Aims: To study the antibiogram of 40 seafood isolates of Salmonella and use of PCR to detect the presence of integrons and genes coding for antibiotic resistance. Methods and Results: In this study, ...40 isolates of Salmonella were used for antibiogram analysis. The multidrug‐resistant isolates were analyzed for the presence of integron using integron‐specific primers. Twenty‐five percentage of the isolates were multidrug resistant while 67·50% were resistant to at least two antibiotics. Antibiotic resistance genes catA1 and tetA were present in 57·52 and 60%, respectively. Although widespread presence of genes was observed, only 26·08% of the catA1‐carrying isolates exhibited phenotypic resistance against the respective antibiotic. Integrons present in representative isolates of Salmonella Weltevreden and Salmonella Newport were sequenced. The former contained class 1 integron with a single gene dfrA7 in the integron cassette and an adjacent dihydropteroate synthetase gene along with the usual quaternary ammonium compound resistance gene, while the later contained class 1 integron with dhfrA1, OrfC, in the integron cassette and an adjacent dihydropteroate synthetase gene along with the usual quaternary ammonium compound resistance gene. Conclusions: This study demonstrates the presence of silent antibiotic resistance genes and class I integrons in seafood‐associated Salmonella strains. The study also demonstrates the first report of class I integron in Salm. Weltevreden. Detection of catA1 genes in phenotypically sensitive bacteria suggests that these could be reservoirs in the environment. Significance and Impact of the Study: The manuscript provides novel results describing the existence of a high rate of antibiotic resistance in the Salmonella populations prevailing in environmental sources as well as an absence of correspondence between the presence of antibiotic resistance genes, and the exhibition of a the corresponding phenotypic trait of resistance against the respective antibiotic compound was observed. In addition, the manuscript reports the presence of the class I integron in Salm. Weltevreden.
Salmonella Infantis (S. Infantis) is one of the most frequent Salmonella serovars isolated from human cases of salmonellosis and the most detected serovar from animal and food sources in Europe. The ...serovar is commonly associated with poultry and there is increasing concern over multidrug resistant clones spreading worldwide, as the dominating clones are characterized by presence of large plasmids carrying multiple resistance genes. Increasing the knowledge of the S. Infantis population and evolution is important for understanding and preventing further spread. In this study, we analysed a collection of strains representing different decades, sources and geographic locations. We analysed the population structure and the accessory genome, in particular we identified prophages with a view to understand the role of prophages in relation to the evolution of this serovar.
We sequenced a global collection of 100 S. Infantis strains. A core-genome SNP analysis separated five strains in e-Burst Group (eBG) 297 with a long branch. The remaining strains, all in eBG31, were divided into three lineages that were estimated to have separated approximately 150 years ago. One lineage contained the vast majority of strains. In five of six clusters, no obvious correlation with source or geographical locations was seen. However, one cluster contained mostly strains from human and avian sources, indicating a clone with preference for these sources. The majority of strains within this cluster harboured a pESI-like plasmid with multiple resistance genes. Another lineage contained three genetic clusters with more rarely isolated strains of mainly animal origin, possibly less sampled or less infectious clones. Conserved prophages were identified in all strains, likely representing bacteriophages which integrated into the chromosome of a common ancestor to S. Infantis. We also saw that some prophages were specific to clusters and were probably introduced when the clusters were formed.
This study analysed a global S. Infantis population and described its genetic structure. We hypothesize that the population has evolved in three separate lineages, with one more successfully emerging lineage. We furthermore detected conserved prophages present in the entire population and cluster specific prophages, which probably shaped the population structure.
Non-typhoidal Salmonella enterica serovars, associated with different foods including poultry products, are important causes of bacterial gastroenteritis worldwide. The colonization of the chicken ...gut by S. enterica could result in the contamination of the environment and food chain. The aim of this study was to compare the genomes of 25 S. enterica serovars isolated from broiler chicken farms to assess their intra- and inter-genetic variability, with a focus on virulence and antibiotic resistance characteristics.
The genomes of 25 S. enterica isolates covering five serovars (ten Typhimurium including three monophasic 4,5,12:i:, four Enteritidis, three Hadar, four Heidelberg and four Kentucky) were sequenced. Most serovars were clustered in strongly supported phylogenetic clades, except for isolates of serovar Enteritidis that were scattered throughout the tree. Plasmids of varying sizes were detected in several isolates independently of serovars. Genes associated with the IncF plasmid and the IncI1 plasmid were identified in twelve and four isolates, respectively, while genes associated with the IncQ plasmid were found in one isolate. The presence of numerous genes associated with Salmonella pathogenicity islands (SPIs) was also confirmed. Components of the type III and IV secretion systems (T3SS and T4SS) varied in different isolates, which could explain in part, differences of their pathogenicity in humans and/or persistence in broilers. Conserved clusters of genes in the T3SS were detected that could be used in designing effective strategies (diagnostic, vaccination or treatments) to combat Salmonella. Antibiotic resistance genes (CMY, aadA, ampC, florR, sul1, sulI, tetAB, and srtA) and class I integrons were detected in resistant isolates while all isolates carried multidrug efflux pump systems regardless of their antibiotic susceptibility profile.
This study showed that the predominant Salmonella serovars in broiler chickens harbor genes encoding adhesins, flagellar proteins, T3SS, iron acquisition systems, and antibiotic and metal resistance genes that may explain their pathogenicity, colonization ability and persistence in chicken. The existence of mobile genetic elements indicates that isolates from a given serovar could acquire and transfer genetic material. Conserved genes in the T3SS and T4SS that we have identified are promising candidates for identification of diagnostic, antimicrobial or vaccine targets for the control of Salmonella in broiler chickens.
Avian systemic salmonellosis is primarily caused by Salmonella enterica serovar Gallinarum and serovar Pullorum causing the diseases Fowl Typhoid and Pullorum Disease respectively. During infection ...interaction with the immune system occurs in three main phases. First is invasion via the gastrointestinal tract. Infection with S. Pullorum or S. Gallinarum does not cause substantial inflammation, unlike S. Typhimurium or S. Enteritidis. Through in vitro models it was found that S. Gallinarum does not induce expression of CXC chemokines or pro-inflammatory cytokines such as IL-1β or IL-6, whilst in an in vivo model S. Pullorum infection leads to down-regulation of CXCLi1 and CXCLi2 in the ileum. The absence of flagella in S. Gallinarum and S. Pullorum means they are not recognised by TLR5, which is believed to play a key role in the initiation of inflammatory responses, though other pathogen-factors are likely to be involved. The second phase is establishing systemic infection. Salmonella invade macrophages and probably dendritic cells and are translocated to the spleen and liver, where replication occurs. Salmonella survival is dependent on the Salmonella pathogenicity island 2 type III secretion system, which inhibits antimicrobial activity by preventing fusion of lysosymes with the phagocytic vacuole and by modulation of MHC and cytokine expression. Studies in resistant and susceptible chicken lines have shown that the interaction with macrophages is central to the progression of infection or immunological clearance. Primary macrophages from resistant animals are more efficient in killing Salmonella through respiratory burst and by induction of cytokine expression including the initiation of protective Th1 responses that leads to the third phase. Where replication of Salmonella is not controlled the death of the animal usually results. If the innate immune system is not able to control replication then cellular and humoral responses, primarily mediated through Th1-associated cytokines, are able to clear infection. In S. Pullorum a significant number of animals develop persistent infection of splenic macrophages. Here we show preliminary evidence of modulation of adaptive immunity away from a Th1 response to facilitate the development of the carrier state. In carrier animals persistence may lead to reproductive tract and egg infection associated with a decline in CD4+ T cell numbers and function associated with the onset of sexual maturity in hens.
Pullorum disease, caused by Salmonella enterica serovar Pullorum (S. Pullorum), is one of the most important bacterial infections in the poultry industry in developing countries, including China. To ...examine the prevalence and characteristics of S. Pullorum, the Multilocus Sequence Typing (MLST) genotypes, fluoroquinolones resistance, and biofilm-forming abilities of S. Pullorum isolates were investigated, collected from 2011 to 2016 in China.
Thirty S. Pullorum isolates collected from 2011 to 2016 were analyzed. Quinolones susceptibility testing showed that 90% of the isolates were resistant to the first generation of quinolines nalidixic acid, but the resistance rates to different fluoroquinolones agents were lower than 13.3%; for some there was even no resistance. Multilocus sequence typing (MLST) showed that ST-92 was the dominating genotype, accounting for 90.0% of all S. pullorum strains. The remaining three isolates were of the new reported sequence type ST-2151. Interestingly, the Asp87Gly substitution in quinolone resistance-determining regions (QRDR) of GyrA was only observed in the three strains of ST-2151, suggesting a potential correlation between Asp87Gly substitution and sequence type (p < 0.05). However, Asp87Gly substitution could not confer the resistant to ofloxacin and ciprofloxacin of these isolates. The plasmid-mediated quinolone resistance (PMQR) gene was not found in any of the tested isolates. Furthermore, an assay measuring biofilm-forming abilities showed that 46.7% of the isolates were non-biofilm producers, while 53.3% could form very weak biofilms, which might explain the relatively lower resistance to fluoroquinolones.
We reported a high resistance rate to the first generation of quinolines nalidixic acid and relatively low resistance rates to fluoroquinolones in S. Pullorum isolates. In addition, weak biofilm-forming abilities were found, which might be an important reason of the low fluoroquinolones resistance rates of S. Pullorum isolates. ST-92 was the dominating genotype demonstrated by MLST, and the new sequence type ST-2151 showed a potential correlation with Asp87Gly substitution in QRDR of GyrA. We believe the characterization of these S. Pullorum isolates will be helpful to develop prevention and control strategies.
Escherichia coli O157:H7 and Salmonella enterica are foodborne pathogens with major public health concern in the U.S. These pathogens utilize several virulence factors to initiate infections in ...humans. The antimicrobial effect of seven glucosinolate hydrolysis compounds against Salmonella and E. coli O157:H7 was investigated by the disc diffusion assay. Among the tested compounds, benzyl isothiocyanate (BIT), which exerted the highest antimicrobial activity, was evaluated for its anti-virulence properties against these pathogens. The effect of BIT on motility of Salmonella and E. coli O157:H7 and Shiga toxin production by E. coli O157:H7 was determined by the motility assay and ELISA procedure, respectively. Confocal and transmission electron microscopy (TEM) procedures were used to determine bacterial damage at the cellular level. Results revealed that sub-inhibitory concentrations (SICs) of BIT significantly inhibited the motility of both bacteria (P < 0.05). Shiga toxin production by E. coli O157:H7 was decreased by ~32% in the presence of BIT at SICs. TEM results showed the disruption of outer membrane, release of cytoplasmic contents, and cell lysis following BIT treatment. Results suggest that BIT could be potentially used to attenuate Salmonella and E. coli O157:H7 infections by reducing the virulence factors including bacterial motility and Shiga toxin production.
•BIT is the most effective compound against E. coli O157:H7 and Salmonella.•BIT kills Salmonella by disrupting bacterial cell membrane.•BIT reduces the motility of E. coli O157:H7 and Salmonella.•BIT decreases shiga toxin production by E. coli O157:H7.•BIT could be a potential anti-virulence compound against bacterial infection.
The present study analyzes the characteristics of Salmonella spp. from broiler chicken farms in Brazil. In total, 82 Salmonella spp. strains were characterized by serotyping, determining ...susceptibility to antimicrobials, and using pulsed-field gel electrophoresis (PFGE). Fifteen Salmonella serotypes were identified, among which Minnesota (40.24%), Infantis (14.63%), Heidelberg (7.31%), Senftenberg (6.09%), and Mbandaka (6.09%) were the most frequent. Salmonella Minnesota occurred mostly in the state of Mato Grosso do Sul and in one of the broiler companies surveyed. Approximately 60% of the strains were resistant to at least one of the antimicrobials tested. From these isolates, 17.07% were resistant to only one antimicrobial (tetracycline or streptomycin), and 9.75% were resistant to 3 or more antimicrobial classes. Thirteen resistance profiles were characterized, the most frequent of which were the resistance to tetracycline (15.85%); to the combination of trimethroprim with sulfamethoxazole, and tetracycline (10.97%); and to the combination of streptomycin and tetracycline (9.75%). Multiple correspondence analysis revealed that susceptibility or resistance of the analyzed strains and also particular Salmonella serotypes were associated with broiler-producing companies where the samples were collected. Strains presented high intraserotype genetic variability, as shown by the 64 PFGE profiles, suggesting the existence of several contamination sources in the surveyed farms.
Brazilian poultry meat samples were screened for colistin-resistant Salmonella enterica. Sixty Salmonella isolates were tested for in vitro colistin resistance and mcr-1, mcr-2, mcr-3 and mcr-4 ...genes. Two isolates harbored the mcr-1 gene and whole-genome analysis determined the serovar to be Schwarzengrund, ST96, harboring the IncX4 plasmid. This is the first report of mcr-1-harboring Salmonella enterica serovar Schwarzengrund in Brazil.
•First report of mcr-1-harboring Salmonella enterica serovar Schwarzengrund.•Assessment of commercial poultry meat as reservoir of colistin-resistant Salmonella.•Colistin-resistant Salmonella did not present multidrug resistance phenotype.
Bacterial ribosome requires elongation factor P to translate fragments harbouring consecutive proline codons. Given the abundance of ORFs with potential EF-P regulated sites, EF-P was assumed to be ...constitutively expressed. Here, we report that the intracellular pathogen Salmonella enterica serovar Typhimurium decreases efp mRNA levels during course of infection. We determined that the decrease in efp mRNA is triggered by low levels of charged tRNA super(Pro), a condition that Salmonella experiences when inside a macrophage phagosome. Surprisingly, downregulation of EF-P selectively promotes expression of the virulence mgtC gene and contributes to Salmonella's ability to survive inside macrophages. The decrease in EF-P levels induces ribosome stalling at the consecutive proline codons of the mgtP open reading frame in the mgtCBR leader RNA, and thus allows formation of a stem-loop structure promoting transcription of the mgtC gene. The substitution of proline codons in the mgtP gene eliminates EF-P-mediated mgtC expression and thus Salmonella's survival inside macrophages. Our findings indicate that Salmonella benefits virulence genes by decreasing EF-P levels and inducing the stringent response inside host. Salmonella enterica serovar Typhimurium decreases the levels of elongation factor P during course of infection, which are mediated by low levels of charged tRNA super(Pro). The decrease of EF-P levels is required for selective induction of the mgtC virulence gene and Salmonella's survival inside macrophages. Low levels of EF-P induce ribosome stalling at the consecutive proline codons of the short open reading frame mgtP in the mgtCBR leader, promoting mgtC expression.
We analyzed the prevalence of resistance to extended-spectrum cephalosporins (ESCs) among clinical strains of Salmonella enterica collected by the Laboratory of Clinical Microbiology in the ...University Clinical Hospital Lozano Blesa in the region of Aragón (Spain), for which very few epidemiological information exists. A total of 2,092 strains of S. enterica were identified in stool samples from patients with gastroenteritis. Five isolates showed an extended-spectrum beta-lactamase (ESBL) phenotype: four isolates of S. enterica serotype Virchow harbored the ESBL-encoding bla(CTX-M-9) gene and an isolate of serotype Enteritidis carried a bla(CTX-M-1) gene, which, to the best of our knowledge, is described here for the first time in this serotype of S. enterica. The five ESC-resistant isolates were also resistant to spectinomycin, streptomycin, kanamycin, sulfonamides, tetracycline, and trimethoprim as well as to nalidixic acid. The ESBL isolate of serotype Enteritidis, however, remained susceptible to kanamycin and nalidixic acid. A class 1 integron of 1.5 kb was detected for the four serotype Virchow isolates with the gene cassette dfrA16-aadA2. The bla(CTX-M-9) gene was carried by an ∼300-kb IncHI2 conjugative plasmid in the case of the S. enterica serotype Virchow isolates. The bla(CTX-M-1) gene was carried by an ∼100-kb IncI1-N conjugative plasmid for the serotype Enteritidis ESC-resistant isolate. All the four ESC-resistant strains of S. enterica serotype Virchow clustered together in a XbaI pulsed-field gel electrophoresis, which also revealed a strong similarity between them and some pulsotypes of S. enterica serotype Virchow from France.
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