Search PubMed⌕ Search

Biomedical subjects

C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 73 records · Page 4Linked to original sources
PubMed1990

Patterns and mechanisms of beta-lactam resistance among isolates of Escherichia coli from hospitals in the United States.

To study the national distribution of beta-lactam resistance patterns and mechanisms among Escherichia coli organisms isolated in U.S. hospitals, 652 ampicillin-resistant (Am(r)) or ampicillin-intermediate (Ami) isolates were submitted to the Centers for Disease Control from March 1983 through July 1984 by nine hospitals participating in the National Nosocomial Infections Study. Among the isolates (most of which caused urinary tract infections), 78% were Am(r) and 22% were Ami by the interpretative criteria established by the National Committee for Clinical Laboratory Standards. Resistance to carboxypenicillins ranged from 73 to 74%, and that to acylureidopenicillins ranged from 43 to 66%. A total of 26% of the isolates were resistant to cephalothin, and 4% were resistant to cefazolin. Resistance to cefoxitin was 1%, while resistances to cefuroxime and cefamandole were 2 and 7%, respectively. With the exception of cefsulodin (98% resistant) and cefoperazone (1% resistant), there was no resistance to newer cephalosporins or aztreonam. In general, only minor differences in the incidence of resistance to beta-lactam antibiotics were noted in hospital-acquired versus non-hospital-acquired isolates as well as among isolates from various regions of the United States. TEM beta-lactamases were produced by 87% of the 237 Am(r) isolates examined. By our methods, OXA and chromosomal (type I) beta-lactamases were detected in 2 and 28 isolates, respectively, and plasmid-mediated extended-spectrum cephalosporinases were detected in none of the isolates. Disk substrate and clavulanic acid inhibition assays revealed that TEM beta-lactamase conferred Am(r) and resistance to carboxypenicillins, acylureidopenicillins, cephalothin, cefamandole, cefsulodin, and cefoperazone. A total of 391 isolates were screened for plasmids, and 259 isolates were examined by DNA hybridization with a TEM probe. Among 462 plasmids probed, 129 plasmids, ranging from 4 to 140 megadaltons, harbored TEM sequences. Although beta-lactam resistance in clinical isolates of E. coli is predominantly mediated by TEM beta-lactamase, the diverse spectrum of resistance appears to be related to additional strain=dependent factors.

Ampicillin↗
PubMed1989

Quality control parameters and interpretive criteria for in vitro susceptibility tests with the macrolide azithromycin. Collaborative Antimicrobial Susceptibility Testing Group.

Quality control parameters for broth microdilution and disk diffusion susceptibility tests were defined and the interpretive criteria for disk diffusion tests reviewed. For interpretation of tests with 15 micrograms azithromycin disks, the following criteria are recommended: greater than or equal to 19 mm for the susceptible category (MIC less than or equal to 2.0 micrograms/ml) and less than or equal to 15 mm for the resistant category (MIC greater than or equal to 8.0 micrograms/ml). Using these criteria, there was 97% overall agreement between broth dilution and disk diffusion tests; Haemophilus influenzae isolates were susceptible to azithromycin by both methods. The quality control strain Staphylococcus aureus ATCC 25923 gave zones of 21 to 26 mm in diameter in a six-laboratory collaborative study. In azithromycin broth microdilution tests the following MIC control limits are recommended: Escherichia coli ATCC 25922, 2.0-8.0 micrograms/ml; Staphylococcus aureus ATCC 29213, 0.25-1.0 micrograms/ml; and Enterococcus faecalis ATCC 29212, 1.0-4.0 micrograms/ml.

Azithromycin↗
PubMed1989

In-vitro activity of the penem, FCE 22101, and tentative interpretive criteria for disc susceptibility tests.

The in-vitro activities of two penems (FCE 22101 and SCH 34343) were compared to those of a carbapenem (imipenem), a monobactam (aztreonam) and three cephalosporins (cefoperazone, ceftazidime, and cefotaxime). FCE 22101 displayed a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive pathogens, including anaerobic bacteria. Imipenem and aztreonam, however, were a little more potent against susceptible species. FCE 22101 was bactericidal against 14 of 18 isolates tested; one strain each of Enterobacter cloacae, Staphylococcus aureus (methicillin sensitive), Staph. aureus (methicillin resistant) and Streptococcus faecalis were not killed by FCE 22101. For disc diffusion tests, a 10 micrograms FCE 22101 disc is tentatively recommended with zones of less than or equal to 13 mm for resistant (MIC greater than 8.0 mg/l) and greater than or equal to 17 mm for susceptible (MIC less than or equal to 4.0 mg/l). Those criteria need to be reevaluated when additional pharmacokinetic information and clinical experience have been gathered.

Anti-Bacterial Agents↗
PubMed1989

In-vitro studies of meropenem.

Meropenem, a new carbapenem, was compared with imipenem and seven other broad-spectrum antimicrobial agents against approximately 1000 clinical isolates. Meropenem was two- to four-fold more active than imipenem against Gram-negative organisms and its spectrum of antimicrobial activity was wider than those of all other drugs tested. However, imipenem was more potent than meropenem against the staphylococci, Streptococcus spp. and enterococci. Many rarely isolated organisms were more susceptible to the carbapenems than to other comparison compounds. All anaerobic bacteria were inhibited by meropenem at less than or equal to 8 mg/l and 50% of strains were inhibited by 0.25 mg/l. Meropenem MICs were not significantly influenced by high inocula and the drug was generally bactericidal. Strains producing various beta-lactamases remained susceptible to meropenem but some isolates producing high levels of chromosomally-mediated enzymes showed an inoculum effect only at 10(7) cfu/ml. Meropenem demonstrated antagonism with several other beta-lactams against strains producing Type I cephalosporinases. Susceptibility tests performed on agar and in broth produced very similar meropenem results. Imipenem and meropenem shared a high degree of cross-susceptibility as measured by dilution test methods. Disc diffusion (10-micrograms disc) regression-line correlations with meropenem MICs are reported with two possible sets of interpretive criteria, using meropenem breakpoints of less than or equal to 2 and less than or equal to 4 mg/l.

Anti-Bacterial Agents↗
PubMed1989

Antibacterial activity of trospectomycin (U-63366F) and initial evaluations of disk diffusion susceptibility tests.

The in vitro activities of trospectomycin sulfate were compared with those spectinomycin against 632 aerobic microorganisms, including 66 Neisseria gonorrhoeae isolates. Against species other than gram-negative bacilli, trospectomycin was about 4- to 16-fold more active than spectinomycin. For disk diffusion tests, a 30-micrograms disk is recommended, with tentative zone size breakpoints of less than or equal to 13 mm for resistance (MIC, greater than or equal to 64 micrograms/ml) and greater than or equal to 17 mm for susceptibility (MIC, less than or equal to 16 micrograms/ml).

Anti-Bacterial Agents↗
PubMed1989

Antimicrobial activity of Ro 23-9424, a novel ester-linked codrug of fleroxacin and desacetylcefotaxime.

Ro 23-9424 is a novel ester-linked codrug of fleroxacin (Ro 23-6240; AM-833) and the cefotaxime metabolite desacetylcefotaxime. Its potency was determined against over 1,000 organisms and found to be intermediate between those of the two components. More than 99% of members of the family Enterobacteriaceae were inhibited by greater than or equal micrograms of Ro 23-9424 per ml; its MIC for 50% of strains tested ranged from greater than or equal to 0.06 to 1 micrograms/ml. Staphylococci, streptococci, Branhamella catarrhalis, Corynebacterium jeikeium, Bacillus spp., Haemophilus influenzae, Listeria monocytogenes, and the pathogenic Neisseria spp., including oxacillin-resistant Staphylococcus aureus, beta-lactamase-producing strains, and penicillin-resistant pneumococci, were also inhibited by Ro 23-9424. Pseudomonas aeruginosa, Enterococcus spp., and Bacteroides fragilis group isolates were more refractory to Ro 23-9424 (the MIC for 90% of strains tested was less than or equal to 32 micrograms/ml). Overall, Ro 23-9424 inhibited 97% of the aerobic strains, compared with 90% for ceftazidime and 92% for cefoperazone. Ro 23-9424 was bactericidal, was relatively stable to inoculum effects on MICs at 10(7) CFU/ml, and was determined to be highly active against organisms resistant to fluoroquinolones or ceftazidime. Preliminary quality control guidelines were determined, and a 30-micrograms disk concentration appears to be the most usable form.

Anti-Infective Agents↗
PubMed1989

Quality control guidelines for testing cefotetan in the reference agar dilution procedure for susceptibility testing of anaerobic bacteria.

Reference values for quality control of in vitro susceptibility tests with cefotetan against anaerobic bacteria were determined in two independent multilaboratory studies with the approved National Committee for Clinical Laboratory Standards agar dilution method and three control strains (Bacteroides fragilis ATCC 25285, Bacteroides thetaiotaomicron ATCC 29741, and Clostridium perfringens ATCC 13124). The results of the two studies were in agreement. The recommended MIC control limits for B. fragilis ATCC 25285 and B. thetaiotaomicron ATCC 29741 are 4.0 to 16 micrograms/ml and 32 to 128 micrograms/ml, respectively. MICs for C. perfringens ATCC 13124 were too variable to be useful for controlling tests with cefotetan.

Bacteria, Anaerobic↗
PubMed1989

Quality control limits for the standard anaerobic reference agar dilution susceptibility test procedure of the National Committee for Clinical Laboratory Standards.

Multilaboratory studies were performed to develop MIC quality control limits for the National Committee for Clinical Laboratory Standards reference agar dilution method for anaerobic susceptibility tests. Acceptable MICs were defined as those which include greater than 95% of all 100 MICs generated by the study. Most MIC control limits included either 2- or 3-dilution intervals rather than the more traditional 3-dilution intervals that are described as the mode +/- 1 doubling dilution.

Amoxicillin↗
PubMed1989

Standardization of disk diffusion and agar dilution susceptibility tests for Neisseria gonorrhoeae: interpretive criteria and quality control guidelines for ceftriaxone, penicillin, spectinomycin, and tetracycline.

A six-laboratory study developed a standardized method for determining the susceptibilities of Neisseria gonorrhoeae strains to penicillin, tetracycline, spectinomycin, and ceftriaxone. Three quality control organisms were also selected, and quality assurance guidelines were initially generated for the disk diffusion and agar dilution methods. The medium recommended for gonococcal susceptibility testing was GC agar with a defined "XV-like" supplement. The supplement should be free of cysteine, a component implicated in the inactivation of some newer beta-lactam compounds. Penicillin, tetracycline, spectinomycin, and ceftriaxone were stable in agar plates stored at 3 to 5 degrees C for at least 2 weeks. Numerous GC agar and drug disk lots were used during the trials without significant variation in test results. Several other gonococcal strains were recommended for additional medium quality assurance. The disk quality control zone limits were established for N. gonorrhoeae ATCC 49226 (formerly CDC F-18) and Staphylococcus aureus ATCC 25923. MIC quality control ranges were also developed for N. gonorrhoeae ATCC 49226 and S. aureus ATCC 29213. The interpretive criteria for penicillin were as follows: susceptibility, greater than or equal to 47 mm (diameter of inhibition zone) (less than or equal to 0.06 micrograms/ml [MIC]); resistance, less than or equal to 26 mm (greater than or equal to 2 micrograms/ml). For tetracycline they were as follows: susceptibility, greater than or equal to 38 mm (less than or equal to 0.25 microgram/ml); resistance, less than or equal to 30 mm (greater than or equal to 2 micrograms/ml). For spectinomycin they were as follows: susceptibility, >/= 18 mm (</= 32 micrograms/ml); resistance, </= 14 mm (>/= 128 micrograms/ml). For ceftriaxone susceptibility, the criterion was >/= 35 mm (</= 0.25 micrograms/ml) with no other category. Criteria of </= 19 mm for plasmid-mediated resistances to penicillin and tetracycline were also confirmed. The false-susceptibility errors were </= 1% with these criteria.

Ceftriaxone↗
PubMed1989

Problems with the disk diffusion test for detection of vancomycin resistance in enterococci.

A total of 53 strains of enterococci, including recently isolated strains with high-level resistance to vancomycin, were tested for vancomycin susceptibility by broth microdilution and disk diffusion using Mueller-Hinton media with and without supplementation with 5% blood. By using currently published parameters of the National Committee for Clinical Laboratory Standards for the disk diffusion test, we found that strains for which MICs were 8 to 32 micrograms/ml were incorrectly placed in the susceptible or intermediate category, which caused both very major (1.9%) and minor (11.5%) errors. When we used newer, recently proposed breakpoints for vancomycin, we found 13.5% minor errors but no very major errors. Changing disk diffusion breakpoints to less than or equal to 14 mm for resistant [corrected] and greater than or equal to 15 mm for susceptible [corrected] would eliminate the problem for the strains with MICs of 32 micrograms/ml but not for those with MICs of 8 micrograms/ml. For those strains, it is necessary to perform an MIC test to differentiate them from strains with MICs of less than or equal to 4 micrograms/ml.

Drug Resistance, Microbial↗
PubMed1989

Methicillin-resistant staphylococci.

Staphylococcus aureus and coagulase-negative staphylococci are among the most frequent causes of nosocomial infections, in addition to their role in community-acquired infections. The incidence of resistance to penicillinase-resistant penicillins (methicillin, oxacillin, nafcillin, and the cloxacillins) is steadily increasing. These methicillin-resistant staphylococci are usually resistant to several classes of antimicrobial agents.

Cross Infection↗
PubMed1988

Susceptibility of multiply resistant Haemophilus influenzae to newer antimicrobial agents.

One hundred and six isolates of Haemophilus influenzae from a national antimicrobial surveillance study demonstrated resistance to two or more of 10 primary antimicrobial agents by mechanisms other than or in addition to beta-lactamase. Of particular note were strains multiply resistant to ampicillin (by beta-lactamase production), chloramphenicol, trimethoprim/sulfamethoxazole, and tetracycline in various combinations. All of the aforementioned strains were shown to be highly susceptible to amoxicillin/clavulanate, the second generation cephalosporins cefuroxime and cefonicid, and the third generation cephalosporins cefotaxime, ceftizoxime, ceftriaxone, ceftazidime, moxalactam, and cefixime. However, 68 strains that demonstrated resistance or marginal susceptibility (MIC greater than or equal to 2 micrograms/ml) to ampicillin by mechanisms other than beta-lactamase, also demonstrated reduced susceptibility to amoxicillin/clavulanate (MICs up to 8 micrograms/ml) and the second generation cephalosporins (MICs up to 32 micrograms/ml). While the latter strains were susceptible to the third generation cephalosporins, MICs were often 10-fold higher than MICs of ampicillin susceptible isolates or of beta-lactamase producing isolates. All of the multiply antimicrobial-resistant strains were highly susceptible (MIC less than or equal to 0.25 micrograms/ml) to the two quinolones ciprofloxacin and pefloxacin.

Ampicillin Resistance↗
PubMed1988

The development of antimicrobial resistance in staphylococci.

Staphylococci are among the most important aetiological agents of both community- and hospital-acquired infections. Staphylococcus aureus isolates resistant to penicillin because they produced beta-lactamase were isolated soon after the introduction of penicillin as a therapeutic agent. The production of beta-lactamase was mediated by a plasmid. The incidence of penicillin resistance in S. aureus increased during the succeeding decades until most clinical isolates were resistant to penicillin. During the 1940s and 1950s resistance to other antimicrobial agents was also demonstrated, usually in combination with penicillin resistance, thus creating multi-resistant strains. Methicillin, a penicillin that was essentially resistant to staphylococcal beta-lactamase, was introduced into clinical use in the early 1960s and this alleviated much of the problem of antimicrobial resistance in S. aureus, but methicillin-resistant strains were soon isolated. Although methicillin-resistant staphylococci had been a nosocomial problem in Europe in the 1960s and early-1970s, it was not until the mid-1970s that they became a problem in the United States. Since then the incidence of methicillin-resistant S. aureus has steadily increased. The methicillin-resistant S. aureus strains are usually multi-resistant including the beta-lactams and one or more of the following: aminoglycosides, macrolides, lincosamides, tetracyclines (usually not minocycline), and chloramphenicol. The methicillin-resistant S. aureus are generally susceptible to vancomycin, teicoplanin, rifampicin, coumermycin, minocycline, the quinolones, and sulphamethoxazole-trimethoprim. The coagulase-negative staphylococci are also important aetiological agents of nosocomial infections and the incidence of these infections has increased in recent years.(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulase↗
PubMed1988

National collaborative study of the prevalence of antimicrobial resistance among clinical isolates of Haemophilus influenzae.

A total of 2,811 clinical isolates of Haemophilus influenzae were obtained during 1986 from 30 medical centers and one nationwide private independent laboratory in the United States. Among these, 757 (26.9%) were type b strains. The overall rate of beta-lactamase-mediated ampicillin resistance was 20.0%. Type b strains were approximately twice as likely as non-type b strains to produce beta-lactamase (31.7 versus 15.6%). The MICs of 12 antimicrobial agents were determined for all isolates. Ampicillin resistance among strains that lacked beta-lactamase activity was extremely uncommon (0.1%). Percentages of study isolates susceptible to cefamandole, cefaclor, cephalothin, and cephalexin were 98.7, 94.5, 87.3, and 43.3%, respectively. For 14 strains (0.5% of the total), chloramphenicol MICs were greater than or equal to 8.0 micrograms, and thus the strains were considered resistant. All of these resistant strains produced chloramphenicol acetyltransferase. In addition, all 14 strains were resistant to tetracycline; 11 produced beta-lactamase. The percentage of isolates susceptible to tetracycline was 97.7%. In contrast, erythromycin and sulfisoxazole were relatively inactive. The combination of erythromycin-sulfisoxazole (1/64) was more active than erythromycin alone but essentially equivalent in activity to sulfisoxazole alone. Finally, small numbers of clinical isolates of H. influenzae were resistant to trimethoprim-sulfamethoxazole and rifampin.

Ampicillin Resistance↗
PubMed1988

In vitro activities of azithromycin (CP 62,993), clarithromycin (A-56268; TE-031), erythromycin, roxithromycin, and clindamycin.

The in vitro activity of azithromycin (CP 62,993 or XZ-450) against Haemophilus influenzae was greater than that of three other macrolides. However, azithromycin was four- to eightfold less active than erythromycin against the gram-positive cocci and against Listeria monocytogenes. Erythromycin and azithromycin were similar in their activity against Legionella pneumophila, Neisseria gonorrhoeae, Neisseria meningitidis, and Branhamella catarrhalis.

Azithromycin↗
PubMed1988

Characteristics of coagulase-negative staphylococci that help differentiate these species and other members of the family Micrococcaceae.

One hundred reference strains and 1,240 clinical isolates representing 26 species of the family Micrococcaceae were used to evaluate the potential of tests for synergistic hemolysis, adherence to glass, pyroglutamyl-beta-naphthylamide hydrolysis, and susceptibility to a set of five antimicrobial agents for differentiating these species and strains within the species. Sixty-eight percent of the clinical isolates exhibited synergistic hemolysis; 69% of the clinical staphylococci but none of the micrococci or stomatococci were adherence positive, and 92% of the strong positive adherence reactions were produced by strains of Staphylococcus epidermidis. Strains from 15 of the species were pyroglutamyl-beta-naphthylamide positive, but this test separated Staphylococcus xylosus from other novobiocin-resistant staphylococci and Staphylococcus intermedius from other coagulase-positive species. A polymyxin B disk helped differentiate S. epidermidis from most other coagulase-negative staphylococci, and a bacitracin disk (10 U) helped differentiate Staphylococcus haemolyticus from most other novobiocin-susceptible staphylococci. All strains that were susceptible to furazolidone and resistant to Taxo A disks (bacitracin, 0.04 U; BBL Microbiology Systems, Cockeysville, Md.) were staphylococci. We observed a 91% correlation between species identification obtained with the Staph-Ident system (Analytab Products, Plainview, N.Y.) and conventional methods; but the micrococci and stomatococci were incorrectly identified as staphylococci with Staph-Ident, and several isolates of S. epidermidis were misidentified as Staphylococcus hominis because they were alkaline phosphatase negative. Both these problems can be prevented by adding the simple tests we describe to those already recommended when the Staph-Ident system is used to identify isolates of gram-positive, catalase-positive cocci.

Bacitracin↗
PubMed1988

Biotyping coagulase-negative staphylococci.

The biochemical profiles obtained with Staph-Ident (Analytab Products, Plainview, N.Y.) panels were combined with the results of adherence and synergistic hemolysis tests to define biotypes among 1,064 clinical isolates representing eight species of coagulase-negative staphylococci. The 672 isolates of Staphylococcus epidermidis were aligned in 69 of 144 potential biotypes in our scheme because of 18 different biochemical profiles and the eight physiologic subtypes. Isolates of most other species were in fewer biotypes because of more uniform adherence and synergistic hemolysis data, as well as fewer biochemical profiles. Since adherence and synergistic hemolysis may prove to be related to virulence and pathogenicity, biotyping with these test results would help evaluate the reliability of adherence and synergistic hemolysis as possible indices of the clinical significance of some of these organisms. When the antimicrobial susceptibility and plasmid profiles obtained on two clusters of S. epidermidis isolates were compared with the biotyping results, one cluster was not further differentiated by plasmid profiles, but was by antimicrobial profiles; the other cluster with only two biotypes was further divided into five distinct types by plasmid profiles but was not separated at all by antimicrobial profiles.

Bacterial Adhesion↗