Distribution of serotypes and genotypes of Salmonella enterica species in French pig production

Virulence and antimicrobial resistance factors in Salmonella enterica serotypes isolated from pigs and chickens in central Chile

Salmonella enterica is a food-borne pathogen with a wide host-range that during decades has been of public health concern in developed and developing countries. In Chile, the poultry and pig industries represent the biggest contribution of meat consumption in the population, and sanitary regulations have been imposed for Salmonella control. The aim of this work was to determine and characterize Salmonella strains isolated from pigs and chicken raised on commercials farms in Chile. For this, isolates belonging to pigs (n = 46) and poultry (n = 57) were genotyped by two multiplex PCR reactions and virulotyped by the PCR detection of virulence-associated genes. In addition, isolates were serotyped and analyzed by the Kirby Bauer assay to determine their antimicrobial resistance phenotypes. From these analyses 52 genotypes, six serotypes and several multidrug resistance phenotypes and different combinations of virulence-associated genes were detected. These results suggest that S. enterica in pigs and poultry in central Chile should be monitored due to potential consequences in public and animal health.

Salmonella Infection in Nursery Piglets and Its Role in the Spread of Salmonellosis to Further Production Periods

Few studies have focused on assessing Salmonella infection in the nursery and its role in further pig production periods. Mesenteric lymph nodes, intestinal content, and meat juice from 389 6-week-old male piglets intended for human consumption from five breeding farms and 191 pooled floor fecal samples from gilt development units (GDU) from the same farms were analyzed to estimate and characterize (by pulsed-field gel electrophoresis and antimicrobial resistance analyses) Salmonella infection. The prevalence of infection and shedding among piglets was 36.5% and 37.3%, respectively, shedding being significantly associated with infection (Odds Ratio = 12.7; CI 7.3-22.0). Salmonella Rissen; S. 4,[⁵],12:i:-; and S. Derby were the most common serotypes. A low level of Salmonella-specific maternal antibodies at the beginning of the nursery period suggested it was a period of high risk of infection. Resistance to 3rd- and 4th-generation cephalosporins was detected in piglet isolates although the piglets never received antibiotics, indicating they could be vectors of antimicrobial resistance. The same Salmonella clones were detected in piglet and GDU isolates, suggesting that infected piglets play a significant role in the infection of gilts and consequently of finishing pigs in the case of production farms. The control of Salmonella infection in nursery piglets may decrease the risk of abattoir and carcass contamination.

Characterization of Salmonella spp. Isolates from Swine: Virulence and Antimicrobial Resistance

Simple Summary

Salmonella is a pathogenic bacterium able to infect both humans and animals. It is diffused worldwide and, generally, animals are a source of infection for humans. Among domestic animals, swine represents an important reservoir and a frequent source of human infection, especially in some countries like Italy. To acquire information on Salmonella, in particular about epidemiology, but also virulence, pathogenesis and antimicrobial resistance, is the basis for a cohesive control program. This manuscript describes an investigation conducted on Salmonella isolates from swine, where two important characteristics were evaluated: the pathogenicity and the antimicrobial resistance. A great variability was observed among investigated strains. Salmonella serovar Typhimurium was confirmed as one of the most virulent serovars; indeed, most isolates belonging to this serovar presented many of the searched virulence factors. A high level of antimicrobial resistance was observed for some compounds (sulfonamide, tetracycline, streptomycin and ampicillin), but not for the so-called “last line antibiotics”, such as, for example, ciprofloxacin. The constant monitoring on circulating strains in reservoir animals is important to acquire information and set up adequate prophylaxis measures.

Abstract

Salmonella is one of the most important zoonotic pathogens worldwide. Swine represent typical reservoirs of this bacterium and a frequent source of human infection. Some intrinsic traits make some serovars or strains more virulent than others. Twenty-nine Salmonella spp. isolated from pigs belonging to 16 different serovars were analyzed for gastric acid environment resistance, presence of virulence genes (mgtC, rhuM, pipB, sopB, spvRBC, gipA, sodCI, sopE), antimicrobial resistance and presence of antimicrobial resistance genes (bla_TEM, bla_PSE-1, aadA1, aadA2, aphA1-lab, strA-strB, tetA, tetB, tetC, tetG, sul1, sul2, sul3). A percentage of 44.83% of strains showed constitutive and inducible gastric acid resistance, whereas 37.93% of strains became resistant only after induction. The genes sopB, pipB and mgtC were the most often detected, with 79.31%, 48.28% and 37.93% of positive strains, respectively. Salmonella virulence plasmid genes were detected in a S. enterica sup. houtenae ser. 40:z₄,z₂₃:-strain. Fifteen different virulence profiles were identified: one isolate (ser. Typhimurium) was positive for 6 genes, and 6 isolates (3 ser. Typhimurium, 2 ser. Typhimurium monophasic variant and 1 ser. Choleraesuis) scored positive for 5 genes. None of the isolates resulted resistant to cefotaxime and ciprofloxacin, while all isolates were susceptible to ceftazidime, colistin and gentamycin. Many strains were resistant to sulfonamide (75.86%), tetracycline (51.72%), streptomycin (48.28%) and ampicillin (31.03%). Twenty different resisto-types were identified. Six strains (4 ser. Typhimurium, 1 ser. Derby and 1 ser. Typhimurium monophasic variant) showed the ASSuT profile. Most detected resistance genes sul2 (34.48%), tetA (27.58%) and strA-strB (27.58%). Great variability was observed in analyzed strains. S. ser. Typhimurium was confirmed as one of the most virulent serovars. This study underlines that swine could be a reservoir and source of pathogenic Salmonella strains.

Experimental infection of pigs by Salmonella Derby, S. Typhimurium and monophasic variant of S. Typhimurium: Comparison of colonization and serology

Salmonella serovars Derby, Typhimurium and the monophasic variant of Salmonella Typhimurium are the most frequently isolated serovars in pigs in France. To compare the excretion patterns, seroconversion to Salmonella and contamination of the organs of pigs inoculated with strains of all three serovars, we conducted an experimental trial with 28 SPF piglets. Four were used as a negative control, while the other 24 were divided equally into three groups. Each group was inoculated at 7 weeks of age with a different strain: S. Derby (SDb), S. Typhimurium (ST), and the monophasic variant of S. Typhimurium (mST). Fecal and blood samples were collected twice a week up until necropsy, on 21 days post-inoculation (DPI) for half of each group and 49 DPI for the remaining piglets. During necropsy, the tonsils, mesenteric lymph nodes and various intestinal contents were collected from each pig. Salmonella bacteria were quantified in CFU/g by a bacteriological method, and levels of Salmonella antibodies were measured using an ELISA Kit. Piglets inoculated with mST continuously excreted Salmonella in their feces throughout the trial. For each of the other serovars, one piglet was Salmonella-negative on one DPI. The quantity of Salmonella excreted was statistically different between the group inoculated with ST and mST (p < 0.05), but no differences were found between the other serovars. The tonsils, cecum and jejunum were the most contaminated organs in all groups. Seroconversion for all the piglets was completed by different DPI: 28 for ST, 31 for mST and 38 for SDb. No major differences were found in terms of excretion and colonization among the studied serovars.

Salmonella in the pork production chain and its impact on human health in the European Union

Salmonella spp. comprise the second most common food-borne pathogens in the European Union (EU). The role of pigs as carriers of Salmonella has been intensively studied both on farm and at slaughter. Salmonella infection in pigs may cause fever, diarrhoea, prostration and mortality. However, most infected pigs remain healthy carriers, and those infected at the end of the fattening period could pose a threat to human health. Contamination of pig carcasses can occur on the slaughter line, and it is linked to cross-contamination from other carcasses and the presence of Salmonella in the environment. Therefore, Salmonella serovars present on pig carcasses can be different from those detected in the same bathes on the farm. In recent years, S. Typhimurium, S. Derby and S. serotype 4,[5],12:i:- (a monophasic variant of S. Typhimurium) have been the most common serovars to be detected in pigs in EU countries, but S. Rissen, S. Infantis, S. Enteritidis and S. Brandenburg have also been reported. In humans, several cases of salmonellosis have been linked to the consumption of raw or undercooked pork and pork products. Among the main serovars of porcine origin detected in confirmed human cases, S. Typhimurium, the monophasic variant S. 4,[5],12:i:- and S. Derby are certainly the most important.

Phenotypic and Genotypic Diversity of Salmonella in Finishing Swine

Salmonella enterica (nontyphoidal) is one of the major causes of foodborne diseases in the United States and worldwide. Molecular typing methods are significant tools used to better understand the transmission and ecology of Salmonella in order to implement pre-harvest control measures. The objectives of this study were to describe the Salmonella genotypes, the distribution of isolate subtypes from different ecological niches (i.e., barn environment, nursery, and individual pigs) and their evolution over time in a longitudinal study conducted in three finishing sites (housing pigs from 10 weeks of age until slaughter at 24-26 weeks of age). Among the 107 Salmonella isolates submitted for pulsed-field gel electrophoresis (PFGE) analysis, there were 25 distinct subtypes. PFGE genotyping results were consistent with the serotype findings. A large number of distinguishable PFGE patterns (i.e., within the same serovar) were observed and different combinations of subtypes were identified within and across sites and cohorts. New subtypes may result of the introduction of new strains, genetic changes, or ongoing transmission of evolved strains within the production system. The same subtypes were detected intermittently during the study period, which suggests the persistence of indistinguishable subtypes in this production system. In addition, this study suggests persistence of the same subtype over several cohorts of pigs and potential residual contamination from the barn. Factors affecting adaptation and transmission of Salmonella within and among ecological systems (e.g., finishing pigs, nursery, and environment) should be further investigated. Understanding genotypic diversity of Salmonella in different ecological niches during pre-harvest may contribute to the development of more targeted and cost effective control programs during nursery and finishing phases.

Antibiotic resistance pattern and gene expression of non-typhoid Salmonella in riversheds

In this study, antibiotic resistance and major phenol and genotypes of non-typhoid Salmonella spp. from riversheds in Taiwan were examined. In 236 water samples tested, 54 (22.9%) contained Salmonella spp. Fifteen Salmonella serovars were identified from the Salmonella isolates, and some common serovars are associated with infections of human and livestock, including Albany (27.8%), Newport (14.8%), Bareilly (13.0%), Derby (11.1%), and Typhimurium (7.4%). Various environmental factors may also affect the presence and proportion of different serovars in the receiving waters. In contrast, serovars with narrower range of hosts, e.g., Dublin, were rarely detected. The Salmonella isolates were subjected to eight antibiotics for drug resistance, and 51.9% of the samples were resistant to at least one tested antibiotics. Tetracycline and sulfadiazine were the two most ineffective antibiotics against the Salmonella isolates, and the results were indicative of long-term antibiotics abuse as fodder supplements in animal husbandry. The more commonly detected serovars such as Albany, Derby, and Typhimurium were also more likely to be resistant to multiple antibiotics. Finally, a significant correlation was observed between resistance to chloramphenicol and the resistance gene cmlA, suggesting that the resistance genotypes could persist in the environment even long after prohibition of the drug use. The high prevalence of antibiotic-resistant Salmonella spp. infers elevated infection risks that must be further examined.

Wild griffon vultures (Gyps fulvus) as a source of Salmonella and Campylobacter in Eastern Spain

The existence of Campylobacter and Salmonella reservoirs in wildlife is a potential hazard to animal and human health; however, the prevalence of these species is largely unknown. Until now, only a few studies have evaluated the presence of Campylobacter and Salmonella in wild griffon vultures and based on a small number of birds. The aim of this study was to evaluate the presence of Campylobacter and Salmonella in wild griffon vultures (n = 97) during the normal ringing programme at the Cinctorres Observatory in Eastern Spain. In addition, the effect of ages of individuals (juveniles, subadult and adult) on the presence were compared. Campylobacter was isolated from 1 of 97 (1.0%) griffon vultures and identified as C. jejuni. Salmonella was isolated from 51 of 97 (52.6%) griffon vultures. No significant differences were found between the ages of individuals for the presence of Salmonella. Serotyping revealed 6 different serovars among two Salmonella enterica subspecies; S. enterica subsp. enterica (n = 49, 96.1%) and S. enterica subsp. salamae (n = 2, 3.9%). No more than one serovar was isolated per individual. The serovars isolated were S. Typhimurium (n = 42, 82.3%), S. Rissen (n = 4, 7.8%), S. Senftenberg (n = 3, 5.9%) and S. 4,12:b[-] (n = 2, 3.9%). Our results imply that wild griffon vultures are a risk factor for Salmonella transmission, but do not seem to be a reservoir for Campylobacter. We therefore rule out vultures as a risk factor for human campylobacteriosis. Nevertheless, further studies should be undertaken in other countries to confirm these results.