Integron types, gene cassettes, antimicrobial resistance genes and plasmids of Shigella sonnei isolates from outbreaks and sporadic cases in Taiwan.

This study analysed the presence, location and transferability of integrons and antibiotic resistance genes in 103 Shigella sonnei outbreak isolates and in 32 sporadic isolates from Taiwan. Multiple antimicrobial resistance was common in both outbreak (95 %) and sporadic (97 %) isolates. Class 1 integrons were present in 34 outbreak isolates (33 %) and in six sporadic isolates (19 %). This study is the first, to our knowledge, to identify an atypical sul3-associated class 1 integron carrying the estX-psp-aadA2-cmlA-aadA1-qacH cassette array in Shigella. Class 2 integrons carrying the dfr1-sat2-aadA1 cassette array were predominant in outbreak isolates (90 %) but were not present in sporadic isolates. Other antimicrobial resistance genes not associated with integrons were found to encode resistance to ampicillin (bla(TEM)), chloramphenicol (cat1), sulfonamide (sul2) and tetracycline (tetA and tetB). The most common plasmid size was 130 kb (observed in 43 and 97 % of 1998 outbreak and sporadic isolates, respectively). In conclusion, the plasmid location of resistance genes and horizontal plasmid transfer promote the spread of multiple resistance genes in outbreak and sporadic isolates of S. sonnei.

Chitinilyticum litopenaei sp. nov., isolated from a freshwater shrimp pond, and emended description of the genus Chitinilyticum.

Strain c1(T), originally isolated from surface water of a freshwater pond located in Pingtung (southern Taiwan) used for culture of Pacific white shrimp (Litopenaeus vannamei), was subjected to a polyphasic taxonomic analysis. The strain exhibited strong chitinolytic activity and was able to grow under aerobic and anaerobic conditions by utilizing chitin exclusively as the carbon, nitrogen and energy source. Phylogenetic analysis of the 16S rRNA gene sequence revealed a clear affiliation to the Betaproteobacteria, with the closest relatives being Chitinilyticum aquatile C14(T) and Chitinibacter tainanensis S1(T), respectively showing 96.7 and 93.6 % 16S rRNA gene sequence similarity. The predominant fatty acids detected in cells of strain c1(T) were C(16 : 0), C(18 : 1)omega7c and summed feature 3 (C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH). The G+C content of the genomic DNA was 62.2+/-1.0 mol%. On the basis of phylogenetic analysis, DNA-DNA hybridization data, physiological and biochemical characteristics and fatty acid compositions, the organism was shown to belong to the genus Chitinilyticum whilst representing a novel species within this genus, for which we propose the name Chitinilyticum litopenaei sp. nov. (type strain c1(T) =DSM 21440(T) =BCRC 17609(T)).

Histamine-related hygienic qualities and bacteria found in popular commercial scombroid fish fillets in Taiwan.

To determine the histamine-related hygienic qualities and bacteria of scombroid fish fillets sold in traditional retail markets, 61 samples were collected from northern and southern Taiwan. It was found that the content of volatile base nitrogen in most samples was below 25 mg/100 g, which is the regulatory level in Taiwan. The ratio of unacceptable samples/total samples for aerobic plate count and Escherichia coli was 100% and 15% in northern samples and 100% and 20% in southern samples, respectively, compared with the requirements of hygienic standards. The average content of various biogenic amines in all samples were lower than 3 mg/100 g, except for histamine average content (4.6 mg/100 g) in southern samples. Among southern samples, four samples contained 12.8 to 28.8 mg/100 g histamine, which is more than 5 mg/100 g that is the allowable limit suggested by the U.S. Food and Drug Administration. Furthermore, 14 bacterial strains were isolated from sailfish fillets on a selective medium for histamine-forming bacteria. These presumptive histamine-forming strains, such as Proteus, Enterobacter, Klebsiella, Rahnella, and Acinetobacter, have been identified and found to produce 20 to 2,000 ppm histamine after incubating at 37 degrees C for 24 h.

Contribution of integrons, and SmeABC and SmeDEF efflux pumps to multidrug resistance in clinical isolates of Stenotrophomonas maltophilia.

OBJECTIVES: The contribution of integrons and efflux pumps to multidrug resistance in Stenotrophomonas maltophilia was evaluated. MATERIALS AND METHODS: Ninety-three S. maltophilia clinical isolates were studied. PCR and direct sequencing were used to detect the presence of integrons. Real-time PCR was performed to assess and quantify the expression of the Sme efflux pumps of S. maltophilia. RESULTS: Class 1 integrons were detected in 22% of clinical isolates and carried cassettes conferring resistance mainly to aminoglycosides and trimethoprim. The small multidrug resistance gene, smr, was found on class 1 integrons in six isolates. Thirty-one percent of the isolates overexpressed the smeDEF gene, as compared with a control strain, and 59% overexpressed the smeABC gene. Extrusion of ciprofloxacin and meropenem was specific to the SmeABC and SmeDEF pumps, respectively. CONCLUSION: SmeABC and SmeDEF efflux pumps play important roles in resistance of S. maltophilia to ciprofloxacin and meropenem.

One predominant type of genetically closely related Shigella sonnei prevalent in four sequential outbreaks in school children.

Seventy-six Shigella sonnei isolates from four sequential outbreaks in school children were analyzed to determine their relatedness. Outbreak strains exhibited two major antibiograms, 9 plasmid profiles, 10 enterobacterial repetitive intergenic consensus sequence (ERIC)-PCR patterns, and 17 pulsed-field gel electrophoresis (PFGE) patterns. Of typing methods, ERIC-PCR types generally coincided with the PFGE types within these outbreak strains. However, ERIC-PCR analysis could not discriminate an epidemiologically unrelated strain from some outbreak strains. Further computer-assisted analysis for similarity of the PFGE patterns revealed that the main culprits of these four sequential outbreaks were strains of pulsotype C (88.2% of total outbreak isolates). The results indicate that PFGE can provide more explicit relatedness of outbreak strains than the other typing methods examined. In conclusion, based on PFGE analysis, one predominant pulsotype of multiple genetically related strains of S. sonnei was prevalent in these four sequential outbreaks.

Characterisation of drug resistance gene cassettes associated with class 1 integrons in clinical isolates of Escherichia coli from Taiwan, ROC.

The presence of class 1 integrons in clinical isolates of Escherichia coli was detected by PCR. Of 104 E. coli isolates from Kaohsiung, 54 (52%) carried class 1 integrons, with inserted DNA regions of 1-3 kb. These integrons were located on plasmids, as demonstrated by Southern hybridisation. DNA sequencing was used to identify the genetic content of the integron-variable regions. Different class 1 integrons contained various numbers, kinds and combinations of gene cassettes within their variable regions. These gene cassettes included those encoding resistance to trimethoprim (dfrIa, dfrV, dfr12 and dfr17), aminoglycosides (aadA1a, aadA2, aadA4 and aadB), chloramphenicol (cmlA), erythromycin (ereA2) and beta-lactams (blaP1). An integron carrying three inserted cassettes - dfr12-orJF-aadA2 - was present in 33 (61%) of the 54 isolates with class 1 integrons. Gene cassettes encoding resistance were expressed phenotypically. The results indicate that class 1 integrons are widespread in clinical E. coli isolates in Taiwan. The types, combinations and frequency of the gene cassettes in integrons may reflect the specific selective pressures to which the isolates were exposed and could provide useful surveillance data for relation to antibiotic usage information.

Molecular analysis of Shigella sonnei isolated from three well-documented outbreaks in school children.

Fifty-eight isolates of Shigella sonnei from three outbreaks in school children and eight control isolates from epidemiologically unrelated sporadic clinical infections in Taiwan were compared by antibiotic susceptibility testing and molecular typing. Antibiotic susceptibility testing showed that all strains except one sporadic isolate were multi-resistant. Ribotyping after restriction endonuclease digestion with SalI, PvuII and HindII generated the same ribosomal pattern in 65 of the 66 isolates. Plasmid profile analysis and pulsed-field gel electrophoresis (PFGE) produced eight and nine distinct patterns, respectively, and were in agreement with the epidemiological relationship of the outbreak strains. Nevertheless, some of the sporadic isolates could be discriminated only by a combination of these two methods. This study showed that plasmid profiling in combination with PFGE may be superior to ribotyping in molecular epidemiological investigations of S. sonnei.