Nonenzymatic Chloramphenicol Resistance Mediated by IncC Plasmid R55 Is Encoded by a floR Gene Variant

Abstract

The IncC plasmid R55, initially described in the 1970s and isolated from Klebsiella pneumoniae, confers nonenzymatic chloramphenicol resistance. The gene coding for this resistance was cloned and sequenced and shows 95 to 97% nucleotide identity with the recently reported floR gene from Salmonella enterica serovar Typhimurium DT104 and from Escherichia coli animal isolates, respectively, conferring cross-resistance to florfenicol.Resistance to chloramphenicol (CHL) has been reported to be mainly due to the production of inactivating enzymes, the CHL acetyl transferases (CATs) (11). Nonenzymatic CHL resistance, however, was described in the late 1970s and early 1980s for plasmids of different incompatibility groups from gram-negative bacteria, such as the IncP-1 plasmid R26 from Pseudomonas aeruginosa and the IncC plasmid R55 from Klebsiella pneumoniae (10, 11). The cml gene of plasmid R26 conferring nonenzymatic CHL resistance was reported in 1986 by Dorman et al. (9) and codes for a putative efflux pump related to the more recently described CmlA protein of the P. aeruginosa In4 integron of transposon Tn1696 (3). Nonenzymatic CHL resistance has gained importance with the spread of multidrug-resistant Salmonella enterica serovar Typhimurium DT104 world-wide epidemic strains, which harbor on their chromosome an antibiotic resistance gene cluster comprising a nonenzymatic CHL resistance gene conferring cross-resistance to florfenicol (FFC) (1, 2, 4, 5).FFC is a fluorinated analog of CHL approved in Europe for use against pasteurellosis in cattle since January 1995. Previous studies have shown that FFC is active against CHL-resistant strains producing either CATs (6) or nonenzymatic CHL resistance mediated by the CmlA efflux pump (3). The gene conferring cross-resistance to FFC has been named floR, floSt, flo, or cmlA-like (1,2,4,5,15) and is closely related (97% identity) to the pp-flo gene described in 1996 from a transferable R plasmid of the fish pathogen Pasteurella piscicida (13), recently renamed Photobacterium damselae subsp. piscicida. Their deduced amino acid sequences show about 47% identity to that of the CmlA protein. All of the gene products are assumed to belong to the 12 transmembrane segments family of export proteins of the major facilitator superfamily reviewed by Paulsen et al. (14). FFC resistance conferred by the floR gene has also recently been reported in Escherichia coli strains isolated from cattle and poultry (7,12,15) and in S. enterica serovar Agona strains isolated from poultry (8).In the present study we analyzed nonenzymatic CHL resistance, with particular attention to possible FFC cross-resistance, conferred by the IncC plasmid R55 (150 kb; Tra ϩ Ap Cm Gm Su), among the first to have been described as conferring nonenzymatic CHL resistance in the 1970s (10, 11). Interestingly, this plasmid, isolated from K. pneumoniae, has been reported to encode enzymatic CHL resistance as well, namely, a type I CAT (11).R55 FFC resistance and detection of the floR gene. E. coli strain K-12 BM14 (p...

Characterization of Multidrug-ResistantEscherichia coliIsolates Associated with Nosocomial Infections in Dogs

“…Although a specific antibiotic resistance gene was never identified, other investigators (37) reported on E. coli isolates from dogs treated with ␤-lactams which possessed transferable cephamycinases with the spectra of activity, MWs, and pIs characteristic of those of Bla CMY2 . There have been other reports on the transmissibility of antibiotic resistance genes (bla CMY2 or flo) in Salmonella (42,64,67), E. coli (13,42,64,67), K. pneumoniae (12,42), P. mirabilis (42), and Vibrio cholerae (24). The cephamycinase gene described by Winokur et al (64) appears to reside on a common plasmid shared between Salmonella and E. coli isolates from cattle.…”

“…This resistance was attributed to widespread dissemination of the cmlA homologue flo among gram-negative bacteria (7,13,14,24,27,28,61). Twenty of 34 E. coli isolates possessed the flo florfenicol resistance gene.…”

Assessing the effect of a single dose florfenicol treatment in feedlot cattle on the antimicrobial resistance patterns in faecal Escherichia coli

“…Florfenicol treatment likely selected for E. coli with plasmids containing multiple antimicrobial resistance genes. Several plasmid types carrying the flo gene in E. coli isolates of bovine origin have been identified, and multiple resistance was a common feature [7].…”

Influence of Anti-FloR Antibody on Florfenicol Accumulation in Florfenicol-Resistant Escherichia coli and Enzyme-Linked Immunosorbent Assay for Detection of Florfenicol-Resistant E. coli Isolates

“…SGI1 or variants of SGI1 have also been identified at the same chromosomal location in another S. enterica serovar, Agona (9,13). The resistant gene was also identified in plasmids and the chromatin of E. coli (4,6,7,12,14,17,24), in the IncC plasmid R55 from Klebsiella pneumoniae (11), and in Vibrio cholerae (16). These studies showed that the genes, referred to in the published literature as pp-flo, cmlA-like, floSt, flo, or floR, mediate combined resistance to chloramphenicol and florfenicol.…”