An-Najah Staff

A total of 200 Staphylococcal and 52 Streptococcal clinical bacterial isolates were collected from January 2012 to April 2013 from different clinical centers in Nablus district. Minimal inhibitory concentration (MIC) values of erythromycin and clindmycin were determined using agar dilution method. Micro-broth dilution method was only applied for S. pneumoniae isolates. A representative 47 isolates of erythromycin resistant strains were examined for antibiotic resistance genes (ermA, ermB, ermC, msr, mef, and ere) by PCR. MIC values of erythromycin and clindamycin, erythromycin-clindamycin induction test and data on resistant genes were combined to predict the most probable mode of resistance among the studied isolates. Relatively high frequencies of erythromycin resistance were found among Streptococci (63.5%) and Staphylococci (65.5%) isolates. The frequency of erythromycin resistance among coagulase negative Staphylococci (CONS) was 76.9%, which was higher than that among S. aureus (64.7%). With respect to clindamycin resistance, 48.1% of Streptococci and 20.5% of Staphylococci isolates were resistant. Resistance of Staphylococci isolates to erythromycin appears to be mediated by efflux mechanism (MS phenotype, 50.4%) and target site modification (MLSB phenotypes, 49.6%). Expression of MLSB phenotype in staphylococci was constitutive in 61.5% and inducible in 38.5% of the isolates. Among Streptococci isolates, resistance to erythromycin was most commonly (75.8%) mediated by target modification (MLSB). However, efflux mechanism of resistance (M phenotype) was detected in 24.2% of the isolates. Among the 36 Staphylococcal isolates analyzed by PCR, msr gene was detected in 20 (55.6%), ermC in11 (30.6%) and ermA in 9 (25%). On the other hand, among examined Streptococcal isolates (11), ermB gene was detected in 9 (81.8%) of isolates, mef in 3 (27.3%), ere in 1 (9.1%) and ermC in 1 (9.1%). The percentage of erythromycin resistant Staphylococci was highest among infants 0-2 years old (74.5%) and older age group >65 years (75%). Similarly, clindamycin resistance among Staphylococci was highest in bacteria isolated from patients >65 years (50%). This was significantly higher than that among 3-14 year age group (3.5%, P= 0). Staphylococci isolates recovered from gynecology department showed the highest erythromycin resistance when compared to isolates from other departments and variations in resistance rates were significant (P=0.000). Erythromycin resistance among Staphylococci bacteria isolated from blood and nasal swab were significantly higher than that among wound swabs (P=0.000).