From 96 pus/wound swab samples processed, 80 (84.21%) were bacterial culture positive. Out of which, S. aureus was isolated from 50 (62.5%) samples. The most frequent bacteria isolated from cultured positive were Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii and Staphylococcus epidermidis, respectively. Among the 50 S. aureus isolated, 13(26%), 15(30%), 22(44%) isolates were MDR, MRSA and MSSA, respectively Table 2. These isolates were collected from the Burn Intensive care Unit (BICU).
Antimicrobial susceptibility testing
The antibiogram results of the S.aureus isolates shown in Table 3. All clinical isolates of S.aureus were susceptible to linezolid, vancomycin, and quinoprestin/dalfoprestin. Nevertheless, they showed various levels of resistance and susceptibility to other antibiotics, with the highest resistance shown to cefoxitin, ciprofloxacin, and gentamicin and the greatest susceptibility exhibited to trimethoprim/sulfamethoxazole and imipenem. The patterns of antibiotic resistance among the MRSA isolates showed the highest resistance to ciprofloxacin Table 3. Out of 50 S. aureus isolates, 15(30%) were methicillin-resistant with cefoxitin disk diffusion method and in addition by detection of mecA gene, of which, 13(26%) isolates were resistant to all the used antibiotics (MDR-MRSA) including ciprofloxacin, gentamicin, clindamycin, and trimethoprim-sulfamethoxazole.
Determination of the minimum inhibitory concentration
Minimum inhibitory concentration of clindamycin, trimethoprim/sulfamethoxazole, gentamicin and cefoxitin were determine according to CLSI recommendations. The results were summarized in Table 4. The minimum inhibitory concentration (MIC) test showed that the resistance to antibiotics in Staphylococcus aureus strains have the different MIC.
The result of identification of biofilm formation by phenotypically method
The frequency distribution of biofilm formation among the 50 clinical isolates of S. aureus, 94% (n = 47) were able to form a biofilm and 6% (n = 3) were non biofilm formers on microtiter plate Table 5.
The frequency of biofilm formation and exfoliative toxin genes in MRSA and MSSA and MDR strains
Genes encoding intercellular adhesion proteins (ica A, ica D.ica C,ica B,ica R) were detected in 25 S. aureus isolates. Between 25 S. aureus isolates 96% (n =24) of the strains were positive for ica A and ica D genes. There were ica C and ica B in 80%, and ica R was found in 84% of isolates. Among 25 S. aureus isolates 84% (n =21) and 92% (n =23) of the strains were positive for eta and etb genes, respectively (Figure 1-2-3-4).
Association of antibiotic resistance in MRSA and MSSA and MDR strains
The highest antibiotic resistance to antibiotics clindamycin and imipenem was observed among MDR strains. The results of this study showed the highest resistance to antibiotics Trimethoprim/Sulfamethoxazole and Ciprofloxacin among MRSA and MSSA strains (Fig 5).
Association of biofilm formation and antibiotic resistance in MSSA and MRSA, MDR isolates
Statistical analysis showed that MRSA strains were strong biofilm producers. MRSA strains exhibited more resistance to antibiotics due to biofilm production (Fig 6). The mean for biofilm biomass in S.aureus MSSA and MRSA isolates were 0.907±0.260 and 1.20 ± 0.315, respectively. The mean for biofilm biomass in total MDR and non-MDR isolates were 0.949 ± 0.289 and 0.656±0.326 respectively. Statistical analysis revealed a significant correlation between MRSA multidrug resistant phenotypes and biofilm formation ability (p=0.007).