Quorum sensing

Antibiofilm activity of Parkia javanica against Pseudomonas aeruginosa: a study with fruit extract

Parkia javanicais a well-known ethno-botanical plant of the north-east region of India.

Molecular typing, antibiotic resistance, virulence gene and biofilm formation of different Salmonella enterica serotypes

Salmonella enterica isolates representing commonly isolated serotypes in Tunisia were analyzed using genotyping and phenotyping methods. ERIC and ITS-PCR applied to 48 Salmonella spp. isolates revealed the presence of 12 and 10 different profiles, respectively. The distribution of profiles among serotypes demonstrated the presence of strains showing an identical fingerprinting pattern. All Salmonella strains used in this study were positive for the sdiA gene. Three Salmonella isolates belonging to serotypes Anatum, Enteritidis and Amsterdam were negative for the invA gene. The spvC gene was detected in thirteen isolates belonging to serotypes Anatum, Typhimurium, Enteritidis, Gallinarum and Montevideo. Antibiotic resistance was frequent among the recovered Salmonella isolates belonging to serotypes Anatum, Typhimurium, Enteritidis, Zanzibar and Derby. The majority of these isolates exhibited resistance to at least two antibiotic families. Four multidrug-resistant isolates were recovered from food animals and poultry products. These isolates exhibited not only resistance to tetracycline, sulphonamides, and ampicillin, but also have shown resistance to fluoroquinolones. Common resistance to nalidixic acid, ciprofloxacin and ofloxacin in two S. Anatum and S. Zanzibar strains isolated from raw meat and poultry was also obtained. Furthermore, wastewater and human isolates exhibited frequent resistance to nalidixic acid and tetracycline. Of all isolates, 33.5% were able to form biofilm.

Anti-biofilm activity of Marula - a study with the standardized bark extract

ETHNOPHARMACOLOGICAL RELEVANCE

Marula (Sclerocarya birrea; family - Anacardiaceae) is an African plant, which enjoys wide socio-economic importance particularly in southern part of Africa. The fruits are consumed as food and also as alcoholic beverage (cream liquor). In different parts of Africa, the decoction of the bark is traditionally used for the treatment of dysentery, diarrhoea, and various other infectious conditions. The aim of the study was to investigate the anti-biofilm properties of the methanol extract of Marula bark (stem bark of Sclerocarya birrea), with a view towards combating the emergence of antimicrobial resistance often associated with bacterial biofilms.

MATERIALS AND METHODS

The standardized methanol extract was initially tested for its antimicrobial property. The crystal violet assay was used for evaluating anti-biofilm (biofilm formation by Pseudomonas aeuginosa) activity. Further in order to study the mechanism of anti-biofilm activity, the same was evaluated for understanding its role on various quorums sensing mediated phenomenon (swarming motility assay, protease and pyoverdin assay) that are known to be associated with the formation of biofilms and pathogenicity.

RESULTS

The methanol extract showed no inhibition of bacterial growth up to a concentration of 200 µg/ml. Interestingly, the sample produced anti-biofilm activity (around 75% decrease; 100 µg/ml) at sub-lethal concentration. Further it also significantly reduced the QS mediated swarming motility. The release of various virulent factors (protease and pyoverdin) was found to be lowered when pre-treated with the extract.

CONCLUSION

The present study illustrates the anti-biofilm property Sclerocarya birrea. The standardized extract significantly disrupted the quorum sensing mediated production of biofilm formation and also inhibited swarming ability of the cells. The extract displayed a regulatory role on the secretion of protease and pyoverdin, two QS dependent pathogenic factors found in Pseudomonas aeruginosa. This study also validates the ethnobotanical use of Marula.

Rapid and simple colorimetric method for the quantification of AI-2 produced from Salmonella Typhimurium

The aim of this study was to evaluate the feasibility of Fe(III) ion reduction for the simple and rapid quantification of autoinducer-2 (AI-2) produced from bacteria using Salmonella Typhimurium as a model. Since the molecular structure of AI-2 is somewhat similar to ascorbic acid it was expected that AI-2 would also act as a reducing agent and reduce Fe(III) ions in the presence of 1,10-phenanthroline to form the colored [(o-phen)3 Fe(II)]SO4 ferroin complex that could be quantified colorimetrically. In support of this, colony rinses and cell free supernatants from cultures of all tested AI-2 producing strains, but not the AI-2 negative Sinorhizobium meliloti, formed a colored complex with a λmax of 510nm. The OD510 values of these culture supernatants or colony rinses were in broad agreement with the % activity observed in the same samples using the standard Vibrio harveyi bioluminescence assay for AI-2 detection, and with previously reported results. This methodology could potentially be developed as an alternative method for the simple and rapid quantification of AI-2 levels produced in bacterial cultures.

Investigation of N-acyl homoserine lactone (AHL) molecule production in Gram-negative bacteria isolated from cooling tower water and biofilm samples

In this study, 99 Gram-negative rod bacteria were isolated from cooling tower water, and biofilm samples were examined for cell-to-cell signaling systems, N-acyl homoserine lactone (AHL) signal molecule types, and biofilm formation capacity. Four of 39 (10 %) strains isolated from water samples and 14 of 60 (23 %) strains isolated from biofilm samples were found to be producing a variety of AHL signal molecules. It was determined that the AHL signal molecule production ability and the biofilm formation capacity of sessile bacteria is higher than planktonic bacteria, and there was a statistically significant difference between the AHL signal molecule production of these two groups (p < 0.05). In addition, it was found that bacteria belonging to the same species isolated from cooling tower water and biofilm samples produced different types of AHL signal molecules and that there were different types of AHL signal molecules in an AHL extract of bacteria. In the present study, it was observed that different isolates of the same strains did not produce the same AHLs or did not produce AHL molecules, and bacteria known as AHL producers did not produce AHL. These findings suggest that detection of signal molecules in bacteria isolated from cooling towers may contribute to prevention of biofilm formation, elimination of communication among bacteria in water systems, and blockage of quorum-sensing controlled virulence of these bacteria.

Phenotypic and genome-wide analysis of an antibiotic-resistant small colony variant (SCV) of Pseudomonas aeruginosa

BACKGROUND

Small colony variants (SCVs) are slow-growing bacteria, which often show increased resistance to antibiotics and cause latent or recurrent infections. It is therefore important to understand the mechanisms at the basis of this phenotypic switch.

METHODOLOGY/PRINCIPAL FINDINGS

One SCV (termed PAO-SCV) was isolated, showing high resistance to gentamicin and to the cephalosporine cefotaxime. PAO-SCV was prone to reversion as evidenced by emergence of large colonies with a frequency of 10(-5) on media without antibiotics while it was stably maintained in presence of gentamicin. PAO-SCV showed a delayed growth, defective motility, and strongly reduced levels of the quorum sensing Pseudomonas quinolone signal (PQS). Whole genome expression analysis further suggested a multi-layered antibiotic resistance mechanism, including simultaneous over-expression of two drug efflux pumps (MexAB-OprM, MexXY-OprM), the LPS modification operon arnBCADTEF, and the PhoP-PhoQ two-component system. Conversely, the genes for the synthesis of PQS were strongly down-regulated in PAO-SCV. Finally, genomic analysis revealed the presence of mutations in phoP and phoQ genes as well as in the mexZ gene encoding a repressor of the mexXY and mexAB-oprM genes. Only one mutation occurred only in REV, at nucleotide 1020 of the tufA gene, a paralog of tufB, both encoding the elongation factor Tu, causing a change of the rarely used aspartic acid codon GAU to the more common GAC, possibly causing an increase of tufA mRNA translation. High expression of phoP and phoQ was confirmed for the SCV variant while the revertant showed expression levels reduced to wild-type levels.

CONCLUSIONS

By combining data coming from phenotypic, gene expression and proteome analysis, we could demonstrate that resistance to aminoglycosides in one SCV mutant is multifactorial including overexpression of efflux mechanisms, LPS modification and is accompanied by a drastic down-regulation of the Pseudomonas quinolone signal quorum sensing system.

Identification and characterization of target genes of the GinI/GinR quorum-sensing system in Gluconacetobacter intermedius

The GinI/GinR quorum-sensing system represses oxidative fermentation, including acetic acid and gluconic acid fermentation, as well as antifoam activity in Gluconacetobacter intermedius NCI1051. An 89 aa protein, GinA, whose production is induced by the quorum-sensing system, represses both oxidative fermentation and antifoam activity via a still unknown mechanism, although an OmpA family protein, GmpA, as a target of the GinI/GinR quorum-sensing system via GinA, has been found to repress oxidative fermentation. In this study, four novel GinA-inducible genes (gltA, pdeA, pdeB and nagA) were identified and their involvement in oxidative fermentation and antifoam activity was examined by gene disruption. Disruption of nagA (which encodes a putative N-acetylglucosamine-6-phosphate deacetylase) decreased the growth rate in the exponential growth phase, indicating that nagA was required for the rapid growth of the strain. This unexpected finding revealed a new aspect of the GinI/GinR quorum-sensing system: it accelerates exponential growth by induction of nagA. In contrast, gltA (a putative glycosyltransferase) and pdeA (a putative cyclic-di-GMP phosphodiesterase) were shown to repress oxidative fermentation, including acetic acid and gluconic acid fermentation. gltA was also shown to repress antifoam activity. Disruption of pdeB (a putative phosphodiesterase/diguanylate cyclase) caused no phenotypic changes. Taking our previous results into consideration, these results showed an apparently complex mechanism for repressing oxidative fermentation by the quorum-sensing system; at least three GinA-inducible genes, gltA, pdeA and gmpA, were involved in the repression of oxidative fermentation by the GinI/GinR quorum-sensing system, the most characteristic feature of the acetic acid bacteria.

An OmpA family protein, a target of the GinI/GinR quorum-sensing system in Gluconacetobacter intermedius, controls acetic acid fermentation

Via N-acylhomoserine lactones, the GinI/GinR quorum-sensing system in Gluconacetobacter intermedius NCI1051, a gram-negative acetic acid bacterium, represses acetic acid and gluconic acid fermentation. Two-dimensional polyacrylamide gel electrophoretic analysis of protein profiles of strain NCI1051 and ginI and ginR mutants identified a protein that was produced in response to the GinI/GinR regulatory system. Cloning and nucleotide sequencing of the gene encoding this protein revealed that it encoded an OmpA family protein, named GmpA. gmpA was a member of the gene cluster containing three adjacent homologous genes, gmpA to gmpC, the organization of which appeared to be unique to vinegar producers, including "Gluconacetobacter polyoxogenes." In addition, GmpA was unique among the OmpA family proteins in that its N-terminal membrane domain forming eight antiparallel transmembrane beta-strands contained an extra sequence in one of the surface-exposed loops. Transcriptional analysis showed that only gmpA of the three adjacent gmp genes was activated by the GinI/GinR quorum-sensing system. However, gmpA was not controlled directly by GinR but was controlled by an 89-amino-acid protein, GinA, a target of this quorum-sensing system. A gmpA mutant grew more rapidly in the presence of 2% (vol/vol) ethanol and accumulated acetic acid and gluconic acid in greater final yields than strain NCI1051. Thus, GmpA plays a role in repressing oxidative fermentation, including acetic acid fermentation, which is unique to acetic acid bacteria and allows ATP synthesis via ethanol oxidation. Consistent with the involvement of gmpA in oxidative fermentation, its transcription was also enhanced by ethanol and acetic acid.

Control of acetic acid fermentation by quorum sensing via N-acylhomoserine lactones in Gluconacetobacter intermedius

A number of gram-negative bacteria regulate gene expression in a cell density-dependent manner by quorum sensing via N-acylhomoserine lactones (AHLs). Gluconacetobacter intermedius NCI1051, a gram-negative acetic acid bacterium, produces three different AHLs, N-decanoyl-l-homoserine lactone, N-dodecanoyl-L-homoserine lactone, and an N-dodecanoyl-L-homoserine lactone with a single unsaturated bond in its acyl chain, as determined by liquid chromatography-tandem mass spectrometry. Two genes encoding an AHL synthase and a cognate regulator were cloned from strain NCI1051 and designated ginI and ginR, respectively. Disruption of ginI or ginR abolished AHL production, indicating that NCI1051 contains a single set of quorum-sensing genes. Transcriptional analysis showed that ginI is activated by GinR, which is consistent with the finding that there is an inverted repeat whose nucleotide sequence is similar to the sequence bound by members of the LuxR family at position -45 with respect to the transcriptional start site of ginI. A single gene, designated ginA, located just downstream of ginI is transcribed by read-through from the GinR-inducible ginI promoter. A ginA mutant, as well as the ginI and ginR mutants, grew more rapidly in medium containing 2% (vol/vol) ethanol and accumulated acetic acid at a higher rate with a greater final yield than parental strain NCI1051. In addition, these mutants produced larger amounts of gluconic acid than the parental strain. These data demonstrate that the GinI/GinR quorum-sensing system in G. intermedius controls the expression of ginA, which in turn represses oxidative fermentation, including acetic acid and gluconic acid fermentation.