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PubMed2003

Comparison and evaluation of Osiris and Sirscan 2000 antimicrobial susceptibility systems in the clinical microbiology laboratory.

The Osiris and Sirscan 2000 systems are two semiautomated systems that can be used to read and interpret the results on disk diffusion agar plates. They are both used for determination of susceptibility to antimicrobial agents. The present study compared both systems versus the NCCLS standard method of visual reading with a ruler. Both inpatient and outpatient samples with a total of 315 nonfastidious gram-negative strains were obtained. In total, 3724 organism-antimicrobial agent combinations that fulfilled the NCCLS guidelines for disk diffusion susceptibility testing were evaluated prospectively. The results obtained with both systems in comparison with those obtained by the classical nonautomated means of interpretation were excellent, with correlation coefficients of 0.96 for both systems. The overall agreements for susceptibility interpretation were 96.56 and 96.24% with the Osiris and Sirscan systems, respectively. Very major errors were obtained for 8 (1.07%) and 10 (1.34%) organism-antimicrobial agent combinations with the Osiris and Sirscan systems, respectively. In addition, major errors were obtained for 2 (0.07%) and 6 (0.21%) combinations with the Osiris and Sirscan systems, respectively. Minor errors were obtained for 118 and 124 organism-antimicrobial agent combinations with the Osiris and Sirscan systems, respectively. Overall, both the Osiris system and the Sirscan system are comparable and reliable systems for determination of interpretative categories from the zone diameters of standard disk diffusion test plates.

Acinetobacter↗

PubMedDate not supplied

[Consensus on antimicrobial sensitivity tests in gram-positive cocci. Subcommittee on Antimicrobials, SADEBAC (Argentinian Society of Clinical Bacteriology), Argentinian Association of Microbiology].

Antimicrobial susceptibility testing is mainly performed in Argentina by disk diffusion method, following National Committee for Clinical Laboratory Standards (NCCLS) recommendations. We worked out new recommendations for the reporting and interpretation of this test when dealing with gram-positive cocci, in accordance to local trends and epidemiology. General considerations for performing the diffusion assay, quality control, and an update on susceptibility testing for gram-positive cocci are reported in this first document. The present update should be considered as a group of recommendations summarized by Argentinean experts and as the result of a consensus meeting coordinated by the Subcomisión de Antimicrobianos of the Sociedad Argentina de Bacteriología Clínica (Asociación Argentina de Microbiología). Experts in antimicrobial agents were convened in order to prepare this final document. These recommendations take into account local needs, affordability and availability to be used in current practice, tending to contribute to the correct antimicrobial treatment election, according to the particular microorganism and the infection sites.

Algorithms↗

PubMedDate not supplied

[Sensitivity to colistin: evaluation of cut-off points available in disk diffusion test].

Infections produced by multidrug resistant organisms are one of the greatest problems in health centers. Often, only polymyxines show good activity "in vitro" against the carbapenem resistant gram-negative strains; but the National Committee for Clinical Laboratory Standards (NCCLS) documents do not currently provide interpretative criteria for testing the polymyxines. The antimicrobial activity of colistin, and the correlation between the agar dilution test and disk diffusion test were evaluated against 186 gram-negative strains isolated at the Hospital de Clínicas "José de San Martín" of Buenos Aires city. All susceptibility tests were performed according to the NCCLS recommendations. Were evaluated two breakpoints, NCCLS 1981 (< or = 8 mm and > or = 11 mm), and R. Jones 2001 (< or = 11 mm and > or = 14 mm). Discrepancies on interpretative category were found (0.5% minor; 2.2% major and 4.4% very major) with NCCLS 1981, and (18.9% minor; 3.8% major and 0.5% very major) with R. Jones 2001 criteria. Conclusions. In spite of the fact that the breakpoint used by R. Jones 2001 decreases the very major error but increases the minor error, according to our results we recommend the use of MIC methods to assist the therapeutic application of colistin; however resistance to colistin was not detected with zone diameters > or = 16 mm.

Adult↗

PubMedDate not supplied

Haemophilus test medium interpretive criteria for disk diffusion susceptibility tests with cefdinir, cefetamet, cefmetazole, cefpodoxime, cefdaloxime (RU29246, HR-916 metabolite), and trospectomycin.

The disk diffusion zones and the MICs of six newer antimicrobials with significant activity against Haemophilus influenzae were compared using the Haemophilus test medium (HTM) and National Committee for Clinical Laboratory Standards methods. The rank order of potency was cefpodoxime (MIC50, < or = 0.03 micrograms/ml) > cefetamet > cefdinir > cefdaloxime = trospectomycin > cefmetazole (MIC50, 2 micrograms/ml). Susceptible breakpoint interpretive criteria for HTM tests were established that conformed to prior recommendations for each drug when tested against other species. Absolute agreement between methods ranged from 89% to 100% with < or = 1% false-susceptible interpretive errors. The recommended, tentative disk diffusion susceptible interpretive criteria were for 5-micrograms cefdinir disks > or = 20 mm (MIC correlate, < or = 1 micrograms/ml); for 10-micrograms cefetamet disks > or = 18 mm (MIC correlate, < or = 4 micrograms/ml); for 30-micrograms cefetamet disks > or = 21 mm (MIC correlate, < or = 4 micrograms/ml); for 30-micrograms cefmetazole disks > or = 16 mm (MIC correlate, < or = 16 micrograms/ml); for 10-micrograms cefpodoxime disks > or = 21 mm (MIC correlate, < or = 2 micrograms/ml); for 30-micrograms cefdaloxime disks > or = 23 mm (MIC correlate, < or = 2 micrograms/ml) and for 30-micrograms trospectomycin disks > or = 17 mm (MIC correlate, < or = 16 micrograms/ml). beta-Lactamase-negative, ampicillin-resistant (BLNAR) H. influenzae isolates consistently had the highest MICs for each cephalosporin tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Ampicillin Resistance↗

PubMed1992

Comparison of five methods, including the PDM Epsilometer test (E test), for antimicrobial susceptibility testing of Pseudomonas aeruginosa.

The antimicrobial susceptibilities of 100 clinical isolates of Pseudomonas aeruginosa to six antipseudomonal antibiotics were tested by five methods: the National Committee for Clinical Laboratory Standards (NCCLS) methods for broth microdilution, agar dilution, and agar disk diffusion; the Vitek Automicrobic System method (Vitek Systems, Hazelwood, Mo.); and the PDM Epsilometer test (E test) (AB Biodisk, Solna, Sweden). The E test results showed excellent correlation with agar dilution results, with over 90% agreement within 1 doubling dilution between the E test and reference agar dilution MICs for all antimicrobial agents tested. The E test results also showed good correlation with the results from the reference agar disk diffusion method, with 90 to 99% complete agreement and 100% essential agreement on categories for all antibiotics tested (essential agreement is the agreement obtained when minor discrepancies are ignored). Comparison of categories with the E test and broth microdilution methods, using the broth microdilution method as the reference method, gave only 59% complete agreement for gentamicin, with 28 minor discrepancies and 13 very major discrepancies. Some discrepancies were observed between results from the E test and broth methods for gentamicin, with the broth microdilution and Vitek methods giving higher MICs than the E test and other methods using agar. The most recent NCCLS guidelines for broth dilution testing have reduced the recommended levels of cation supplementation, which may enhance future agreement between results for the aminoglycosides and P. aeruginosa on broth and on agar. We found that the E test offers a simple, labor-efficient, and accurate method for MIC determination on an agar medium.

Adult↗

PubMed2006

A case of ventricular drainage infection with a rare pathogen in cerebrospinal fluid: vancomycin-resistant Enterococcus faecium.

The purpose of this study was to describe a patient, 7-month-old child with ventriculoperitoneal shunts for hydrocephalus with ventriculitis caused by vancomycin-resistant Enterococcus faecium. Two ventriculoperitoneal shunts were inserted just after birth and on the second month. On the sixth month, both shunts were removed because of dysfunction, and external drainage was inserted. The child developed fever, and lumbar puncture revealed a high leukocyte count and protein concentration after external drainage. Cerebrospinal fluid (CSF) cultures yielded E. faecium, which was resistant to ampicillin, erythromycin, gentamicin, penicillin G, vancomycin, and teicoplanin and was susceptible to chloramphenicol, ciprofloxacin, streptomycin, levofloxacin, and rifampin, as determined by the disk diffusion method. As a result of the antimicrobial susceptibility tests, multidrug antibiotic therapy was changed from vancomycin and ceftazidime to chloramphenicol, rifampin, and meropenem. In addition, a rifampin-clindamycin-impregnated shunt (The Codman Hakim Bactiseal, Raynham, MA) was inserted. The patient became afebrile, and CSF cultures were sterile after 15 days of yielding E. faecium. Implantation of the rifampin-clindamycin-impregnated shunt and timely use of appropriate antibiotics for 10 days according to antimicrobial susceptibility testing seem to be important in the resolution of vancomycin-resistant enterococci infections, especially in countries where linezolid and quinupristin-dalfopristin are not in use yet.

Cerebrospinal Fluid↗

PubMedDate not supplied

Composition and antimicrobial activity of the essential oil of Dicyclophora persica Boiss. from Iran.

The chemical composition of the essential oil of Dicyclophora persica Boiss. was identified by GC and GC-MS analysis. The analysis of the oil resulted in the identification of forty-five components constituting 98.6% of the total oil. The main constituents were a-pinene (31.5%), (Z)-beta-ocimene (23.3%), p-cymene (6.7%) and (E)-beta-ocimene (5.4%). The antimicrobial activity of the oil was tested by the disk diffusion method against four Gram-positive (Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis) and three Gram-negative (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa) bacteria together with a fungus (Aspergillus niger). The oil showed strong inhibition activity toward all the tested microorganisms except for Pseudomonas aeruginosa.

Anti-Infective Agents↗

PubMed2003

The status of drug resistance and ampC gene expression in Enterobacter cloacae.

OBJECTIVE: To investigate the status of the drug resistance and the ampC gene expression of Enterobacter cloacae. METHODS: Disk diffusion tests were made for detecting the susceptibility of antimicrobial agents against Enterobacter cloacae. AmpC gene was amplified by polymerase chain reaction (PCR) and verified by DNA sequencing. AmpC gene expression was analyzed according to antimicrobial agent sensitive phenotype. RESULTS: The sensitivity rates of 144 strains to imipenam, cefepime and cefoperazone/sulbactam were 98.61%, 65.97% and 63.89%, respectively. The sensitivity rates of 144 strains to other antimicrobial agents were lower. Among the 144 strains 120 were found to be positive by PCR for ampC. The PCR product showed high homology to the GenBank ampC sequence. Stably derepressed strains, hyperinducible strains and unexpressing or lower level expressing strains accounted for 30.0% (36/120), 37.5% (45/120), and 32.5% (39/120), respectively. Fifty-six out of 120 strains (46.67%) also produced extended spectrum beta-lactamases (ESBLs). The hyperinducible strains were highly sensitive to all the antimicrobial agents except amoxicillin/clavulanic acid and cefuroxime, while the stably derepressed strains were only sensitive to imipenam and cefepime. However, sensitivity to cefepime decreased if the strains also produced ESBLs. CONCLUSIONS: The drug resistant status of Enterobacter cloacae is severe. Clearing out the expressive status of ampC gene will be helpful in selection of antimicrobial agents in the treatment of clinical infection.

Cefoperazone↗

PubMed2002

Antimicrobial resistance of Listeria monocytogenes isolated from various cabbage farms and packing sheds in Texas.

Twenty-one isolates of Listeria monocytogenes from cabbage, environmental, and water samples were evaluated for antimicrobial resistance by the disk diffusion method. Ninety-five percent (20 of 21) of the isolates tested were resistant to two or more antimicrobial agents. This finding is significant, since multiresistant strains of Listeria spp. are not commonly found in nature. Eighty-five percent (17 of 20) of the multiresistant strains were resistant to penicillin, and the remaining multiresistant isolates were somewhat sensitive to penicillin. A multiresistant strain showing intermediate sensitivity to penicillin was resistant to gentamicin. One isolate was susceptible to all antimicrobial agents except penicillin. Penicillin- and gentamicin-resistant L. monocytogenes have not previously been reported from human, food, or environmental samples. This study provides evidence of the emergence of multiresistant L. monocytogenes strains, pointing to an increase in the potential threat to human health posed by this pathogen.

Anti-Bacterial Agents↗

PubMed1982

Agar disk diffusion for the quality control testing of Autobac elution disks.

The standard disk diffusion method of Bauer et al. (Am. J. Clin. Pathol. 45:493-496, 1966; National Committee for Clinical Laboratory Standards, Performance standards for antimicrobial disc susceptibility tests, approved standard ASM-2, 2nd ed., 1979) was used to monitor the potency of 16 Autobac antibiotic elution disks over an 8-month period. Results obtained by using the three recommended Autobac control strains showed excellent reproducibility. Zones sizes were all within a 5-mm range, and standard deviations ranged from 0.6 to 1.3 mm.

Agar↗

PubMedDate not supplied

Incidence of bloodstream infections in a speciality hospital in Kuwait: 8-year experience.

OBJECTIVES: To determine the frequency of isolation and antibiotic-susceptibility patterns of clinically significant bacterial pathogens isolated from blood. MATERIALS AND METHODS: The study was conducted over a period of 8 years (1995-2002) at Infectious Diseases Hospital (IDH), Kuwait. Demographic and clinical data were obtained from medical records. 18,535 blood cultures were analyzed. Disk diffusion method was used to perform antibiotic-susceptibility testing. Minimum inhibitory concentrations of 9 antimicrobials were determined using E-test. Double disk (potentiation) test and E-test ESBL strips were used to detect the production of extended-spectrum beta-lactamases (ESBLs). RESULTS: Salmonella spp. and Brucella spp. were predominant blood isolates, and represented 60.6 and 30.0% of all clinically significant episodes of bloodstream infections, respectively. Among the Salmonella, Salmonella enterica serotypes typhi and paratyphi A were most frequently isolated. The percentage of multidrug resistance (MDR) among them varied from 22 to 51%. A high percentage (40%) of MDR S. enterica serotypes typhi and paratyphi A also showed reduced susceptibility to ceftriaxone and ciprofloxacin. CONCLUSION: During the study period, Salmonella spp. and Brucella spp. were predominant blood isolates. MDR S. enterica serotypes typhi and paratyphi A, with reduced susceptibility to ceftriaxone and ciprofloxacin, are among the most frequent causes of bloodstream infections in IDH, suggesting the need to monitor their susceptibility.

Adolescent↗

PubMed1982

Antimicrobial resistance among Pasteurella spp recovered from Missouri and Iowa cattle with bovine respiratory disease complex.

A retrospective study was conducted to determine the prevalence of antimicrobial resistance among Pasteurella spp recovered from cattle with bovine respiratory disease complex. The study extended from January 1976 through May 1980, and included a review of the necropsy records of 386 beef cattle. Susceptibility or resistance of the Pasteurella isolants was determined by using the standard disk diffusion susceptibility test. Each isolant was tested for susceptibility with 15 different antimicrobial agents. A high prevalence of resistance (greater than 80%) was found when Pasteurella was tested with triple sulfonamides. For P haemolytica isolants, 57% to 70% were resistant to ampicillin (56/97), penicillin (58/101), and streptomycin (70/100); for unidentified Pasteurella spp isolants, 64% to 91% were resistant to ampicillin (83/129), penicillin (89/129), and streptomycin (118/129). For P haemolytica (21/100) and P multocida (34/146) isolants, 21% to 23% were resistant to tetracycline. Most of the P multocida isolants did not show marked antimicrobial resistance to 9 of the 15 drugs tested. However, 58% of the P multocida isolants (84/145) were resistant to streptomycin and 88% of them were resistant to three combined sulfonamides (126/144).

Animals↗

PubMed2001

Standardization of broth microdilution and disk diffusion susceptibility tests for Actinobacillus pleuropneumoniae and Haemophilus somnus: quality control standards for ceftiofur, enrofloxacin, florfenicol, gentamicin, penicillin, tetracycline, tilmicosin, and trimethoprim-sulfamethoxazole.

Quality control (QC) standards for the in vitro antimicrobial susceptibility testing of two fastidious veterinary pathogens, Actinobacillus pleuropneumoniae and Haemophilus somnus, were developed in a multilaboratory study according to procedures established by the National Committee for Clinical Laboratory Standards for broth microdilution and disk diffusion testing. The medium recommended for the broth microdilution testing is cation-adjusted Mueller-Hinton broth supplemented with 2% lysed horse blood, 2% yeast extract, and 2% supplement C. This medium has been designated veterinary fastidious medium. The medium recommended for the disk diffusion testing is chocolate Mueller-Hinton agar. The recommended QC organisms are A. pleuropneumoniae ATCC 27090 and H. somnus ATCC 700025. The QC MICs of ceftiofur, enrofloxacin, florfenicol, gentamicin, penicillin, tetracycline, tilmicosin, and trimethoprim-sulfamethoxazole were determined for each isolate, as were the zone size ranges. Of the results from the participating laboratories, 94.0% of the zone diameter results and 97.0% of the MIC results fell within the suggested QC ranges for all compounds. These QC guidelines should allow greater accuracy in interpreting results when testing these antimicrobial agents against fastidious pathogens.

Actinobacillus Infections↗

PubMed1996

Survey of antimicrobial activity of four commonly used third generation cephalosporins tested against recent bacterial isolates from ten American medical centers, and assessment of disk diffusion test performance. AST Surveillance Group.

Over 2,000 clinical isolates from ten American medical centers were tested for susceptibility to cefotaxine, ceftriaxone, ceftizoxime, and ceftazidime by both broth microdilution and disk diffusion methods. Typically resistant (e.g. enterococci) and highly susceptible (e.g. streptococci) isolates showed no change in susceptibility patterns compared to previous surveys. Pseudomonas aeruginosa and Stenotrophomonas maltophilia exhibited significant decreases in susceptibility to these cephalosporins. Among Escherichia coli and Klebsiella spp isolates, two to three percent were resistant to one of the four drugs whereas they were very susceptible to the other three. Of the four antibiotics, the cefotaxime disk diffusion test results correlated best with the microdilution results. With the other three drugs the disk diffusion test yielded 1 to 9% more susceptible test results and 1 to 20% fewer resistant test results than broth microdilution when testing gram negative bacilli. The clinical significance of such discrepancies is not known, but the impact on antibiotic susceptibility surveys and antibiogram comparisons could be significant.

Ceftazidime↗

PubMed2006

Antimicrobial resistance of Pseudomonas aeruginosa strains isolated from surgical infections in a 7-year period at a general hospital in Venezuela.

BACKGROUND: By definition, the term "surgical infection" implies that surgery plays the major role in therapy, whereas antimicrobial chemotherapy is only supplementary. Despite this view, the efficacy of such drugs is relevant, and for this reason, drug activity surveillance is necessary, especially for opportunistic and nosocomial pathogens such as Pseudomonas aeruginosa. We evaluated bacterial isolates from patients with suspected surgical infections in a hospital of Caracas, Venezuela (West General Hospital) between 1997 and 2003. METHODS: Clinical samples were processed and identified with standard cultures and biochemical tests. The antimicrobial susceptibility of the isolates in vitro was assessed by an agar disk diffusion method using Mueller-Hinton agar, as recommended by the National Committee for Clinical Laboratory Standards (now the Clinical and Laboratory Standards Institute). Isolates were tested against 22 drugs, including piperacillin, ceftazidime, cefoperazone, amikacin, gentamicin, ciprofloxacin, meropenem, and imipenem. RESULTS: From a total of 16,287 bacterial strains isolated from surgical infections during the study period, 243 (1.5%) were P. aeruginosa. Of this total, 30.9% were resistant to gentamicin, 26.3% to tobramicin, 23.0% to cefoperazone, 22.8% to piperacillin, 22.5% to ciprofloxacin, 17.6% to amikacin, 13.6% to imipenem, and 12.9% to meropenem. The best antimicrobial activity was observed with cefepime (90.1% susceptible strains, 1.9% intermediate resistance, and 8.0% resistant strains) and aztreonam (77.7% susceptible strains, 15.2% intermediate resistance, and 7.1% resistant strains). CONCLUSIONS: In our setting, cefepime is most active against strains of P. aeruginosa. In comparison with third-generation cephalosporins, cefepime may be less likely to induce resistance. Surveillance of antimicrobial activity should be done periodically to guide therapy of surgical infections.

Adolescent↗

PubMed1982

Comparison of antimicrobial susceptibility patterns among coagulase-negative staphylococci.

Coagulase-negative staphylococci, identified as S. epidermidis, S. saprophyticus, S. haemolyticus, S. hominis, and S. warneri, were tested for susceptibility to a number of antimicrobial agents by disk agar diffusion and broth microdilution methods, S. warneri and S. saprophyticus were found to be the most susceptible, and S. haemolyticus and S. epidermidis were found to be the least susceptible. Differences in antimicrobial susceptibility patterns are discussed, along with their epidemiological and therapeutic implications.

Anti-Bacterial Agents↗

PubMed1998

Evaluation of a computerized antimicrobial susceptibility system with bacteria isolated from animals.

The BIOMIC is a computerized system used to calculate the minimal inhibitory concentration (MIC) of an antimicrobial agent from a zone of inhibition generated by a disk diffusion test. This system was developed using bacterial pathogens of human origin. This study investigated the use of the BIOMIC system for determining MICs for bacterial pathogens from animals. The MICs generated by the BIOMIC system were compared with the MICs generated using a broth microdilution testing method. A total of 663 drug-organism combinations was tested. These combinations included 3 species of gram-positive bacteria, 5 species of gram-negative bacteria, and the antimicrobial agents ampicillin, gentamicin, cephalothin, ciprofloxacin, enrofloxacin, trimethoprim/sulfamethoxazole, tetracycline, and erythromycin. Overall, the MICs generated by the BIOMIC system correlated with the broth microdilution MICs for 72% of the total drug-organism combinations tested. The Pseudomonas aeruginosa strains tested showed the highest agreement between the 2 systems, with 100% for all antibacterial agents tested, whereas Pasteurella haemolytica, Pasteurella multocida, and enterococci showed the least agreement (76%, 57%, and 47%, respectively). Among these organisms, trimethoprim-sulfa showed the least agreement (31%) and ciprofloxacin showed the greatest (91%). These results indicate that the BIOMIC system could be a useful tool in veterinary medicine for producing quantitative antimicrobial susceptibility results. However, it is currently unreliable for some drug-bacteria combinations. This discrepancy possibly could be corrected by modification of the software using data points generated by a large-scale study.

Animals↗

PubMedDate not supplied

[Study of the susceptibility of Staphylococcus sp. and Enterococcus sp. to teicoplanin and vancomycin].

PURPOSE: The study was performed in order to evaluate the susceptibility of Enterococcus and Staphylococcus to teicoplanin and vancomycin. METHODS: 150 Enterococcus strains and 450 Staphylococcus strains (298 Staphylococcus aureus and 152 negative coagulase strains) isolated in three Brazilian hospitals were studied. The MICs were determined using teicoplanin and vancomycin E Test strips. The range of the antimicrobial concentration in each strip went from 256 mcg/mL to 0.016 mcg/mL. Diffusion tests using disks impregnated with 10 mcg of teicoplanin and 30 mcg of vancomycin were also performed. RESULTS: All the 298 Staphylococcus aureus strains were susceptible to the two antimicrobials. Three of the 152 negative coagulase strains presented intermediate susceptibility to teicoplanin (MICs between 8 and 16 mcg/mL). Four of the 150 Enterococcus strains presented intermediate susceptibility to vancomycin but were totally susceptible to teicoplanin. CONCLUSION: According to these results teicoplanin and vancomycin are good therapeutical options in the treatment of staphylococcal and enterococcal infections.

Anti-Bacterial Agents↗