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Comparison of two disc diffusion methods with minimum inhibitory concentration for antimicrobial susceptibility testing of Neisseria gonorrhoeae isolates

Abstract number: P1181

Khaki P., Bhalla P., Sharma P., Moradi Bidhendi S.

Background: Gonorrhoea remains a public health problem in developing countries. Antimicrobial susceptibility testing of N. gonorrhoeae helps in monitoring the trends and efficacy of treatment guidelines for syndromic management of gonorrhoea. Antimicrobial susceptibility testing of N. gonorrhoeae isolates is widely performed as per the CLSI guidelines or by the AGSP method. Results of antimicrobial susceptibility testing by disc diffusion method should be reliable when compared to MIC values.

Objective: The present study was carried out to compare two disc diffusion methods (CLSI and AGSP) with MIC determination for antimicrobial susceptibility testing of gonococcal isolates.

Methods: A total of 100 N. gonorrhoeae isolates were studied. The strains were isolated from 89 (86.4%) out of 103 men with urethritis, 5 (12.8%) out of 39 women with endocervicitis and 6 (46.1%) out of 13 sexual contacts who attended the STD clinic of Lok Nayak Hospital, New Delhi between January 2004 and June 2006. All isolates were examined for susceptibility to penicillin, ciprofloxacin, tetracycline, ceftriaxone and spectinomycin by the disc diffusion methods (CLSI and AGSP). MIC was determined by E-test method. b-lactamase production was assayed by chromogenic cephalosporin method. Quality control strains were included for both disc diffusion and MIC methods.

Results: All isolates were susceptible to ceftriaxone and spectinomycin while 99 (99%) were resistant to ciprofloxacin by both disc diffusion methods. Thirty-two (32%) strains were found to be resistant to penicillin by CLSI method, while 40(40%) were resistant to penicillin by AGSP method. Seventeen (17%) isolates were PPNG and 20 (20%) were TRNG. All PPNG strains had no zone of inhibition by AGSP, while they had an inhibition zone ± 19 by CLSI. There was complete agreement between results of antimicrobial susceptibility testing by both disc diffusion methods and MIC values for all antibiotics except penicillin for which the kappa was 0.7 for AGSP and 1 for CLSI.

Conclusion: The continual spread and ongoing emergence of resistance among N. gonorrhoeae isolates require that an accurate and simple test be performed to determine antimicrobial susceptibilities. Both disc diffusion methods showed a high degree of agreement with MIC values. Although AGSP method is more economical, its feasibility depends on the availability antimicrobial discs of low potency and it requires more accuracy in measuring the inhibition zones.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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