Determination of antibiotic resistance in the bacterial community of Boiling Springs Lake in Lassen Volcanic National Park

Boiling Springs Lake is a pristine, oligotrophic, acidic hot spring in Lassen Volcanic National Park. In 2008, 25 isolates from BSL were tested for resistance to 14 different antimicrobial compounds or a sub-set of the 14 antimicrobial agents. All isolates were resistant to at least two of the antimicrobials and some were resistant to six or more. This thesis project expanded upon the preliminary research to achieve the following goals: (1) determine the antimicrobial resistance profiles of 50 BSL isolates; (2) determine the minimum inhibitory concentrations for select multi-drug resistant isolates; (3) analyze microarray data obtained from Geochip 3.0 to assess the levels of antibiotic- and metal-resistance genes present and their phylogenetic origins; and (4) use PCR to screen selected BSL isolates for the presence of multi-drug resistant efflux genes. All 50 isolates that were screened were resistant to at least one antimicrobial compound with 74% being resistant to four or more. One hundred and twenty-four antibiotic-resistance genes and 221 metal-resistance genes were detected in BSL. The emrB/qacA efflux gene amplicon sequence was obtained from 20 of the BSL isolates and was found to be 99-100% identical. This identity spanned species, genus, and phylum levels of taxonomic hierarchy. These results support the findings of other studies that multi-drug resistance is common in pristine habitats, and that pristine habitats are reservoirs of antimicrobial resistance genes. These results also suggest that the emrB/qacA gene has been horizontally transferred between the BSL isolates.