Wide distribution of plasmid mediated quinolone resistance gene, qnrS, among Salmonella spp. isolated from canal water in Thailand.

AIMS: This research focused on assessing the prevalence of plasmid-mediated quinolone resistance (PMQR) determinants and antimicrobial susceptibility in Salmonella strains isolated from Thai canal water. METHODS AND RESULTS: From 2016 to 2020, 333 water samples were collected from six canals across Bangkok, Thailand. Salmonella spp. was isolated, PMQR genes were detected through polymerase chain reactions, and the antimicrobial susceptibility was examined using the disk diffusion method. The results indicated a 92.2% prevalence of Salmonella spp. in canal water, being serogroups B and C the most frequently detected. Overall, 35.3% of isolates harbored PMQR genes, being qnrS the most prevalent gene (97.2%, n = 137/141). Other PMQR genes, including qnrB, qnrD, oqxAB, and aac(6')-Ib-cr, were detected. Notably, six isolates harbored multiple PMQR genes. Furthermore, 9.3% and 3.8% of the overall isolates were resistant to nalidixic acid (NAL) and ciprofloxacin (CIP), respectively. PMQR-positive isolates showed higher rates of non-susceptibility to both NAL (48.2%, n = 68/141) and CIP (92.2%, n = 130/141) compared to PMQR-negative isolates (NAL: 8.9%, n = 23/258; CIP: 11.2%, n = 30/258). CONCLUSIONS: The high prevalence of Salmonella spp., significant PMQR-positive, and reduced susceptibility isolates in canal water is of public health concern in Bangkok.

Genetic diversity and antimicrobial resistance pattern of Salmonella enterica serovar Enteritidis clinical isolates in Thailand.

OBJECTIVE: To trace the history of antimicrobial resistance in Salmonella enterica serovar Enteritidis (S. Enteritidis, SE) circulating in Thailand, we characterised clinical isolates obtained during 2004-2007. METHODS: Antimicrobial resistance profiles, multi-locus variable number tandem repeat analysis (MLVA) types and 3 representative virulence determinants (spvA, sodCI and sopE) were established from SE isolates (n = 192) collected from stool and blood of patients throughout Thailand during the period 2004-2007. RESULTS: Resistance was found in SE against 10 out of 11 antimicrobials studied. The highest resistance ratios were observed for nalidixic acid (83.2%), ciprofloxacin (51.1%) and ampicillin (50.5%), and 25.5% were multidrug resistant. Based on five polymorphic tandem repeat loci analysis, MLVA identified 20 distinct types with three closely related predominant types. A significant increase of AMP resistance from 2004 to 2006 was strongly correlated with that of a MLVA type, 5-5-11-7-3. CONCLUSION: The usage of antimicrobials in human medicine or farm settings might act as selective pressures and cause the spread of resistant strains. Hence, a strict policy on antimicrobial usage needs to be implemented to achieve the control of resistant SE in Thailand.

Recovery and Quantification of Norovirus in Air Samples from Experimentally Produced Aerosols.

Norovirus is the leading cause of acute gastroenteritis in humans across all age groups worldwide. Norovirus-infected patients can produce aerosolized droplets which play a role in gastroenteritis transmission. The study aimed to assess bioaerosol sampling in combination with a virus concentrating procedure to facilitate molecular detection of norovirus genogroup (G) II from experimentally contaminated aerosols. Using a nebulizer within an experimental chamber, aerosols of norovirus GII were generated at known concentrations. Air samples were then collected in both 5 mL and 20 mL water using the SKC BioSampler at a flow rate of 12.5 L/min, 15 min. Subsequently, the virus in collected water was concentrated using speedVac centrifugation and quantified by RT-qPCR. The optimal distances between the nebulizer and the SKC BioSampler yielded high recoveries of the virus for both 5 and 20 mL collections. Following nebulization, norovirus GII RNA was detectable up to 120 min in 5 mL and up to 240 min in 20 mL collection. The concentrations of norovirus GII RNA recovered from air samples in the aerosol chamber ranged from 102 to 105 genome copies/mL, with average recoveries of 25 ± 12% for 5 mL and 22 ± 19% for 20 mL collections. These findings provide quantitative data on norovirus GII in aerosols and introduce a novel virus concentrating method for aerosol collection in water, thus enhancing surveillance of this virus.

Genomic analysis of Salmonella isolated from canal water in Bangkok, Thailand.

Antimicrobial resistance (AMR) poses an escalating global public health threat. Canals are essential in Thailand, including the capital city, Bangkok, as agricultural and daily water sources. However, the characteristic and antimicrobial-resistance properties of the bacteria in the urban canals have never been elucidated. This study employed whole genome sequencing to characterize 30 genomes of a causal pathogenic bacteria, Salmonella enterica, isolated from Bangkok canal water between 2016 and 2020. The dominant serotype was Salmonella Agona. In total, 35 AMR genes and 30 chromosomal-mediated gene mutations were identified, in which 21 strains carried both acquired genes and mutations associated with fluoroquinolone resistance. Virulence factors associated with invasion, adhesion, and survival during infection were detected in all study strains. 75.9% of the study stains were multidrug-resistant and all the strains harbored the necessary virulence factors associated with salmonellosis. One strain carried 20 resistance genes, including mcr-3.1, mutations in GyrA, ParC, and ParE, and typhoid toxin-associated genes. Fifteen plasmid replicon types were detected, with Col(pHAD28) being the most common type. Comparative analysis of nine S. Agona from Bangkok and 167 from public databases revealed that specific clonal lineages of S. Agona might have been circulating between canal water and food sources in Thailand and globally. These findings provide insight into potential pathogens in the aquatic ecosystem and support the inclusion of environmental samples into comprehensive AMR surveillance initiatives as part of a One Health approach. This approach aids in comprehending the rise and dissemination of AMR and devising sustainable intervention strategies.IMPORTANCEBangkok is the capital city of Thailand and home to a large canal network that serves the city in various ways. The presence of pathogenic and antimicrobial-resistant Salmonella is alarming and poses a significant public health risk. The present study is the first characterization of the genomic of Salmonella strains from Bangkok canal water. Twenty-two of 29 strains (75.9%) were multidrug-resistant Salmonella and all the strains carried essential virulence factors for pathogenesis. Various plasmid types were identified in these strains, potentially facilitating the horizontal transfer of AMR genes. Additional investigations indicated a potential circulation of S. Agona between canal water and food sources in Thailand. The current study underscores the role of environmental water in an urban city as a reservoir of pathogens and these data obtained can serve as a basis for public health risk assessment and help shape intervention strategies to combat AMR challenges in Thailand.

16S ribosomal RNA gene-based phylogenetic analysis of abundant bacteria in river, canal and potable water in Bangkok, Thailand.

In Southeast Asian countries, industrialization and urbanization is occurring rapidly, and water pollution in rivers and canals poses serious problems in some areas, especially in cities. Excess inflow of domestic, agricultural, and industrial wastewater to freshwater environments disturbs the aquatic microbial ecosystem, which can further pollute water by inhibiting biodegradation of pollutants. Therefore, monitoring of microbes in freshwater environment is important to identify changes in indigenous microbial populations and to estimate the influence of wastewater inflows on them. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis is suitable for monitoring changes in microbial communities caused by human activities, but this method can be difficult in eutrophic freshwater samples that contain PCR inhibitors. In this study, we optimized DNA extraction procedures and PCR conditions for DGGE analysis of bacterial populations in freshwater samples (canal, river, and tap water) collected in Bangkok, Thailand. A simple freeze-thaw procedure was effective for extracting DNA from bacterial cells in the samples, and LA Taq with added bovine serum albumin provided the best PCR amplification. The PCR-DGGE approach revealed that the most common bacteria in freshwater samples belonged to Gammaproteobacteria, while a Gram-positive bacterium was present at Bangkok Noi Canal. Temporally and spatially continuous analyses of bacterial populations in Bangkok canals and rivers by PCR-DGGE approach should be useful to recognize disturbances of microbial ecosystems caused by excess inflows of wastewater.

Exploration of the novel fluoroquinolones with high inhibitory effect against quinolone-resistant DNA gyrase of Salmonella Typhimurium.

IMPORTANCE: Quinolone-resistant nontyphoidal Salmonella is a pressing public health concern, demanding the exploration of novel treatments. In this study, we focused on two innovative synthetic fluoroquinolones, WQ-3034 and WQ-3154. Our findings revealed that these new compounds demonstrate potent inhibitory effects, even against mutant strains that cause resistance to existing quinolones. Hence, WQ-3034 and WQ-3154 could potentially be effective therapeutic agents against quinolone-resistant Salmonella Typhimurium. Furthermore, the data obtained in this study will be baseline information for antimicrobial drug development.

Noroviruses in oysters from local markets and oyster farms in southern Thailand.

One hundred and eighteen oyster samples collected from local markets and oyster farms in southern Thailand were examined for noroviruses (NoVs) and bacterial indicators of fecal contamination (fecal coliforms and Escherichia coli). Using a virus concentration procedure followed by RT-nested PCR, NoVs were detected in 38% of the samples. Oysters collected from oyster farms were found with NoVs at a higher detection rate (25/53 samples) than oysters from local markets (20/65 samples). Of the 45 NoV-positive oyster samples, 67% belonged to NoV genogroup I (GI), 15% to GII, and 18% to both GI and GII. DNA sequencing showed that 2 NoVs belonged to NoV GI-2 genotype. Fecal coliforms in NoV-positive oyster samples were in the range of < 3.0 to 1.5 x 10(4) most probable number (MPN)/g and 33% of NoV-positive oyster samples contained fecal coliforms within the standard acceptable level of raw shellfish (< 20 MPN/g). E. coli was found in the range of < 3.0 to 1.5 x 10(4) MPN/g and 9% of NoV-positive oyster samples were within acceptable levels of E. coli contamination (< 3 MPN/g). These findings indicate that NoV contamination in oysters obtained from both markets and oyster farms might pose a potential risk of acute gastroenteritis associated with raw oyster consumption. Examination for both fecal bacterial indicators and enteric viruses should be conducted for microbiological food safety of shellfish.

Amino Acid Substitution Ser83Ile in GyrA of DNA Gyrases Confers High-Level Quinolone Resistance to Nontyphoidal Salmonella Without Loss of Supercoiling Activity.

Aims: Quinolone-resistant nontyphoidal Salmonella having serine replaced by isoleucine at the 83rd amino acid in GyrA (GyrA-Ser83Ile) has recently been found in Asian countries. In this study, we aimed to examine the direct effect of substitution Ser83Ile on DNA gyrase activity and/or resistance to quinolones. Materials and Methods: Using 50% of the maximal inhibitory concentrations (IC50s) of quinolones, recombinant wild type (WT) and seven mutant DNA gyrases having amino acid substitutions, including Ser83Ile, were screened for enzymatic activity that causes supercoils in relaxed plasmid DNA and resistance to quinolones. Results: Little differences in supercoiling activity were observed between WT and mutant DNA gyrases. By contrast, the IC50s of ciprofloxacin and norfloxacin against GyrA-Ser83Ile/GyrB-WT were 11.6 and 73.3 µg/mL, respectively, which were the highest used against the DNA gyrases examined in this study. Conclusion: Ser83Ile in GyrA was shown to confer high-level quinolone resistance to DNA gyrases of nontyphoidal Salmonella, with no loss of supercoiling activity. Salmonella strain carrying GyrA with Ser83Ile may emerge under a high-concentration pressure of quinolones and easily spread even with no selection bias by quinolones. Hence, avoiding the overuse of quinolones is needed to prevent the spread of Salmonella with Ser83Ile in GyrA.

Detection of hepatitis A virus and bacterial contamination in raw oysters in Thailand.

This study was conducted to determine the presence of hepatitis A virus (HAV) in raw oysters (Crassostrea belcheri) using a virus concentration method and reverse transcription-nested polymerase chain reaction (RT-nested PCR). A total of 220 oyster samples were collected from oyster farms and local markets in Thailand. HAV was found in three oyster samples. Nested PCR products of HAV detected in oysters were characterized further by DNA sequencing of the VP1/2A region and subjected to phylogenetic analysis. All HAV sequences (168 basepairs) were associated with human HAV subgenotype IB (GIB). Fecal coliforms and Escherichia coli were determined using the multiple tube fermentation method, to assess the microbiological quality of collected oysters. Among oyster samples tested, 65% had fecal coliforms higher than the standard level for raw shellfish [< 20 Most Probable Numbers (MPN)/g]; MPN values in the range of 21.0-4.6 x 10(4)/g. Most oyster samples (85%) were contaminated with E. coli in the range of 3.0-4.6 x 10(4) MPN/g. One oyster sample with an acceptable level of fecal coliforms contained HAV GIB. E. coli was found in all HAV-positive oyster samples. The results suggest a significant presence of HAV and bacterial indicators of fecal contamination in raw oysters, which are a health risk for consumers and a source of gastrointestinal illness. Enteric viruses should also be tested to assess the microbiological quality of oysters.

Detection of Salmonella invA gene in shrimp enrichment culture by polymerase chain reaction.

Contamination of seafood with salmonellae is a major public health concern. Detection of Salmonella by standard culture methods is time consuming. In this study, an enrichment culture step prior to polymerase chain reaction (PCR) was applied to detect 284 bp fragment of Salmonella invA in comparison with the conventional culture method in 100 shrimp samples collected from four different shrimp farms and fresh food markets around Bangkok. Samples were pre-enriched in non-selective lactose broth (LB) and selective tetrathionate broth (TTB). PCR detection limit was 10 pg and 10(4) cfu/ml of viable salmonellae with 100% specificity. PCR assay detected 19 different Salmonella serovars belonging to 8 serogroups (B, C1, C2-C3, D1, E1, E4 and K) commonly found in clinical and environmental samples in Thailand. The detection rate of PCR following TTB enrichment (24%) was higher than conventional culture method (19%). PCR following TTB, but not in LB enrichment allowed salmonella detection with 84% sensitivity, 90% specificity and 89% accuracy. Shrimp samples collected from fresh food markets had higher levels of contaminated salmonellae than those from shrimp farms. The results indicated that incorporation of an enrichment step prior to PCR has the potential to be applied for detection of naturally contaminated salmonellae in food, environment and clinical samples.

Dissemination of class I integron in Acinetobacter baumliannii isolated from ventilator-associated pneumonia patients and their environment.

Multidrug resistant Acinetobacter baumannii has become the most common cause of health care-associated infections at Maharaj Nakhon Si Thammarat Hospital, Thailand. The objective of the study was to detect integrons using PCR-based method from 96 A. baumannii isolates from ventilator-associated pneumonia (VAP) patients and their environment. Antibiotic susceptibility was determined using a disk diffusion technique. Forty-six isolates exhibited integrase genes, with only class I and class II integron detected in 43 and 3 A. baumannii isolates, respectively. Twenty-seven of 52 clinical and 19 of 44 environmental isolates were integron-positive. Detection rate of integron-positive A. baumannii isolated from VAP patients increased from 25% to 83% over the 4 month study period. The majority (91%) of integron-positive A. baumannii showed resistance to 6 or more of 11 antibiotics tested and 72% of class I integron-positive isolates were imipenem-resistant. Thus, class I integron-positive A. baumannii had spread among the VAP patients and into hospital environment, the latter acting as reservoirs of potential pathogens possessing drug resistance genes.

Clonal spread of carbapenem resistant Acinetobacter baumannii in the patients and their environment at BMA Medical College and Vajira Hospital.

OBJECTIVE: To determine the clonal spread of carbapenem-resistant Acinetobacter baumannii (CRAB) in the patients and their environment at BMA Medical College and Vajira Hospital. MATERIAL AND METHOD: A prospective study on CRAB isolated from the clinical specimens of 30 patients and 300 from their environmental samples were carried out from September 1-15, 2008. The CRAB isolates were genotyped using PCR-based typing method. RESULTS: Twenty-six (86.7%) and 20 (66.7%) cases of 30 patients had their environment contaminated with A. baumannii and CRAB, respectively Environmental contamination rates of A. baumannii and CRAB were 18.0% (54/300) and 13.0% (39/300), respectively. The most contaminated sites with CRAB were bedside cupboards (26.7%), followed by bedrails and bed sheets (20%), BP cuffs (16.7%), over bed tables and nurse station counters (13.3% each) and push carts (10%). Four molecular types were classified among 65 CRAB isolates. Molecular type 1 was the most prevalent (90.7%) and found in all kinds of environmental samples except patient record folder and computer keyboard/mouse. About 37% of the patients had at least one of their environmental samples contaminated with CRAB clonally related with their own types. CONCLUSION: Clonal spread of CRAB was demonstrated to emphasize the important of hand hygiene, contact precaution and patient's environmental decontamination in controlling the spread of CRAB in the hospital.

Epidemiological characteristics of Acinetobacter baumannii infections at Phramongkutklao Hospital.

OBJECTIVE: To describe epidemiological characteristics of Acinetobacter baumannii infections and identify molecular patterns of A. baumannii isolated from the patients admitted in Phramongkutklao Hospital. MATERIAL AND METHOD: A retrospective study on previously isolated A. baumannii from the clinical specimens submitted to the microbiology laboratory of Phramongkutklao Hospital from January to March 2008 were carried out together with molecular typing using PCR-based method. Clinical data were obtained from IC surveillance and patients' records. RESULTS: 114 A. baumannii were isolated from 80 patients. A. baumannii was a cause of healthcare-associated infection (90%, 72 of 80 cases), colonization (7.5%), and community-acquired infection (2.5%) with mortality rate of 50%. Majority of the patients from which A. baumannii were isolated were male (58.8%), age over 60 years (56.3%), diagnosed with lower respiratory diseases (26.3%), had A. baumannii ventilator-associated pneumonia (66.7%), and admitted in medical department (57.5%) with median length of hospital stay 35 days. PDR- and MDR- A. baumannii were accounted for 67.5% and 21.1%, respectively. All isolates showed sensitive to tigecycline and colistin. Using PCR-based typing was able to distinguish 6 molecular types among 114 A. baumannii isolates. Molecular type 2 was the most common type (47.4%) and widely spread in 14 wards. Spread of clonally related isolates was found in 14 cases admitted in 8 medical wards and ICUs. CONCLUSION: Multiple clones of PDR- and MDR- A. baumannii were widely spread in the hospital. Clonally related A. baumannii infected 14 cases in 8 wards.

Development of a method for concentrating and detecting rotavirus in oysters.

Identification of enteric viruses in outbreak-implicated bivalve shellfish is difficult because of low levels of contamination and natural inhibitors present in shellfish tissue. In this study, the acid adsorption-alkaline elution method developed in our laboratory was proposed for the detection of rotavirus from oyster samples. The acid adsorption-alkaline elution process included the following steps: acid adsorption at pH 4.8, elution with 2.9% tryptose phosphate broth containing 6% glycine, pH 9.0, two polyethylene glycol precipitations, chloroform extraction and reconcentration using speedVac centrifugation. Oyster concentrates were extracted for RNA and examined for rotavirus using reverse transcription-nested polymerase chain reaction (RT-nested PCR). A comparison of SuperScript One-Step RT-PCR system and RT followed by PCR before the nested PCR reaction showed the former detecting four-fold lower concentration of rotavirus (78.12 plaque forming units [PFU]/ml or 0.26 PFU/assay) than the latter (3.12 x 10(2) PFU/ml or 1.04 PFU/assay). In the seeding experiment, the developed acid adsorption-alkaline elution gave high sensitivity of rotavirus detection (125 PFU/g of oyster). From August 2005 to February 2006, 120 oyster samples (Crassostrea belcheri) were collected from local markets and oyster farms, concentrated, and tested for naturally occurring rotaviruses. Four oyster samples were group A rotavirus-positive. Based on phylogenetic analysis of rotavirus DNA sequences in those positive samples, the oyster samples contained the sequences associated with human rotavirus G9 (two samples), G3 (one sample), and G1 (one sample). The present study demonstrates the successful application of developed virus concentration method and RT-nested PCR for the detection of rotaviruses in naturally contaminated oyster samples. The method might be used as a tool for evaluating the presence of enteric viruses in shellfish for monitoring and control of public health.

Bed rails and endotracheal tube connectors as possible sources for spreading Acinetobacter baumannii in ventilator-associated pneumonia patients.

This study aimed to determine molecular patterns of Acinetobacter baumannii using a PCR-based technique with REP-1, REP-2 and M13 primers to distinguish the patients' strains and the environmental strains (condensate, endotracheal tube connector, bed rail and nurses hands). There were 67 cases of ventilator-associated pneumonia (VAP) among 600 patients using mechanical ventilators in 10 wards from March to July 2006. The incidence of VAP was 11.2% or 8.9/1,000 ventilator days with a 54.5% fatality rate. Among 19 of 22 A. baumannii VAP patients, 68.4% (13/19) had their environmental samples contaminated with A. baumannii and the most common contaminated sites were bed rails and endotracheal tube connectors (36.8% each). Multidrug resistant (MDR) A. baumannii were involved in 77.3% of A. baumannii VAP. Molecular typing of 96 A. baumannii isolates was able to differentiate A. baumannii isolates into 7 types. Type 2 was the most common and found in 77.3% (17/22) of A. baumannii VAP patients admitted in 6 of 7 wards. Identical fingerprints were found in clinical isolates and their bed rails, endotracheal tube connectors and condensates of 5 patients. The results demonstrate that multiple clones of MDR A. baumannii were widely spread in the hospital. Bed rails and contaminated endotracheal tube connectors could be potential sources of A. baumannii spread.

Quinolone Resistance Determinants of Clinical Salmonella Enteritidis in Thailand.

Salmonella Enteritidis has emerged as a global concern regarding quinolone resistance and invasive potential. Although quinolone-resistant S. Enteritidis has been observed with high frequency in Thailand, information on the mechanism of resistance acquisition is limited. To elucidate the mechanism, a total of 158 clinical isolates of nalidixic acid (NAL)-resistant S. Enteritidis were collected throughout Thailand, and the quinolone resistance determinants were investigated in the context of resistance levels to NAL, norfloxacin (NOR), and ciprofloxacin (CIP). The analysis of point mutations in type II topoisomerase genes and the detection of plasmid-mediated quinolone resistance genes showed that all but two harbored a gyrA mutation, the qnrS1 gene, or both. The most commonly affected codon in mutant gyrA was 87, followed by 83. Double codon mutation in gyrA was found in an isolate with high-level resistance to NAL, NOR, and CIP. A new mutation causing serine to isoleucine substitution at codon 83 was identified in eight isolates. In addition to eighteen qnrS1-carrying isolates showing nontypical quinolone resistance, one carrying both the qnrS1 gene and a gyrA mutation also showed a high level of resistance. Genotyping by multilocus variable number of tandem repeat analysis suggested a possible clonal expansion of NAL-resistant strains nationwide. Our data suggested that NAL-resistant isolates with single quinolone resistance determinant may potentially become fluoroquinolone resistant by acquiring secondary determinants. Restricted therapeutic and farming usage of quinolones is strongly recommended to prevent the emergence of fluoroquinolone-resistant isolates.

An efficient virus concentration method and RT-nested PCR for detection of rotaviruses in environmental water samples.

Water samples were concentrated by the modified adsorption-elution technique followed by speedVac reconcentration of the filter eluates. Reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) was used to detect rotavirus RNA in concentrates of the water. The detection limit of the rotavirus determined by RT-nested PCR alone was about 1.67 plaque forming units (PFU) per RT-PCR assay and that by RT-nested PCR combined with concentration from 1l seeded tap water sample was 1.46 plaque forming units per assay. Water samples were collected from various sources, concentrated, and determined rotavirus RNA. Of 120 water samples, rotavirus RNA was detected in 20 samples (16.7%); 2/10 (20%) of the river samples, 8/30 (26.7%) of the canal samples, and 10/40 (25%) of the sewage samples but was not found in any tap water samples (0/40). Only three water samples were positive for rotavirus antigen determined using an enzyme-linked immunosorbent assay (ELISA). Alignment analysis of the sequenced PCR product (346-bp fragment) was performed in eight rotavirus-positive samples using the rotavirus sequence deposited in the GenBank. All samples gave the correct VP7 sequence. Results of analysis showed two samples similar to human rotavirus (97-98%), five similar to rotavirus G9 sequence (94-99%), and one sample similar to animal rotavirus (97%). PCR inhibitors were not observed in any concentrated water samples. In all 20 (of 120) samples where rotaviruses were found, fecal coliforms including Escherichia coli were also found, but of the samples testing negative for rotaviruses, 76 were fecal coliforms positive and 69 were E. coli positive. The combination of the virus concentration method and RT-nested PCR described below made it possible to effectively detect rotaviruses in environmental water samples.

Characterization of Salmonella Typhimurium DNA gyrase as a target of quinolones.

Quinolones exhibit good antibacterial activity against Salmonella spp. isolates and are often the choice of treatment for life-threatening salmonellosis due to multi-drug resistant strains. To assess the properties of quinolones, we performed an in vitro assay to study the antibacterial activities of quinolones against recombinant DNA gyrase. We expressed the S. Typhimurium DNA gyrase A (GyrA) and B (GyrB) subunits in Escherichia coli. GyrA and GyrB were obtained at high purity (>95%) by nickel-nitrilotriacetic acid agarose resin column chromatography as His-tagged 97-kDa and 89-kDa proteins, respectively. Both subunits were shown to reconstitute an ATP-dependent DNA supercoiling activity. Drug concentrations that suppressed DNA supercoiling by 50% (IC50 s) or generated DNA cleavage by 25% (CC25 s) demonstrated that quinolones highly active against S. Typhimurium DNA gyrase share a fluorine atom at C-6. The relationships between the minimum inhibitory concentrations (MICs), IC50 s and CC25 s were assessed by estimating a linear regression between two components. MICs measured against S. Typhimurium NBRC 13245 correlated better with IC50 s (R = 0.9988) than CC25 s (R = 0.9685). These findings suggest that the DNA supercoiling inhibition assay may be a useful screening test to identify quinolones with promising activity against S. Typhimurium. The quinolone structure-activity relationship demonstrated here shows that C-8, the C-7 ring, the C-6 fluorine, and N-1 cyclopropyl substituents are desirable structural features in targeting S. Typhimurium gyrase.

Antimicrobial Resistance, Extended-Spectrum ß-Lactamase Productivity, and Class 1 Integrons in Escherichia coli from Healthy Swine.

Administration of antimicrobials to food-producing animals increases the risk of higher antimicrobial resistance in the normal intestinal flora of these animals. The present cross-sectional study was conducted to investigate antimicrobial susceptibility and extended-spectrum ß-lactamase (ESBL)-producing strains and to characterize class 1 integrons in Escherichia coli in healthy swine in Thailand. All 122 of the tested isolates had drug-resistant phenotypes. High resistance was found to ampicillin (98.4% of isolates), chloramphenicol (95.9%), gentamicin (78.7%), streptomycin (77.9%), tetracycline (74.6%), and cefotaxime (72.1%). Fifty-four (44.3%) of the E. coli isolates were confirmed as ESBL-producing strains. Among them, blaCTX-M (45 isolates) and blaTEM (41 isolates) were detected. Of the blaCTX-M-positive E. coli isolates, 37 carried the blaCTX-M-1 cluster, 12 carried the blaCTX-M-9 cluster, and 5 carried both clusters. Sequence analysis revealed blaTEM-1, blaTEM-135, and blaTEM-175 in 38, 2, and 1 isolate, respectively. Eighty-seven (71%) of the 122isolates carried class 1 integrons, and eight distinct drug-resistance gene cassettes with seven different integron profiles were identified in 43 of these isolates. Gene cassettes were associated with resistance to aminoglycosides (aadA1, aadA2, aadA22, or aadA23), trimethoprim (dfrA5, dfrA12, or dfrA17), and lincosamide (linF). Genes encoding ß-lactamases were not found in class 1 integrons. This study is the first to report ESBL-producing E. coli with a class 1 integron carrying the linF gene cassette in swine in Thailand. Our findings confirm that swine can be a reservoir of ESBL-producing E. coli harboring class 1 integrons, which may become a potential health risk if these integrons are transmitted to humans. Intensive analyses of animal, human, and environmental isolates are needed to control the spread of ESBL-producing E. coli strains.

Sero-epidemiological study of hepatitis A virus infection among hill-tribe youth and household environmental sanitation, a hill-tribe community in northern Thailand.

A cross-sectional analytic study of 190 hill-tribe youth in a community in the north of Thailand was conducted to investigate the sero-prevalence of HAV and factors related to positive anti-HAV antibody. The studied youth, whose ages ranged from 15 to 24 years, were interviewed about socio-economic status and personal hygiene. Blood specimens were collected to detect anti-HAV by ELISA commercial kit. Household environmental sanitation conditions were observed and drinking water samples were screened for bacterial contamination using SI2 medium. Following the anti-HAV assay, the studied youth were divided into two groups: anti-HAV positive, and anti-HAV negative. The studied variables of the two groups were analyzed by chi2 test to find factors related to anti-HAV positivity. The results revealed that 87% of the studied youth were positive for anti-HAV. There was no statistically significant difference between age group/gender and anti-HAV positivity, p = 0.46 and 0.16, respectively. Approximately 35.79 to 45.79% washed their hands with soap before preparing food, before eating and after using the latrine. About 88% did not improve the potability of their drinking water. The results of screening for bacterial contamination in drinking water samples found that 73.53% were contaminated with coliform bacteria. Factors related to positive anti-HAV antibody included monthly income, number of household members, use of latrine, hand-washing with soap after using latrine, household refuse management and control of insects and rodents; p = 0.04, 0.007, 0.013, 0.008, <0.001 and <0.001, respectively. The findings suggested that appropriate household environmental management should be improved in this community to reduce HAV transmission.