- Email: [email protected]
Quality control parameters for cefditoren susceptibility tests
Concise Communications
the first study. Guess [10] found that 20 in 100000 children
93
chickenpox before the first year of age and herpes zoster in
under the age of 5 fall ill, and 63 in 100 000 of persons between
children was not analyzed, because the number of children with
the ages of 15 and 19. Herpes zoster was significantly more
chickenpox at the age ofless than 1 year was insufficient to form
frequent in children with acute lymphocytic leukemia. Accord-
a sample.
ing to the data from this study, the risk factor for childhood
Even though herpes zoster is a disease of the elderly, it is not
herpes zoster was chickenpox before the first year of age.
all that rare in children; however, the course of the disease is
Another study [11], which was conducted a few years ago,
mainly mild and without sequelae.
reported an even higher incidence ofherpes zoster; it affects 160 in 100 000 persons younger than 19. Herpes zoster most frequently appeared in the thoracic region. The course of the disease was mainly mild, and none of the patients had post-herpetic neuralgia. A significantly higher number of complications were observed in adult patients [3]. The data we collected do not differ from those of the abovementioned studies. The number of patients was found to increase with age. The interval between chickenpox and herpes zoster was 5.6 years on average. In a study conducted on the popnlation of Iceland, on average slightly more than 8 years passed from chickenpox to the appearance of herpes zoster, but adolescents with herpes zoster aged up to 19 were also included. In all of our patients, the course of the disease was extremely mild and there were no complications. It is therefore disputable whether treatment with acyclovir is justified, apart from exceptional cases (e.g. in severely immunocompromised children). In the children from this study as well, herpes zoster was most often located in the thoracic area and only in one child in the ophthalmic area. In adnlts, however, thoracic herpes zoster is found in only half of the cases and cranial herpes zoster in over 10% of patients [5]. In children whose mothers had chickenpox during pregnancy, herpes zoster may appear as early as the first year oflife. In only one of86 children did the mother have chickenpox during pregnancy, and herpes zoster appeared very soon after the first year of life. The immune system of the fetus is undoubtedly immature, which, in the opinion of some, is the reason for the early appearance of the disease [2]. The correlation between
REFERENCES 1. Straus SE. Introduction to Herpesviridae. In: Mandell GL, Bennets JE, Dolin R, eds. Principles and Practice of Infectious Diseases, 4th edn, Vol. 2. New York: Churchill Livingstone, 1995: 1330-5. 2. Miller E, Marshall R, Vurdien J. Epidemiology, outcome and control of varicella-zoster infection. Rev Med Microbial 1993; 4: 222-30. 3. Weller TH. Varicella and herpes zoster. Changing concepts of the natural history, control, and importance of not-so-benign virus. N Engl] Med 1983; 309: 1362-8. 4. Straus SE, Ostrove JM, Inchaupse G et a1. Varicella-zoster infections. Biology, natural history, treatment, and prevention. Ann Intern Med 1988; 108: 221-37. 5. Ragozzino M\JII, Melton MJ, Kurland LT, Chu Cp' Pery HO. Population-based study of herpes zoster and its sequelae. Medicine 1982; 61: 310-16. 6. Wutzler P, Doerr H\JII, von EssenJ et al. Epidemiology of herpes zoster. Biotest Bull 1997; 5: 301--6. 7. Donahue JG, Choo P\JII, Manson JE, Platt R. The incidence of herpes zoster. Arch Intern Med 1995; 155: 1605-9. 8. Mazur MH, Dolin R. Herpes zoster at NIH: a 20-year experience. Am] Med 1978; 65: 738-4. 9. Latif R, Shope TC. Herpes zoster in normal and immunocompromised children. Am] Dis Child 1983; 137: 801-2. 10. Guess HA, Broughton DD, Melton LJ, Kurland LT. Epidemiology of herpes zoster in children and adolescents: a population-based study. Pediatrics 1985; 76: 512-17. 11. Petursson G, Helgason S, Gudmundsson S, Sigurdsson A. Herpes zoster in children and adolescents. Pediatr Infect Dis] 1998; 17: 905-8.
Quality control parameters for cefditoren susceptibility tests P C. Fuchs', A. L. Barry, S. D. Brown and M. M. Traczewski
The Clinical Microbiology Institute, 9725 SW Commerce Circle, Wilsonville, OR 97070, USA *Tel:
+1 503
682 3232
Fax:
+1 503
682 2065
E-mail: [email protected]
Accepted 30 November 2000
Cefditoren is a new expanded-spectrum orally administered
[1]. Its antimicrobial spectrum includes both Gram-positive and
cephalosporin currently undergoing clinical trials in the USA
Gram-negative species, but it is noteworthy for its particnlar
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102
Clinical Microbiology and Infection, Volume 7 Number 2, February 2001
94
Table 1 Distribution of MICs for six QC strains" Broth microdilution MICs (mg(L) Organism (ATCC No.)
No. of tests
Escherichia coli (25922) Staphylococcus aureus (29213) Streptococcus pneumoniae (49619) H influenzae (49247) H influenzae (49766)
594
0.004
0.008
0.016
0.03
0.06
279
245
600 500
5
300 45
499
424
28
2
"Number of times each MIC was reported; values in bold are within the proposed QC limits for each strain.
potency against the major respiratory pathogens Haemophilus infiuenzae and Streptococcus pneumoniae [1,2]. In order to ensure
for H. infiuenzae ATCC 49766, and three lots for H. infiuenzae ATCC 49247. These media were freshly prepared and stored at
accurate in vitro susceptibility tests with this drug, quality
<;- 60°C until used (up to 14 days). Serial dilutions of
control (QC) parameters are necessary for the standard QC
cefotaxime or cefuroxime were prepared in one lot of broth
organisms. In the course ofour in vitro studies of cefditoren, we
as control drugs. Three lots of Mueller-Hinton agar (MBA)
have conducted a multilaboratory study to determine the QC parameters for cefditoren when tested by the National Com-
from three different manufacturers were used for disk diffusion tests, along with two lots of 5-J-lg cefditoren disks prepared by
mittee for Clinical Laboratory Standards (NCCLS) methods for
two different manufacturers. The MHA was supplemented with
broth microdilution [3] and disk diffusion [5] susceptibility tests.
5% sheep blood or HTM supplements for testing S. pneumoniae
The design of these studies exceeded the minimum require-
or H. infiuenzae. HTM agar was freshly prepared and used
ments of the NCCLS [4]. Ten North American medical centers participated in each study. Each laboratory performed the broth
within 14 days. Cefotaxime 30-J-lg disks or cefixime 5-J-lg disks served as controls. On each of 10 separate days, all participants
micro dilution and disk diffusion tests as outlined by the NCCLS
inoculated one microdilution tray and three different MBA agar
[3,5]. Broth microdilution trays were prepared to contain serial
plates for each organism tested. This resulted in a total of 600
dilutions of cefditoren with concentrations ranging from 0.004
disk diffusion zone diameter measurements for each QC strain
to 32 mg/L in each of six different lots of cation-adjusted
tested, 600 MIC determinations for each non-fastidious QC
Mueller-Hinton broth (CAMHB) from four different manufacturers for testing non-fastidious strains, and five lots of
strain, 500 MIC determinations for the S. pneumoniae QC strain and H. infiuenzae ATCC 49766, and 300 MIC determinations
CAMHB with 3% lysed horse blood for Streptococcus pneumoniae,
for H. infiuenzae ATCC 49247. Whenever the control drug
five lots with Haemophilus Test Medium (HTM) supplements
results were outside the NCCLS range, the corresponding
Table 2 Distribution of zone diameters for six QC strains" Disk diffusion zone diameters (mm) Organism
No. of
(ATCCNo.)
tests
EC
590
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
14
76
175
195
89
34
7
34
108
188
149
51
23
17
5
597
3
5
21
45
77
120
154
98
44
19
11
576
11
21
75
106
110
122
66
40
8
8
3
36
37
4
2
(25992) SA
590
10
(25923) SP (49619) HI (49247) "Number of times each zone diameter was reported; values in bold are within the proposed QC limits for each strain. EC,Escherichia coli; SA, Staphylococcus
aureus; SP,Streptococcus pneumoniae; HI, Haemophilus influenzae.
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102
Concise Communications
95
Table 3 Recommended QC ranges for cefditoren" and percentage of results in range MICs (mg(L)
Zone diameters (mm)
Organism (ATCC No.)
Range
% in range
Range
% in range
Escherichiacoli (25922) Staphylococcus aureus (29213) Staphylococcus aureus (25923) Streptococcus pneumoniae (49619) Haemophilus influenzae (49247) Haemophilus influenzae (49766)
0.12-1.0 0.25-2.0
100 100
22-28
100
a
NA
20-28 27-35 25-34
NA
0.016-0.12 0.06-0.25 0.004-0.016
100 100 99.6
98.3 98.7 98.3
NR
These QC ranges were approved by the NCClS in June, 1999. NA, not applicable; NR, no recommendations (results off-scale or zones too large).
J.
cefditoren results were omitted from the calculations even
Center, Worcester, MA, USA; M.
though these would not have influenced the cefditoren pro-
General Hospital, Boston, MA, USA; D. Goldman, Children's
posed ranges. Colony counts were performed on the growth
Hospital and Medical Center, Boston, MA, USA; D. Hardy,
control suspension on each test day to ensure appropriate inoculum density.
Ferraro, Massachusetts
University of Rochester Medical Center, Rochester, NY, USA;
J. Hindler,
UCLA Medical Center, Los Angeles, CA, USA; S.
The distribution of MICs and zone diameter results with
Jenkins, Carolinas Medical Center, Charlotte, NC, USA; C.
these control organisms are summarized in Tables 1 and 2.
Knapp, Trek Diagnostic Systems, Westlake, OH, USA; G.
There were no appreciable differences in these distributions
Overturf, University of New Mexico Medical Center, Albu-
when the results were stratified by media lot or laboratories.
querque, NM, USA; M. Pfaller, University ofIowa, Iowa City,
The QC organisms tested, the proposed ranges and the per-
lA, USA; R. Rennie, University of Alberta Hospital, Edmon-
centage of results falling within these ranges are summarized in
ton, Alberta, Canada; M. Saubolle, Good Samaritan Hospital,
Table 3. A four-dilution MIC range was proposed for most
Phoenix AZ, USA; and J. Washington, The Cleveland Clinic,
strains because the mode fell between two adjacent concentra-
Cleveland, OH, USA.
tions that were tested. One laboratory also performed cefditoren agar dilution tests with each QC strain on 15 separate days, and all MIC results fell within these proposed ranges. The MIC QC range for H. influenzae ATCC 49247 was approved by the NCCLS in June 2000; all other QC ranges listed in Tables 1 and 2 for both disk diffusion and dilution tests were approved by the NCCLS subcommittee on antimicrobial susceptibility tests in June 1999.
ACKNOWLEDGMENTS This study was supported by a grant from TAP Pharmaceuticals. Portions of this material have been previously presented at the 39th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, USA, 26-29 September 1999, as Abstract 2324. Participants included: M. Bauman, Providence St Vincent Medical Center, Portland, OR, USA; B.
Brogden-Torres, University of Massachusetts Medical
REFERENCES 1. Felmingham D, Robbins MJ, Ghosh G et al. An in vitro
characterization of cefditoren, a new oral cephalosporin. Drugs cu« Res 1994; 20: 127-47. 2. Jones RN, Biedenbach DJ, Croco MAT, Barrett MS. In vitro evaluation of a novel orally administered cephalosporin (cefditoren) tested against 1249 recent clinical isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae. Diagn Microbial Infect Dis 1998; 31: 573-8. 3. National Committee for Clinical Laboratory Standards. Methods of Exp
dilution antimicrobial susceptibility tests for bacteria that grow aerobically,
4th edn. Approved Standard M7-A4. Wayne, PA: NCCLS, 1997. 4. National Committee for Clinical Laboratory Standards. Development of in vitro susceptibility testing criteria and quality control parameters. Tentative Guideline, M23-T3. Wayne, PA: NCCLS, 1998. 5. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility tests, 6th edn. Approved Standard M2-A6. Wayne, PA: NCCLS, 1997.
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102
the first study. Guess [10] found that 20 in 100000 children
93
chickenpox before the first year of age and herpes zoster in
under the age of 5 fall ill, and 63 in 100 000 of persons between
children was not analyzed, because the number of children with
the ages of 15 and 19. Herpes zoster was significantly more
chickenpox at the age ofless than 1 year was insufficient to form
frequent in children with acute lymphocytic leukemia. Accord-
a sample.
ing to the data from this study, the risk factor for childhood
Even though herpes zoster is a disease of the elderly, it is not
herpes zoster was chickenpox before the first year of age.
all that rare in children; however, the course of the disease is
Another study [11], which was conducted a few years ago,
mainly mild and without sequelae.
reported an even higher incidence ofherpes zoster; it affects 160 in 100 000 persons younger than 19. Herpes zoster most frequently appeared in the thoracic region. The course of the disease was mainly mild, and none of the patients had post-herpetic neuralgia. A significantly higher number of complications were observed in adult patients [3]. The data we collected do not differ from those of the abovementioned studies. The number of patients was found to increase with age. The interval between chickenpox and herpes zoster was 5.6 years on average. In a study conducted on the popnlation of Iceland, on average slightly more than 8 years passed from chickenpox to the appearance of herpes zoster, but adolescents with herpes zoster aged up to 19 were also included. In all of our patients, the course of the disease was extremely mild and there were no complications. It is therefore disputable whether treatment with acyclovir is justified, apart from exceptional cases (e.g. in severely immunocompromised children). In the children from this study as well, herpes zoster was most often located in the thoracic area and only in one child in the ophthalmic area. In adnlts, however, thoracic herpes zoster is found in only half of the cases and cranial herpes zoster in over 10% of patients [5]. In children whose mothers had chickenpox during pregnancy, herpes zoster may appear as early as the first year oflife. In only one of86 children did the mother have chickenpox during pregnancy, and herpes zoster appeared very soon after the first year of life. The immune system of the fetus is undoubtedly immature, which, in the opinion of some, is the reason for the early appearance of the disease [2]. The correlation between
REFERENCES 1. Straus SE. Introduction to Herpesviridae. In: Mandell GL, Bennets JE, Dolin R, eds. Principles and Practice of Infectious Diseases, 4th edn, Vol. 2. New York: Churchill Livingstone, 1995: 1330-5. 2. Miller E, Marshall R, Vurdien J. Epidemiology, outcome and control of varicella-zoster infection. Rev Med Microbial 1993; 4: 222-30. 3. Weller TH. Varicella and herpes zoster. Changing concepts of the natural history, control, and importance of not-so-benign virus. N Engl] Med 1983; 309: 1362-8. 4. Straus SE, Ostrove JM, Inchaupse G et a1. Varicella-zoster infections. Biology, natural history, treatment, and prevention. Ann Intern Med 1988; 108: 221-37. 5. Ragozzino M\JII, Melton MJ, Kurland LT, Chu Cp' Pery HO. Population-based study of herpes zoster and its sequelae. Medicine 1982; 61: 310-16. 6. Wutzler P, Doerr H\JII, von EssenJ et al. Epidemiology of herpes zoster. Biotest Bull 1997; 5: 301--6. 7. Donahue JG, Choo P\JII, Manson JE, Platt R. The incidence of herpes zoster. Arch Intern Med 1995; 155: 1605-9. 8. Mazur MH, Dolin R. Herpes zoster at NIH: a 20-year experience. Am] Med 1978; 65: 738-4. 9. Latif R, Shope TC. Herpes zoster in normal and immunocompromised children. Am] Dis Child 1983; 137: 801-2. 10. Guess HA, Broughton DD, Melton LJ, Kurland LT. Epidemiology of herpes zoster in children and adolescents: a population-based study. Pediatrics 1985; 76: 512-17. 11. Petursson G, Helgason S, Gudmundsson S, Sigurdsson A. Herpes zoster in children and adolescents. Pediatr Infect Dis] 1998; 17: 905-8.
Quality control parameters for cefditoren susceptibility tests P C. Fuchs', A. L. Barry, S. D. Brown and M. M. Traczewski
The Clinical Microbiology Institute, 9725 SW Commerce Circle, Wilsonville, OR 97070, USA *Tel:
+1 503
682 3232
Fax:
+1 503
682 2065
E-mail: [email protected]
Accepted 30 November 2000
Cefditoren is a new expanded-spectrum orally administered
[1]. Its antimicrobial spectrum includes both Gram-positive and
cephalosporin currently undergoing clinical trials in the USA
Gram-negative species, but it is noteworthy for its particnlar
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102
Clinical Microbiology and Infection, Volume 7 Number 2, February 2001
94
Table 1 Distribution of MICs for six QC strains" Broth microdilution MICs (mg(L) Organism (ATCC No.)
No. of tests
Escherichia coli (25922) Staphylococcus aureus (29213) Streptococcus pneumoniae (49619) H influenzae (49247) H influenzae (49766)
594
0.004
0.008
0.016
0.03
0.06
279
245
600 500
5
300 45
499
424
28
2
"Number of times each MIC was reported; values in bold are within the proposed QC limits for each strain.
potency against the major respiratory pathogens Haemophilus infiuenzae and Streptococcus pneumoniae [1,2]. In order to ensure
for H. infiuenzae ATCC 49766, and three lots for H. infiuenzae ATCC 49247. These media were freshly prepared and stored at
accurate in vitro susceptibility tests with this drug, quality
<;- 60°C until used (up to 14 days). Serial dilutions of
control (QC) parameters are necessary for the standard QC
cefotaxime or cefuroxime were prepared in one lot of broth
organisms. In the course ofour in vitro studies of cefditoren, we
as control drugs. Three lots of Mueller-Hinton agar (MBA)
have conducted a multilaboratory study to determine the QC parameters for cefditoren when tested by the National Com-
from three different manufacturers were used for disk diffusion tests, along with two lots of 5-J-lg cefditoren disks prepared by
mittee for Clinical Laboratory Standards (NCCLS) methods for
two different manufacturers. The MHA was supplemented with
broth microdilution [3] and disk diffusion [5] susceptibility tests.
5% sheep blood or HTM supplements for testing S. pneumoniae
The design of these studies exceeded the minimum require-
or H. infiuenzae. HTM agar was freshly prepared and used
ments of the NCCLS [4]. Ten North American medical centers participated in each study. Each laboratory performed the broth
within 14 days. Cefotaxime 30-J-lg disks or cefixime 5-J-lg disks served as controls. On each of 10 separate days, all participants
micro dilution and disk diffusion tests as outlined by the NCCLS
inoculated one microdilution tray and three different MBA agar
[3,5]. Broth microdilution trays were prepared to contain serial
plates for each organism tested. This resulted in a total of 600
dilutions of cefditoren with concentrations ranging from 0.004
disk diffusion zone diameter measurements for each QC strain
to 32 mg/L in each of six different lots of cation-adjusted
tested, 600 MIC determinations for each non-fastidious QC
Mueller-Hinton broth (CAMHB) from four different manufacturers for testing non-fastidious strains, and five lots of
strain, 500 MIC determinations for the S. pneumoniae QC strain and H. infiuenzae ATCC 49766, and 300 MIC determinations
CAMHB with 3% lysed horse blood for Streptococcus pneumoniae,
for H. infiuenzae ATCC 49247. Whenever the control drug
five lots with Haemophilus Test Medium (HTM) supplements
results were outside the NCCLS range, the corresponding
Table 2 Distribution of zone diameters for six QC strains" Disk diffusion zone diameters (mm) Organism
No. of
(ATCCNo.)
tests
EC
590
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
14
76
175
195
89
34
7
34
108
188
149
51
23
17
5
597
3
5
21
45
77
120
154
98
44
19
11
576
11
21
75
106
110
122
66
40
8
8
3
36
37
4
2
(25992) SA
590
10
(25923) SP (49619) HI (49247) "Number of times each zone diameter was reported; values in bold are within the proposed QC limits for each strain. EC,Escherichia coli; SA, Staphylococcus
aureus; SP,Streptococcus pneumoniae; HI, Haemophilus influenzae.
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102
Concise Communications
95
Table 3 Recommended QC ranges for cefditoren" and percentage of results in range MICs (mg(L)
Zone diameters (mm)
Organism (ATCC No.)
Range
% in range
Range
% in range
Escherichiacoli (25922) Staphylococcus aureus (29213) Staphylococcus aureus (25923) Streptococcus pneumoniae (49619) Haemophilus influenzae (49247) Haemophilus influenzae (49766)
0.12-1.0 0.25-2.0
100 100
22-28
100
a
NA
20-28 27-35 25-34
NA
0.016-0.12 0.06-0.25 0.004-0.016
100 100 99.6
98.3 98.7 98.3
NR
These QC ranges were approved by the NCClS in June, 1999. NA, not applicable; NR, no recommendations (results off-scale or zones too large).
J.
cefditoren results were omitted from the calculations even
Center, Worcester, MA, USA; M.
though these would not have influenced the cefditoren pro-
General Hospital, Boston, MA, USA; D. Goldman, Children's
posed ranges. Colony counts were performed on the growth
Hospital and Medical Center, Boston, MA, USA; D. Hardy,
control suspension on each test day to ensure appropriate inoculum density.
Ferraro, Massachusetts
University of Rochester Medical Center, Rochester, NY, USA;
J. Hindler,
UCLA Medical Center, Los Angeles, CA, USA; S.
The distribution of MICs and zone diameter results with
Jenkins, Carolinas Medical Center, Charlotte, NC, USA; C.
these control organisms are summarized in Tables 1 and 2.
Knapp, Trek Diagnostic Systems, Westlake, OH, USA; G.
There were no appreciable differences in these distributions
Overturf, University of New Mexico Medical Center, Albu-
when the results were stratified by media lot or laboratories.
querque, NM, USA; M. Pfaller, University ofIowa, Iowa City,
The QC organisms tested, the proposed ranges and the per-
lA, USA; R. Rennie, University of Alberta Hospital, Edmon-
centage of results falling within these ranges are summarized in
ton, Alberta, Canada; M. Saubolle, Good Samaritan Hospital,
Table 3. A four-dilution MIC range was proposed for most
Phoenix AZ, USA; and J. Washington, The Cleveland Clinic,
strains because the mode fell between two adjacent concentra-
Cleveland, OH, USA.
tions that were tested. One laboratory also performed cefditoren agar dilution tests with each QC strain on 15 separate days, and all MIC results fell within these proposed ranges. The MIC QC range for H. influenzae ATCC 49247 was approved by the NCCLS in June 2000; all other QC ranges listed in Tables 1 and 2 for both disk diffusion and dilution tests were approved by the NCCLS subcommittee on antimicrobial susceptibility tests in June 1999.
ACKNOWLEDGMENTS This study was supported by a grant from TAP Pharmaceuticals. Portions of this material have been previously presented at the 39th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, USA, 26-29 September 1999, as Abstract 2324. Participants included: M. Bauman, Providence St Vincent Medical Center, Portland, OR, USA; B.
Brogden-Torres, University of Massachusetts Medical
REFERENCES 1. Felmingham D, Robbins MJ, Ghosh G et al. An in vitro
characterization of cefditoren, a new oral cephalosporin. Drugs cu« Res 1994; 20: 127-47. 2. Jones RN, Biedenbach DJ, Croco MAT, Barrett MS. In vitro evaluation of a novel orally administered cephalosporin (cefditoren) tested against 1249 recent clinical isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae. Diagn Microbial Infect Dis 1998; 31: 573-8. 3. National Committee for Clinical Laboratory Standards. Methods of Exp
dilution antimicrobial susceptibility tests for bacteria that grow aerobically,
4th edn. Approved Standard M7-A4. Wayne, PA: NCCLS, 1997. 4. National Committee for Clinical Laboratory Standards. Development of in vitro susceptibility testing criteria and quality control parameters. Tentative Guideline, M23-T3. Wayne, PA: NCCLS, 1998. 5. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility tests, 6th edn. Approved Standard M2-A6. Wayne, PA: NCCLS, 1997.
© 2001 Copyright by the European Society of Clinical Microbiology and Infectious Diseases, GMI, 7, 88-102