Distribution of the Multidrug Resistance Gene cfr in Staphylococcus Species Isolates from Swine Farms in China

Abstract

A total of 149 porcine Staphylococcus isolates with florfenicol MICs of >16 g/ml were screened for the presence of the multiresistance gene cfr, its location on plasmids, and its genetic environment. In total, 125 isolates carried either cfr (16 isolates), fexA (92 isolates), or both genes (17 isolates). The 33 cfr-carrying staphylococci, which included isolates of the species Staphylococcus cohnii, S. arlettae, and S. saprophyticus in which the cfr gene has not been described before, exhibited a wide variety of SmaI pulsed-field gel electrophoresis patterns. In 18 cases, the cfr gene was located on plasmids. Four different types of cfr-carrying plasmids-pSS-01 (n ‫؍‬ 2; 40 kb), pSS-02 (n ‫؍‬ 3; 35.4 kb), pSS-03 (n ‫؍‬ 10; 7.1 kb), and pBS-01 (n ‫؍‬ 3; 16.4 kb)-were differentiated on the basis of their sizes, restriction patterns, and additional resistance genes. Sequence analysis revealed that in plasmid pSS-01, the cfr gene was flanked in the upstream part by a complete aacA-aphD-carrying Tn4001-like transposon and in the downstream part by a complete fexA-carrying transposon Tn558. In plasmid pSS-02, an insertion sequence IS21-558 and the cfr gene were integrated into transposon Tn558 and thereby truncated the tnpA and tnpB genes. The smallest cfr-carrying plasmid pSS-03 carried the macrolide-lincosamide-streptogramin B resistance gene erm(C). Plasmid pBS-01, previously described in Bacillus spp., harbored a Tn917-like transposon, including the macrolide-lincosamide-streptogramin B resistance gene erm(B) in the cfr downstream region. Plasmids, which in part carry additional resistance genes, seem to play an important role in the dissemination of the gene cfr among porcine staphylococci.

The Genetic Environment of the cfr Gene and the Presence of Other Mechanisms Account for the Very High Linezolid Resistance of Staphylococcus epidermidis Isolate 426-3147L

“…The immediate genetic environment of cfr in p7LC resembles that discovered in the recently described 40-kb plasmid pSS-01, which is found in staphylococcal isolates from swine (accession no. JQ041372) (25). A complete Tn4001-like transposon is found upstream of cfr in the p7LC plasmid.…”

“…The cfr gene is often found on plasmids (16,24,25,41,42). However, in some clinical and animal staphylococcal isolates it resides in the chromosome (25)(26)(27)43).…”

“…While the role of these ORFs in controlling cfr expression has not been elucidated, their presence argues that cfr is inducible and, similar to several other resistance genes, could be controlled by translational attenuation (22,23). Several other staphylococcal isolates from farm animals have been reported to harbor plasmids carrying cfr, where it is often associated with mobile genetic elements, such as transposons and insertion elements (24,25).…”

Identification and characterization of cfr-positive Staphylococcus aureus isolates from community-onset infectious patients in a county hospital in China

“…It is believed that this high occurrence is related to the widespread use of chloramphenicol in animals. Recently, plasmids that harbour the cfr gene, such as pSS-01, pSS-02, pSS-03 (Wang et al, 2012a) and pMSA16 (Wang et al, 2012b), were isolated from staphylococci of animal origin in China. In these plasmids, the cfr gene was flanked by mobile genetic elements such as IS21-558, IS256 and pre/mob, which are involved in the recombination and mobilization of the plasmid (He et al, 2014).…”

A Novel FexA Variant from a Canine Staphylococcus pseudintermedius Isolate That Does Not Confer Florfenicol Resistance

“…Since the first description of the fexA gene in a bovine Staphylococcus lentus isolate (2), this gene has been detected-either as part of the small nonconjugative transposon Tn558 or in combination with the cfr gene in transposition-deficient Tn558 variants-in S. aureus and several coagulase-negative staphylococcal species from healthy and diseased cattle, swine, horses, or humans (3)(4)(5)(6)(7)(8)(9). The fexA gene has also been detected in a Bacillus isolate from swine feces and in environmental pollutants from swine feedlots in China (10,11).…”