Characterization of the Multi-Drug Resistance Gene cfr in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Isolated From Animals and Humans in China.

Shu-Min Li,Liang Li,Jian Sun,Ya-Hong Liu,Wei-Qi Gu,Fan-Rui Liu,Yu-Feng Zhou,Hua-Qing Liang,Liang-Xing Fang,Jia-Hong Duan,Xiao-Ping Liao,Yan-Qiong Xiong,Yu-Ting Wu

doi:10.3389/fmicb.2018.02925

Abstract

We investigated cfr-positive and -negative MRSA strains isolated from animals and humans in different geographical areas of China, from 2011 to 2016. Twenty cfr-positive strains (15.6%) were identified from 128 MRSA strains including 17 from food animals and three from humans. The resistance rates and prevalence of the tested antibiotic resistance genes (ARGs) in the cfr-positive MRSA isolates were higher than that in the cfr-negative MRSA isolates. All cfr-positive MRSA isolates were co-carrying fexA and ermC, and had significantly higher optrA incidence rate vs. the cfr-negative isolates (P < 0.05). In addition, multilocus sequence typing (MLST) assays showed that ST9 and spa-type t899 were the most prevalent ST and spa types in the study strains. However, all of the 20 cfr-positive and 10 randomly selected cfr-negative MRSA isolates were clonally unrelated as determined by pulsed-field gel electrophoresis (PFGE) analyses. Importantly, the cfr gene was successfully transferred to a recipient Staphylococcus aureus strain RN4220 from 13 of the 20 cfr-positive MRSA isolates by electroporation. Among these 13 cfr-positive MRSA isolates, two different genetic contexts surrounding cfr were determined and each was associated with one type of cfr-carrying plasmids. Of note, the predominant genetic context of cfr was found to be a Tn558 variant and locate on large plasmids (∼50 kb) co-harboring fexA in 11 of the 13 MRSA isolates. Furthermore, the cfr gene was also identified on small plasmids (∼ 7.1 kb) that co-carried ermC in two of the 13 MRSA isolates. Our results demonstrated a high occurrence of multi-drug resistance in cfr-positive MRSA isolates, and the spread of cfr might be attributed to horizontal dissemination of similar cfr-carrying transposons and plasmids.

Highlights

IntroductionThe chloramphenicol–florfenicol resistance (cfr) gene encodes a methyltransferase that modifies position A-2503 in bacterial 23S rRNA and confers resistance to five classes of antibiotics (phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A) (Long et al, 2006; Morales et al, 2010)
The chloramphenicol–florfenicol resistance gene encodes a methyltransferase that modifies position A-2503 in bacterial 23S rRNA and confers resistance to five classes of antibiotics (Long et al, 2006; Morales et al, 2010)
We demonstrated that >80% of the 128 Methicillin-resistant Staphylococcus aureus (MRSA) isolates were resistant to all tested antimicrobial agents with the exception of sulfamethozaxole/trimethoprim (43.8%), rifampicin (21.1%), linezolid (1.56%), vancomycin (0%), and daptomycin (0%) (Figure 1)

Summary

Introduction

The chloramphenicol–florfenicol resistance (cfr) gene encodes a methyltransferase that modifies position A-2503 in bacterial 23S rRNA and confers resistance to five classes of antibiotics (phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A) (Long et al, 2006; Morales et al, 2010). These antibiotics have been widely used for the treatment of infections in human and animal (Inkster et al, 2017; Li J. et al, 2017). LA-MRSA containing the plasmid-borne cfr gene has been identified in infections of farmers suggesting zoonotic transmission (Wulf et al, 2006; Cui et al, 2009)

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