S K Spangler

Beta-lactamase production and susceptibilities to amoxicillin, amoxicillin-clavulanate, ticarcillin, ticarcillin-clavulanate, cefoxitin, imipenem, and metronidazole of 320 non-Bacteroides fragilis Bacteroides isolates and 129 fusobacteria from 28 U.S. centers.

beta-Lactamase production (nitrocefin disk method) and agar dilution susceptibility of amoxicillin, amoxicillin-clavulanate, ticarcillin, ticarcillin-clavulanate, cefoxitin, imipenem, and metronidazole were determined for 320 Bacteroides species (not Bacteroides fragilis group) and 129 fusobacteria from 28 U.S. centers. Overall, 64.7% of Bacteroides species and 41.1% of fusobacteria were beta-lactamase positive. Among the Bacteroides species, positivity rates were highest for B. bivius (85.0%), followed by B. splanchnicus (83.3%), B. eggerthii (77.8%), and B. oralis (77.1%); 54.5% of black-pigmented Bacteroides species were beta-lactamase positive. Among the fusobacteria, Fusobacterium mortiferum showed the highest rate of beta-lactamase positivity (76.9%). MICs of amoxicillin (128 micrograms/ml) and ticarcillin (64 micrograms/ml) for 90% of all beta-lactamase-positive strains were reduced to 4 and 2 micrograms/ml, respectively, with the addition of clavulanate. MICs of amoxicillin and ticarcillin for 90% of all beta-lactamase-negative strains were 1 and 4 micrograms/ml, respectively, and greater than or equal to 98.4% of the strains were susceptible to the beta-lactams tested. Of the beta-lactamase-producing strains, 45.9% were susceptible to amoxicillin at less than or equal to 4 micrograms/ml and 93.4% were susceptible to ticarcillin at less than or equal to 64 micrograms/ml; the addition of clavulanate raised the rates to 90.4 and 100%, respectively. All strains were susceptible to cefoxitin, imipenem, and metronidazole. The activity of amoxicillin against 29 beta-lactamase-producing strains (10 Bacteroides species and 19 fusobacteria) was not enhanced by the addition of clavulanate; however, 82.7% of these strains were susceptible to amoxicillin, and all were susceptible to ticarcillin. Although beta-lactamase positivity is on the increase in non-B. fragilis group Bacteroides species and fusobacteria, amoxicillin-clavulanate, ticarcillin, cefoxitin, imipenem, and metronidazole should be suitable for the treatment of infections with these strains. The addition of clavulanate does not appreciably improve the efficacy of ticarcillin against these organisms.

Activity of CP 99,219 compared with those of ciprofloxacin, grepafloxacin, metronidazole, cefoxitin, piperacillin, and piperacillin-tazobactam against 489 anaerobes.

Agar dilution was used to compare the in vitro activity of CP 99,219 with those of ciprofloxacin, grepafloxacin, metronidazole, cefoxitin, piperacillin, and piperacillin-tazobactam against 489 anaerobes. CP 99,219 yielded a MIC for 50% of the strains tested (MIC50) of 0.25 micrograms/ml and a MIC90 of 1.0 microgram/ml, with 99.6% of the strains susceptible at a breakpoint of 2.0 micrograms/ml. Ciprofloxacin and grepafloxacin were less active (MIC50, 4.0 micrograms/ml; MIC90, 32.0 micrograms/ml and 2.0 and 16.0 micrograms/ml, respectively). Metronidazole was active against all gram-negative rods (MIC90, 4.0 micrograms/ml), but 31% of the gram-positive anaerobes were resistant at > 8.0 micrograms/ml. Cefoxitin was active against 84% of all strains at < or = 16.0 micrograms/ml, with a MIC50 of 4.0 micrograms/ml and a MIC90 of 32.0 micrograms/ml. Tazobactam enhanced the activity of piperacillin against > 95% of the beta-lactamase-producing gram-negative anaerobic rods (MIC90, 16.0 micrograms/ml).

Susceptibilities of penicillin-susceptible and -resistant strains of Streptococcus pneumoniae to RP 59500, vancomycin, erythromycin, PD 131628, sparfloxacin, temafloxacin, win 57273, ofloxacin, and ciprofloxacin.

The MICs of four new quinolones, sparfloxacin (AT-4140, CI-978), PD 131628 (the active form of the prodrug CI-990), temafloxacin, and Win 57273, compared with those of ciprofloxacin and ofloxacin were tested against 53 penicillin-susceptible, 35 penicillin intermediate-resistant, and 51 penicillin-resistant pneumococci. Susceptibility to RP 59500, a new streptogramin, was also tested and compared with those to the quinolones, erythromycin, and vancomycin. All MICs were determined by a standardized agar dilution method by using Mueller-Hinton agar supplemented with sheep blood. Quinolone, vancomycin, and RP 59500 susceptibilities were not affected by susceptibility or resistance to penicillin. For Win 57273, the MICs for 50% (MIC50) and 90% (MIC90) of strains tested were 0.015 and 0.03 micrograms/ml, respectively. MIC50S of both sparfloxacin and PD 131628 were 0.25 micrograms/ml, and MIC90S were 0.5 micrograms/ml. The MIC50 of temafloxacin was 0.5 micrograms/ml, and the MIC90 was 1.0 micrograms/ml. By comparison, ofloxacin and ciprofloxacin both yielded MIC50S of 1.0 micrograms/ml and MIC90s of 2.0 micrograms/ml. RP 59500 yielded an MIC50 of 0.5 microgram/ml and an MIC90 of 1.0 microgram/ml and was only 1 doubling dilution less active against 17 erythromycin-resistant strains. Vancomycin was active against all strains (MIC50, 0.25 microgram/ml; MIC90, 0.5 microgram/ml). All four experimental quinolones as well as RP 59500 show promise for therapy of infections with penicillin-resistant and -susceptible pneumococci.

Susceptibilities of 177 penicillin-susceptible and -resistant pneumococci to FK 037, cefpirome, cefepime, ceftriaxone, cefotaxime, ceftazidime, imipenem, biapenem, meropenem, and vancomycin.

MICs of six extended-spectrum cephalosporins (cefotaxime, ceftriaxone, ceftazidime, FK 037, cefpirome, cefepime), three carbapenems (imipenem, meropenem, biapenem), and vancomycin for 49 penicillin-susceptible (S), 77 penicillin intermediate-resistant (I), and 51 penicillin-resistant (R) pneumococci were determined by agar dilution. Compared with ceftazidime (MICs for 90% of strains tested [MIC90s] of 2.0, 16.0, and 16.0 micrograms/ml for S, I, and R strains, respectively), all other cephalosporins yielded lower MICs (MIC90s of 0.06 to 0.125, 0.5 to 1.0, and 1.0 to 2.0 micrograms/ml against S, I, and R strains, respectively). All three carbapenems were very active, with MIC90s, even for R strains, of < or = 1.0 micrograms/ml. All strains were susceptible to vancomycin (MIC90 of 0.5 micrograms/ml).

Comparative activity of beta-lactamase inhibitors YTR 830, clavulanate, and sulbactam combined with beta-lactams against beta-lactamase-producing anaerobes.

The in vitro activities of the beta-lactamase inhibitors YTR 830, clavulanate, and sulbactam combined with six beta-lactams against 88 beta-lactamase-producing anaerobes were determined. When combined with the beta-lactams, the three beta-lactamase inhibitors showed no synergy against the 10 Bacteroides fragilis homology group II strains. When the beta-lactams were combined with the inhibitors, their geometric mean MICs against the remaining 78 strains were reduced from 4.2 to 150.2 micrograms/ml to 0.2 to 12.9 micrograms/ml. The activity of the beta-lactams combined with the beta-lactamase inhibitors was significantly greater than that of the beta-lactams alone against all groups except B. fragilis homology group II, with 76 to 100% of the strains susceptible to ampicillin plus inhibitor and greater than or equal to 90% susceptible to the other combinations.

In vitro susceptibilities of 185 penicillin-susceptible and -resistant pneumococci to WY-49605 (SUN/SY 5555), a new oral penem, compared with those to penicillin G, amoxicillin, amoxicillin-clavulanate, cefixime, cefaclor, cefpodoxime, cefuroxime, and cefdinir.

In vitro susceptibility of 185 penicillin-susceptible and -resistant pneumococci to WY-49605, a new oral penem, was compared with susceptibility to penicillin G, amoxicillin with and without clavulanate, cefixime, cefaclor, cefpodoxime, cefuroxime, and cefdinir. WY-49605 yielded MICs for 50 and 90% of the strains tested (MIC50 and MIC90, respectively) of 0.03 and 0.06, 0.125 and 0.5, and 0.5 and 1.0 micrograms/ml, respectively, against penicillin-susceptible, intermediately resistant, and fully resistant strains, respectively. The MIC50 and MIC90 for both amoxicillin and amoxicillin-clavulanate were identical and approximately 1 doubling dilution higher than those for WY-49605 and were < or = 0.06 and 0.125, 0.25 and 1.0, and 1.0 and 1.0 micrograms/ml, respectively. Cephalosporin MIC90s were all significantly higher than those of the latter three compounds for intermediately resistant and fully resistant strains.

Susceptibilities of 394 Bacteroides fragilis, non-B. fragilis group Bacteroides species, and Fusobacterium species to newer antimicrobial agents.

The susceptibilities of 374 selected beta-lactamase-producing gram-negative anaerobes (including 22 cefoxitin-resistant strains and 36 strains refractory to the enhancing effect of beta-lactamase inhibitors) and 20 beta-lactamase-negative strains were tested by agar dilution against selected new agents. The organisms included 217 Bacteroides fragilis group strains, 137 non-B. fragilis group Bacteroides spp., and 40 fusobacteria. All strains were susceptible to piperacillin-tazobactam, imipenem, and meropenem. For the B. fragilis group, 96% were susceptible to ampicillin-sulbactam, 95% were susceptible to amoxicillin-clavulanate and cefoperazone-sulbactam, 94% were susceptible to tosufloxacin, 91% were susceptible to cefoxitin, 88% were susceptible to trospectomycin, and 73% were susceptible to cefotetan. For the beta-lactamase-positive non-B. fragilis group Bacteroides spp., greater than or equal to 94% were susceptible to cefoxitin, amoxicillin-clavulanate, ampicillin-sulbactam, cefoperazone-sulbactam, and trospectomycin, 90% were susceptible to cefotetan, and 85% were susceptible to tosufloxacin (the most resistant strains were B. bivius and B. disiens). For the beta-lactamase-positive fusobacteria, greater than or equal to 97% were susceptible to amoxicillin-clavulanate, ampicillin-sulbactam, cefoperazone-sulbactam, trospectomycin, and cefoxitin, 90% were susceptible to cefotetan, and 89% were susceptible to tosufloxacin. All agents showed excellent activity against beta-lactamase-negative strains (for trospectomycin, 95% were susceptible; for all other drugs, 100% were susceptible). Overall, both carbapenems and piperacillin-tazobactam were most active. Amoxicillin-clavulanate, ampicillin-sulbactam, and cefoperazone-sulbactam lacked activity against some cefoxitin-resistant B. fragilis group strains but had excellent activity against other organisms. Tosufloxacin, a new quinolone, had very good activity against B. fragilis group strains (94% susceptible), good activity against other beta-lactamase-positive strains (less than or equal 85% susceptible), and excellent activity against beta-lactamase-negative strains (100% susceptible; MIC for 90% of strains, 0.5 microgram/ml). Trospectomycin was active against >90% of all strains except for B. fragilis group strains (88% susceptible; MIC for 90% of strains, 32 microgram/ml). Clinical studies are required to delineate the role of newer agents in the therapy of anaerobic infections.

Characterization of beta-lactamases from non-Bacteroides fragilis group Bacteroides spp. belonging to seven species and their role in beta-lactam resistance.

Twelve beta-lactamase-positive non-Bacteroides fragilis group Bacteroides spp. belonging to seven different species were examined by MIC determination and enzyme characterization. MICs of most beta-lactams except cefoxitin, cefotetan, imipenem, and meropenem were relatively high or very high. All enzymes hydrolyzed cephaloridine (Vmax, 100%; Km, 12 to 70 microM), cephalothin (Vmax, 25 to 826%; Km, 8 to 143 microM), cefamandole (Vmax, 13 to 158%; Km, 17 to 170 microM), and cefuroxime (hydrolysis rate, 19 to 98%), and 11 of 12 hydrolyzed cefotaxime (Vmax, 26 to 145%; Km, 13 to 127 microM); no hydrolysis of cefoxitin or moxalactam was observed. Penicillins were hydrolyzed at lower rates, with Vmax values less than or equal to 20% of that obtained with cephaloridine. Addition of clavulanate, sulbactam, or tazobactam led to a 4- to 2,048-fold lowering of MICs of penicillins as well as cephalosporins. All enzymes were inhibited by clavulanate (50% inhibitory concentration [IC50], 0.01 to 1.8 microM), sulbactam (IC50, 0.02 to 1.9 microM), tazobactam (IC50, 0.001 to 0.9 microM), cefoxitin (IC50, 0.002 to 0.35 microM), and moxalactam (IC50, 0.03 to 6.6 microM). No enzymes were inhibited by 100 microM EDTA or p-chloromercuribenzoic acid; an enzyme of one strain of B. loescheii was inhibited by 100 microM cloxacillin (IC50, 2.35 microM). Ten enzymes had optimal activity at pH 5.0 to 6.0, and two had optimal activity at pH 8.0. Isoelectric focusing revealed pIs between 4.2 and 5.6. These enzymes seem to belong to a previously unclassified group of beta-lactamases, related (but not identical) to beta-lactamases of the B. fragilis group. Images

Beta-lactamase production and susceptibility of US and European anaerobic gram-negative bacilli to beta-lactams and other agents

The susceptibility of 1,476 US and European strains of anaerobic gram-negative bacilli to amoxicillin, amoxicillin/clavulanate, ticarcillin, ticarcillin/clavulanate, cefoxitin, imipenem and metronidazole was determined. All of theBacteroides fragilis group and 51 % of the non-Bacteroides fragilis group were β-lactamase positive. Amongst the non-Bacteroides fragilis group, β-lactamase positivity rates were higher for US strains (58 %) than for European strains (39 %). All strains were susceptible to imipenem and metronidazole. MIC90s of amoxicillin and ticarcillin for all β-lactamase negative strains were 0.5 and 2 µg/ml, respectively. The addition of clavulanate reduced the MIC90s of amoxicillin (≥ 256 µg/ml) and ticarcillin (≥ 64 µg/ml) to 16 and 8 µg/ml, respectively, for theBacteroides fragilis group, and to 4 µg/ml for both agents for the non-Bacteroides fragilis β-lactamase producing group. Twenty-nine cefoxitin-resistant strains were found, mainly in theBacteroides fragilis group, while 95 β-lactamase producing strains (predominantlyBacteroides fragilis group and fusobacteria) did not show synergy between β-lactams and clavulanate. Of the newer agents tested, meropenem and piperacillin-tazobactam were the most active (100 % of strains susceptible), followed by amoxicillin-BRL 42715 (99 % of strains susceptible); 94 to 98 % of the strains were susceptible to cefoperazone-sulbactam, tosufloxacin, tempafloxacin and clindamycin. Only 73 % of the strains were susceptible to cefotetan, compared to 91 % to cefoxitin; 88 % of the strains were susceptible to trospectomycin. Overall, all of the β-lactam/β-lactamase inhibitor combinations, imipenem, meropenem, cefoxitin, tosufloxacin, temafloxacin and clindamycin had good activity against β-lactamase producing strains, while all agents tested had good activity against β-lactamase negative strains.

Evaluation of two methods for rapid testing for beta-lactamase production inBacteroides andFusobacterium

A total of 978 strains ofBacteroides andFusobacterium were tested for beta-lactamase production by a disk test (Cefinase) and a microtiter nitrocefin assay. In 83 % of strains both tests were positive and in 14.8 % both were negative. In 1.7 % of strains the disk test was positive and the microtiter test negative, and in 0.4 % the disk test negative but the microtiter test positive. The disk test was less discriminatory in detecting amoxicillin-resistant strains. The microtiter test was less sensitive than the disk test, but more discriminatory if results were read within 1 h forFusobacterium spp., within 8 h for theBacteroides fragilis group, and within 2 h for otherBacteroides spp. Neither test should be used clinically at present.