A pulsed-field gel electrophoresis typing scheme for Vibrio parahaemolyticus isolates from fifteen countries

Vibrio parahaemolyticus is an important foodborne pathogen in Taiwan and many other maritime Asian countries where seafood is frequently consumed. A total of 535 strains of V. parahaemolyticus were recovered mostly (97%) from clinical samples obtained in Taiwan or in 14 other countries. These strains were typed by pulsed-field gel electrophoresis following SfiI digestion and a typing scheme was generated. The 115 different patterns identified were grouped into 13 types with dissimilarity values less than 15, plus 16 miscellaneous patterns not grouped into any of the types. Types I, A, D and J contained the most patterns, with the numbers of patterns being 17, 13, 12, and 11, respectively. However, types I, B, D, A, H and C contained the most strains, with the numbers of strains being 204, 73, 71, 54, 29 and 25, respectively. Type I consisted exclusively of the pandemic O3:K6 strains and genetically closely related strains. This PFGE typing scheme for V. parahaemolyticus could be used for the characterization of pathogenic isolates.

Unstable lysogeny and pseudolysogeny in Vibrio harveyi siphovirus-like phage 1

Exposure of Vibrio harveyi (strain VH1114) to V. harveyi siphovirus-like phage 1 (VHS1) resulted in the production of a low percentage of lysogenized clones of variable stability. These were retrieved most easily as small colonies within dot plaques. Analysis revealed that VHS1 prophage was most likely carried by VH1114 as an episome rather than integrated into the host chromosome. In the late exponential growth phase, lysogenized VH1114 continuously produced VHS1 but also gave rise to a large number of cured progeny. The absence of phage DNA in the cured progeny was confirmed by the absence of VHS1 DNA in Southern blot and PCR assays. Curiously, these very stable, cured subclones did not show the parental phenotype of clear plaques with VHS1 but instead showed turbid plaques, both in overlaid lawns and in dot plaque assays. This phenotypic difference from the original parental isolate suggested that transient lysogeny by VHS1 had resulted in a stable genetic change in the cured clones. Such clones may be called pseudolysogens (i.e., false lysogens), since they have undergone transient lysogeny and have retained some resistance to full lytic phage development, despite the loss of viable or detectable prophage.

Bacterial causes of AIDS-associated diarrhea in Thailand

The incidence of bacterial diarrhea in AIDS patients has increased steadily and has led to enormous medical and public health problems. In this study, the clinical data together with 350 rectal swab samples each from AIDS patients with diarrhea (APD) and non-AIDS patients with diarrhea (NAPD), were collected and examined for bacterial enteropathogens at the Bamrasnaradura Infectious Diseases Hospital (BIDH), Nonthaburi, Thailand from May to December 1996. Patients were matched by age and sex. The majority of these patients were male (79%, 554/700), aged between 15 and 34 years (70.9%). The study found that the isolation rates of bacterial enteropathogens causing diarrhea in APD (18%, 62/350) were considerably lower than those in NAPD (43%, 152/350) (p<0.05). The infection rate with Salmonella group B (19.7%, 12/61) in APD was found to be significantly higher than that in NAPD (14.3%, 2/14) (p<0.05). Vibrio parahaemolyticus (53.3%, 81/152), Plesiomonas shigelloides (27%, 41/152), Aeromonas spp (19.1%, 29/152) and V. cholerae O1 (15.1%, 23/152), were more frequently detected in NAPD than in APD (p<0.05). Only nine Escherichia coli strains were isolated from APD, of which six were enteroinvasive E. coli, two enterotoxigenic E. coli and one enterohemorrhagic E. coli (non O157) possessing both vtl and vt2. No V. cholerae strains were detected in APD. The least effective antibiotics were ampicillin, tetracycline and cotrimoxazole. Antibiotic resistant patterns of the isolated organisms were similar from both groups. The results from this study might be useful in Thailand in the diagnosis and management of clinical cases of bacterial diarrhea, especially APD.

Bacterial contamination of bottle milk in infants under 6 months in Children's Hospital, Bangkok, Thailand

The bacterial contamination of bottle milk samples obtained randomly from 500 infants under 6 months of age who came to the Out-patient Department of Children's Hospital Bangkok was determined by collecting bottle milk samples prepared at home following interview of their caretakers after obtaining their consent. Bacterial contamination was found in 91.8% (459/500) of bottle milk samples. Among the positive samples, 82.8% (380/459) contained enteric bacteria, another 17.2% were unidentified bacteria. The dominant enteric bacteria isolated from bottle milk were Klebsiella spp (56.6%), Enterobacter spp (41.3%), Aeromonas spp (14.4%), E. coli (13.4 %) and Vibrio cholerae non 0-1 (1.8%). Isolated E. coli were further identified as enteropathogenic E. coli (7.8%, 4/51) and enterotoxigenic E. coli (3.9%, 2/51). About 74% of the contaminated bottle milk contained one type of bacteria, 23.7% had two types and 2.3 % had 3 or more types of bacteria. A level of bacterial contamination greater than the US government limited number (USGLN 2x10(4) CFU/ml) was found in 86.4% of total examined samples (432/500) [geometric mean (GM) of 2.9 x 10(6) CFU/ml]. About 66% (333/500) of bottle milk samples had coliforms greater than the USGLN (1 x l0(2) CFU/ml) with GM of 1.3 x 10(4) CFU/ml. Therefore, in the preparation of bottle milk, feeding practice should be emphasized in every setting of maternal-child health care and promotion of breast-feeding should be encouraged by the health personnel.

Overview reflection of primary health care in Thailand supported from 1976 to 1996 by Japan-Thailand partnership

The international health cooperation of Japan for developing countries has been mostly concentrated on matters such as improvement of hygienic environment, prevention of tropical infectious diseases, establishment of hospitals with modern medical instruments and devices, and dispatch of medical experts. PHC (Primary Health Care) activities based on voluntary participation of local inhabitants in developing countries have been largely neglected. In the field of health and medical care, sufficient effect may not be achieved unless the local health activity is based on voluntary participation of the inhabitants. The introduction of advanced modern medical technics may be beneficial to some of the inhabitants, while most of the local inhabitants may not have the chance to receive such benefits, and additionally it is difficult to propagate modern medical care and technics widely to rural areas. In Thailand, PHC activity based on community participation was started in 1985, with the following three main themes: (1) Training of Village Health Volunteers (VHV) and Village Health Communicators (VHC), and development of their activities. (2) Establishment and operation of Health Centers. (3) Establishment and operation of a Drug Cooperative System (DC). Earlier, one of PHC activities developed by Japan, "Thailand Local Health Activity Improvement Project" based on the program of Thailand-Japan Partnership, was initiated in 1976 in rural areas of Chanthaburi Prefecture. From 1982, third country training programs have been carried out by the Japan International Cooperation Agency (JICA). As 10 years have elapsed since the initiation of PHC activity in rural areas in Thailand under the cooperation of the Governments of Thailand and Japan, it seems to be time to reconsider how PHC activity should be developed in future based on a candid evaluation of achievements and results.

Close proximity of the tdh, trh and ure genes on the chromosome of Vibrio parahaemolyticus

The distribution and location of the virulence-factor genes of Vibrio parahaemolyticus, tdh and trh, and the structural gene of urease, ureC, were examined on the genomic DNAs of 115 clinical isolates of V. parahaemolyticus. The majority of strains (81%) had two copies of tdh on the chromosome, and no copies of trh or ure. Southern hybridization with a tdh probe, after pulsed-field gel electrophoresis of Notl-digested genomic DNA of each strain revealed only single bands, suggesting that the two copies of the exist on single Notl fragments in each strain. Of the 115 strains, 7% had the tdh, trh and ure genes on chromosomal DNA. The three genes were also detected on single Notl fragments in these strains. More detailed analysis revealed that the three genes were localized within 40 kb. By long and accurate polymerase chain reactions (LA-PCR) the distance between trh and ure was shown to be less than 8.5 kb. These results reveal a close proximity of the tdh, trh and ure genes on the chromosome of pathogenic V. parahaemolyticus strains.

Evidence for genetic linkage between the ure and trh genes in Vibrio parahaemolyticus

Although V. parahaemolyticus does not generally produce urease, several studies have reported urease-positive V. parahaemolyticus isolates from clinical sources. Recently, studies have shown a complete coincidence between the urease-producing phenotype of V. parahaemolyticus strains and the possession of the thermostable direct haemolysin (TDH)-related haemolysin (TRH) gene (trh). TRH, like TDH, is considered to be an important virulence factor in the pathogenesis of V. parahaemolyticus gastroenteritis. The present study attempted to identify the gene ure encoding urease in V. parahaemolyticus to clarify the relationship between urease production and possession of trh. The polymerase chain reaction with mixed oligonucleotide primers targeted for conserved sequences of reported ure genes from other species was used to prepare a DNA probe to detect the V. parahaemolyticus ure gene. Colony hybridisation with this ure probe demonstrated that all the ure-positive strains produced urease. Considering the coincidence between production of urease and possession of trh in V. parahaemolyticus, it was concluded that the presence or absence of the ure gene is completely coincident with that of the trh gene in V. parahaemolyticus strains. Furthermore, the relative location of ure and trh on V. parahaemolyticus chromosomal DNA was analysed by pulsed-field gel electrophoresis. The results showed that, in all the strains examined, ure and trh were detected on the same NotI fragment, showing that the two genes localise within a relatively small portion of the chromosome DNA. These results suggest that the ure and trh genes are genetically linked in V. parahaemolyticus strains.

Restriction fragment length polymorphism of the tdh and trh genes in clinical Vibrio parahaemolyticus strains

The restriction fragment length polymorphism of the genes encoding thermostable direct hemolysin (tdh) and thermostable direct hemolysin-related hemolysin (trh) was analyzed for 137 strains of Vibrio parahaemolyticus isolated from specimens from diarrheal patients in Thailand. The HindIII restriction fragment patterns of tdh and trh were grouped into five and four types, respectively. A strong association between the restriction fragment patterns of tdh and trh was observed with V. parahaemolyticus strains.

Monoclonal antibody-based dot-blot ELISA for the detection of Salmonella in foods

Monoclonal antibody (MAb) produced to polysaccharides in the LPS molecule of salmonellae was used in a dot-blot ELISA for detecting Salmonella in 873 food samples, ie 100 fresh chicken, 261 frozen chicken, 78 pork, 84 beef, 100 hen eggs, 100 duck eggs, 50 sea-mussels, 50 shrimps and 50 squids in comparison with the conventional culture method. Salmonella culture from foods involved the following steps: pre-enrichment, enrichment in selective medium, isolation on selective and indicator media, followed by biochemical and serological identification of appropriate colonies, respectively. The whole culture procedure took 5 days. Food samples from the selective enrichment medium were also subjected to the MAb-based dot-blot ELISA. The whole procedure of dot-blot ELISA took less than 2 hours. Among 873 food samples, salmonellae could be recovered from 7.4% of the samples by the bacterial isolation method (16% of fresh chicken, 8.8% of frozen chicken, 24.4% of pork, 3.6% of beef and 2% each of hen eggs and duck eggs, respectively). Salmonella derby were predominant among pork samples while S.paratyphi B biovar java predominated in chicken. The MAb-based dot-blot ELISA were positive in 19.5% of the food samples, i.e. 30% of fresh chicken, 27.6% of frozen chicken, 34.6% of pork, 21.4% of beef, 20% of shrimp, 16% of sea-mussels, 2% of hen eggs and 4% of duck eggs. The sensitivity and specificity of the MAb-based dot-blot ELISA compared to the bacterial culture method were 81.5% and 85%, respectively. The discrepancy of the data between the culture method and the dot-blot ELISA might be due to the fact that the culture method could detect only living cells at numbers that gave at least one isolated colony on the selective/differential plate while the dot-blot ELISA detects any form of Salmonella antigen. The monoclonal antibody-based dot-blot ELISA offers several advantages over the conventional bacterial culture method when it is used for screening of Salmonella contamination in foods, especially export foods. These include rapidity, cost-effectiveness and simplicity (the dot-blot ELISA does not need highly trained personnel or equipment, in contrast to the culture method). The test can be performed in field conditions and the result can be read visually. It also offers multisample analysis at one time which renders more samples of food for screening possible, thus false negative results are fewer which, in turn, assures the quality of the export food in a cost-saving, short time frame.

Urease production correlates with possession of the trh gene in Vibrio parahaemolyticus strains isolated in Thailand

A total of 489 Vibrio parahaemolyticus isolates from patients in Thailand with diarrhea was examined for the presence of thermostable direct hemolysin (TDH) and TDH-related hemolysin genes (tdh and trh, respectively), their serovars, TDH production, and urease activity. Of the strains, 81% were positive only for the tdh gene, 6% for both trh and tdh genes, and 2% for the trh gene only. Thirty-seven (8%) of the 489 isolates were positive for urease production. Of special interest, all urease-positive strains possessed the trh gene, and conversely, urease-negative strains lacked the gene, indicating that urease production by V. parahaemolyticus strains strongly correlates with the possession of the trh gene. Thus, the urease-positive phenotype of V. parahaemolyticus can be considered an indication of virulent (trh-possessing) V. parahaemolyticus strains in clinical diagnosis.

First isolation of Salmonella blockley in Thailand

The first isolation of Salmonella blockley in Thailand was found in 2 strains of animal feed samples and 3 strains of chicken feather samples from a private poultry company in 1989. From 1987 to 1992, the number of S. blockley isolates increased and found in various sources. The major sources were the stools of diarrheal patients, mainly children. Another source of S. blockley was frozen chicken meat which increased every year studied. S. blockley isolated from human and other sources showed a high percentage resistance to streptomycin, tetracycline, kanamycin and chloramphenicol and a low percentage resistance to ampicillin and cotrimoxazole. Thus, S. blockley must now be listed as a possible cause of Salmonella food poisoning in Thailand.

Dot-ELISA for seroepidemiological study of exposure to Shigella flexneri

A seroepidemiological study for determining serum antibodies to lipopolysaccharides (LPS) of Shigella flexneri using dot--ELISA was carried out in Krabi Province, Thailand, from January 1989 to December 1990. From 363 serum samples obtained from cord blood and from venous blood of the healthy persons aged from 6 months to over 50 years, 56% and 22%, respectively, were found to be positive for specific IgG and IgM antibodies to S. flexneri LPS. The IgG prevalence was initially detected at 3-4 years of age and then rose sharply with age. In contrast, IgM was detectable earlier, with much lower prevalence than that of IgG. The highest seroprevalence values were in the age groups 30-49 years for IgG and 15-19 years for IgM. The seroprevalence of S. flexneri infection was statistically higher among males, Buddhists, businessmen, and those with elementary education. S. flexneri infection was not associated with family income, home location, eating behaviour or water supply. These seroepidemiologic data demonstrated that most of the population in Krabi Province had been infected with S. flexneri.

Retroviral reverse transcriptase inhibitory activity in Thai herbs and spices: screening with Moloney murine leukemia viral enzyme

Fifty-seven Thai herbs and spices were examined for their retroviral reverse transcriptase inhibitory activity. All herbs and spices were extracted with hot-water and methanol. Reverse transcriptase inhibitory activity of the extracts was determined by using Moloney Murine Leukemia Virus reverse transcriptase (M-MuLV-RT) reacted with 3H-dTTP and radioactivity measured with a scintillation counter. Eighty-one per cent (46/57) of hot-water extracts and 54% (31/57) of methanol extracts showed inhibitory activities. At a concentration of 125 micrograms/ml, 13% (6/46) of hot-water extracts, namely Eugenia caryophyllus Bullock et Harrison, Phyllanthus urinaria Linn., Terminalia belerica Roxb., Nelumbo nucifera Gaertn., Psidium guajava Linn. and Lawsonia inermis Linn., had a relative inhibitory ratio (IR) over 50%. They showed ratios of 100%, 91%, 75%, 74%, 61% and 60%, respectively. For methanol extracts, only 10% (3/31) had IR values over 50%. They were T. belerica, E. caryophyllus and N. nucifera which exhibited IR values of 83%, 54% and 54%, respectively.

Bacteriophage typing of Vibrio fluvialis

Six stable bacteriophages of Vibrio fluvialis were isolated from 44 surface water specimens collected in Thailand and Japan. Twelve different phages types were found among 109 V. fluvialis isolated from feces of diarrheal patients and the environment. Seventy-three percent (80/109) of these 109 isolates were typable with these phages. One phage type, designated as A (1) was predominant and accounted for 43% of the V. fluvialis examined. The six bacteriophages used in this typing scheme were stable for at least during a three-month storage at 4 degrees C. This proposed bacteriophage typing scheme may be of valuable aid in tracing sources and routes of infection in outbreaks of V. fluvialis infection in man.

ELISA for seroepidemiological study of exposure to Vibrio cholerae of population in Krabi Province, Thailand

Seroepidemiological study of Vibrio cholerae exposure was carried out in Krabi Province during January 1989 to December 1990 using indirect ELISA to determine serum antibodies to lipopolysaccharides (LPS) of V. cholerae. Among 363 serum samples obtained from cord blood and venous blood of healthy persons, aged from 6 months to over 50 years, 65% and 64% were found positive for specific IgG and IgM against LPS of V. cholerae, respectively. The seroprevalence of V. cholerae infection increased with age from that found at 6 months, being highest in the age groups of 30-49 years for IgG and 15-29 years for IgM. The seroprevalence of V. cholerae infection was higher among female Muslims and home-makers, and increased with the family income. The seroprevalence of cholera infection was also influenced by home location, methods of food storage and water supply. These data suggested that a large number of Krabi's population had V. cholerae infection.

Shiga-like-toxin-producing Escherichia coli in retail meats and cattle in Thailand

Specific DNA probes were used to identify Shiga-like toxin I (SLT I)- and SLT II-producing Escherichia coli in vegetables, meats, cattle, and farm animals in Thailand. SLT-producing E. coli was isolated from 9% of market beef specimens, from 8 to 28% of fresh beef specimens at slaughterhouses, and from 11 to 84% of fecal specimens from cattle. Animals were frequently infected with several different SLT-producing E. coli types that hybridized with either the SLT I, SLT II, or both SLT probes. Of 119 SLT-producing E. coli isolates, 24% hybridized with the SLT I probe, 31% hybridized with the SLT II probe, and 44% hybridized with both SLT probes. The enterohemorrhagic E. coli plasmid probe hybridized with 64% (68 of 106) of SLT-producing E. coli isolates from food and cattle and with 8% (17 of 201) of E. coli isolates from pigs. No SLT-producing E. coli was detected in pigs. Seventy-six percent (26 of 34) of E. coli isolates that hybridized with the SLT II probe were cytotoxic to Vero but not to HeLa cells, suggesting that they produced the variant of SLT II. The high prevalence of SLT-producing E. coli in beef-producing animals suggests that exposure to animals and eating beef may pose a health risk for acquiring enterohemorrhagic E. coli infections in Thailand.

Antimicrobial resistance of Escherichia coli isolated from chickens

Faecal Escherichia coli isolated from healthy farm chickens, from farm chickens with avian influenza, and from chickens with diarrhoea were more resistant to antimicrobial agents (94-100%) than those isolated from healthy domestic chickens (20%). Transfer of drug resistance was readily achieved from strains isolated from both healthy and sick farm chickens, and from diarrhoeic chickens; it was more difficult to demonstrate in strains from domestic chickens. Resistant E. coli showing serotypes suspected to be enteropathogenic for man, i.e 0126:K71(B16), 044:K74 (L) and 0119:K69(B14), were isolated from faecal samples of healthy and sick farm chickens, but not from healthy domestic birds.

A comparison of methods for the isolation of Campylobacter species from stool specimens

Eight methods used for isolation of Campylobacter species were compared. Using a combination of methods Campylobacter species were isolated from 30 (11%) of 270 children with diarrhea seen at Bamrasnaradura Infectious Disease Hospital, Nonthaburi, Thailand. The membrane filter method using a gas generating envelope at 37 degrees C identified 73% of the total positive specimens and was found to be the best isolation method for Campylobacter species from stool specimens. This method identified two strains that failed to grow on antibiotic containing media, and also gave a higher isolation rate of C. jejuni than could be isolated with conventional methods. The combination of the membrane filter method and a selective antibiotic method identified 90% of all isolates. At present the cost of the membrane filter method is higher than other methods. Therefore, the selective antibiotic method (Campy-BAP) with sheep blood under gas mixture at 42 degrees C is recommended for laboratories with limited supplies. Diagnosis by direct smear with 1% basic fuchsin revealed high degree of sensitivity and specificity. This rapid, inexpensive, and simple method could be used to make a presumptive diagnosis of Campylobacter enteritis when isolation methods are unavailable.

DNA probes to identify Shiga-like toxin I- and II-producing enteric bacterial pathogens isolated from patients with diarrhea in Thailand

When Shigella species, Escherichia coli, and five other bacterial enteric pathogens isolated from children with diarrhea in Thailand were tested for hybridization under stringent conditions with probes for Shiga-like toxins I and II, only 30 Shigella dysenteriae 1 hybridized with the Shiga-like toxin I probe.

Foods as a source of enteropathogens causing childhood diarrhea in Thailand

Foods obtained in markets in Bangkok were cultured for bacterial enteric pathogens and examined for their similarity to strains isolated from children under 5 years of age in Bangkok in 1986. Salmonella was isolated from 17%, Campylobacter from 12%, and enterotoxigenic Escherichia coli (ETEC) from 3% of 510 foods examined. Campylobacter was isolated from 13.5%, ETEC from 13%, and Salmonella from 12% of 1,230 children under 5 years of age with diarrhea. Eighty-eight percent of children infected with Salmonella were infected with serotypes isolated from foods of animal origin. Six percent of children with Salmonella were infected with the same serotype containing plasmids with identical endonuclease restriction patterns as isolates from food. Eighty-seven percent of children with Campylobacter were infected with the same serotypes and biotypes found in food of animal origin. Thirty-one percent of heat-labile enterotoxin (LT) producing ETEC from foods containing genes coding for LT II, but LT II ETEC was not isolated from children. Twenty-one percent of ETEC isolated from foods vs. 53% isolated from children were resistant to 2 or more antibiotics (P less than 0.01). Salmonella and Campylobacter, but not ETEC, isolated from foods were similar to strains isolated from children. Foods of animal origin are an important source of Salmonella and Campylobacter in Thailand.