Investigation of Salmonella enterica in Sardinian slaughter pigs: prevalence, serotype and genotype characterization

In order to improve the knowledge about the presence of Salmonella in pork meat in Sardinia (Italy), the prevalence and the sources of Salmonella at 5 pig slaughterhouses (slaughtered pigs and environment) were investigated and the isolates were characterised. A total of 462 samples were collected, 425 from pigs at slaughter and 41 from the slaughterhouse environment. Salmonella was isolated from 26/85 (30.5%) mesenteric lymph nodes, 14/85 (16.4%) colon contents, and from 12/85 (14.1%) carcasses and livers. Salmonella prevalence was 38% (8/21) in samples from surfaces not in contact with meat, and 35% (7/20) in those from surfaces in contact with meat. Thirty-one pigs were identified as carriers of Salmonella in lymph nodes and/or colon content, but of these, only 8 carcasses were positive. A total of 103 Salmonella isolates were serotyped and genotyped. Eight different serotypes were detected; the most common were S. Derby (44/103, 42.7%) and S. Typhimurium (24/103, 23.3%). The most prevalent S. Typhimurium phage type was DT193. Thirty-two isolates were found to be resistant to more than one antimicrobial (MDR). Pulse-field gel electrophoresis (PFGE) permitted the resolution of XbaI macrorestriction fragments of the Salmonella strains into 20 distinct pulsotypes. Combined application of a plasmid profiling assay (PPA) and PFGE gave useful additional information to assist in tracing the routes of Salmonella contamination in abattoirs. To reduce Salmonella prevalence some preventive measures should be encouraged: the origin of infected slaughter animals should be identified and direct and cross-contamination of carcasses should be avoided by adhering to HACCP principles in association with good hygiene procedures (GHP).     

Molecular characterization of antibiotic resistant Salmonella isolates from Indian foods

Salmonella isolates belonging to five serovars, Salmonella enterica Ohio, S. Oslo, S. Tennessee, S. Weltevreden and S. Typhimurium, isolated during 2006-2008 from food samples like sprouts and different varieties of fresh water and marine fish were tested for antibiotic resistance. High percentages (97%) of the isolates were resistant to at least one antibiotic and 82% of the isolates were resistant to more than one antibiotic. S. Oslo was the most resistant serovar and it exhibited resistance to 13 out of 16 antibiotics tested. Integron 1, which has been shown to confer multidrug resistance to various Salmonella serovars, was detected in multidrug resistant S. Oslo. PFGE studies revealed that serovars showed very high genetic diversity. The multidrug resistant S. Oslo showed unique PFGE pattern, which could be used in epidemiological studies.     

Phenotypic and genetic characterization of antimicrobial resistance in Salmonella serovars isolated from retail meats in Alberta, Canada

This study determined the prevalence of Salmonella serovars, antimicrobial resistance (AMR) and resistance genes in Salmonella isolated from retail meats purchased in Alberta, Canada. Samples were collected during one year period (May 2007–April 2008) on weekly basis from 19 census divisions in Alberta. A total of 564 samples including chicken (n = 206), turkey (n = 91), beef (n = 134) and pork (n = 133) were purchased. Salmonella were recovered from chicken (40%), turkey (27%) and pork (2%) samples and was not found in ground beef. A total of 21, 8, and 3 different serovars were recovered from chicken, turkey and pork meats, respectively. Salmonella Hadar was most common in chicken whereas S. Heidelberg was common in turkey meat. Overall 29% (32/110) of isolates were susceptible to tested antimicrobials and resistance to ciprofloxacin, amikacin and nalidixic acid was not found in any isolate. Multiresistance (≥2 antimicrobials) was found in 56% of isolates. Resistance to amoxicillin–clavulanic acid (AMC), ceftiofur (TIO), and ceftriaxone (CRO) was found in about 21% of chicken and 25% of turkey isolates. Resistance to either of tetracycline (TET), streptomycin (STR) or ampicillin (AMP) was unconditionally associated with S. Hadar but resistance to either of TET, AMP, AMC, TIO, CRO or cefoxitin was associated with S. Heidelberg. The strA/B (42% isolates), tet(A) (28% isolates), bla_CMY-2 (21% isolates) and bla_TEM (17% isolates) were the most common resistance genes found. The bla_CMY-2 and bla_TEM genes were unconditionally associated with S. Heidelberg; tet(A) and strA/B with S. Hadar and tet(B) gene with S. Kentucky. The strA/B genes were not associated with S. Heidelberg. Our data suggests that the prevalence of Salmonella serovars varied by the meat type and that AMR and resistance genes varied by the Salmonella serovars.     

The combination of CRISPR-MVLST and PFGE provides increased discriminatory power for differentiating human clinical isolates of Salmonella enterica subsp. enterica serovar Enteritidis

Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) is a major cause of foodborne salmonellosis. Rapid, efficient and accurate methods for identification are required to track specific strains of S. Enteritidis during outbreaks of human salmonellosis. By exploiting the hypervariable nature of virulence genes and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs), we previously developed a powerful sequence-based subtyping approach, designated CRISPR-MVLST. To substantiate the applicability of CRISPR-MVLST, we analyzed a broad set of S. Enteritidis isolates collected over a six-year period. Among 141 isolates we defined 22 Enteritidis Sequence Types (ESTs), the majority of which were novel. Notably, strains exhibiting the common PFGE pattern, JEGX01.0004 (characteristic of ∼40% of S. Enteritidis isolates in the United States), were separated into twelve distinct sequence types. Conversely, isolates of EST4, the most predominant EST we observed, comprised eight different PFGE patterns. Importantly, we showed that some genotypes that were previously associated with the food supply chain at the farm level have now been identified in clinical samples.     

A review of the ecology,colonization and genetic characterization of Salmonella enterica serovar Sofia,a prolific but avirulent poultry serovar in Australia

The distribution of Salmonella serovars on Australian poultry is dominated by the presence of Salmonella enterica subspecies II 1,4,12,27:b:[e,n,x](S. Sofia). The predominance on poultry (40–60%) and a very low level of disease in humans in Australia (0.3%) is unique compared to the rest of the world. This review aims to consolidate the published information on S. Sofia and suggests factors which may be relevant as to why this unique situation exists in Australia. An increase in percentage survival of this serovar relative to other Salmonella serovars through poultry processing, suggests a possible survival mechanism against poultry processing stresses. Factors related to survival including those involved in attachment to surfaces, have been investigated in different strains of S. Sofia. The ability of S. Sofia to adhere to abiotic surfaces was strain dependent and production of cellulose was found to be a poor indicator of attachment potential. Genetic characterization studies of S. Sofia in comparison to Salmonella Typhimurium noted major differences between the Salmonella pathogenicity islands 1, 3 and 5. It is unclear which, if any of these play a role in the dominance of S. Sofia within Australian poultry or the lack of disease causing strains in humans. Further investigation into the mechanism of colonization of chickens, survival through processing, and avirulence for humans may lead to a greater understanding of factors impacting on the ecology of Salmonella in poultry. These may in turn assist in the development of controls and management systems for the more virulent Salmonella serovars.     

Prevalence, distribution, and molecular characterization of Salmonella recovered from swine finishing herds and a slaughter facility in Santa Catarina, Brazil

Swine can carry Salmonella strains that may be transmitted to humans by pork products. This investigation determined the distribution and types of Salmonella in 12 swine finishing herds and a slaughter facility in Santa Catarina, Brazil. A total of 1258 samples, consisting of environmental, feed, carcass, lymph node, and fecal material were collected and submitted to bacteriological isolation of Salmonella. From 487 positive samples, 1255 isolates were recovered and confirmed to be Salmonella. The distribution of positive samples was as follows: finishing pen floors 26% (16/61); feed 29% (42/143); feces 44% (52/119); pooled feces 59% (35/59); slaughter holding pens 90% (36/40); lymph nodes 46% (220/478); pre-chilled carcass surfaces 24% (24/98); and post-chilled carcass surfaces 24% (62/260). The most prevalent serovars were Typhimurium, Panama, Senftenberg, Derby, and Mbandaka. By pulsed-field gel electrophoresis, 1071 isolates were subtyped using XbaI, and duplicate isolates were removed. From the remaining 747 isolates, 163 macrorestriction profiles (pulsotypes) were identified. Six pulsotypes were considered very frequent, occurring in 33 isolates or more. The multiple correspondence analyses showed correlations between pulsotypes from shedding pigs (feces), herd environment (pen floors), and subiliac and prescapular lymph nodes and between lairage and carcass surface samples before and after chilling. All sources of Salmonella investigated contributed to the carrier state; however, pre-slaughter contamination at lairage was the variable most strongly associated with carcass contamination. A total of 59 different antimicrobial resistance profiles were observed in 572 Salmonella isolates. From these isolates, 17% (97/572) were susceptible to all 15 antibiotics tested, 83% (475/572) were resistant to at least one, and 43% (246/572) were resistant to four or more antibiotics (multi-resistant). The AmpGenKanTet profile was the most prevalent in carcass isolates and was associated with farm origin.     

Occurrence,Characterization, and Antimicrobial Susceptibility of Salmonella enterica in Slaughtered Pigs in Sardinia

The aim of this study was to determine Salmonella occurrence in slaughtered finishing pigs and piglets and in slaughterhouse environment in order to characterize the isolates with phenotypical (antimicrobial testing) and molecular (PFGE, MLVA) methods. Nine slaughterhouses located in Sardinia were visited. Six hundred and eight samples collected from 106 pigs and 108 environmental samples were collected and analyzed. Salmonella was isolated in 65 of 504 (12.9%) samples from finishing pigs, with an occurrence of 15.1% in colon content, 12.7% in lymph nodes and liver, and 11.1% in carcass surface samples. Salmonella was never detected in piglets. The combined results of serotyping and PFGE showed a possible self‐contamination in 71.5% of Salmonella positive carcasses of lymph nodes and/or colon content carriers, pointing out the role of healthy pigs for carcass contamination. A significantly higher (P < 0.05) occurrence was detected in finishing pigs of EC countries origin (23%) than in pigs of local farms (8%). Salmonella was also detected in 3.7% of environmental samples. The most prevalent serovar was S. Anatum, followed by S. Rissen, S. Derby, and monophasic S. Typhimurium. Resistance to at least 3 antimicrobial was observed in 97.1% of strains and 7 different patterns of multiple resistance were identified. The most common resistance was detected against sulphonamide compounds. A strict slaughterhouse application of hygiene standards is essential to control the risk of Salmonella contamination.     

Pulsed field gel electrophoresis (PFGE) analysis for multidrug resistant Salmonella enterica serovar Schwarzengrund isolates collected in six years (2000-2005) from retail chicken meat in Taiwan

Salmonella Schwarzengrund is one of the causative agents of human salmonellosis and animal infections. High prevalence of multidrug resistant strains of S. Schwarzengrund from chicken meat has been recently reported in Taiwan. With an attempt to see if such prevalence in chicken meat was due to the recirculation of S. Schwarzengrund strains in traditional marketplaces, a total of 173 S. Schwarzengrund strains isolated between 2000 and 2005 from 417 retail chicken meat samples purchased from Taipei, Taiwan were analyzed using pulsed field gel electrophoresis (PFGE) method. For XbaI and AvrII digested DNA, a total of 23 and 16 PFGE patterns, respectively, were obtained. When these patterns were combined, a total of 47 subtypes were obtained and the major subtypes were X3A2, X1A2 and X2A1. Since it was found that these major subtypes were repeatedly found for multidrug resistant strains collected from 2000 to 2005, we then collected the chicken meat isolates from central and southern Taiwan in 2006. These strains did not show similar major subtypes as those found in Taipei. Such results might also suggest that the repeated appearance of some major subtypes for S. Schwarzengrund strains isolated each year in Taipei was due to the recirculation of these strains in retail marketplace during these years.     

Prevalence and serovars of Salmonella enterica on pig carcasses,slaughtered pigs and the environment of four Spanish slaughterhouses

The purpose of this study was to investigate the prevalence of Salmonella contamination and main serovars in pig slaughterhouses in Spain including carcasses, live animals and the environment. A total of 896 pig carcasses were randomly selected and swabbed before chilling in 3–5 visits to four pig slaughterhouses (A, B, C and D). Salmonella contamination was detected in 39.7% of the carcasses. The prevalence of positive carcasses was similar amongst slaughterhouses but significant differences were observed when taking sampling day into consideration within each of the slaughterhouses. Furthermore, a significant reduction in the prevalence of Salmonella contaminated carcasses (10.8%) was demonstrated in slaughterhouses C and D after chilling and cooling procedures.Sixteen batches of 10 animals were tracked from farm-to-slaughterhouse in slaughterhouses A and B to investigate the relationship between carcass contamination and contamination in live animals entering the slaughterhouse. No difference was found between infected and uninfected animals with respect to Salmonella contamination of the carcass although an increase in Salmonella contamination during the processing of live pigs into pork carcasses was evident. Regarding contamination in the slaughterhouse environment, Salmonella was isolated from most of the evaluated points in the slaughter line of the four studied slaughterhouses. Holding pens were identified as highly contaminated and what is more the ineffectiveness of the routinely cleaning protocols at this level was demonstrated in slaughterhouses C and D.The predominant Salmonella serovars found in carcasses, live pigs entering the slaughterhouse and the environment of the slaughterhouse were S. Typhimurium, S. Rissen, S. Derby and S. 4,[5],12:i:-. The same serovars were found in all the stages supporting the hypothesis that infected pigs are the main source of Salmonella contamination within slaughterhouses.     

Introduction of new multidrug-resistant Salmonella enterica strains into commercial dairy herds

A longitudinal observational study of 59 dairy herds was conducted in Washington State to estimate the rate of introduction of new multidrug-resistant (MDR) Salmonella enterica strains onto commercial dairy herds. Samples were collected on these herds over 7 visits separated by intervals of 2 to 4 mo over a period of 15 to 21 mo. Samples were cultured for Salmonella spp. and serogroup, serovar, and antimicrobial susceptibility patterns were identified for MDR Salmonella isolates. Fingerprinting generated by pulsed-field gel electrophoresis (PFGE) using XbaI restriction enzyme digestion generated genotyping profiles for all MDR isolates identified in the study. The rate of new MDR Salmonella strain introduction was 0.9 per herd-year (95% confidence interval: 0.6-1.4). The rates for the most commonly introduced MDR Salmonella serovars were 0.4/herd-year for Typhimurium, 1.2/herd-year for Newport, and 0.1/herd-year for Dublin. Thirty-three of 59 herds (56%) had at least one new MDR Salmonella introduction during the study period. The number of new MDR Salmonella strains acquired by dairy herds ranged from zero to 8. Thirteen of the 59 herds had a history of clinical salmonellosis. Among these 13 herds, 6 herds acquired new MDR Salmonella strains, although these strains were different than historical clinical strains. These data indicate that acquisition of new MDR Salmonella strains by dairy herds was a common event in participating herds, although the number of strains introduced varied greatly among herds.     

High hydrostatic pressure processing reduces Salmonella enterica serovars in diced and whole tomatoes

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. One effective post harvest treatment to reduce Salmonella enterica in tomatoes may be high pressure processing (HPP). The objectives of the study were to determine the potential for HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant of the four serovars from fresh diced and whole tomatoes. To evaluate pressure resistance, TSB containing 8 log CFU/ml of one of the four serovars was packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450 or 550 MPa) for 120 s. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150 g) and whole red round tomatoes (approximately 150 g) were inoculated with 0.1 ml of 9.1 log CFU/ml S. Braenderup, and subjected to the same pressure treatments (350, 450 or 550 MPa). Significant reductions of S. Braenderup concentrations in diced tomatoes (P < 0.05) were seen after processing at 350 (0.46 CFU/g), 450 (1.44 log CFU/g), and 550 MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P < 0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550 MPa (3.35 log CFU/g). HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in whole and diced tomatoes.     

Salmonella status of pigs at slaughter--bacteriological and serological analysis

Apart from Salmonella monitoring of pig herds during the period of growth to evaluate the efficacy of control programmes, monitoring at harvest level is of relevance to assess the Salmonella status of fattening pigs and the associated risk of introducing Salmonella organisms in the slaughter process. Samples from 1830 fattening pigs were gathered at slaughter. Ileocaecal lymph nodes, rectal and caecal content as well as tonsils were collected for bacteriological examinations, and a part of the diaphragm pillar muscle was taken to gain meat-juice for serological analysis. Salmonella spp. was recovered from 13.8% of all pigs examined. Salmonella Typhimurium and Derby were the dominating serovars. The highest detection rates were found in caecal content followed by ileocaecal lymph nodes. By analysing both organs nearly 90% of all Salmonella positive pigs could be identified. Serological examination revealed 9.6% of the pigs as positive using a cut-off value of OD % ≥ 40. Only one quarter of all Salmonella positive pigs showed also a positive serological result. A reduction of the cut-off value does not necessarily result in a higher compliance between bacteriologically and serologically positive slaughter pigs. Detection of antibodies is useful to verify whether pig herds were previously exposed to Salmonella organisms. However, the Salmonella status of pigs at time of slaughter and the associated risk of dissemination of Salmonella organisms can only be assessed by bacteriological examinations which should include both lymph nodes and caecal content.     

Characterization ofListeriastrains isolated from soft and semi-soft cheeses

Two hundred strains ofListeria monoctyogenespreviously isolated from 19 soft and semi-soft cheeses by enrichment were characterized by serotyping and pulsed-field gel electrophoresis (PFGE). Strains of serogroup 1/2 predominated, with 33.5% of all strains belonging to serovar 1/2a, 58.5% to serovar 1/2b and 5% to serovar 1/2c. By using a PFGE method, 16 different clonal types were obtained. All 10 isolates ofL. monocytogenesrecovered from one white mould cheese were serovar 1/2a, but displayed two different PFGE profiles. Another 10L. monocytogenesisolates from white mould cheese recovered after a 48-h enrichment broth procedure revealed two clonal types, only one of which could be detected after 5 additional days of incubation in the same enrichment broth. Cross-contamination in dairy plants and/or retail stores may play an important role in the incidence and diversity ofL. monocytogenesclonal types recovered from soft and semi-soft cheeses. Therefore, it is necessary to characterize several isolates from the same sample when conducting epidemiological investigations.     

Molecular characteristics and virulence potential of Listeria monocytogenes isolates from Chinese food systems

In this study, we examined Listeria monocytogenes isolates from Chinese food sources in an attempt to gain further insights on the molecular characteristics and virulence potential of this important foodborne pathogen. Of the 88 L. monocytogenes food isolates recovered, 42 (47.7%) were of serovars 1/2a or 3a; 23 (26.1%) of serovars 1/2b or 3b; 15 (17.0%) of 1/2c or 3c; 6 (6.8%) of serovars 4b, 4d or 4e; and 2 (2.2%) of serovars 4a or 4c. In contrast to inlAB locus conserved in all serovars, internalin cluster between ascB and dapE varies with different serovars, with inlC2DE, inlGC2DE and inlGHE predominantly in serovars 1/2b or 4b, serovar 1/2a and serovar 1/2c. While inlF existed in all the inlGHE- and inlGC2DE-containing isolates but 17.4% of those having inlC2DE, lmo2026 existed in all the inlGHE-containing isolates but 20.0% of those bearing inlGC2DE, suggesting that inlF might have co-evolved with inlGC2DE and inlGHE while lmo2026 with inlGHE only. With the exception of serovar 4a isolate, most serovar isolates demonstrated remarkable ability to form plaques on L929 cells and produced significant mouse mortality irrespective of the internalin gene organization and whether an intact actA gene is present or not. These results indicate that majority of these food isolates may have the potential to cause human diseases if ingested via contaminated foods. Given that serovar 4b accounts for nearly half of human clinical listeriosis cases documented, the relative low proportion of serovar 4b food isolates suggests that this serovar is probably more tolerant of the adverse conditions in the host's stomach and/or more efficient in entering host cells than serovars 1/2a, 1/2b and 1/2c.     

Characterization of the quinolone resistance mechanism in foodborne Salmonella isolates with high nalidixic acid resistance

Sixteen Salmonella strains resistant to nalidixic acid isolated from kimbab, the most popular ready-to-eat (RTE) food in Korea, and chicken meat were selected for this study. The resistant strains were shown to have high minimal inhibitory concentrations (MICs) against nalidixic acid (512 ~ 4096 μg/mL). Among them, 4 Salmonella enterica serovar Haardt isolates showed multi-drug resistance (MDR) patterns with reduced susceptibility to fluoroquinolone (0.5 μg/mL of ciprofloxacin MICs). The mechanisms of quinolone resistance in the nalidixic acid resistant strains were characterized by PCR and sequence analysis. The presence of plasmid-mediated quinolone resistance (PMQR) genes and amino acid changes in the quinolone resistance determining region (QRDR) were investigated by PCR-based detection and sequencing, and the efflux pump inhibition test was also done using phe-arg-β-naphthylamide (PAβN). Although PMQR genes were not detected in any of the tested strains, the QRDR mutations were found in this study: single mutation in gyrA (Asp87Tyr, Asp87Gly, and Asp87Asn), double mutations in gyrA (Ser83Thr) and parC (Thr57Ser), and single mutation in parC (Thr57Ser). MICs of nalidixic acid were reduced by 2- to 32-folds by the efflux pump inhibitor, PAβN. Pulsed-field gel electrophoresis (PFGE) was carried out to confirm the epidemiological relationship between the nalidixic acid resistant strains. The PFGE patterns were classified into 6 groups at cutoff level of 70 ~ 100% correlation on the dendrogram. Some strains of serotype Haardt and Enteritidis showed several values of genomic identity in accordance with strains, sources, and isolation year. We suggest that point mutation on QRDR and efflux pump systems involved in antimicrobials had independent effects on drug-resistance regardless of bacterial genomic variation.     

Comparison of the pulsed field gel electrophoresis patterns and virulence profiles of the multidrug resistant strains of Salmonella enterica serovar Schwarzengrund isolated from chicken meat and humans in Taiwan

Salmonella Schwarzengrund is one of the frequent serovars isolated from chicken meat in Taiwan. This organism is also one of the invasive Salmonella serovars which may cause human salmonellosis and animal infections. In this study, a total of 466 strains of S. Schwarzengrund including 232 retail chicken meat isolates and 234 human isolates in Taiwan were analyzed for their antibiotic resistance and pulsed field gel electrophoresis (PFGE) patterns. For XbaI-digested DNA, a total of 110 PFGE patterns were obtained. When patterns from both origins were analyzed, of these patterns, 21 were shared by isolates from chicken meat samples and humans. In these 21 patterns, 153 (32.8%) isolates from both origins shared the top five patterns. Since ACSSXTT R-type strains are the major concern worldwide and they accounted for 74.5% of total strains used in this study, such R-type strains in the top five XbaI-digested patterns were then further analyzed with AvrII digestion followed by PFGE and PCR assay targeted to 10 Salmonella virulence genes, i.e., avrA, ssaQ, mgtC, siiD, sopB, gipA, sodC1, sopE1, spvC, and bcfC. When PFGE patterns and virulence gene profiles were combined for the analysis of ACSSXTT R-type strains of S. Schwarzengrund, 29 strains from both origins showed the same pattern combinations. Such results suggested the possible transmission of S. Schwarzengrund from chicken meat to humans.     

Prevalence and characterization of Salmonella enterica serovar Weltevreden from imported seafood

During 2001-2005, 210 Salmonella enterica strains were isolated from seafood samples imported into US. Strains of S. enterica serovar Weltevreden were the most predominantly found among the 64 different serovars isolated. A total of 37 Salmonella Weltevreden isolates were characterized by pulsed-field gel electrophoresis (PFGE), plasmid profiles and antibiotic susceptibility to assess genetic diversity. Our results showed a low frequency of antibiotic resistance; 35 of the 37 isolates were sensitive to ampicillin, tetracycline, chloramphenicol, gentamicin, sulfisoxazole, streptomycin and kanamycin. Only two isolates, from samples originating in the Philippines and India, showed resistance to ampicillin and tetracycline and to streptomycin, sulfisoxazole and tetracycline, respectively. Of the 37 isolates, two isolates did not carry any plasmid and 35 isolates harbored several small and mega-plasmids. These isolates were differentiated into 10 distinct types based on plasmid profiles. Four different PFGE clusters were obtained with a genetic similarity of 66-76%. Four groups of isolates (formed by two or three isolates each) showed 100% similarity in the PFGE profiles. One of these groups included strains isolated in Vietnam in 2003, 2004 and 2005 from fish and shrimp. The other groups included strains isolated in Vietnam, Indonesia and Thailand in 2000, 2004 and 2005 from snail, shrimp and fish. Our findings show genetic diversity and temporal persistence of S. enterica serovar Weltevreden in recently monitored seafood imports.     

Characterization of Salmonella Enteritidis isolated from human samples

This study aimed to characterize Salmonella Enteritidis (SE) isolated from blood (n = 12) and feces (n = 68) of salmonellosis victims in Southern Brazil. All isolates were submitted to antimicrobial susceptibility testing, PCR-ribotyping, and XbaI macrorestriction Pulsed-Field Gel Eletrophoresis (PFGE). Results demonstrated high levels of ampicillin and nalidixic acid resistance, and strains isolated in different geographic regions were clustered together, presenting a common resistance profile. All strains demonstrated similar and related PCR-ribotyping patterns (R1, R2, and R3); being that the predominant profile R1 grouped 47.5% of the strains. PFGE profile P1 grouped the majority of the strains (96.25%), suggesting a clonal relationship among the strains or inability of molecular typing methods to discriminate strains of this serovar. Results suggested on an increase in antimicrobial resistance and that strains of S. Enteritidis with similar PFGE and PCR-ribotyping profiles were involved in several salmonellosis outbreaks in Southern Brazil.     

Antibiotic Resistance and Molecular Characterization of Seafood Isolates of Nontyphoidal Salmonella by PFGE

Emergence of multidrug resistant nontyphoidal Salmonella is a major health concern worldwide due to the predominant occurrence of Salmonella enterica sub-species enterica serovar Typhimurium phage type 104 (DT104) conferring resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline. Apart from antibiotic resistance, the identification and genotypic characterization of pathogens is essential for epidemiological surveillance and outbreak investigations. In this study 39 isolates of Salmonella obtained from seafood samples were examined for their susceptibility to various antibiotics and subjected to PFGE analysis using the restriction enzyme Xba1. The highest percentage resistance was for erythromycin (100%) followed by nalidixic acid (15.38%), co-trimoxazole (15.38%), chloramphenicol (12.82%), ampicillin (12.82%) and tetracycline (10.25%). Six (15.38%) of the 39 isolates were multidrug resistant. The XbaI digested chromosomal DNA generated 7 clusters suggesting the presence of diverse Salmonella strains in seafood. The Discriminatory Index for PFGE obtained by XbaI restriction enzyme was 0.91. The PFGE has been found highly discriminatory for subtyping S. Weltevreden and S. Newport. The XbaI PFGE was not only discriminatory but could also distinguish multidrug-resistant strains from the sensitive ones as the two groups they belonged to different pulsotypes. The study also demonstrated multiple clones of S. Weltevreden, S. Newport and S. Oslo present in seafood from the south west coast of India. Genetic diversity among the similar seafood sources suggests the presence of different clones of Salmonella which further increases the risk of seafood being a potential source of highly pathogenic bacteria like Salmonella.     

Characterization of the novel Listeria monocytogenes PCR serogrouping profile IVb-v1

The World Health Organization Collaborating Centre for Listeria (WHOCCL) has developed in 2004 a multiplex PCR assay that separates the 4 major Listeria monocytogenes serovars (1/2a, 1/2b, 1/2c, and 4b) into distinct PCR serogroups. A new PCR profile has been recently identified, constituted of amplified DNA fragments of prs, ORF2819, ORF2110 and lmo0737. Here we characterize 22 L. monocytogenes isolates of the WHOCCL collection with this PCR IVb variant 1 (IVb-v1) profile. The 22 isolates belong to the clinically predominant serovar 4b, exhibit 6 distinct pulsed-field gel electrophoresis ApaI/AscI combined profiles, and belong to 2 unrelated multilocus sequence types, indicating that the novel profile does not correspond to a recent clonal emergence. We have updated the WHOCCL serogroup-related PCR typing scheme to include this new profile.