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C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 19 recordsLinked to original sources
PubMed1999

In vitro antibacterial properties of pexiganan, an analog of magainin.

Pexiganan, a 22-amino-acid antimicrobial peptide, is an analog of the magainin peptides isolated from the skin of the African clawed frog. Pexiganan exhibited in vitro broad-spectrum antibacterial activity when it was tested against 3,109 clinical isolates of gram-positive and gram-negative, anaerobic and aerobic bacteria. The pexiganan MIC at which 90% of isolates are inhibited (MIC90) was 32 micrograms/ml or less for Staphylococcus spp., Streptococcus spp., Enterococcus faecium, Corynebacterium spp., Pseudomonas spp., Acinetobacter spp., Stenotrophomonas spp., certain species of the family Enterobacteriaceae, Bacteroides spp., Peptostreptococcus spp., and Propionibacterium spp. Comparison of the MICs and minimum bactericidal concentrations (MBCs) of pexiganan for 143 isolates representing 32 species demonstrated that for 92% of the isolates tested, MBCs were the same or within 1 twofold difference of the MICs, consistent with a bactericidal mechanism of action. Killing curve analysis showed that pexiganan killed Pseudomonas aeruginosa rapidly, with 10(6) organisms/ml eliminated within 20 min of treatment with 16 micrograms of pexiganan per ml. No evidence of cross-resistance to a number of other antibiotic classes was observed, as determined by the equivalence of the MIC50s and the MIC90s of pexiganan for strains resistant to oxacillin, cefazolin, cefoxitin, imipenem, ofloxacin, ciprofloxacin, gentamicin, and clindamicin versus those for strains susceptible to these antimicrobial agents. Attempts to generate resistance in several bacterial species through repeated passage with subinhibitory concentrations of pexiganan were unsuccessful. In conclusion, pexiganan exhibits properties in vitro which make it an attractive candidate for development as a topical antimicrobial agent.

Anti-Bacterial Agents↗
PubMed1997

Surveillance of antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the United States in 1996-1997 respiratory season. The Laboratory Investigator Group.

A U.S. surveillance study of antimicrobial resistance in respiratory tract pathogens in the respiratory season (1996-1997) is reported that included 11,368 isolates from 434 institutions in 45 states and the District of Columbia. beta-lactamase was produced by 33.4% of Haemophilus influenzae and 92.7% of Moraxella catarrhalis. Of the 9,190 Streptococcus pneumoniae isolates tested, 33.5% were not susceptible to penicillin (MIC > or = 0.12 microgram/mL), with 13.6% having high-level resistance (MICs > 1 microgram/mL). For H. influenzae, the most active antimicrobials (based on percent of strains susceptible) were levofloxacin (100%) and ceftriaxone (99.9%); the least active were ampicillin (67.2%) and clarithromycin (58.1%). For M. catarrhalis, the most active drugs were amoxicillin-clavulanate, ceftriaxone, and levofloxacin (100%); the least active was ampicillin. The order of the activity of the drugs against S. pneumoniae were levofloxacin (97.3%) > ceftriaxone (87.1%) > amoxicillin-clavulanate (81.7%) = clarithromycin (80.9%) > cefuroxime (74.5%) > penicillin (66.5%). The activity of the beta-lactams and clarithromycin against isolates of S. pneumoniae was closely associated with the resistance to penicillin. Levofloxacin was more active against S. pneumoniae overall, because it exhibited no cross-resistance. These data indicate that the incidence of beta-lactamase production in H. influenzae (33.4%) and M. catarrhalis (92.7%) is similar to other recent studies, and that the incidence of penicillin-intermediate and -resistant S. pneumoniae is increasing, particularly the high-level penicillin-resistant (MICs > 1 microgram/mL) strains, which were often multi-resistant.

Amoxicillin-Potassium Clavulanate Combination↗
PubMed1997

The activity of a combination of penicillin and novobiocin against bovine mastitis pathogens: development of a disk diffusion test.

The combination of penicillin and novobiocin is currently available for the treatment of bovine mastitis, but methods are not available for susceptibility testing of the combination by veterinary diagnostic laboratories. The minimum inhibitory concentration (MIC) and disk diffusion data were determined for penicillin, novobiocin, and a combination of the two in a 1:2 ratio for 225 staphylococcal, streptococcal, and Gram-negative isolates from bovine intramammary infections. Based on the drug concentrations in milk following infusion, linear regression analysis, and error rate bounding, the interpretive zone diameters selected were < or = 16 mm for resistant isolates and > or 17 mm for susceptible isolates with a disk containing 10 U of penicillin and 30 micrograms of novobiocin. Additionally, MIC breakpoints of < or = 2 micrograms/ml of penicillin and 4 micrograms/ml of novobiocin were selected to categorize isolates as susceptible and > or = 4 micrograms/ml of penicillin and 8 micrograms/ml of novobiocin were selected to categorize isolates as resistant. The MIC and disk diffusion results, as well as studies to monitor bacterial killing by antimicrobial agents over time, indicated that the combination of penicillin and novobiocin in a 1:2 ratio was more active than were the individual drugs. Kinetics of the kill curves with the penicillin and novobiocin combination (1:2 ratio) showed that the combination was bactericidal for Staphylococcus aureus and Staphylococcus xylosus.

Animals↗
PubMed1996

Comparative activity of eight antimicrobial agents against clinical bacterial isolates from the United States, measured by two methods.

In a surveillance study conducted during 1992-1993 at 83 medical institutions of different types and sizes (e.g., laboratories, community hospitals, teaching hospitals) and from different geographical areas of the United States, clinical bacterial isolates were tested for their susceptibility to eight comparative antimicrobial agents (cefepime, ceftazidime, cefotaxime, ceftriaxone, ciprofloxacin, gentamicin, imipenem, and piperacillin). A total of 12,574 isolates were tested by either the Etest method (AB Biodisk) or a microdilution method (MicroScan) in the participating laboratories; 11.8% of these isolates were subsequently retested for quality assurance purposes by both methods in a central laboratory. The results obtained in the central laboratory were essentially the same as the results obtained in the participating laboratories. This article presents data for gram-negative and gram-positive isolates other than Streptococcus pneumoniae, the results of which have been previously published. Antimicrobial susceptibility results obtained with the two different minimum inhibitory concentration (MIC) methods--MicroScan and Etest--showed that most isolates of Enterobacteriaceae were susceptible to cefepime, exceeding the activity of ceftazidime, ceftriaxone, and cefotaxime, principally because of the greater activity of cefepime against the species that produce Bush group 1 beta-lactamases (predominantly Enterobacter cloacae, Enterobacter aerogenes, and Citrobacter freundii). In addition, the activity of cefepime against Pseudomonas aeruginosa isolates was essentially equivalent to that of ceftazidime and greater than that of third-generation cephalosporins. Most methicillin-susceptible Staphylococcus aureus were susceptible to all the cephalosporins, whereas methicillin-resistant S. aureus and enterococci were resistant. Overall, the most active antimicrobials in this study were imipenem, ciprofloxacin, and cefepime, but the activity of all the antimicrobials varied with different species. Categorically, the results from the microdilution and Etest methods were equivalent.

Anti-Bacterial Agents↗
PubMed1996

Methods of measuring susceptibility of anaerobic bacteria to trovafloxacin, including quality control parameters.

Three methods approved by the National Committee for Clinical Laboratory Standards for testing the susceptibility of anaerobic bacteria were used to evaluate the fluoroquinolone, trovafloxacin. The methods gave essentially comparable results with 126 anaerobes and with three quality control strains. A collaborative study defined the quality control range for trovafloxacin MICs. Trovafloxacin had good in vitro activity against the more common anaerobes (MIC 90 < = or 2.0 micrograms/ml).

Anti-Infective Agents↗
PubMed1996

Activity of penicillin and three third-generation cephalosporins against US isolates of Streptococcus pneumoniae: a 1995 surveillance study.

In a surveillance study of Streptococcus pneumoniae from the United States the incidence of resistance (including both resistant and relatively resistant strains) to penicillin was 37.2% when tested by the oxacillin disk-diffusion test, or 27.2% when tested by microdilution minimum inhibitory concentrations. Strains that were susceptible to penicillin by the oxacillin test were also susceptible to the third-generation cephalosporins cefotaxime, ceftriaxone, and ceftizoxime. The overall resistance (without regard to penicillin resistance) to cefotaxime was 8.8%, to ceftriaxone was 7.9%, and to ceftizoxime was 17.2%; the rates of resistance among penicillin-resistant and relatively resistant strains (combined), however, were 23.6% for cefotaxime, 21.4% for ceftriaxone, and 43.2% for ceftizoxime. The incidence of penicillin resistance and relative resistance in these pneumococcal isolates varied from one institution to another, but all institutions had these strains and the incidence varied from 4.3% to 60.9%. Having ceftizoxime, the least active of the third-generation cephalosporins, tested on the formulary did not appear to increase selection of beta-lactam-resistant strains. The increased resistance to penicillin with the concomitant increase in resistance to third-generation cephalosporins may greatly increase the difficulty of selecting optimal therapy of patients with life-threatening infections due to S. pneumoniae.

Cefotaxime↗
PubMed1996

Interpretive criteria for antimicrobial susceptibility testing of ceftiofur against bacteria associated with swine respiratory disease.

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.

Actinobacillus pleuropneumoniae↗
PubMed1996

Emerging resistance in clinically important gram-positive cocci.

In the first half of the decade of the 1990s, we in the United States have seen the emergence and escalation of substantial antimicrobial resistance in medically important gram-positive cocci. The incidence of methicillin resistance of Staphylococcus aureus continues to increase (now 18%), resulting in many more isolates that are multiply resistant; all S aureus isolates are still susceptible to vancomycin. Enterococci, particularly Enterococcus faecium, have increasingly developed resistance to penicillin, gentamicin, streptomycin, and vancomycin (the last plasmid-mediated). More than a fourth of Streptococcus pneumoniae strains are now resistant to penicillin, and these strains tend to be multiply resistant, including to cephalosporins and macrolides.

Drug Resistance, Microbial↗
PubMed1995

Subgingival bacteria--comparison of culture results in dogs and cats with gingivitis.

Aerobic and anaerobic subgingival bacteria were cultured and identified from 49 dogs and 40 cats with spontaneous gingivitis. The most common organisms were gram-negative anaerobes (37% of canine isolates and 39% of feline isolates) and gram-positive aerobes (36% of canine isolates and 29% of feline isolates). No major differences were found between the subgingival floras of dogs and cats with gingivitis.

Animals↗
PubMed1995

Antimicrobial susceptibility of subgingival bacterial flora in dogs with gingivitis.

The aerobic and anaerobic flora from gingival pockets of 49 dogs with severe gingivitis and periodontitis were cultured. The susceptibility of each isolate to four antimicrobial agents currently approved for veterinary use in the USA (amoxicillin-clavulanic acid; clindamycin; cefadroxil; and enrofloxacin) was determined. Amoxicillin-clavulanic acid (Clavamox Pfizer Animal Health) had the highest in-vitro susceptibility against all isolates (96%), all aerobes (94%) and all anaerobes (100%) tested. For gram-negative aerobes, enrofloxacin (Baytril, Bayer Corp.) had the highest in-vitro susceptibility activity. For bacteria associated with treatment of gingivitis, which typically are mixed aerobic/anaerobic and gram-positive/gram-negative organisms, the antimicrobial of choice for clinical use based on these susceptibility tests is amoxicillin-clavulanic acid.

Amoxicillin-Potassium Clavulanate Combination↗
PubMed1995

Antimicrobial susceptibility of subgingival bacterial flora in cats with gingivitis.

The aerobic and anaerobic flora from gingival pockets of 40 cats with established gingivitis were cultured. The susceptibility of each isolate to four antimicrobial agents currently approved for use in cats (amoxicillin-clavulanic acid; clindamycin; cefadroxil; enrofloxacin) was determined. Amoxicillin-clavulanic acid (Clavamox) had the highest in-vitro susceptibility against all isolates (92%) and all anaerobes (99% [co-equal with clindamycin]) tested; enrofloxacin (Baytril) had the highest in-vitro susceptibility against all aerobes (90%) tested.

Amoxicillin-Potassium Clavulanate Combination↗
PubMed1994

Susceptibility of clinical bacterial isolates to ciprofloxacin in the United States.

In 1990-1991, in a national surveillance study of bacterial resistance, ciprofloxacin data from geographic and demographically diverse institutions were collected. Most of the isolates were from hospitalized patients. Ciprofloxacin susceptibility was obtained on 154,689 clinical isolates comprising 48 genera and 128 species or groups; 60.2% of the species or groups and 62.3% of the isolates were gram-negative. MIC tests and identification tests also were performed on 12,012 of these isolates, which had been submitted to our in-house laboratory. For all surveillance isolates, 88.2% were susceptible, 4.6% were moderately susceptible, and 7.2% were resistant to ciprofloxacin. Most isolates (96.2%) of the surveillance Enterobacteriaceae were susceptible to ciprofloxacin, as were 87.7% of the Pseudomonas aeruginosa (7.8% resistant). A majority of the methicillin-susceptible strains of Staphylococcus aureus were susceptible (95.7%) or moderately susceptible (1.4%) to ciprofloxacin. But a majority of methicillin-resistant isolates were resistant (76.4%) to ciprofloxacin. Most of the pneumococci (96.5%) were susceptible or moderately susceptible to ciprofloxacin with 92.7% of these isolates having MICs of 1 mg/l (susceptible) or 2 mg/l (moderately susceptible). The ciprofloxacin data for the isolates tested in our in-house laboratory generally confirmed the susceptibility rates of those from the surveillance data. This study shows that, with the exception of methicillin-resistant staphylococci, ciprofloxacin has retained a high level of activity against most bacterial pathogens.

Bacterial Infections↗
PubMed1994

Epidemiology of staphylococcal infections--a USA perspective.

Data collected from the National Nosocomial Infection Surveillance show that Gram-positive organisms, and Staphylococcus aureus in particular, are a major cause of nosocomial infections, especially wound infections, pneumonia and bacteraemia. Currently in the United States, approximately 18% of S. aureus isolates show intrinsic resistance to methicillin.

Anti-Bacterial Agents↗
PubMed1993

A comparative study of the in-vitro activity of cefepime and other antimicrobial agents against penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae.

Using the national surveillance programme of USA hospitals, we selected 162 strains of Streptococcus pneumoniae for sensitivity testing using the NCCLS breakpoints for benzylpenicillin and the oxacillin discs screen test. Included in the group of isolates were 85 relatively penicillin-resistant and 33 penicillin-resistant strains. The activity of cefepime, a new cephalosporin, was compared with other cephalosporins and penicillins as well as some non-beta-lactam antimicrobials. Imipenem was the most active agent but, cefepime, cefotaxime, ceftriaxone and ciprofloxacin were only slightly less active. The least active agents were ceftazidime, cefuroxime, piperacillin/tazobactam and ticarcillin/clavulanate. Cefepime is a potential alternative treatment to penicillin, particularly when penicillin-resistant and relatively penicillin-resistant S. pneumoniae are encountered. The clinical importance of screening for penicillin resistance by the use of the oxacillin disc is emphasized.

Anti-Bacterial Agents↗
PubMed1993

In-vitro activity of cefepime and other antimicrobials: survey of European isolates.

Cefepime, a new cephalosporin which has a broad-spectrum of activity was tested in vitro against 1961 Gram-positive and Gram-negative clinical isolates obtained from European hospitals. Cefepime was highly active against Gram-negative organisms, inhibiting over 94% of strains tested. The overall susceptibility rate for cefepime against all isolates was 81%. Cefepime was more active than any of the third-generation cephalosporins tested against species capable of producing type I beta-lactamases, e.g. Enterobacter cloacae, Citrobacter freundii, and Enterobacter aerogenes. The activity of cefepime against Pseudomonas aeruginosa was similar to that of ceftazidime and substantially greater than those of cefotaxime and ceftriaxone. All cephalosporins except ceftazidime exhibited high activity against methicillin-susceptible Staphylococcus aureus but poor activity was observed against methicillin-resistant strains. Overall susceptibility to cefepime is lower in Europe than it is in North America.

Anti-Bacterial Agents↗
PubMed1993

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.

Animals↗