Indian Journal of Medical Microbiology Home 

Year : 2001  |  Volume : 19  |  Issue : 4  |  Page : 222--223

Antimicrobial susceptibility testing in India - A status survey

V Sudha, A Prasad, S Khare, R Bhatia 
 National Institute of Biologicals, Noida-201 301, India

Correspondence Address:
V Sudha
National Institute of Biologicals, Noida-201 301
India

Abstract

Resistance to a variety of antimicrobial agents is emerging in bacterial pathogens throughout the world. Since the accuracy of the antimicrobial susceptibility data is associated with the performance standard of the test, strict adherence to the standard procedures is essential. The Kirby-Bauer disc diffusion susceptibility test, performed in accordance to NCCLS method gives reliable results and hence predicts clinical efficacy of the antibiotic tested. To assess the standard of performance of the antimicrobial susceptibility test, a survey was conducted by National Institute of Biologicals during 1999-2000. The findings indicated an urgent need of setting up a national quality control laboratory to provide the performance standards, reference Q.C. strains and quality antibiotic discs to ensure reproducible and reliable results.

How to cite this article:
Sudha V, Prasad A, Khare S, Bhatia R. Antimicrobial susceptibility testing in India - A status survey.Indian J Med Microbiol 2001;19:222-223

How to cite this URL:
Sudha V, Prasad A, Khare S, Bhatia R. Antimicrobial susceptibility testing in India - A status survey. Indian J Med Microbiol [serial online] 2001 [cited 2020 Jul 4 ];19:222-223
Available from: http://www.ijmm.org/text.asp?2001/19/4/222/8197

Full Text

The emergence of antimicrobial resistant strains of pathogenic bacteria has become a great threat to the public health. Early detection of emerging trends in antimicrobial resistance may facilitate implementation of effective control measures. The laboratory testing of antibiotic susceptibility contributes directly to patient care and the expertise of the microbiology laboratory can have powerful influence on antibiotic usage and hence on the pressures that facilitate the emergence of antimicrobial drug resistance.

The findings of National External Microbiological Quality Assessment Scheme, United Kingdom, indicated that the poor performance of many laboratories is associated with the use of inappropriate methods.[1] The Kirby-Bauer disc diffusion susceptibility test[2], performed in accordance to NCCLS method[3],[4],[5] gives reliable results and hence predicts clinical efficacy of the antibiotic tested. A survey on the standard of performance of the test in India was conducted by National Institute of Biologicals, NOIDA in 1999-2000. Ten state level medical college microbiology laboratories who were being trained on WHONET - a software developed by WHO for data analysis of the susceptibility test, were included in the survey.

A questionnaire pertaining to all important aspects of testing was given to each laboratory representative. The response revealed that 90% of the laboratories use the Muller-Hinton agar media for sensitivity testing while 10% use both nutrient agar and Muller-Hinton agar as per the availability. The reproducibility of the Antimicrobial Susceptibility Test (AST) result was greatly affected by different batches of the media (60%). Of the laboratories included in the survey, 80% laboratories check the sterility of each new batch of the media while pH was checked in 60%. Majority of the laboratories procure commercial antibiotic discs (Himedia, Biodisk, Dynamicro, Pasteur, Span etc.); rest either prepare their own discs (20%) or use both commercial and self prepared disc as per their convenience. Out of ten, eight laboratories use 0.5 McFarland turbidity standard while others have introduced its use recently and the period of its replacement varies from one month to six months. The sensitivity testing of Haemophilus species and N.gonnorrheae is done very rarely by these laboratories that too not on the special media recommended by NCCLS. None of the participating laboratories has all the quality control strains (viz. E.coli ATCC 25922, S.aureus ATCC 25923, E.faecalis ATCC 29212, H.influenzae ATCC 49247, ATCC 49766, N.gonorrheae ATCC 49226, S.pneumoniae ATCC 49619) for disc diffusion test. Further these strains are stocked in Nutrient Agar or Muller-Hinton Agar and not in Tryptic - Soy Agar (non-fastidious organism) or on Enriched Chocolate Agar (Fastidious) slants as recommended by NCCLS.

The survey indicates that the reproducibility of the AST test results is affected by change in the batch of the medium thus enforcing the use of quality controlled media and reagents. For that matter, the quality of commercial antibiotic discs too needs to be considered and their in-house preparation also requires careful standardisation. Other aspects like testing pH of the media, preparation and regular replacement of 0.5 McFarland Standard are not followed in many laboratories as per NCCLS recommendations. A comparative study of the inhibition zone on Muller - Hinton Agar and the special media recommended by the NCCLS for sensitivity testing of Haemophilus influenzae and Neisseria gonnorrheae need to be done and critically evaluated. Non-availability of the appropriate standard bacterial culture for the quality control of the test also contributes to unreliable results.

The survey thus concludes that there is an urgent need of setting up a national quality control laboratory to provide the performance standards, reference Q.C. strains and quality antibiotic discs to ensure reproducible and reliable results. An External Quality Assessment Service in Microbiology[6] conducted by Indian Association of Medical Microbiologists also support the above findings. Further, there is a need of greater awareness amongst microbiologists regarding the performance of AST as per the NCCLS method and hence to conduct Continuing Medical Education (CME) Programme to train them in this regard. These initiatives will contribute to generate a reliable data for emerging bacterial antibiotic resistance needed for framing the drug policies and preventing indiscriminate use of antibiotics.

References

1Snell JJS, Brown DFJ, Gardner PS. Comparison of results from two antibiotic susceptibility testing trials that formed part of the United Kingdom national external quality assessment scheme. J Clin Pathol 1984; 37: 321 - 328.
2Bauer AW, Kirby M. Antibiotic Susceptibility Testing by standardised single disc method Am. J Clin Pathol 1966; 45: 493-496.
3National Committee For Clinical Laboratory Standards. Approved Standard M2-A6. Performance Standards for antimicrobial disc susceptibility testing . 6th edition. NCCLS, Waynae, Pa. 1997.
4National Committee For Clinical Laboratory Standards. Approved standard M7-A4. Method for dilution antimicrobial Susceptibility test for bacteria that grow aerobically. 4th edition. NCCLS, Waynae, Pa. 1997.
5National Committee For Clinical Laboratory Standards. NCCLS document M100 - S8 . Performance Standards for Antimicrobial Susceptibility Testing. 8th edition, NCCLS, Waynae, Pa. 1998.
6Jesudason MV, Mukundan U, Ohri VC, Badrinath S, Jacob John T. An external quality assessment service in Microbiology in India - A six year experience. Ind J Med Microbiol 2001; 19 (1): 20 - 25.