Incidence of plasmid and antibiotic resistance in psychrotrophic bacteria isolated from Antarctic sponges

Abstract

A total of 297 bacterial strains were isolated from five Antarctic sponge species and tested by agarose gel electrophoresis for the presence of plasmid molecules. At least one kind of plasmid was carried by 69 isolates (about 23%). The disc diffusion susceptibility test was used to assay the resistance of plasmid-harbouring bacteria towards 11 antibiotics. A multiple resistance was observed for the 72% of strains, among which the 33% were resistant to only two antibiotics. Bacteria showed a high degree of resistance towards O/129 (71%), tetracycline (42%) and nalidixic acid (25%), whereas any isolate showed resistance to gentamicin. The 16S rDNA sequencing revealed that plasmid-harbouring strains were mainly affiliated to the Gammaproteobacteria (81%), whereas the other detected phylogenetic groups (i.e. Firmicutes, Alphaproteobacteria, Actinobacteria and CFB group of Bacteroidetes) were less abundant, each representing between 1% and 6% of the total isolates. The present study will contribute to the poor and fragmentary knowledge on plasmid incidence in natural microbial populations. In addition, monitoring antibiotic resistance in bacteria from remote areas, such as Antarctica, could also be a useful tool to evaluate the impact of anthropic pressure.

Keywords

• Plasmid
• Antibiotic resistance
• Antarctica
• Marine Sponges