No abstract

Antibiotic-resistant bacteria (ARB) have been surveyed widely in water bodies, but few studies have determined the diversity of ARB in sediment, which is the most taxon-abundant habitat in aquatic environments. We isolated 56 extended-spectrum ␤-lactamase (ESBL)-producing bacteria from a single sediment sample taken from an urban river in China. All strains were confirmed for ESBL-producing capability by both the clavulanic acid combination disc method and MIC determination. Of the isolated strains, 39 were classified as Enterobacteriaceae (consisting of the genera Escherichia, Klebsiella, Serratia, and Aeromonas) by 16S rRNA gene sequencing and biochemical analysis. The present study identifies, for the first time, ESBL-producing strains from the families Brucellaceae and Moraxellaceae. The bla CTX-M gene was the most dominant of the ESBL genes (45 strains), while the bla TEM gene was the second-most dominant (22 strains). A total of five types of bla CTX-M fragments were identified, with both known and novel sequences. A library of bla CTX-M cloned from the sediment DNA showed an even higher diversity of bla CTX-M sequences. The discovery of highly diverse ESBL-producing bacteria and ESBL genes, particularly bla CTX , in urban river sediment raises alarms for potential dissemination of ARB in communities through river environments.Antibiotic-resistant bacteria (ARB) have been found widely in aquatic environments (1,18,24). ARB in rivers may originate from anthropogenic sources, such as hospital, municipal, and aquaculture effluents (3,16,23); in addition, they could occur naturally, since many acquired resistance mechanisms originated in producers of antibiotics, such as actinomycetes (12). Both anthropogenic and naturally occurring ARB in water environments may compromise human health, since people may be infected by ARB through drinking water, aquatic products, and direct contact with water bodies. Moreover, the ARB may transfer the antibiotic resistance genes to other pathogens through horizontal gene transfer (1).Sediment has the highest microbial diversity in water environments. The species richness and abundance of the sediment community are comparable to those of soil and are orders of magnitude higher than those of the planktonic community in the upper water layer (10,20). It is reasonable to deduce that a wide variety of ARB might exist in sediment environments, as they are taxon-rich habitats, particularly in sediments receiving wastewater. Nevertheless, despite extensive studies surveying ARB in water columns, the diversity of antibiotic resistance in sediment environments has seldom been investigated.The present study therefore focused on an urban river sediment environment as a model, concentrating on the diversity of extended-spectrum ␤-lactamase (ESBL)-producing bacteria. ESBL-producing organisms have been emerging both in nosocomial and in community settings since the 1980s (4,13,14). In aquatic environments, ESBL-producing bacteria have been found in sewage and water samples (11,13,16), but th...

b CTX-M-producing Escherichia coli is the predominant type of extended-spectrum ␤-lactamase (ESBL)-producing E. coli worldwide. In this study, molecular typing was conducted for 139 CTX-M-producing E. coli isolates, phenotypically positive for ESBLs, isolated from environmental water, swine, healthy humans, and hospitalized patients in Hangzhou, China. The antibiotic resistance profiles of the isolates for the cephalosporins and fluoroquinolones were determined. The isolates showed 100% resistance to cefotaxime and ceftriaxone while maintaining relatively high susceptibility to cefoxitin, cefepime, and ceftazidime. A total of 61.9% (86/139) of the isolates, regardless of origin, showed high resistance to fluoroquinolones. PCRs and DNA sequencing indicated that bla CTX-M-14 was the most prevalent CTX-M-9 group gene and that bla CTX-M-15 and bla CTX-M-55 were the dominant CTX-M-1 group genes. Isolates from all sources with CTX-M types belonging to the CTX-M-1 or CTX-M-9 group were most frequently associated with epidemics. Molecular homology analysis of the isolates, conducted by phylogenetic grouping, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST), demonstrated that the dominant clones belonged to B2-ST131, D-ST648, D-ST38, or A-CC10. These four sequence types (STs) were discovered in E. coli isolates both from humans and from environmental water, suggesting frequent and continuous intercompartment transmission between humans and the aquatic environment. Seven novel sequence types were identified in the current study. In conclusion, this study is the first to report the molecular homology analysis of CTX-M-producing E. coli isolates collected from water, swine, and healthy and hospitalized humans, suggesting that pathogens in the environment might originate both from humans and from animals.

Burkholderia ambifaria BC-F, a biocontrol strain reported previously to exhibit broad-spectrum antifungal activity, was highly active in formation of N-acyl homoserine lactones (AHLs). We constructed AHL-deficient derivatives of strain BC-F in which the genes specifying AHL synthase (bafI) and AHL-binding transcriptional activator (bafR) were inactivated by allelic exchange. The resulting AHL-deficient mutants had decreased antifungal activity.

A novel, Gram-stain-positive, rod-shaped, non-motile, non-spore-forming, obligately anaerobic bacterium, designated strain ZHW00191T, was isolated from human faeces and characterized by using a polyphasic taxonomic approach. Growth occurred at 25–45 °C (optimum, 37–42 °C), at pH 5.5–10.0 (optimum, pH 6.5–7.0) and with 0–2 % (w/v) NaCl (optimum, 0 %). The end products of glucose fermentation were acetic acid, isobutyric acid and isovaleric acid and a small amount of propionic acid. The dominant cellular fatty acids (>10 %) of strain ZHW00191T were C16 : 0, C18 : 1 ω9с and C18 : 2ω6,9с. Its polar lipid profile comprised diphosphatidylglycerol, phosphatidylglycerol, three unidentified phospholipids and ten unidentified glycolipids. Respiratory quinones were not detected. The cell-wall peptidoglycan contained meso-2,6-diaminopimelic acid, and the whole-cell sugars were ribose and glucose. The genomic DNA G+C content was 32.8 mol%. Analysis of the 16S rRNA gene sequence indicated that ZHW00191T was most closely related to Clostridium hiranonis TO-931T (95.3 % similarity). Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) analyses with closely related reference strains indicated that reassociation values were both well below the thresholds of 95–96% and 70 % for species delineation, respectively. Based on phenotypic, chemotaxonomic and genetic studies, a novel genus, Peptacetobacter gen. nov., is proposed. The novel isolate ZHW00191T (=JCM 33482T=GDMCC 1.1530T) is proposed as the type strain of the type species Peptacetobacter hominis gen. nov., sp. nov. of the proposed new genus. Furthermore, it is proposed that Clostridium hiranonis be transferred to this novel genus, as Peptacetobacter hiranonis comb. nov.