Two novel synthetic peptides inhibit quorum sensing-dependent biofilm formation and some virulence factors in Pseudomonas aeruginosa PAO1.

Quorum sensing (QS) regulates virulence factor expression in Pseudomonas aeruginosa. Inhibiting the QS-controlled virulence factors without inhibiting the growth of P. aeruginosa is a promising approach for overcoming the widespread resistance of P. aeruginosa. This study was proposed to investigate the effects of two novel synthetic peptides on the biofilm development and virulence factor production of P. aeruginosa. The tested strain was P. aeruginosa PAO1. The results indicated that both of the synthetic peptides (LIVRHK and LIVRRK) inhibited (P < 0.05) the formation of biofilms and the production of virulence factors, including pyocyanin, protease, and rhamnolipids, without inhibiting the growth of PAO1. Additionally, we detected transcriptional changes related to QS and found a significant reduction in the levels of gene expression of lasI, lasR, rhlI, and rhlR. This study demonstrates that LIVRRK and LIVRHK are novel synthetic peptides that can act as potent inhibitors of QS-regulated virulence factors in P. aeruginosa. Moreover, these synthetic peptides have potential applications in the treatment of biofilmrelated diseases. Both peptides may be able to control chronic infections and biofilm-associated problems of P. aeruginosa.

Synthesis and antimicrobial activity of some new 2-indolinone derived oximes and spiro-isoxazolines.

The synthesis and spectral analysis of some new 1,3-dihydro-3-hydroxy-3-[2-hydroxyimino-2-(substituted phenyl)ethyl]-2H-indol-2-ones (21-32) and spiro[3H-indol-3,5'-(4'H)-isoxazol]-2(1H)-ones (33-44) are described. Sixteen of the synthesized compounds were screened in vitro for their growth inhibitory activity against thirteen species of microorganisms, viz, S. aureus, S. epidermidis, S. faecalis, B. subtilis, B. cereus, E. aerogens, E. coli, P. aeruginosa, P. vulgaris, A. baumonia, A. faecalis, C. albicans and S. cervicae. Most of the compounds exhibited significant antimicrobial activity especially the oximes 28 and 29.

Modulation of biofilms of Pseudomonas aeruginosa by quinolones.

The interaction between four fluoroquinolones (ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin) and biofilms of Pseudomonas aeruginosa in wells of microtiter plates and on segments of vascular catheters were studied in an in vitro model of vascular catheter colonization. Subinhibitory concentrations (one-half, one-fourth, and one-eight of the MIC) of the fluoroquinolones reduced the adherence of P. aeruginosa to 30 to 33, 44 to 47, and 61 to 67% of that of controls, respectively. The addition of high concentrations of the fluoroquinolones (12.5 and 400 micrograms/ml) to preformed biofilms (grown for 48 h at 37 degrees C) decreased the adherence of P. aeruginosa to 69 to 77 and 39 to 60% of that of controls, respectively. In an in vitro model of vascular catheter colonization, subinhibitory concentrations (one-half, one-fourth, and one-eight of the MIC) of fluoroquinolones reduced the number of adherent bacteria to 21 to 23, 40 to 46, and 55 to 70% of that of the controls, respectively. Scanning electron microscopy demonstrated a significant reduction in glycocalyx formation and adherent bacteria in the presence of pefloxacin at one-half to one-eight of the MIC. Vascular catheter segments precolonized with P. aeruginosa for 24 h and exposed to the fluoroquinolones at 4 to 25 times the MIC (50 micrograms/ml) for 2 h showed <5% growth of adherent cells compared with controls. No adherent organisms were cultured in the presence of 8 to 50 times the MIC (100 micrograms/ml). Scanning electron microscopy studies of preformed biofilms exposed to pefloxacin verified the results obtained by culture. These data show that subinhibitory concentrations of ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin inhibit the adherence of P. aeruginosa to plastic surfaces and vascular catheters. Clinically achievable concentrations of fluoroquinolones (50 to 100 micrograms/ml) were able to eradicate preformed biofilms on vascular catheters.

Relationships between beta-lactamase production and beta-lactam susceptibility of environmental strains of Yersinia kristensenii.

Strains of Yersinia kristensenii display high susceptibility to carbenicillin (MIC90 less than 8 micrograms/ml) in comparison with the majority of environmental strains of Yersinia closely related to Y. enterocolitica which are resistant to this antibiotic (MIC90 greater than 256 micrograms/ml). beta-lactamases of 39 strains of Y. kristensenii isolated from foods were analysed by isoelectric focusing and gel electrophoresis of ultrasonically disrupted uninduced cultures. beta-lactamase patterns showed the presence of only one out of three classes of enzymes of pI 6.7, 7.6 and 8.2, respectively, by strain. One beta-lactamase showed electrophoretic mobility different (EM + 2.0 cm/h) from that of all the other enzymes (EM + 1.6 cm/h) belonging to the class of pI 7.6. Induction by cefoxitin revealed the existence of inducible beta-lactamases in two out of eight selected strains. The substrate profile of these enzymes, which are probably chromosomally mediated, showed a predominant cephalosporinase activity. None of the type A and B beta-lactamases described by Cornelis and Abraham in Y. enterocolitica were found in any of the strains examined. The lack of beta-lactamase A (a penicillinase) accounts for the carbenicillin susceptibility of Y. kristensenii strains.

Antimicrobial susceptibilities of food-isolated strains of Yersinia enterocolitica, Y. intermedia, Y. frederiksenii, and Y. kristensenii.

The in vitro antimicrobial susceptibility of Yersinia enterocolitica and newly related species isolated from foods was examined. Only 4 of 375 isolates displayed resistance to non-ss-lactam antibiotics. MICs of ampicillin and carbenicillin determined by agar dilution with respect to 125 isolates showed the high susceptibility of Y. kristensenii and biovar 3 of Y. enterocolitica to carbenicillin (MIC for 90% of the strains, less than or equal to 8 micrograms/ml).