Correspondence
> 3 2 -a 32 4 16 4 1
(a)
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1
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11
1
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1
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-
i
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1
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coefficient was only 0-79 and zones were rather small ( ^ 8 mm for resistant and ;> 14 mm for susceptible). For clindamycin, the NCCLS interpretive criteria produced no false susceptible or false-resistant disc test results and a 1-7% minor error rate. Based on available phannacokinctic data for lincomycin (Weinstein, 1975), we selected MIC breakpoints, of ^ 2-0 and i 8-0 mg/1 for susceptible and resistant, respectively. With these MIC breakpoints, the 10 and 15 fig lincomycin in discs yielded no false susceptible or false resistant results: the 2 fig disc was less satisfactory, with two major errors. The 10 fig disc was selected as the preferred disc because the inhibitory zone diameters were smaller than those of the 15/ig disc, and because zone-size breakpoints were in a range comparable with those of clindamycin (Figure 1). Our data support the following interpretive criteria for the lincomycin 10 fig disc when the NCCLS method (NCCLS, 1988a) is used for disc diffusion testing: susceptible = £ 21 mm (MIC £ 2 0 mg/1); intermediate = 17-20 mm (MIC 4 0 mg/1); resistant =• £ 16 mm (MIC £ 80 mg/1). PETER C. FUCHS St. Vincent Medical Center, Portland, Oregon 97225, USA ARTHUR L. BARRY The Clinical Microbiology Institute, Tualatin, Oregon 97062, USA
1
20
i
25
i
>
30
35
Zone (Santter (mm)
Flgmc 1. Scattergrams depicting the correlation of etindamyem 2fi$ disc zone diameters with clindamycin MICs (a), and lincomycin lOpg disc zone diameten with lincomycin MICs (b). Horizontal and vertical lines represents the MIC and zone diameter breakpoints respectively as recommended by the NCCLS (a) (NCCLS, 1988a. b) and as proposed in this study (b).
National Committee for Clinical Laboratory Standards (1988a). Performance Standards for Antimicrobial Disk Susceptibility Tests. Tentative Standard, 4th ed. M2-T4. NCCLS, Vfflanova, PA. National Committee for Clinical Laboratory Standards (19886). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AerobicaUy. Tentative Standard, 2nd ed, M7-T2. NCCLS, Villanova, PA. Weinstein, C. (1975). Antimicrobial agents: Miscellaneous antibacterial agents, antifungal and antiviral agents. In The Pharmacological Basis of Therapeutics, 5th edn (Goodman, L S. & Girman, A Eds), pp. 1224-7. MacMillan, New York.
The preralence of antibiotic resistance in HaemopkUus iaftuenzae in Ireland Sir, The recent report on the prevalence of antibiotic resistance in Haemophilus influenzae in Ireland (Howard & Williams, 1989) gives an ampicillin resistance level of 10-9%, which the authors rightly report to be higher than those
Downloaded from http://jac.oxfordjournals.org/ at New York University on May 22, 2015
by broth microdilution and disc diffusion methods. Those organisms included 170 strains of staphylococci (including 30 oxacillinresistant strains), 20 enterococci, 70 streptococci, 20 Branhamella catarrhalis and 70 Gram-negative bacilli (38 Enterobacteriaceae and 32 non-enteric bacilli). The NCCLSrecommended procedures for broth microdilution and disc diffusion susceptibility testing were followed (NCCLS, 1988a, *). Filter paper discs impregnated with 2, 10 and 15 pg of lincomycin were prepared by Oxoid, Ltd, (Basingstoke, Hampshire, England) and were tested in parallel with 2 fig clindamycin discs. All 70 Gram-negative bacilli were highly resistant to both drugs and were excluded from subsequent analysis. There was good correlation between broth microdilution and disc diffusion tests for 2 fig clindamycin discs (correlation coefficient = 0-85) and for 10 and IS fig lincomycin discs (correlation coefficients = 0-87 and 0-88, respectively). For tests with 2 fig lincomycin discs, the correlation
1025
1026
Correspondence
Hne, 4-7% (1%) trimethoprim, 0% (3%) cefuroxime, and 0% (3%) ccfaclor, which shows no significant increase since the previous survey in Northern Ireland in 1982-83. While nationwide surveys are of interest in monitoring trends in resistance and may achieve greater statistical significance, we feel that monitoring resistance at a local level is of equal or possibly greater relevance to local prescribing practices. PHILIP G. MURPHY IAN CRAIG CYRIL LAFONG Department of Bacteriology, Belfast City Hospital, Usbum Road, Belfast BT9 7AD. UK
References Howard, A J. & Williams, H. M. (1989). The prevalence of antibiotic resistance in Haemophilia tnflueruae in Ireland. Journal of Antimicrobial Chemotherapy 24, 963-71. Lafong, A. C. (1985). Ampicillin resistance in Haemophihu inftuenzae. Ulster Medical Journal 54,58-60. Philpott-Howard, J. & Williams, J. D. (1982). Increase in antibiotic resistance in Hoemophilus inftuenzae in the United Kingdom since 1977: report of study group. British Medical Journal 284, 1597-601. PowelL M., Kouttia-Carouzou, C , Voutsinas, D., Seymour, A & Williams, J. D. (1987). Resistance of clinical isolates of Haemophibis inftuenzae in the United Kingdom. British Medical Journal 295,
176-9.
Downloaded from http://jac.oxfordjournals.org/ at New York University on May 22, 2015
found in other studies from Wales in the same year, of 8-4%, and from England and Scotland in 1986, of 7-8%. Levels of resistance in H.influemae in Northern Ireland have in fact been reported previously (Lafong, 1985); ampicillin resistance was found in 9-3% of ISO isolates in 1982-1983. At that time this result represented a higher level of resistance than that encountered in other parts of the UK, as a level of 6-2% was reported from a survey in England and Scotland in 1981 (Philpott-Howard & Williams, 1982). More recently, we have observed a level of 15% in a survey of 192 isolates collected in 1985-1986. This compares with a prevalence of 7-8% in 2434 isolates from England and Scotland in 1986 (Powell et al., 1987). We have therefore observed not only a persistently higher prevalence of ampicillin resistance than in the rest of the UK, but also an increasing level of resistance over this time. The most recently available data from routine monitoring in this hospital, using the Microbe Base 1 system (Academic Press), during January and February 1989 confirms our previous study, showing no further increase in resistance since 1986 and a static level of 15% ampicillin resistance in 132 isolates. Resistance levels (with intermediate susceptibility in brackets) to other antimicrobials in our 1985-1986 survey (disc sensitivity testing) were 3% (3%) amoxyciUin-clavulanate, 0-5% (2%) chloramphenicol, 0-5% (5%) tetracyc-
> 3 2 -a 32 4 16 4 1
(a)
e4
1
4 2 1 0-5 0-25 0-13
11
1
1 1 1 I1 1 1 1 111
1
i < imi i
-
i
I OS -
0-25 0-I3 3 2 -M 32 4
t
1
>aa«4iiii
1IIII11ITIIIII it
1 1111 i i
i -
1
10
1
15
coefficient was only 0-79 and zones were rather small ( ^ 8 mm for resistant and ;> 14 mm for susceptible). For clindamycin, the NCCLS interpretive criteria produced no false susceptible or false-resistant disc test results and a 1-7% minor error rate. Based on available phannacokinctic data for lincomycin (Weinstein, 1975), we selected MIC breakpoints, of ^ 2-0 and i 8-0 mg/1 for susceptible and resistant, respectively. With these MIC breakpoints, the 10 and 15 fig lincomycin in discs yielded no false susceptible or false resistant results: the 2 fig disc was less satisfactory, with two major errors. The 10 fig disc was selected as the preferred disc because the inhibitory zone diameters were smaller than those of the 15/ig disc, and because zone-size breakpoints were in a range comparable with those of clindamycin (Figure 1). Our data support the following interpretive criteria for the lincomycin 10 fig disc when the NCCLS method (NCCLS, 1988a) is used for disc diffusion testing: susceptible = £ 21 mm (MIC £ 2 0 mg/1); intermediate = 17-20 mm (MIC 4 0 mg/1); resistant =• £ 16 mm (MIC £ 80 mg/1). PETER C. FUCHS St. Vincent Medical Center, Portland, Oregon 97225, USA ARTHUR L. BARRY The Clinical Microbiology Institute, Tualatin, Oregon 97062, USA
1
20
i
25
i
>
30
35
Zone (Santter (mm)
Flgmc 1. Scattergrams depicting the correlation of etindamyem 2fi$ disc zone diameters with clindamycin MICs (a), and lincomycin lOpg disc zone diameten with lincomycin MICs (b). Horizontal and vertical lines represents the MIC and zone diameter breakpoints respectively as recommended by the NCCLS (a) (NCCLS, 1988a. b) and as proposed in this study (b).
National Committee for Clinical Laboratory Standards (1988a). Performance Standards for Antimicrobial Disk Susceptibility Tests. Tentative Standard, 4th ed. M2-T4. NCCLS, Vfflanova, PA. National Committee for Clinical Laboratory Standards (19886). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AerobicaUy. Tentative Standard, 2nd ed, M7-T2. NCCLS, Villanova, PA. Weinstein, C. (1975). Antimicrobial agents: Miscellaneous antibacterial agents, antifungal and antiviral agents. In The Pharmacological Basis of Therapeutics, 5th edn (Goodman, L S. & Girman, A Eds), pp. 1224-7. MacMillan, New York.
The preralence of antibiotic resistance in HaemopkUus iaftuenzae in Ireland Sir, The recent report on the prevalence of antibiotic resistance in Haemophilus influenzae in Ireland (Howard & Williams, 1989) gives an ampicillin resistance level of 10-9%, which the authors rightly report to be higher than those
Downloaded from http://jac.oxfordjournals.org/ at New York University on May 22, 2015
by broth microdilution and disc diffusion methods. Those organisms included 170 strains of staphylococci (including 30 oxacillinresistant strains), 20 enterococci, 70 streptococci, 20 Branhamella catarrhalis and 70 Gram-negative bacilli (38 Enterobacteriaceae and 32 non-enteric bacilli). The NCCLSrecommended procedures for broth microdilution and disc diffusion susceptibility testing were followed (NCCLS, 1988a, *). Filter paper discs impregnated with 2, 10 and 15 pg of lincomycin were prepared by Oxoid, Ltd, (Basingstoke, Hampshire, England) and were tested in parallel with 2 fig clindamycin discs. All 70 Gram-negative bacilli were highly resistant to both drugs and were excluded from subsequent analysis. There was good correlation between broth microdilution and disc diffusion tests for 2 fig clindamycin discs (correlation coefficient = 0-85) and for 10 and IS fig lincomycin discs (correlation coefficients = 0-87 and 0-88, respectively). For tests with 2 fig lincomycin discs, the correlation
1025
1026
Correspondence
Hne, 4-7% (1%) trimethoprim, 0% (3%) cefuroxime, and 0% (3%) ccfaclor, which shows no significant increase since the previous survey in Northern Ireland in 1982-83. While nationwide surveys are of interest in monitoring trends in resistance and may achieve greater statistical significance, we feel that monitoring resistance at a local level is of equal or possibly greater relevance to local prescribing practices. PHILIP G. MURPHY IAN CRAIG CYRIL LAFONG Department of Bacteriology, Belfast City Hospital, Usbum Road, Belfast BT9 7AD. UK
References Howard, A J. & Williams, H. M. (1989). The prevalence of antibiotic resistance in Haemophilia tnflueruae in Ireland. Journal of Antimicrobial Chemotherapy 24, 963-71. Lafong, A. C. (1985). Ampicillin resistance in Haemophihu inftuenzae. Ulster Medical Journal 54,58-60. Philpott-Howard, J. & Williams, J. D. (1982). Increase in antibiotic resistance in Hoemophilus inftuenzae in the United Kingdom since 1977: report of study group. British Medical Journal 284, 1597-601. PowelL M., Kouttia-Carouzou, C , Voutsinas, D., Seymour, A & Williams, J. D. (1987). Resistance of clinical isolates of Haemophibis inftuenzae in the United Kingdom. British Medical Journal 295,
176-9.
Downloaded from http://jac.oxfordjournals.org/ at New York University on May 22, 2015
found in other studies from Wales in the same year, of 8-4%, and from England and Scotland in 1986, of 7-8%. Levels of resistance in H.influemae in Northern Ireland have in fact been reported previously (Lafong, 1985); ampicillin resistance was found in 9-3% of ISO isolates in 1982-1983. At that time this result represented a higher level of resistance than that encountered in other parts of the UK, as a level of 6-2% was reported from a survey in England and Scotland in 1981 (Philpott-Howard & Williams, 1982). More recently, we have observed a level of 15% in a survey of 192 isolates collected in 1985-1986. This compares with a prevalence of 7-8% in 2434 isolates from England and Scotland in 1986 (Powell et al., 1987). We have therefore observed not only a persistently higher prevalence of ampicillin resistance than in the rest of the UK, but also an increasing level of resistance over this time. The most recently available data from routine monitoring in this hospital, using the Microbe Base 1 system (Academic Press), during January and February 1989 confirms our previous study, showing no further increase in resistance since 1986 and a static level of 15% ampicillin resistance in 132 isolates. Resistance levels (with intermediate susceptibility in brackets) to other antimicrobials in our 1985-1986 survey (disc sensitivity testing) were 3% (3%) amoxyciUin-clavulanate, 0-5% (2%) chloramphenicol, 0-5% (5%) tetracyc-
