Profiles and Antimicrobial Response Patterns of Human Feet Bacterial Isolates of Individuals with Differential Attraction to Anopheles Gambiae in Kilifi, Kenya

Malaria is a mosquito-borne illness caused by Plasmodium parasites carried by certain species of mosquitoes. It is currently a global problem where more than 2 billion people in 110 countries at risk, with an estimated 2.7 million deaths per year of which the majority are children. In Kenya, Anopheles gambiae s.s is the most effective vector in human malaria transmission. Studies have indicated that some of the chemical cues in the feet odour that mediate attraction of An. gambiae s.s to their preferred feeding site may be of microbial origin. However, the profiles and phylogenetic affiliations of the microbes have not been fully characterized. The objectives of this study were to determine the different levels of attraction of female Anopheles gambiae s.s to the feet odours, to isolate and characterize the bacterial isolates, and to assess their antimicrobial response patterns. Ten volunteer male adult participants in Kilifi, Kenya, were recruited for the differential attraction experiment. Swab samples from the most to the least attractive individuals were used to isolate feet derived bacterial isolates. The isolates were then characterized based on cultural, morphological and molecular techniques. Specifically, the isolates were characterized based on 16S rRNA gene-based Sanger sequencing using 27F and 1492R bacterial primer pair. The phylogenetic analyses were then done on MEGA7 together with its available software tools. The antimicrobial patterns of the bacterial isolates were characterized using commercially available antibiotics and antiseptics. Results indicate that, of the ten (10) participants recruited in the study, participant two (2) was the most attractive while participant six (6) was the least attractive to the female An. gambiae s.s mosquitoes. There was a significant (p=0.001) variation in the attraction of the female mosquitoes to the feet sites (front and back), the front site being more attractive. On the other hand, the attraction of the mosquitoes to the left and right legs did not differ significantly (p=0.274). Nineteen (19) bacterial morpho-groups were obtained from the samples with a majority of them fourteen (14) being mainly present on the front part of the feet. Phylogenetic analysis revealed diverse bacterial communities belonging to different genera. Based on phylogeny, participant two (2) was mainly dominated by isolates belonging to Staphylococcus capitis and Staphylococcus simulans, both are associated with the production of lipase enzyme that breaks down lipids in sweat leading to production of foot odour. Isolates belonging to Staphylococcus xylosus and Bacillus pumilus were shared among participant two (2) and participant six (6). Two novel isolates, PTXV and PTXVI, could not be identified based on phylogeny. Antibiotic response patterns revealed that isolates belonging to Bacillus safensis, Bacillus pumilus and a potentially novel isolate PTXV were susceptible to the six antibiotics. Ciprofloxacin was the most effective antibiotic while antiseptic A was the most effective antiseptic against the bacterial isolates. The results show that the differential attraction of Anopheles gambiae s.s females to individuals in malaria-endemic regions is evident and mediated by differing bacterial numbers among the participants.