Detection of aminoglycoside resistance genes by multiplex PCR among coagulase negative staphylococci isolated from Ventriculoperitoneal shunt infections

ABSTRACT

A Ventriculoperitoneal [VP] shunt infection is a cause of significant morbidity causing shunt malfunction and chronic ill health. This study was carried out to detect the causative pathogens associated with VP shunt infections, to assess the frequency of Coagulase negative Staphylococci [CoNS] as well as study their phenotypic resistance pattern to methicillin and different aminoglycosides [AGs], and genotypic pattern for gene encoding aminoglycosides modifying enzymes [AMEs] by multiplex PCR. This study was carried out in Medical Microbiology and Immunology and Neurosurgery Departments, Faculty of Medicine, Zagazig University during the period from June 2008 to June 2010. During this period 240 shunt procedures were carried on 175 infants and children with hydrocephalus. CoNS were identified using standard microbiological laboratory techniques. Antimicrobial susceptibility testing was performed using disc diffusion method with 4 aminoglycosides and methicillin. Multiplex PCR assay was used to identify AMEs encoding genes. 58 out of 240 shunt procedures cases showed shunt infections, [64%] caused by CoNS, [28%] by Gram negative rods [5%] by Staph aureus and [3%] by candida. 26 [70%] of CoNS isolates were methicillin resistant [MRCoNS]. 25 [67.5%] isolates of CoNS were resistant to at least one of the tested AGs and the highest resistance was to gentamicin and tobramycin [67.5%] for both followed by amikacin [27%] and streptomycin [19%]. As regard results of multiplex PCR aac [6'] le+aph [2' '] gene encoding for the bifunctional enzyme was the most common [54%] followed by ant[4]la gene encoding for the ANT[4'] - la enzyme [46%] and the aph [3']-llla gene encoding APH[3'] - Illa enzyme [40.5%]. In conclusion this study increased our knowledge about the causative pathogens of VP shunt infections, the phenotypic pattern of CoNS susceptibility to different AGs and the distribution of AMEs encoding genes in relation to methicillin susceptibility. The usage of appropriate antibiotic according to antimicrobial susceptibility testing at the probable time and the removal of the shunt apparatus are essential for successful treatment of VP shunt infection. Continued surveillance at both phenotypic and genotypic levels are recommended for monitoring the presence of other variant of the genes or new AGs resistance genes that may be produced within CoNS population