Comparison of the etest and the routine multi-disc agar diffusion susceptibility of staphylococcus species

الملخص EN

Aims : the present study, tend to evaluate the validity and accuracy of E test as a method for performing in-vitro antimicrobial susceptibility testing of Staphylococcus with comparison to the routine multi disc agar diffusion.

This is because the E test susceptibility method is not yet known as a rapid, simple reliable technique in developing countries as it combine the functions of both dilution and diffusion technique.

Materials and methods : Ninety-seven Staphylococcus aureus and eighty-three Staphylococcus epidermidis isolates were obtained from wound samples and identified according to standard morphological and biochemical methods.

The antibiotics susceptibility patterns were determined both by agar disc diffusion and E test methods in accordance to NCCLS (1997) criteria and manufacturer (AB Bio disk Sweden) respectively.

Result : on the E test strips, Staph aureus was 83.5 % sensitive to ciprofloxacin, 52.6 % to gentamicin, 48.5 % to ampicillin and 8.2 % to chloramphenicol while on the multi-disc agar diffusion plates 80.4 % of Staph aureus were sensitive to ciprofloxacin, 49.5 % to gentamicin, 39.2 % to ampicillin and 12.4 % to chloramphenicol..

On the E test strips, 80.7 % of Staph epidermis's were sensitive to ciprofloxacin, 34.9 % to gentamicin, 25.3 % to ampicillin and 15.7 % to chloramphenicol while on the multi- disc agar diffusion plates 89.2 % of Staph epidermis's were sensitive to ciprofloxacin, 34.9 % to gentamicin, 25.3 % to ampicillin and 32.5 % to chloramphenicol.

Conclusion : the sensitivity patterns between the two methods were essentially similar, however, the E test method clearly demonstrated intermediate sensitivities which to an extent were absent in routine multi-disc agar diffusion method.

Most of the isolates E test MICs clustered around the sensitive and resistance break points.

E test also demonstrated the MIC and diffusion results on the same strips.