Eric Molitoris

In vitro activities of three of the newer quinolones against anaerobic bacteria.

The antimicrobial activities of three new quinolone compounds, sparfloxacin, temafloxacin, and WIN 57273, against anaerobic bacteria were determined in three separate studies. The Wadsworth agar dilution technique using brucella-laked blood agar was used throughout. The activities of other antimicrobial agents, including ciprofloxacin, imipenem, chloramphenicol, metronidazole, cefotetan, cefoxitin, and amoxicillin-clavulanic acid, were also determined. The breakpoints of the new quinolones were 2 micrograms/ml for sparfloxacin and WIN 57273 and 4 micrograms/ml for temafloxacin. WIN 57273 displayed very good activity against anaerobes, inhibiting all strains of Bacteroides fragilis group species at 2 micrograms/ml. Only two strains of Fusobacterium species were resistant (MIC, 4 micrograms/ml). Sparfloxacin inhibited 78% of B. fragilis strains and 44% of other B. fragilis group isolates at 2 micrograms/ml. At 2 micrograms/ml, the percentages of other anaerobic species susceptible were as follows: B. gracilis, 70%; other Bacteroides species, 61%; Clostridium species, 50%; Fusobacterium species, 70%; Peptostreptococcus species, 91%; non-spore-forming gram-positive rods, 71%. Temafloxacin inhibited 91% of B. fragilis strains and 87% of other B. fragilis group species at 4 micrograms/ml. All strains of other Bacteroides species, 78% of Fusobacterium species, 80% of Clostridium species, and 90% of Peptostreptococcus species were inhibited at 4 micrograms of temafloxacin per ml.

Sources and Antimicrobial Susceptibilities of Campylobacter gracilis and Sutterella wadsworthensis

Table 2. In vitro susceptibility data for isolates of Campylobacter Sutterella wadsworthensis is a newly described gram-negagracilis and Sutterella wadsworthensis. tive, asaccharolytic, microaerophilic rod that can be confused with Campylobacter gracilis. The description of S. wadsworC. gracilis (n Å 10) S. wadsworthensis (n Å 19) thensis was based on 20 strains isolated from appendiceal tissue and peritoneal or abdominal fluid. C. gracilis strains (with the Antimicrobial Percent exception of one strain isolated from appendiceal tissue) have agent Range MIC90 Range MIC90 susceptible* been isolated from infections above the diaphragm [1]. The identification of these species is the result of further study of Amoxicillin/ the ‘‘Bacteroides ureolyticus group’’; these strains have been clavulanate 0.06–0.5 0.12 0.5–4 2 100 characterized as asaccharolytic, nitrate-positive organisms that Cefoxitin 1–16 2 0.5–8 4 100

In vitro activity of DU-6859a against anaerobic bacteria.

The activity of a new quinolone agent, DU-6859a, against 330 strains of anaerobic bacteria was determined by using the National Committee for Clinical Laboratory Standards-approved Wadsworth brucella laked blood agar method; the activity of DU-6859a was compared with those of amoxicillin-clavulanate (2:1), chloramphenicol, ciprofloxacin, clindamycin, fleroxacin, imipenem, lomefloxacin, metronidazole, sparfloxacin, and temafloxacin. DU-6859a and chloramphenicol inhibited all of the isolates at concentrations of 1 and 16 micrograms/ml, respectively; amoxicillin-clavulanate, imipenem, and metronidazole inhibited > or = 94% of the isolates at their respective breakpoints (8, 8, and 16 micrograms/ml). MICs of DU-6859a at which 90% of the strains were susceptible were 1 to 5 twofold dilutions lower than those of the other quinolones for every group of organisms. MICs of DU-6859a at which 90% of the strains were susceptible (total numbers of strains tested are in parentheses) were < or = 0.25 micrograms/ml for Bacteroides fragilis (57), other B. fragilis group species (84), Bilophila wadsworthia (15), Clostridium species (27) (including C. difficile, C. perfringens, and C. ramosum), Fusobacterium nucleatum (16), Fusobacterium mortiferum-F. varium group species (10), Peptostreptococcus species (20), non-spore-forming gram-positive rods (20), and Prevotella species (25).

Comparison of spiral gradient and conventional agar dilution for susceptibility testing of anaerobic bacteria.

Antimicrobial susceptibility tests were performed on brucella laked blood agar with 340 isolates and 14 antimicrobial agents by the standard agar dilution technique and the spiral gradient technique in which antibiotic concentrations were established by diffusion from the agar surface. For comparison, spiral gradient MICs were determined by calculating antimicrobial concentrations at growth endpoints and rounding up to the next twofold incremental concentration. The cumulative percentage of strains susceptible at the breakpoint determined from spiral gradient data was within 10%, generally, of the percentage of strains susceptible at the breakpoint determined from agar dilution data. The overall agreement between the two techniques (within one doubling dilution) was 90.6%. The spiral gradient agar dilution technique is a reasonable alternative to the conventional agar dilution technique for susceptibility testing of anaerobic bacteria. Images

In vitro activities of two new glycylcyclines, N,N-dimethylglycylamido derivatives of minocycline and 6-demethyl-6-deoxytetracycline, against 339 strains of anaerobic bacteria.

The in vitro activities of the N,N-dimethylglycylamido derivatives of minocycline (DMG-MINO) and 6-demethyl-6-deoxytetracycline (DMG-DMDOT) were compared with those of minocycline, tetracycline, clindamycin, and metronidazole by using the National Committee for Clinical Laboratory Standards-approved Wadsworth agar dilution method. The MICs of DMG-MINO, DMG-DMDOT, and metronidazole at which 90% of the strains were susceptible (0.5, 1, and 1 micrograms/ml, respectively) were lower than those for clindamycin, minocycline, and tetracycline (4, 8, and 32 micrograms/ml, respectively). All of the strains of anaerobes tested, except one strain of Bacteroides ovatus (MIC, 16 micrograms/ml), were susceptible to DMG-MINO and DMG-DMDOT at 8 micrograms/ml.

In vitro activity of Bay Y3118 against anaerobic bacteria.

The antimicrobial activity of a new quinolone, Bay Y3118, was determined against 326 strains of anaerobic bacteria and compared with the activities of ampicillin-sulbactam, cefotetan, clindamycin, imipenem, metronidazole, and sparfloxacin. The National Committee for Clinical Laboratory Standards-approved Wadsworth agar dilution technique with Brucella-laked blood agar was used throughout the study. Breakpoints used to determine the percent susceptible were 2 micrograms/ml for Bay Y3118 and sparfloxacin, 4 micrograms/ml for clindamycin, 8 micrograms/ml for imipenem, 16 micrograms/ml for metronidazole and ampicillin-sulbactam, and 32 micrograms/ml for cefotetan. Species tested included Bacteroides fragilis (57 strains), other B. fragilis group species (79 strains), Bacteroides gracilis (10 strains), other Bacteroides spp. (9 strains), Prevotella spp. (30 strains), Porphyromonas spp. (9 strains), Fusobacterium spp. (36 strains), Bilophila wadsworthia (14 strains), Clostridium spp. (36 strains), Peptostreptococcus spp. (20 strains), and gram-positive non-spore-forming rods (26 strains). Bay Y3118 inhibited all but 1 of 326 anaerobic bacteria tested at the breakpoint level or lower.

In vitro activity of grepafloxacin (OPC-17116) against anaerobic bacteria

In vitro activity of the quinolone grepafloxacin (OPC-17116) was compared with that of ciprofloxacin, fleroxacin, clindamycin, imipenem, and metronidazole by using the NCCLS-approved Brucella-base-laked blood agar dilution method and breakpoints, when available. Clindamycin, metronidazole, and imipenem inhibited > or = 98% of Bacteroides fragilis at the breakpoint; grepafloxacin, ciprofloxacin, and fleroxacin inhibited 83%, 6%, and 0, respectively, at 2 micrograms/ml. Grepafloxacin inhibited 39% of other B. fragilis group species isolated (80) at breakpoint (< or = 2 micrograms/ml) compared with 100% for metronidazole and imipenem, 83% for clindamycin, 6% for ciprofloxacin, and 1% for fleroxacin. Grepafloxacin demonstrated substantially better activity against B. fragilis than did ciprofloxacin or fleroxacin; overall activity against anaerobes was marginally better than that of ciprofloxacin or fleroxacin.

Statistical analysis of the effects of trial, reader, and replicates on MIC determination for cefoxitin.

A pilot study was designed to estimate the variance components in the determination of the MIC of cefoxitin for isolates of the Bacteroides fragilis group. Twenty different organisms were tested, and replicate, trial, and reader variabilities were examined. When the total-variance component was used, if the true MIC was 16 micrograms/ml, then the chance that the observed MIC was between 8 and 32 micrograms/ml, inclusive, was 95%. For all analyses, the isolate (P = 0.0001) and reader (P less than 0.03) effects were significant. The probability of specific MIC observations for various true MICs (over the range of 16 to 32 micrograms/ml at 4-micrograms/ml increments) was calculated. For true MICs of 20, 24, and 28 micrograms/ml, the probabilities of observing an MIC of 16 or 32 micrograms/ml (inclusive) were 86, 75, and 62%, respectively. An upward bias was shown to exist in addition to sources of sizeable variation. The recommendation stemming from recognition of this inherent variability is that ranges of percent susceptibility at various concentrations be included in reports of in vitro susceptibility studies.