Detection of multidrug-resistant Salmonella typhimurium DT104 by multiplex polymerase chain reaction

Simultaneous stream assessment of antibiotics, bacteria, antibiotic resistant bacteria, and antibiotic resistance genes in an agricultural region of the United States

Antimicrobial resistance (AMR) is now recognized as a leading global threat to human health. Nevertheless, there currently is a limited understanding of the environment's role in the spread of AMR and antibiotic resistance genes (ARGs). In 2019, the U.S. Geological Survey conducted the first statewide assessment of antibiotic resistant bacteria (ARB) and ARGs in surface water and bed sediment collected from 34 stream locations across Iowa. Environmental samples were analyzed for a suite of 29 antibiotics and plated on selective media for 15 types of bacteria growth; DNA was extracted from culture growth and used in downstream polymerase chain reaction (PCR) assays for the detection of 24 ARGs. ARGs encoding resistance to antibiotics of clinical importance to human health and disease prevention were prioritized as their presence in stream systems has the potential for environmental significance. Total coliforms, Escherichia coli (E. coli), and staphylococci were nearly ubiquitous in both stream water and stream bed sediment samples, with enterococci present in 97 % of water samples, and Salmonella spp. growth present in 94 % and 67 % of water and bed sediment samples. Bacteria enumerations indicate that high bacteria loads are common in Iowa's streams, with 23 (68 %) streams exceeding state guidelines for primary contact for E. coli in recreational waters and 6 (18 %) streams exceeding the secondary contact advisory level. Although antibiotic-resistant E. coli growth was detected from 40 % of water samples, vancomycin-resistant enterococci (VRE) and penicillinase-resistant Staphylococcus aureus (MRSA) colony growth was detected from nearly all water samples. A total of 14 different ARGs were detected from viable bacteria cells from 30 Iowa streams (88 %, n = 34). Study results provide the first baseline understanding of the prevalence of ARB and ARGs throughout Iowa's waterways and health risk potential for humans, wildlife, and livestock using these waterways for drinking, irrigating, or recreating.

Antibacterial and Biofilm Production Inhibition Activity of Thymus vulgaris L. Essential Oil against Salmonella spp. Isolates from Reptiles

Salmonellosis is an infectious disease affecting both animals and humans. Antimicrobial resistant (AMR) and biofilm-producing Salmonella spp., frequently detected in reptiles (who can then act as asymptomatic carriers for warm-blooded animals), have developed resistance to biocides; this represents a warning for the emergence of biocide/antimicrobial cross-resistance. The aim of this study was to evaluate the efficacy of Thymus vulgaris L. essential oil (TEO) in inhibiting bacterial growth and biofilm production of Salmonella spp., which had been isolated from wild reptiles housed in a Zoo in Italy. The resistance profile against different classes of antibiotics showed that all the isolates were susceptible to the tested antibiotics, despite the presence of several AMR genes. All the isolates were also tested with aqueous solutions of TEO at different dilutions (5% to 0.039%). Interestingly, TEO proved effective both in inhibiting bacterial growth at low dilutions, with MIC and MBC values ranging between 0.078% and 0.312%, and in inhibiting biofilm production, with values ranging from 0.039% to 0.156%. TEO demonstrated effective bioactivity against the biofilm producer Salmonella spp., proving to be a valid disinfectant for the prevention of salmonellosis from reptiles, a possible source of infection for humans exposed to the reptiles' environment.

Anti-Biofilms’ Activity of Garlic and Thyme Essential Oils against Salmonella typhimurium

Biofilm control by essential oil (EO) application has recently increased to preclude biofilm production on foods and environmental surfaces. In this work, the anti-biofilm effects of garlic and thyme essential oils using the minimum inhibitory concentration (MIC) method against Salmonella typhimurium recovered from different abattoir samples were investigated along with the virulence genes (InvA, SdiA and Stn genes), and the antimicrobial susceptibility profile of S. typhimurium as well. The obtained results revealed that S. typhimurium contaminated abattoir samples to varying degrees. The InvA gene was investigated in all isolates, whereas the SdiA and Stn genes were observed in four and three isolates, respectively. Utilizing the disc diffusion method, S. typhimurium isolates demonstrated substantial resistance to most of the examined antibiotics with a high multiple antibiotic resistance index. S. typhimurium isolates demonstrated biofilm formation abilities to various degrees at varied temperatures levels (4 °C and 37 °C). In conclusion, the obtained samples from the research area are regarded as a potential S. typhimurium contamination source. Furthermore, garlic essential oil (GEO) has more potential to inhibit S. typhimurium biofilm at different sub-minimum inhibitory concentrations as compared to thyme essential oil (TEO). Therefore, these EOs are considered as potential natural antibacterial options that could be applied in food industry.

Antimicrobial Resistance in Loggerhead Sea Turtles (Caretta caretta): A Comparison between Clinical and Commensal Bacterial Isolates

Simple Summary

Gram negative organisms are frequently isolated from Caretta caretta and may contribute to the dissemination of antimicrobial resistance. In this study, commensal bacteria isolated from oral and cloacal samples of 98 healthy C. caretta were compared to clinical isolates isolated from the wounds of 102 injured animals, in order to investigate the presence of antimicrobial resistance bacteria in free-living loggerheads from the Adriatic Sea. A total of 410 bacteria were cultured and differences were noted in the isolated genera, as some of them were isolated only in healthy animals, while others were isolated only from injured animals. When tested for susceptibility to antimicrobials, clinical isolates showed highly significant differences in the antimicrobial resistance rates vs. commensal isolates for all the drugs tested, except for doxycycline. The detection of high antimicrobial resistance rates in loggerhead sea turtles is of clinical and microbiological significance since it impacts both the choice of a proper antibiotic therapy and the implementation of conservation programs.

Abstract

Gram negative organisms are frequently isolated from Caretta caretta turtles, which can act as reservoir species for resistant microorganisms in the aquatic environment. C. caretta, which have no history of treatment with antimicrobials, are useful sentinel species for resistant microbes. In this culture-based study, commensal bacteria isolated from oral and cloacal samples of 98 healthy C. caretta were compared to clinical isolates from the wounds of 102 injured animals, in order to investigate the presence of AMR bacteria in free-living loggerheads from the Adriatic Sea. A total of 410 isolates were cultured. Escherichia coli and genera such as Serratia, Moraxella, Kluyvera, Salmonella were isolated only in healthy animals, while Acinetobacter, Enterobacter, Klebsiella and Morganella were isolated only from the wounds of the injured animals. When tested for susceptibility to ampicillin, amoxicillin + clavulanic acid, ceftazidime, cefuroxime, gentamicin, doxycycline, ciprofloxacin and enrofloxacin, the clinical isolates showed highly significant differences in AMR rates vs. commensal isolates for all the drugs tested, except for doxycycline. The detection of high AMR rates in loggerheads is of clinical and microbiological significance since it impacts both the choice of a proper antibiotic therapy and the implementation of conservation programs.

Salmonella enterica Subsp. houtenae Associated with an Abscess in Young Roe Deer (Capreolus capreolus)

BACKGROUND

S. enterica subsp. houtenae has been rarely documented, and very limited genomic information is available. This report describes a rare case of primary extraintestinal salmonellosis in a young roe deer, associated with Salmonella enterica subsp. houtenae. Methods: A traditional cultural-based analysis was carried out from the contents of a neck abscess; biochemical identification and PCR assay were performed to isolate and identify the pathogen. Through whole-genome sequencing (WGS), multilocus sequence typing (MLST), core genome MLST (cgMLST), and the Salmonella pathogenicity islands (SPIs) survey, resistome and virulome genes were investigated to gain insight into the virulence and antimicrobial resistance of S. houtenae.

RESULTS

Biochemical identification and PCR confirmed the presence of Salmonella spp. in the swelling. The WGS analysis identified Salmonella enterica subspecies houtenae serovar 43:z4,z23:- and ST 958. The virulence study predicted a multidrug resistance pattern with resistance shown against aminoglycosides, tetracycline, beta-lactamase, fluoroquinolones, fosfomycin, nitroimidazole, aminocoumarin, and peptide. Fifty-three antibiotic-resistant genes were identified. No plasmids were detected.

CONCLUSION

This study demonstrates the importance of continuous surveillance of pathogenic salmonellae. Biomolecular analyses combined with epidemiological data can provide important information about poorly described Salmonella strains and can help to improve animal welfare.

Characterisation of Phage Susceptibility Variation in Salmonellaenterica Serovar Typhimurium DT104 and DT104b

The surge in mortality and morbidity rates caused by multidrug-resistant (MDR) bacteria prompted a renewal of interest in bacteriophages (phages) as clinical therapeutics and natural biocontrol agents. Nevertheless, bacteria and phages are continually under the pressure of the evolutionary phage-host arms race for survival, which is mediated by co-evolving resistance mechanisms. In Anderson phage typing scheme of Salmonella Typhimurium, the epidemiologically related definitive phage types, DT104 and DT104b, display significantly different phage susceptibility profiles. This study aimed to characterise phage resistance mechanisms and genomic differences that may be responsible for the divergent phage reaction patterns in S. Typhimurium DT104 and DT104b using whole genome sequencing (WGS). The analysis of intact prophages, restriction-modification systems (RMS), plasmids and clustered regularly interspaced short palindromic repeats (CRISPRs), as well as CRISPR-associated proteins, revealed no unique genetic determinants that might explain the variation in phage susceptibility among the two phage types. Moreover, analysis of genes coding for potential phage receptors revealed no differences among DT104 and DT104b strains. However, the findings propose the need for experimental assessment of phage-specific receptors on the bacterial cell surface and analysis of bacterial transcriptome using RNA sequencing which will explain the differences in bacterial susceptibility to phages. Using Anderson phage typing scheme of Salmonella Typhimurium for the study of bacteria-phage interaction will help improving our understanding of host-phage interactions which will ultimately lead to the development of phage-based technologies, enabling effective infection control.

Poultry litter as potential source of pathogens and other contaminants in groundwater and surface water proximal to large-scale confined poultry feeding operations

Manure from livestock production has been associated with the contamination of water resources. To date, research has primarily focused on runoff of these contaminants from animal operations into surface water, and the introduction of poultry-derived pathogenic zoonoses and other contaminants into groundwater is under-investigated. We characterized pathogens and other microbial and chemical contaminants in poultry litter, groundwater, and surface water near confined poultry feeding operations (chicken layer, turkey) at 9 locations in Iowa and one in Wisconsin from May and June 2016. Results indicate that poultry litter from large-scale poultry confined feeding operations is a likely source of environmental contamination and that groundwater is also susceptible to such poultry-derived contamination. Poultry litter, groundwater, and surface water samples had detections of viable bacteria growth (Salmonella spp., enterococci, staphylococci, lactobacilli), multi-drug resistant Salmonella DT104 flo_st and int genes, F⁺ RNA coliphage (group I and IV), antibiotic resistance genes (ARGs; bla_DHA, bla_OXA-48, bla_TEM, bla_CMY-2, tetM), phytoestrogens (biochanin A, daidzein, formononetin), and a progestin (progesterone). In addition, mcr-1 (a colistin ARG), was detected in a groundwater sample and in another groundwater sample, antibiotic resistant isolates were positive for Brevibacterium spp., a potential signature of poultry in the environment. Detectable estrogenicity was not measured in poultry litter, but was observed in 67% of the surface water samples and 22% were above the U.S. Environmental Protection Agency trigger level of 1 ng/L. The transport of microbial pathogens to groundwater was significantly greater (p < 0.001) than the transport of trace organic contaminants to groundwater in this study. In addition to viable pathogens, several clinically important ARGs were detected in litter, groundwater, and surface water, highlighting the need for additional research on sources of these contaminants in livestock dominated areas.

High mortality in foals associated with Salmonella enterica subsp. enterica Abortusequi infection in Italy

Salmonella enterica subsp. enterica serovar Abortusequi is frequently reported as a cause of abortion in mares and neonatal septicemia and polyarthritis in Asian and African countries, but only sporadically in Europe and the United States. We report an outbreak of S. Abortusequi in foals in Italy, characterized by high mortality. In a herd of Murgese horses, 10 of 34 newborns died at birth and a further 7 died, after developing severe clinical signs, during the first 10 d of life. Tissue specimens from different organs of 2 dead foals, synovial fluids from 4 sick foals, and vaginal and rectal swabs from their dams were cultured. A total of 16 isolates, all as pure cultures, were obtained and identified as Salmonella. The isolates exhibited the same antimicrobial resistance pattern and the same sequence type, ST251, a type that has been associated with S. Abortusequi. Six of 16 isolates were serotyped and found to be S. Abortusequi 4,12:-:e,n,x. Equine practitioners should be aware of S. Abortusequi infection as a cause of neonatal mortality in foals.

Risk for zoonotic Salmonella transmission from pet reptiles: A survey on knowledge, attitudes and practices of reptile-owners related to reptile husbandry

Reptiles are becoming increasingly popular as pets. Those animals are reservoirs of a wide variety of Salmonella serotypes, that may be transmitted to warm-blooded animals, including humans. Accordingly, good hygiene practices related to husbandry are important for prevention of Reptile-associated salmonellosis (RAS). A cross-sectional study was conducted among reptile owners, by administration of a detailed questionnaire. In addition, the cloacal swabs of the sampled reptiles were screened for Salmonella spp. and the husbandry management practices were evaluated in order to assess any possible link between the presence of Salmonella spp. and the hygiene practices. The response rate to the questionnaire was 66.6% (100 out of 150 contacted owners). In 26 out of 100 families, members at risk of RAS (children and elderly) were present. One hundred animals were screened for the presence of Salmonella spp. The prevalence of Salmonella spp. carriers was 57% (Confidence interval 47-66%). Co-habitation of the animals with other reptiles in the same terrarium was associated with a 2-fold increase in the risk of infection by Salmonella spp.(Odds ratio=2.3, CI 1.2;13, p=0.02). Animals handled by owners that did not report washing their hands after the cleaning procedures or the handling were exposed to a 3-fold increase in the risk of infection (OR=3.1, CI 1.1;16, p=0.019). When drinking water was not replaced regularly, the animals were 7 times more exposed to infection (OR=6.8, CI 1.8;25, p=0.005). When the diet was constituted by rodents, 27 out of 48 reptiles (56.3%) were fed with live animals. In the present survey the typical reptile owner was a person, aware of ethological aspects of reptile husbandry but ignorant of some ethical recommendations and poorly informed about the health risks for himself and for the other family members. Prevention of RAS must rely mainly on information and education, with the veterinarian health bodies primarily involved in this difficult task.

Molecular detection and antibiogram of virulent Salmonellae isolated from chicken meat

Salmonella has emerged as one of the most common and frequent pathogen associated with the food poisoning. In the present study, a total of 240 chicken meat samples were collected from retail markets of Shivamogga region; where, 13 samples were found positive for Salmonella species by genus specific PCR targeting invA virulent gene, giving an overall prevalence of 5.4%. Retail outlets (slaughter-cum-retailing units) that traditionally processed chicken meat showed higher prevalence of 7.5% (n=120); whereas, retail chicken meat originated from organized abattoirs showed prevalence of 3.3% (n=120). Among traditional retail outlets, those retail units processing multiple animal species showed higher prevalence (8.3%, n=60) of Salmonella spp. compared to those that processed chicken meat alone (6.6%, n=60). All the Salmonella species (n=13) isolated from the chicken meat possessed virulence (invA) gene indicating their potential pathogenic mechanisms and also showed varying degree of susceptibility against common antimicrobials (multiple antibiotic resistance index of 0.1176 to 0.3529). High prevalence rate of Salmonella spp. has important public health concern and underscores a need for intense surveillance and monitoring of retail chicken meat and implementation of food quality assurance systems across the chicken supply chain.

Simultaneous detection of Salmonella pathogenicity island 2 and its antibiotic resistance genes from seafood

Salmonella enterica serovars are virulent pathogens of humans and animals with many strains possessing multiple drug resistance traits. They have been found to carry resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracycline (ACSSuT-resistant). A rapid and sensitive multiplex PCR (mPCR)-based assay was developed for the detection of Salmonella serovars from seafood. Six sets of primers which are one primer pair targeting Salmonella specific gene invA (284 bp), two Salmonella pathogenicity island 2 (SPI-2) genes ssaT (780 bp) and sseF (888 bp) and three antibiotic resistance genes floR (198 bp), sul1 (425 bp), tetG (550 bp) were used for the study. The specificity and sensitivity of the assay were tested by spiking shrimp/fish/clam homogenate with viable cells of Salmonella. This assay allows for the cost effective and reliable detection of pathogenic Salmonella enterica from seafood. The mPCR developed in the present study proved to be a potent analytical tool for the rapid identification of multidrug-resistant Salmonella serovars from seafood.

Quantifying Salmonella population dynamics in water and biofilms

Members of the bacterial genus Salmonella are recognized worldwide as major zoonotic pathogens often found to persist in non-enteric environments including heterogeneous aquatic biofilms. In this study, Salmonella isolates that had been detected repeatedly over time in aquatic biofilms at different sites in Spring Lake, San Marcos, Texas, were identified as serovars Give, Thompson, Newport and -:z10:z39. Pathogenicity results from feeding studies with the nematode Caenorhabditis elegans as host confirmed that these strains were pathogenic, with Salmonella-fed C. elegans dying faster (mean survival time between 3 and 4 days) than controls, i.e., Escherichia coli-fed C. elegans (mean survival time of 9.5 days). Cells of these isolates inoculated into water at a density of up to 10(6) ml(-1) water declined numerically by 3 orders of magnitude within 2 days, reaching the detection limit of our quantitative polymerase chain reaction (qPCR)-based quantification technique (i.e., 10(3) cells ml(-1)). Similar patterns were obtained for cells in heterogeneous aquatic biofilms developed on tiles and originally free of Salmonella that were kept in the inoculated water. Cell numbers increased during the first days to more than 10(7) cells cm(-2), and then declined over time. Ten-fold higher cell numbers of Salmonella inoculated into water or into biofilm resulted in similar patterns of population dynamics, though cells in biofilms remained detectable with numbers around 10(4) cells cm(-2) after 4 weeks. Independent of detectability by qPCR, samples of all treatments harbored viable salmonellae that resembled the inoculated isolates after 4 weeks of incubation. These results demonstrate that pathogenic salmonellae were isolated from heterogeneous aquatic biofilms and that they could persist and stay viable in such biofilms in high numbers for some time.

Diversity of Salmonella in biofilms and water in a headwater ecosystem

The diversity of Salmonella was analysed in biofilm and water samples from the spring and slough arms of Spring Lake, the headwaters of the San Marcos River, Texas, during the drought of 2011, with only one potential run-off event at the beginning of the study. Salmonellae were detected in semiselective enrichment cultures by end-point PCR during the entire sampling period of (11 sampling events during 2 months). From the spring arm site, 73% of the biofilms and 41% of the water samples were positive for salmonellae, while only 9% of the biofilms and 23% of the water samples were positive from the slough arm site. Salmonellae could be isolated from all positive samples, with higher diversity in biofilms compared with water samples and more strains obtained from the spring arm than from the slough arm. Differences between sites were generally caused by less frequently detected isolates, while the majority of isolates that were present in both biofilms and water from both sites was represented by three strains only. Quantification attempts by quantitative PCR directly in samples without prior enrichment did not result in a reliable detection of salmonellae, suggesting that numbers in all samples were below the detection limit.

Hobi-like pestivirus in aborted bovine fetuses

An outbreak of abortion affecting multiparous cows was associated with Hobi-like pestivirus infection. Viral RNA and antigens were detected in the tissues of two aborted fetuses. Molecular assays for other common abortogenic agents tested negative. At the genetic level, the Hobi-like pestivirus displayed the closest relatedness to Italian, Australian, and South American viruses, whereas it diverged from the prototype Thai isolate. These findings may have important implications for the pestivirus control/eradication programs in cattle herds.

Detection of aacA-aphD, qacEδ1, marA, floR, and tetA genes from multidrug-resistant bacteria: Comparative analysis of real-time multiplex PCR assays using EvaGreen(®) and SYBR(®) Green I dyes

We have developed multiplex real-time PCR assays that utilize DNA-intercalating dyes, SYBR Green I (SG) and EvaGreen (EG), with two primer sets (set 1=qacEδ1, tetA and aacA-aphD; set 2=tetA, marA, and floR) to simultaneously amplify the qacEδ1, tetA, aacA-aphD, marA, and floR genes. Validity of the multiplex PCR assays was confirmed by testing 83 bacterial isolates, including Staphylococcus aureus (28 isolates), Enterococcus spp. (17 isolates), Salmonella enterica serovar Typhimurium (8 isolates), Citrobacter spp. (9 isolates), Escherichia coli (14 isolates) and Aeromonas veronii (7 isolates), and performing sequence analysis of representative PCR products. Agarose gel analysis revealed the presence of correct size PCR products, and the differences in their thermal melting (T(m)) curves were used to distinguish various PCR products. Although T(m) peaks of different amplicons after EG-based singleplex and multiplex PCR assays were resolved nicely, only one or two peaks were seen for SG-bound amplicons. EG-based multiplex real-time PCR assays provided better peak resolution. There was a good correlation with a better linear relationship between the C(t) and log input DNA concentration for the set 1 and set 2 genes in EG-based assays (R(EG)(2)=0.9813and0.9803) than in SG-based assays (R(SG)(2)=0.5276and0.6255). The sensitivities of detection were 2.5-25fg and 25-250fg of template DNA in EG and SG-based singleplex and multiplex PCR assays, respectively. The assays, which could be completed in less than 45min, offer sensitive and rapid detection of qacEδ1, aacA-aphD, marA, floR, and tetA genes from a diverse group of multiple antibiotic-resistant bacterial strains.

Environmental monitoring and analysis of faecal contamination in an urban setting in the city of Bari (Apulia region, Italy): health and hygiene implications

Few studies have been conducted in Italy to quantify the potential risk associated with dynamics and distribution of pathogens in urban settings. The aim of this study was to acquire data on the environmental faecal contamination in urban ecosystems, by assessing the presence of pathogens in public areas in the city of Bari (Apulia region, Italy). To determine the degree of environmental contamination, samples of dog faeces and bird guano were collected from different areas in the city of Bari (park green areas, playgrounds, public housing areas, parkways, and a school). A total of 152 canine faecal samples, in 54 pools, and two samples of pigeon guano from 66 monitored sites were examined. No samples were found in 12 areas spread over nine sites. Chlamydophila psittaci was detected in seven canine and two pigeon guano samples. Salmonella species were not found. On the other hand, four of 54 canine faecal samples were positive for reovirus. Thirteen canine faecal samples were positive for parasite eggs: 8/54 samples contained Toxocara canis and Toxascaris leonina eggs and 5/54 samples contained Ancylostoma caninum eggs. Our study showed that public areas are often contaminated by potentially zoonotic pathogens.

Development of microarray and multiplex polymerase chain reaction assays for identification of serovars and virulence genes in Salmonella enterica of human or animal origin

Salmonella enterica is an important enteric pathogen consisting of many serovars that can cause severe clinical diseases in animals and humans. Rapid identification of Salmonella isolates is especially important for epidemiologic monitoring and controlling outbreaks of disease. Although immunologic and DNA-based serovar identification methods are available for rapid identification of isolates, they are time consuming or costly or both. In the current study, 2 molecular methods for identification of Salmonella serovars were developed and validated. A 70-mer oligonucleotide spotted microarray was developed that consisted of probes that detected genes responsible for genetic variation among isolates of Salmonella that can be used for serotyping. A multiplex polymerase chain reaction (PCR) assay was also developed, which is capable of identifying 42 serovars, thus providing a valuable prediction of the pathogenicity of the isolates by detecting the presence of virulence genes sseL, invA, and spvC. The gene spvC was the best predictor of pathogenicity. In a blind study, traditional serologic methods were correlated at 93.3% with the microarray-based method and 100% with the multiplex PCR-based serovar determination.

Elucidation of Antimicrobial Susceptibility Profiles and Genotyping of Salmonella enterica Isolates from Clinical Cases of Salmonellosis in New Mexico in 2008

In this study, we investigated the antimicrobial susceptibility profiles and the distribution of some well known genetic determinants of virulence in clinical isolates of Salmonella enterica from New Mexico. The minimum inhibitory concentrations (MICs) for various antimicrobials were determined by using the E-test strip method according to CLSI guidelines. Virulence genotyping was performed by polymerase chain reaction (PCR) using primers specific for known virulence genes of Salmonella enterica. Of 15 isolates belonging to 11 different serovars analyzed, one isolate of Salmonella Typhimurium was resistant to multiple drugs namely ampicillin, amoxicillin / clavulanic acid, chloramphenicol and tetracycline, that also harbored class 1 intergron, bla(TEM) encoding genes for β-lactamase, chloramphenicol acetyl transferase (cat1), plus floR, tet(C) and tet(G). This strain was phage typed as DT104. PCR analysis revealed the presence of invA, hilA, stn, agfA and spvR virulence genes in all the isolates tested. The plasmid-borne pefA gene was absent in 11 isolates, while 5 isolates lacked sopE. One isolate belonging to serogroup E4 (Salmonella Sombre) was devoid of multiple virulence genes pefA, iroB, shdA and sopE. These results demonstrate that clinical Salmonella serotypes from New Mexico used here are predominantly sensitive to multiple antimicrobial agents, but vary in their virulence genotypes. Information on antimicrobial sensitivity and virulence genotypes will help in understanding the evolution and spread of epidemic strains of Salmonella enterica in the region of study.

Inter- and intraspecies plasmid-mediated transfer of florfenicol resistance in Enterobacteriaceae isolates from swine

Florfenicol resistance was analyzed in 230 enteric pig isolates collected between 1998 and 2006. PCR, plasmid profiling, Southern blot hybridization, and a mixed-broth conjugation assay suggested the intra- and interspecies plasmid-mediated transfer of florfenicol resistance among the isolates that exhibited MICs for florfenicol between 4 to 128 mg/liter.

Molecular beacon-based real-time PCR detection of primary isolates of Salmonella Typhimurium and Salmonella Enteritidis in environmental and clinical samples

Background

A fast and simple two-step multiplex real-time PCR assay has been developed to replace the traditional, laborious Salmonella serotyping procedure. Molecular beacons were incorporated into the assay as probes for target DNA. Target sequences were regions of the invA, prot6E and fliC genes specific for Salmonella spp. Salmonella Enteritidis and Salmonella Typhimurium, respectively, the two most clinically relevant serotypes. An internal amplification positive control was included in the experiment to ensure the optimal functioning of the PCR and detect possible PCR inhibition. Three sets of primers were used for the amplification of the target sequences. The results were compared to those of the Kauffmann-White antigenic classification scheme.

Results

The assay was 100% sensitive and specific, correctly identifying all 44 Salmonella strains, all 21 samples of S. Enteritidis and all 17 samples of S. Typhimurium tested in this work. Therefore, the entire experiment had specificity and sensitivity of 100%. The detection limit was down to 10 copies of DNA target per 25 μl reaction.

Conclusion

The assay can amplify and analyse a large number of samples in approximately 8 hours, compared to the 4 to 5 days conventional identification takes, and is thus considered a very promising method for detecting the two major serotypes of Salmonella quickly and accurately from clinical and environmental samples.

Real-time subtyping via PFGE reveals potential epidemiological relatedness among human salmonellosis cases in Northern Italy

AIM

This study aimed to assess the applicability of a combined approach of traditional and molecular epidemiology in order to detect salmonellosis outbreaks in the Piedmont region (Italy), characterized by high Salmonella prevalence.

METHODS AND RESULTS

Pulsed field gel electrophoresis (PFGE) was used in real-time and in combination with clinical surveillance to assess the relatedness of salmonellosis human cases; subsequently, PFGE profiles of clinical isolates were compared with those of isolates from food items collected during the same study period to identify putative food sources of Salmonella. The real-time subtyping approach allowed the identification of an outbreak (21 isolates), which was undetected by epidemiological surveillance.

CONCLUSIONS

Traditional epidemiological investigation did not allow the formulation of hypotheses on food items possibly associated with the outbreak owing mainly to patients' difficulties in remembering foods they ate, and the tendency of health-care professionals to direct patient's suspicion towards specific food items.

SIGNIFICANCE AND IMPACT OF THE STUDY

This finding highlighted the value of real-time molecular subtyping in salmonellosis outbreak identification. In order to improve national epidemiological investigations implementing public health agency network and planning, information campaigns for health-care professionals are required.

Identification and characterization of Class 1 integron resistance gene cassettes among Salmonella strains isolated from imported seafood

A total of 210 Salmonella isolates, representing 64 different serovars, were isolated from imported seafood samples, and 55/210 isolates were found to be resistant to at least one antibiotic. Class 1 integrons from three multidrug-resistant Salmonella enterica strains (Salmonella enterica serovars Newport [strain 62], Typhimurium var. Copenhagen [strain 629], and Lansing [strain 803], originating from Hong Kong, the Philippines, and Taiwan, respectively) were characterized. Southern hybridization of plasmids isolated from these strains, using a class 1 integron probe, showed that trimethoprim-sulfamethoxazole and streptomycin resistance genes were located on a megaplasmid in strain 629. Our study indicates that imported seafood could be a reservoir for Salmonella isolates resistant to multiple antibiotics.

Antimicrobial susceptibility and molecular detection of chloramphenicol and florfenicol resistance among Escherichia coli isolates from diseased chickens

Seventy Escherichia coli isolates recovered from diseased chickens diagnosed with colibacillosis in Henan Province, China, between 2004 and 2005 were characterized for antimicrobial susceptibility profiles via a broth doubling dilution method. Overall, the isolates displayed resistance to trimethoprim-sulfamethoxazole (100%), oxytetracycline (100%), ampicillin (83%), enrofloxacin (83%), and ciprofloxacin (81%), respectively. Among the phenicols, resistance was approximately 79% and 29% for chloramphenicol and florfenicol, respectively. Molecular detection revealed that the incidence rates of the floR, cmlA, cat1, cat2 and cat3 were 29, 31, 16, 13, and 0%, respectively. Additionally, 10% of the isolates were positive for both floR and cmlA. As these antimicrobial agents may potentially induce cross-resistance between animal and human bacterial pathogens, their prudent use in veterinary medicine is highly recommended.

Invasiveness and intracellular growth of multidrug-resistant salmonella and other pathogens in Caco-2 cells

The increase of multidrug-resistant pathogens of human and animal origins is a major public health concern. For a better understanding of the health consequences of multidrug-resistant bacteria transmitted from animal products to humans, the host interaction of zoonotic Salmonella isolates along with other pathogenic and commensal bacteria was evaluated using a human intestinal Caco-2 cell system. Multidrug-resistant S. Agona, S. Heidelberg, and S. Typhimurium possessed plasmid-mediated class 1 integrons. The S. Typhimurium DT104 isolate from ground beef showed the well-known genotypic and phenotypic resistance characteristics of the species, and contained the chromosomally located class 1 integron. Among the multidrug-resistant Salmonella isolates, the S. Heidelberg 219 had the highest invasion number at 1.0 x 10(4) CFU/mL, followed by the S. Typhimurium DT104 isolate at 7.7 x 10(3) CFU/mL. Listeria monocytogenes was the best performer among the tested species in invading the Caco-2 cell. Multidrug-resistant opportunistic pathogens Klebsiella pneumoniae and Pseudomonas aeruginosa were also able to invade the cells. The invasion of S. Heidelberg 219, S. Typhimurium DT104, L. monocytogenes, K. pneumoniae, and P. aeruginosa into the Caco-2 cells was not affected even in the presence of commensal E. coli. During the intracellular growth of S. Heidelberg 219, S. Typhimurium DT104, and L. monocytogenes, the bacterial counts increased 2 log cycles in 9 h in the Caco-2 cells. Therefore, these strains could rapidly proliferate after their invasion into the cells.

Detection and Identification of Salmonella Typhimurium in Bovine Diarrhoeic Fecal Samples by Immunomagnetic Separation and Multiplex PCR Assay

The aim of this study was to use the immunomagnetic separation (IMS) test plus a multiplex polymerase chain reaction (m-PCR) assay to detect Salmonella at genus level and also for the identification of Salmonella enterica serovar Typhimurium in bovine diarrhoeic fecal samples. In all, 400 bovine diarrhoeic fecal specimens were examined by conventional bacterial culture, IMS, and m-PCR. For m-PCR assay, four set primers were selected: 139-141, specific for inv-A gene of Salmonella spp and the RfbJ, FliC and FljB, specific for the rfbJ, FliC and fljB genes of Salmonella Typhimurium or other Salmonella serovars with similar antigenic properties. Thirty-three (8.25%) out of the 400 fecal samples were culture positive for Salmonella serovars. Of these, 66.7% (22 of 33) were Salmonella enterica serovar Typhimurium, and 9.1% (three of 33) were serovar Dublin. In the IMS + m-PCR, four amplified product (663, 526, 284 and 183 bp) were found in all specimens that had serovar Typhimurium (4,5,12:i:1,2), they corresponded, respectively, to the rfbJ, fljB, inv-A and Flic genes of this serovar. In serovar Dublin (1,9,12:g,p:-), Georgia (6,7:b:e,n,z(15)) and, Enteritidis (1,9,12;g,m:-) only one PCR product (284 bp) was amplified from the inv-A gene. In serovars Augustenborg (6,7:i:1,2) and Lindenburg (6,8:i:1,2) three positive bands (526, 284 and 183 bp) were amplified corresponding to the fljB, inv-A and Flic genes, respectively. In serovar Virchow (6,7:r:1,2) two amplified products (284 and 526 bp) from the inv-A and FliC genes were observed. In serovar Gloucster (1,4,12(27):i:1,w) three fragments (183, 284 and 663) from the FliC, inv-A and, rfbJ genes respectively, were observed. In the positive control as expected, four PCR products were amplified corresponding to the FliC, inv-A, fljB and rfbJ genes, respectively. In conclusion, the results of this study showed that detection of Salmonella at genus level with universal ST139-141 primers and identification of Salmonella Typhimurium by using specific primers of O4, H(2):1, 2 and H(1) antigens can potentially permit to more readily evaluate fecal and other types of samples for the presence of these organisms. Compared to bacteriological culture the combination of IMS and m-PCR resulted a faster method for the detection and identification of Salmonella at genus and serovar level by using of universal and specific primers.

Characterization of an antibiotic resistant Clostridium hathewayi strain from a continuous-flow exclusion chemostat culture derived from the cecal contents of a feral pig

The chemostat model has been an important tool in studying intestinal microflora. To date, several competitive exclusion products have been developed from such studies as prophylactic treatment against pathogenic bacteria. A continuous-flow chemostat model of a feral pig was developed using inocula from the cecal contents of a wild boar caught in East Texas. Several strains of antibiotic-sensitive bacteria were isolated including Bacteroides, Lactobacillus, Enterococcus and Clostridium sp. This study reports on the characterization of a multidrug-resistant Clostridium hathewayi strain that was isolated from this feral pig's cecal contents maintained in a continuous-flow chemostat system showing high resistance to carbapenems and macrolides (including the growth promoter tylosin). Clostridium hathewayi has been documented to be pathogenic to both humans and animals. Feral pigs may be an important source of pathogenic and antibiotic resistant bacteria and may pose potential risk to domestic species. Further work is needed to elucidate the prevalence of these reservoirs and assess the contribution these may play in the spread of disease and resistance.

High-resolution analysis of salmonellae from turtles within a headwater spring ecosystem

Sediments and water from the pristine headwaters of the San Marcos River, Texas, USA, as well as swabs from biofilms on the carapace and from the cloacae of 17 musk turtles (Sternotherus odoratus) and one snapping turtle (Chelydra serpentina serpentina) caught at the same site, were analysed for salmonellae by culture and molecular techniques. Whereas enrichment cultures from sediment and water samples were negative for salmonellae in PCR- and in situ hybridization-based analyses, both techniques detected salmonellae after enrichments from both carapace and cloacae of nine (i.e. of 53%) musk turtles. Further characterization of 10 isolates obtained from the enrichment cultures of four selected individuals and confirmed as salmonellae by PCR analysis was achieved by fingerprinting techniques (rep-PCR). The results show differences between individuals and, in one case, variation among isolates from a single individual. All isolates from two individuals displayed identical profiles. These profiles were different from those obtained from the isolates of the third individual, which were, themselves, also identical for all isolates. Salmonellae were much more diverse in samples from the carapace of the last individual with five different rep-PCR profiles retrieved. Serotyping of seven isolates representative for each rep-PCR profile identified all isolates as representing Salmonella enterica subspecies enterica serotype Rubislaw, which demonstrates the presence of different strains of potentially human pathogenic salmonellae naturally occurring on turtles even within pristine environments. The frequent detection of these organisms in biofilms on the carapace opens the door for speculations on the role of this habitat as a reservoir for salmonellae, and on potential implications for turtles acting as a dispersal vector.

Clonal relatedness of Salmonella isolates associated with invasive infections in captive and wild-caught rattlesnakes

This study examines the serotype distribution and clonal relatedness among Salmonella isolates obtained from healthy and diseased snakes. Isolates from extraintestinal body sites were obtained through routine diagnostic lab submissions from snakes in two facilities that had experienced a high prevalence of osteomyelitis in Crotalus species. Gastrointestinal isolates were predominantly from fecal samples collected from healthy snakes of both crotalid and non-crotalid species in one facility. PFGE macrorestriction analysis of Salmonella isolates confirmed the clonal and species-restricted nature of Salmonella serotype IIIa 56: z4, z23: - in one facility. Fourteen of 15 isolates from suspected osteomyelitis lesions in wild-caught snakes at the second facility were also from Salmonella subgroup IIIa (serotype IIIa 18: z4, z23: -) and appeared to be closely related by PFGE. Evaluation of a PCR assay for the spvC gene in 209 isolates demonstrated that this method consistently distinguished isolates of subgroup IIIa from those of subgroup IIIb. The data presented establish that Salmonella of subgroup IIIb are abundant and regularly associated with gastrointestinal shedding in snakes but that Salmonella in subgroup IIIa disproportionately cause infections in bone or other extraintestinal sites.

Influence of anti-FloR antibody on florfenicol accumulation in florfenicol-resistant Escherichia coli and enzyme-linked immunosorbent assay for detection of florfenicol-resistant E. coli isolates

To detect florfenicol-resistant Escherichia coli isolates by enzyme-linked immunosorbent assay (ELISA), anti-FloR1 antibodies were produced in mice using a recombinant glutathione S-transferase (GST)-FloR1 protein, which was expressed in a prokaryote expression system, as the antigen. The specificity of the murine anti-GST-FloR1 antibody and its influence on florfenicol accumulation in florfenicol-resistant isolates were investigated using Western blotting and high-performance liquid chromatography, respectively. Western blotting using the anti-FloR1 antibody showed specific binding of the antibody to the florfenicol-resistant FloR protein. Preincubation of florfenicol-resistant strains with the antibody significantly increased the intracellular accumulation of florfenicol and enhanced the bacterial susceptibility to florfenicol, suggesting that antibody binding to the FloR protein inhibited the activity of the efflux protein conferred by the floR gene. Analyses of florfenicol-resistant and -sensitive isolates by ELISA using the anti-FloR1 antibody showed good correlation between FloR protein expression and the floR genotype. The anti-FloR1 antibody-based ELISA is a useful tool for the detection of florfenicol-resistant bacteria harboring the floR gene.

DNA microarray detection of antimicrobial resistance genes in diverse bacteria

High throughput genotyping is essential for studying the spread of multiple antimicrobial resistance. A test oligonucleotide microarray designed to detect 94 antimicrobial resistance genes was constructed and successfully used to identify antimicrobial resistance genes in control strains. The microarray was then used to assay 51 distantly related bacteria, including Gram-negative and Gram-positive isolates, resulting in the identification of 61 different antimicrobial resistance genes in these bacteria. These results were consistent with their known gene content and resistance phenotypes. Microarray results were confirmed by polymerase chain reaction and Southern blot analysis. These results demonstrate that this approach could be used to construct a microarray to detect all sequenced antimicrobial resistance genes in nearly all bacteria.

Antimicrobial Resistance and Class 1 Integrons in Pathogenic Escherichia coli from Dairy Farms

The goal of this study was to assess the prevalence of antimicrobial resistance and class 1 integrons, including integron-associated genes, in 24 Escherichia coli isolates from dairy farms. Escherichia coli isolates (n = 14) from dairy cows with mastitis (ECDM), Shiga toxin-producing (STEC) O157:H7 from cull dairy cow fecal samples (n = 9) and bulk tank milk (n = 1) were evaluated for sensitivity to 19 antimicrobial agents used commonly in human and/or veterinary medicine. Multiplex PCR was used to determine presence of genes associated with class 1 integrons (intI1, qacEDelta1, and sulI1). Class 1 integrons were found only in eight of 10 isolates (one STEC O157:H7 and seven ECDM) that demonstrated antimicrobial resistance, and seven of these were resistant to two or more antimicrobial agents. Eight of 10 STEC O157:H7 and six of 14 ECDM were susceptible to all commonly used antibiotics. Five ECDM demonstrated multiple resistances to four or more antibiotics. Most of the 24 isolates examined exhibited resistance against sulfamethoxazole, followed by streptomycin and tetracycline. STEC O157:H7 strains had less prevalence of antibiotic resistance and integron carriage than ECDM. The multiplex PCR method developed for detection of intI1, qacEDelta1, and sulI1 can be used routinely for monitoring presence of these genes. Class 1 integrons were found in eight of 10 E. coli strains that demonstrated antimicrobial resistance; seven of these were resistant to two or more antibiotics. It appears that integrons played a role in the incidence of antimicrobial resistance of the strains used in this study.

Characterization of Salmonella enterica serovar Typhimurium strains of veterinary origin by molecular typing methods

Twenty-eight strains of Salmonella enterica serovar Typhimurium were characterized by three PCR-based methods. Ten strains harbored type I integrons and two different integron profiles were detected. Typing by amplified fragment length polymorphism (AFLP) resulted in observation of 10 profiles that differed by one to six bands. Salmonella strains were screened for presence of phage genes using a PCR-phage typing; five genes from P22 phage and genes encoding putative virulence factors from phages Gifsy-1, Gifsy-2 and Fels-1 were selected for testing. This set of genes was sufficient for dividing the strains into eight different PCR-phage profiles. Similar grouping of strains was observed in case of all the employed DNA techniques and they corresponded well with the phage type and antimicrobial resistance of the strains. The highest discriminating power was achieved with use of the AFLP, yet the detection of integrons and PCR-phage typing also proved to be valuable in typing the S. Typhimurium strains.

Polymerase chain reaction detection of foodborne Salmonella spp. in animal feeds

Foodborne salmonellosis continues to be a public health issue of considerable concern. Animal feed has been a major link in pre-harvest food animal production. Although monitoring systems and control measures are available to limit Salmonella spp. contamination on animal feeds detection methodology is relatively time consuming in the context of time inputs for feed processing and mixing. Current cultural methods of Salmonella spp. detection in feeds require several days for confirmation. This amount of time represents significant problems if control measures are to be effectively implemented in a fashion that keeps feed processing costs low. Molecular methods offer improved sensitivity and potential reduction in assay time. In particular, several commercial polymerase chain reaction (PCR) assays, and combined PCR-hybridization assays have been suggested as possible means to implement more rapid detection of Salmonella spp. extracted from animal feeds. It has now become possible to rapidly detect and confirm the presence of foodborne Salmonella spp. in feed matrices by commercial amplification detection systems. The primary challenges remaining are to develop more reliable recovery and extraction procedures for routine processing of samples from a wide variety of feed matrices and apply molecular techniques for assessing physiological status of Salmonella spp. contaminants in animal feeds.

Molecular analysis of Salmonella isolates recovered from processed Turkey carcasses

This study was carried out to determine the prevalence of some virulence characteristics associated with Salmonella isolates recovered from processed turkey carcasses in the Midwestern region of the United States. A total of 94 Salmonella isolates recovered from turkey carcasses from two processing plants (A and B) were examined to determine the prevalence of invA, pagC, and spvC genes. Bioassays also were used to evaluate aerobactin and colicin production. All isolates (100%) were positive for the presence of invA and pagC but were negative for spvC. Overall, 19.1% of all isolates tested were positive for aerobactin production, and 25.5% of all isolates were positive for colicin. Aerobactin and colicin production differed among isolates recovered from the two plants; more isolates from plant B produced these compounds. The Salmonella isolates examined in this study possess significant potential for causing human illness.

Identification and characterization of class 1 integron resistance gene cassettes among Salmonella strains isolated from healthy humans in China

Twenty-three strains of Salmonella spp. isolated from healthy humans in Guangdong, China, were examined for their susceptibility to ten common antibiotics and the presence of antibiotic resistance integrons. All the strains were resistant to at least one antibiotic, and 4 strains were positive for the intI1 gene. Polymerase chain reaction using in-F and in-B primers showed the existence of amplicons of 1,009 bp in two, 1,664 bp in one, and 1,009 bp and 1,664 bp in one of the intI1 -positive isolates, respectively. Sequence analysis revealed that the 1,009-bp amplicon harbored gene cassette aadA2, conferring resistance to spectinomycin, and the 1,664-bp amplicon harbored genes aadA5 and dfr17, conferring resistance to spectinomycin, streptomycin and trimethoprim. Meanwhile the experiments of plasmid conjugation and Southern hybridization with intI1 as the DNA probe indicated that all the integrons found in these strains were chromosomal. Because the strains carrying class 1 integrons were isolated from healthy humans, it suggests the need for all-round surveillance of the antibiotic resistance of pathogens.

Antibiotic resistance of Salmonella isolated from hog, beef, and chicken carcass samples from provincially inspected abattoirs in Ontario

The emergence of antimicrobial-resistant Salmonella organisms, especially Salmonella Typhimurium DT104, has been reported in many countries, including the United States and Canada. The purposes of this study were to determine the antimicrobial resistance patterns of Salmonella isolated from hog, beef, and chicken carcasses from provincially inspected abattoirs in Ontario and to determine the agreement between the agar dilution method and the microbroth dilution method for measurement of antimicrobial resistance of the isolates. Antimicrobial resistance of Salmonella isolates from hogs (n = 71), beef (n = 24), and chicken (n = 295) to amikacin, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, and tetracycline was determined using the two methods. None of the 390 isolates were resistant to ciprofloxacin at levels of 0.125 microg/ml. All chicken and hog isolates were sensitive to amikacin, whereas all beef isolates were sensitive to both amikacin and gentamicin. Multiple antimicrobial resistance (resistance to more than one antimicrobial) was found in 29% of bovine isolates and 42% of porcine isolates using both methods for testing and in 42% by the agar dilution and 33% by the microbroth dilution methods in the chicken isolates. Overall, there was good agreement between the two test methods for resistance to most of the antimicrobials, with disagreement found in the results in 1.3% of the isolates for ampicillin and sulfamethoxazole, 8.2% for streptomycin, 5.6% for cephalothin, and 1.0% of the isolates for tetracycline. The lack of agreement between the two test methods was found mostly among the chicken isolates.

A descriptive study of human Salmonella serotype typhimurium infections reported in Ontario from 1990 to 1998

BACKGROUND

Salmonella infections cause gastrointestinal and systemic diseases worldwide and are the leading causes of food-borne illnesses in North America (1-4). Salmonella serotype typhimurium (ST), in particular, is increasingly becoming a major public health concern because of its ability to acquire multiple resistant genes (5,6).

OBJECTIVE

To describe demographic, temporal and geographical distributions, and reported risk factors of nonoutbreak cases of ST reported to a surveillance system in Ontario.

METHODOLOGY

Descriptive analyses were performed on data on salmonellosis cases reported in Ontario between 1990 and 1998. Direct age- and sex-standardized rates were computed, and temporal trend analyses were performed using simple linear regression and a general additive model with a locally weighted regression (LOESS) smoother.

RESULTS

The mean annual rates of infections with all Salmonella serotypes and with ST were 27 cases per 100,000 persons and 3.7 cases per 100,000 persons, respectively. Males and children under five years of age had significantly higher rates of both ST and ST definitive type 104 (DT104) infections. There was also evidence of temporal clustering of all strains of Salmonella, with significantly more cases being reported during the summer. Significantly higher rates of ST DT104 were observed in urban areas compared with rural areas, suggesting potential differences in the geographical distribution of risk factors.

CONCLUSIONS

Information on demographic, temporal and geographical distributions, and risk factors is critical in planning disease control strategies. Further prospective analytical observation studies are needed to gain a better understanding of the epidemiology of ST and ST DT104 in Ontario, which will better guide disease control decisions.

Comparison of phenotypic traits and genetic relatedness of Salmonella enterica subspecies arizonae isolates from a colony of ridgenose rattlesnakes with osteomyelitis

Reptiles are well-known sources of human Salmonella infections; however, little is known about the ability of Salmonella to cause disease in reptiles. Thirty-seven isolates of Salmonella enterica subspecies arizonae (S. arizonae) were obtained from retrospective and prospective studies of a closed colony of ridgenose rattlesnakes (Crotalus willardi) with osteomyelitis. All isolates (N = 7) from bone lesions were of a single serotype, 56:z4,z23, and this serotype was found on only 1 occasion among 8 other serotypes isolated from 21 cloacal and intestinal samples. The remainder (N = 7) of serotype 56:z4,z23 isolates were from other extraintestinal sites, including liver, ovary, blood, and testis. S. arizonae isolates were susceptible to most antimicrobials, and plasmid profiles did not correlate with serotype or antimicrobial resistance. Isolates of the 56:z4,z23 serotype (N = 14) formed a tight cluster with 95% similarity by XbaI macrorestriction analysis. Individual isolates of serotypes, 56:z4,z23, 38:(k)-z35, and 48:i-z invaded HeLa cells but an isolate of serotype 50:r-z did not. The same individual isolates of serotype 56:z4,z23 and 48:i-z also invaded viper heart cells. The Salmonella InvA gene was detected by polymerase chain reaction (PCR) in all S. arizonae serotypes tested, including 5 serotype 56:z4,z23 isolates and individual isolates of serotypes 48:i-z and 50:r-z. A source or possible explanation for increased virulence of S. arizonae serotype 56:z4,z23 in this unique host has not been found.

Diversity in antimicrobial resistance and other characteristics among Salmonella typhimurium DT104 isolates

Multiresistant Salmonella enterica subspecies enterica serovar Typhimurium definitive type 104 (S. Typhimurium DT104 or DT104) bacteria are important pathogens in animals and humans. DT104 isolates are often called pentaresistant strains that spread clonally. The purpose of this study was to determine phenotypic, genotypic, and epidemiologic characteristics of 175 S. Typhimurium DT104 strains isolated from food-producing animals in Canada. More than 90% of the isolates were resistant to ampicillin (Amp), chloramphenicol (Chl), florfenicol (Flo), sulfisoxazole (Sul), and tetracycline (Tet), 53% of the isolates were additionally resistant to spectinomycin (Spc) and streptomycin (Str), and 28% to kanamycin (Kan) and neomycin (Neo). Sixty-one percent of the strains harbored a single 60-MDa plasmid, 21% contained 60- and 2.0-MDa plasmids, and 4% had 60, 4.6- and 2.0-MDa plasmids. Resistance to Kan and Neo was encoded by the aminoglycoside aphA-1 gene on 2.0-MDa plasmids, whereas resistance to trimethoprim (Tmp) and Sul was encoded by the dhfrIb gene on 4.6-MDa plasmids. Polymerase chain reactions (PCR) showed the presence of integrons with the ant (3")-Ia aminoglycoside adenyltransferase and the bla(PSE-1) beta-lactamase gene cassettes, and the presence of the flost gene in all but one strain resistant to Spc and Str, Amp, and Chl and Flo, respectively. DT104 isolates from cattle at six feedlots represented a separate clone; they were sensitive to Str and Spc and lacked the ant (3")-Ia gene. Pulsed-field gel electrophoresis (PFGE) using Bln I, Spe I, and Xba I resulted in 15, 12, and 8 PFGE patterns, respectively. In summary, we observed considerable diversity in phenotypic, genotypic, and epidemiological characteristics among the DT104 isolates.

Antibiotic resistance genes and Salmonella genomic island 1 in Salmonella enterica serovar Typhimurium isolated in Italy

Fifty-four epidemiologically unrelated multidrug-resistant Salmonella enterica serovar Typhimurium isolates, collected between 1992 and 2000 in Italy, were analyzed for the presence of integrons. Strains were also tested for Salmonella genomic island 1 (SGI1), carrying antibiotic resistance genes in DT104 strains. A complete SGI1 was found in the majority of the DT104 strains. Two DT104 strains, showing resistance to streptomycin-spectinomycin and sulfonamides, carried a partially deleted SGI1 lacking the flo(st), tetR, and tetA genes, conferring chloramphenicol-florfenicol and tetracycline resistance, and the integron harboring the pse-1 gene cassette, conferring ampicillin resistance. The presence of SGI1 was also observed in serovar Typhimurium strains belonging to other phage types, suggesting either the potential mobility of this genomic island or changes in the phage-related phenotype of DT104 strains.