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.