الفهرس 
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Abstract
The increasing prevalance of methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant Staphylococcus aureus (VRSA) and linezolid resistant Staphylococcus aureus (LRSA) representes a significant threat to public health. One of the most virulent factors and important antimicrobial mechanisms of S. aureus is biofilm formation. There are several new strategies that are alternative to antibiotics like nanotechnology. Nanoparticles (NPs) have antimicrobial effect on several microorganisms like S. aureus.
This study aimed to detect the ability of S. aureus strains isolated from wound samples and endotracheal secretion samples to form biofilm and detect prevalence of resistance of these strains to different antibiotics. The study aimed also to evaluate the effect of ZnO NPs on biofilm formation and antibiotics resistance among S. aureus isolates by phenotypic and genotypic methods.
In this study out of 250 samples, 116 isolates of S. aureus were obtained from wound swabs recovered from outpatiens attended the plastic surgery depattment and endotracheal secretion samples collected from inpatients of ICU of neurological department in Minia University Hospitals.
All samples were cultured on mannitol salt agar media then the isolated organisms were identified by colonial morphology, Gram staining and biochemical reactions. Antibiotic sensitivity of the isolated strains was done using disc diffusion method and microdilution method. Biofilm formation was detected using microtiter plates among S. aureus isolates. The effect of ZnO NPs on antimicrobials resistance and biofilm formation was determined. The expression of antibiotics resistance genes (mec A, van A and cfr) and biofilm formation genes (ica A, ica B, ica D and fnb A) was detected in comparison with 16 sRNA that used as internal control by real time rTPCR technique before and after ZnO treatment.
Out of 116 isolates 85 (73%) were positive biofilm producers: 7.7% were strong biofilm producers, 27.6% were moderate biofilm producers and 38% were weak biofilm producers.
Out of 116 S. aureus isolates, 108 isolates (93%) were sensitive to teicoplanin followed by chloramphenicol 92 isolates (79%), linezolid 82 isolates (71%), vancomycin 71 isolates (61%), amoxicillin clavuronic 66 isolates (57%), cefoxitin 53 isolates (46%), amikacin 51 isolates (44%). However, the sensitivity rates to cefotriaxone and oxacillin were low (22 isolates (19%) and 21 isolates (18%)) respictively.
Resistance to all used antibiotics and MDR were higher among biofilm producing than non-biofilm producing strains, but the difference was significant only in vancomycin and linezolid.
The percentage of resistance to all antibiotics in ICU were higher than plastic surgery, while percentage of biofilm formation was higher in plastic department in all degrees except weak degree was higher in ICU than in plastic sugery departement.
On application of ZnO NPs on biofilm positive S. aureus isolates, the biofilm formation decreased to 65 isolates (76%) non biofilm, 19 isolates (22%) weak biofilm and one isolate (1%) moderate biofilm.
There was synergism between antibiotics and ZnO NPs as MRSA decreased from 81.9% (95 isolates) to 13.3% (15 isolates), VRSA decreased from 33.6% (39 isolates) to 0% additionally to LRSA decreased from 29.3% (34 isolates) to 0%.
Regarding the molecular study of S. aureus isolates, there was downregulation of all genes expression of biofilm genes (ica A, ica D and fnb A) and antibiotics resistance genes (mec A, van A and cfr) after application of ZnO NPs with significant p value (≤ 0.008).
Using ROC curve analysis for assessment of diagnostic accuracy of our results revealed that there were significant reduction of the expression of the study genes after ZnO NPs wit p values were all> 0.05. Sensitivity and specificity of biofilm genes (ica A, ica D and fnb A) were (66.7, 66 and 71.7%) and (83, 83.3 and 85 %) respectively. Sensitivity and specificity of antibiotics resistance genes (mec A, van A and cfr) were (88, 76 and 62%) and (97, 92 and 87) respectively.