Antimicrobial susceptibility pattern of microorganisms involved in the pathogenesis of surgical site infection (SSI); A 1 year of surveillance.

The aim of this study is to identify the antibiotic sensitivity pattern of pathogens involved in the process of surgical site infection, in surgical wards. Changes made in the pattern of antibiotic use will result in different microorganism susceptibility patterns, which needs correct determination for precise empiric antibiotic therapy. One thousand patients (62% men and 38% women, 18- 74-years-old, with mean age 43 +/- 8)) who underwent surgical treatment, in Alzahra University Hospital, Isfahan University of Medicine, Isfahan, Iran, were studied from 2005 to 2006. Surgical wound infections, based on the reported criteria, were aspirated for culturing within 1 plus gram staining of prepared smears. Minimum Inhibitory Concentrations (MICs) were determined for samples and all derived data were compared by SPSS 13 and WHO net 5 software. The prevalence of SSI was 13.3% with 150 positive cultures, totally. Of 150 bacteria, isolated from surgical site infections Staphylococcus aureus had most frequency (43%). Resistance of isolated organisms was 41.7% in amikacin, 65 and 78.6% in ceftazidime, 85.7% in ceftriaxone, 61.5% in ciprofloxacin, 78.8% in gentamicine, 6.4% in imipenem, 13% in meropenem and 70.6% in trimethoprim/sulfamethoxazole, respectively. 78.9% of Staphylococcus aureus isolates were MRSA and vancomycine was the most effective antibiotic without any resistance. Among 10 isolates of coagulase negative Staphylococcus, no vancomycine resistance was seen, but in contrast all cases were resistant to oxacillin. The most common gram negative organism was Klebsiella (18 isolates) in which 100 and 80% were sensitive to imipenem and meropenem, respectively. Seventeen cases were E. coli, in which the most sensitivity was to meropenem (80%) and imipenem (77.8%). Thirteen cases of Pseudomonas were detected, in which 16.7% were resistant to imipenem and 8.3% to meropenem. Our results demonstrated that the total antibiotic resistance is increasing among SSIs, with an up sloping pattern, which will contact with a constant empiric antibiotic therapy. So, precise up to date antibiogram tantalize us toward balancing the rate of total antibiotic resistance to SSIs.

Frequency of mecA gene and borderline oxacillin resistant Staphylococcus aureus in nosocomial acquired methicillin resistance Staphylococcus aureus infections.

The aim of the study was to determine the frequency and type of MRSA strains and antibiotic susceptibility in Al-Zahra Hospital, Isfahan, Iran. In an analytic descriptive survey in 2005 and early 2006, patients admitted to the hospital who contracted S. aureus nosocomial infections were enrolled in the study. All isolates were identified by the conventional laboratory tests. Minimal Inhibitory Concentration (MIC) of oxacillin on isolated bacteria was determined by E-Test method. According to Clinical and Laboratory Standard Institute (CLSI) criteria all strains with MIC of > or = 4 microg for oxacillin were identified as MRSA. Intrinsic high level resistance (mecA positive) and borderline oxacillin resistant Staphylococcus aureus (BORSA) were detected by amoxicillin-clavulanate E-test strips. Strains with MIC of > or = 4 microg for oxacillin and > or = 8 microg for amoxicillin-clavulanate were identified as mecA positive MRSA. Other staphylococcus with MIC > or = 4 microg for oxacillin and < or = 4 for amoxicillin-clavulanate were identified as mecA negative MRSA (BORSA). MIC of vancomycin also was determined on isolated bacteria. Data were analyzed by SPSS version 13 and Who net version 5. Out of 134 Staphylococcus aureus samples which were isolated from nosocomial infections 90 (67.2%) were MRSA. Sixty seven out of 90 (74.5%) MRSA were mecA positive and 23 out of 90 (25.5%) were mecA negative (BORSA). Although most of the MRSA strains were isolated from surgical site infections, there were no statistically significant differences between types of Staphylococcus aureus growing from variant sites of infections. Only one (1.49) of the mecA positive MRSA had reduced susceptibility to vancomycin but all of the mecA-negative MRSA (BORSA) were sensitive to it. Because one fourth of our staphylococcus strains are mecA negative BORSA and there is no alternative for vancomycin against mecA positive MRSA and Enterococcus spp. in our hospital, vancomycin should be reserved only for life threatening infections due to these organisms. Thus MRSA typing should be done to choose appropriate antibiotic for optimal treatment of MRSA infections.