Andry Rasamindrakotroka

Pseudomonas aeruginosa Biofilm Formation and Persistence, along with the Production of Quorum Sensing-Dependent Virulence Factors, Are Disrupted by a Triterpenoid Coumarate Ester Isolated from Dalbergia trichocarpa, a Tropical Legume.

Recently, extracts of Dalbergia trichocarpa bark have been shown to disrupt P. aeruginosa PAO1 quorum sensing (QS) mechanisms, which are key regulators of virulence factor expression and implicated in biofilm formation. One of the active compounds has been isolated and identified as oleanolic aldehyde coumarate (OALC), a novel bioactive compound that inhibits the formation of P. aeruginosa PAO1 biofilm and its maintenance as well as the expression of the las and rhl QS systems. Consequently, the production of QS-controlled virulence factors including, rhamnolipids, pyocyanin, elastase and extracellular polysaccharides as well as twitching and swarming motilities is reduced. Native acylhomoserine lactones (AHLs) production is inhibited by OALC but exogenous supply of AHLs does not restore the production of virulence factors by OALC-treated cultures, indicating that OALC exerts its effect beyond AHLs synthesis in the QS pathways. Further experiments provided a significant inhibition of the global virulence factor activator gacA by OALC. OALC disorganizes established biofilm structure and improves the bactericidal activity of tobramycin against biofilm-encapsulated PAO1 cells. Finally, a significant reduction of Caenorhabditis elegans paralysis was recorded when the worms were infected with OALC-pre-treated P. aeruginosa. Taken together, these results show that triterpenoid coumarate esters are suitable chemical backbones to target P. aeruginosa virulence mechanisms.

Endemic Malagasy Dalbergia species inhibit quorum sensing in Pseudomonas aeruginosa PAO1

Various species of the plant genus Dalbergia are traditionally used as medicine for sundry ailments and some of them have been shown recently to quench the virulence of Gram-positive and Gram-negative bacteria. Cell-to-cell communication mechanisms, quorum sensing (QS) in particular, are key regulators of virulence in many pathogenic bacteria. Screening n-hexane extracts of leaves, roots and bark of endemic Malagasy Dalbergia species for their capacity to antagonize QS mechanisms in Pseudomonas aeruginosa PAO1 showed that many reduced the expression of the QS-regulated genes lasB and rhlA. However, only the extract of Dalbergia trichocarpa bark (DTB) showed a significant reduction of QS gene expression without any effect on the aceA gene encoding a QS-independent isocitrate lyase. Further characterization of DTB impact on QS revealed that the QS systems las and rhl are inhibited and that swarming, twitching, biofilm formation and the production of pyocyanin, elastase and proteases are also hampered in the presence of the DTB extract. Importantly, compared with the known QS inhibitor naringenin, the DTB extract showed a stronger negative effect on twitching, biofilm formation and tobramycin resistance. Preliminary structural characterization of these potent biofilm disrupters suggests that they belong to the phytosterols. The strong inhibition of motility and biofilm formation suggests that the DTB extract contains agents disrupting biofilm architecture, which is an important observation in the context of the design of new drugs targeting biofilm-encapsulated pathogens.

Evaluation of methicillin-resistant Staphylococcus aureus nasal carriage in Malagasy pig and poultry non-industrial farmers

INTRODUCTION The laboratory of Training and Research in Medical Biology of Madagascar conducted a cross-sectional study to estimate the rate of S. aureus nasal carriage of pig and poultry Malagasy farmers. METHODOLOGY Pig and poultry farmers from capital town of Madagascar were selected for nasal swabs collection with information on potential risk factors for S. aureus colonization, including animal exposure. RESULTS Nasal swabs from 180 farmers (M/F sex ratio: 0.74), enabled isolation after culture and biochemical identification, 69 (38.33%) S. aureus strains among which 45 (25%) were methicillin-resistant (MRSA). Risk factors analysis revealed that farming duration, number of animals, direct contact with poultry, and frequent contact with manure increased risk of S. aureus and MRSA nasal carriage. Likewise, farm practices that imply close contact with pigs such as food distribution and pigsty washing increased risk of S. aureus and MRSA nasal carriage among pig farmers. Among MRSA isolates, resistance rate to other antibiotics was similar to that of MRSA isolates from the non-farmer Malagasy population. However, gentamycin resistance was noticeably higher (32.5% versus 4.44%). CONCLUSIONS This study shows a high rate of S. aureus and MRSA nasal carriage with high rate of multidrug resistance among healthy people frequently in contact with animals. A strategic policy against the spread of multidrug-resistant strains is desirable in farms and veterinary areas.