الفهرس 
Investigating the distribution and potential function of members of the Mmp-protein superfamily in escherichia coli
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Abstract
Escherichia coli is a beneficial common resident of the intestine, but a few strains can be pathogenic, e.g.E. coli O157:H7, which causes serious diseases. Because of E. coli{u2019}s versatility and genome plasticity, the bacteria have alarmingly developed resistance against many commonly used antibiotics by different mechanisms. Although E. coli has been extensively studied, around 25% of its genes remain unknown. Thus, it is possible to discover novel resistance genes. One resistance mechanism is the acquisition of genes encoding efflux pumps, among which are the mycobacterial membrane proteins (Mmp), classified as resistance, nodulation and division (RND) efflux pumps. In Mycobacteria, these proteins are involved in the transport of mycolic acid precursors outside the cell wall. In methicillin-resistant S. aureus, an MmpL homolog is involved in oxadiazole resistance. In E. coli, members of this family were characterized in commensal strains as coli K-12, but not in pathogenic ones. In this study we investigated the distribution of mmpL genes (z4861 and yegN) found in E. coli O157:H7 and their potential function by designing knockout mutants and studying the impact of their deletion. Both bioinformatics analysis and PCR screening of clinical isolates demonstrated that yegN is more abundant than z4861. All mutants, when compared to the WT strain, did not show any change in their growth pattern under either aerobic or anaerobic condition. The three mutant strains showed significant increased susceptibility to fluoroquinolones than the WT strain, and this finding was further corroborated by transcriptional analysis that showed a significant increase in z4861 and yegN RNA levels when subjected to ciprofloxacin