New antibiotic resistance genes associated with CTX-M plasmids from uropathogenic Nigerian Klebsiella pneumoniae

OBJECTIVES: To determine antibiotic resistance genes associated with 17 Nigerian CTX-M-positive Klebsiella pneumoniae plasmids from patients with community-acquired urinary tract infections. METHODS: The size and restriction patterns of the plasmids were determined, and antibiotic resistance genes were identified using DNA-DNA hybridization, PCR assays, hybridization of PCR products with internal probes, and sequencing. RESULTS: All CTX-M plasmids were large (58-320 kb) and carried the following genes: aac(6')-Ib (aminoglycoside resistance) which included aac(6')-Ib-cr (aminoglycoside-fluoroquinolone resistance), aadA2 (aminoglycoside resistance), erm(B) (macrolide-lincosamide-streptogramin B resistance), blaTEM-1 (ampicillin resistance), tet(A) (tetracycline resistance), sul1 (sulphonamide resistance), dfr (trimethoprim resistance) and intI1, an integrase associated with class 1 integrons. Eleven (65%) plasmids carried an mph(A) gene (macrolide resistance), seven (41%) plasmids carried a qnrB1 gene (low-level quinolone resistance) and four (24%) plasmids carried multiple cat genes (chloramphenicol resistance). catA2, catA3 and qnrB1 genes and a 6 kb PstI fragment, carrying the blaCTX-M gene, were sequenced. CONCLUSIONS: This is the first description of catA2 and catA3 genes in Klebsiella spp. and the first description of the erm(B) and floR genes associated with a CTX-M plasmid. This is also the first report of qnrB1 and aac(6')-Ib-cr in isolates from Africa and the first report of these two genes on the same plasmid.