[Prevalence of constitutive and inducible resistance to clindamycin in staphylococci isolates from Hajar and Kashani hospitals in Shahrekord, 2008]

Resistance to clindamycin [CL] in Staphylococcus aureus is both constitutive and inducible. In the present study, the prevalence of the constitutive and inducible resistance to CL was investigated by disk diffusion and double-disk diffusion [D-test] methods. This descriptive-analytical study was performed on 230 Staphylococcus isolates. D-test was carried out for all the isolates with resistant phenotype for erythromycin and susceptible phenotype for CL. 15 micro g erythromycin and 2 micro g CL disks were placed on plate at a distance of 15 mm. The appearance of D-shaped zones around the strains was checked after proper incubation. Of the 230 staphylococcus isolates, 55.6% were susceptible to CL, 37.5% had constitutive and 5.2% had inducible resistance to CL. The frequencies of constitutive and inducible resistance for CL in methicillin-resistant Staphylococcus aureus [MRSA] isolates were 66% and 9%, respectively and the frequencies of constitutive and inducible resistance for CL in methicillin-susceptible isolates [MSSA] were 15.4% and 2.3%, respectively. Statistical tests revealed the inducible resistance in MRS isolates to be 4.2 times more frequent than that in MSS isolates. The inducible resistance frequency was 10.8- fold in MRSA compared to MSSA isolates. The study results showed that the inducible resistance should be determined by D-test in all methicillin-resistant staphylococcus isolates and also staphylococcus strains resistant to erythromycin and susceptible to CL

[Comparison of agar screen and duplex-PCR in determination of methicillin resistant Staphylococcus aureus [MRSA] strains isolated from nose of personnel in Hajar hospital of Shahre-kord, 2007]

Methicillin resistant staphylococcus aureus strains are the most important agents of nosocomial infections. The conventional antibiotic susceptibility methods such as disk diffusion are not suitable for detection of these strains due to their heteroresistancy. Therefore, in this study, agar screen and duplex-PCR were compared in determination of methicillin resistant Staphylococcus aureus [MRSA] strains isolated from nose of personnel in Hajar hospital of Shahre-kord, 2007. In this experimental study a total of 204 nasal swabs from personnel of Hajar hospital over a period of 6 months were collected. The specimens were cultured on mannitol salt agar for primary isolation and identification of Staphylococcus aureus strains and their susceptibility pattern to oxacillin was assessed using agar screen method. Finally, using duplex PCR, the isolates were tested for the presence of mecA gene. Results were compared and sensitivity and specificity of the method was determined. In this study, 23 of the 52 [44%] Staphylococcus aureus isolates were resistant to oxacillin using agar screen method. However, mecA gene was detected in 27 of the 52 strains [52%]. Our results showed that the sensitivity and specificity of agar screen method in determination of MRSA strains were 81.5% and 96%, respectively comparing with PCR. Oxacillin agar screen, comparing PCR, is an inexpensive, applied and phenotypical method with low false positive and suitable for screening of MRSA. However, due to its relatively high false negative results is not appropriate for screening of MRSA strains isolated from hospital-employed nasal carriers