ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Sept. 1990, p. 1858-1861 0066-4804/90/091858-04$02.00/0 Copyright © 1990, American Society for Microbiology
Vol. 34, No. 9
Comparative In Vitro Activities of a New Quinolone, WIN 57273, and Piperacillin plus Tazobactam against Anaerobic Bacteria RICHARD A.
VENEZIA,'*
DIANE M. YOCUM,1 ELLEN M. ROBBIANO,2
Division of Laboratory
Medicine'
AND
ROGER M. ECHOLS2t
and Division of Infectious Diseases,2 Albany Medical Center, Albany, New York 12208
Received 16 January 1990/Accepted 6 July 1990
The in vitro activities of a new quinolone, WIN 57273, and the combination of piperacillin and tazobactam, l-lactamase inhibitor, were compared with those of cefoxitin, ceftizoxime, chloramphenicol, clindamycin, imipenem, metronidazole, and piperacillin for 123 clinical anaerobic isolates. Ceftizoxime and cefoxitin had equivalent activities, while metronidazole was active against gram-negative isolates. In the Bacteroides fragilis group, species other than B. fragiis were the most resistant. The combination of piperacillin with tazobactam in a ratio of 8 to 1 was more effective than piperaciflin against B. fragilis group organisms when the MIC of piperacillin was .64 ,ug/ml. Overall, WIN 57273 (i) and imipenem (ii) were the most active agents, with MICs for 50 and 90% of strains of (i) 0.25 and 0.5 and (ii) 0.125 and 2 ,ug/ml, respectively. a
Treatment of anaerobic infections usually requires a combination of surgical drainage or excision of the infected tissue with effective empiric antimicrobial therapy. Routine susceptibility testing of suspected anaerobic pathogens is not recommended (1, 2, 6). However, the ability to predict the susceptibilities of certain anaerobic bacteria to antimicrobial agents in order to choose suitable therapy has eroded because of several factors. These include prior antibiotic usage, which may select for resistant strains; the increased number of antimicrobial agents available for treating anaerobic infections; and variability in the susceptibility patterns of certain groups of anaerobic bacteria at different medical centers (6, 8). In addition, routine susceptibility testing has been hampered by the difficulty of the procedure and the lack of a standardized method. The establishment of a reference method for broth microdilution determination of MICs of antimicrobial agents by the National Committee for Clinical Laboratory Standards (NCCLS) has provided a uniform procedure for testing anaerobic bacteria (4, 11). Because of the availability of commercial reagents, the NCCLS broth microdilution method can be performed in a clinical laboratory setting and should allow comparison of susceptibility data from various institutions. Accordingly, it is suggested that susceptibility trends for anaerobic bacteria be prepared periodically by clinical laboratories for the institutions they service (6). This becomes more important with the introduction of newer antibiotics for treating anaerobic infections and the lack of predictable activity among current antimicrobial agents. This study evaluated the susceptibilities of clinical anaerobic isolates from our institution to a variety of antimicrobial agents by using the broth microdilution method recommended by the NCCLS. Included with the antimicrobial agents routinely prescribed at our institution were two new agents, a new quinolone antibiotic, WIN 57273, and the combination of piperacillin and a ,-lactamase inhibitor, tazobactam. One hundred twenty-three recent clinical isolates of grampositive and gram-negative anaerobic bacteria were isolated * Corresponding author. t Present address: Miles Pharmaceuticals, West Haven, CT 06516.
from specimens submitted to the Albany Medical Center microbiology laboratory. Species were identified by routine laboratory procedures, which included chromatography, colony morphology, Gram-staining characteristics, and biochemical reactions using the API 20A test system (Analytab Products, Plainview, N.Y.). Clostridium perfringens ATCC 13124, Bacteroides fragilis ATCC 25285, and B. thetaiotaomicron ATCC 29741 were used as quality control strains for the susceptibility tests. All isolates were maintained in sterile skim milk at -70°C. Before being tested, the isolates were subcultured twice onto Wilkins-Chalgren agar (Difco Laboratories, Detroit, Mich.). The standard powders of nine antimicrobial agents were obtained from their manufacturers, dissolved in solvents as recommended, and diluted to a concentration of 1,000 ,g of the active agent per ml or 10-fold higher than the highest concentration used for the dilution series. These solutions were stored at -20°C until used. The antimicrobial agents and their manufacturers were as follows: piperacillin and piperacillin-tazobactam (8:1), Lederle Inc., Pearl River, N.Y.; cefoxitin and imipenem, Merck Sharp & Dohme, Rahway, N.J.; chloramphenicol, Parke-Davis/Warner Lambert, Morris Plains, N.J.; ceftizoxime, Smith Kline & French Laboratories, Philadelphia, Pa.; clindamycin, The Upjohn Co., Kalamazoo, Mich.; metronidazole, G. D. Searle & Co., Skokie, Ill.; WIN 57273, Sterling Winthrop Research Institute, Rensselaer, N.Y. The broth microdilution method was performed in duplicate as described in the procedures outlined by the NCCLS (11). Inocula were prepared from isolates grown in thioglycolate broth without indicators and supplemented with vitamin K (0.5 ,ug/ml) and hemin (5 ,g/ml), and turbidity was visually standardized to a 0.5 McFarland standard. This was then diluted 102 in anaerobe broth (Difco), and a total volume of 100 RIl per well was prepared by adding 50 RI of the inoculum in broth to 50 RI of broth containing the diluted antimicrobial agent. Colony counts were performed on representative isolates to ensure an appropriate inoculum size of approximately 105 CFU per well. The MIC endpoints were determined by visual inspection to be the first dilution of the antimicrobial agent in which there was absence of growth after 48 h of incubation. The activities of the antimicrobial agents are presented as the MIC range and the lowest 1858
NOTES
VOL. 34, 1990
1859
TABLE 1. MICs for quality control strains Strain
MIC
Antimicrobial agent
(ILg/ml) Target valuesb
Broth rangea
Mode
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
0.25-1 0.5-4 2 s0.03-0.125 16 >8 >4 >16 >128 >128 >4
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
4->64 0.5->64 1-16 s0.03->32 -0.06-2 O.5-8 .0.5->128 O.5-128
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
s0.06--8 sO.06-16
Cefoxitin Ceftizoxime
>32 >32 >16 >8 >4 >16 >128 >128 >4
50.06-8 s0.06-16 s0.125-2
>32 >32 >16 >8 >4 >16 >128 >128 >4
s0.06 O0.06 s0.125-0.25 -0.03->32 s0.06 32->32 32 >32 >16 >8 >4 >16 >128 >128 >4
64->64 64->64 2->16 0.5->32 2-8
>64 >64 4 16 4 0.125 8 4 0.25
Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273 Cefoxitin Ceftizoxime
Metronidazole
Piperacillin Piperacillin-tazobactam WIN 57273 Cefoxitin Ceftizoxime
Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273 Clostridium perfringens (10)
2-31 2
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
Chloramphenicol Clindamycin Imipenem
Clostridium difficile (13)
Broth MIC (Lg/ml)a _ _ _ _ 9P0% 50%6
Breakpoint
(~i.g/ml) _ Range _ _ _ (Begkmi)
Cefoxitin Ceftizoxime
Chloramphenicol Clindamycin Imipenem Metronidazole
>32 >32 >16 >8 >4 >16
2->>64 1-8 cs0.03-3.2
sO.06-2 O.5-2 0.125->>64 s4-3:,2 0.125-2
0.06-0.5
sO.125-2
s0.03->32 s0.06 C0.5 4->64 s4-16 0.03-2
sO.03-16
s0.06-0.25 O.5
64 O0.5-8 0.008-0.25
'0.03-1 2-32 1-16 0.125-1
s0.06-4 s0.06-4 1-4 _0.03-4 _0.06 0.25-8
16 16 4 0.25
s0.06 1 8 -554 0.25
32 64 4 4
0.125 1 64 16 0.25 1 sO.06 1 sO.03 s0.06 50.5 16 s4 0.25
s0.06 0.125 64 8 2 0.125 2 64 16 0.5 >64 >64 8 >32 2 2 >128 128 0.5 4 8 2 0.06 sO.06 SO.5
>64 8 1
4 4 2 0.125 0.25
cO.5
SO.5
sO.5
>64 8 0.25
s0.5
0.06
0.125 0.5
0.015
0.5
32 2 1 0.06 >64 >64 >16 >32 8 0.25 16 16 0.5
4 1 2 2 sO.06 8
Continued on following page
NOTES
VOL. 34, 1990
1861
TABLE 2-Continued
g.agent Antimicrobial
Breakpoint
Piperacillin Piperacillin-tazobactam WIN 57273
>128 >128 >4
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
Organism
. .
(no. of isolates)
Clostridium sp. (15)
Brapmi)
Broth MIC
(4g/ml)"
50%o
90o
s0.5 s0.5 s0.004
sO.5 O0.5 s0.004
O0.5 s0.5 s0.004
s0.06->64 8->64 0.5-16 s0.03->16 s0.06-4 s0.03-8 sO.5-16 s0.5-16 64 4 8 4 4 16 8 0.25
a50% and 90%o, MIC for 50 and 90%o of isolates tested, respectively.
nized. Consequently, P-lactam antibiotics have been combined with 1-lactamase inhibitors to overcome this type of enzyme-mediated resistance (3, 10). Tazobactam (YTR-830) is a compound without significant antibacterial activity but is a potent inhibitor of P-lactamases (N.-X. Chin and H. C. Neu, 28th ICAAC, abstr. no. 119, 1988). The nitrocefin assays were quantitated by measuring the time to a positive test. Isolates that give positive results within 30 min were suggestive of bacteria producing greater or more efficient enzyme activity and were, therefore, more likely to be resistant to P-lactam antimicrobial agents. Addition of tazobactam was an advantage for piperacillin against rapidly f-lactamase-producing isolates with high MICs of piperacillin. This appeared to be true in that all nitrocefin-negative isolates were susceptible to piperacillin and addition of tazobactam did not lower the MICs of piperacillin for these isolates. However, resistance to 1-lactam antimicrobial agents could not be correlated with 1-lactamase production alone, suggesting that additional resistance mechanisms exist. Similar results have been reported with other P-lactamase inhibitors and 3-lactamase detection assays (1, 3). This leads us to conclude that 3-lactamase detection should not replace susceptibility testing as a predictor of efficacy of 1-lactam antimicrobial agents. WIN 57273 appeared to have excellent activity for the clinical isolates tested. Addition of tazobactam enhanced the activity of piperacillin for certain isolates, and both agents warrant further testing. LITERATURE CITED 1. Aldidge, K. E., A. Henderberg, D. D. Schiro, and C. V. Sanders. 1988. Susceptibility of Bacteroides fragilis group isolates to broad-spectrum ,-lactams, cindamycin, and metronidazole: rates of resistance, cross-resistance, and importance of 3-lactamase production. Adv. Ther. 5:273-282. 2. Aldrge, K. E., H. M. Wexler, C. V. Sanders, and S. M. FinegoBd. 1990. Comparison of in vitro antibiograms ofBacteroidesfragilis group isolates: differences in resistance rates in two institutions because of differences in susceptibility testing methodology. Antimicrob. Agents Chemother. 34:179-181.
3. Bourgault, A., and F. Lamothe. 1986. In-vitro activity of amoxicillin and ticarcillin in combination with clavulanic acid compared with that of new 1-lactam agents against species of the Bacteroides fragilis group. J. Antimicrob. Chemother. 17: 593-603. 4. Brown, W. J. 1988. National Committee for Clinical Laboratory Standards agar dilution susceptibility testing of anaerobic gramnegative bacteria. Antimicrob. Agents Chemother. 32:385-390. 5. Chu, D. T. W., and P. B. Fernandes. 1989. Structure-activity relationships of the fluoroquinolones. Antimicrob. Agents Chemother. 33:131-135. 6. Cuchural, G. J., Jr., F. P. Tally, N. V. Jacobus, K. Aldridge, T. Cleary, S. M. Finegold, G. Hill, P. Tannini, J. P. O'Keefe, C. Pierson, D. Crook, T. Russo, and D. Hecht. 1988. Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation. Antimicrob. Agents Chemother. 32:717-722. 7. Fernandes, P. B., N. Shipkowitz, R. R. Bower, K. P. Jarvis, J. Weisz, and D. T. W. Chu. 1986. In-vitro and in-vivo potency of five new fluoroquinolones against anaerobic bacteria. J. Antimicrob. Chemother. 18:693-701. 8. Fnegold, S. M., and the National Committee for Clinical Laboratory Standards Working Group on Anaerobic Susceptibility Testig. 1988. Susceptibility testing of anaerobic bacteria. J. Clin. Microbiol. 26:1253-1256. 9. Hooper, D. C., and J. S. Wolfson. 1989. Mode of action of the quinolone antimicrobial agents: review of recent information. Rev. Infect. Dis. 2(Suppl. 5):S902-S911. 10. Lamothe, F., F. Auger, and J.-M. Lacroix. 1984. Effect of clavulanic acid on the activities of ten P-lactam agents against members of the Bacteroidesfragilis group. Antimicrob. Agents Chemother. 25:662-665. 11. National Committee for Cinical Laboratory Standards. 1985. Alternative methods for antimicrobial susceptibility testing of anaerobic bacteria. Proposed guideline M17-P. National Committee for Clinical Laboratory Standards, Villanova, Pa. 12. Neu, H. C., A. Novelli, and N.-X. Chin. 1989. Comparative in vitro activity of a new quinolone, AM-1091. Antimicrob. Agents Chemother. 33:1036-1041. 13. Prabhala, R. H., B. Rao, R. Marshall, M. B. Bansal, and H. Thadepalli. 1984. In vitro susceptibility of anaerobic bacteria to ciprofioxacin (Bay o 9867). Antimicrob. Agents Chemother. 26:785-786.
Vol. 34, No. 9
Comparative In Vitro Activities of a New Quinolone, WIN 57273, and Piperacillin plus Tazobactam against Anaerobic Bacteria RICHARD A.
VENEZIA,'*
DIANE M. YOCUM,1 ELLEN M. ROBBIANO,2
Division of Laboratory
Medicine'
AND
ROGER M. ECHOLS2t
and Division of Infectious Diseases,2 Albany Medical Center, Albany, New York 12208
Received 16 January 1990/Accepted 6 July 1990
The in vitro activities of a new quinolone, WIN 57273, and the combination of piperacillin and tazobactam, l-lactamase inhibitor, were compared with those of cefoxitin, ceftizoxime, chloramphenicol, clindamycin, imipenem, metronidazole, and piperacillin for 123 clinical anaerobic isolates. Ceftizoxime and cefoxitin had equivalent activities, while metronidazole was active against gram-negative isolates. In the Bacteroides fragilis group, species other than B. fragiis were the most resistant. The combination of piperacillin with tazobactam in a ratio of 8 to 1 was more effective than piperaciflin against B. fragilis group organisms when the MIC of piperacillin was .64 ,ug/ml. Overall, WIN 57273 (i) and imipenem (ii) were the most active agents, with MICs for 50 and 90% of strains of (i) 0.25 and 0.5 and (ii) 0.125 and 2 ,ug/ml, respectively. a
Treatment of anaerobic infections usually requires a combination of surgical drainage or excision of the infected tissue with effective empiric antimicrobial therapy. Routine susceptibility testing of suspected anaerobic pathogens is not recommended (1, 2, 6). However, the ability to predict the susceptibilities of certain anaerobic bacteria to antimicrobial agents in order to choose suitable therapy has eroded because of several factors. These include prior antibiotic usage, which may select for resistant strains; the increased number of antimicrobial agents available for treating anaerobic infections; and variability in the susceptibility patterns of certain groups of anaerobic bacteria at different medical centers (6, 8). In addition, routine susceptibility testing has been hampered by the difficulty of the procedure and the lack of a standardized method. The establishment of a reference method for broth microdilution determination of MICs of antimicrobial agents by the National Committee for Clinical Laboratory Standards (NCCLS) has provided a uniform procedure for testing anaerobic bacteria (4, 11). Because of the availability of commercial reagents, the NCCLS broth microdilution method can be performed in a clinical laboratory setting and should allow comparison of susceptibility data from various institutions. Accordingly, it is suggested that susceptibility trends for anaerobic bacteria be prepared periodically by clinical laboratories for the institutions they service (6). This becomes more important with the introduction of newer antibiotics for treating anaerobic infections and the lack of predictable activity among current antimicrobial agents. This study evaluated the susceptibilities of clinical anaerobic isolates from our institution to a variety of antimicrobial agents by using the broth microdilution method recommended by the NCCLS. Included with the antimicrobial agents routinely prescribed at our institution were two new agents, a new quinolone antibiotic, WIN 57273, and the combination of piperacillin and a ,-lactamase inhibitor, tazobactam. One hundred twenty-three recent clinical isolates of grampositive and gram-negative anaerobic bacteria were isolated * Corresponding author. t Present address: Miles Pharmaceuticals, West Haven, CT 06516.
from specimens submitted to the Albany Medical Center microbiology laboratory. Species were identified by routine laboratory procedures, which included chromatography, colony morphology, Gram-staining characteristics, and biochemical reactions using the API 20A test system (Analytab Products, Plainview, N.Y.). Clostridium perfringens ATCC 13124, Bacteroides fragilis ATCC 25285, and B. thetaiotaomicron ATCC 29741 were used as quality control strains for the susceptibility tests. All isolates were maintained in sterile skim milk at -70°C. Before being tested, the isolates were subcultured twice onto Wilkins-Chalgren agar (Difco Laboratories, Detroit, Mich.). The standard powders of nine antimicrobial agents were obtained from their manufacturers, dissolved in solvents as recommended, and diluted to a concentration of 1,000 ,g of the active agent per ml or 10-fold higher than the highest concentration used for the dilution series. These solutions were stored at -20°C until used. The antimicrobial agents and their manufacturers were as follows: piperacillin and piperacillin-tazobactam (8:1), Lederle Inc., Pearl River, N.Y.; cefoxitin and imipenem, Merck Sharp & Dohme, Rahway, N.J.; chloramphenicol, Parke-Davis/Warner Lambert, Morris Plains, N.J.; ceftizoxime, Smith Kline & French Laboratories, Philadelphia, Pa.; clindamycin, The Upjohn Co., Kalamazoo, Mich.; metronidazole, G. D. Searle & Co., Skokie, Ill.; WIN 57273, Sterling Winthrop Research Institute, Rensselaer, N.Y. The broth microdilution method was performed in duplicate as described in the procedures outlined by the NCCLS (11). Inocula were prepared from isolates grown in thioglycolate broth without indicators and supplemented with vitamin K (0.5 ,ug/ml) and hemin (5 ,g/ml), and turbidity was visually standardized to a 0.5 McFarland standard. This was then diluted 102 in anaerobe broth (Difco), and a total volume of 100 RIl per well was prepared by adding 50 RI of the inoculum in broth to 50 RI of broth containing the diluted antimicrobial agent. Colony counts were performed on representative isolates to ensure an appropriate inoculum size of approximately 105 CFU per well. The MIC endpoints were determined by visual inspection to be the first dilution of the antimicrobial agent in which there was absence of growth after 48 h of incubation. The activities of the antimicrobial agents are presented as the MIC range and the lowest 1858
NOTES
VOL. 34, 1990
1859
TABLE 1. MICs for quality control strains Strain
MIC
Antimicrobial agent
(ILg/ml) Target valuesb
Broth rangea
Mode
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
0.25-1 0.5-4 2 s0.03-0.125 16 >8 >4 >16 >128 >128 >4
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
4->64 0.5->64 1-16 s0.03->32 -0.06-2 O.5-8 .0.5->128 O.5-128
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
s0.06--8 sO.06-16
Cefoxitin Ceftizoxime
>32 >32 >16 >8 >4 >16 >128 >128 >4
50.06-8 s0.06-16 s0.125-2
>32 >32 >16 >8 >4 >16 >128 >128 >4
s0.06 O0.06 s0.125-0.25 -0.03->32 s0.06 32->32 32 >32 >16 >8 >4 >16 >128 >128 >4
64->64 64->64 2->16 0.5->32 2-8
>64 >64 4 16 4 0.125 8 4 0.25
Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273 Cefoxitin Ceftizoxime
Metronidazole
Piperacillin Piperacillin-tazobactam WIN 57273 Cefoxitin Ceftizoxime
Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273 Clostridium perfringens (10)
2-31 2
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
Chloramphenicol Clindamycin Imipenem
Clostridium difficile (13)
Broth MIC (Lg/ml)a _ _ _ _ 9P0% 50%6
Breakpoint
(~i.g/ml) _ Range _ _ _ (Begkmi)
Cefoxitin Ceftizoxime
Chloramphenicol Clindamycin Imipenem Metronidazole
>32 >32 >16 >8 >4 >16
2->>64 1-8 cs0.03-3.2
sO.06-2 O.5-2 0.125->>64 s4-3:,2 0.125-2
0.06-0.5
sO.125-2
s0.03->32 s0.06 C0.5 4->64 s4-16 0.03-2
sO.03-16
s0.06-0.25 O.5
64 O0.5-8 0.008-0.25
'0.03-1 2-32 1-16 0.125-1
s0.06-4 s0.06-4 1-4 _0.03-4 _0.06 0.25-8
16 16 4 0.25
s0.06 1 8 -554 0.25
32 64 4 4
0.125 1 64 16 0.25 1 sO.06 1 sO.03 s0.06 50.5 16 s4 0.25
s0.06 0.125 64 8 2 0.125 2 64 16 0.5 >64 >64 8 >32 2 2 >128 128 0.5 4 8 2 0.06 sO.06 SO.5
>64 8 1
4 4 2 0.125 0.25
cO.5
SO.5
sO.5
>64 8 0.25
s0.5
0.06
0.125 0.5
0.015
0.5
32 2 1 0.06 >64 >64 >16 >32 8 0.25 16 16 0.5
4 1 2 2 sO.06 8
Continued on following page
NOTES
VOL. 34, 1990
1861
TABLE 2-Continued
g.agent Antimicrobial
Breakpoint
Piperacillin Piperacillin-tazobactam WIN 57273
>128 >128 >4
Cefoxitin Ceftizoxime Chloramphenicol Clindamycin Imipenem Metronidazole Piperacillin Piperacillin-tazobactam WIN 57273
>32 >32 >16 >8 >4 >16 >128 >128 >4
Organism
. .
(no. of isolates)
Clostridium sp. (15)
Brapmi)
Broth MIC
(4g/ml)"
50%o
90o
s0.5 s0.5 s0.004
sO.5 O0.5 s0.004
O0.5 s0.5 s0.004
s0.06->64 8->64 0.5-16 s0.03->16 s0.06-4 s0.03-8 sO.5-16 s0.5-16 64 4 8 4 4 16 8 0.25
a50% and 90%o, MIC for 50 and 90%o of isolates tested, respectively.
nized. Consequently, P-lactam antibiotics have been combined with 1-lactamase inhibitors to overcome this type of enzyme-mediated resistance (3, 10). Tazobactam (YTR-830) is a compound without significant antibacterial activity but is a potent inhibitor of P-lactamases (N.-X. Chin and H. C. Neu, 28th ICAAC, abstr. no. 119, 1988). The nitrocefin assays were quantitated by measuring the time to a positive test. Isolates that give positive results within 30 min were suggestive of bacteria producing greater or more efficient enzyme activity and were, therefore, more likely to be resistant to P-lactam antimicrobial agents. Addition of tazobactam was an advantage for piperacillin against rapidly f-lactamase-producing isolates with high MICs of piperacillin. This appeared to be true in that all nitrocefin-negative isolates were susceptible to piperacillin and addition of tazobactam did not lower the MICs of piperacillin for these isolates. However, resistance to 1-lactam antimicrobial agents could not be correlated with 1-lactamase production alone, suggesting that additional resistance mechanisms exist. Similar results have been reported with other P-lactamase inhibitors and 3-lactamase detection assays (1, 3). This leads us to conclude that 3-lactamase detection should not replace susceptibility testing as a predictor of efficacy of 1-lactam antimicrobial agents. WIN 57273 appeared to have excellent activity for the clinical isolates tested. Addition of tazobactam enhanced the activity of piperacillin for certain isolates, and both agents warrant further testing. LITERATURE CITED 1. Aldidge, K. E., A. Henderberg, D. D. Schiro, and C. V. Sanders. 1988. Susceptibility of Bacteroides fragilis group isolates to broad-spectrum ,-lactams, cindamycin, and metronidazole: rates of resistance, cross-resistance, and importance of 3-lactamase production. Adv. Ther. 5:273-282. 2. Aldrge, K. E., H. M. Wexler, C. V. Sanders, and S. M. FinegoBd. 1990. Comparison of in vitro antibiograms ofBacteroidesfragilis group isolates: differences in resistance rates in two institutions because of differences in susceptibility testing methodology. Antimicrob. Agents Chemother. 34:179-181.
3. Bourgault, A., and F. Lamothe. 1986. In-vitro activity of amoxicillin and ticarcillin in combination with clavulanic acid compared with that of new 1-lactam agents against species of the Bacteroides fragilis group. J. Antimicrob. Chemother. 17: 593-603. 4. Brown, W. J. 1988. National Committee for Clinical Laboratory Standards agar dilution susceptibility testing of anaerobic gramnegative bacteria. Antimicrob. Agents Chemother. 32:385-390. 5. Chu, D. T. W., and P. B. Fernandes. 1989. Structure-activity relationships of the fluoroquinolones. Antimicrob. Agents Chemother. 33:131-135. 6. Cuchural, G. J., Jr., F. P. Tally, N. V. Jacobus, K. Aldridge, T. Cleary, S. M. Finegold, G. Hill, P. Tannini, J. P. O'Keefe, C. Pierson, D. Crook, T. Russo, and D. Hecht. 1988. Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation. Antimicrob. Agents Chemother. 32:717-722. 7. Fernandes, P. B., N. Shipkowitz, R. R. Bower, K. P. Jarvis, J. Weisz, and D. T. W. Chu. 1986. In-vitro and in-vivo potency of five new fluoroquinolones against anaerobic bacteria. J. Antimicrob. Chemother. 18:693-701. 8. Fnegold, S. M., and the National Committee for Clinical Laboratory Standards Working Group on Anaerobic Susceptibility Testig. 1988. Susceptibility testing of anaerobic bacteria. J. Clin. Microbiol. 26:1253-1256. 9. Hooper, D. C., and J. S. Wolfson. 1989. Mode of action of the quinolone antimicrobial agents: review of recent information. Rev. Infect. Dis. 2(Suppl. 5):S902-S911. 10. Lamothe, F., F. Auger, and J.-M. Lacroix. 1984. Effect of clavulanic acid on the activities of ten P-lactam agents against members of the Bacteroidesfragilis group. Antimicrob. Agents Chemother. 25:662-665. 11. National Committee for Cinical Laboratory Standards. 1985. Alternative methods for antimicrobial susceptibility testing of anaerobic bacteria. Proposed guideline M17-P. National Committee for Clinical Laboratory Standards, Villanova, Pa. 12. Neu, H. C., A. Novelli, and N.-X. Chin. 1989. Comparative in vitro activity of a new quinolone, AM-1091. Antimicrob. Agents Chemother. 33:1036-1041. 13. Prabhala, R. H., B. Rao, R. Marshall, M. B. Bansal, and H. Thadepalli. 1984. In vitro susceptibility of anaerobic bacteria to ciprofioxacin (Bay o 9867). Antimicrob. Agents Chemother. 26:785-786.
