Right option is (a) Absence of linkage to the drug resistance markers
Easy explanation: The common feature of mercury resistance bacteria compared to the clinical isolates is due to the absence of linkage to the drug resistance markers. In clinical isolates, there is presence of linkage to the antibiotic resistance markers. In bacteria Mercury resistance is usually found in metal contaminated sites. The mercury resistance elements in bacteria are generally plasmid coded and is usually associated with gram negative bacteria.