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Biomedical subjects

F C Tenover

Publications and source records attributed to F C Tenover.

At least 127 records · Page 7Linked to original sources
PubMed1994

Evaluation of Alamar colorimetric MIC method for antimicrobial susceptibility testing of gram-negative bacteria.

The Alamar (Alamar Biosciences, Inc., Sacramento, Calif.) colorimetric antimicrobial susceptibility testing method is a new approach to the determination of broth microdilution MICs. The method uses a color indicator to detect growth of microorganisms within the wells of a microdilution tray. The color changes can be read visually or with a fluorometer. The system contains growth and sterility control wells and 20 antimicrobial agents per MIC tray with eight twofold dilutions for each antimicrobial agent. We tested 186 multiresistant, gram-negative bacterial isolates against 33 antimicrobial agents and compared the results to those obtained by agar dilution. Categorical agreement for all agents was 90.9% and ranged from 78.2% for ampicillin-sulbactam to 98.1% for amikacin. Percent agreement for MIC results (within +/- 1 log2 dilution) was 91.0% for all agents and ranged from 69.1% for gentamicin to 97.9% for ciprofloxacin. Most of the disagreements were with the penicillins and cephalosporins for beta-lactamase-producing strains. The Alamar MIC system is very easy to read visually and appears to be a satisfactory addition to currently used MIC determination methods.

Agar↗
PubMed1994

Development of a standardized screening method for detection of vancomycin-resistant enterococci.

The incidence of vancomycin resistance among enterococci is increasing in the United States and elsewhere in the world, but automated susceptibility testing methods have difficulty detecting resistance expressed by certain strains. The agar screening method described by Willey et al. (B. M. Willey, B. N. Kreiswirth, A. E. Simor, G. Williams, S. R. Scriver, A. Phillips, and D. E. Low, J. Clin. Microbiol. 30:1621-1624, 1992) has been proposed as a reliable method for confirming vancomycin resistance. In this study, we investigated various parameters associated with the agar screening method and, on the basis of the findings, established optimum testing conditions for the method. First, to evaluate media and vancomycin concentrations, one laboratory used Mueller-Hinton and brain heart infusion agars supplemented with 4, 6, and 8 micrograms of vancomycin per ml to test 100 genetically characterized enterococcal strains. On the basis of the results obtained, brain heart infusion agar supplemented with 6 micrograms of vancomycin per ml was selected for further study. Subsequently, eight laboratories used the medium to test both reference and clinical isolates. There was very good performance with the reference strains and, among 158 clinical isolates tested, the method demonstrated sensitivity and specificity of 100% and from 96 to 99%, respectively.

Culture Media↗
PubMed1993

A survey of clinical isolates of Enterobacteriaceae using a series of DNA probes for aminoglycoside resistance genes.

DNA probes specific for the aminoglycoside adenylyltransferase ANT(2"), the aminoglycoside phosphotransferases APH(3')-I and APH(3')-II, and the aminoglycoside acetyltransferases AAC(3)-I, AAC(3)-V and AAC(6')-I were used to screen 151 clinical isolates for the presence of these resistance determinants. The two most common resistance genes in the study isolates were those encoding ANT(2") and APH(3')-I. The phenotypic pattern of aminoglycoside resistance, as determined by a modified disk diffusion test correlated well with the genotypes of the organisms as established using DNA probes, although strains carrying the ANT(2") gene could express one of several phenotypes.

Acetyltransferases↗
PubMed1993

Interpretive criteria and quality control parameters for determining bacterial susceptibility to fosfomycin tromethamine.

Studies with fosfomycin tromethamine disks containing 200 micrograms of fosfomycin and 50 micrograms of glucose-6-phosphate confirmed the following zone diameter criteria for the NCCLS method: < or = 12 mm for resistant (MIC > or = 256 micrograms/ml), 13-15 mm for intermediate (MIC 128 micrograms/ml) and > or = 16 mm for susceptible (MIC < or = 64 micrograms/ml). Additional studies defined acceptable MIC and zone diameter ranges for the following quality control strains: Escherichia coli ATCC 25922, MIC 0.5 to 4.0 micrograms/ml, zone diameter 23 to 29 mm; Staphylococcus aureus ATCC 25923, zone diameter 26 to 32 mm; Pseudomonas aeruginosa ATCC 27813, MIC 2.0 to 8.0 micrograms/ml; and Enterococcus faecalis, ATCC 29212, MIC 16 to 64 micrograms/ml.

Bacteria↗
PubMed1993

Tetracycline resistance in periodontal pathogens.

Antimicrobial agents are used in combination with debridement to eliminate putative periodontal pathogens, including Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans, from diseased tissues. The most frequently used antimicrobial agents are the tetracyclines. However, these agents are not effective in some patients. This lack of efficacy may be due to antimicrobial resistance. As many as 75% of the bacteria in the subgingival flora may be resistant to tetracycline after long-term, low-dose treatment. Tetracycline resistance is mediated by the tet(M) determinant in some isolates of Veillonella species and Fusobacterium nucleatum, while a DNA probe to the tet(Q) determinant hybridizes to isolates of Prevotella denticola and P. intermedia. The mechanism of tetracycline resistance for most periodontal organisms, however, has yet to be determined. Before tetracycline is used as adjunctive therapy for refractory periodontitis, the subgingival bacterial flora should be tested for susceptibility.

Bacteria↗
PubMed1993

Characterization of glycopeptide-resistant enterococci from U.S. hospitals.

We examined 105 clinical isolates of glycopeptide-resistant enterococci collected from 31 U.S. hospitals in 14 states during May 1988 to July 1992. The isolates included 82 Enterococcus faecium, 8 E. faecalis, 6 Enterococcus spp., 5 E. gallinarum, 3 E. casseliflavus, and 1 E. raffinosus. The isolates were categorized into the following four phenotypes of glycopeptide resistance on the basis of their MIC patterns: (i) 70 VanA (vancomycin [Vm] MIC, > or = 64 micrograms/ml; teicoplanin [Tei] MIC, 16 to > or = 128 micrograms/ml), (ii) 26 VanB (Vm MIC, 16 to 1,024 micrograms/ml; Tei MIC, < or = 2 micrograms/ml), (iii) 5 VanC (Vm MIC, 4 to 16 micrograms/ml; Tei MIC, < or = 2 micrograms/ml) in E. gallinarum, and (iv) 3 E. casseliflavus and 1 E. raffinosus isolates for which Vm MICs were 4 to 16 micrograms/ml and Tei MICs were < or = 1 micrograms/ml were called unclassified. Of the 101 isolates with the VanA, VanB, and VanC phenotypes, 99 were confirmed by production of a specific 1,030-, 433-, or 796-bp polymerase chain reaction product, respectively, and hybridization with the respective gene probe. The vanA gene was also detected in the E. raffinosus isolate for which the Vm MIC was 16 micrograms/ml and the Tei MIC was 1 microgram/ml. The vanA gene was located on either a 34- or a 60-kb plasmid in all of the U.S. isolates examined. Pulsed-field gel electrophoresis demonstrated both intrahospital and interhospital diversity among Vmr enterococci in the United States and was more useful than plasmid analysis for epidemiologic studies.

Anti-Bacterial Agents↗
PubMed1993

Two percent sodium chloride is required for susceptibility testing of staphylococci with oxacillin when using agar-based dilution methods.

The need to add NaCl to agar media to ensure accuracy of results when testing staphylococci with oxacillin was investigated. The results of four antimicrobial susceptibility testing methods (agar and broth dilution, E test, and disk diffusion) in which the growth medium contained 0, 2, 4, or 5% NaCl were compared with the results of a hybridization assay using a mec gene probe. We tested 223 strains of staphylococci, 128 of which were mec gene positive. A total of 7 of the 128 positive strains were coagulase-negative staphylococci with 24-h oxacillin MICs of < or = 2 micrograms/ml. Ninety-five isolates were mec gene negative, including seven strains of Staphylococcus aureus with oxacillin MICs of > or = 4 micrograms/ml. The oxacillin MICs for mec gene-positive, oxacillin-resistant strains of staphylococci increased two- to fourfold with the addition of NaCl to the test medium, while the MICs for mec gene-negative strains did not change in the presence of added salt. Very major error rates for the agar dilution and E test methods in the absence of salt ranged from 18.2 to 20.2%. Major error rates for mec gene-negative S. aureus isolates were > 17% for all test methods when 4 or 5% NaCl was added to the test medium. The addition of 2% NaCl to Mueller-Hinton agar for testing of oxacillin resulted in very major error rates of < 1% for the agar dilution and E test methods although the major error rates for the two methods with added NaCl were 8.5 and 6.9%, respectively. The disk diffusion test did not perform well in this study, showing essential error rates of > or = 18.3%. We recommended the addition of 2% NaC1 to Mueller-Hinton agar when testing staphylococci with oxacillin by either the agar dilution or E test method. NaC1 should not be added for the disk diffusion test.

Culture Media↗
PubMed1993

Parallel comparison of accuracy of API 20E, Vitek GNI, MicroScan Walk/Away Rapid ID, and Becton Dickinson Cobas Micro ID-E/NF for identification of members of the family Enterobacteriaceae and common gram-negative, non-glucose-fermenting bacilli.

We compared the API 20E (21 h) (API; bioMérieux Vitek, Hazelwood, Mo.), the Vitek GNI card (4 to 18 h) (Vitek; bioMérieux Vitek), the identification portion of the MicroScan Walk/Away Rapid Neg Combo 3 panel (2 h) (W/A; Baxter Diagnostics, Inc., West Sacramento, Calif.), and the Becton Dickinson Cobas Micro ID-E/NF rotor (21 h) (Cobas; Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.), versus conventional biochemicals for their abilities to identify accurately 252 strains of biochemically typical and atypical members of the family Enterobacteriaceae and common non-glucose-fermenting gram-negative bacilli. All strains used were included in the data base of each product. At the end of the initial incubation, 194 (77.0%), 213 (84.5%), 198 (78.6%), and 192 (76.2%) strains were correct to the genus and species levels with the API, Vitek, W/A, and Cobas systems, respectively. After additional biochemical tests were performed, as directed by each manufacturer's protocol, the numbers of strains correctly identified to the genus and species levels were 241 (95.6%), 234 (92.8%), 243 (96.4%), and 230 (91.3%) with the four systems, respectively. The errors were random in all systems, with the exception of two atypical Salmonella enteritidis strains, each of which was misidentified by three systems. After the initial recommended incubation period, both API and Cobas were significantly less accurate than Vitek (Yates' corrected P < 0.05). No significant differences were noted between the results of Vitek and W/A or between the results of API and W/A. After additional tests were completed, Cobas was significantly less accurate than W/A (P < 0.05) but was equal in accuracy to Vitek and API. API, Vitek, and W/A were equal in accuracy after these same additional tests. All four systems were significantly more accurate after additional biochemical testing than after the initial reporting period (194 of 252 versus 241 of 252 for API, 213 of 252 versus 234 of 252 for Vitek, 198 of 252 versus 243 or 252 for W/A, and 192 of 252 versus 230 of 252 for Cobas [P<0.05]).

Bacteriological Techniques↗
PubMed1993

Susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations: interpretive criteria and quality control limits for standardized tests.

In vitro studies evaluated methods for testing the susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations. Ampicillin-resistant beta-lactamase-nonproducing strains of H. influenzae may be presumed to be relatively resistant to combinations of piperacillin-tazobactam, even though they frequently appear to be susceptible by disk diffusion methods. Other ampicillin-resistant or -susceptible strains were predictably susceptible; i.e., 130 such strains gave zones of inhibition > or = 26 mm in diameter, and MICs for these strains were < or = 0.125/4.0 micrograms/ml (< or = 1.0/0.12 micrograms/ml when an 8:1 ratio was tested). A resistant category has yet to be defined. For quality control purposes, H. influenzae ATCC 49247 should give zones of inhibition 32 to 38 mm in diameter, and broth microdilution MICs should be 0.12/4.0 to 0.5/4.0 micrograms/ml.

Ampicillin Resistance↗
PubMed1993

Ability of clinical laboratories to detect antimicrobial agent-resistant enterococci.

To test the ability of clinical laboratories to detect antimicrobial resistance among enterococci, we sent four vancomycin-resistant enterococcal strains and one beta-lactamase-producing enterococcus to all 93 nongovernment, hospital-based clinical laboratories in New Jersey; 76 (82%) participated in the study. Each organism was tested by the laboratory's routine antimicrobial susceptibility testing method. The proportion of laboratories that correctly reported that an isolate was resistant to vancomycin varied according to the resistance level of the isolate: high-level resistance (MIC for Enterococcus faecium = 512 micrograms/ml), 96% of laboratories correct; moderate-level resistance (MIC for E. faecium = 64 micrograms/ml), 27% correct; low-level resistance (MIC for Enterococcus faecalis = 32 micrograms/ml), 16% correct; and intrinsic low-level resistance (MIC for Enterococcus gallinarum = 8 micrograms/ml), 74% correct. The beta-lactamase-producing E. faecalis isolate was identified as resistant to penicillin and ampicillin by 66 and 8% of laboratories, respectively, but only three laboratories recognized that it was a beta-lactamase producer. This survey suggests that many laboratories may fail to detect antimicrobial agent-resistant enterococci.

Ampicillin Resistance↗
PubMed1993

Tentative criteria for confirming the in vitro susceptibilities of Haemophilus influenzae and Neisseria gonorrhoeae to two fluoroquinolones (sparfloxacin and levofloxacin), including quality control parameters.

Sparfloxacin and levofloxacin were evaluated against 150 Haemophilus influenzae isolates and 149 Neisseria gonorrhoeae isolates in order to define susceptibility testing parameters. Sparfloxacin-susceptible H. influenzae strains were defined as those for which the MICs were < or = 0.25 microgram/ml and the zones were > or = 30 mm, and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.03 microgram/ml and the zones were > or = 39 mm (5-micrograms disks). Levofloxacin-susceptible strains of H. influenzae included those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 32 mm and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 37 mm (5-micrograms disks). Criteria for a resistant category cannot yet be defined for either quinolone. In multilaboratory studies with different lots of Haemophilus Test Medium, replicate tests with the standard control strain of H. influenzae (ATCC 49247) were evaluated. For sparfloxacin disk tests, the proposed zone size limits were 33 to 42 mm and broth microdilution MIC limits were 0.004 to 0.016 microgram/ml, whereas for levofloxacin tests, zone size limits were 32 to 41 mm and broth microdilution MIC limits were 0.008 to 0.03 microgram/ml. Other multilaboratory studies evaluated tests with supplemented GC agar and N. gonorrhoeae ATCC 49226; for both drugs, zone size limits were 44 to 52 mm and agar dilution MIC limits were 0.004 to 0.016 microgram/ml.

Anti-Infective Agents↗
PubMed1993

DNA hybridization techniques and their application to the diagnosis of infectious diseases.

Several commercial DNA probe assays are widely used in clinical microbiology laboratories. These include culture-confirmation assays for Mycobacterium species, which are recommended by CDC because they are both rapid and accurate, and culture-confirmation assays for N. gonorrhoeae. Probe assays for direct detection of N. gonorrhoeae and C. trachomatis are also widely used in public health and large reference laboratories. In many cases, the probe assays have decreased the time to identification of positive cultures and improved detection of these pathogens because they do not depend on the presence of viable organisms to achieve a positive result. Nucleic acid amplification assays hold promise for the rapid detection and identification of many infectious agents. PCR using universal primers enables researchers to identify new agents of disease that cannot be cultured in vitro; more importantly, PCR provides a method for detecting the presence of any bacterial species, including common organisms, in normally sterile body fluids, such as blood and cerebrospinal fluids. The use of such primers may well give PCR the broad-based approach needed to identify organisms in the clinical microbiology laboratory of the future.

Base Sequence↗
PubMed1992

Identification of an epidemic strain of Acinetobacter baumannii using electrophoretic typing methods.

Nosocomial infections due to Acinetobacter baumannii dramatically increased in a Lebanese medical center following an outbreak of hostilities in Lebanon in 1984. The incidence of infection caused by this organism has remained high in this institution, thus requiring the implementation of a strain typing system to aid in infection control. Three methods were investigated for their utility in differentiating among a representative group of 36 nosocomial Acinetobacter baumannii isolates obtained over a 10 month period from specimens of hospitalized patients. Isolates were typed by antibiogram analyses, plasmid fingerprinting, and total cell protein profiles. Only three distinct total cell protein profiles were detected, with one pattern accounting for 26 (72.2%) of the isolates. However, eight different plasmid profiles were observed, with 20 (55.5%) isolates having the same profile. Eleven distinct antibiograms were seen with the most prevalent pattern occurring in 21 isolates. Twenty of the 21 (95%) isolates with the common antibiogram also had the same plasmid profile and total protein profile (44.4% of total isolates). The combination of these three typing methods was useful in tracing the spread of these organisms in the medical center. The data obtained suggest the distribution of a common strain among at least six wards of this hospital.

Acinetobacter↗
PubMed1992

Analysis of multiply antimicrobial-resistant isolates of Streptococcus pneumoniae from the United States.

Streptococcus pneumoniae isolates resistant to penicillin, chloramphenicol, tetracycline and sulfamethoxazole-trimethroprim are being recovered with increasing frequency in the United States. We analyzed the penicillin-binding proteins (PBPs), multilocus enzyme electrophoresis (MLEE) genotypes, and ribotypes of 22 multiresistant serotype 23F isolates of S. pneumoniae from the United States and 1 isolate each from Spain and South Africa. Also included were seven multiresistant isolates of other serotypes, three penicillin-resistant but chloramphenicol-susceptible serotype 23F isolates, and two penicillin-susceptible isolates (one penicillin-susceptible isolate was serotype 23F). Fifteen of the 22 multiresistant isolates from the United States and the isolates from Spain and South Africa had identical PBP patterns, MLEE profiles, and ribotypes. Six of the remaining seven multiresistant isolates were related by PBP pattern, but demonstrated slightly different MLEE and/or ribotype profiles, possibly because of acquisition of additional resistance markers (four of the six isolates were also resistant to erythromycin). The remaining multiresistant serotype 23F isolate had a unique PBP pattern and ribotype and was only distantly related to the other pneumococcal isolates by MLEE analysis. The PBP patterns, MLEE profiles, and ribotypes of the multiresistant serotype 23F isolates were easily distinguished from those of six multiresistant isolates of other serotypes; three other penicillin-resistant, chloramphenicol-susceptible, serotype 23F isolates; and two penicillin-susceptible isolates. One exception was a multiresistant serotype 19A isolate that was highly related to the clonal group by PBP pattern and MLEE analysis and that had a ribotype similar to those of the other erythromycin-resistant serotype 23F isolates. MLEE analysis and ribotyping were more discriminating than were the PBP patterns in discerning strain differences. These data strongly suggest that a multiresistant clone of S. pneumoniae serotype 23F that is related to multiresistant isolates from Spain and South Africa has become disseminated in the United States. Clinicians should be alerted to the spread of these multiresistant strains in the United States.

Autoradiography↗