Investigating the quorum-sensing inhibitory and potential HIV activity of indigenous South African sponge-associated bacterial extracts.

Abstract

With bacterial antimicrobial resistance on the rise, alternative therapeutic agents are being sought. One such alternative is the use of anti-virulence strategies such as quorum-sensing inhibition (QSI), which has been proposed as a viable treatment option for pathogenic microorganisms such as multi-drug resistant Pseudomonas aeruginosa. Ninety-eight bacterial isolates from seven South African sponges harvested off the coast of KwaZulu-Natal underwent primary QSI screening using C. violaceum biosensor sandwich assays. Fifteen isolates presenting putative QSI activity were selected for further study, five of which were identified as Bacillus spp. while ten were identified as Actinomycete spp., following 16S rRNA PCR and sequencing. Crude extracts were obtained from these 30 isolates following shake-flask fermentations with two production media, mannitol and medium 5294, and ethyl acetate extractions. Extracts were then screened against QS-mediated P. aeruginosa virulence factor production, viz. pyocyanin, pyoverdine, elastase, protease, rhamnolipid, initial and mature biofilm production as well as swimming and swarming motilities. Extracts were additionally screened for putative anti-HIV reverse transcriptase (RT) activity due to the lack of current research examining the anti-HIV potential of sponge-associated bacteria. Actinomycete-derived mannitol extracts yielded the most significant inhibition for most of the P. aeruginosa virulence factors tested, while for the Bacillus spp. isolates medium 5294 extracts resulted in more significant inhibitions, indicating that the selection of production media may need to be carefully considered. This was not the case for the anti-HIV RT activity, with mannitol and medium 5294 extracts yielding similar activity. Broad spectrum QSI activity was observed with a number of extracts, including those from Streptomyces spp. SP4-AB2 and SP3-AB22, and Bacillus weihenstephanensis SP5-AB7, each of which was able to significantly (p < 0.05) inhibit virulence factors mediated by each of the three P. aeruginosa quorum sensing systems, with inhibitions as high as 93% being observed. It was further observed that 13 of the 30 extracts yielded RT-inhibition >90%; higher than that of the positive control nevirapine. Due to the high percentage of QSI and HIV-RT inhibition observed, sponge-associated bacterial extracts should indeed be screened further for their QSI and anti-HIV potential, especially those belonging to the genus Bacillus and the family Actinomycetes. Sponge-associated bacteria, therefore, possess the QSI and anti-HIV RT potential necessary to serve as the solution to the current resistance crisis and should be further studied in this regard.