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Biomedical subjects

C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 181 records · Page 10Linked to original sources
PubMed1983

Proposed zone standards for interpretation of fortimicin A disk diffusion tests.

Fortimicin A microdilution tests and disk diffusion tests (10-, 30-, and 50-micrograms disks) were performed with 454 selected bacterial strains. Tests with 30-micrograms disks were preferred, with zone standards of less than or equal to 14 mm of resistant strains (minimal inhibitory concentration, greater than 16 micrograms/ml) and greater than or equal to 17 mm for susceptible strains (minimal inhibitory concentration, less than 16 micrograms/ml).

Aminoglycosides↗
PubMed1983

Medium-dependent zone size discrepancies associated with susceptibility testing of group D streptococci against various cephalosporins.

Mueller-Hinton (MH) agar media from various commercial sources, either supplemented or not supplemented with 5% sheep blood, were studied to determine their effect on disk diffusion susceptibility testing results obtained with 90 strains of group D streptococci and four cephalosporins. The cephalosporins investigated included cephalothin, cefamandole, moxalactam, and cefotaxime. Results showed that a number of Streptococcus faecalis and Streptococcus faecium strains were susceptible to cephalothin, cefamandole, and cefotaxime, but the number varied with both the commercial source and blood content of the MH medium used. Regardless of the MH medium used, none of the S. faecalis or S. faecium strains were found to be susceptible to moxalactam. The apparently medium-associated variations in the number of strains susceptible to cephalothin, cefamandole, and cefotaxime were largely due to minor discrepancies (one result being intermediate) among the various types of MH media used. However, major discrepancies (one result being resistant and the other susceptible or vice versa) were observed when S. faecalis strains were tested against cefotaxime. These major discrepancies were associated with both the commercial source of the MH medium and the blood content of the medium.

Cephalosporins↗
PubMed1983

Successful use of broth microdilution in susceptibility tests for methicillin-resistant (heteroresistant) staphylococci.

We studied the broth microdilution antimicrobial susceptibility testing procedure to see whether it could be made reliable for determining resistance of staphylococci to methicillin, oxacillin, nafcillin, and cephalothin. With 45 selected strains of Staphylococcus aureus and 12 selected strains of Staphylococcus epidermidis we found that the addition of 2% NaCl to cation-supplemented Mueller-Hinton broth permitted us to discriminate reliably between resistant and susceptible organisms. A screening test in which resistant staphylococci grew on agar containing 4% NaCl and methicillin (10 micrograms/ml), oxacillin (6 micrograms/ml), or nafcillin (6 micrograms/ml) incubated at 35 degrees C for 24 h (additional 24 h if no growth) was also reliable. In vitro cephalothin resistance occurred in heteroresistant S. aureus but usually did not occur in heteroresistant S. epidermidis.

Cephalothin↗
PubMed1982

Ampicillin-resistant Haemophilus influenzae. 1. Incidence, mechanism, and detection.

Ampicillin resistance in Haemophilus influenzae, an organism once thought to be universally susceptible to ampicillin, is increasing. It varies from one institution or community to another, and rates of 6.6% to 48% have been reported. The vast majority of resistant strains produce beta-lactamase, an enzyme that hydrolyzes the beta-lactam ring of ampicillin and other susceptible beta-lactam antibiotics. The beta-lactamase production is mediated by a gene contained on a plasmid (piece of extrachromosomal DNA). It is important for physicians and microbiologists to be aware that an infection such as meningitis or otitis media could be caused by ampicillin-resistant strain of H influenzae. Knowledge of the incidence of resistance for the institution or community is particularly pertinent in selection of empiric therapy.

Ampicillin↗
PubMed1982

Ampicillin-resistant Haemophilus influenzae. 2. Therapeutic considerations.

The increasing incidence of Haemophilus influenzae resistant to ampicillin has clinical implications not only for pediatricians but also for family physicians, because the bacterium is recognized more frequently as the etiologic agent for diseases in adults as well as in young children. Ampicillin is no longer the automatic choice for treatment of patients thought to have life-threatening H influenzae disease, and empiric treatment of otitis media must be reexamined. Chloramphenicol, as well as ampicillin, must be considered for the treatment of meningitis and other serious systemic H influenzae infections. Once the infective organism has been isolated and tested for resistance, ampicillin alone may be used if indicated or desired. Alternatives to ampicillin for middle ear infection are trimethoprim-sulfamethoxazole (Bactrim, Septra), erythromycin-sulfonamide (Pediazole), and cefaclor (Ceclor). Isolation and susceptibility tests are seldom done because they necessitate tympanocentesis.

Adult↗
PubMed1982

Rapidly growing mycobacteria: testing of susceptibility to 34 antimicrobial agents by broth microdilution.

A total of 18 strains of Mycobacterium fortuitum, 15 strains of M. chelonei, and 31 strains of M. chelonei-like organisms were tested by both broth microdilution and agar dilution to determine their susceptibility to 34 antimicrobial agents. All strains grew well enough in cation-supplemented Mueller-Hinton broth for endpoints to be read after 72 h of incubation. Some strains of M. chelonei did not grow on Mueller-Hinton agar. A few discrepancies were noted between the broth and agar procedures. For M. fortuitum, doxycycline, minocycline, amikacin, sulfamethoxazole, and sulfamethoxazole-trimethoprim were the most active agents. For M. chelonei, amikacin, sisomicin, tobramycin, and erythromycin were the most active agents. The M. chelonei-like organisms were most susceptible to ampicillin, doxycycline, minocycline, amikacin, erythromycin, sulfamethoxazole, and sulfamethoxazole-trimethoprim. Broth microdilution appears to be a reliable method for susceptibility testing of rapidly growing mycobacteria, although clinical studies are needed to determine how well in vitro results correlate with therapeutic in vivo outcome.

Anti-Bacterial Agents↗
PubMed1982

Cefotetan, a new cephamycin: comparison of in vitro antimicrobial activity with other cephems, beta-lactamase stability, and preliminary recommendations for disk diffusion testing.

Cefotetan is a new, potent, 7 alpha-methoxy cephalosporin (cephamycin). The in vitro activity of cefotetan tested in a multiphasic, collaborative study against 12,260 consecutive clinical isolates and 448 selected isolates showed 93% of Enterobacteriaceae, 90% of methicillin-susceptible Staphylococcus aureus (broth dilution), 83% of Bacteroides fragilis, and 72% of non-enterococcal streptococci to be inhibited by less than or equal to 8 micrograms/ml. Beta-Lactamase-producing and -nonproducing Haemophilus influenzae strains were inhibited by less than or equal to 1.0 micrograms/ml. Cefotetan's inhibitory spectrum paralleled those of the newest generation of cephems and exceeded those of cefoxitin and cefamandole. No useful activity was present against Streptococcus faecalis or Pseudomonas aeruginosa. Cefotetan was bactericidal without significant inoculum effect and was highly resistant to hydrolysis by Richmond-Sykes types I, III, and IV beta-lactamases. Hydrolysis of the chromogenic cephalosporin PADAC (pyridine-2-azo-p-dimethylaniline cephalosporin) by type I beta-lactamases was markedly inhibited by concentrations of cefotetan similar to those of the potent inhibitor dicloxacillin. Analysis of agar disk diffusion for several disk potencies and broth dilution susceptibility tests by regression and error rate-bounding methods produced preliminary tentative zone standards (30-micrograms disk, using minimal inhibitory concentration breakpoints of less than or equal to 8 micrograms/ml susceptible and greater than 32 micrograms/ml resistant, or 75-micrograms disk, using minimal inhibitory concentration breakpoints of less than or equal to 16 micrograms/ml susceptible and greater than or equal to 64 micrograms/ml resistant) of greater than or equal to 18 mm susceptible, less than or equal to 14 mm resistant, and 15 to 17 mm indeterminate. Staphylococcus aureus testing with the 30-micrograms disk is not recommended.

Anti-Bacterial Agents↗
PubMed1982

Tentative interpretive standards for agar disk diffusion antimicrobial susceptibility testing of cefoperazone.

Cefoperazone is a new cephalosporin with a very wide spectrum of activity, including activity against Pseudomonas aeruginosa. It has less activity on enterococci and Acinetobacter. Of the 459 selected bacterial strains tested in this study, only 1.5% (7 strains and 6 genera) had minimum inhibitory concentrations of greater than or equal to 128 micrograms/ml. For a minimum inhibitory concentration breakpoint of less than or equal to 32 micrograms/ml (susceptible), we recommend that the disk diffusion test be done with a 75-micrograms disk and breakpoints of greater than or equal to 18 mm for susceptible, 15 to 17 mm for intermediate, and less than or equal to 14 mm for resistant. Diffusion tests using these criteria yielded only 1.1% very major or major errors.

Acinetobacter↗
PubMed1982

Cefoperazone disk diffusion susceptibility test: confirmation of the tentative interpretive criteria, Pseudomonas aeruginosa cross-resistance, and determination of quality control performance limits.

Cefoperazone disk diffusion test and minimum inhibitory concentration comparison studies were performed on 421 recent bacterial isolates, using 30- and 75-micrograms commercially prepared disks. Acceptable correlation coefficients (-0.82 to -0.86) and very major (false-susceptible) interpretive error rates (less than 1%) were obtained with both disk concentrations. The interpretive criteria for both disks were identical. Using the preferred 75-micrograms disk, the Thornsberry et al. criteria (J. Clin. Microbiol. 15:769-776, 1982) of greater than or equal to 18 mm = susceptible (less than or equal to 32 micrograms/ml) and less than or equal to 14 mm = resistant (greater than 64 micrograms/ml) resulted in only 5.5% of strains having indeterminate-range zone diameters; the 30-micrograms disk had 6.9% of strains with indeterminate zone diameters. The 75-micrograms disk, excluding the testing of enterococci, minimized the very major and other interpretive errors to less than 5%. Larger zone diameters will contribute few technical problems with either disk concentration. Data from 1,320 zone diameters submitted for each quality control strain indicated no significant (P greater than 0.05) difference between disks made by the three major manufacturers, and consistent results were obtained within each laboratory with numerous lots of Mueller-Hinton agar (except for one manufacturer). Individual daily test and accuracy quality control ranges were calculated from clinical investigator laboratory data at 16 hospitals based on mean zone sizes and from an additional 8 laboratories with both mean and median calculations. The quality control data were nearly identical, and ranges calculated by the two methods were very similar. Susceptibility tests of Pseudomonas aeruginosa indicate that the cefoperazone disk or minimum inhibitory concentration test would accurately predict P. aeruginosa susceptibility test results for other pseudomonas-active cephalosporins (cefsulodin and ceftazidime), thus producing no very major interpretive errors.

Cefoperazone↗
PubMed1982

In vitro evaluation of CENTA, a new beta-lactamase-susceptible chromogenic cephalosporin reagent.

CENTA is a newly synthesized, beta-lactamase-labile, chromogenic cephalosporin reagent which changes color from light yellow (lambda maximum ca. 340 nm) to chrome yellow (lambda maximum ca. 405 nm) concomitant with hydrolysis of the beta-lactam ring. This compound offers promise as a diagnostic reagent comparable to other chromogens (PADAC and nitrocefin) for the early detection of beta-lactamase-producing clinical isolates, while retaining some antimicrobial effect against Escherichia coli, Klebsiella spp., Proteus mirabilis, Staphylococcus aureus, and non-enterococcal Streptococcus spp. CENTA is relatively unaffected by commonly used microbiological media and human serum.

Bacteriological Techniques↗
PubMed1982

Azlocillin, a ureido penicillin active against Pseudomonas aeruginosa: interpretive zone standards and quality control parameters for tests with 75-mu g disks.

A nine-laboratory coordinated study was performed to establish tentative control limits for 75-mu g azlocillin disks tested against the standard control strain of Pseudomonas aeruginosa (ATCC 27853). Control limits for individual tests were 24 to 30 mm (25 to 29 mm for means of five separate tests). To establish interpretive zone standards for 75-mu g azlocillin disks, three separate laboratories each tested 93 strains of P. aeruginosa or related species. Geometric mean minimal inhibitory concentrations (MICs) were plotted against arithmetic mean zone diameters. Regression analyses were performed with zone diameter as the independent variable and also with MIC as the independent variable. The following interpretive categories were recommended: resistant, less than or equal to 14 mm (MIC, greater than 128 mu g/ml); intermediate, 15 to 17 mm (MIC, 128 mu g/ml); and susceptible, greater than or equal to 18 mm (MIC, less than or equal to 64 mu g/ml).

Azlocillin↗
PubMed1982

Evaluation of the MICUR system for quantitative antimicrobial susceptibility testing: a multiphasic comparison with reference methods.

Four laboratories participated in a three-phase study to evaluate the MICUR antimicrobial broth microdilution system (Boehringer Mannheim Diagnostics, Inc., Houston, Tex.). The dried-antimicrobial agent MICUR system was compared with a reference broth microdilution method (National Committee for Clinical Laboratory Standards) by using 304 recently isolated clinical strains and two collections of stock or challenge organisms. Of 7,092 minimum inhibitory concentration (MIC) datum pairs derived from the clinical isolates, 96.6% were within an acceptable (+/- 1 log2 dilution) range. MICUR MICs agreed with the reference broth microdilution method MICs in 95.3% of 6,840 MIC pair determinations performed on stock or challenge cultures. The MICUR intralaboratory reproducibility within +/- 1 log2 dilution step for the clinical isolates was 98.4%. The MICUR intralaboratory and interlaboratory reproducibilities for 26 stock cultures were 98.4 and 95.1%, respectively. For 180 challenge cultures (4,199 MIC pairs) which were included in the MICUR testing to provide a wide variety of antimicrobial susceptibility and resistance patterns, the results for 92.5% were in close agreement with the reference broth microdilution results. No specific resistance mechanism went unrecognized by this new commercial system. The MICUR system gives comparable MIC results when evaluated against the reference broth microdilution method, and it would be acceptable for use in clinical microbiology laboratories.

Anti-Bacterial Agents↗
PubMed1982

The emergence of methicillin-resistant Staphylococcus aureus infections in United States hospitals. Possible role of the house staff-patient transfer circuit.

Infections with methicillin-resistant strains of Staphylococcus aureus appear to be occurring with increasing frequency in some U.S. hospitals about a decade after a similar increase in Britain and other countries. In the United States, clustered methicillin-resistant S. aureus infections reported in scientific journals and in three hospital surveys have been almost entirely in large, tertiary referral hospitals affiliated with medical schools. Among 63 hospitals regularly reporting infections from 1974 to 1981 in the National Nosocomial Infections Study, the increase in methicillin-resistant S. aureus infections was entirely due to substantial increases in only four hospitals, all of which were large, tertiary referral centers affiliated with medical schools. The predominance of methicillin-resistant S. aureus infections in these large hospitals may be due to the large numbers of patients at high risk of infection and to the interhospital spread of the organism by the transfer of infected patients and house staff from similar hospitals or from nursing homes.

Cross Infection↗
PubMed1981

Gentamicin, tobramycin, and sisomicin disc susceptibility tests. Revised zone standards for interpretation.

Studies were undertaken to reevaluate interpretive zone standards for gentamicin and tobramycin disc tests. Disc tests with an investigational aminoglycoside, sisomicin, were also evaluated. The data suggest modification of zone standards for gentamicin disc tests to R (resistant) less than or equal to 12 mm and S (susceptible) greater than or equal to 16 mm. Currently recommended standards for tobramycin disc tests (R less than or equal to 12 mm and S greater than or equal to 15 mm) were found to be satisfactory. For 10-microgram sisomicin discs, zone standards of R less than or equal to 12 mm and S greater than or equal to 15 mm were also appropriate. Although gentamicin is structurally similar to sisomicin, it was less active against Pseudomonas aeruginosa. The activity spectrum of sisomicin against the collection of 470 bacterial isolates studied more nearly resembled that of tobramycin. Data analysis suggested that tobramycin disc tests might be used to predict susceptibility to sisomicin. However, these two drugs differ in their susceptibilities to aminoglycoside-inactivating enzymes produced by some resistant strains. In those institutions where such strains are endemic, the class concept of disc testing may not be applicable.

Anti-Bacterial Agents↗