Characterization of Chloramphenicol and Florfenicol Resistance in Escherichia coli Associated with Bovine Diarrhea

Abstract

Florfenicol, a veterinary fluorinated analog of thiamphenicol, is approved for treatment of bovine respiratory pathogens in the United States. However, florfenicol resistance has recently emerged among veterinary Escherichia coli isolates incriminated in bovine diarrhea. The flo gene, which confers resistance to florfenicol and chloramphenicol, has previously been identified inPhotobacterium piscicida and Salmonella enterica serovar Typhimurium DT104. The flo gene product is closely related to the CmlA protein identified inPseudomonas aeruginosa. The cmlA gene confers nonenzymatic chloramphenicol resistance via an efflux mechanism. Forty-eight E. coli isolates recovered from calves with diarrhea, including 41 that were both chloramphenicol and florfenicol resistant, were assayed for the presence of both flo andcmlA genes. Forty-two of the 44 isolates for which florfenicol MICs were ≥16 μg/ml were positive via PCR for theflo gene. All E. coli isolates for which florfenicol MICs were ≤8 μg/ml were negative for the flogene (n = 4). Twelve E. coli isolates were positive for cmlA, and chloramphenicol MICs for all 12 were ≥32 μg/ml. Additionally, eight isolates were positive for bothflo and cmlA, and both florfenicol and chloramphenicol MICs for these isolates were ≥64 μg/ml. DNA sequence analysis of the E. coli flo gene demonstrated 98% identity to the published GenBank sequences of both serovar TyphimuriumfloSt and P. piscicida pp-flo. Theflo gene was identified on high-molecular-weight plasmids of approximately 225 kb among the majority of florfenicol-resistantE. coli isolates. However, not all of the florfenicol-resistant E. coli isolates tested contained the large flo-positive plasmids. This suggests that several of the E. coli isolates may possess a chromosomalflo gene. The E. coli flo gene specifies nonenzymatic cross-resistance to both florfenicol and chloramphenicol, and its presence among bovine E. coli isolates of diverse genetic backgrounds indicates a distribution much wider than previously thought.

The chloramphenicol resistance genecmlAis disseminated on transferable plasmids that confer multiple-drug resistance in swineEscherichia coli

“…The flo gene is similar in primary structure to cmlA and confers resistance to both florfenicol and chloramphenicol. It has previously been shown to be disseminated on large plasmids among genetically diverse strains of E. coli, and the use of florfenicol for treatment of respiratory infections in cattle may explain the selection of flo in bovine E. coli [23]. But neither chloramphenicol acetyltransferase nor cmlA confers resistance to florfenicol [24].…”

Characterization of class 1 integrons-mediated antibiotic resistance among calf pathogenic Escherichia coli

“…Calf diarrhea caused by colibacillosis, which is severe and costly, is becoming an increasingly challenging disease in animal production. Escherichia coli is considered as the most important bacterial cause, especially the enterotoxigenic E. coli [1]. One of the measures taken in treating E. coli-related colibacillosis is antimicrobial therapy.…”

Characterization of florfenicol resistance among calf pathogenic Escherichia coli

“…Phylogenetic tree of the floR amino acid sequences from DDBJ/EMBJ/GenBank and those used in this study. E. coli floR (CAD57670 [15], AAG21808 [12], AAG16656 [11], AAS00447 (C83286), AAS16363 (C83262), AAS16362 (C83260)) exist in cluster I. S. Typhimuium flo st , ppflo-like, floR (AAC83804 [4], AAC98494 [3] and AAD33243 [5]) belong to cluster II. Klebsiella pneumoniae floR (AAL33886 [1]) and Photobacterium damselae subsp.…”

“…piscicda that encoded resistance to both florfenicol and chloramphenicol [2]. More recently, florfenicol resistance conferred by the floR gene has also been reported in Salmonella enteria serovar Typhimuium definitive phage type (DT) 104 [3][4][5][6][7][8], Salmonella enterica serovar Agona [8,9], Escherichia coli [10][11][12][13][14][15], and Vibrio cholerae [16]. Sequence analysis of the deduced FloR protein suggests that it belongs to the 12-transmembrane segments efflux pumps family.…”