Bacteria from hypersaline environments: a bioactivity reservoir of anti-methicillin resistant Staphylococcus aureus

In the past decades, novel pharmaceutical compounds have been produced by a wide diverse groups of marine bacteria. These marine bacteria are potential reservoirs for antimicrobial products. In this study, we investigated 40 soil samples collected from the Great Salt Plain of Oklahoma GSP for anti-methicillin resistant Staphylococcus aureus bioactivities. A total number of 499 heterotrophic bacterial isolates (202 mesophilic halotolerant isolates, 125 thermophilic isolates, 84 halophilic isolates and 88 thermophile-halophile isolates) were recovered by culture dependent isolation and subjected to high-throughput screening to investigate their bioactivities against two strains of methicillin resistant Staphylococcus aureus MRSA. A total of 101 isolates (20.2%) out of 499 isolates possessed bioactivities against MRSA strains. They included; eighty (40%) isolates out of the 202 mesophilic halotolerant isolates showed anti-MRSA bioactivity. Twenty one bioactive (7%) isolates out of the 297 enrichment isolates showed anti-MRSA bioactivity. They involved; eleven bioactive (11%) isolates out of 125 of the thermophilic group and ten bioactive isolates (10%) out of 84 halophilic group isolates. No anti-MRSA bioactivity was revealed by the 88 isolates of the thermophile-halophile group. These 101 bioactive isolates (80 mesophilic halotolerant, 11 thermophilic and 10 halophilic) exhibited bioactivities against at least one Staphylococcus aureus MRSA using well diffusion technique. In regard to biogeographical distribution, a total of 29 (29%) and 72 (71%) bioactive isolates were isolated from vegetation and salt flat areas respectively. Thirty four (34%) isolates showed bioactivity against both methicillin resistant Staphylococcus aureus strains and fourteen (14%) isolates showed antimicrobial bioactivity against Staphylococcus aureus B-8-41-D-4, whereas fifty two (52%) isolates revealed antagonism against Staphylococcus aureus 4656. Furthermore, 16S rRNA-based study exposed that, Firmicutes harbored the highest number of bioactive isolates 77 (77%) including Bacillus (n=45 isolates), Halobacillus (n=13 isolates), Virgibacillus (n=7 isolates), Brevibacillus (n=7 isolates), Paenibacillus (n=1 isolates), Sediminibacillus (n=2 isolates), Oceanobacillus (n=1 isolates) and Staphylococcus (n=1 isolate). Proteobacteria- Gammaproteobacteria contained seven bioactive isolates (7%), including Halomonas (n=5 isolates), Marinobacter (n=1 isolate) and Pseudomonas (n=1 isolate). Actinobacteria were the third group and contained two bioactive isolates (2%), including, Cellulomonas (n=1 isolate) and Micrococcus (n=1 isolates). To our knowledge, this is the first study to explore the anti- methicillin resistant Staphylococcus aureus bioactivities of bacteria isolated from GSP. We consider our findings promising for further research to develop novel antimicrobial antibiotics.