Molecular characterization of extended-spectrum cephalosporin and fluoroquinolone resistance genes in Salmonella and Shigella isolated from clinical specimens in Thailand

Antimicrobial resistance of Salmonella and Shigella has become a major clinical and public health problem. The incident of co-resistance to third generation cephalosporins and fluoroquinolone is a serious therapeutic issue in Thailand. The present study aimed to investigate the antimicrobial resistance and molecular character of clinical Shigella and Salmonella isolates. A total of 33 Salmonella and 53 Shigella cefotaxime-resistant isolates were collected from human clinical cases in Thailand during the period from 2011-2018. The antimicrobial susceptibility of Salmonella and Shigella was determined by the disk diffusion method, and extended-spectrum beta-lactamase (ESBL) production was characterized by the double-disk synergy test. Genotype characterization was performed by PCR and DNA sequencing. Thirty-two (97.0%) and fifty-two (98.1%) isolates of cefotaxime-resistant Salmonella and Shigella, respectively, were identified as ESBL producers. Shigella sonnei (4 isolates), Salmonella serovar 4,5,12:i:- (6 isolates), Salmonella serovar Agona (2 isolates) and Salmonella serovar Rissen (2 isolates) showed co-resistance to ciprofloxacin and cefotaxime or ceftriaxone. The combination of bla _CTX-M-15 plus other ESBL and/or AmpC β-lactamase genes was the most dominant of the genotype patterns in ESBL-producing isolates. The plasmid harbouring the aac(6')-Ib-cr gene and mutations of gyrA (S83F, D87Y or D87G) and parC (T57S) genes was found in 2 ESBL-producing Salmonella isolates. Three Shigella sonnei isolates harboured mutations in gyrA (S83L, D87Y or D87G), and only one Shigella sonnei phase I isolate showed mutations in both gyrA (S83L and D87G) and parC (S80I) genes. Among these clinical Shigella sonnei isolates, qnrS determinants were identified. Production of ESBLs is an important mechanism for resistance to extended-spectrum cephalosporins in Salmonella and Shigella. The emergence of a decreased susceptibility to extended-spectrum cephalosporins and fluoroquinolone in ESBL-producing isolates has important clinical and therapeutic implications.

Prevalence and Multidrug Resistance of Salmonella in Swine Production Chain in a Central Province, Thailand

ABSTRACT

Salmonella causes foodborne disease outbreaks worldwide and raises concerns about public health and economic losses. To determine prevalence, serovar, antimicrobial resistance patterns, and the presence of extended-spectrum β-lactamase (ESBL) genes in a cross-sectional study, 418 total samples from feces and carcasses (from three slaughterhouses) and pork and cutting boards (from four markets) were collected in a central Thailand province in 2017 and 2018. Of the 418 samples, 272 (65.1%) were positive for Salmonella. The prevalence of Salmonella-positive samples from markets (158 of 178; 88.8%) was significantly higher than that among samples from slaughterhouses (114 of 240; 47.5%) (P < 0.05). A total of 1,030 isolates were identified; 409 were assigned to 45 serovars, with Salmonella Rissen the most common (82 of 409; 20%). Two serovars, Salmonella Cannstatt and Salmonella Braubach, were identified for the first time in Thailand in market and slaughterhouse samples, respectively. Among 180 isolates representing 19 serovars, 133 (73.9%) exhibited multidrug resistance. Screening for ESBL production revealed that 41 (10.3%) of 399 isolates were ESBL positive. The prevalence of ESBL-producing Salmonella isolates was significantly higher among the market isolates (31 of 41; 75.6%) than among the slaughterhouse isolates in (10 of 41; 24.4%) (P < 0.05). In market samples, 24 (77.4%) of 31 isolates were recovered from pork and 7 (22.6%) were recovered from cutting boards. Nine ESBL-producing isolates carried single ESBL genes, either blaTEM (4 of 41 isolates; 9.8%) or blaCTX-M (5 of 41 isolates; 12.2%), whereas 11 (26.8%) carried both blaTEM and blaCTX-M. No ESBL-producing Salmonella isolate carried the blaSHV gene. These results suggest that pigs, their flesh, and cutting boards used for processing pork could be reservoirs for widespread ESBL-producing Salmonella isolates with multidrug resistance and outbreak potential across the food chain.

HIGHLIGHTS

Prevalence and antimicrobial susceptibility of Campylobacter isolated from retail chickens in Thailand

Campylobacter is an important foodborne pathogen causing bacterial gastroenteritis worldwide; however, there has been a lack of information over the past decade on its occurrence, antibiotic susceptibility and genetic diversity in Thailand. Poultry meat is considered as a reservoir for transmission of Campylobacter to humans. This study determines the prevalence and antimicrobial resistance patterns of Campylobacter spp. on chicken samples purchased from 50 local wet markets and supermarkets in central Thailand. Of the 296 samples, 99 (33.5%) were contaminated with C. jejuni, 54 (18.2%) were C. coli and 15 (5.1%) were contaminated with both species. Antibiotic resistance rate is higher among C. coli isolates; 100%, 76.8%, 37.7%, 36.2% and 13.0% were resistant to quinolones, cyclines, macrolides, clindamycin and gentamicin, respectively. Most of the C. jejuni isolates were resistant to quinolones (79.8%) and cyclines (38.6%) whereas resistance to macrolides, clindamycin and gentamicin was found to be 1.8%. Multi-drug resistance (i.e. to three or more unrelated antimicrobials) was detected in 37.7% of C. coli and 1.8% of C. jejuni isolates. This study has revealed high contamination rates and alarming levels of antimicrobial resistance in Campylobacter spp. isolated from retail chicken samples in Thailand, suggesting the necessity of implementing interventions to reduce its prevalence from farm to table in the country.

Risk of Antimicrobial Resistant Non-Typhoidal Salmonella during Asymptomatic Infection Passage between Pet Dogs and Their Human Caregivers in Khon Kaen, Thailand

To explore the risk of antimicrobial resistant (AMR) non-typhoidal Salmonella during asymptomatic infection passage between pet dogs and human caregivers in Khon Kaen, Thailand, one hundred forty paired fecal samples (n = 280) were obtained from companion dogs and their human caregivers, interviewed from 140 households during 2019-2020. The purified Salmonella isolates were serotype-identified and tested for antimicrobial resistance against ampicillin, ciprofloxacin, chloramphenicol, nalidixic acid, streptomycin, sulfamethoxazole-trimethoprim, and tetracycline. The homologous Salmonella isolate pairs (suggesting Salmonella infections may have been due to passage between each one of the pair, or derived from the same source) were subsequently characterized by serotype screening, pulsed field gel electrophoresis (PFGE), and Synchrotron Fourier transform infrared spectroscopy (SR-FTIR). The Salmonella prevalence observed in dogs, 12.86% (18/140), was not significantly different from that observed in humans, 17.86% (25/140) using McNemar's test. The AMR patterns (the patterns among the isolates of pet dogs and caregivers) and the serotypes (thirteen serotypes with 18 isolates from pet dogs plus thirteen serotypes with 25 isolates from humans) between pet dogs and humans were not significantly different using Pearson's chi-squared test. The homologous Salmonella isolates from the Salmonella-present households was 5.13% (2/39). This study demonstrated that the hypothesis that there is a high risk of Salmonella infection passage between dogs and humans with close contact in Khon Kaen is doubtful. Only 5.13% of homologous Salmonella isolates from Salmonella-present households were found in Khon Kaen, Thailand, although the prevalence of Salmonella-positive samples, serotypes, and antimicrobial resistance patterns were quite similar among the two populations.

CRISPR 2 PCR and high resolution melting profiling for identification and characterization of clinically-relevant Salmonella enterica subsp. enterica

Background

Nontyphoidal Salmonella spp. constitute a major bacterial cause of food poisoning. Each Salmonella serotype causes distinct virulence to humans.

Method

A small cohort study was conducted to characterize several aspects of Salmonella isolates obtained from stool of diarrheal patients (n = 26) admitted to Phayao Ram Hospital, Phayao province, Thailand. A simple CRISPR 2 molecular analysis was developed to rapidly type Salmonella isolates employing both uniplex and high resolution melting (HRM) curve analysis.

Results

CRISPR 2 monoplex PCR generated a single Salmonella serotype-specific amplicon, showing S. 4,[5],12:i:- with highest frequency (42%), S. Enteritidis (15%) and S. Stanley (11%); S. Typhimurium was not detected. CRISPR 2 HRM-PCR allowed further classification of S. 4,[5],12:i:- isolates based on their specific CRISPR 2 signature sequences. The highest prevalence of Salmonella infection was during the summer season (April to August). Additional studies were conducted using standard multiplex HRM-PCR typing, which confirmed CRISPR 2 PCR results and, using a machine-learning algorithm, clustered the majority of Salmonella serotypes into six clades; repetitive element-based (ERIC) PCR, which clustered the serotypes into three clades only; antibiogram profiling, which revealed the majority resistant to ampicillin (69%); and test for extended spectrum β-lactamase production (two isolates) and PCR-based detection of bla alleles.

Conclusion

CRISPR 2 PCR provided a simple assay for detection and identification of clinically-relevant Salmonella serotypes. In conjunction with antibiogram profiling and rapid assay for β-lactamase producers, this approach should facilitate detection and appropriate treatment of Salmonellosis in a local hospital setting. In addition, CRISPR 2 HRM-PCR profiling enabled clustering of S. 4,[5],12:i:-isolates according to CRISPR 2 locus signature sequences, indicative of their different evolutionary trajectories, thereby providing a powerful tool for future epidemiological studies of virulent Salmonella serotypes.

Occurrence of a novel class 1 integron harboring qnrVC4 in Salmonella Rissen

We described qnrVC4 in S. Rissen 166ANSS50, a swine isolate, which was detected in the study on quinolone resistance mechanisms of nontyphoidal Salmonella in Thailand. The isolate was found to harbor a ̴17-kb non-conjugative plasmid carrying qnrVC4 within 8.91kb of a novel In4-like class 1 integron (In805). It contained the multi-drug resistance gene cassettes of qnrVC4-qacH4-aacA4-cmlA7-bla_OXA-10-aadA1-dfrA14 and unusual 3'-CS of mobC-IS6100. This 1014-bp qnrVC4 cassette included with promoter (P_qnrVC4: -35 TTGAGA and -10 TAGTCT) showed high homology with qnrVC4 in superintegron of V. cholerae O1 El Tor. The qnrVC4 recombinant plasmid resulted in 4-, 8-, and 16-fold increase in the MICs of nalidixic acid (2-8μg/mL), ciprofloxacin (0.015-0.125μg/mL), and norfloxacin (0.03-0.5μg/mL), respectively. In addition, the backbone plasmid revealed a novel replicon belonging to the MOB_Q1 group from the broad-host-range mobilisable IncQ1 plasmid RFS1010 based on relaxase sequences. This is the first known report of qnrVC in Salmonella enterica. The qnrVC4 gene was co-transferred with other resistance genes via a novel plasmid-borne In805. This allowed the spread of this resistance gene to Enterobacteriaceae.

Strengthening public health laboratory capacity in Thailand for International Health Regulations (IHR) (2005)

INTRODUCTION

Thailand conducted a national laboratory assessment of core capacities related to the International Health Regulations (IHR) (2005), and thereby established a baseline to measure future progress. The assessment was limited to public laboratories found within the Thai Bureau of Quality and Safety of Food, National Institute of Health and regional medical science centres.

METHODS

The World Health Organization (WHO) laboratory assessment tool was adapted to Thailand through a participatory approach. This adapted version employed a specific scoring matrix and comprised 16 modules with a quantitative output. Two teams jointly performed the on-site assessments in December 2010 over a two-week period, in 17 public health laboratories in Thailand. The assessment focused on the capacity to identify and accurately detect pathogens mentioned in Annex 2 of the IHR (2005) in a timely manner, as well as other public health priority pathogens for Thailand.

RESULTS

Performance of quality management, budget and finance, data management and communications was considered strong (>90%); premises quality, specimen collection, biosafety, public health functions, supplies management and equipment availability were judged as very good (>70% but ≤90%); while microbiological capacity, staffing, training and supervision, and information technology needed improvement (>60% but ≤70%).

CONCLUSIONS

This assessment is a major step in Thailand towards development of an optimized and standardized national laboratory network for the detection and reporting of infectious disease that would be compliant with IHR (2005). The participatory strategy employed to adapt an international tool to the Thai context can also serve as a model for use by other countries in the Region. The participatory approach probably ensured better quality and ownership of the results, while providing critical information to help decision-makers determine where best to invest finite resources.

Dissemination of clonal Salmonella enterica serovar Typhimurium isolates causing salmonellosis in Mauritius

Salmonella enterica serotype Typhimurium is one of the leading causes of salmonellosis in Mauritius, where it has also been associated with outbreaks of foodborne illness. However, little is known about its molecular epidemiology in the country. This study was therefore undertaken to investigate the clonality and source of Salmonella Typhimurium in Mauritius by studying human, food, and poultry isolates by pulsed-field gel electrophoresis (PFGE) and antibiotic minimum inhibitory concentration determination. Forty-nine isolates collected between 2008 and 2011 were analyzed, including 25 stool isolates from foodborne illness outbreaks and sporadic gastroenteritis cases, four blood isolates, one postmortem colon isolate, 14 food isolates, and five poultry isolates. All isolates were pansusceptible to the 16 antibiotics tested, except for two isolates that were resistant to sulfamethoxazole and trimethoprim. Overall characterization of the isolates by PFGE digested with XbaI and BlnI resulted in eight different patterns. The largest of the clusters in the composite dataset consisted of 20 isolates, including two raw chicken isolates, four poultry isolates, and nine human stool isolates from two outbreaks. A second cluster consisted of 18 isolates, of which 12 originated from human blood and stool samples from both sporadic and outbreak cases. Six food isolates were also found in this cluster, including isolates from raw and grilled chicken, marlin mousse, and cooked pork. One poultry isolate had a closely related PFGE pattern. The results indicate that one clone of Salmonella Typhimurium found in poultry has been causing outbreaks of foodborne illness in Mauritius and another clone that has caused many cases of gastrointestinal illness and bacteremia in humans could also be linked to poultry. Thus, poultry appears to be a major reservoir for Salmonella Typhimurium in Mauritius. Initiating on-farm control strategies and measures against future dissemination may substantially reduce the number of cases of salmonellosis in the country.

Characterization of Salmonella enterica serovar Enteritidis isolates recovered from blood and stool specimens in Thailand

Background

Bacteremia due to Salmonella spp. is a life-threatening condition and is commonly associated with immune compromise. A 2009 observational study estimated risk factors for the ten most common non-typhoidal Salmonella (NTS) serovars isolated from Thai patients between 2002–2007. In this study, 60.8% of Salmonella enterica serovar Enteritidis isolates (n = 1517) were recovered from blood specimens and infection with Salmonella serovar Enteritidis was a statistically significant risk factor for bacteremia when compared to other NTS serovars. Based on this information, we characterized a subset of isolates collected in 2008 to determine if specific clones were recovered from blood or stool specimens at a higher rate. Twenty blood isolates and 20 stool isolates were selected for antimicrobial resistance testing (MIC), phage typing, PFGE, and MLVA.

Result

Eight antibiogrammes, seven MLVA types, 14 XbaI/BlnI PFGE pattern combinations, and 11 phage types were observed indicating considerable diversity among the 40 isolates characterized. Composite analysis based on PFGE and MLVA data revealed 22 genotypes. Seven of the genotypes containing two or more isolates were from both stool and blood specimens originating from various months and zones. Additionally, those genotypes were all further discriminated by phage type and/or antibiogramme. Ninety percent of the isolates were ciprofloxacin resistant.

Conclusions

The increased percentage of bloodstream infections as described in the 2009 observational study could not be attributed to a single clone. Future efforts should focus on assessing the immune status of bacteriaemic patients and identifying prevention and control measures, including attribution studies characterizing non-clinical (animal, food, and environmental) isolates.

Salmonella serovar distribution in cobras (Naja kaouthia), snake-food species, and farm workers at Queen Saovabha Snake Park, Thailand

The purpose of the current study was to investigate the prevalence and serovar distribution of Salmonella isolates in cobras and their environment at a snake park. A total of 166 fecal or intestinal samples were examined, comprising 39 samples from captive cobras (Naja kaouthia), 70 from recently wild-caught cobras, 19 from wild-caught cobras that had been kept on the farm for over 3 months, 18 from mice (Mus musculus), 12 from frogs (Hoplobatrachus rugulosus), and 8 from farm workers. Specific serological identification was performed, and pulsed-field gel electrophoresis (PFGE) was utilized for DNA analysis. Out of all snakes (n = 128), 20 of the 30 animals used for snake food and 3 of the 8 samples from personnel were positive for Salmonella spp. There were 228 Salmonella isolates, with a total of 29 serovars from subspecies I and IIIb, composed of 24 serovars from cobras and 5 from the other sources. Salmonella Amsterdam was predominant in captive-born and captive cobras, followed by S. Poona and S. Bareilly, respectively (P < 0.05). Salmonella I 4,[5],12:i:- was the sole serovar detected from the mice, while 3 serovars including Ramatgan, I 4,[5],12:e,h:-, and rough strain were detected only from frogs (P < 0.001). Salmonella Derby was only detected in workers. On the basis of the PFGE results, evidence of movement of isolates between human beings and snakes, and between snakes and frogs, was found for S. Poona and S. Wandsworth, respectively. The study suggests that Salmonella spp. act as true residents in the intestinal tract of cobras with high risk of environmental contamination through fecal shedding.

Epidemiological investigation of Salmonella enterica serovar Kedougou in Thailand

OBJECTIVE

Salmonella enterica serovar Kedougou is among the top 10 serovars reported in northern Thailand. The objective of this study was to identify risk factors associated with Salmonella Kedougou infection in Thailand and to compare the molecular types and antimicrobial resistance with Salmonella Kedougou isolates of human origin from United States and of animal origin from the United Kingdom.

METHODS

Data from 13,976 Salmonella infections of which 253 were Salmonella Kedougou collected in Thailand between 2002 and 2008 were analyzed by logistic regression. Antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) were performed on selected Salmonella Kedougou strains causing infections in Thailand (n = 66), and compared to isolates from the United States (n = 5) and the United Kingdom (n = 20).

RESULTS

Logistic analysis revealed season (hot/dry; p = 0.023), region (northern Thailand; p < 0.001), and specimen (stool; p < 0.001) as significant risk factors associated with Salmonella Kedougou infection compared to other nontyphoid Salmonella. Of the Salmonella Kedougou isolates of human origin, 84% exhibited resistance to at least three antimicrobial classes. Three strains recovered from human stool in Thailand were resistant to third-generation cephalosporins: two harbored bla(CTX-M-63) and one bla(CMY-2). PFGE revealed 45 unique clusters. Isolates obtained from humans in Thailand and the United States presented identical PFGE profiles suggesting a travel association, whereas the majority of the animal isolates from United Kingdom clustered separately.

CONCLUSIONS

This study reveals Salmonella Kedougou as a major cause of human infections in northern Thailand especially during the hot period and suggests a global spread probably due to travel. The clonal types causing infections in humans differed from those observed in animals in United Kingdom, which suggests the absence of an epidemiological link and could suggest differences in virulence. The high frequency of antimicrobial resistance, including emergence of resistance to fluoroquinolones and third-generation cephalosporins, might pose problems for treatment of infections.

Risk factors and epidemiology of the ten most common Salmonella serovars from patients in Thailand: 2002-2007

We conducted a retrospective observational study to assess epidemiological trends and risk factors associated with the 10 most common Salmonella serovars isolated from humans in Thailand between 2002 and 2007. A total of 11,656 Salmonella isolates covering all 6 years were included in the study. The top 10 Salmonella serovars identified during the course of this study were Enteritidis, Stanley, Weltevreden, Rissen, I [1],4,[5],12:i:-, Choleraesuis, Anatum, Typhimurium, Corvallis, and Panama, which accounted for 8108 (69.6%) of the isolates. Most isolates were from patients <5 years (33%), were isolated during June (13%), and were recovered from stool (82%) and from patients in Bangkok (27%). Statistical analysis revealed that S. Enteritidis and S. Choleraesuis were recovered from blood with a higher frequency than other nontyphoidal serovars. While both serovars tended to be isolated from patients >5 years; S. Choleraesuis was recovered with a higher frequency from patients in Bangkok and the central region, whereas S. Enteritidis was recovered predominantly from patients in the southern region. This study also indicates a shift in prevalence of the most common Salmonella serovars responsible for human infections in Thailand compared to previous studies. Notably, there was an increase in human infections with S. Stanley, S. Corvallis, and S. Choleraesuis, three serovars that have previously been associated with swine, and a decrease in infections due to S. Weltevreden and S. Anatum. The study also revealed differences in the epidemiology among the different serovars, suggesting that serovar-specific interventions are needed. We recommend initiating targeted interventions for the two serovars associated with a high odds ratio for submitted blood samples, S. Enteritidis and S. Choleraesuis. The authors also recommend additional epidemiologic studies to investigate the observed increase in swine associated serovars (S. Stanley, S. Corvallis, and S. Choleraesuis) and determine interventions to reduce the burden of disease from these serovars.

Shigella species and serotypes among clinical isolates in Thailand from 2001 to 2005

OBJECTIVE

To study the species and the serotypes of the clinical isolates of Shigella obtained from patients in Thailand.

MATERIAL AND METHOD

The World Health Organization National Salmonella and Shigella Center Thailand, had confirmed the species and performed serotype identification of 1,913 clinical isolates of Shigella collected from the laboratory network of Department of Medical Sciences and the collaborated hospitals across Thailand from 2001 to 2005.

RESULTS

Between the year 2001 and 2005, 728, 481, 160, 247, 297 clinical isolates were tested, respectively. There were 5 isolates of S. dysenteriae (group A), 416 isolates of S. flexneri (group B), 4 isolates of S. boydii (group C) and 1,488 isolates of S. sonnei (group D). A total of 21 Shigella serotypes were identified and there were 3 serotypes in group A, 11 serotypes in group B, 4 serotypes in group C, and 3 serotypes in group D. Throughout these five years, the five common serotypes were S. sonnei Phases I and II, 28.6% (548 isolates); S. sonnei Phase I, 24.6% (470 isolates); S. sonnei Phase II, 24.6% (470 isolates); S. flexneri Type 2a, 10.9% (208 isolates), and S. flexneri Type 3a, 6.3% (121 isolates), respectively.

CONCLUSION

At the national scale in Thailand from 2001 to 2005, S. sonnei was the most frequent Shigella spp. isolated from patients in Thailand. In addition, S. dysenteriae and S. boydii were extremely uncommon. These findings are important in future vaccine development.

Shigella from humans in Thailand during 1993 to 2006: spatial-time trends in species and serotype distribution

In Thailand during 1993-2006, a total of 9063 Shigella isolates from different medical centers were serotyped and trends over time and spatial clustering analyzed. Of 3583 cases with age information, 1315 (37%) cases were from children between 0 and 4 years and 684 (19%) from children between 5 and 8 years. Most infections were recorded during 1993-1994 (> 1500 per year), decreasing to < 200 in 2006. The relative species distribution also changed. During 1993-1994, Shigella flexneri accounted for 2241 (65%) of 3474 isolations. This proportion decreased to 64 (36%) of 176 infections in 2006. Most infections occurred during July and August, and fewest in December. S. flexneri clustered around Bangkok, and Shigella sonnei in southern Thailand. Most S. flexneri infections were caused by serotype 2a (1590 of 4035) followed by serotype var X (1249). For both serotypes, a pronounced decrease in the number of isolates occurred over time. A much smaller decrease was observed for serotype 3a isolates. Phase I S. sonnei was initially most common, but shifted gradually over phase I, II, to only phase II. No differences in spatial distribution were found. The three most common S. flexneri serotypes all clustered in, around, and west of Bangkok. Serotypes 2a and 3a also clustered in southern Thailand, whereas var X clustered north and northeast of Bangkok. In conclusion, looking at Shigella species, Thailand changed from being a developing country to a developed country between 1995 and 1996. In addition, major shifts in the types of S. sonnei were observed as were differences in spatial clustering of S. flexneri and S. sonnei and S. flexneri serotypes.

The epidemiological relationship between Salmonella enterica serovar typhimurium and Salmonella enterica serovar 4,[5],12:i:- isolates from humans and swine in Thailand

A total of 138 isolates of S. Typhimurium and S. 4,[5],12:i:- from humans and swine in Thailand during 2003-2006, were evaluated for antimicrobial sensitivity by the disk diffusion method against 10 antimicrobial drugs and pulsed-field gel electrophoresis (PFGE) with endonuclease Xbal to investigate the epidemiological relationship among isolates. It was found that all isolates were classified into 27 antimicrobial resistance patterns, and 80% of S. Typhimurium and 95.4% of S. 4,[5],12:i:- isolates were resistant to three or more antimicrobial agents. By PFGE testing, the 84 PFGE patterns were categorized into A to Z patterns. Eighty percent of S. Typhimurium and 71.3% of S. 4,[5],12:i:- isolates in 7 major PFGE patterns had close clonal relationships (_85% similarity). Our studies indicate the spread of genetically identical clones of S. Typhimurium and S. 4,[5],12:i:- in humans and swine in Thailand.

International spread of multidrug-resistant Salmonella Schwarzengrund in food products

This serovar was isolated from persons, food, and food animals in Thailand, Denmark, and the United States.

We compared 581 Salmonella enterica serotype Schwarzengrund isolates from persons, food, and food animals in Denmark, Thailand, and the United States by antimicrobial drug susceptibility and pulsed-field gel electrophoresis (PFGE) typing. Resistance, including resistance to nalidixic acid, was frequent among isolates from persons and chickens in Thailand, persons in the United States, and food imported from Thailand to Denmark and the United States. A total of 183 PFGE patterns were observed, and 136 (23.4%) isolates had the 3 most common patterns. Seven of 14 isolates from persons in Denmark had patterns found in persons and chicken meat in Thailand; 22 of 390 human isolates from the United States had patterns found in Denmark and Thailand. This study suggests spread of multidrug-resistant S. Schwarzengrund from chickens to persons in Thailand, and from imported Thai food products to persons in Denmark and the United States.

Recovery of Salmonella using a combination of selective enrichment media and antimicrobial resistance of isolates in meat in Thailand

From November 2004 to March 2005, 50 samples (chicken, pork and beef) of registered meat and non-registered meat were purchased from supermarkets and retail markets located in Bangkok, Thailand. Each sample was evaluated for Salmonella spp by a conventional method using combination of selective enrichment media (RV+MSRV) and compared with selective enrichment medium alone (DIASALM). Our study revealed the performance of RV+MSRV for the detection of Salmonella spp was significantly better than those of DIASALM alone since the recovery of Salmonella spp in both groups of meat was high using RV+MSRV, particularly in the registered meat. In addition, the recovery of serovars in registered meat was significantly higher than those in non-registered meat. Antimicrobial resistance of 62 Salmonella isolates in both groups of meat was determined for 10 antimicrobial drugs using the disk diffusion method. The results show that 100% of isolates from both groups were susceptible to amoxicillin/clavulanic acid, ciprofloxacin, cefotaxime and norfloxacin and 50-60% of isolates from both groups were resistant to tetracycline, streptomycin and ampicillin. Sixty percent of Salmonella isolates from meat showed multiresistance antimicrobial patterns.

Salmonella lamphun: first isolation of a new Salmonella serovar in Thailand

Two isolates of a new Salmonella serovar, Salmonella Lamphun were discovered from animal feeds in Thailand, in 2003, which belongs to group C, with antigenic formula 6,8:y: 1,2. Both isolates were susceptible to all antimicrobials tested. The pulsed field gel electrophoresis pattern of both isolates comprises 11 DNA fractions sized 48, 65, 77, 105, 110, 170, 244, 330, 337,453 and 1,135 kbp. Up to April 2005, no human or animal infection by this new Salmonella serovar was reported.

Salmonella serovars from humans and other sources in Thailand, 1993-2002

We serotyped 44,087 Salmonella isolates from humans and 26,148 from other sources from 1993 through 2002. The most common serovar causing human salmonellosis in Thailand was Salmonella enterica Weltevreden. Serovars causing human infections in Thailand differ from those in other countries and seem to be related to Salmonella serovars in different food products and reservoirs.