ENVIRONMENTAL KLEBSIELLA PNEUMONIAE WITH HEAVY METAL AND ANTIBIOTIC RESISTANCE GENES

The presence of antibiotic resistant bacteria in clinics and in the environment is a growing concern because plasmid encoded genes that confer antibiotic resistance are becoming more prevalent in gram-negative bacteria. Among the most common antibiotic resistance genes are those that confer resistance to aminoglycosides, used heavily in clinics and agriculture. Within the environment the presence of heavy metals and antibiotics may apply an additional selective pressure on bacteria resulting in the accumulation of heavy metal resistance genes in plasmids which can be transmitted to other bacteria. Pathogenic Klebsiella pneumoniae can cause respiratory and urinary tract infections and the presence of resistance genes may make treatment of such infections more difficult. The objective of this study was to describe the genes present on the plasmids of an environmentally isolated aminoglycoside-resistant bacteria. A Klebsiella pneumoniae was isolated from a creek in Southern California. Disk diffusion test determined the strain is resistant to aminoglycosides (neomycin, kanamycin, streptomycin), tetracycline, sulfisoxazole and trimethoprim. Plasmid DNA of the strain was isolated and sequenced. The isolate was found to have four plasmids including an IncN conjugative plasmid of 48,760 base pairs, capable of being transferred to other bacteria which was confirmed with conjugation experiments using J53 E. coli as a recipient. Within this plasmid approximately four thousand base pairs upstream of the IncN conjugative region, there is a multiresistance region encoding resistance to neomycin (aph-(3’)-I) followed by genes that confer resistance to puromycin, streptomycin (aada1-like), spectinomycin (aada1-like), and trimethoprim (dfr12). The isolate also contains a plasmid with a chromate resistance gene (chrA) adjacent to an arsenic resistance operon. Upstream of the arsenic resistance operon is a heavy metal response regulator gene followed by genes that confer resistance to heavy metals: copper, lead, cadmium, zinc, and mercury. This arrangement of the chromate resistance (chrA) gene and arsenic resistance operon has been described in the plasmids of three other isolates, one of which was isolated clinically in Virginia, U.S.A. while the other two samples were isolated environmentally in a Citrobacter amalonaticus in South Korea and in a Pluralibacter gergoviae in Malaysia. This is the first report of an isolate that contains this arrangement of the arsenic resistance operon, chrA gene, and multiple antibiotic resistance genes encoded on plasmids. The accumulation of heavy metal resistance genes and a multidrug-resistance region in an environmental bacterial isolate could indicate a reservoir of heavy metal resistance genes which may aid in the persistence of multidrug-resistance bacteria in the environment.