Journal of Antimicrobial Chemotherapy (1991) 27, 243-252
Correspondence In-vitro activity of four penidUin/fMactamase inhibitor combinations against cefoxitinsnsceptible and cefoxitin-resistant Bacteroides fragilis isolates
Table I. In-vitro activity ofcefoxitin and four penicillins, with and without a /Mactamase inhibitor, against 27 cefoxitin-susceptible and 27 cefoxitin-resistant B. fragilis isolates
Antimicrobial agent(s) Amoxicillin Amoxicillin + clavulanic acid (2:1) Ampicillin Ampicillin + sulbactam (2:1) Ticarcillin Ticarcillin + clavulanic acid (2-0 mg/1) Piperacillin Piperacillin + tazobactam (8:1) Cefoxitin
Cefoxitin-susceptible mean M I C MIC,, 20-7
0-4 24-8
0-4 18-7
10 17-7
4-8 2-5
32 0-5 64 20 32 2-0 32 4-0 16
Cefoxitin-resistant mean M I C MIC* 64-0
2-8 691 5-7
>64 8-0 >64 16
112-6
> 128
4-3 990
> 128
16-8 78-6
> 128
32 16
"Geometric mean MICs (mg/1). For purposes of these calculations, MICs greater than the highest concentration tested were assumed to be at the next highest concentration. For the drug combinations, MICs are expressed as the concentration of the active penicillin in the presence of the designated /Mactamase inhibitor. 243
Downloaded from http://jac.oxfordjournals.org/ at University of Chicago on July 4, 2015
Sir, Most members of the species Bacteroides fragilis are capable of producing /Mactamase enzymes which inactivate many cephalosporins and penicillins. Those /Mactam compounds should be more effective if they are combined with /Mactamase inhibitors such as clavulanic acid, sulbactam or tazobactam (YTR-830). The in-vitro activity of several /Mactam//?lactamase inhibitor combinations against the B. fragilis group has been doccumented by others (Appelbaum et al, 1986; Barry, Jones & Packer, 1986; Bourgault & Lamothe, 1988; Fuchs et ai, 1988; Moosdeen, Williams & Yanabe, 1988; Jones et al, 1989). The majority of published studies involve tests with strains that are predominantly susceptible to cefoxitin. Aldridge, Henderberg & Sanders (1990) recently evaluated several /Mactamase inhibitor combinations against a collection of cefoxitin-resistant B. fragilis isolates, but cefoxitinsusceptible strains were not tested at the same time. Among the B. fragilis group, resistance to cefoxitin is becoming increasingly common in
some medical centres and that causes important clinical and therapeutic problems (Bieluch et al., 1987). Cefoxitin-resistant strains have been shown to be less susceptible to other /Mactam antibiotics (Jones et al, 1987; Jones & Barry, 1988). The diminished susceptibility to cefoxitin and to a wide range of other /Mactams might be due to the presence of an altered penicillin binding protein or to the presence of a cell membrane permeability barrier (Piddock & Wise, 1987). A /Mactamase-associated resistance to cefoxitin has also been described (Cuchural et al, 1986). We have recently had the opportunity to test four different penicillins (amoxycillin, ampicillin, ticarcillin, and piperacillin) alone and in combination with one of three /Mactamase inhibitors (clavulanic acid, sulbactam or tazobactam). Clinical isolates of cefoxitin-resistant and cefoxitin-susceptible B. fragilis strains (27 of each) were evaluated using the broth microdilution procedure that is recommended by the National Committee for Clinical Laboratory Standards (NCCLS, 1989). The inoculum was approximately 1 x 106 cfu/ml, the drugs were diluted in a broth version of Wilkins-Chalgren medium and MICs were recorded after 48 h of incubation in an anaerobic jar. Doubling dilutions of ticarcillin were prepared with clavulanic acid at a concentration of 2-0 mg/1.
Correspondence
244
'The Clinical Microbiology Institute PO Box 947 Tualatin. Oregon 97062; b St. Vincent Hospital and Medical Center, Portland. Oregon 97225. USA
References Aldridge, K. E., Henderberg, A. & Sanders, C. V. (1990). Enhanced antimicrobial activity of old and new /Mactams against cefoxitin-resistant Bacieroides fragilis group isolates by /Mactamase inhibitors. Journal of Antimicrobial Chemotherapy 25, 873-5. Appelbaum, P. C , Jacobs, M. R., Spangler, S. K. & Yamabe, S. (1986). Comparative activity of /?lactamase inhibitors YTR 830, clavulanate, and sulbactam combined with /Mactams against /)-
lactamase-producing anaerobes. Antimicrobial Agents and Chemotherapy 30, 789-91. Barry, A. L., Jones, R. N. & Packer, R. R. (1986). In vitro susceptibility of the Bacteroides fragilis group to cefoperazone, ampicillin, ticarcillin and amoxycillin combined with /J-lactamase inhibitors. Journal of Antimicrobial Chemotherapy 17, 125-7. Bieluch, V. C , Cuchural, G. J., Snydman, D. R., Gorboch, S. L. & Tally, F. P. (1987). Clinical importance of cefoxitin-resistant Bacteroides fragilis isolates. Diagnostic Microbiology and Infectious Disease 7, 119-26. Bourgault, A.-M. & Lamothe, F. (1986). In vitro activity of amoxycillin and ticarcillin in combination with clavulanic acid compared with that of new /Mactam agents against species of the Bacieroides fragilis group. Journal of Antimicrobial Chemotherapy 17, 593-603. Cuchural, G. J., Tally, F. P., Storey, J. R. & Malamy, M. H. (1986). Transfer of /Mactamaseassociated cefoxitin resistance in Bacieroides fragilis. Antimicrobial Agents and Chemotherapy 29, 918-20. Fuchs, P. C , Jones, R. N., Barry, A. L., Allen, S. D., Aldridge, K. E., Gerlach, E. H. et al (1988). Effects of clavulanic acid on the susceptibility of clinical anaerobic bacteria to ticarcillin: a multicenter study. Diagnostic Microbiology and Infectious Disease 9, 47-50. Jones, R. N. & Barry, A. L. (1988). In vitro activity of ampicillin/sulbactam against cefoxitin-resistant anaerobic bacteria. Journal of Antimicrobial Chemotherapy 21, 135-8. Jones, R. N., Barry, A. L., Aldridge, K. E. & Gerlach, E. H. (1987). Comparative antimicrobial activity of aminothiazolyl methoxyimino cephalosporins against anaerobic bacteria, including 100 cefoxitin-resistant isolates. Diagnostic Microbiology and Infectious Disease 8, 157-63. Jones, R. N., Pfaller, M. A., Fuchs, P. G , Aldridge, K., Allen, S. D. & Gerlach, E. H. (1989). Piperacillin/tazobactam (YTR 830) combination: comparative antimicrobial activity against 5889 recent aerobic clinical isolates and 60 Bacteroides fragilis group strains. Diagnostic Microbiology and Infectious Disease 12, 489-94. Moosdeen, F., Williams, J. D. & Yanabe, S. (1988). Antibacterial characteristics of YTR 830, a sulfone /Mactamase inhibitor, compared with those of clavulanic acid and sulbactam. Antimicrobial Agents and Chemotherapy 32, 925-7. National Committee for Clinical Laboratory Standards (1989). Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria. Tentative Standard MI1-T2, 2nd edn. National Committee for Clinical Laboratory Standards, Villanova, PA. Piddock, L. J. V. & Wise, R. (1987). Cefoxitin resistance in Bacteroides species: evidence indicating two mechanisms causing decreased susceptibility. Journal of Antimicrobial Chemotherapy 19, 161-70.
Downloaded from http://jac.oxfordjournals.org/ at University of Chicago on July 4, 2015
Amoxycillin-clavulanic acid and ampicillinsulbactam combinations were diluted as 2:1 ratios. Piperacillin and tazobactam were combined in an 8:1 ratio. Table I summarizes the results of this exercise. For the four penicillins alone, geometric mean MICs ranged from 17-7 to 24-8 mg/1 when cefoxitin-susceptible strains were being tested. However, for cefoxitin-resistant strains, geometric mean MICs ranged from 64 to 112 mg/1. /Mactamase inhibitors reduced the geometric mean MICs to 0-4-16-8 mg/1. Cefoxitin-susceptible strains were very susceptible to all four drug combinations, i.e. MIQpS were 0-5-40 mg/1. Cefoxitin-resistant strains were less susceptible (MlCy 8-0-32 mg/I), but both types of strains were inhibited by concentrations that could be achieved in the blood of treated patients. Jones & Barry (1988) reported that resistance of the B. fragilis group to cefoxitin was not influenced by the addition of clavulanic acid and thus excess /Mactamase production did not explain the decreased susceptibility to cefoxitin. A non-/?-lactamase associated resistance mechanism would explain the observations presented in the current report. /S-lactamase inhibitors influenced susceptibility to the penicillins among the two types of microorganisms by similar orders of magnitude (see Table I), but cefoxitin-resistant strains were innately more resistant to all four penicillins. In spite of minor differences, all four combinations are effective in vitro against cefoxitin-resistant B. fragilis as well as cefoxitin-susceptible strains. Whether that in-vitro activity accurately predicts clinical utility in treating infections due to cefoxitin-resistant anaerobes remains to be seen. ARTHUR L. BARRY1 PETER C. FUCHS"
Correspondence In-vitro activity of four penidUin/fMactamase inhibitor combinations against cefoxitinsnsceptible and cefoxitin-resistant Bacteroides fragilis isolates
Table I. In-vitro activity ofcefoxitin and four penicillins, with and without a /Mactamase inhibitor, against 27 cefoxitin-susceptible and 27 cefoxitin-resistant B. fragilis isolates
Antimicrobial agent(s) Amoxicillin Amoxicillin + clavulanic acid (2:1) Ampicillin Ampicillin + sulbactam (2:1) Ticarcillin Ticarcillin + clavulanic acid (2-0 mg/1) Piperacillin Piperacillin + tazobactam (8:1) Cefoxitin
Cefoxitin-susceptible mean M I C MIC,, 20-7
0-4 24-8
0-4 18-7
10 17-7
4-8 2-5
32 0-5 64 20 32 2-0 32 4-0 16
Cefoxitin-resistant mean M I C MIC* 64-0
2-8 691 5-7
>64 8-0 >64 16
112-6
> 128
4-3 990
> 128
16-8 78-6
> 128
32 16
"Geometric mean MICs (mg/1). For purposes of these calculations, MICs greater than the highest concentration tested were assumed to be at the next highest concentration. For the drug combinations, MICs are expressed as the concentration of the active penicillin in the presence of the designated /Mactamase inhibitor. 243
Downloaded from http://jac.oxfordjournals.org/ at University of Chicago on July 4, 2015
Sir, Most members of the species Bacteroides fragilis are capable of producing /Mactamase enzymes which inactivate many cephalosporins and penicillins. Those /Mactam compounds should be more effective if they are combined with /Mactamase inhibitors such as clavulanic acid, sulbactam or tazobactam (YTR-830). The in-vitro activity of several /Mactam//?lactamase inhibitor combinations against the B. fragilis group has been doccumented by others (Appelbaum et al, 1986; Barry, Jones & Packer, 1986; Bourgault & Lamothe, 1988; Fuchs et ai, 1988; Moosdeen, Williams & Yanabe, 1988; Jones et al, 1989). The majority of published studies involve tests with strains that are predominantly susceptible to cefoxitin. Aldridge, Henderberg & Sanders (1990) recently evaluated several /Mactamase inhibitor combinations against a collection of cefoxitin-resistant B. fragilis isolates, but cefoxitinsusceptible strains were not tested at the same time. Among the B. fragilis group, resistance to cefoxitin is becoming increasingly common in
some medical centres and that causes important clinical and therapeutic problems (Bieluch et al., 1987). Cefoxitin-resistant strains have been shown to be less susceptible to other /Mactam antibiotics (Jones et al, 1987; Jones & Barry, 1988). The diminished susceptibility to cefoxitin and to a wide range of other /Mactams might be due to the presence of an altered penicillin binding protein or to the presence of a cell membrane permeability barrier (Piddock & Wise, 1987). A /Mactamase-associated resistance to cefoxitin has also been described (Cuchural et al, 1986). We have recently had the opportunity to test four different penicillins (amoxycillin, ampicillin, ticarcillin, and piperacillin) alone and in combination with one of three /Mactamase inhibitors (clavulanic acid, sulbactam or tazobactam). Clinical isolates of cefoxitin-resistant and cefoxitin-susceptible B. fragilis strains (27 of each) were evaluated using the broth microdilution procedure that is recommended by the National Committee for Clinical Laboratory Standards (NCCLS, 1989). The inoculum was approximately 1 x 106 cfu/ml, the drugs were diluted in a broth version of Wilkins-Chalgren medium and MICs were recorded after 48 h of incubation in an anaerobic jar. Doubling dilutions of ticarcillin were prepared with clavulanic acid at a concentration of 2-0 mg/1.
Correspondence
244
'The Clinical Microbiology Institute PO Box 947 Tualatin. Oregon 97062; b St. Vincent Hospital and Medical Center, Portland. Oregon 97225. USA
References Aldridge, K. E., Henderberg, A. & Sanders, C. V. (1990). Enhanced antimicrobial activity of old and new /Mactams against cefoxitin-resistant Bacieroides fragilis group isolates by /Mactamase inhibitors. Journal of Antimicrobial Chemotherapy 25, 873-5. Appelbaum, P. C , Jacobs, M. R., Spangler, S. K. & Yamabe, S. (1986). Comparative activity of /?lactamase inhibitors YTR 830, clavulanate, and sulbactam combined with /Mactams against /)-
lactamase-producing anaerobes. Antimicrobial Agents and Chemotherapy 30, 789-91. Barry, A. L., Jones, R. N. & Packer, R. R. (1986). In vitro susceptibility of the Bacteroides fragilis group to cefoperazone, ampicillin, ticarcillin and amoxycillin combined with /J-lactamase inhibitors. Journal of Antimicrobial Chemotherapy 17, 125-7. Bieluch, V. C , Cuchural, G. J., Snydman, D. R., Gorboch, S. L. & Tally, F. P. (1987). Clinical importance of cefoxitin-resistant Bacteroides fragilis isolates. Diagnostic Microbiology and Infectious Disease 7, 119-26. Bourgault, A.-M. & Lamothe, F. (1986). In vitro activity of amoxycillin and ticarcillin in combination with clavulanic acid compared with that of new /Mactam agents against species of the Bacieroides fragilis group. Journal of Antimicrobial Chemotherapy 17, 593-603. Cuchural, G. J., Tally, F. P., Storey, J. R. & Malamy, M. H. (1986). Transfer of /Mactamaseassociated cefoxitin resistance in Bacieroides fragilis. Antimicrobial Agents and Chemotherapy 29, 918-20. Fuchs, P. C , Jones, R. N., Barry, A. L., Allen, S. D., Aldridge, K. E., Gerlach, E. H. et al (1988). Effects of clavulanic acid on the susceptibility of clinical anaerobic bacteria to ticarcillin: a multicenter study. Diagnostic Microbiology and Infectious Disease 9, 47-50. Jones, R. N. & Barry, A. L. (1988). In vitro activity of ampicillin/sulbactam against cefoxitin-resistant anaerobic bacteria. Journal of Antimicrobial Chemotherapy 21, 135-8. Jones, R. N., Barry, A. L., Aldridge, K. E. & Gerlach, E. H. (1987). Comparative antimicrobial activity of aminothiazolyl methoxyimino cephalosporins against anaerobic bacteria, including 100 cefoxitin-resistant isolates. Diagnostic Microbiology and Infectious Disease 8, 157-63. Jones, R. N., Pfaller, M. A., Fuchs, P. G , Aldridge, K., Allen, S. D. & Gerlach, E. H. (1989). Piperacillin/tazobactam (YTR 830) combination: comparative antimicrobial activity against 5889 recent aerobic clinical isolates and 60 Bacteroides fragilis group strains. Diagnostic Microbiology and Infectious Disease 12, 489-94. Moosdeen, F., Williams, J. D. & Yanabe, S. (1988). Antibacterial characteristics of YTR 830, a sulfone /Mactamase inhibitor, compared with those of clavulanic acid and sulbactam. Antimicrobial Agents and Chemotherapy 32, 925-7. National Committee for Clinical Laboratory Standards (1989). Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria. Tentative Standard MI1-T2, 2nd edn. National Committee for Clinical Laboratory Standards, Villanova, PA. Piddock, L. J. V. & Wise, R. (1987). Cefoxitin resistance in Bacteroides species: evidence indicating two mechanisms causing decreased susceptibility. Journal of Antimicrobial Chemotherapy 19, 161-70.
Downloaded from http://jac.oxfordjournals.org/ at University of Chicago on July 4, 2015
Amoxycillin-clavulanic acid and ampicillinsulbactam combinations were diluted as 2:1 ratios. Piperacillin and tazobactam were combined in an 8:1 ratio. Table I summarizes the results of this exercise. For the four penicillins alone, geometric mean MICs ranged from 17-7 to 24-8 mg/1 when cefoxitin-susceptible strains were being tested. However, for cefoxitin-resistant strains, geometric mean MICs ranged from 64 to 112 mg/1. /Mactamase inhibitors reduced the geometric mean MICs to 0-4-16-8 mg/1. Cefoxitin-susceptible strains were very susceptible to all four drug combinations, i.e. MIQpS were 0-5-40 mg/1. Cefoxitin-resistant strains were less susceptible (MlCy 8-0-32 mg/I), but both types of strains were inhibited by concentrations that could be achieved in the blood of treated patients. Jones & Barry (1988) reported that resistance of the B. fragilis group to cefoxitin was not influenced by the addition of clavulanic acid and thus excess /Mactamase production did not explain the decreased susceptibility to cefoxitin. A non-/?-lactamase associated resistance mechanism would explain the observations presented in the current report. /S-lactamase inhibitors influenced susceptibility to the penicillins among the two types of microorganisms by similar orders of magnitude (see Table I), but cefoxitin-resistant strains were innately more resistant to all four penicillins. In spite of minor differences, all four combinations are effective in vitro against cefoxitin-resistant B. fragilis as well as cefoxitin-susceptible strains. Whether that in-vitro activity accurately predicts clinical utility in treating infections due to cefoxitin-resistant anaerobes remains to be seen. ARTHUR L. BARRY1 PETER C. FUCHS"
