Analysis of the 16S rRNA gene sequences of species currently assigned to the genus Flexibacter has shown extensive intrageneric phylogenetic heterogeneity. It has been shown in previous studies that the species [Flexibacter] sancti, [Flexibacter] filiformis and [Flexibacter] japonensis were most closely related to Chitinophaga pinensis. In addition, [Cytophaga] arvensicola and species of the genus Terrimonas also clustered into this phylogenetic group. Although the similarities of 16S rRNA gene sequences were low (88.5–96.4 %), there is no evidence for clear phenotypic differences between these organisms that justify assignment to different genera. A proposal is made to transfer these species to the genus Chitinophaga as Chitinophaga sancti comb. nov., Chitinophaga filiformis comb. nov., Chitinophaga japonenis comb. nov. and Chitinophaga arvensicola comb. nov. on the basis of phylogenetic and phenotypic data. Furthermore, a novel species is described within this genus, Chitinophaga skermanii sp. nov., with strain CC-SG1B^T (=CCUG 52510^T=CIP 109140^T) as the type strain.

A yellow-pigmented bacterial strain (CC-H3-2^T), isolated from the rhizosphere of Lactuca sativa L. (garden lettuce) in Taiwan, was investigated using a polyphasic taxonomic approach. The cells were Gram-negative, rod-shaped and non-spore-forming. Phylogenetic analyses using the 16S rRNA gene sequence of the isolate indicated that the organism belongs to the genus Chryseobacterium, with the highest sequence similarity to the type strains of Chryseobacterium indoltheticum (97·7 %), Chryseobacterium scophthalmum (97·5 %), Chryseobacterium joostei (97·2 %) and Chryseobacterium defluvii (97·2 %). The major whole-cell fatty acids were iso-C_15 : 0 (52·2 %) and iso-C_17 : 0 3-OH. DNA–DNA hybridization experiments revealed levels of only 27·4 % to C. scophthalmum, 27·1 % to C. indoltheticum, 14·1 % to C. joostei and 7·8 % to C. defluvii. DNA–DNA relatedness and biochemical and chemotaxonomic properties demonstrate that strain CC-H3-2 ^T represents a novel species, for which the name Chryseobacterium formosense sp. nov. is proposed. The type strain is CC-H3-2^T (=CCUG 49271^T=CIP 108367^T).

Development of drug resistance in opportunistic pathogens is one of the major healthcare challenges associated with infection management. Combination therapy has many advantages due to the simultaneous action of two drugs on two separate cellular targets. However, selection of the drugs should offer safety and synergistic interaction against most of the strains. Here, the efficacy of antibiotics in combination with quercetin, a natural flavonoid capable of targeting quorum sensing was tested against biofilm-forming Pseudomonas aeruginosa strains previously isolated from catheter associated urinary tract infection. Based on the antibiotic susceptibility pattern, synergistic effect of quercetin with selected antibiotics (levofloxacin, ceftriaxone, gentamycin, tobramycin and amikacin) was tested at the fractional concentrations of MIC by the checkerboard method and the fractional inhibitory concentration index (FIC_i) was calculated to estimate the synergistic effect. Effect of the synergistic combinations were further tested using time-kill assay, and against biofilm formation and biofilm cell viability. Cytotoxicity assays were performed using Human Embryonic Kidney 293T cells (HEK-293T) using the effective drug combinations with respective controls. The biofilm formation and biofilm cell viability were drastically affected with quercetin and selected antibiotics combinations with ≥80% inhibition. In vitro infection studies showed that all the strains could exert significant cell killing (68 to 85%) and the drug combinations decreased the infection rate significantly by reducing the cell killing effect of P. aeruginosa (p<0.05). The synergistic effect of quercetin is attributed to its quorum sensing inhibitory properties. These findings indicate that quercetin along with existing antibiotics can potentiate the treatment against P. aeruginosa infection and may reduce the selection pressure due to antibiotic overuse.

Inhibition of quorum sensing (QS), a cell-density dependent regulation of gene expression in bacteria by autoinducers is an attractive strategy for the development of antipathogenic agents. In this study, the anti-QS activity of the ethanolic extract of the traditional herb Centella asiatica was investigated by the biosensor bioassay using Chromobacterium violaceum CV026. The effect of ethyl acetate fraction (CEA) from the bioassay-guided fractionation of ethanol extract on QS-regulated violacein production in C. violaceum ATCC12472 and pyocyanin production, proteolytic and elastolytic activities, swarming motility, and biofilm formation in Pseudomonas aeruginosa PAO1 were evaluated. Possible mechanism of QS-inhibitory action on autoinducer activity was determined by measuring the acyl homoserine lactone using C. violaceum ATCC31532. Anti-QS compounds in the CEA fraction were identified using thin layer chromatography biosensor overlay assay. Ethanol extract of C. asiatica showed QS inhibition in C. violaceum CV026. Bioassay-guided fractionation of ethanol extract revealed that CEA was four times more active than the ethanol extract. CEA, at 400 μg/mL, completely inhibited violacein production in C. violaceum ATCC12472 without significantly affecting growth. CEA also showed inhibition of QS-regulated phenotypes, namely, pyocyanin production, elastolytic and proteolytic activities, swarming motility, and biofilm formation in P. aeruginosa PAO1 in a concentration-dependent manner. Thin layer chromatography of CEA with biosensor overlay showed anti-QS spot with an Rf value that corresponded with that of standard kaempferol. The anti-QS nature of C. asiatica herb can be further exploited for the formulation of drugs targeting bacterial infections where pathogenicity is mediated through QS.