AUTHOR=Xu Su , Fu Zhuyingjie , Zhou Ying , Liu Yang , Xu Xiaogang , Wang Minggui 

TITLE=Mutations of the Transporter Proteins GlpT and UhpT Confer Fosfomycin Resistance in Staphylococcus aureus

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00914

DOI=10.3389/fmicb.2017.00914

ISSN=1664-302X

ABSTRACT=<p>With the increasing spread of methicillin-resistant <italic>Staphylococcus aureus</italic> worldwide, fosfomycin has begun to be used more often, either alone or in combination with other antibiotics, for treating methicillin-resistant <italic>S. aureus</italic> infections, resulting in the emergence of fosfomycin-resistant strains. Fosfomycin resistance is reported to be mediated by fosfomycin-modifying enzymes (FosA, FosB, FosC, and FosX) and mutations of the target enzyme MurA or the membrane transporter proteins UhpT and GlpT. Our previous studies indicated that the <italic>fos</italic> genes might not the major fosfomycin resistance mechanism in <italic>S. aureus</italic>, whereas mutations of <italic>glpT</italic> and <italic>uhpT</italic> seemed to be more related to fosfomycin resistance. However, the precise role of these two genes in <italic>S. aureus</italic> fosfomycin resistance remains unclear. The aim of the present study was to investigate the role of <italic>glpT</italic> and <italic>uhpT</italic> in <italic>S. aureus</italic> fosfomycin resistance. Homologous recombination was used to knockout the <italic>uhpT</italic> and <italic>glpT</italic> genes in <italic>S. aureus</italic> Newman. Gene complementation was generated by the plasmid pRB473 carrying these two genes. The fosfomycin minimal inhibitory concentration (MIC) of the strains was measured by the <italic>E</italic>-test to observe the influence of gene deletion on antibiotic susceptibility. In addition, growth curves were constructed to determine whether the mutations have a significant influence on bacterial growth. Deletion of <italic>uhpT, glpT</italic>, and both of them led to increased fosfomycin MIC 0.5 μg/ml to 32 μg/ml, 4 μg/ml, and &gt;1024 μg/ml, respectively. By complementing <italic>uhpT</italic> and <italic>glpT</italic> into the deletion mutants, the fosfomycin MIC decreased from 32 to 0.5 μg/ml and from 4 to 0.25 μg/ml, respectively. Moreover, the transporter gene-deleted strains showed no obvious difference in growth curves compared to the parental strain. In summary, our study strongly suggests that mutations of <italic>uhpT</italic> and <italic>glpT</italic> lead to fosfomycin resistance in <italic>S. aureus</italic>, and that <italic>uhpT</italic> mutation may play a more important role. The high resistance and low biological fitness cost resulting from <italic>uhpT</italic> and <italic>glpT</italic> deletion suggest that these strains might have an evolutionary advantage in a fosfomycin-rich clinical situation, which should be closely monitored.</p>