetic relatedness, and antimicrobial resistance of Salmonella in cattle in two local slaughterhouses, in beef at retail shops, and in diarrheic patients in the only hospital in Bishoftu, Ethiopia. Salmonella was detected in 2.5% (6/240) of cattle samples, in 8.7% (11/127) of beef samples, and in 2.3% (5/216) of the diarrheic patients. Four Salmonella serotypes: Salmonella Typhimurium, Salmonella Eastbourne, Salmonella Saintpaul, and Salmonella Cotham were identified. Salmonella Typhimurium and Salmonella Eastbourne were isolated from cattle and beef, whereas Salmonella Saintpaul and Salmonella Cotham were isolated only from diarrheic patients. Except for serotype Salmonella Saintpaul, all isolates were grouped into five pulsotypes, of which two pulsotypes contained isolates from cattle and beef. Isolates from humans represented unique pulsotypes. Among the 22 Salmonella isolates tested, 95.5% were resistant to at least 1 of the 14 antimicrobials tested. Three Salmonella isolates originating from cattle were multidrug resistant. One human isolate was susceptible to all antimicrobials tested. More specifically, resistance to ampicillin, sulfamethoxazole, tetracycline, tigecycline, and trimethoprim were observed. The most frequently observed resistance was to sulfamethoxazole (90.9%, 20/22) followed by trimethoprim (22.7%, 5/22). The study revealed considerable Salmonella contamination of beef at retail shops, antimicrobial resistance to commonly used antimicrobials, and shared genetically similar Salmonella serotypes between cattle and beef; the link with humans could not be established. Still, the findings of Salmonella in cattle and beef, the propensity of transfer of Salmonella from cattle to beef coupled with the common consumption of raw/undercooked beef are likely to pose public health risk in Ethiopia.

Bacteriophage as an alternative to prevent reptile-associated Salmonella transmission

Salmonellosis is a major global public health issue; its most common infection, gastroenteritis, accounts for approximately 90 million illnesses and 150,000 mortalities per year. Eradicating salmonellosis requires surveillance, prevention and treatment, entailing large expenditures. However, it is difficult to control Salmonella transmission because it occurs via multiple routes; exotic reptiles are a reservoir of Salmonella and comprise one such route. As the popularity of exotic pets and animal exhibition has increased, human encounters with reptiles have also increased. As a result, reptile-associated salmonellosis (RAS) has been recognized as an emerging disease. The development of antimicrobial resistance in RAS-causing Salmonella sp. requires alternatives to antibiotics. In this study, bacteriophages have been established as an alternative to antibiotics because only target bacteria are lysed; thus, they are promising biocontrol agents. Here, bacteriophage pSal-SNUABM-02, which infects and lyses reptile Salmonella isolates, was isolated and characterized. The morphology, host range, growth traits and stability of the phage were investigated. The phage was assigned to Myoviridae and was stable in the following conditions: pH 5-9, 4-37°C, and ultravioletA/ultravioletB (UVA/UVB) exposure. Salmonella clearance efficacy was tested using planktonic cell lysis activity and biofilm degradation on polystyrene 96-well plates and reptile skin fragments. The phage exhibited vigorous lysis activity against planktonic cells. In in vitro biofilm degradation tests on reptile skin and polystyrene plates, both low- and high-concentration phage treatments lowered bacterial cell viability by approximately 2.5-3 log colony-forming units and also decreased biomass. Thus, bacteriophages are a promising alternative to antibiotics for the prevention and eradication of RAS.

Absence of high priority critically important antimicrobial resistance in Salmonella sp. isolated from Australian commercial egg layer environments

The development of antimicrobial resistance in foodborne pathogens is a growing public health concern. This study was undertaken to determine the antimicrobial susceptibility of Salmonella enterica subspecies enterica isolated from the Australian commercial egg layer industry. S. enterica subspecies enterica (n=307) isolated from Australian commercial layer flock environments (2015-2018) were obtained from reference, research and State Government laboratories from six Australian states. All Salmonella isolates were serotyped. Antimicrobial susceptibility testing (AST) for 16 antimicrobial agents was performed by broth microdilution. Antimicrobial resistance genes and sequence types (STs) were identified in significant isolates by whole genome sequencing (WGS). Three main serotypes were detected, S. Typhimurium (n=61, 19.9%), S. Senftenburg (n=45, 14.7%) and S. Agona (n=37, 12.1%). AST showed 293/307 (95.4%) isolates were susceptible to all tested antimicrobial agents and all isolates were susceptible to amoxicillin-clavulanate, azithromycin, ceftiofur, ceftriaxone, ciprofloxacin, colistin, florfenicol, gentamicin, kanamycin and trimethoprim-sulfamethoxazole. Low levels of non-susceptibility were observed to streptomycin (2.3%, n=7), sulfisoxazole (2.0%, n=6), chloramphenicol (1.3%, n=4) and tetracycline (1.0%, n=3). Very low levels of non-susceptibility were observed to ampicillin (2/307; 0.7%) and cefoxitin (2/307; 0.7%). Two isolates (S. Havana and S. Montevideo), exhibited multidrug-resistant phenotypes to streptomycin, sulfisoxazole and tetracycline and possessed corresponding antimicrobial resistance genes (aadA4, aac(6')-Iaa, sul1, tetB). One S. Typhimurium isolate was resistant to ampicillin and tetracycline, and possessed both tetA and bla_TEM-1B. WGS also identified these isolates as belonging to ST4 (S. Montevideo), ST578 (S. Havana) and ST19 (S. Typhimurium). The absence of resistance to highest priority critically important antimicrobials as well as the extremely low level of AMR generally among Australian commercial egg layer Salmonella isolates likely reflect Australia's conservative antimicrobial registration policy in food-producing animals and low rates of antimicrobial use within the industry.

Biofilm Production Potential of Salmonella Serovars Isolated from Chickens in North West Province, South Africa

Bacterial biofilms have recently gained considerable interest in the food production and medical industries due to their ability to resist destruction by disinfectants and other antimicrobials. Biofilms are extracellular polymer matrices that may enhance the survival of pathogens even when exposed to environmental stress. The effect of incubation temperatures (25°C, 37°C, and 40°C) and Salmonella serotype on biofilm-forming potentials was evaluated. Previously typed Salmonella serotypes (55) isolated from the gut of chickens were accessed for biofilms formation using a standard assay. Salmonella Typhimurium ATCC 14028TM and Salmonella Enteritidis ATCC 13076TM (positive controls), Escherichia coli (internal control) and un-inoculated Luria Bertani (LB) broth (negative control) were used. The isolates formed no biofilm (11.86-13.56%), weak (11.86-45.76%), moderate (18.64-20.34%), strong biofilms (23.73-54.24%) across the various temperatures investigated. Serotypes, Salmonella Heidelberg and Salmonella Weltevreden were the strongest biofilm formers at temperatures (25°C, 37°C, and 40°C, respectively). The potential of a large proportion (80%) of Salmonella serotypes to form biofilms increased with increasing incubation temperatures but decreased at 40°C. Findings indicate that average temperature favours biofilm formation by Salmonella serotypes. However, the influence of incubation temperature on biofilm formation was greater when compared to serotype. A positive correlation exists between Salmonella biofilm formed at 25°C, 37°C and 40°C (p ≥ 0.01). The ability of Salmonella species to form biofilms at 25°C and 37°C suggests that these serotypes may present severe challenges to food-processing and hospital facilities.

Multidrug Resistance and Virulence Profiles of Salmonella Isolated from Swine Lymph Nodes

Salmonella spp. is a foodborne pathogen present in the pork production chain, leading to potential contamination of end products and causing salmonellosis cases and outbreaks worldwide. The emergence of multidrug-resistant (MDR) Salmonella spp., especially isolates obtained from animal origin food, is a global concern. This study aimed to isolate Salmonella from swine mesenteric lymph nodes (MLN) and to characterize the virulence and antibiotic resistance profiles. MLN samples were obtained from a swine slaughterhouse and subjected to Salmonella spp. isolation. Ten MLN samples were positive and 29 isolates were identified based on PCR (invA and ompC) and serotyping: Derby, Cerro, and Give. Pulsed-field gel electrophoresis allowed to group the isolates based on their serotypes, resulting in three major clusters. All isolates presented the virulence-related genes pefA, sipA, sopB, spaN, and pagC. Relatively high numbers of Salmonella spp. were resistant to neomycin, polymyxin B, ciprofloxacin, tetracycline, and nalidixic acid. Furthermore, 25 isolates presented simultaneous resistance to three or more antibiotic classes, being characterized as MDR. The obtained results confirmed the relevance of swine as reservoirs of Salmonella spp. in the pork production chain and demonstrated the MDR profiles of isolates. Proper control and surveillance are required to avoid the contamination of end products.

Non-Typhoidal Salmonella at the Human-Food-of-Animal-Origin Interface in Australia

Non-typhoidal Salmonella is a major zoonotic pathogen that plays a significant role in foodborne human salmonellosis worldwide through the consumption of contaminated foods, particularly those of animal origin. Despite a considerable reduction in human salmonellosis outbreaks in developed countries, Australia is experiencing a continuous rise of such outbreaks in humans. This review of the literature highlights the reported non-typhoidal Salmonella outbreaks in humans as well as the occurrence of the pathogen in foods from animal sources throughout Australia. Non-typhoidal Salmonella infections from food animals are more often associated with at-risk people, such as immunocompromised and aged people or children. Although several animal-sourced foods were recognised as the catalysts for salmonellosis outbreaks in Australia, egg and egg-based products remained the most implicated foods in the reported outbreaks. This review further highlights the antimicrobial resistance trends of non-typhoidal Salmonella isolates at the human-food interface, with a focus on clinically important antimicrobials in humans, by collating evidence from previous investigations in Australia. The rise in antimicrobial-resistant Salmonella, especially to antimicrobials commonly prescribed to treat human salmonellosis, has become a significant global public health concern. However, the overall prevalence of antimicrobial resistance in Australia is considerably lower than in other parts of the world, particularly in terms of critically important antimicrobials for the treatment of human salmonellosis. The present review adds to our understanding of the global epidemiology of non-typhoidal Salmonella with emphasis on the past few decades in Australia.

Prevalence and antimicrobial resistance of retail-meat-borne Salmonella in southern China during the years 2009-2016: The diversity of contamination and the resistance evolution of multidrug-resistant isolates

Salmonella, one of the most important foodborne pathogens, can be the cause of bacterial food-borne illness and is commonly associated with the consumption of retail meat. Multidrug-resistant Salmonella isolates with high adaptability, have been responsible for many foodborne disease outbreaks. Here we present an investigation on the contamination and the antimicrobial resistance of Salmonella in retail meat obtained from supermarkets and from open markets in Guangxi, China. From the years 2009 to 2016, a total of 604 Salmonella isolates were recovered from a total of 3340 meat samples including 797 beef, 911 pork, 942 chicken and 690 duck, representing 18.08% of the samples tested. Pork was the most contaminated meat. Salmonella was detected in 322 samples from supermarkets and the positive rate of 21.03% was higher than that of 15.70% in 284 samples from open markets (P<0.05). The prevalence of Salmonella in retail meat in the summer and fall months: June (2015, 40.63%), October (2012, 34.6%; 2016, 43.75%) was higher than in other seasons of the year. One hundred and twenty-seven serotypes were identified among the 604 Salmonella enterica isolates, and S. Derby (28.48%), S. Agona (9.77%), S. London (4.97%) and S. Enteritidis (4.47%) were the most common serotypes. Tests of susceptibility to 21 antimicrobial agents showed that 87.58% of the isolates were resistant to at least one antimicrobial, and 57.79% exhibited multidrug resistance (MDR), as they were resistant to at least three antimicrobials. The presence of most of the antimicrobial-resistant genes tested was consistent with the resistant phenotypes found. Among all the antimicrobial resistant genes (ARGs) examined in this study, bla_TEM-1, aadA1, cmlA, tetA, sul1 and sul2 were the most prevalent resistant genes in the multidrug resistant isolates. Our findings show that there was a trend that the Salmonella contamination in retail meat had increased and isolates showed an MDR phenotype and that the MDR had become more and more serious. Twenty-one isolates of S. Agona were randomly analyzed by using the enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) and six different types were found, indicating the existence of cross-contamination in the food market. The results indicate that the hazard analysis of the critical control points (HACCP) system for the whole food chain of retail meat should be further analyzed and improved.

Prevalence and antimicrobial susceptibility of Salmonella in the commercial eggs in China

Salmonellosis is a challenge to public health globally, and many infections have been principally linked to the consumption of contaminated eggs. The objective of this study is to estimate the prevalence of Salmonella in commercial eggs and susceptibilities of isolates to a panel of 14 antimicrobial agents which were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. A total of 33,288 eggs (5548 pooled samples of six eggs) were collected across China in 2016 and the prevalence of Salmonella was 0.5% (27/5548). The most predominant serotype was S. enteritidis. No significant differences were observed on the basis of the egg component tested, shell condition, packaging type, sampling site or sampling season. However, there were significant differences among provincial regions. About 64.3% (n = 18) isolates were resistant to nalidixic acid, followed by ampicillin (39.3%) and ampicillin/sulbactam (39.3%). All isolates were susceptible to ceftazidime, cefalothin, ciprofloxacin, cefepime, cefotaxime, imipenem and meropenem. Three Salmonella isolates exhibited resistance to multiple antibiotics. This study provides valuable baseline data of the occurrence of Salmonella in eggs, which will be used for risk assessments of possible human foodborne infections associated with the consumption of contaminated eggs.

Occurrence, quantification, pulse types, and antimicrobial susceptibility of Salmonella sp. isolated from chicken meat in the state of Paraná, Brazil

The aim of this work was to verify the occurrence, quantification, pulse types, and antimicrobial susceptibility profiles of Salmonella sp. isolated from chicken meat produced and marketed in the state of Paraná, considered to be the state with the highest production of poultry meat in Brazil. Ninety-five of 300 (31.5%) frozen cuts of chicken were found to contain Salmonella sp., and 98 different isolates of Salmonella sp. were cultured from the positive samples. Quantification showed low Salmonella sp. loading, ranging from 0.12 to 6.4 MPN/g. The antimicrobial resistance test was performed against 16 agents from 6 different classes. All isolates were sensitive to meropenem, imipenem, chloramphenicol, and amikacin. The highest resistance rates were observed for nalidixic acid (95%), tetracycline (94%), doxycycline (94%), ampicillin (87%), amoxicillin with clavulanic acid (84%), ceftriaxone (79%), and ciprofloxacin (76%). A total of 84 (85.7%) of the isolates were identified with a multidrug resistant profile, 13 of which were found to have encoding genes extended-spectrum beta-lactamase (ESBL), especially blaCTX-M-2 e blaTEM-1. The major serovars identified were S. Typhimurium (43%) and S. Heidelberg (39%). The third most isolated serovar was S. Ndolo (6%), without previous reports of its presence in poultry meat in Brazil. Molecular characterization of S. Typhimurium and S. Heidelberg isolates by pulsed field gel electrophoresis (PFGE) showed a clonal relationship between all isolates of the same serovar (genetic similarity greater than 80%). Isolates of S. Typhimurium and S. Heidelberg with 100% similarity were found in up to five different geographic regions of the state, showing the potential for the spread of this pathogen in the Paraná poultry chain. Epidemiological surveys like this are important to understand the dynamics of dissemination and to monitor the prevalence of pathogens in the final products of poultry chains. In addition, to know the resistance profile of strains of Salmonella sp. present in food that contributes to the adoption of faster and more effective therapeutic measures, when necessary.

In vitro and in vivo efficacy study of cefepime, doripenem, tigecycline, and tetracycline against extended-spectrum beta-lactamases Escherichia coli in chickens

BACKGROUND AND AIM

At present, there are no data about the efficacy of some recent antibiotics on Escherichia coli in broiler chickens in the study area. This study was designed to evaluate the in vitro and in vivo efficacy of cefepime, doripenem, tigecycline, and tetracycline against multidrug-resistant-extended-spectrum beta-lactamases (MDR-ESBLs) producing E. coli in broiler chicks.

MATERIALS AND METHODS

A total of 34 MDR-ESBLs E. coli isolates were used in this study. In vitro evaluation of the antibacterial efficacy of cefepime, doripenem, tigecycline, and tetracycline were performed using disk diffusion and minimum inhibitory concentration (MIC) assays. In vivo evaluation of the efficacy of the antibiotics was perfumed using 180, 2-week-old chicks challenged with MDR-ESBL-producing E. coli strain O78. Chicks were divided into six groups (30 chicks each) according to the treatment regimen. Treatment was administered to chicks in Groups 3-6 intravenously, twice per day for 1 week using one antibiotic per group at concentration 10 times the determined MIC. Chicks in the positive control (Group 1) were challenged and received 0.2 ml of sterile Tryptone Soy Broth (TSB), while those in the negative control (Group 2) were not challenged and received 0.2 ml of sterile TSB. The severity of clinical signs, gross lesions, and mortality rate was scored and compared between groups.

RESULTS

All E. coli isolates were sensitive to doripenem and tigecycline, while 88% were sensitive to cefepime and only 23% were sensitive to tetracycline. In vivo antibiotic efficacy evaluation in challenged chicks revealed a significant reduction in the severity of clinical signs, gross lesions, and mortality (3%) in chicks treated with cefepime compared to non-treated chicks (55%). There was no significant effect on the severity of clinical signs, gross lesions, and mortality in chicks treated with doripenem, tigecycline, and tetracycline compared to non-treated chicks. The mortality rates of chicks treated with doripenem, tigecycline, and tetracycline were 57%, 50%, and 90%, respectively.

CONCLUSION

The results of this study indicate that most MDR-ESBLs producing E. coli isolates were sensitive to doripenem, tigecycline, and cefepime. However, in vivo study indicated that only cefepime was effective and resulted in a significant reduction in clinical signs, gross lesions, and mortality in infected chicks. Therefore, cefepime could be used to treat naturally infected chickens with MDR-ESBLs producing strains of E. coli.

Characteristics of virulence, resistance and genetic diversity of strains of Salmonella Infantis isolated from broiler chicken in Brazil

ABSTRACT: Salmonella Infantis is frequently associated with human infections worldwide and is transmitted by consumption of contaminated foods, particularly those of animal origin, especially the chicken meat. We aimed to evaluate virulence characteristics, antimicrobial resistance and the genetic similarity of 51 strains of S. Infantis isolated from samples of poultry origin. The strains were isolated from 2009 to 2010 in a company with full cycle of broiler’s production in the state of São Paulo, Brazil. The antimicrobial susceptibility test was performed and, by PCR, we evaluated the presence of the genes lpfA (hem-adhesion), agfA (hem-biofilm) and sefA (hem-adhesion) and resistance genes to beta-lactams (blaTEM, blaSHV, bla CTX-M and blaAmpC ). The phylogenetic relationship was determined by RAPD-PCR method. Among the drugs tested, the highest percentages of resistance were to amoxicillin (35.3%) and to sulfonamide (15.7%). Eleven antimicrobial resistance patterns were identified (A1 to A11), none of them presented a multiresistance profile (> 3 antimicrobials classes). There was 100% of positivity for the agfA gene, 92.2% for the lpfA gene, and no strain presented the sefA gene. Most of the isolates showed similarities in virulence potential, since they were simultaneously positive for two studied genes, agfA and lpfA (92.2%, 47/51). Of the 18 (35.3%) strains resistant to antimicrobials of the β-lactam class, 10 (55.5%) were positive to blaAmpC gene, five (27.8%) for blaCTX-M , two (11.1%) to blaSHV and no strain presented the blaTEM gene. The phylogenetic evaluation has shown the presence of five clusters (A, B, C, D and E) with similarity greater than 80%, and three distinct strains which were not grouped in any cluster. Cluster B grouped 33 strains, all positive for lpfA and agfA genes, from both, the broiler farming facility and the slaughterhouse, persistent throughout all the study period. This cluster also grouped 18 strains clones with genetic similarity greater than 99%, all isolated in the slaughterhouse. The presence of virulence genes associated with persistent strains clones for a long period, warns to the possibility of S. Infantis to form biofilm, and should be constantly monitored in broilers’ production chain, in order to know the profile of the strains that may contaminate the final product and evaluate the hazards that represents to public health.

Genotypic characterization and antimicrobial resistance profile of Salmonella isolated from chicken, pork and the environment at abattoirs and supermarkets in Chongqing, China

Background

Salmonella is one of the most important foodborne pathogens, causing outbreaks of human salmonellosis worldwide. Owing to large scales of consumption markets, pork and poultry that contaminated by Salmonella could pose a tremendous threat to public health. The aim of this study was to investigate the contamination of Salmonella from chicken, pork and the environment in slaughtering and retail processes in Chongqing, China.

Results

A total of 115 Salmonella isolates were recovered from 1112 samples collected from pork, chicken and the environment. Compared with the isolation rate of samples from chicken (9.50%) and the environment (6.23%), samples from pork had a significant higher isolation rate (44.00%). The isolation rates in slaughterhouses (10.76%) and in supermarkets (10.07%) showed no statistical difference. Thirty different serotypes were identified among all the isolates. S. Derby (n = 26), S. London (n = 16) and S. Rissen (n = 12) were the dominant serotypes. Antimicrobial susceptibility testing revealed that 73.04% isolates were resistant to tetracycline, followed by 66.96% to ampicillin and 59.13% to doxycycline. More than half (50.43%) of the isolates were multidrug resistant (MDR), and most of the MDR isolates were from supermarkets. Multilocus sequence typing results showed 24 out of 115 isolates were ST40, which was the most prevalent. Furthermore, isolates from supermarkets had 20 different sequence types while isolates from slaughterhouses only had 8 different sequence types.

Conclusion

Our study highlighted that Salmonella was more frequently isolated in pork production chain than that in chicken. Compared with isolates from slaughterhouses, isolates from supermarkets had more MDR profiles and represented a wider range of serotypes and sequence types, indicating that the retail process had more diverse sources of Salmonella contamination than that of slaughtering process.

Antibiogram, virulotyping and genetic diversity of Escherichia coli and Salmonella serovars isolated from diarrheic calves and calf handlers

Antimicrobial resistance profile of E. coli and Salmonella serovars isolated from diarrheic calves and handlers in Egypt is unknown due to the absence of monitoring. Therefore, this study aimed to determine the virulence, genetic and antimicrobial resistance profiles of E. coli and Salmonella serovars associated with diarrhea in calves and handlers in intensive dairy farms in Egypt. A total of 36 bacterial strains (20 E. coli and 16 Salmonella) were isolated from fecal samples of 80 diarrheic Holstein dairy calves (10 E. coli and 13 Salmonella) and hand swabs of 35 handlers (10 E. coli and 3 Salmonella) in two intensive dairy farms in Sharkia Governate in Egypt. E. coli strains belonged to six different serogroups and O114:K90 was the most prevalent serogroup (30%). However, Salmonella strains were serotyped into four different serogroups and S. Kiel was the most prevalent serotype (50%). Thirteen (65%) E. coli isolates were harbouring either stx2, eaeA and/or astA virulence-associated genes. However, stn and spvC virulence genes were detected in 2 (12.5%) and 4 (25%) of Salmonella isolates, respectively. E. coli isolates showed marked resistance to ampicillin (75%), while Salmonella strains exhibited high resistance to amikacin (100%), gentamicin (93.75%) and tobramycin (87.5%). Results of the present study showed that E. coli and Salmonella serovars isolated from diarrheic calves and handlers in intensive dairy farms in Egypt exhibited resistance to multiple classes of antimicrobials, which may pose a public health hazard. Thus, the continuous monitoring of antimicrobial resistance is necessary for both humans and veterinary medicine to decrease the economic losses caused by antimicrobial-resistant strains in animals as well as the zoonotic risk.

Incidence and Characterization of Salmonella Isolates From Raw Meat Products Sold at Small Markets in Hubei Province, China

Salmonella is a leading cause of foodborne disease and is often associated with the consumption of foods of animal origin. In this study, sixty-six Salmonella isolates were obtained from 631 raw meat samples purchased at small retail suppliers in Hubei Province, China. The most prevalent Salmonella serotypes were Thompson (18.2%) and Agona (13.6%). Frequent antimicrobial resistance was observed for the sulfonamides (43.9%), tetracycline (43.9%), and the β-lactams amoxicillin and ampicillin (36.4% for each). Interestingly, a high incidence of resistance to cephazolin was observed in strains of the most common serotype, S. Thompson. Class I integrons were found in 27.3% (18/66) of the isolates and five of these integrons contained different gene cassettes (aacA4C-arr-3-dfr2, dfrA12-aadA21, aadA2, dfrA12-aadA2, dfr17-aadA5). Additional antimicrobial resistance genes, including bla _TEM-1, bla _CTX-M-65, bla _CTX-M-15, qnrB, and qnrS, were also identified among these Salmonella isolates. Results of replicon typing and conjugation experiments revealed that an integron with qnrB and bla _CTX-M-15 genes was present on incH12 mobile plasmid in S. Thompson strain. Multilocus sequence typing (MLST) analysis revealed 32 sequence types, indicating that these isolates were phenotypically and genetically diverse, among which ST26 (18.2%) and ST541 (12.1%) were the predominant sequence types. The integrons, along with multiple antimicrobial resistance genes on mobile plasmids, are likely contributors to the dissemination of multidrug resistance in Salmonella.

Salmonella Panama: Genetic Diversity of the Isolates Collected from Human and Non-human Sources

INTRODUCTION

Salmonella enterica serovar Panama belongs to the D1 serogroup and is frequently associated with nontyphoidal salmonellosis in humans. This study aimed to characterize isolates collected from Northeast Brazil by phenotypic and molecular methods.

METHODS

Forty four S. Panama strains were examined for antimicrobial susceptibility, virulence genes, and pulsed field gel electrophoresis (PFGE) types.

RESULTS

All strains were susceptible to antibiotics (except for streptomycin), presented classical virulence factors, and could be clustered into four groups and 18 pulsotypes.

CONCLUSIONS

This work calls for continuous surveillance for the emergence of antibiotic resistance and new clones in a geographical area.

Comparative evaluation of structure and characteristic of peptidyl-prolyl cis-trans isomerase proteins and their function in Salmonella Typhimurium stress responses and virulence

Peptidyl-prolyl cis-trans isomerases (PPIase) exhibit chaperone activity and assist in protein folding by increasing the rate of cis-trans transition on proline-peptide bonds. The current study aimed to identify and characterize three genes, ppiA, ppiB, and ppiC, which encode proteins of the PPIase family in the bacterium Salmonella enterica serovar Typhimurium. Salmonella Typhimurium is a facultative intracellular zoonotic pathogen that causes food- and water-borne gastroenteritis in humans (leading to bacteremia in immune-compromised subjects). Recombinant clones for the three genes were constructed and sequenced and the sequences submitted to NCBI GenBank. Three-dimensional structures for the corresponding proteins were predicted by comparative modeling. A maximum-likelihood phylogenetic gene tree constructed for the three genes showed a low evolutionary mean diversity, indicating strong evolutionary conservation. Further, single-gene deletion mutant strains, generated for the respective genes, were observed to be more susceptible to the stationary phase of growth and heat stress conditions and showed reduced survival within macrophage cells line. The present study thus indicates that ppiA, ppiB, and ppiC genes are conserved among Salmonella genome, are critical for the growth of Salmonella Typhimurium in the examined stress conditions, and may play a role in its responses and virulence.

Childhood Diarrhoea in the Eastern Mediterranean Region with Special Emphasis on Non-Typhoidal Salmonella at the Human⁻Food Interface

Diarrhoeal disease is still one of the most challenging issues for health in many countries across the Eastern Mediterranean region (EMR), with infectious diarrhoea being an important cause of morbidity and mortality, especially in children under five years of age. However, the understanding of the aetiological spectrum and the burden of enteric pathogens involved in diarrhoeal disease in the EMR is incomplete. Non-typhoidal Salmonella (NTS), the focus of this review, is one of the most frequently reported bacterial aetiologies in diarrhoeal disease in the EMR. Strains of NTS with resistance to antimicrobial drugs are increasingly reported in both developed and developing countries. In the EMR, it is now widely accepted that many such resistant strains are zoonotic in origin and acquire their resistance in the food-animal host before onward transmission to humans through the food chain. Here, we review epidemiological and microbiological aspects of diarrhoeal diseases among children in the EMR, with emphasis on the implication and burden of NTS. We collate evidence from studies across the EMR on the zoonotic exposure and antimicrobial resistance in NTS at the interface between human and foods of animal origin. This review adds to our understanding of the global epidemiology of Salmonella with emphasis on the current situation in the EMR.

A review of Salmonella enterica with particular focus on the pathogenicity and virulence factors, host specificity and antimicrobial resistance including multidrug resistance

Salmonella genus represents the most common foodborne pathogens frequently isolated from food-producing animals that is responsible for zoonotic infections in humans and animal species including birds. Thus, Salmonella infections represent a major concern to public health, animals, and food industry worldwide. Salmonella enterica represents the most pathogenic specie and includes > 2600 serovars characterized thus far. Salmonella can be transmitted to humans along the farm-to-fork continuum, commonly through contaminated foods of animal origin, namely poultry and poultry-related products (eggs), pork, fish etc. Some Salmonella serovars are restricted to one specific host commonly referred to as "host-restricted" whereas others have broad host spectrum known as "host-adapted" serovars. For Salmonella to colonize its hosts through invading, attaching, and bypassing the host's intestinal defense mechanisms such as the gastric acid, many virulence markers and determinants have been demonstrated to play crucial role in its pathogenesis; and these factors included flagella, capsule, plasmids, adhesion systems, and type 3 secretion systems encoded on the Salmonella pathogenicity island (SPI)-1 and SPI-2, and other SPIs. The epidemiologically important non-typhoidal Salmonella (NTS) serovars linked with a high burden of foodborne Salmonella outbreaks in humans worldwide included Typhimurium, Enteritidis, Heidelberg, and Newport. The increased number of NTS cases reported through surveillance in recent years from the United States, Europe and low- and middle-income countries of the world suggested that the control programs targeted at reducing the contamination of food animals along the food chain have largely not been successful. Furthermore, the emergence of several clones of Salmonella resistant to multiple antimicrobials worldwide underscores a significant food safety hazard. In this review, we discussed on the historical background, nomenclature and taxonomy, morphological features, physical and biochemical characteristics of NTS with a particular focus on the pathogenicity and virulence factors, host specificity, transmission, and antimicrobial resistance including multidrug resistance and its surveillance.

Risk Characterization of Antibiotic Resistance in Bacteria Isolated from Backyard, Organic, and Regular Commercial Eggs

This study was conducted to assess the risk due to antimicrobial-resistant strains of Salmonella spp., Listeria monocytogenes, and Escherichia coli isolated from the eggshell and the contents of eggs bought in markets in Valencia (Spain). Thirty-four samples from three different production styles were analyzed: standard ( n = 34), organic ( n = 16), and backyard ( n = 10) eggs. L. monocytogenes was not isolated in any style of production. Only one strain of Salmonella was isolated from standard production, which was resistant to ciprofloxacin and amoxicillin. E. coli strains were resistant in 22% of the isolates from organic production, 12.25% from standard production, and 11.23% from backyard production. In all cases, the highest resistance was observed for amoxicillin-clavulanate. None of the isolates from standard and backyard eggs were resistant to chloramphenicol, ciprofloxacin, gentamycin, and streptomycin, while only ceftriaxone was found to be effective against all E. coli isolates from organic eggs. β-Lactamase genes bla_TEM , bla_SHV, and bla_CMY-2 and the resistance genes for tetracycline tetA, tetB, and tetC were tested. The most commonly detected antimicrobial resistance genes among the E. coli isolates were tetA (49.30%), bla_TEM (47.89%), and tetB (36.62%). Overall, a maximum public health risk is associated with β-lactam antibiotics.

Salmonella Typhimurium and Salmonella Enteritidis Infections in Sporadic Diarrhea in Children: Source Tracing and Resistance to Third-Generation Cephalosporins and Ciprofloxacin

OBJECTIVES

This study aimed to trace the transmission source of Salmonella enterica serovar Typhimurium and Salmonella enterica serovar Enteritidis strains associated with enteric infections in Shanghainese children, and understand the molecular mechanism of resistance to third-generation cephalosporins and ciprofloxacin.

MATERIALS AND METHODS

The profiles of pulsed-field gel electrophoresis (PFGE) were compared among the isolates from children, animal, and environment. Antimicrobial susceptibility was determined using the minimal inhibitory concentrations and Kirby-Bauer disk diffusion method. Extended-spectrum β-lactamase (ESBL) producing isolates mediated by resistance genes were identified using polymerase chain reaction and sequencing.

RESULTS

Based on PFGE patterns, 49 (33.1%) of 148 human Salmonella Typhimurium isolates located in the dominant PFGE clusters were genetically related to the isolates from poultry source, environment water, aquatic products, and reptiles, whereas 97 (97.0%) of 100 human Salmonella Enteritidis isolates were genetically related to isolates from poultry and water. The rates of resistance to ceftriaxone among clinical Salmonella Typhimurium and Salmonella Enteritidis isolates were 42.0% and 14.2%, respectively. Besides, 35.1% of Salmonella Typhimurium isolates displayed resistance to ciprofloxacin; 64.9% of Salmonella Typhimurium isolates and 97.0% of Salmonella Enteritidis isolates displayed reduced susceptibility to ciprofloxacin. Of 64 ESBL/AmpC-producing strains, CTX-M, TEM, DHA, and CMY were detected at frequencies of 86.0%, 62.5%, 7.8%, 3.1%, and 3.1%, respectively.

CONCLUSIONS

The transmission sources of Salmonella Typhimurium and Salmonella Enteritidis infections in Shanghainese children were diverse. The high prevalence of resistance to third-generation cephalosporins and ciprofloxacin mediated by multiple molecular mechanisms needs continuous monitoring and intervention.

Characterization of Antimicrobial Resistant (AMR) Salmonella Enterica Isolates Associated With Cattle at Harvest in Mexico

Despite being the target of control efforts for many decades, Salmonella enterica continues to be linked with a large amount of foodborne illnesses and outbreaks worldwide. Over the years, Salmonella isolated from meat products have exhibited a high level of antibiotic resistance. In this study, a total of 351 Salmonella isolates, recovered from cattle fecal samples (n = 31), hides (n = 105), and beef carcasses (n = 215) from 3 abattoirs in Mexico were analyzed for antimicrobial susceptibility. Resistance to at least one antimicrobial drug was found in 205 (58.4%) isolates and 20 different resistance phenotypes were observed among this Salmonella isolates set. Resistance to tetracycline (40.2%) and nalidixic acid (21.1%) was most commonly observed. Additionally, the most common multidrug-resistant (MDR) phenotypes shared resistance to chloramphenicol, streptomycin, tetracycline, and trimethopin/sulfamethoxazole (11.3%), resistance to ampicillin, tetracycline, and trimethopin/sulfamethoxazole (3.4%), and resistance to ampicillin, streptomycin, and tetracycline (2.5%). When it came to antimicrobial resistance phenotypes in each abattoir, we determined there was no statistical difference in the frequency of resistant vs. susceptible Salmonella isolates among the three abattoirs (P > 0.05). These data indicate that Salmonella isolates recovered from beef cattle in Mexico are commonly resistant to antimicrobials and often multiple antimicrobials. In Mexico, antimicrobial resistance, and in particular, multidrug-resistance, maybe of particular concern due to the much higher prevalence of Salmonella in retail beef. This may lead to the spread of resistance and to the reduction of antibiotic efficacy for the control of animal and human infections. Promoting control measures and inspection standards on imported animals and food products should be applied to avoid the spread of antibiotic resistance in various populations and among countries.

Analyses of prevalence and molecular typing reveal the spread of antimicrobial-resistant Salmonella infection across two breeder chicken farms

In this study, Salmonella prevalence and antimicrobial resistance were evaluated at various production stages in 2 geographically separated breeder farms (referred to as G and F). Day-old chicks for the breeder flock at farm F were purchased from farm G. A total of 219 Salmonella isolates, all identified as Salmonella enterica subsp. enterica serovar Enteritidis, were recovered from 1,430 samples (sick chicken carcasses and/or dead embryos). The isolation rates at breeder farms G and F were 10.53% (56/532) and 18.15% (163/898), respectively. Resistance to 4-6 antimicrobial agents was the most frequent phenotype during the laying stage at both farms, suggesting that chicks are exposed to higher risk of antimicrobial-resistant Salmonella infection during this stage of the breeding process. Using clustered regularly interspaced short palindromic repeat (CRISPR) typing, 5 CRISPR patterns were identified, out of which one pattern was shared by the 2 farms. In addition, pulsed-field gel electrophoresis (PFGE) typing result indicated that 2 clusters (PF-1 and PF-2) were shared among the 2 breeder farms, suggesting that strains were transmitted from breeder farm G to farm F via the trade of day-old chicks. Our findings suggested that the trade of day-old breeder chicks could be one of the potential Salmonella transmission routes, and antibiotics should be administered with caution during the laying stage.