Survey of anaerobic susceptibility patterns in Canada

A total of 94 clinical isolates of the Bacteroides fragilis group was tested for susceptibility to metronidazole, chloramphenicol, clindamycin, cefoxitin, cefotetan, cefmetazole, moxalactam, mezlocillin, amoxicllin-clavulanic acid, and imipenem. All the strains tested were susceptible to imipenem, metronidazole, amoxicillinclavulanic acid, and chloramphenicol. The rate of resistance to clindamycin was 21%. The results of this study demonstrate a difference in resistance rates from one species of the B. fragilis group to another.During the last few years, anaerobic bacteria have shown an increase in resistance to most of the traditionally used antimicrobial agents and some of the newer beta-lactam agents (8,12,14,24 Tables 1 and 2. ,B-Lactamase production was detected in 95% of strains.All the strains tested were susceptible to metronidazole and chloramphenicol. Imipenem and amoxicillin-clavulanic acid were the most active beta-lactam drugs and had similar activities against all species of the B. fragilis group. No resistance was found.Mezlocillin showed good activity with low resistance rates for the entire group (3%) as well as for the individual species. The inhibitory activity of mezlocillin was found to be lowest against B. ovatus, with a resistance rate of 10%.The resistance rate of the B. fragilis group to clindamycin was 21%. Clindamycin-resistant strains occurred at rates of 50, 30, and 33% in B. thetaiotaomicron, B. ovatus, and B. distasonis, respectively, whereas in B. fragilis the resistance rate was lower (12%) ( Table 2). All the B. vulgatus strains tested were susceptible to clindamycin.The activities of cefoxitin, cefotetan, and moxalactam were comparable for the B. fragilis group, with MICs for 90% of the strains of 16, 32, and 16 ,ug/ml, respectively. Cefmetazole was less active; the MIC for 90% of the strains was 64 p,g/ml. As reported previously (3,8,16, 26) (Table 2).The results of this study indicate that several of the new beta-lactam agents are effective in vitro against the B. fragilis group. As expected, chloramphenicol and metronidazole were uniformly effective against all 94 isolates. Imipenem was the most effective beta-lactam drug in this study; the MIC for 90% of the strains was 0.5 ,ug/ml, and we detected no resistance, which was in accordance with the 671

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confidence: 69%

Susceptibilities of species of the Bacteroides fragilis group to 10 antimicrobial agents

Betriú

Campos

Cabronero

et al. 1990

“…3-lactamase-negative strains was 2 ,ug/ml; that for 3-lactamelaninogenicus (two), B. intermedius (one), F. mortiferum mase-positive strains was 8 ,ug/ml (Tables 3 and 4 (5). Other recent studies did not find any penicillin-resistant fusobacteria in 31 strains studied (7,16,23 ,ug/ml.…”

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confidence: 72%

“…,-Lactamase production has been reported for several non 19,26,29,30). ,B-Lactamase positivity has also recently been described in fusobacteria, notably, Fusobacterium nucleatum (5,31 32 ,ug/ml; 9 of these 10 isolates were ,-lactamase positive.…”

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confidence: 99%

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

Appelbaum

Spangler

Jacobs

1990

160

13-Lactamase production (nitrocefin disk method) and agar dilution susceptibility of amoxicillin, amoxicillin- Among the fusobacteria, Fusobacterium mortferum showed the highest rate of 3-lactamase positivity (76.9%).MICs of amoxicillin (128 ,g/ml) and ticarcillin (64 ,g/ml) for 90% of all ,B-lactamase-positive strains were reduced to 4 and 2 ,ug/ml, respectively, with the addition of clavulanate. MICs of amoxicillin and ticarcillin for 90% of all 1-lactamase-negative strains were 1 and 4 ,ug/ml, respectively, and .98.4% of the strains were susceptible to the P-lactams tested. Of the j-lactamase-producing strains, 45.9% were susceptible to amoxicilHin at c4 pg/ml and 93.4% were susceptible to ticarcillin at c64 ,ug/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 ,B-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 P-lactamase positivity is on the increase in non-B. fragilis group Bacteroides species and fusobacteria, amoxicillin-clavulanate, ticarcilHin, 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.

“…Amoxicillin, temafloxacin, and clindamycin inhibited all 44 13-lactamase-negative strains (MICs for 90%o of the strains tested, <2.0 ,ug/ml). BRL 42715 will not be developed, but temafloxacin merits clinical evaluation.,B-Lactamase production and concomitant resistance to many ,B-lactams are usually encountered in the Bacteroides fragilis group but have been increasingly reported in other anaerobic gram-negative rods (2,6,7,13,14). We have examined the susceptibilities of 304 B. fragilis strains; 171 non-B.…”

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confidence: 99%

Susceptibilities of 540 anaerobic gram-negative bacilli to amoxicillin, amoxicillin-BRL 42715, amoxicillin-clavulanate, temafloxacin, and clindamycin

Appelbaum

Spangler

Shiman

et al. 1992

Agar dilution MIC testing of amoxicillin, amoxicillin-BRL 42715, amoxicillin-clavulanate, temafloxacin, and clindamycin against 496 ,-lactamase-producing anaerobic gram-negative rods revealed MICs for 90o% of the strains tested of 256.0 (amoxicillin), 2.0 (amoxicillin-BRL 42715 and amoxicillin-clavulanate), and 4.0 (temafloxacin and clindamycin) ,ug/ml. Amoxicillin, temafloxacin, and clindamycin inhibited all 44 13-lactamase-negative strains (MICs for 90%o of the strains tested, <2.0 ,ug/ml). BRL 42715 will not be developed, but temafloxacin merits clinical evaluation.,B-Lactamase production and concomitant resistance to many ,B-lactams are usually encountered in the Bacteroides fragilis group but have been increasingly reported in other anaerobic gram-negative rods (2,6,7,13,14). We have examined the susceptibilities of 304 B. fragilis strains; 171 non-B. fragilis group Bacteroides, Prevotella, and Porphyromonas species (142 were P-lactamase positive); and 65 Fusobacterium species (50 were 1-lactamase positive) to amoxicillin, amoxicillin-BRL 42715 (a potent new ,B-lactamase inhibitor [8,9,17,23]), amoxicillin-clavulanate, temafloxacin (10,11,16,19), and clindamycin.Organisms were selected from clinical isolates collected over the past 4 years from diverse sources as previously described (2-6, 13, 14). Prior to being tested, strains were identified (1, 12, 20) as described previously. P-Lactamase production was tested by the nitrocefin disk method (BBL Microbiology Systems, Cockeysville, Md.) (4). MICs of amoxicillin, amoxicillin-clavulanate, amoxicillin-BRL 42715 (SmithKline Beecham Pharmaceuticals, Brockham Park, Betchworth, United Kingdom), temafloxacin (Abbott Laboratories, Chicago, Ill.), and clindamycin (The Upjohn Co., Kalamazoo, Mich.) were determined by agar dilution (2) extracts were standardized to contain similar units of activity against nitrocefin.In Tables 1 and 2, percent susceptibility rates of amoxicillin with and without inhibitors are presented at breakpoints of 2.0, 4.0, and 8.0 ,ugIml, respectively. Susceptibility data for ,B-lactamase-producing strains are shown in Table 1. Against all 3-lactamase-positive strains, addition of BRL 42715 to amoxicillin lowered the MICs for 50 and 90% of the strains tested (MlC50 and MIC90, respectively) from 32 and 256 to 0.25 and 2 ,ug/ml, respectively, and 99% of the strains were susceptible at all three amoxicillin breakpoints (27% of the strains were susceptible to amoxicillin at the NCCLS breakpoint of 4 ,ug/ml). Addition of clavulanate to amoxicillin lowered the MIC50 and MIC90 to 0.5 and 2.0 ,ug/ml, respectively, with 97% of the strains susceptible at the NCCLS amoxicillin breakpoint of 8 ,ug/ml (18). Temafloxacin and clindamycin showed good activity against 13-lactamase-producing strains (95 and 98%, respectively, were susceptible at .4 ,ug/ml), but clustering near the breakpoint was seen with both compounds.All ,B-lactamase-negative strains were susceptible to amoxicillin, temafloxacin, and clindamycin (Table 2), and many were susceptible to the...