Quorum Sensing Interfering Strategies and Their Implications in the Management of Biofilm-Associated Bacterial Infections

Abstract The bacterial species employ various types of molecular communication systems recognized as quorum sensing for the synchronization of differential gene expression to regulate virulence traits and biofilm formation. A variety of quorum sensing inhibitors; molecules that interfere with quorum sensing among bacteria have been examined which can block the action of autoinducers. Moreover, the studies have scrutinized various enzymes for their quorum quenching activity resulting in the degradation of signaling molecules or blocking of gene expression. So far, the studies have found that these approaches are not only capable to reduce the pathogenicity and biofilm formation but also resulted in increased bacterial susceptibility to antibiotics and bacteriophages. The effectiveness of these strategies has been validated in different animal models and it seems that these practices will be transformed in near future to develop the medical devices including catheters, implants, and dressings for the prevention of bacterial infections. Although many of these approaches are still in the research stage, the increasing library of quorum quenching molecules and enzymes will open innovative perspectives for the development of antibacterial approaches which will extend the therapeutic arsenal against the pathogenic bacterial species.

Corynebacterium diphtheriae putative tellurite-resistance protein (CDCE8392_0813) contributes to the intracellular survival in human epithelial cells and lethality of Caenorhabditis elegans

Corynebacterium diphtheriae, the aetiologic agent of diphtheria, also represents a global medical challenge because of the existence of invasive strains as causative agents of systemic infections. Although tellurite (TeO3^2-) is toxic to most microorganisms, TeO3^2--resistant bacteria, including C. diphtheriae, exist in nature. The presence of TeO3^2--resistance (Te^R) determinants in pathogenic bacteria might provide selective advantages in the natural environment. In the present study, we investigated the role of the putative Te^R determinant (CDCE8392_813gene) in the virulence attributes of diphtheria bacilli. The disruption of CDCE8392_0813 gene expression in the LDCIC-L1 mutant increased susceptibility to TeO3^2- and reactive oxygen species (hydrogen peroxide), but not to other antimicrobial agents. The LDCIC-L1 mutant also showed a decrease in both the lethality of Caenorhabditis elegansand the survival inside of human epithelial cells compared to wild-type strain. Conversely, the haemagglutinating activity and adherence to and formation of biofilms on different abiotic surfaces were not regulated through the CDCE8392_0813 gene. In conclusion, the CDCE8392_813 gene contributes to the Te^R and pathogenic potential of C. diphtheriae.

Phage-resistance of Salmonella enterica serovar Enteritidis and pathogenesis in Caenorhabditis elegans is mediated by the lipopolysaccharide

Phage therapy has been used in the past as an alternative therapy against bacterial pathogens. However, phage-resistant bacterial strains can emerge. Some studies show that these phage-resistant strains are avirulent. In this study, we report that phage-resistant strains of Salmonella enterica serovar Enteritidis (hereafter S. Enteritidis) were avirulent in the Caenorhabditis elegans animal model. We isolated phage-resistant strains of S. Enteritidis ATCC 13076 by using three lytic phages (f2aSE, f3aSE and f18aSE). In these mutants, we explored different virulence factors like lipopolysaccharide (LPS), virulence plasmid (Pla), motility and type I fimbriae, all of which may have effects on virulence and could furthermore be related to phage resistance. The phage-resistant strains of S. Enteritidis showed loss of O-Polysaccharide (O-PS) and auto-agglutination, present a rough phenotype and consequently they are avirulent in the C. elegans animal model. We speculate that the O-PS is necessary for phage attachment to the S. Enteritidis cell surface.

Detection of virulence attributes of Burkholderia pseudomallei.

BACKGROUND & OBJECTIVES: Melioidosis caused by Burkholderia pseudomallei is an emerging disease in India. This study examined the toxin activity of bacteria-free culture filtrate in three different cell lines (cytotoxic assay) and its effect on Caenorhabditis elegans (nematode toxicity assay). Endotoxic activity of the viable bacteria was also studied in C. elegans (co-culture killing assay). METHODS: For toxin studies, serial doubling dilutions of unheated, heated crude and ultra filtrate of bacteria-free culture supernatants of B. pseudomallei were tested in 96-well microtitre plate containing confluent mono layers of McCoy, Hep-2 and HeLa cell lines. For the effects on C. elegans, the worms were exposed to heated and unheated bacteria-free culture supernatants in 24-well microtitre plate for 24h and then transferred to OP50 Escherichia coli lawn culture. The endotoxic activity of the live bacterium was studied by feeding the worms in the lawn culture of B. pseudomallei. RESULTS: All the clinical isolates (n=38) produced cytotoxic changes in all the cell lines. No difference was observed in the cytotoxicity of unheated, heated and ultra-filtered culture supernatant. The septicaemic isolates were observed to produce cytotoxic changes in high dilutions (1:160) of culture filtrate. None of the unheated and heated crude filtrate had deleterious effect on C. elegans, while all the live bacteria were found to be lethal to the nematode. INTERPRETATION & CONCLUSION: The culture supernatants, though produced cytopathic effect in various tissue cultures, failed to have any deleterious effect on the worms. However, live bacteria were lethal to the worms B. pseudomallei. Use of C. elegans model to detect virulence attributes of B. pseudomallei is recommended as an alternative to tissue culture methods as this can be carried out in laboratories where a tissue culture set up is not available.