Soil bacteria may be the natural reservoirs of drug resistance genes

Abstract

Soil bacteria are the main source of antibiotics because they produce them naturally to get territorial advantage. We collected deep soil samples and characterized cultivable microbes. We used morphological and cultural characters, biochemical reactions, 16s RNA PCR and DNA sequencing to identify the isolates. The isolates included Pseudomonas spp (12), Shigella spp (2), E. coli (1), Klebsiella/Citrobacter spp (1), Micrococcus spp (2), unidentified Bacillus spp.(18), Bacillus paramycoides (3), Paenibacillus lautus (2), Bacillus pacificus (2), and Lysinibacillus pakistanensis (1). Out of these 44 isolates, 33 (75%) were multi-drug resistant. Clinically relevant and clinically irrelevant bacteria had similar drug resistance patterns (88.9% and 88.0%, 88.9% and 88.0%, 100 and 96.0%, 61.1% and 92%, 83.3% and 96%, 33.3% and 36%, 55.6% and 68.0%, and 83.3% and 60%) towards Ampicillin, Amoxicillin, Oxacillin, Azithromycin, Streptomycin, Gentamicin, Ceftriaxone and Sulfamethoxazole respectively. The observation that bacteria which cannot colonize humans/animals and therefore cannot enter the horizontal drug resistance gene transfer cycle in clinical settings also have a large and similar arsenal of drug resistance genes, may indicate that they are actually the natural reservoirs. Because they are more dynamic in their ability to survive in different conditions, they provide better fitness for maintenance of these reservoirs. Impact StatementWe think this study has raised interesting questions and further probing at a larger scale and a greater depth will provide new insight that may be very helpful for understanding the phenomenon of spread of drug resistance among bacteria which is one of the paramount challenges for humanity.