In vitro activity of josamycin and rosamicin against Bacteroides fragilis compared with clindamycin, erythromycin, and metronidazole

The inhibitory and bactericidal activities of josamycin and rosamicin against 29 clinical isolates of Bacteroides fragilis were compared with those of clindamycin, erythromycin, and metronidazole by a broth dilution technique. Josamycin and rosamicin had similar inhibitory activity to metronidazole and clindamycin. Rosamicin had similar bactericidal activity to clindamycin but was less bactericidal than metronidazole (the most bactericidal agent tested). Josamycin was slightly more bactericidal than erythromycin (the least bactericidal agent tested), but less so than rosamicin and clindamycin.     

In vitro activity of fleroxacin against multiresistant gram-negative bacilli isolated from patients with nosocomial infections

In order to evaluate the in vitro activity of fleroxacin against nosocomial gram-negative organisms, 263 multiresistant gram-negative bacilli (203 Enterobacteriaceae and 60 non-fermenting gram-negative bacilli) were isolated from adult patients with nosocomial infections. The different patterns of resistance to eight different antimicrobial agents (ampicillin, carbenicillin, piperacillin, cephalothin, cefamandole, ceftazidime, gentamicin and amikacin) were determined by minimum inhibitory concentration (MIC), using the agar dilution method. The most prevalent multiresistant species isolated were Klebsiella pneumoniae (28.9%), Escherichia coli (24%) and Pseudomonas aeruginosa (12.2%). All these bacterial strains showed three to five resistance patterns to at least three different antibiotics. Resistance to ceftazidime was observed in at least one of the resistance patterns of isolated bacteria. The activity of fleroxacin against multiresistant enteric bacteria was excellent; these strains showed a susceptibility of 79-100%. The susceptibility of P. aeruginosa to antipseudomonal agents was low; however, the activity of fleroxacin against these strains was higher than 60% (MIC < or = 2 microg/ ml), broadly comparable with ciprofloxacin. The resistance to fluoroquinolones detected in this study was no cause for alarm (3%). Consequently, fleroxacin maintains a remarkable activity against Enterobacteriaceae and remains highly active against other gram-negative bacilli. Nevertheless, actions directed at preventing or limiting resistance will be crucial to maintain the viability of fluoroquinolones as important therapeutic agents.     

Antimicrobial activity of carbapenem antibiotics against gram-negative bacilli

Antimicrobial activities of meropenem (MEPM), imipenem (IPM), panipenem (PAPM), ceftazidime (CAZ), cefozopran (CZOP), aztreonam (AZT), norfloxacin (NFLX) and tetracycline (TC) against clinically isolated Gram-negative bacilli [271 strains of Enterobacteriaceae and 242 strains non-fermentative Gram-negative bacteria (NFB)] were investigated. Among carbapenem antibiotics, MEPM showed the lowest MIC90, which activity was about four-hold higher than those of IPM and PAPM. The activity of IPM was equal or slightly superior to that of PAPM. Resistance to IPM (> 16 micrograms/ml) was observed in 3 strains of Enterobacteriaceae (1.1%) and 14 strains of NFB (5.8%). It is conceivable that these strains produce metallo-beta-lactamase. Referring to the correlation among MICs of MEPM, IPM and PAPM, 3 strains in 3 species of Enterobacteriaceae showed cross resistance to carbapenems; while 14 strains of NFB showed cross resistance to MEPM and IPM, 15 strains to MEPM and PAPM, and 29 strains to IPM and PAPM, and all of these strains were Pseudomonas aeruginosa. Fifteen of 29 strains of IPM-resistant and 77 of 92 strains of PAPM-resistant P. aeruginosa were susceptible to MEPM. Thirty-three strains (12%) of the Enterobacteriaceae were resistant to CAZ and AZT (> or = 32 micrograms/ml) and these were considered as ESBL-producing strains.     

Josamycin and rosamicin: in vitro comparisons with erythromycin and clindamycin

The macrolide antibiotics josamycin and rosamicin were compared in vitro with erythromycin for activity against Staphylococcus aureus, S. epidermidis, and enterococci and with clindamycin for activity against a variety of anaerobic organisms. Rosamicin and erythromycin were similar in activity and superior to josamycin against aerobic cocci. Most isolates of S. aureus (96%), S. epidermidis (79%), and the enterococci (87%) were inhibited by 1.56 mug of either of the new macrolide compounds per ml. Clindamycin was the most active compound against the anaerobic organisms.     

Comparison of the antibacterial activity of nine cephalosporins against Enterobacteriaceae and nonfermentative gram-negative bacilli

The in vitro antibacterial activity of nine cephalosporins (cephalothin, cephaloridine, cephalexin, cefazolin, cefamandole, cefuroxime, cefatrizine, cefoxitin, and cefazaflur) was determined against 344 strains of Enterobacteriaceae and 99 nonfermentative gram-negative bacilli. Cefamandole, cefazaflur, and cefuroxime were the most active cephalosporins against the Enterobacteriaceae (with the exception of Serratia marcescens). However, cefoxitin was the only cephalosporin that inhibited all 30 S. marcescens strains in a concentration of 16 mug/ml and was by far the most active compound against selected cephalothin-resistant strains of Escherichia coli, Klebsiella, and Proteus mirabilis. Acinetobacter spp. were inhibited best by cefuroxime, but none of the cephalosporins had appreciable activity against the Pseudomonas spp.     

In vitro activity of levofloxacin against a selected group of anaerobic bacteria isolated from skin and soft tissue infections

The in vitro activity of levofloxacin was compared to the activities of ofloxacin, ciprofloxacin, ampicillin-sulbactam (2:1), cefoxitin, and metronidazole for a selected group of anaerobes (n = 175) isolated from skin and soft tissue infections by using the National Committee for Clinical Laboratory Standards-approved Wadsworth method. Ampicillin-sulbactam and cefoxitin inhibited 99% of the strains of this select group, levofloxacin and ofloxacin inhibited 73 and 50%, respectively, at 2 microg/ml, and ciprofloxacin inhibited 51% at 1 microg/ml. The geometric mean MIC of levofloxacin was lower than those of ofloxacin and ciprofloxacin for every group except Veillonella.     

In vitro activity of dirithromycin against Chlamydia trachomatis

Dirithromycin is a new macrolide antibiotic with an active metabolite, erythromycylamine. We evaluated the in vitro activities of both drugs against 16 isolates of Chlamydia trachomatis and compared them with that of doxycycline. In vitro susceptibility testing was performed with McCoy cell monolayers. The MIC was defined as the lowest concentration of antibiotic without inclusions. The MBC was defined as the lowest concentration of antibiotic yielding no inclusions after passage onto 24-h-old antibiotic-free McCoy cell monolayers. Dirithromycin and erythromycylamine appeared to be equally effective against these 16 strains of C. trachomatis (MIC for 90% of strains tested, 1 mg/ml; MBC for 90% of strains tested, 2 micrograms/ml). Both were less active than doxycycline (MIC for 90% of strains tested, 0.06 micrograms/ml; MBC for 90% of strains tested, 0.12 micrograms/ml). The combination of dirithromycin and erythromycylamine appeared to be additive.     

In vitro activity of macrolides against intracellular Legionella pneumophila

The antibacterial effects of clarithromycin, azithromycin, and erythromycin were determined against five strains of Legionella pneumophila including L. pneumophila ATCC 33823 and four clinical isolates. Extracellular minimum inhibitory concentrations (MICs) and MBCs were determined by a microdilution method. Clarithromycin was the most active drug (MIC < or = 0.015-0.06), followed by azithromycin (MIC 0.03-0.12) and erythromycin (MIC 0.06-0.25). The antibacterial effect of these macrolides was then determined against L. pneumophila grown intracellularly in MRC-5 human fetal lung fibroblast cells. At two and eight times the extracellular MBC, erythromycin, azithromycin, and clarithromycin were equally effective in inhibiting growth of these five strains of intracellular L. pneumophila.     

In vitro activity of biapenem against beta-lactamase producing Enterobacteriaceae

The activity of biapenem was compared with that of imipenem and cefotaxime against 108 strains of beta-lactamase producing Enterobacteriaceae. Biapenem and imipenem were very active, inhibiting 90% of the strains at a concentration of 0.5 microgram/ml. Both carbapenems were very active against plasmidic beta-lactamase producers, with MIC90s below 1 microgram/ml. However, the MIC90 of biapenem for cephalosporinase producers was 1 microgram/ml. Against strains producing extended-spectrum beta-lactamases, biapenem exhibited better activity against TEM-type producers (MIC90 0.25 microgram/ml) than against SHV-type producers (MIC90 0.5 microgram/ml). Overall, the in vitro antibacterial activity of biapenem is similar to that of imipenem.     

Comparison of activity of sisomicin and gentamicin in mouse protection tests with gram-negative bacilli

The efficacy of sisomicin and gentamicin was compared in mouse protection studies against strains of Escherichia coli, Klebsiella sp., Enterobacter aerogenes, Serratia marcescens, Proteus mirabilis, and Pseudomonas aeruginosa. There was no significant difference in mortality of the mice in any of the protocol groups when five different dosages of sisomicin and gentamicin given by three separate schedules were compared for each bacterial inoculum in each antibiotic protocol. The mean protective dose values of sisomicin were at least one-half those of gentamicin for each protocol against Pseudomonas aeruginosa.     

In vitro activity of temocillin, a new beta-lactamase-stable penicillin active against enterobacteria

The activity of temocillin was investigated in vitro against 523 clinical isolates of enterobacteria and Pseudomonas aeruginosa. The minimum inhibitory concentration of the new compound for all ampicillin-susceptible enterobacteria and for 90% of ampicillin-resistant enterobacteria was 16 micrograms/ml or less, a concentration readily achieved in plasma. P. aeruginosa strains were uniformly resistant to temocillin. All but 3 of a separate group of 48 enterobacteria exhibiting resistance to the combination of clavulanic acid and amoxicillin were found to be inhibited by 16 micrograms or less of temocillin per ml. The new compound also displayed good activity against a group of laboratory stock cultures selected on the basis of differential resistance to presently available beta-lactam agents. Two of these strains were cefotaxime resistant.     

In vitro activities of azithromycin, clarithromycin, erythromycin, and tetracycline against 13 strains of Chlamydia pneumoniae

Thirteen strains of Chlamydia pneumoniae were evaluated for their in vitro susceptibilities to azithromycin, clarithromycin, erythromycin, and tetracycline. The MIC ranges were 0.125 to 0.5 micrograms/ml for azithromycin, 0.031 to 1.0 micrograms/ml for clarithromycin, 0.125 to 1.0 micrograms/ml for erythromycin, and 0.25 to 1.0 micrograms/ml for tetracycline. The ranges for the minimal lethal concentrations were 0.125 to 0.5 micrograms/ml for azithromycin, 0.031 to 1.0 micrograms/ml for clarithromycin, 0.125 to 1.0 micrograms/ml for erythromycin, and 0.25 to 1.0 micrograms/ml for tetracycline. Clarithromycin and azithromycin were the most active antibiotics against C. pneumoniae in vitro.     

In vitro activity of BAY 12-8039, a new fluoroquinolone against mycoplasmas

The in vitro activity of the fluoroquinolone BAY 12-8039 against 66 strains of different mycoplasma species and 30 strains of Ureaplasma urealyticum was compared with those of three other antimicrobial agents. BAY 12-8039 at 0.5 microg/ml inhibited 100% of all the mycoplasmal and ureaplasmal strains tested. The minimal bactericidal concentrations of BAY 12-8039 increased only two- to eightfold compared to the MICs. Furthermore, they were comparable to those of sparfloxacin and lower than those of doxycycline and clarithromycin.     

Comparison of the in vitro activity of several cephalosporin antibiotics against gram-negative and gram-positive bacteria resistant to cephaloridine

The in vitro activity of each of two oral [cefatrizine (BL-S640), cephalexin] and three parenteral (cefamandole, cefazolin, cephapirin) cephalosporin antibiotics was compared with that of cephalothin against 168 clinical isolates of gram-negative and gram-positive bacteria selected as resistant to 20 mug of cephaloridine per ml on the basis of agar dilution susceptibility test data. Each of the five other cephalosporins inhibited a greater percentage of gram-negative bacillary isolates than did cephalothin or cephaloridine, with minimal inhibitory concentration values ranging 2- to 50-fold lower. Significant differences between minimal inhibitory concentrations of the compounds tested were also observed in tests against strains of Streptococcus faecalis and of methicillin-resistant Staphylococcus aureus. Potential advantages of including more than a single cephalosporin antibiotic in the panel of antibiotics used for routine susceptibility testing, suggested by these observations, are discussed.     

In vitro efficacy and fungicidal activity of voriconazole against Aspergillus and Fusarium species

Twenty-nine Aspergillus isolates and 25 Fusarium isolates underwent in vitro antifungal susceptibility testing by a broth macrodilution procedure adapted from the National Committee for Clinical Laboratory Standards guidelines. The MIC50s of both voriconazole and amphotericin B were 0.5 microg/ml and 1 microg/ml against species of Aspergillus and Fusarium, respectively, while the MIC90s of both agents were 1 and 2 microg/ml. Voriconazole was more active in vitro than amphotericin B: the geometric mean MICs of voriconazole and amphotericin B against Aspergillus spp. were 0.36 microg/ml and 0.64 microg/ml, respectively. Voriconazole also demonstrated fungicidal activity against Aspergillus spp., with 86% (24/29) of isolates exhibiting minimum lethal concentrations of < or = 4 microg/ml.     

In vitro activity of RU 64004, a new ketolide antibiotic, against gram-positive bacteria

The comparative in vitro activity of RU 64004 (also known as HMR 3004), a new ketolide antibiotic, was tested by agar dilution against approximately 500 gram-positive organisms, including multiply resistant enterococci, streptococci, and staphylococci. All streptococci were inhibited by < or = 1 microg of RU 64004 per ml. The ketolide was more potent than other macrolides against erythromycin A-susceptible staphylococci and was generally more potent than clindamycin against erythromycin A-resistant strains susceptible to this agent. Clindamycin-resistant staphylococci (MIC, > 128 microg/ml) proved resistant to the ketolide, but some erythromycin A- and clindamycin-resistant enterococci remained susceptible to RU 64004.     

In vitro activity of a new ketolide antibiotic, HMR 3647, against Chlamydia pneumoniae

The in vitro activities of HMR 3647, roxithromycin, erythromycin, and azithromycin against 19 strains of Chlamydia pneumoniae were tested. The MIC at which 90% of the isolates are inhibited and the minimum bactericidal concentration at which 90% of the isolates are killed of HMR 3647 were 0.25 microgram/ml (range, 0.015 to 2 micrograms/ml). Nine recently obtained clinical isolates from children with pneumonia were more susceptible (MICs, 0.015 to 0.0625 microgram/ml) than older strains that had been passaged more extensively.     

Low-level colonization and infection with ciprofloxacin-resistant gram-negative bacilli in a skilled nursing facility

BACKGROUND: We report a 1-year surveillance study that evaluates colonization and infection with ciprofloxacin-resistant gram-negative bacilli (CR GNB) and the relation to quinolone use and other possible risk factors in a proprietary skilled nursing facility (SNF) with no history of outbreaks. METHODS: Rectal swabs obtained quarterly were streaked on MacConkey agar with ciprofloxacin discs (5 microg) to screen for CR GNB and later were speciated and the antimicrobial susceptibilities were confirmed by standardized disc-diffusion tests. RESULTS: The mean prevalence of CR GNB colonization was 2.6% (range 0.9% to 5.3%). The colonization frequency was higher in the last survey than it was in the first survey. CR GNB-colonized strains included Pseudomonas species (21%), but more than half were non-Pseudomonas enterics such as Acinetobacter baumannii (25%), Proteus mirabilis (17%), and Providencia stuartii (13%). None of the patients who had colonization with CR GNB had subsequent infections with the same species. Patients with colonization had more exposure to ciprofloxacin and they were more likely to have been recently admitted from an acute-care hospital and have decubitus ulcers. During the study period, of 336 patients surveyed, 98 (29%) patients developed suspected infections and cultures were done; the infection rate was 4.7 per 1000 patient days. Of these infected patients, 59 (60%) were infected by GNBs; the infection rate was 2.3 per 1000 patient days. Nineteen percent of the GNB infections were treated with a quinolone. (Overall, quinolones constituted about 17% of antibiotic usage in the SNF). Only 3 (5%) of the patients infected with GNB were infected with CR GNB, including Pseudomonas and Providenci a species. The CR GNB infections involved multiple sites, multiple organisms, and long length of stay in the SNF. CONCLUSIONS: The findings indicate that in this community SNF, a low frequency of colonization or infection with CR GNB existed. Whether continued moderate use of quinolones will lead to increasing levels of CR GNB will require further study.