Phenotypic & Genotypic Study of Biofilm and  Effectiveness on the Ability of CONS to Oxacillin  Resistance Using Muller–Hinton Agar & Mannitol Salt  Agar

Israa Mohamed safi al– kadmy

Volume : III, Issue : IX, September - 2013

Phenotypic & Genotypic Study of Biofilm and Effectiveness on the Ability of CONS to Oxacillin Resistance Using Muller–Hinton Agar & Mannitol Salt Agar

Israa Mohamed Safi Al Kadmy

Abstract :

The aim of this study is to analyze the phenotypic and genotypic indicators of biofilm formation of Coagulase negative staphylococci (CONS) and Oxacillin resistance by using many different detection methods. Thirty–six CONS isolated from patients with chronic otitis media diagnosed using API Staph . PCR amplification was used to detect ica A and D gene and also to detect mec A gene, cultured strains were tested for biofilm formation ability with Congo red agar (CRA), phenotypic prediction of mecA gene positive or negative (historically referred to methicillin resistance, MR and methicillin susceptible, MS) was conducted by both Oxacillin and Cefoxitin disk diffusion tests also agar screening test both of tests on Muller Hinton agar (MHA) and mannitol salt agar (MSA) and minimum inhibition concentration (MIC) was determined by agar dilution method with MHA corporation with MIC on MHA containing 2% NaCl both of them Oxacillin concentration (0.25 to 256 μg/mL). The above tests applied to compare their MRCONS and MSCONS detection the sensitivity & specificity were determined to compare between the tests which is used in this study. A total of 36 CONS isolates from patients with chronic otitis media studied, the high percentage of this isolates belonging to staph xylosus 20 isolates (55%), of a total 36 isolates 31(86%) were found to be CRA plate test positive, ica A and D genes were found to be present in 30 isolate, the concordance between phenotypic and genotypic of biofilm formation was 90.9% (p<0.05). All isolates of study were divided in to MRCONS 29(80.5%) mecA positive and MSCONS 7(19.4%) mecA negative, all phenotypic tests used to detect MSCONS gave false resistance with high percentage (19.4%). Cefoxitin disk diffusion on MHA & MSA yielded the highest sensitivity value (100%), Oxacillin disk diffusion on MHA gave a specifcity of 16.6%, Oxacillin screen MSA(2 μg/mL) gave the highest sensitivity value (93%), Oxacillin screening on MHA (6 μg/mL with 4% NaCl) gave the highest specificity value (100%)and MIC on MHA & MSA with 2% NaCl gave the same highest sensitivity value(100%), from 31 isolates positive biofilm CONS isolates 24 (77.4%) were confirmed as MRCONS while 7(23%) confirmed as MSCONS, negative biofilm CONS isolates found only between MRCONS isolates 5(14%) which means an essential role of resistance to Oxacillin referred to biofilm.