Antimicrobial activity of RU-66647, a new ketolide

A new macrolide subclass called ketolides, possess a mode of action similar to the macrolide-lincosamide-streptogramin (MLS) compounds. Utilizing reference in vitro tests, the in vitro activity of RU-66647 (a ketolide) was compared to other MLS compounds against 376 Gram-positive organisms and over 400 representative strains of Gram-negative bacilli. The ketolide's spectrum was most similar to clindamycin and an earlier drug in the series (RU-64004 or RU-004) against staphylococci and streptococci. However, RU-66647 was more active than erythromycin and azithromycin against oxacillin-resistant Staphylococcus spp. and vancomycin-resistant enterococci. Ketolide activity was more potent than other MLS drugs against vancomycin-susceptible enterococci (MIC90, 0.25-4 micrograms/ml) and all streptococci (MICs, < or = 0.25 microgram/ml). Erythromycin-resistant (constitutive) strains were generally inhibited by < or = 2 micrograms RU-66647/ml (staphylococci, 31 to 36%; streptococci, 100%; enterococci, 72%). RU-66647 was active against Haemophilus influenzae (MIC90, 2 micrograms/ml), Moraxella catarrhalis (MIC90, 0.12 microgram/ml), and pathogenic Neisseria spp. (MIC90 0.5 microgram/ml). The ketolide failed to inhibit Enterobacteriaceae, nonfermentative Gram-negative bacilli, and Bacteriodes fragilis group strains. RU-66647 was observed to be a promising new compound directed toward some organisms resistant to other MLS-class drugs.     

MIC and time-kill study of antipneumococcal activities of RPR 106972 (a new oral streptogramin), RP 59500 (quinupristin-dalfopristin), pyostacine (RP 7293), penicillin G, cefotaxime, erythromycin, and clarithromycin against 10 penicillin-susceptible and -resistant pneumococci

Broth MICs and time-kill studies were used to test the activity of RP 59500 (quinupristin-dalfopristin), RPR 106972, pyostacine (RP 7293), erythromycin, clarithromycin, and cefotaxime for four penicillin-susceptible (MICs of 0.008 to 0.03 microgram/ml), two penicillin-intermediate (MIC of 0.25 microgram/ml), and four penicillin-resistant (MIC of 2.0 to 4.0 micrograms/ml) strains of pneumococci: 6 of 10 strains were resistant to macrolides (MICs of > or = 0.5 microgram/ml). MICs of RP 59500 (0.5 to 1.0 microgram/ml), RPR 106972 (0.125 to 0.25 microgram/ml), and pyostacine (0.125 to 0.25 microgram/ml) did not alter with the strain's penicillin or macrolide susceptibility status. Three penicillin-susceptible strains and one penicillin-intermediate strain were susceptible to macrolides (MICs of < or = 0.25 microgram/ml); the macrolide MICs for the remaining strains were > or = 4.0 micrograms/ml. Cefotaxime MICs rose with those of penicillin G, but all strains were inhibited at MICs of < or = 2.0 micrograms/ml. RP 59500 was bactericidal for all strains after 24 h at 2 x MIC and yielded 90% killing of all strains at 6 h at 2 x MIC; at 8 x MIC, RP 59500 showed 90% killing of six strains within 10 min (approximately 0.2 h). In comparison, RPR 106972 was bactericidal for 9 of 10 strains at 2 x MIC after 24 h and yielded 90% killing of all strains at 2 x MIC after 6 h; 90% killing of six strains was found at 8 x MIC at 0.2 h. Results for pyostacine were similar to those of RPR 106972. Erythromycin and clarithromycin were bactericidal for three of four macrolide-susceptible strains after 24 h at 4 x MIC. Clarithromycin yielded 90% killing of three strains at 8 x MIC after 12 h. Cefotaxime was bactericidal for all strains after 24 h at 4 x MIC, yielding 90% killing of all strains after 6 h at 4 x MIC. All three streptogramins yielded rapid killing of penicillin- and erythromycin-susceptible and -resistant pneumococci and were the only compounds which killed significant numbers of strains at 0.2 h.     

Activity of pirlimycin against pathogens from cows with mastitis and recommendations for disk diffusion tests

Pirlimycin is an analog of clindamycin that will be recommended for therapy of bovine mastitis. It has good activity against staphylococci and streptococci, the major pathogens for bovine mastitis. Five hundred and thirty bacterial isolates recovered from cows with mastitis were studied to confirm the spectrum of activity and to develop recommendations for susceptibility testing. Pirlimycin is not active against isolates of Enterobacteriaceae, it varies in its activity against enterococci, and it is active against veterinary isolates of streptococci (MIC for 50% of strains tested, < or = 0.03 to 0.06 microgram/ml) and staphylococci (MIC for 50% of strains tested, 0.25 to 1.0 microgram/ml). On the basis of levels of drug attained in the milk with recommended dosing schedules, we chose MIC breakpoints of < or = 2 micrograms/ml for susceptibility and > or = 4 micrograms/ml for resistance. We also recommended a disk diffusion test using a disk containing 2 micrograms/ml and breakpoints of < or = 12 mm for resistance and > or = 13 mm for susceptibility.     

In vitro activity of the new fluoroquinolone CP-99,219

The in vitro activity of the new fluoroquinolone CP-99,219 [7-(3-azabicyclo[3.1.0]hexyl)naphthyridone] was compared with those of four other quinolones against 541 gram-negative, 283 gram-positive, and 70 anaerobic bacterial isolates. CP-99,219 inhibited 90% of many isolates in the family Enterobacteriaceae at a concentration of < or = 0.25 micrograms/ml (range, < 0.008 to 1 microgram/ml), an activity comparable to those of tosufloxacin and sparfloxacin and two times greater than that of temafloxacin. Ninety percent of the Proteus vulgaris, Providencia rettgeri, Providencia stuartii, and Serratia marcescens isolates were inhibited by 0.5 to 2 micrograms of CP-99,219 per ml. CP-99,219 inhibited 90% of the Pseudomonas aeruginosa and Haemophilus influenzae isolates at 1 and 0.015 micrograms/ml, respectively. The compound inhibited methicillin-susceptible Staphylococcus aureus at 0.06 micrograms/ml, whereas a ciprofloxacin concentration of 1 microgram/ml was required to inhibit these organisms. CP-99,219 inhibited 90% of methicillin-resistant S. aureus isolates at a concentration of < or = 4 micrograms/ml, while ciprofloxacin and temafloxacin had MICs against these isolates of > 16 micrograms/ml. Streptococci were inhibited by < or = 0.25 micrograms/ml, an activity comparable to that of tosufloxacin. CP-99,219 was eight times more active than ciprofloxacin against Streptococcus pneumoniae. Bacteroides species were inhibited by CP-99,219 at a concentration of 2 micrograms/ml, whereas inhibition of these species required 4- and 16-microgram/ml concentrations of tosufloxacin and ciprofloxacin, respectively. The MBCs of CP-99,219 ranged from two to four times the MICs, and inoculum size had a minimal effect on MIC. CP-99,219 was active against P. aeruginosa at pH 5.5, with only a fourfold increase in MIC compared with values obtained at pH 7.5. The addition of up to 9 mM Mg(2+) increased the MIC range from 0.03 to 0.06 microgram/ml to 0.12 to 0.5 microgram/ml. In view of its excellent in vitro activity against both gram-positive and gram-negative bacteria, CP-99,219 merits further study to determine it's clinical pharmacologic properties and potential for therapeutic use.     

Antipneumococcal activities of RP 59500 (quinupristin-dalfopristin), penicillin G, erythromycin, and sparfloxacin determined by MIC and rapid time-kill methodologies

Previous time-kill studies have shown that RP 59500 is rapidly bactericidal against pneumococci. To extend these findings, the activities of RP 59500, its two components RP 57669 RP 54476, penicillin G, erythromycin and sparfloxacin against 26 penicillin-susceptible, 25 penicillin-intermediate, and 25 penicillin-intermediate, and 25 penicillin-resistant pneumococci were determined by the agar dilution MIC and the time-kill testing methodologies within 10 min (ca. 0.2 h) and at 1 and 2 h. Respective agar dilution MICs at which 90% of isolates are inhibited for penicillin-susceptible, -intermediate, and -resistant strains were as follows: penicillin G, 0.03, 1, and 4 micrograms/ml;RP 59500, 1, 1, and 1 microgram/ml; RP 57669, 8, 32, and 16 micrograms/ml; RP 54476, > 128, > 128, and > 128 micrograms/ml; erythromycin, 0.06, 2, and > 128 micrograms/ml; and sparfloxacin, 1, 0.5, and 0.5 microgram/ml. RP 59500 was equally active (MIC at which 90% of isolates are inhibited, 1.0 microgram/ml) against erythromycin-susceptible and -resistant strains. Time-kill testing results showed that only RP 59500 at one to four times the MIC killed pneumococci at 0.2 h; RP 59500 was also the most active compound at 1 and 2 h. By comparison, penicillin and sparfloxacin at one, two, and four times the MICs reduced the original inoculum by > or = 1 log at 2 h for 46, 80, and 95% and for 50, 72, and 86% of strains, respectively. The killing activity of RP 59500 was the same against erythromycin-susceptible and -resistant strains. RP 57669, RP 54479, and erythromycin were either inactive or bacteriostatic at 2 h. Of all drugs tested, RP 59500 yielded the most rapid killing.     

Development of interpretive breakpoints for antifungal susceptibility testing: conceptual framework and analysis of in vitro-in vivo correlation data for fluconazole, itraconazole, and candida infections. Subcommittee on Antifungal Susceptibility Testing of the National Committee for Clinical Laboratory Standards

The availability of reproducible antifungal susceptibility testing methods now permits analysis of data correlating susceptibility in vitro with outcome in vivo in order to define interpretive breakpoints. In this paper, we have examined the conceptual framework underlying interpretation of antimicrobial susceptibility testing results and then used these ideas to drive analysis of data packages developed by the respective manufacturers that correlate fluconazole and itraconazole MICs with outcome of candidal infections. Tentative fluconazole interpretive breakpoints for MICs determined by the National Committee for Clinical Laboratory Standards' M27-T broth macrodilution methodology are proposed: isolates for which MICs are < or = 8 microg/mL are susceptible to fluconazole, whereas those for which MICs are > or = 64 microg/mL appear resistant. Isolates for which the MIC of fluconazole is 16-32 microg/mL are considered susceptible dependent upon dose (S-DD), on the basis of data indicating clinical response when > 100 mg of fluconazole per day is given. These breakpoints do not, however, apply to Candida krusei, as it is considered inherently resistant to fluconazole. Tentative interpretive MIC breakpoints for itraconazole apply only to mucosal candidal infections and are as follows: susceptible, < or = 0.125 microg/mL; S-DD, 0.25-0.5 microg/mL; and resistant, > or = 1.0 microg/mL. These tentative breakpoints are now open for public commentary.     

Antimicrobial susceptibility testing of 59 strains of Campylobacter fetus subsp. fetus

The susceptibilities of 59 Campylobacter fetus subsp. fetus isolates to eight antibiotics were studied by the agar dilution, E-test, and disk diffusion methods. None of the isolates were beta-lactamase producers. All were susceptible to ampicillin, gentamicin, imipenem, and meropenem as determined by the three methods, with MICs at which 90% of the isolates are inhibited (MIC90s) (determined by agar dilution) of 2, 1, < or = 0.06, and 0.12 microgram/ml, respectively. Twenty-seven percent of the isolates were resistant to tetracycline, with complete agreement between the agar dilution and disk diffusion results. The MIC90s determined by agar dilution were 2 micrograms/ml for erythromycin, 1 microgram/ml for ciprofloxacin, and 8 micrograms/ml for cefotaxime.     

Comparison of E test with standard broth microdilution for determining antibiotic susceptibilities of penicillin-resistant strains of Streptococcus pneumoniae

We compared the E test (AB Biodisk North America, Inc., Culver City, Calif.) with the National Committee for Clinical Laboratory Standards broth microdilution method for the determination of MICs of penicillin and cefotaxime for 108 isolates of Streptococcus pneumoniae. The E test was performed following manufacturer's recommendations with Mueller-Hinton blood agar, and the broth microdilution procedure was performed with lysed horse blood-supplemented Mueller-Hinton broth. The microdilution method classified 26 isolates as highly penicillin resistant (MIC, > or = 2 micrograms/ml), 33 as intermediately resistant to penicillin (MIC, > or = 0.1 < 2.0 micrograms/ml), and 49 as susceptible to penicillin (MIC, < 0.1 micrograms/ml). Discordant results obtained with the E test for penicillin susceptibility testing compared with broth microdilution occurred for 19 of the 108 isolates tested. Cefotaxime MICs for 90% of isolates found highly resistant, intermediately resistant, and susceptible to penicillin by broth microdilution were 2.0, 0.5, and 0.06 micrograms/ml, respectively. There were 16 susceptibility category changes when the E test was used to determine cefotaxime MICs. All of the discrepancies in the penicillin and cefotaxime MICs determined by the E test occurred at the susceptibility category breakpoints, and all represented differences of only one twofold dilution factor. Properly performed and controlled, the E test should be a reliable quantitative procedure for more accurately predicting the susceptibility of S. pneumoniae to several antibiotics.     

Erythromycin, clarithromycin, and azithromycin: use of frequency distribution curves, scattergrams, and regression analyses to compare in vitro activities and describe cross-resistance

MICs of erythromycin, clarithromycin, and azithromycin for 852 recent clinical isolates were determined by broth microdilution methods. Frequency distribution curves, scattergrams, and regression analyses were used to compare in vitro activities and describe cross-resistance. Clarithromycin was the most active drug against Bacteroides spp. but the least active against Haemophilus influenzae. Azithromycin was most active against H. influenzae, Moraxella catarrhalis, Pasteurella multocida, and Fusobacterium spp. but the least active against Streptococcus spp. and Enterococcus spp. All three drugs had equivalent activities against Staphylococcus spp. and gram-positive anaerobes. None of the three drugs was particularly active against members of the family Enterobacteriaceae or nonfermentative gram-negative bacilli, although concentrations of 4 micrograms of azithromycin per ml inhibited some strains of the family Enterobacteriaceae (particularly Escherichia coli and Citrobacter diversus) and Acinetobacter baumannii. Although relative drug activities varied by organism, organisms relatively susceptible to one were relatively susceptible to all and organisms relatively resistant to one were relatively resistant to all; an exception was fusobacteria, which were usually susceptible only to azithromycin. Cross-susceptibility and cross-resistance were, therefore, the rule (except for Fusobacterium spp.), although the percentage of susceptible organisms could be varied considerably on the basis of the selection of breakpoints.     

Comparative studies on activities of antimicrobial agents against causative organisms isolated from patients with urinary tract infections (1995). I. Susceptibility distribution]

The frequencies of isolation and susceptibilities to antimicrobial agents were investigated on 704 bacterial strains isolated from patients with urinary tract infections (UTIs) in 11 hospitals during the period of June 1995 to May 1996. Of the above bacterial isolates, Gram-positive bacteria accounted for 29.8% and a majority of them were Enterococcus faecalis. Gram-negative bacteria accounted for 70.2% and most of them were Escherichia coli. Susceptibilities of several isolated bacteria to antimicrobial agents were as followed; 1. Enterococcus faecalis Ampicillin (ABPC) and imipenem (IPM) showed the highest activities against E. faecalis isolated from patients with UTIs. The MIC90S of them were 1 microgram/ml. Vancomycin (VCM) and piperacillin (PIPC) were also active with the MIC90S of 2 micrograms/ml and 4 micrograms/ml, respectively. The others had low activities with the MIC90S of 16 micrograms/ml or above. 2. Staphylococcus aureus including MRSA VCM showed the highest activities against S. aureus isolated from patients with UTIs. Its MIC90 was 1 microgram/ml against both S. aureus and MRSA. Arbekacin (ABK) was also active with the MIC90 of 2 micrograms/ml. The other except minocycline (MINO) had very low activities with the MIC90S of 64 micrograms/ml or above. 3. Staphylococcus epidermidis ABK and MINO showed the strongest activities against S. epidermidis isolated from patients with UTIs. The MIC90S of them were 0.25 microgram/ml. VCM was also active with the MIC90 of 1 microgram/ml. The MIC90S of cephems ranged from 2 micrograms/ml to 16 micrograms/ml in 1994, but they ranged from 8 micrograms/ml to 128 micrograms/ml in 1995. These results indicated that some resistances existed among S. epidermidis to cephems. 4. Streptococcus agalactiae All drugs except gentamicin (GM) were active against S. agalactiae. ABPC, cefmenoxime (CMX), IPM, erythromycin (EM), clindamycin (CLDM) and clarithromycin (CAM) showed the highest activities. The MICs for all strains were lower than 0.125 microgram/ml. The MIC90S of the others were 2 micrograms/ml or below. 5. Citrobacter freundii IPM showed the highest activity against C. freundii isolated from patients UTIs. Its MIC90 was 1 microgram/ml. GM was also active with the MIC90 of 2 micrograms/ml. Cefpirome (CPR), cefozopran (CZOP) and amikacin (AMK) were also active with the MIC90S of 4 micrograms/ml. Penicillins and cephems except CMX, CPR and CZOP showed low activities with MIC90S of 256 micrograms/ml or above. 6. Enterobacter cloacae IPM showed the highest activity against E. cloacae. The MICs for all strains were equal to or lower than 1 microgram/ml. MINO and tosufloxacin (TFLX) were also active with the MIC90S of 8 micrograms/ml. Penicillins and cephems except CPR and CZOP showed lower activities with the MIC90S of 256 micrograms/ml or above. 7. Escherichia coli. Most of the antimicrobial agents were active against E. coli. Particularly CPR, CZOP and IPM showed the highest activities against E. coli. The MICs for all strains were equal to or lower than 0.5 microgram/ml. CMX and TFLX were also active with the MIC90S of 0.125 microgram/ml or below. Penicillins were slightly active with MIC90S of 128 micrograms/ml or above. 8. Klebsiella pneumoniae K. pneumoniae was susceptible to all drugs except penicillins, with MIC90S of 2 micrograms/ml or below. Carumonam (CRMN) had the strongest activity against K. pneumoniae, the MICs for all strains were equal to or lower than 0.125 microgram/ml. Comparing with the result of 1994, the sensitivities of K. pneumoniae against all drugs had obviously changed into a better state. For example, the MIC90S of cephems ranged from 0.25 microgram/ml to 16 micrograms/ml in 1994, but they were all lower than 2 micrograms/ml in 1995. 9. Proteus mirabilis P. mirabilis was susceptible to a majority of drugs. CMX, ceftazidime (CAZ), cefixime (CFIX), and CRMN showed the highest activities against P. mirabilis isolated from patients with UTIs. MICs of CRMN for all     

In vitro activity of RP59500, an injectable streptogramin antibiotic, against vancomycin-resistant gram-positive organisms

The in vitro activity of RP59500, a streptogramin antibiotic, against 146 clinical isolates of vancomycin-resistant gram-positive bacteria was examined. Five strains of the species Enterococcus casseliflavus and Enterococcus gallinarum, for which the MIC of vancomycin was 8 micrograms/ml, were also studied. Twenty-eight vancomycin-susceptible strains of Enterococcus faecalis and Enterococcus faecium were included for comparison. The drug was highly active against Leuconostoc spp., Lactobacillus spp., and Pediococcus spp. (MICs, < or = 2 micrograms/ml). RP59500 was more active against vancomycin-susceptible strains of E. faecium than E. faecalis (MICs for 90% of the strains [MIC90s], 1.0 versus 32 micrograms/ml). Vancomycin-resistant strains of E. faecalis were as resistant to RP59500 as vancomycin-susceptible strains (MIC90, 32 micrograms/ml), but some vancomycin-resistant E. faecium strains were relatively more resistant to the new agent (MIC90, 16; MIC range, 0.5 to 32 micrograms/ml) than were vancomycin-susceptible organisms of this species.     

Metronidazole and clarithromycin resistance in Helicobacter pylori determined by measuring MICs of antimicrobial agents in color indicator egg yolk agar in a miniwell format. The Gastrointestinal Physiology Working Group of Universidad Peruana Cayetano Heredia and the Johns Hopkins University

Resistance of Helicobacter pylori to metronidazole often causes failure of commonly used combination drug treatment regimens. We determined the MICs of metronidazole and clarithromycin against 18 H. pylori strains from Peru using tetrazolium egg yolk (TEY) agar. The MIC results obtained by agar dilution with petri dishes were compared with the results found through a miniwell format. The results of the two protocols for measuring drug susceptibility differed by no more than 1 dilution in all cases. On TEY agar, bright-red H. pylori colonies were easy to identify against a yellow background. Sixty-one percent (11 of 18) of the strains were resistant to metronidazole (MIC, > or = 4 micrograms/ml) and 50% (9 of 18) were resistant to clarithromycin (MIC, > or = 0.125 micrograms/ml), whereas none (0 of 5) of the strains tested were resistant to tetracycline (MIC, > or = 1 micrograms/ml). Thus, the prevalence of metronidazole and clarithromycin resistance in Peru is higher than that in developed regions of the world. The miniwell plate with TEY agar allows easy H. pylori colony identification, requires about one-third less of the costly medium necessary for petri dish assaying, conserves space, and yields MICs equivalent to those with agar dilution in petri dishes.     

Antimicrobial activity of the new carbapenem biapenem compared to imipenem, meropenem and other broad-spectrum beta-lactam drugs

The in vitro activity of biapenem was compared to that of imipenem, meropenem and other broad-spectrum beta-lactams. A total of 716 isolates from recent cases of clinical septicemia and an additional 137 stock strains possessing known beta-lactamases or other well-characterized resistance mechanisms were tested. The minimal concentrations inhibiting 90% of strains (MIC90) of Enterobacteriaceae species were for biapenem 0.03 to 1 mg/l and for imipenem 0.25 to 2 mg/l. No member of the Enterobacteriaceae was found to be resistant to biapenem. Biapenem and meropenem were the most active drugs against Pseudomonas aeruginosa, with an MIC90 of 1 mg/l. Biapenem was more active than ceftazidime against most gram-negative and gram-positive bacteria tested. Biapenem was as potent as imipenem against anaerobic bacteria (including Bacteroides fragilis), with an MIC90 of 0.25 mg/l. High MICs of biapenem were demonstrated for Xanthomonas maltophilia, oxacillin-resistant Staphylococcus spp. and Enterococcus spp. These species have demonstrated resistance to other carbapenems and to most of the newer cephalosporins. The results of this study, coupled with previously documented favorable qualities of biapenem, endorse further investigation of this broad-spectrum antibacterial agent for clinical use.     

Enterococcus faecium: in vitro activity of antimicrobial drugs, singly and combined, with and without defibrinated human blood, against multiple-antibiotic-resistant strains

The minimal inhibitory (MICs) and bactericidal concentrations of 14 antimicrobial drugs were determined against 17 clinical isolates of Enterococcus faecium, including 4 glycopeptide-resistant strains. Both teicoplanin and vancomycin lacked bactericidal activity against all 13 susceptible isolates. Time-kill experiments served to test various antibiotic combinations chiefly against glycopeptide-resistant strains in Mueller-Hinton broth (MHB) and in MHB supplemented with 65% (v/v) fresh defibrinated human blood. Co-trimoxazole, fusidic acid, and novobiocin yielded bacteriostatic effects. Rifampin was bactericidally active against rifampin-susceptible strains (MICs = 0.125 micrograms/ml), but less so against low-level-rifampin-resistant (MICs = 2-8 micrograms/ml) strains in MHB. However, in the presence of human blood, rifampin (2 micrograms/ml) combined with co-trimoxazole (0.25/4.75 micrograms/ml) killed rifampin-susceptible and low-level-rifampin-resistant, but not moderate-level-rifampin-resistant (MICs = 16-32 micrograms/ml) strains of E. faecium. Of two topical drugs examined, mupirocin merely inhibited strains of E. faecium; conversely, taurolidine at 2,000 micrograms/ml was efficacious against all strains examined, although the kinetics of bactericidal activity were retarded somewhat in the presence of 65 vol% human blood.     

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.     

Tissue water content in rats measured by desiccation

The in vitro activity of cefepime was compared to that of ceftazidime, ceftriaxone, and cefotaxime in a multicenter study involving 10 clinical microbiology laboratories and clinical isolates from 18 Brazilian hospitals from 7 cities (4 states). A total of 982 isolates consecutively collected between December 1995 and March 1996 were susceptibility tested by using Etest and following the NCCLS procedures for agar diffusion tests. The cefepime spectrum was broader than that of the other broad-spectrum cephalosporins against both Gram-negative rods and Gram-positive cocci. Cefepime was particularly more active against Enterobacter sp. (MIC90, 2 micrograms/ml), Serratia sp. (MIC90, 2 micrograms/ml) and oxacillin-susceptible Staphylococcus aureus (MIC90, 3 micrograms/ml). Against Pseudomonas aeruginosa, cefepime (MIC90, 16 micrograms/ml) was slightly more active than ceftazidime (MIC90, 32 micrograms/ml) and 8- to 16-fold more active than ceftriaxone of cefotaxime (MIC90, > 256 micrograms/ml). Our results show that nosocomial bacteria, especially Gram-negative rods, have a high rate of cephalosporin resistance in Brazil. However, part of these resistant bacteria remains susceptible to cefepime. The Etest was shown to be an excellent method for multicenter studies of the in vitro evaluation of new antimicrobial agents.     

Correlation between in vitro and in vivo activity of amoxicillin against Streptococcus pneumoniae in a murine pneumonia model

We studied the relationship between in vitro bacteriological parameters [minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and killing rate, defined as the reduction in the inoculum within 1, 3 or 6 hr] and in vivo activity of amoxicillin against 12 strains of Streptococcus pneumoniae, with penicillin MICs of < 0.01 to 16 micrograms/ml, in a cyclophosphamide-induced neutropenic murine pneumonia model. Dose-response curves were determined for amoxicillin against each strain, and three quantitative parameters of in vivo amoxicillin activity were defined, i.e., maximal attainable antimicrobial effect attributable to the drug [i.e., reduction in log colony-forming units (CFU) per lung, compared with untreated controls], dose required to reach 50% of maximal effect and dose required to achieve a reduction of 1 log CFU/lung. We demonstrated a highly significant correlation between the dose required to reach 50% of maximal effect and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) for amoxicillin against strains of S. pneumoniae with a wide range of amoxicillin MICs (0.01-8 micrograms/ml). Significant correlations between the dose required to achieve a reduction of 1 log CFU/lung and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) were also observed. In contrast, there were no significant correlations between the maximal attainable antimicrobial effect attributable to the drug and MIC, MBC or killing rate or between killing rate and the dose required to reach 50% of maximal effect or the dose required to achieve a reduction of 1 log CFU/lung. We conclude that in vitro susceptibility test results (MICs and MBCs) correlated well with in vivo amoxicillin activity against pneumococcal strains, including highly penicillin-resistant strains, in this animal model. Furthermore, these data suggest that the estimated MIC breakpoints for amoxicillin against S. pneumoniae would be 2 micrograms/ml for intermediate-resistant and 4 micrograms/ml for resistant, although this remains to be confirmed in clinical studies.     

In vivo activities of amoxicillin and amoxicillin-clavulanate against Streptococcus pneumoniae: application to breakpoint determinations

The in vivo activities of amoxicillin and amoxicillin-clavulanate against 17 strains of Streptococcus pneumoniae with penicillin MICs of 0.12-8.0 mg/liter were assessed in a cyclophosphamide-induced neutropenic murine thigh infection model. Renal impairment was produced by administration of uranyl nitrate to prolong the amoxicillin half-life in the mice from 21 to 65 min, simulating human pharmacokinetics. Two hours after thigh infection with 10(5) to 10(6) CFU, groups of mice were treated with 7 mg of amoxicillin per kg of body weight alone or combined with clavulanate (ratio, 4:1) every 8 h for 1 and 4 days. There was an excellent correlation between the MIC of amoxicillin (0.03 to 5.6 mg/liter) and (i) the change in log10 CFU/thigh at 24 h and (ii) survival after 4 days of therapy. Organisms for which MICs were 2 mg/liter or less were killed at 1.4 to 4.2 and 1.6 to 4.1 log10 CFU/thigh at 24 h by amoxicillin and amoxicillin-clavulanate, respectively. The four strains for which MICs were >4 mg/liter grew 0.2 to 2.6 and 0.6 to 2. 3 logs at 24 h despite therapy with amoxicillin and amoxicillin-clavulanate, respectively. Infection was uniformly fatal by 72 h in untreated mice. Amoxicillin therapy resulted in no mortality with organisms for which MICs were 1 mg/liter or less, 20 to 40% mortality with organisms for which MICs were 2 mg/liter, and 80 to 100% mortality with organisms for which MICs were 4.0-5.6 mg/liter. Lower and higher doses (0.5, 2, and 20 mg/kg) of amoxicillin were studied against organisms for which MICs were near the breakpoint. These studies demonstrate that a reduction of 1 log10 or greater in CFU/thigh at 24 h is consistently observed when amoxicillin levels exceed the MIC for 25 to 30% of the dosing interval. These studies would support amoxicillin (and amoxicillin-clavulanate) MIC breakpoints of 1 mg/liter for susceptible, 2 mg/liter for intermediate, and 4 mg/liter for resistant strains of S. pneumoniae.     

Fungicidal properties of defensin NP-1 and activity against Cryptococcus neoformans in vitro

Defensin NP-1, derived from the neutrophils of rabbits, was tested for its fungistatic and fungicidal activity against strains of Cryptococcus neoformans. The MICs for the encapsulated strains tested ranged from 3.75 to 15.0 micrograms of NP-1 per ml. The minimum fungicidal concentrations for these strains were similar to the MICs. An acapsular strain, however, had a lower MIC of 0.93 and minimum fungicidal concentration of 1.88 micrograms/ml. NP-1 demonstrated time-dependent and concentration-dependent killing of C. neoformans. Killing occurred rapidly in the first 20 min of exposure to NP-1 and was maximum at 90 to 120 min. Killing of C. neoformans by NP-1 was concentration dependent with 31% +/- 9% survival at 25 micrograms/ml, 13% +/- 4% survival at 50 micrograms/ml, 9% +/- 5% survival at 75 micrograms/ml, and 5% +/- 3% survival at 100 micrograms/ml. NP-1's fungicidal effect on C. neoformans was also inoculum dependent, with increased activity observed at 10(4) versus 10(5) or 10(6) cells per ml. In addition, stationary-phase C. neoformans was less susceptible to NP-1 killing than yeast cells in the logarithmic phase. Subinhibitory concentrations of both NP-1 (0.25 x MIC) and fluconazole (0.25 x MIC) acted synergistically in inhibiting growth of C. neoformans. Similar combinations of NP-1 and amphotericin B, however, did not yield synergy.     

Biology and gene therapy of glioma

Ceftiofur, an extended-spectrum cephalosporin, is active against a variety of animal pathogens, including organisms associated with swine respiratory disease. However, minimum inhibitory concentration (MIC) breakpoint and disk diffusion interpretive criteria have not been established for swine pathogens. Susceptibility tests were performed by broth microdilution MIC and disk diffusion methods on 246 bacterial species that cause swine respiratory disease. Ceftiofur was active against Salmonella sp., Pasteurella multocida, Actinobacillus pleuropneumoniae, Streptococcus suis, and Escherichia coli but was not active against Bordetella bronchiseptica measured by MIC. Based on pharmacokinetic studies of ceftiofur in swine after a single intramuscular injection of 3 or 5 mg/kg body weight of ceftiofur and on the MIC and disk diffusion data, we recommend MIC breakpoints and disk diffusion distances, respectively, of < or = 2 micrograms/ml and > or = 21 mm for susceptible, 4 micrograms/ml and 18-20 mm for intermediate, and > or = 8 micrograms/ml and > or = 17 mm for resistant classification for swine pathogens. When these breakpoints were applied to data from a previous study using bovine pathogens, only 1 minor interpretive error occurred.