The spread of methicillin resistance amongst S.aureus strains

The virulence of  S. aureus is associated with its capacity with the ability to adhere and form the biofilm on host surfaces and extracellular protein toxins production and resistance to antibiotics (18, 26). The ability of S. aureus to produce biofilms helps the bacterium to remain within the host and is considered to be responsible for chronic or persistent infections (14, 27). Consequently, biofilm formation is an essential virulence factor of S. aureus and several mechanisms are used by MSSA and MRSA for biofilm formation. Clinical MSSA and MRSA strains mainly form biofilm dependent on the icaADBC operon (18, 26). Infection in burn wound is one of the most common types of trauma that requires necessary medical care and cause of morbidity and mortality in both developed and developing countries (5, 28). Between 96 positive cultures obtained from burn patients  swab samples, 50 (62.5%) S.aureus were isolated. The most frequent bacteria isolated from cultured positive were Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii and Staphylococcus epidermidis, respectively. S.aureus was the most commonly isolated bacteria amongst burn patients with burn wound infection in Hamadan city. This finding is similar to the results study performed by Aynalem Mohammed et al.(29), Tigist Alebachew et al.(30), Neelam Taneja et al.(31). According to the results of this study, high antibiotic resistance was observed in s. aureus strains. In addition, the high prevalence of s. aureus in burn patients with burn wound infection can a serious risk. Among the isolated S. aureus, 15 (30%) were MRSA and 35 (70%) were MSSA which was more or less similar to the other studies (32-34). This rate of MRSA in this study was less than another study, which on burn wound infection in Iran, where it was shown that (61.53%) isolates were MRSA (15). The outbreak of MRSA varies in different burn units, which may be due to the performance of various infection control procedures. The spread of methicillin resistance amongst S.aureus strains led to problems in the treatment of infections caused by this MRSA (35). The S. aureus isolates described in this study were quite susceptible to Vancomycin and Linezolid and quinoprestin/dalfoprestin and these results are similar to the previous study (36). The present study suggested differential resistance rates against Ciprofloxacin, Gentamicin, and Clindamycin at rates of 30%, 28%, and 30%, respectively. These rates are lower than that of other studies, that showed resistance rates against Ciprofloxacin, Gentamicin, of 52% and 70%, respectively (15). This study confirmed that overall rates of susceptibility to generally prescribed antibiotics in S.aureus isolates were above 75%, with the exception of Vancomycin and Linezolid and Quinupristin/dalfopristin. Amongst the 13 isolates of Methicillin-resistant Staphylococcus aureus showed MDR and this alarms that multiple drug-resistant strains of S.aureus. The pattern of bacterial resistance is important for epidemiological and clinical purposes. The results of the antimicrobial resistance pattern to give serious cause for concern because the predominant bacterial isolates were highly resistant to the commonly available antimicrobial agents. A related observation of high antimicrobial resistance by biofilm producing bacterial isolates has been performed in other studies (36). In the current study, biofilm formation was seen in 94% isolates, while 6% bacterial isolates showed no biofilm production.  In our study, the majority (94%) of S.aureus produced biofilm, and most (100%) of the biofilm-producing S.aureus isolates were Methicillin resistant (MRSA) (p<0.05). Among MRSA strains strong biofilm producer, the high antibiotic resistance was observed. While in strains that did not produce biofilm less resistance was observed. This confirms the importance of biofilm in increasing the duration of treatment in patients with burn wound infection. Similar results were shown by Ohadian Moghadam et al. (15). Burn wound infection isolates that were resistant to multiple antibiotics were mostly biofilm producers, indicating that the majority of MDR pathogens are biofilm producers. A relationship was observed with other studies (4). In the present study, biofilm producing bacterial isolates displayed a high level of resistance to all drugs that are commonly prescribed, like Ciprofloxacin, Gentamicin, and Clindamycin. The categories of biofilm among all of the S. aureus isolates were weak (20 %%), Moderate (24%) and strong (50%) and 6% isolates were non biofilm formers. Our study indicated that ica A, ica D (96%) was the most frequent gene in the S.aureus isolates from burn patients. Our analysis also showed that the frequency of ica A, ica D had the significant difference between biofilm production and resistance antibiotic (p< 0.05). Similar to our findings, many recent studies reported the similar prevalence of the ica A and ica D biofilm genes in S.aureus can produce a multilayered biofilm (29). The frequency of biofilm genes (ica B and ica C, ica R) in the S.aureus isolates was similar to past studies (38). Another virulence factor studied in these strains was exfoliative toxin A and B genes. The exfoliative toxin is of predominant importance in Staphylococcus aureus. The prevalence of exfoliative toxin A and B genes in the study were very high. Zarei Koosha  et al.  studied the prevalence of exfoliative toxin A and B genes in Staphylococcus aureus isolated from clinical specimens. They reported  186 (94.4%), 15 (7.6%) of the 197 isolates expressed  the  eta, etb,  respectively. That the high prevalence of eta genes was the same with the current study (39). Regarding to the frequency of biofilm genes and the ability of biofilm formation, the significant statistical difference was observed between MRSA and MSSA S. aureus strains. In the current study, some significant points concerning the parameters (pattern antibiogram, biofilm production, prevalence biofilm and exfoliative toxin A and B  gene, determine the minimal inhibitory concentration antibiotics and identification MRSA) needed on the risk of S.aureus in burn wound infections were determined. Our finding would be applied in the improvement of treatment plans to control burn wound infections. Consequently, increase awareness of the mechanisms underlying biofilm formation and development of drug resistance will allow us to more efficiently control and treat biofilm infections.