Chaiwat Pulsrikarn

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.

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.

Antimicrobial Resistance and Molecular Epidemiology of Salmonella Rissen from Animals, Food Products, and Patients in Thailand and Denmark

Recently we reported increases in both the number of Salmonella infections due to Salmonella Rissen in Thailand and the isolation of this serovar from pork products in Thailand. The objectives of the present study were to determine the genetic diversity and antimicrobial resistance of Salmonella Rissen isolates recovered from humans, food products, and animals in Denmark and Thailand. Additionally, risk factors due to travel and consumption of specific food products were analyzed and evaluated. A total of 112 Salmonella Rissen isolates were included in this study from Thailand and Denmark. Thai isolates were recovered from humans, uncooked food, and ready-to-eat food. Danish isolates were obtained from humans (with and without a history of travel to Thailand prior to the infection), Danish pig or pork products, imported pig or pork products, turkeys, and animal feed. A total of 63 unique XbaI PFGE patterns were observed. The predominant pattern was shared by 22 strains. Limited antimicrobial resistance was observed in the Danish strains, and a higher degree of resistance was observed in strains originating from Thailand. Virtually all isolates were resistant to tetracycline. The tet A gene was detected in tetracycline-resistant isolates. Statistical analysis and molecular subtyping identified the combination of travel to Thailand and consumption of imported pig or pork products as well consumption of as pig or pork products produced in Denmark as risk factors for Salmonella Rissen infection among the Danish patients. The outcome of this study might be used as a supplement for future Salmonella Rissen investigations and outbreak detection.

Prevalence and Characterization of Human Shigella Infections in Henan Province, China, in 2006

ABSTRACT In 2006, 3,531 fecal samples were collected from patients with diarrhea in Henan Province, China. A total of 467 (13.2%) Shigella strains were isolated and serotyped. Seventy-one Shigella flexneri strains were characterized by MIC determination, pulsed-field gel electrophoresis (PFGE), and detection of genes encoding cephalosporin resistance. Most infections were caused by S. flexneri variant X [IV:(7),8] (27.6%), S. sonnei (24.2%), and S. flexneri 2a (20.8%). However, large regional differences were observed. Significantly higher odds (2.0) of females compared to males were infected with S. flexneri 2a. Untypeable S. flexneri (−:6) isolates were absent among males, as were untypeable S. flexneri [I:(7),8] isolates among females. Patient ages ranged from 2 months to 82 years, with 231 subjects (49.7%) <5 years of age. Most of the patients were male (62.1% [n = 290]). Infections peaked in July; week 27 with 38 cases (8.1%). All of the 71 S. flexneri conferred resistance to nalidixic acid; in addition, 21% (n = 15) and 79% (n = 56) were high- and low-level resistant to ciprofloxacin, respectively. Six S. flexneri isolates {serotype 2b [II:7,(8)] and 2b [II:(3),4;7,(8)]} harbored the bla CTX-M-14 or bla CTX-M-15 gene. A total of 52 unique XbaI PFGE patterns were observed among the 71 S. flexneri isolates with 11 distinct PFGE clusters. This study revealed a high prevalence of shigellosis with geographical differences in the distribution of serotypes in the distribution of serotypes and also differences in comparisons by gender. A high frequency of resistance, including 100% resistance to ciprofloxacin and resistance to extended-spectrum cephalosporins, was observed. We detected several isolates exhibiting the same PFGE type and MIC profile, indicating multiple undetected outbreaks.

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.

Molecular Characterization of Extended-Spectrum Cephalosporinase-Producing Salmonella enterica Serovar Choleraesuis Isolates from Patients in Thailand and Denmark

ABSTRACT The objective of this study was to characterize extended-spectrum cephalosporinase (ESC)-producing isolates of Salmonella enterica serovar Choleraesuis recovered from patients in Thailand and Denmark. Twenty-four blood culture isolates from 22 patients were included in the study, of which 23 isolates were recovered from 21 Thai patients during 2003, 2007, or 2008 and one isolate was recovered from a Danish traveler to Thailand. ESC production was confirmed in 13 out of the 24 isolates by MIC testing. Microarray and plasmid profiling (replicon typing and restriction fragment length polymorphism [RFLP]) were used to characterize the genetic mechanisms of antimicrobial resistance in the 13 ESC-producing isolates. Pulsed-field gel electrophoresis (PFGE) and MIC testing were used to compare the clonality between the 13 ESC-producing isolates and the 11 non-ESC-producing isolates. Based on susceptibility patterns, the ESC-producing isolates were more closely related than non-ESC-producing isolates. Microarray, PCR, plasmid profiling, and replicon typing revealed that the 13 ESC-producing isolates harbored either bla CMY-2 containing incA/C or bla CTX-M-14 containing incFIIA, incFrepB, and an unknown replicon located on plasmids ranging in size from 75 to 200 kb. The RFLP and replicon typing clustered the isolates into four distinct groups. PFGE revealed 16 unique patterns and five clusters; each cluster contained two or three of the 24 isolates. The isolate from the Danish patient was indistinguishable from two Thai clinical isolates by PFGE. This study revealed the emergence of the bla CTX-M-14 gene among several clones of Salmonella serovar Choleraesuis. Numerous plasmids were identified containing up to two different ESC genes and four distinct replicons. A “travel-associated” spread was confirmed. Overall, a high degree of clonal diversity between isolates resistant and susceptible to cephalosporins was observed. The findings represent a serious threat to public health for the Thai people and tourists.

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.

Characterization of Isolates of Salmonella enterica Serovar Stanley, a Serovar Endemic to Asia and Associated with Travel

ABSTRACT Salmonella enterica serovar Stanley (S. Stanley) is a common serovar in Southeast Asia and was the second most common serovar implicated in human salmonellosis in Thailand in the years 2002 to 2007. In contrast, this serovar is relatively uncommon in Europe. The objective of this study was to characterize a collection of S. Stanley strains isolated from Thai (n = 62), Danish (n = 39), and French (n = 24) patients to gain a broader understanding of the genetic diversity, population dynamics, and susceptibility to antimicrobials. All isolates were characterized by pulsed-field gel electrophoresis and antimicrobial susceptibility testing. The molecular mechanisms of resistance to extended-spectrum cephalosporins and plasmid-mediated resistance to quinolones were characterized by PCR and sequencing. Plasmid profiling, replicon typing, and microarray analysis were used to characterize the genetic mechanisms of antimicrobial resistance in 10 extended-spectrum cephalosporinase-producing isolates. Considerable genetic diversity was observed among the isolates characterized with 91 unique XbaI pulsed-field gel electrophoresis (PFGE) patterns, including 17 distinct clusters consisting of two to seven indistinguishable isolates. We found some of the S. Stanley isolates isolated from patients in Europe were acquired during travel to Southeast Asia, including Thailand. The presence of multiple plasmid lineages carrying the extended-spectrum cephalosporinase-encoding bla CMY-2 gene in S. Stanley isolates from the central part of Thailand was confirmed. Our results emphasize that Thai authorities, as well as authorities in other countries lacking prudent use of antimicrobials, should improve the ongoing efforts to regulate antimicrobial use in agriculture and in clinical settings to limit the spread of multidrug-resistant Salmonella isolates and plasmids among humans and pigs in Thailand and abroad.

Drug-resistant nontyphoidal Salmonella bacteremia, Thailand.

To the Editor: Despite improved public health, serious infections with nontyphoidal Salmonella enterica remain a major clinical and public health concern in Thailand and worldwide (1,2). Life-threatening Salmonella infections resistant to fluoroquinolones, extended-spectrum cephalosporins, or both, have been increasingly reported (3). Use of antimicrobial drugs for disease prevention and growth promotion in food animals has been implicated in this increase in drug resistance (4). Because of extensive global travel, such increases affect the medical community domestically and internationally (5). We report a pilot survey of drug resistance in Salmonella spp. in Thailand.

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

BackgroundBacteremia 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.ResultEight 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.ConclusionsThe 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.