Derby Isolates Research Articles

Population genomics of emerging multidrug-resistant Salmonella derby from pork and human in Guangdong, China

Salmonella is a foodborne pathogen that poses a severe public health threat. Salmonella enterica serovar Derby (S. Derby) is one of the top five serovars isolated from humans and animals, and it carries the potential risk of transmission to humans through consumption of pork and related products. This study isolated 98 S. Derby, mainly from pork, and clinical samples in Guangdong to investigate and compare their molecular characteristics, phylogenetic relationships, transmission routes, antimicrobial resistance phenotypes, genotypes, and virulence profiles. Whole-genome sequencing (WGS) revealed that all S. Derby isolates belonged to ST40 and displayed a relatively large core genome. Phylogenomic analysis indicated the possibility of clonal transmission of S. Derby not only between pork and humans but also across geographic areas in Guangdong over an extended period of time. Discriminant analysis of principal components (DAPC) model showed that a significant proportion of S. Derby isolates retrieved from multiple hosts originated from pork. Furthermore, similar antimicrobial resistance phenotypes and genotypes were found in S. Derby strains recovered from animal products and humans. All S. Derby isolates were found to contain numerous virulence genes, primarily related to fimbrial adherence determinants and secretion system components. This study offers valuable insights into the transmission routes of S. Derby between pork and humans and provides essential data for public health management.

Genomic typing and virulence gene profile analysis of Salmonella Derby from different sources

Salmonella enterica serovar Derby (S. Derby) is one of the most common Salmonella serovars which can infect poultry, swine, and humans. With the reduction of the sequencing cost and the improvement of sequencing technology, whole genome sequencing (WGS) has become an important method for bacterial determination, molecular investigation, and pathogenic tracing analysis. In this study, we investigated S. Derby isolates from different sources in China using in-silico multilocus sequence typing (MLST), core genome MLST (cgMLST) and whole genome MLST (wgMLST) analysis based on WGS. The results showed that 21 S. Derby strains were divided into 3 STs using MLST analysis, including ST40 (n = 19, accounting for 90.48%), ST71 (n = 1, accounting for 4.76%) and ST8016 (n = 1, accounting for 4.76%). cgMLST and wgMLST analysis categorized the tested strains into 13 cgSTs and 21 wgSTs, respectively. The minimum spanning trees of cgMLST and wgMLST both divided these strains into 3 clusters and 4 singletons. In addition, virulence gene profiles of S. Derby isolates were also analyzed, and a total of 174 virulence genes belonged to 8 categories were identified. In summary, we studied genomic typing, phylogenetic relationship and virulence gene profiles of S. Derby strains from different sources in China. These findings were beneficial for the epidemiology and pathogenesis of Salmonella.

Population dynamics and antimicrobial resistance of Salmonella Derby ST40 from Shenzhen, China.

Salmonella enterica subsp. enterica serovar Derby (S. Derby) is one of the most common serotypes responsible for salmonellosis in humans and animals. The two main sequence types (ST) observed in China are ST40 and ST71, with ST40 presently being the most common in Shenzhen. Recent years have seen an increasing number of cases of salmonella caused by ST40 S. Derby, but the epidemiology is not clear. We gathered 314 ST40 S. Derby isolates from food and patient samples for 11 years in Shenzhen; 76 globally prevalent representative strains were also collected. Whole-genome sequencing (WGS) combined with drug resistance phenotyping was used to examine population structural changes, inter-host associations, drug resistance characteristics, and the food-transmission risks of ST40 S. Derby in Shenzhen over this period. The S. enterica evolutionary tree is divided into five clades, and the strains isolated in Shenzhen were primarily concentrated in Clades 2, 4, and 5, and thus more closely related to strains from Asian (Thailand and Vietnam) than European countries. Our 11-year surveillance of S. Derby in Shenzhen showed that Clades 2, 4, and 5 are now the dominant epidemic branches, and branches 2 and 5 are heavily multi-drug resistant. The main resistance pattern is ampicillin-tetracycline-ciprofloxacin-chloramphenicol-nalidixic acid-streptomycin-sulfamethoxazole/trimethoprim. This may lead to a trend of increasing resistance to ST40 S. Derby in Shenzhen. Using a segmentation of ≤3 SNP among clone clusters, we discovered that Clades 2 and 4 contained multiple clonal clusters of both human- and food-derived strains. The food-derived strains were mainly isolated from pig liver, suggesting this food has a high risk of causing disease outbreaks in Shenzhen.

Salmonella Derby from pig production chain over a 10-year period: antimicrobial resistance, biofilm formation, and genetic relatedness.

The aim of this study was to evaluate 140 Salmonella Derby isolates collected over a 10-year period from porcine origins (environment, pig carcass, lymph nodes, intestinal content, and pork) for their phenotypic and genotypic antimicrobial resistance, their ability to produce biofilm, and their genetic relatedness. The minimum inhibitory concentration (MIC) was determined using microdilution broth method and antimicrobial resistance genes were investigated by PCR. The quantification of biofilm formation was performed in sterile polystyrene microtiter plates. Genetic relatedness was determined by Xba-I macrorestriction analysis. The highest frequencies of non-wildtype (nWT) populations were observed against tetracycline (75.7%), streptomycin (70%), and colistin (11.4%), whereas wildtype populations were observed against ciprofloxacin, ceftazidime, and gentamicin. The resistance genes found were blaTEM (ampicillin), aadA variant (streptomycin/spectinomycin), tetA (tetracycline), and floR (florfenicol). On 96-well polystyrene microtiter plate, 68.6% of the isolates proved to be biofilm producers. Among 36 S. Derby isolates selected to PFGE analysis, 22 were clustered with 83.6% of similarity. Additionally, 27 isolates were clustered in 11 pulsotypes, which presented more than one strain with 100% of similarity. Most of S. Derby isolates were able to form biofilm and were classified as nWT or resistant to tetracycline, streptomycin, and colistin. PFGE allowed the identification of closely related S. Derby isolates that circulated in pig slaughterhouses and pork derived products along a decade.

Whole-genome sequencing analysis of highly prevalent Salmonella serovars in wild boars from a national park in Sardinia

The study investigated Salmonella prevalence in slaughtered wild boars from Asinara island National Park in Sardinia (Italy). Salmonella isolates were serotyped and the antimicrobial resistance profile was evaluated. Isolates were furthermore characterized with Whole Genome Sequencing. Additional analysis were performed in order to evaluate the microbial hygiene of wild boars carcasses. A total of 306 samples were tested for Salmonella presence, of which n. 270 were from n. 90 slaughtered wild boars and n. 36 were from slaughterhouse environment. Salmonella was detected in 32/90 (35.6%) colon content and 16/90 (17.8%) mesenteric lymph nodes samples. The overall prevalence of Salmonella carriers wild boars, either in colon content and/or lymph nodes, was 42/90 (46.7%) but only one animal was found positive at carcass level. Prevalence was not influenced ( P > 0.05) by the age and the gender of the animals. Eight different Salmonella serotypes were identified between 50 isolates, with the most common ones being Abony and Newport. The sequence analysis showed that S. Abony and S. Newport strains clustered separately from public genomes. This finding refects the origin of the animals from the geographical closed environment of Asinara island. Moreover, sequence analysis showed high similarity between strains belonging to the same serovar. S . Derby and S . Agona strains exhibited phenotypic resistance to fosfomycin and harboured the fosA7 gene. The mean aerobic colony count and Enterobacteriaceae values showed a good hygiene level of the carcasses. This study demonstrated that Salmonella enterica is widespread in wild boar population of Asinara island and could play an important role in transmission to humans. The finding of Salmonella strains resistant to fosfomycin is of primary importance as this drug is used as an alternative treatment for infections caused by multi-drug resistant microorganisms. • Salmonella in wild boar play a role in transmission to humans. • High variability of Salmonella serovars. • High similarity of Salmonella serovars with whole genome sequencing. • Extended sensitivity to antimicrobials. • Fosfomycin resistance encoded by the gene fosA 7 in S. Agona and S. Derby isolates.

Genetic Diversity of Salmonella Derby from the Poultry Sector in Europe.

Salmonella Derby (S. Derby) is emerging in Europe as a predominant serovar in fattening turkey flocks. This serovar was recorded as being predominant in the turkey sector in 2014 in the United Kingdom (UK). Only two years later, in 2016, it was also recorded in the turkey and broiler sectors in Ireland and Spain. These S. Derby isolates were characterised as members of the multilocus sequence type (MLST) profile 71 (ST71). For the first time, we characterise by whole genome sequencing (WGS) analysis a panel of 90 S. Derby ST71 genomes to understand the routes of transmission of this emerging pathogen within the poultry/turkey food trade. Selected panel included strains isolated as early as 2010 in five leading European g countries for turkey meat production. Twenty-one of the 90 genomes were extracted from a public database—Enterobase. Five of these originated from the United States (n = 3), China (n = 1) and Taiwan (n = 1) isolated between 1986 and 2016. A phylogenomic analysis at the core-genome level revealed the presence of three groups. The largest group contained 97.5% of the European strains and included both, turkey and human isolates that were genetically related by an average of 35 ± 15 single nucleotide polymorphism substitutions (SNPs). To illustrate the diversity, the presence of antimicrobial resistance genes and phages were characteised in 30, S. Derby ST71 genomes, including 11 belonging to this study This study revealed an emergent turkey-related S. Derby ST71 clone circulating in at least five European countries (the UK, Germany, Poland, Italy, and France) since 2010 that causes human gastroenteritis. A matter of concern is the identification of a gyrA mutation involved in resistance to quinolone, present in the Italian genomes. Interestingly, the diversity of phages seems to be related to the geographic origins. These results constitute a baseline for following the spread of this emerging pathogen and identifying appropriate monitoring and prevention measures.

Characterization of ciprofloxacin-resistant and ESBL-producing Salmonella enteric serotype Derby in Eastern China

BackgroundFluoroquinolone resistance and ESBL-production are concurrently found in a limited number of Salmonella serotypes. The present study was aimed to characterize fluoroquinolone-resistant and ESBL-producing Salmonella enteric serotype Derby (S. Derby) isolates in terms of antimicrobial susceptibility, relevant genetic mechanisms, and PFGE.ResultsFrom 2013 to 2017 in Ningbo China, 52 S. Derby isolates were identified out of 826 non-typhoidal Salmonella isolates from patient feces, food, and environmental water samples. Three S. derby isolates were identified to be fluoroquinolone-resistant and ESBL-producing with cefotaxime MIC of 64 μg/mL and ciprofloxacin MIC of 4 μg/mL. The three isolates contained the same genetic structure of quinolone resistance, including a silent gyrA mutation S (TCC) 83S (TCT) and three PMQR genes qnrB, qnrS and aac(6′)-Ib-cr. As withβ-lactams resistance mechanisms, two isolates contained blaTEM, blaOXA, and blaCTX-M genes and one isolate contained blaOXA and blaCTX-M genes. Additionally, two isolates displayed more identical PFGE pattern than the third isolate, whereas three isolates showed the same plasmid profile of I1, W and P by PCR-based replicon typing. The conjugation experiment showed no dissemination of β-lactam resistance by direct contact among isolates; the transformation experiment failed to transfer plasmid conferring ampicillin resistance to E. coli DH5a.ConclusionThe present study demonstrates the emerging fluoroquinolone-resistant and ESBL-producing S. Derby in both humans and the environment. Seeing that S. Derby has become one of the most common Salmonella serotypes, this situation gives rise to a new major risk of food-borne diseases.

Diversity of Salmonella isolates and their distribution in a pig slaughterhouse in Huaian, China

In order to ascertain the contamination status of Salmonella from carcass, equipment, environment and the intestinal contents in a pig slaughterhouse in Huaian, China, we investigated the prevalence and characteristics of Salmonella isolates in one slaughterhouse. A total of 636 samples were collected; Salmonella was laboratory-confirmed from 154/441 (34.9%) carcass swab-samples, 13/57 (22.8%) pieces of equipment, 30/86 (34.9%) environmental samples and the intestinal contents of 19/52 (36.5%) animals. Salmonella was found to be at its highest and lowest frequency during splitting (55.9%) and flaming (17.2%) processes, respectively. All Salmonella isolates were characterized by serotyping, multilocus sequence typing (MLST) and 69 S. Derby isolates were analyzed using pulsed-field gel electrophoresis (PFGE). Four serovars (S. Derby, S. Rissen, S. Typhimurium, and S. London) were shared from the four sources and predominant serovars were S. Derby and S. Rissen. MLST results indicated that ten different STs were distinguished, of which ST40 was identified as the most prominent ST. Moreover, ST40, ST469, ST34 and ST155 comprised Salmonella isolates obtained from carcass, equipment, the slaughterhouse environment and intestinal contents. PFGE results showed that 33 pulsotypes (PF1-PF33) were identified. PF21, PF25 and PF29 suggested that many isolates from carcass-swab samples at different slaughterhouse process points were of the same pulsotype which also partly comprised isolates from equipment, the environment and intestinal contents. The present study provides an insight into Salmonella distribution in a pig slaughterhouse and revealed that cross-contamination occurs frequently at different sites, which provides data support for proposing some interventions to control Salmonella.

Salmonella isolated from the slaughterhouses and correlation with pork contamination in free market

This study surveyed the distribution, antimicrobial susceptibility profiles and serotype of Salmonella isolated from three slaughterhouses, and performed molecular typing on these isolates, to understand the relationship between strains of Salmonella obtained from the pork production chain in Yangzhou, China. Samples from slaughtered pigs and the slaughtering environment were collected from three slaughterhouses in Yangzhou, Jiangsu province, from October 2012 to July 2013. The positive identification rates of Salmonella in slaughtered pigs and the environmental samples were 46.6% and 48.8%, respectively. The prevalence of Salmonella in slaughterhouses were affected by seasonal factors and reached the peak in summer. Among the Salmonella serovars identified, S. Derby was most prevalent in slaughterhouses, but other serovars like S. Typhimurium, S. Meleagridis and S. Anatum were also widespread. Antimicrobial susceptibility testing revealed that 32 and 131 different MDR patterns were found among the strains from the environment and slaughtered pig samples, respectively. Fifty-six isolates of S. Derby and 16 strains of S. Typhimurium were characterized by the technique of pulsed-field gel electrophoresis (PFGE) using the restriction enzyme Xba I. 35 and 11 PFGE patterns were generated among the selected isolates. Four isolates of S. Derby isolates with the same pattern (PF26) were isolated from cooling water, evisceration and carcass, suggesting that cross contamination occurred between the environment and the slaughtered pigs. Six S. Typhimurium in cluster 1 with the same ST type (ST19) came from different parts of the slaughtered pig, which could have occurred because of horizontal transmissions along the slaughtering process. The same PFGE patterns of Salmonella were found in both samples from carcasses in the slaughterhouse and in the Yangzhou pork market, proving that Salmonella had spread from the slaughterhouse to the pork market. In conclusion, our study demonstrate that serious cross contamination occurred in Yangzhou slaughterhouses and can contribute Salmonella contamination in pork sold in the local public market.

SPI-23 of S. Derby: role in adherence and invasion of porcine tissues.

Salmonella enterica serovars Derby and Mbandaka are isolated from different groups of livestock species in the UK. S. Derby is predominantly isolated from pigs and turkeys and S. Mbandaka is predominantly isolated from cattle and chickens. Alignment of the genome sequences of two isolates of each serovar led to the discovery of a new putative Salmonella pathogenicity island, SPI-23, in the chromosome sequence of S. Derby isolates. SPI-23 is 37 kb in length and contains 42 ORFs, ten of which are putative type III effector proteins. In this study we use porcine jejunum derived cell line IPEC-J2 and in vitro organ culture of porcine jejunum and colon, to characterise the association and invasion rates of S. Derby and S. Mbandaka, and tissue tropism of S. Derby respectively. We show that S. Derby invades and associates to an IPEC-J2 monolayer in significantly greater numbers than S. Mbandaka, and that S. Derby preferentially attaches to porcine jejunum over colon explants. We also show that nine genes across SPI-23 are up-regulated to a greater degree in the jejunum compared to the colon explants. Furthermore, we constructed a mutant of the highly up-regulated, pilV-like gene, potR, and find that it produces an excess of surface pili compared to the parent strain which form a strong agglutinating phenotype interfering with association and invasion of IPEC-J2 monolayers. We suggest that potR may play a role in tissue tropism.

Identification and characterization of Salmonella enterica subsp. enterica serovar Derby isolates carrying a new aadA26 gene cassette in a class 1 integron obtained at pig slaughterhouses.

Salmonella enterica subsp. enterica (S.) serovar Derby is one of the most prevalent serovars in pigs. Twenty-seven multiresistant S. Derby isolates, obtained at two pig slaughterhouses in Southern Brazil, were investigated for their molecular relationships, genotypic resistance and presence of class 1 and 2 integrons. All isolates shared the same XbaI-macrorestriction pattern and showed a common resistance genotype with resistance to streptomycin/spectinomycin (aadA variant), sulphonamides (sul1) and tetracycline [tet(A)]. They carried chromosome-located class 1 integrons with a new aadA gene variant, designated aadA26, as part of a gene cassette. The sequence of the flanking regions of this integron and the amplification of the merA gene may indicate the location of the class 1 integron into a Tn21-related transposon. The close relationships among these isolates and isolates from an earlier study suggest the persistence of a resistant clone of S. Derby in the pig production chain in Southern Brazil.

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

The population of Salmonella found at various stages of pig production in France was characterised to analyse the distribution and spread of Salmonella in the pig production chain. We serotyped...

Sero- and genotyping of Salmonella in slaughter pigs, from farm to cutting plant, with a focus on the slaughter process

The objective of this study was to investigate the role of the slaughtering process in Salmonella carcass contamination by typing isolates recovered previously in a double study of the following: (1) a tracking survey from the farm to the slaughterhouse and (2) a survey of the slaughterhouse environment (i.e., lairage area, slaughter line, cutting plant and carcasses).The Salmonella serotypes identified on the carcasses of the 16 tracked batches were frequently linked to lairage, whereas the serotypes detected at the farm, transport or pig-related samples (i.e., caecum content and lymph nodes) were only occasionally detected at the carcass level. Multi-locus variable-number tandem repeats (MLVA) of 77 Salmonella enterica ser. Typhimurium isolates from seven of these batches confirmed the link between the isolates recovered from carcasses and holding pens. Only four of the 16 positive carcasses had profiles previously isolated from lymph nodes or caecal content.In the second part of the study, a total of 131 S. enterica ser. Typhimurium and 74 S. enterica ser. Derby isolates were further characterised by MLVA and Pulsed Field Gel Electrophoresis (PFGE), respectively. The MLVA profiles identified in carcasses varied throughout the working day and were frequently linked to those identified in samples from the slaughter line points collected close in time. PFGE and MLVA profiles identified at lairage were also detected in later processing facilities (i.e., slaughter line and cutting plant) as well as in carcasses. Finally, most of the profiles found at the cutting plants were previously identified in the slaughter line or carcass samples. The results from this study show that Salmonella contamination in pigs entering the slaughterhouse can be attributed to several sources. Typing of isolates by MLVA and PFGE clarified the sources of carcass contamination and improved the accuracy of cross-contamination attributable values. Without obviating the relevant role of infected pigs entering the slaughterhouse, the present study highlights the lairage and slaughtering as important sources of carcass contamination.

First Detection ofoqxABin Salmonella spp. Isolated from Food

Food-borne salmonellosis is an important public health problem worldwide and the second leading cause of food-borne illnesses in Hong Kong. In this study, the prevalence and antimicrobial resistance of Salmonella in meat products in Hong Kong were determined. Interestingly, a plasmid-mediated quinolone resistance (PMQR) gene combination, oqxAB, which mediates resistance to nalidixic acid, chloramphenicol, and olaquindox, was for the first time detectable on the chromosomes of two Salmonella enterica serovar Derby isolates. Further surveillance of oqxAB in Salmonella will be needed.

Prevalence of Integrons in Antibiotic-Resistant <i>Salmonella</i> spp. in Hong Kong

Of the 834 Salmonella spp. isolates collected from 2002 to 2004 in the New Territories East Cluster hospitals in Hong Kong, 21% were resistant to 3-14 antibiotics and 30% were resistant to nalidixic acid with reduced susceptibility to ciprofloxacin. A class 1 integron was present in 105 (13%) isolates, of which more than 50% were Salmonella Typhimurium. Class 2 or 3 integrons were not detected in any of the isolates. DNA sequencing showed that there were 16 different integrons, of which the most common, detected in 40% of isolates, was dfrA12-orfF-aadA2. Almost half of the isolates had lost the qacEΔ1-sulI 3′ conserved segment (3′CS). Four isolates had an orf513 gene downstream of the 3′CS. There was probably one predominant clone among each heterogeneous population of integron-harboring S. Typhimurium, S. Virchow, and S. Derby isolates in our community. This is the first thorough study of the prevalence and characteristics of integrons in Salmonella isolates in Hong Kong and the first to report a class 1 integron in S. Birkenhead, S. Landwasser, S. Litchfield, and S. Reading.

Molecular Fingerprinting of Salmonella enterica subsp. enterica Typhimurium and Salmonella enterica subsp. enterica Derby Isolated from Tropical Seafood in South India

Salmonella enterica subsp. enterica Typhimurium and Salmonella enterica subsp. enterica Derby strains isolated from different seafood were genotyped by PCR-ribotyping and ERIC-PCR assays. This study has ascertained the genetic relatedness among serovars prevalent in tropical seafood. PCR-ribotyping exhibited genetic variation in both Salmonella serovars, and ribotype profile (II) was most predominant, which was observed in 10/18 of Salmonella enterica subsp. enterica Typhimurium and 7/17 Salmonella enterica subsp. enterica Derby isolates. Cluster analysis of ERIC-PCR for Salmonella enterica subsp. enterica Typhimurium strains exhibited nine different banding patterns and four strains showed >95% genetic homology within the cluster pairs. ERIC-PCR produced more genetic variations in Salmonella enterica subsp. enterica Typhimurium; nevertheless, both methods were found to be comparable for Salmonella enterica subsp. enterica Derby isolates. Discrimination index of PCR-ribotyping for Salmonella enterica subsp. enterica Typhimurium isolates was obtained at 0.674 and index value 0.714 was observed for Salmonella enterica subsp. enterica Derby strains. Molecular fingerprinting investigation highlighted the hypothesis of diverse routes of Salmonella contamination in seafood as multiple clones of Salmonella enterica subsp. enterica Typhimurium and Salmonella enterica subsp. enterica Derby were detected in same or different seafood throughout the study period.

Salmonella in slaughter pigs in Northern Ireland: Prevalence and use of statistical modelling to investigate sample and abattoir effects

A cross-sectional survey of pigs at slaughter in Northern Ireland was undertaken to determine the overall prevalence of Salmonella infection. In total 513 pigs were sampled across four abattoirs, with Salmonella spp. isolated from the caecal contents of 31.4% (95% confidence interval [CI] 27.4%–35.4%) and from 40.0% (95% CI 35.8%–44.3%) of swabs taken from the surface of carcasses post-evisceration. Two serovars, S. Typhimurium and S. Derby, were predominant and accounted for 52% and 35% respectively, of isolates from caecal contents. Antimicrobial resistance was most common amongst isolates of S. Typhimurium with 63.9% multiresistant compared to 10.8% of S. Derby isolates and 8.0% of other Salmonella spp. The proportion of pigs showing serological evidence of infection was significantly lower, with 11.5% (95% CI 8.9%–14.6%) and 10.1% (95% CI 7.7%–13.1%) of meat-juice samples giving positive and suspect reactions, respectively. The ratio of caecal positive to serologically positive animals is higher than in a number of other studies and may suggest recent infection, such as infection occurring during transport or lairage, in a proportion of animals. Statistical (logistic regression) modelling was used to investigate the association between the risk of Salmonella on carcasses and the isolation of Salmonella from caecal contents, and/or the serological status of the animal, while adjusting for other possible explanatory and confounding variables such as abattoir, season, day and time of sampling. The occurrence of Salmonella in caecal contents (odds ratio [OR] 2.39; 95% CI 1.52–3.77) or a suspect/positive serological reaction (OR 2.15; 95% CI 1.28–3.61) were both independently associated with the occurrence of Salmonella on carcasses in homebred, but interestingly not in imported animals. In most multivariable models there were also significant differences in carcass contamination between seasons with the highest odds of carcass contamination occurring in the April to June quarter and the lowest in the October to December quarter. Differences between sampling days were also evident with the highest odds of carcass contamination at the end of the week (Fridays) and the lowest at the start of the week (Mondays). These associations, after adjusting for the caecal or serological result, would suggest the occurrence of abattoir effects, such varying residual levels of abattoir contamination, which are independent of the individual pig status.

Phenotypic and genotypic differentiation of porcine Salmonella enterica subsp. enterica serovar Derby isolates

Sixty-two Salmonella enterica subsp. enterica serovar Derby isolates from slaughter pigs and meat products isolated in Southern Brazil were analyzed for their genomic relationships and for the presence of antimicrobial resistance genes. Twenty-four S. Derby isolates were indistinguishable by their subtracted restriction fingerprinting (SRF) pattern, XbaI- and BlnI-macrorestriction patterns, phage type, plasmid profile, and resistance pattern. In contrast to the BlnI-macrorestriction patterns, the XbaI-macrorestriction patterns were in good agreement with the results of SRF analysis and phage typing. Among the four phage types detected, PT10 and PT21 were the most common. The combination of all typing methods revealed a great diversity among the S. Derby isolates. All strains carried plasmids and the 60 resistant isolates showed at least tetracycline resistance. The resistance genes found were sul1 and/or sul2 (sulfonamide resistance), aadA2 (streptomycin/spectinomycin resistance), tet(A) (tetracycline resistance), tet(B) (tetracycline/minocycline resistance), bla TEM (ampicillin resistance), and dfrA14 (trimethoprim resistance). A correlation of the geno- and phenotypic characteristics with the origin of the isolates revealed a substantial temporal variation in the occurrence of specific S. Derby isolates in different independent pig production lines in Southern Brazil. The large number of resistant isolates underlined the potential risk that S. Derby isolates can pose to human health when they enter the food chain.

Identification of an aadA2 Gene Cassette from Salmonella enterica subsp. enterica Serovar Derby

During a study on Salmonella enterica subsp. enterica serovar Derby from slaughter-age pigs in Brazil, two epidemiologically unrelated multi-resistant S. Derby isolates were found to carry a class 1 integron with a single gene cassette. Sequence analysis confirmed that this gene cassette harboured an aadA2 gene. The aadA2 gene codes for an aminoglycoside adenyltransferase, which mediates resistance to the aminoglycoside streptomycin and the aminocyclitol spectinomycin. Although aadA2 gene cassettes are widely distributed among Salmonella, database searches identified an AadA2 protein indistinguishable from that of S. Derby only in single isolates of S. enterica subsp. enterica Enteritidis from France and S. enterica subsp. enterica Typhimurium from Japan. Structural analysis of the 59-base element revealed at least one base pair difference between the 59-base element of the aadA2 cassette from S. Derby and any of the 59-base elements deposited in the databases.

Phenotypic and molecular typing of Salmonella strains reveals different contamination sources in two commercial pig slaughterhouses.

This study aimed to define the origin of Salmonella contamination on swine carcasses and the distribution of Salmonella serotypes in two commercial slaughterhouses during normal activity. Salmonellae were isolated from carcasses, from colons and mesenteric lymph nodes of individual pigs, and from the slaughterhouse environment. All strains were serotyped; Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Derby isolates were additionally typed beyond the serotype level by pulsed-field gel electrophoresis (PFGE) and antibiotic resistance profiling (ARP); and a subset of 31 serotype Typhimurium strains were additionally phage typed. PFGE and ARP had the same discriminative possibility. Phage typing in combination with PFGE could give extra information for some strains. In one slaughterhouse, 21% of the carcasses were contaminated, reflecting a correlation with the delivery of infected pigs. Carcass contamination did not result only from infection of the corresponding pig; only 25% of the positive carcasses were contaminated with the same serotype or genotype found in the corresponding feces or mesenteric lymph nodes. In the other slaughterhouse, 70% of the carcasses were contaminated, and only in 4% was the same genotype or serotype detected as in the feces of the corresponding pigs. The other positive carcasses in both slaughterhouses were contaminated by genotypes present in the feces or lymph nodes of pigs slaughtered earlier that day or from dispersed sources in the environment. In slaughterhouses, complex contamination cycles may be present, resulting in the isolation of many different genotypes circulating in the environment due to the supply of positive animals and in the contamination of carcasses, probably through aerosols.