Oxacillin-susceptible Staphylococci Research Articles

In vitro evaluation of broad-spectrum β-lactams tested in medical centers in Korea: role of fourth-generation cephalosporins

Levels of resistance to the “third-generation” cephalosporins among isolates of clinical bacteria in Korea have been increasing at a rapid rate. This study evaluated the activity of cefepime, a “fourth-generation” cephalosporin, and six other broad-spectrum β-lactam antimicrobials (cefpirome, ceftazidime, ceftriaxone, imipenem, piperacillin/tazobactam [4 μg/mL fixed concentration], oxacillin) against 404 isolates of clinical bacteria from Korea. Susceptibility profiles of each isolate were established using the Etest (AB BIODISK, Solna, Sweden) method of susceptibility testing. Only the carbapenem imipenem was > 90% effective in inhibiting each of the species tested ( Escherichia coli, Klebsiella, spp., Citrobacter spp., Enterobacter spp., indole-positive Proteae, Serratia spp., Acinetobacter spp., Pseudomonas aeruginosa, and oxacillin-susceptible staphylococci). Imipenem was followed by cefepime > cefpirome > piperacillin/tazobactam > ceftazidime > ceftriaxone in overall rank order of usable spectrum against the isolates tested. Extended spectrum β-lactamase producing phenotypes were much more prevalent among the Klebsiella spp. (48.8%) than the E. coli (5.0%) isolates. Cefepime was much more active than cefpirome, 95.1% susceptible as compared with 70.7% susceptible, against the 41 isolates of Klebsiella spp. The results of this study corroborates findings from earlier studies with levels of resistance to the broad-spectrum β-lactams in Korea continuing to rise indicating the need for intervention strategies.

In vitro evaluation of broad-spectrum β-lactams in the Philippines medical centers: role of fourth-generation cephalosporins

Cefepime is a potent broad-spectrum “fourth-generation” cephalosporin. The in vitro activity of cefepime was compared to that of cefpirome, ceftazidime, ceftriaxone, imipenem, and piperacillin/tazobactam in a multilaboratory (nine medical centers) Philippine surveillance project from March through October 1998. A total of 626 Gram-positive and Gram-negative organisms (10 species groups) were tested by the Etest method (AB BIODISK, Solna, Sweden) with results validated by current quality control strain analysis. The overall rank order of usable spectrum of activity was imipenem (4.2% resistance), cefepime (4.5%), cefpirome (5.0%), piperacillin/tazobactam (5.8%) > ceftriaxone (11.2%) > ceftazidime (15.3%), and results did not differ significantly between medical centers. Ceftazidime-resistant Escherichia coli and Klebsiella spp. occurred at rates of 13.3% and 31.1%, respectively, indicating extended-spectrum β-lactamase (ESBL) activity. Imipenem (100% susceptible), cefepime, and cefpirome (both ≥ 97.8% susceptible) were active in vitro against these ESBL phenotypes. Organisms with ceftazidime and/or ceftriaxone-resistant profiles consistent for hyper-production of Amp C cephalosporinases were detected at high rates among the Citrobacter spp. (29.2%) and Enterobacter spp. (45.8%); however, imipenem (100.0% susceptible) and cefepime (98.9%) remained active. Cefepime and imipenem (both 87.5% susceptible) were the most active agents tested against Acinetobacter spp. whereas piperacillin/tazobactam was most effective against P. aeruginosa (80.0% susceptible). Most tested β-lactams (except ceftazidime) were active versus oxacillin-susceptible staphylococci. These data should be used as a guide for treatment selection with β-lactam compounds in the Philippines and to serve as a resistance benchmark in comparisons with future studies in this nation.

Important and Emerging β-Lactamase-mediated Resistances in Hospital-based Pathogens: The Amp C Enzymes

Resistance to third-generation cephalosporins mediated by β-lactamases is an increasing problem for clinical therapeutics. A wide range of Enterobacteriaceae produce these AmpC enzymes (Bush-Jacoby-Medeiros group 1), including Enterobacter spp., Citrobacter freundii, Morganella morganii, Providencia spp., and Serratia marcescens. Resistance via this mechanism has been shown to be statistically correlated with the use of some third-generation cephalosporins, and the infections caused by these stably derepressed enzyme-producing species seem to occur most frequently in the seriously ill. More recently the genes encoding this enzyme have been documented on plasmids capable of transfer into other species such as Klebsiella pneumoniae. Fourth-generation cephalosporins, with stability and low affinity for the Amp C β-lactamases and the ability to penetrate rapidly into the periplasmic space of Gram-negative organisms, offer a viable alternative in the treatment of these infections or as empiric regimens. Furthermore, these compounds (example: cefpirome) possess greater potency against the frequently occurring Gram-positive cocci such as oxacillin-susceptible staphylococci and the streptococci (including some penicillin-resistant strains) as compared to previously used anti-pseudomonal cephalosporias, ceftazidime.

Multicenter Evaluation of the In Vitro Activity of Six Broad-Spectrum β-Lactam Antimicrobial Agents in Puerto Rico

The minimum inhibitory concentrations of 6 broad-spectrum β-lactam antimicrobial agents were determined by use of the Etest versus a total of 569 bacteria in 7 Puerto Rican hospital laboratories. These included 342 recent clinical isolates of Enterobacteriaceae, 63 Pseudomonas aeruginosa, 54 Acinetobacter species, and 110 oxacillin-susceptible staphylococci. Extended spectrum β-lactamase production was noted among 11% of Klebsiella pneumoniae isolates. Hyperproduction of Amp C cephalosporinase was observed with >20% of isolates of Enterobacter spp., Serratia spp., and Citrobacter freundii. The overall rank order of activity of the six β-lactams examined in this study versus all clinical isolates was imipenem (95.8% susceptible) > cefepime (91.1%) > piperacillin/ tazobactam (82.3%) > cefotaxime (77.6%) > piperacillin (72.5%) > ceftazidime (67.0%).

Multicenter Evaluation of the Antimicrobial Activity for Six Broad-Spectrum β-Lactams in Venezuela Using the Etest Method

In early 1997, a 15-laboratory surveillance project was initiated in Venezuela to monitor the potency and spectrum of 6 broad-spectrum antimicrobial agents (cefepime, cefotaxime, ceftazidime, piperacillin, piperacillin/tazobactam, and imipenem) tested against approximately 100 organisms per participant center (1297 strains). Ten groups of organisms were tested by the Etest method (AB BIODISK, Solna, Sweden) with results validated by concurrent quality control strain analysis. Results from all centers were tabulated and 96.3% of quality assurance tests were within ranges recommended by the National Committee for Clinical Laboratory Standards. Among the six β-lactam class drugs tested, imipenem and cefepime were the most active against all isolates tested. Overall, the rank order of susceptibility of the six agents was imipenem (97.2% susceptible; MIC 90 2 μg/mL) > cefepime (92.8%; MIC 90 6 μg/mL) > piperacillin/tazobactam (77.2–83.0%; MIC 90 > 256 μg/mL) > cefotaxime (72.2%; MIC 90 > 256 μg/mL) > piperacillin (56.8–65.8%; MIC 90 > 256 μg/mL) > ceftazidime (64.6%; MIC 90 128 μg/mL). Both cefepime and imipenem were active against ceftazidime-resistant strains of Enterobactericaeae as well as against Pseudomonas aeruginosa and oxacillin-susceptible staphylococci. Resistance phenotypes consistent with extended spectrum β-lactamases (ESBLs) and stably derepressed Bush group 1 cephalosporinases were documented in strains of Klebsiella spp. and Enterobacters, respectively. These data should be used to guide empiric therapy with β-lactams in Venezuela, and additionally will provide a reference statistical baseline to which future studies in this nation can be compared.

Multicenter evaluation of antimicrobial resistance to six broad-spectrum β-lactams in Colombia using the etest method

The need for comprehensive and quantitative accurate antimicrobial resistance surveillance systems has become acute as a guide to problem recognition and to focus local interventions. A multilaboratory (10 medical centers) Colombia surveillance project was initiated in early 1997 to monitor the potency and spectrum of six (cefepime, cefotaxime, ceftazidime, cefoperazone/sulbactam, aztreonam, and imipenem) broad-spectrum antimicrobial agents tested against 100 organisms per participant center (802 strains). Ten groups of organisms were tested by a reference-quality method (Etest; AB BIODISK, Solna, Sweden) with results validated by concurrent quality control and additional challenge strain analysis. Results from nine qualifying medical centers were tabulated, and 95.7 to 96.8% of quality assurance tests were within expected ranges. Only cefepime (90.1–100.0% susceptible) and imipenem (96.3–100.0%) were active against all Enterobacteriaceae at >90% of susceptible isolates using the breakpoint concentrations recommended by the National Committee for Clinical Laboratory Standards. Among ceftazidime- (or cefotaxime- or aztreonam-) resistant Enterobacter spp. and Citrobacter freundii, cefepime remained active, but not cefoperazone with sulbactam. Escherichia coli and Klebsiella spp. strains having resistance phenotypes consistent with extended spectrum β-lactamase production were discovered in approximately 5 to 10% of isolates. All tested drugs except ceftazidime (31.8–57.7% susceptible) were active against >94% of oxacillin-susceptible staphylococci. Similar rates of resistance (9.1–14.8%) were observed in Pseudomonas aeruginosa for five of six drugs (not cefotaxime; 15.9% of strains were susceptible). Acinetobacter spp. isolates were most susceptible to imipenem (95.8%), cefepime (86.1%), and cefoperazone/sulbactam (83.3%). Overall for the 1997 order of antimicrobial spectrums for these tested compounds was: imipenem (96.6%) > cefepime (93.6%) > cefoperazone/sulbactam (90.5%) > cefotaxime (74.9%) > aztreonam (74.3% for Gram-negative bacilli only) > ceftazidime (73.2%). These data should be used to guide empiric regimens in Colombia, and additionally will provide a resistance statistical baseline to which future studies in this nation can be compared.

CQ-397 and CQ-414: antimicrobial activity and spectrum of two fluoroquinolone---cephalosporin, dual-action compounds with carboxamido bonds.

OBJECTIVE: To evaluate the potential spectrum of activity of two novel dual-action compounds with carboxamido bonds (CQ-397 and CQ-414; Laboratorios Aranda, San Rafael, Mexico) against human pathogens. METHODS: Approximately 800 Gram-positive and Gram-negative aerobic clinical bacteria were tested in vitro using the Mueller-Hinton broth microdilution method of the National Committee of Clinical Laboratory Standards. RESULTS: CQ-397 (cefamandole+enrofloxacin) and CQ-414 (cefamandole+norfloxacin) were equally potent against Enterobacteriaceae (MIC90 range, 0.06--0.5 microg/mL and 0.06--1 microg/mL, respectively). Citrobacter freundii (MIC90, 4 microg/mL) and Providencia spp. (MIC90, >32 microg/mL) exhibited elevated study drug MICs. Enterobacteriaceae resistant to fluoroquinolones generally remained resistant. CQ-397 and CQ-414 were active against Stenotrophomonas maltophilia (MIC90, 4 microg/mL) and oxacillin-susceptible staphylococci (MIC90, 0.25 microg/mL), but not oxacillin-resistant Staphylococcus aureus (MIC90, >32 microg/mL), Staphylococcus epidermidis (MIC90, 8 microg/mL), and enterococci (MIC90s, 8 to >32 microg/mL). There was no difference in the dual-action drug activity (MIC90, 2 microg/mL) between penicillin-susceptible and -resistant pneumococci. Haemophilus influenzae and Moraxella catarrhalis were very susceptible (MIC range, less-than-or-equal0.015--0.06 microg/mL) to both compounds. CONCLUSIONS: The activity of these novel dual-action compounds, formed from the bonding of older antimicrobials, warrants further investigation for potential human and/or animal health use, including toxicology and pharmacokinetics.

Cefotaxime in the treatment of staphylococcal infections: Comparison of in vitro and in vivo studies

Staphylococcus aureus strains are well-established pathogens that may cause mild to serious life-threatening disease. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, also have a pathogenic role in humans and cause infections primarily associated with prosthetic devices and indwelling catheters, whereas Staphylococcus saprophyticus usually causes urinary tract infections. Cefotaxime is a “third-generation” cephalosporin that is stable to the staphylococcal β-lactamases. In vitro studies over the last 15 years have shown that this patenteral cephalosporin has remained highly active (MIC 90 ranges of ≤2–8 μg/ml) against oxacillin-susceptible staphylococci. Cefotaxime therapy of staphylococcal infections has resulted in clinical curelimprovement rates ranging from 78%–100% and bacteriologic eradication rates ranging from 85%–100% in a wide variety of infections. Contrary to contemporary dogma, this “third-generation” cephalosporin appears to be efficacious against staphylococcal infections from a review of 15 years of clinical experience.

Multicenter in vitro comparative study of fluoroquinolones against 25,129 Gram-positive and Gram-negative clinical isolates

In vitro activities of fleroxacin, ciprofloxacin, ofloxacin, and lomefloxacin were evaluated against 25,129 fresh bacterial isolates from 51 US hospital or medical center laboratories, beginning in October of 1990. Susceptibility rates were ⩾85% against most species of Gram-negative bacteria. Notable exceptions were Pseudomonas, Acinetobacter, Xanthomonas, and Providencia. The study drugs displayed similar activity against most Gram-negative species. At least 90% of oxacillin-susceptible staphylococci were susceptible but, of oxacillin-resistant strains, only approximately 60% of Staphylococcus epidermidis and 25% of Staphylococcus aureus were susceptible to the quinolones tested. Staphylococcus saprophyticus strains were less susceptible to fleroxacin (42%) than to the other compounds (79%–97%). Ofloxacin and ciprofloxacin were more active against streptococci, and none of the compounds demonstrated appreciable activity against enterococci. Thus, the spectra of activity of fluoroquinolones illustrate that they remain effective agents for the treatment of many types of infections caused by Gram-negative pathogens.

A multicentre study: Staphylococcus and Enterococcus susceptibility to antibiotics.

A multicentre study to evaluate the susceptibility of Gram-positive cocci isolated from clinical samples, was performed by six centres working in different areas of Italy. We examined 4,544 strains of Staphylococcus aureus, 4,381 strains of coagulase-negative staphylococci and 2,478 strains of enterococci. The following antibiotics were tested: penicillin G, ampicillin, amoxicillin, piperacillin, imipenem, oxacillin, ofloxacin, pefloxacin, ciprofloxacin, gentamicin, tobramycin, amikacin, netilmicin, rifampicin, clindamycin, tetracycline, cotrimoxazole, erythromycin, chloramphenicol, vancomycin and teicoplanin. Oxacillin-susceptible staphylococci confirmed their susceptibility to many other antimicrobial agents while oxacillin-resistant strains confirmed their multiple and frequent resistance to antibiotics. Resistance to oxacillin, cotrimoxazole and chloramphenicol was more frequent in coagulase-negative staphylococci than in Staphylococcus aureus. Aminoglycosides, rifampicin and quinolones were more active against coagulase-negative staphylococci than against Staphylococcus aureus. Enterococci were susceptible to penicillins and imipenem, and moderately susceptible to ciprofloxacin. Susceptibility of 70-79% was observed with high levels of aminoglycosides. Excellent results against staphylococci and enterococci were observed with vancomycin and teicoplanin.

LevofloxacinIn VitroActivity: Results from an International Comparative Study with Ofloxacin and Ciprofloxacin

Levofloxacin, the S-(-)-isomer of ofloxacin, was compared to ofloxacin and ciprofloxacin against > 6000 recent clinical isolates of Gram-positive and Gram-negative bacteria from six different countries. This international multicenter study demonstrated a high level of antibacterial activity of levofloxacin against all the members of Enterobacteriaceae [minimum inhibitory concentration (MIC)50s, < or = 0.03 to 0.12 mg/L] except Providencia rettgeri (MIC50, 2 mg/L), and Providencia stuartii (MIC50, 1 mg/L). Oxacillin-susceptible staphylococci (MIC50s, 0.12 to 0.25 mg/L), enterococci (MIC50s, 0.5 to 2 mg/L), and streptococci (MIC50s, 0.5 mg/L) were also susceptible to levofloxacin, but most isolates of oxacillin-resistant staphylococci had MICs of > or = 4 mg/L. Levofloxacin was also active against non-enteric Gram-negative bacilli, including Acinetobacter species (MIC50s, < or = 0.03 to 1 mg/L), Pseudomonas species (MIC50s, 0.5 to 1 mg/L) and Xanthomonas maltophilia (MIC50, 0.5 mg/L). Overall, levofloxacin inhibited 50% and 90% of all the tested strains at the concentrations of 0.12 and 4 mg/L, respectively. The activity of levofloxacin was generally two-fold greater than ofloxacin and equal to or slightly less potent than ciprofloxacin.

Antimicrobial activity of FK-037, a new broad-spectrum cephalosporin international in vitro comparison with cefepime and ceftazidime

The in vitro activity of FK-037, a new parenteral 7-aminothiazolyl-methoxyimino cephalosporin, was compared with cefepime and ceftazidime against 6094 aerobic isolates collected in six medical centers worldwide. FK-037 demonstrated potent activity against the Enterobacteriaceae family except for some Enterobacter spp., Providencia spp., and Serratia liquefaciens (MIC 90s, ⩾16 μg/ml). Against nonenteric Gram-negative bacilli, all compounds tested showed similar, but more limited activity. The FK-037 MIC 50s for Pseudomonas spp. and P. aeruginosa were 2 and 4 μg/ml, respectively. The least susceptible organisms were Xanthomonas maltophilia, enterococci, and Bacillus spp. (MIC 50s, >16 μg/ml), followed by Flavobacterium spp., other nonenterics, and oxacillin-resistant Staphylococcus aureus (MIC 50s, 16 μg/ml). Good FK-037 activity was observed against oxacillin-susceptible staphylococci as well as against β-hemolytic and viridans-group streptococci (MIC 90 range, ⩽0.12 to 2 μg/ml). While FK-037 was slightly more active than cefepime against Gram-positive organisms, enteric bacilli were most susceptible to cefepime. Overall, the antibacterial spectrum of both FK-037 and cefepime was superior to ceftazidime.

Antimicrobial activity of a new antipseudomonal dual-action drug, Ro 25-0534

Ro 25-0534, a tertiary amine-linked dual action combination (DAC) of a catechol cephalosporin and ciprofloxacin, was compared with a previously described DAC (Ro 23-9424), ciprofloxacin and cefotaxime. A total of 688 recent clinical isolates were tested and an additional collection of 110 Gram-negative bacilli possesing documented resistance to broad-spectrum antimicrobials were used. Ro 25-0534 was active against all tested species of Enterobacteriaceae (MIC 90 range, 0.06–2 μg/ml), oxacillin-susceptible staphylococci, β-hemolytic streptococci, and penicillin-susceptible pneumococci (MIC 90 range, 1–2 μg/ml), Haemophilus influenzae (MIC 90 range, 0.25–0.5 μg/ml), Moraxella catarrhalis (MIC 90, 0.5 μg/ml), and most nonenteric Gram-negative bacilli (MIC 90 range, 2–4 μg/ml) such as Pseudomonas aeruginosa, Acinetobacter spp., and Xanthomonas maltophilia. Enterococci and Bacteroides fragilis isolates were resistant to Ro 25-0534. The Ro 25-0354 potency against most susceptible strains was generally severalfold less than that of Ro 23-9424 (except for Pseudomonas-Xanthomonas) or ciprofloxacin alone.

Prediction of bacterial susceptibility to cefpodoxime by using the ceftriaxone minimum inhibitory concentration result

The cross-resistance or cross-susceptibility of cefpodoxime and ceftriaxone for 3700 strains of Enterobacteriaceae, oxacillin-susceptible staphylococci, Streptococcus spp., Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae was evaluated. With the exception of tests with Enterobacter spp. and Morganella morganii, the ceftriaxone minimum inhibitory concentration (MIC) result interpretive criteria predicted bacterial susceptibility (or resistance) to cefpodoxime with an acceptable rate of serious interpretive errors (1.5%) and an absolute categorical agreement >92%. By using cefpodoxime interpretive criteria for ceftriaxone MICs, the interpretive errors for testing enteric bacilli were reduced from 2.1% to 1.5%.

In vitro comparison of E4868, a new trifluoroquinolone, with ciprofloxacin and temafloxacin tested against 5192 recent clinical isolates from five medical centers

The in vitro activity of E4868 was compared with that of ciprofloxacin and temafloxacin in a multicenter study. More than 90% of Enterobacteriaceae and 82% of the 651 isolates of Pseudomonas aeruginosa, as well as >95% of the oxacillin-susceptible staphylococci, 100% of the β-hemolytic streptococci, and 76% of the enterococcal isolates were susceptible to E4868 (minimum inhibitory concentrations, ≤2 μg/ml). E4868 was generally equivalent or slightly less active than ciprofloxacin against the Enterobacteriaceae and Pseudomonas and more active against straphylococci and β-hemolytic streptococci. The activity of E4868 was generally equivalent to or slightly greater than that of temafloxacin against all major groups of organisms.

In VittoComparison Activity ofOPC-17116, a New Fluoroquinolone, Against More Than 5,000 Recent Clinical Isolates from Five Medical Centers

The in vitro activity of OPC-17116, a new fluoroquinolone, was compared with those of ciprofloxacin, ofloxacin and cefixime. A total of 5,231 fresh clinical isolates from five geographically separate US medical centers were tested. The primary results of this study are: 1. OPC-17116 is very active against Enterobacteriaceae [MIC90s, 0.015-1 microgram/ml, except Providencia rettgeri (MIC90, > 8 micrograms/ml)], 2. among nonenteric Gram-negative bacilli (e.g. Xanthomonas maltophilia, MIC90, 2 micrograms/ml) and Gram-positive cocci (e.g. oxacillin-susceptible staphylococci, MIC90s, 0.12-0.5 microgram/ml) OPC-17116 demonstrated higher activity than ciprofloxacin or ofloxacin, 3. the quinolones were more active than cefixime against most of the species tested, especially against Gram-positive and non-enteric Gram-negative organisms. The results of this study, associated with prior documented favorable qualities, support continued investigation of OPC-17116 for clinical use.

In vitro activity of cefpodoxime compared with other oral cephalosporins tested against 5556 recent clinical isolates from five medical centers

A multicenter study was conducted in which the in vitro activity of cefpodoxime (the active metabolite of the prodrug ester cefpodoxime proxetil) was compared with those of cefixime, cefuroxime, cefaclor, cefadroxil, and clarithromycin against 5556 recent clinical isolates. Cefpodoxime demonstrated potent activity against members of the Enterobacteriaceae, in particular against species generally resistant to the established oral cephalosporins such as Proteus vulgaris [minimum inhibitory concentration (MIC) 50, 0.12 μg/ml], Providencia rettgeri (MIC 50, 0.015 μg/ml), and Serratia marcescens (MIC 50, 2 μg/ml). Cefpodoxime was very effective against the fastidious organisms most frequently associated with respiratory infections, such as Streptococcus pneumoniae (MIC 90, 0.12 μg/ml), Haemophilus influenzae (MIC 90, 0.12 μg/ml), and Moraxella catarrhalis (MIC 90, 1 μg/ml). In contrast to other orally administrated third-generation cephalosporins (cefixime or ceftibuten), cefpodoxime demonstrated reasonable activity against oxacillin-susceptible staphylococci, with MIC 90 ranging from 1 to 2 μg/ml. All cephalosporins tested demonstrated poor activity against Pseudomonas spp., Xanthomonas spp., Enterococcus spp., and oxacillin-resistant staphylococci. Cefpodoxime had the widest spectrum of activity of all tested oral cephalosporins.

In vitro activity of sparfloxacin, ciprofloxacin, ofloxacin, and other antibiotics against bloodstream isolates of gram-positive cocci

The in vitro activity of sparfloxacin was compared with the activities of ciprofloxacin, ofloxacin, and six other antimicrobial agents against 323 bloodstream isolates of staphylococci (both oxacillin susceptible and resistant) enterococci, and pneumococci. Sparfloxacin was more active than both ciprofloxacin and ofloxacin against all the isolates tested. Its activity (MIC for 90% of strains tested ≤0.10 μg/ml) against oxacillin-susceptible staphylococci was superior to that of ciprofloxacin and ofloxacin by at least fourfold. Sparfloxacin was also more potent against pneumococci. However, fluoroquinolone resistance was noted among oxacillin-resistant strains of Staphylococcus aureus and coagulase-negative staphylococci.

A Multicenter Study on the Comparative In Vitro Activity of Fleroxacin and Three Other Quinolones: An Interim Report from 27 Centers

A multicenter study was designed to compare the in vitro activity of fleroxacin to that of three other oral quinolones (ciprofloxacin, ofloxacin, and lomefloxacin) against fresh clinical bacterial isolates in hospital or medical center laboratories throughout the United States. Each of the 50 centers was asked to test 500 gram-negative and gram-positive strains using the MicroScan (Baxter) microtiter system. This report includes the results of the study, begun in October 1990, on 12,013 isolates tested in 27 centers. Susceptibility was based on minimum inhibitory concentration (MIC) interpretive criteria from the National Committee for Clinical Laboratory Standards guidelines or published literature. Fleroxacin and the three other quinolones were all active against Enterobacteriaceae, with 95-97% of the strains susceptible. Against other aerobic gram-negative bacilli, 79-83% of the strains were susceptible to fleroxacin, ciprofloxacin, and ofloxacin, and 75% were susceptible to lomefloxacin. With regard to the gram-positive isolates, 79% were susceptible to ofloxacin, 74% to ciprofloxacin, and 52% to fleroxacin and lomefloxacin. The susceptibility data were further delineated for the various species in each of the three major bacterial groups. All four quinolones were highly active against Enterobacteriaceae and were moderate to excellent in activity against other aerobic gram-negative organisms. Activity against oxacillin-susceptible staphylococci was also excellent; however, all four agents were generally much less active against oxacillin-resistant strains. Ofloxacin and ciprofloxacin were clearly superior to fleroxacin and lomefloxacin against streptococci and enterococci.

Comparative in vitro activity of cefdinir (CI-983; FK-482) against staphylococci, gram-negative bacilli and respiratory tract pathogens

The in vitro activity of cefdinir (CI-983; FK-482), a new oral cephalosporin, was compared with that of other antimicrobial agents against clinical isolates of staphylococci, gram-negative bacilli and common respiratory tract pathogens. Cefdinir (MIC90 less than or equal to 2.0 micrograms/ml) was more active than cefixime (MIC90 greater than 64 micrograms/ml) and equally as active as cefuroxime (MIC90 2.0 micrograms/ml) against oxacillin-susceptible staphylococci. Cefdinir was active against Haemophilus influenzae, including beta-lactamase producers (MIC90 0.5 microgram/ml), Moraxella catarrhalis (MIC90 less than or equal to 0.12 microgram/ml), Streptococcus pneumoniae (MIC90 less than or equal to 0.06 microgram/ml) and Streptococcus pyogenes (MIC90 less than or equal to 0.06 microgram/ml). The activity of cefdinir against gram-negative bacilli was variable; organisms with chromosomal cephalosporinases were often resistant.