The bacterium Pseudomonas aeruginosa may grow in a biofilm structure, which can be up to 1000 times more resistant to antibiotics compared to planktonic isolates. The P. aeruginosa biofilms have serious implications with regard to infection, especially in individuals with weakened immune defenses such as burn and cystic fibrosis patients. Antibiotic studies are usually based on planktonic antibiotic susceptibility results, so the treatment may be less effective when used in patients. The aim of this study was to further screen previously studied cave bacterial isolates with potential activity and determine their antimicrobial capabilities against P. aeruginosa biofilms. Three strains; A1A3, RA003 and 58B were cultured in different media over 10 days, with collections of supernatant on days 2, 4, 6, 8, and 10. The MBEC P&G Assay device was used to culture P. aeruginosa biofilms, which were then exposed to the collected supernatants. After exposure, the surviving biofilms were recovered, and spot plated in order to measure any inhibition of P. aeruginosa. Dilution and spot plating were also used to enumerate surviving cells, and give a percent survival quantification of antimicrobial activity. As well, Kirby-Bauer disc diffusion assays were used to determine the cave isolates’ inhibitory effect on planktonic cells. Scanning electron microscopy was used to examine biofilms structures and 16S rRNA sequencing was used to identify cave bacterial isolates. The biofilms showed a noticeably decreased percent survival when exposed to the cave isolate supernatant. The cave isolate 58B showed to be very promising, demonstrating significant reduction in the surviving biofilm cells. This study shows that cave bacteria produce antimicrobials that are effective against pathogenic bacteria even in a biofilm structure.
