Journal of Antimicrobial Chemotherapy (1979) 5, 67-72
Antibiotic susceptibility testing of Neisseria gonorrhoeae
R. M. Robins-Browne,* M. C. GaiDard and H. J. Koornhof
The minimal inhibitory concentrations (MICs) of penicillin G, ampicillin, erythromycin, tetracycline and spectinomycin were determined for a number of clinical isolates of Neisseria gonorrhoeae, and the results compared with those obtained using a modified Bauer-Kirby disc diffusion technique. Close statistical correlation of penicillin G, ampicillin and tetracycline MICs and disc susceptibilities was demonstrated. Owing to the relatively wide scatter of points, however, regression lines constructed from these data did not enable reliable prediction of MICfromthe diameter of antibiotic inhibition zones. Bauer-Kirby disc susceptibility testing is, therefore, unsuitable for the laboratory differentiation of partially resistant from fully sensitive strains of N. gonorrhoeae.
Introduction Relative resistance of Neisseria gonorrhoeae to penicillin G was first noted 20 years ago, and has subsequently increased in frequency and magnitude (Sparling, 1972). During the same period, increased resistance to tetracycline, erythromycin and streptomycin has also been documented (Sparling, 1972). Recently the problem of antibiotic resistance in gonococci has been aggravated by the emergence of penicillinase-producing strains, which are completely resistant to penicillin G and ampicillin (Leading article, Lancet, 1976; Sparling, Holmes, Weisner & Puziss, 1977). These developments are likely to result in wider use being made of antimicrobial susceptibility tests to aid in the treatment of gonorrhoea. The antimicrobial susceptibility of N. gonorrhoeae is generally expressed in terms of minimal inhibitory concentrations (MICs), investigations too cumbersome for routine execution in most clinical laboratories. In the present study we examined the feasibility of substituting MIC determinations by disc sensitivity tests. We compared the results of the two investigations performed on a number of gonococcal isolates. Materials and methods Isolation and identification o/N. gonorrhoeae Gonococci were recovered on a selective medium (Thayer & Martin, 1966) from patients attending a clinic for sexually transmitted diseases in Johannesburg. The identity of •Correspondence: Dr R. M. Robins-Browne, SAIMR, P.O. Box 1038, Johannesburg 2000, RSA. 67 0305-7453/79/010067+06 $01.00/0 © 1979 The British Society for Antimicrobial Chemotherapy
Downloaded from http://jac.oxfordjournals.org/ at Simon Fraser University on June 11, 2015
Department of Microbiology, School of Pathology of the University of the Witwatersrand and the South African Institute for Medical Research, Johannesburg, South Africa
R. M. Robins-Browne, M. C Galllard and H. J. Koornhof
68
the bacteria was established by the morphologically characteristic oxidase-positive colonies comprising Gram-negative diplococci, which fermented glucose but not sucrose, maltose or lactose in cysteine tryptic agar. Bacteria so identified were stored at — 70°C in beef infusion broth supplemented with 10% horse serum until required. 50
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Antibiotic susceptibility testing of Neisseria gonorrhoeae
R. M. Robins-Browne,* M. C. GaiDard and H. J. Koornhof
The minimal inhibitory concentrations (MICs) of penicillin G, ampicillin, erythromycin, tetracycline and spectinomycin were determined for a number of clinical isolates of Neisseria gonorrhoeae, and the results compared with those obtained using a modified Bauer-Kirby disc diffusion technique. Close statistical correlation of penicillin G, ampicillin and tetracycline MICs and disc susceptibilities was demonstrated. Owing to the relatively wide scatter of points, however, regression lines constructed from these data did not enable reliable prediction of MICfromthe diameter of antibiotic inhibition zones. Bauer-Kirby disc susceptibility testing is, therefore, unsuitable for the laboratory differentiation of partially resistant from fully sensitive strains of N. gonorrhoeae.
Introduction Relative resistance of Neisseria gonorrhoeae to penicillin G was first noted 20 years ago, and has subsequently increased in frequency and magnitude (Sparling, 1972). During the same period, increased resistance to tetracycline, erythromycin and streptomycin has also been documented (Sparling, 1972). Recently the problem of antibiotic resistance in gonococci has been aggravated by the emergence of penicillinase-producing strains, which are completely resistant to penicillin G and ampicillin (Leading article, Lancet, 1976; Sparling, Holmes, Weisner & Puziss, 1977). These developments are likely to result in wider use being made of antimicrobial susceptibility tests to aid in the treatment of gonorrhoea. The antimicrobial susceptibility of N. gonorrhoeae is generally expressed in terms of minimal inhibitory concentrations (MICs), investigations too cumbersome for routine execution in most clinical laboratories. In the present study we examined the feasibility of substituting MIC determinations by disc sensitivity tests. We compared the results of the two investigations performed on a number of gonococcal isolates. Materials and methods Isolation and identification o/N. gonorrhoeae Gonococci were recovered on a selective medium (Thayer & Martin, 1966) from patients attending a clinic for sexually transmitted diseases in Johannesburg. The identity of •Correspondence: Dr R. M. Robins-Browne, SAIMR, P.O. Box 1038, Johannesburg 2000, RSA. 67 0305-7453/79/010067+06 $01.00/0 © 1979 The British Society for Antimicrobial Chemotherapy
Downloaded from http://jac.oxfordjournals.org/ at Simon Fraser University on June 11, 2015
Department of Microbiology, School of Pathology of the University of the Witwatersrand and the South African Institute for Medical Research, Johannesburg, South Africa
R. M. Robins-Browne, M. C Galllard and H. J. Koornhof
68
the bacteria was established by the morphologically characteristic oxidase-positive colonies comprising Gram-negative diplococci, which fermented glucose but not sucrose, maltose or lactose in cysteine tryptic agar. Bacteria so identified were stored at — 70°C in beef infusion broth supplemented with 10% horse serum until required. 50
45
40
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-
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35
N
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