Effect of pstC mutation on expression of efflux pump genes in Shiga toxin-producing Escherichia coli O15 and O157:H7

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Effect of pstC mutation on expression of efflux pump genes in Shiga toxin-producing Escherichia coli O15 and O157:H7


Author: Kwok, Ka Man Garfield
Title: Effect of pstC mutation on expression of efflux pump genes in Shiga toxin-producing Escherichia coli O15 and O157:H7
Degree: M.Sc.
Year: 2013
Subject: Escherichia coli O157:H7 -- Genetic aspects.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: xvii, 98 leaves : col. ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2637230
URI: http://theses.lib.polyu.edu.hk/handle/200/7064
Abstract: Shiga toxin-producing Escherichia coli (STEC) produces Shiga-like toxin as its virulence factor that cause bloody diarrhea. In complicated condition, it may further developed to life-threatening hemolytic uremic syndrome (HUS), thrombotic thrombocytopenic purpura (TTP) or even death. It is believed that medication can induce lysis of bacterial cell walls to release toxin. Bacterial infections caused by this pathogen are usually not aggressively treated. Hence, the bacterial strains survive under this condition would acquire antibiotic resistance. Multidrug efflux systems are machineries that confer antibiotic resistance, which can be classified into five families, namely the major facilitator superfamily (MFS), the adenosine triphosphate (ATP)-binding cassette (ABC) superfamily, the small multidrug resistance (SMR) family, the resistance-nodulation-cell division (RND) superfamily and the multidrug and toxic compound extrusion (MATE) family. Some systems could efflux a wide variety of toxic substances, leading to the emergence of antibiotic-resistant strains. Pst system encoded by pst operon (pstSCAB-phoU) is a member of the Pho regulon. Pst system in E. coli mainly responsible for transportation of inorganic phosphate (Pi) and regulation of the Pho regulon. Previous studies showed that mutation in the pst operon not only influenced Pi metabolism but also affected the susceptibilities of bacterial strains to drugs.
In this study, expression levels of efflux pump genes and were compared between the wild type STEC serotypes O15 and O157:H7 and their isogenic mutants under different phosphate concentrations. Genes studied included acrA (RND), emrB (MFS), emrE (SMR), macA, macB (ABC), mdtK (MATE), and the outer membrane protein tolC. Gene expression was determined using real-time transcription polymerase chain reaction. In addition, phenotypic expression in STEC serotype O15 was determined by disc diffusion, E-test and microbroth dilution method. For gene expression in STEC O15 mutant (13-21), it was found that expression of emrE was not affected by pstC disruption. However, the remaining six genes were influenced. We also found that phosphate concentration could regulation of expression of the studied genes in STEC O15. For gene expression in STEC O157 Mut 1, only acrA and tolC were not affected by pstC disruption. For STEC O157 Mut 2, only emrE was affected. From the gene expression study of STEC O15 mutant, it suggested that this strain would be more drug-resistant than the wild type, but phenotypic results were not quite agreed with the finding. The phenotypic results suggested that the mutant was more sensitive to ciprofloxacin and nalidixic acid, as well as benzalkonium chloride and chlorhexidine. The STEC O15 mutant only was found to be more resistant to ampicillin and tigecycline when compare with the wild type. In this study, expression levels of efflux pump genes in STEC O15 and O157 were affected by pstC gene disruption, and the pst operon is involved in regulating other exporters in effluxing of drugs.

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