Iffat Javeid, Sohaila Mushtaq, Aasma Noveen Ajmal.
Inducible Clindamycin Resistance in Staphylococcus aureus Isolates Recovered in Specimen from Tertiary Care Hospital.
Pak J Med Health Sci Jan ;6(4):1049-52.

Objective: To find out the percentage of Staphylococcus aureus having inducible Clindamycin resistance in our hospital using D-Test and to know the relationship between Methicillin-resistant Staphylococcus aureus (MRSA) and inducible Clindamycin resistance. Materials and methods: This was a descriptive cross-sectional study conducted on 93 Staph aureus isolates in a tertiary care hospital of Lahore during period of April 2012 to June 2012. Susceptibility to Penicillin (10µg), Cefoxitin (30µg), Erythromycin (15µg), Clindamycin (2µg), Linezolid (30µg), Ciprofloxacin (15µg), Gentamycin (10µg) Trimethoprim/Sulfmethoxazole (1.25/23.75µg) discs by Kirby Bauer disc diffusion method was determined as per NCCLS guideline. A disc containing Erythromycin (15 µg) was placed 15mm from centre to centre of a Clindamycin (2 µg) disc. Inducible resistance to Clindamycin is manifested by flattening or blunting of the Clindamycin zone of inhibition adjacent to the Erythromycin disc, giving a D-shape to the zone of inhibited growth. D-shaped Clindamycin susceptibility patterns where considered as D-test positive. Results: Total 93 Staph aureus was isolated from different clinical samples, 42 (45%) were Methicillin-resistant Staphylococcus aureus (MRSA) and 51 (55%) were Methicillin-sensitive Staphylococcus aureus (MSSA). Maximum isolates of Staph aureus were recovered from pus. Out of 42 MRSA isolates, 5 (12%) were D-Test positive and out of 51 MSSA only 1 (2%) isolate was D-Test positive. Maximum resistance was observed with Penicillin (96%) followed by Trimethoprim/ sulfamethoxazole (91%). All isolates were sensitive to Linezolid (100%), sensitivity to Clindamycin and Erythromycin was 73% and 51% respectively. Out of total 93 Staph aureus isolates 43(46%) were sensitive to both Erythromycin and Clindamycin, 20(22%) isolates were resistant to both antibiotics and 6 (6%) isolates were resistant to Erythromycin and sensitive to Clindamycin (D-Test positive) 24 (26%) isolates were resistant to Erythromycin and sensitive to Clindamycin (D-Test negative). Out of 30 isolates which were resistant to Erythromycin and sensitive to Clindamycin, 6 isolates (20%) were D-Test positive and 24 isolates (80%) were D-Test negative. Conclusion: All laboratories should routinely evaluate Staph aureus isolates that initially test as resistant to erythromycin and susceptible to clindamycin for inducible Clindamycin resistance using the “D- test.” When inducible Clindamycin resistance is present, the isolate is presumed to be resistant, and use of an alternative agent should be considered.

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