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Results for “Disk Diffusion Antimicrobial Tests”

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PubMed1993

In vitro susceptibility test practices with Haemophilus influenzae among College of American Pathologists survey participants in the United States.

Questionnaire results from 5233 clinical microbiology laboratories participating in the College of American Pathologists (CAP) survey program in the United States were used to establish current standards of practice with respect to in vitro susceptibility testing of Haemophilus influenzae. The results of this CAP survey indicated that the recently developed National Committee for Clinical Laboratory Standards (NCCLS) guidelines for H. influenzae susceptibility tests have been widely adopted, particularly with regard to the medium used to perform susceptibility tests. Haemophilus test medium (HTM) is now the most commonly used medium and there exists a general level of satisfaction (approximately 80%) with medium performance. Specific methodologic recommendations of the NCCLS, however, are often not being followed, for example, length and atmosphere of incubation and means of preparing inocula. beta-Lactamase assays constitute a very commonly employed means of assessing ampicillin activity. Among susceptibility test methods, disk diffusion (82.2%) is much more commonly used compared with broth microdilution (17.8%) procedures. Data are provided regarding the most commonly tested antimicrobials as well as some of the problems encounted when using current NCCLS methods for susceptibility tests with H. influenzae. Finally, the CAP survey questionnaire revealed that many laboratories have applied HTM to susceptibility tests with other fastidious bacteria such as pathogenic Neisseria sp., streptococci, and Moraxella catarrhalis.

Culture Media↗

PubMed2002

Evaluation of the antinflammatory and analgesic activity of Sideritis canariensis var. pannosa in mice.

A previous chemical study of Sideritis canariensis var. pannosa demonstrated the presence of some important classes of related organic compounds with anti-inflammatory activities. In the present study, the crude ethanol extract and the chloroformic and aqueous fractions of S. canariensis have been examined for their antimicrobial actions through the disk-diffusion method and for their anti-inflammatory and analgesic effects in several animal models. No relevant antimicrobial activity against the tested microorganisms was found. The chloroformic fraction was the most interesting, exhibiting a good analgesic and anti-inflammatory activity.

Acetic Acid↗

PubMed2006

Surveillance of human salmonellosis in Bulgaria, 1999-2004: trends, shifts and resistance to antimicrobial agents.

This article analyses the distribution of resistant salmonella and resistance mechanisms among the most frequently encountered serotypes in Bulgaria. Culture, biochemical tests and serotyping were used for identification. Screening for resistance to 14 antimicrobial agents with the standard Bauer-Kirbi disk-diffusion method. The double disk synergy method was used to determine production of extended-spectrum a-lactamases (ESBL). Transfer of genes coding for ESBLs with experimental conjugation. Specific primers were used for PCR detection of bla-CTX-M, bla-SHV and bla-TEM. 245 resistant salmonella strains were determined in our study; the majority originated from sporadic cases of human illness or asymptomatic infection and the remaining 23 were isolated from outbreaks. 79 producers of ESBL were detected: 5 S. Enteritidis, 1 S. Typhimurium, 9 S. Isangi and 62 S. Corvallis with types of enzymes: CTX-M3, TEM and SHV. Gene coding for extended-spectrum a- lactamases were successfully transferred into a recipient Escherichia coli C1A strain simultaneously with genes coding for resistance to aminoglycosides and sulphonamides (for bla-CTX-M3) and gene coding for resistance to aminoglycosides and chloramphenicol (for bla-SHVand bla-TEM). PCR amplification revealed bla-CTX-M3 genes in S. Enteritidis, and bla-SHV and bla-TEM in S. Corvallis. Salmonellae have revealed increasing resistance to all clinically important groups of antimicrobial agents. Bulgaria is the first country in the world where ESBL in serotype Corvallis has been reported. A wide diversity of resistance genes is found among the leading serotypes of salmonella causing human disease in Bulgaria.

Bulgaria↗

PubMed1999

Harmonization of antibiotic susceptibility testing for Salmonella: results of a study by 18 national reference laboratories within the European Union-funded Enter-net group.

For the effective surveillance of antimicrobial drug resistance within Salmonella organisms from humans, harmonization of methods used for sensitivity testing by laboratories responsible for the typing of such organisms is essential. A study of resistance or sensitivity to a panel of 11 antimicrobials by the Enter-net international surveillance network was therefore undertaken. There are 18 national Salmonella reference laboratories within this European Union-funded network. Forty-eight strains of Salmonella enterica were distributed to each laboratory for testing for resistance or sensitivity to ampicillin, cefotaxime, chloramphenicol, gentamicin, kanamycin, streptomycin, sulfonamides, tetracyclines, trimethoprim, nalidixic acid, and ciprofloxacin. Over 8,500 tests were assessed involving disk diffusion (DD), agar breakpoint (BP), or full minimum inhibitory concentration (MIC). Results indicated that whichever method was used, there was a high degree of concordance for the detection of resistance to most antimicrobials; only for decreased sensitivity to ciprofloxacin was there substantial nonconcordance. Because all isolates with decreased sensitivity to ciprofloxacin were resistant to nalidixic acid, it is suggested that, if required, MICs to ciprofloxacin could be determined for isolates resistant to nalidixic acid. For the detection of sensitivity, the main area of nonconcordance was in the detection of sensitivity to streptomycin. With the exception of decreased sensitivity to ciprofloxacin, we are confident that a database of antimicrobial susceptibilities can now be established and harmonized antibiogram data for Salmonella can now be exchanged for national Salmonella reference laboratories within the European Union.

Drug Resistance, Microbial↗

PubMed1977

Insuring effective antimicrobial therapy: laboratory evaluation.

Specialized tests for the susceptibility of pathogenic microorganisms are not indicated for most clinical infections. Primary attention should be focused on proper collection of representative culture material and subsequent accurate identification of the offending organism. Specific antimicrobial therapy can then be empirically instituted based upon previously known susceptibility patterns. An overview of the broth dilution, agar dilution, and agar (disk) diffusion techniques is presented. The absolute indications for these tests are as follows: (1) infections with gram-negative bacilli; (2) staphylococcal infections; and (3) enterococcal and other group D beta hemolytic streptococcal infections. The following situations are relative indications for susceptibility testing: (1) infections occurring in immunosuppressed hosts; (2) infections that by their location are more susceptible to certain types of antibiotics; and (3) infections that should be treated with a bactericidal rather than a bacteriostatic drug. The rationale and indications for the serum bactericidal test (SBT or Schlichter test) and antibiotic assay techniques are described. The cases reported illustrate appropriate application of the specialized tests for susceptibility.

Aged↗

PubMed1998

Antimicrobial susceptibility of Haemophilus influenzae in the respiratory tracts of patients with cystic fibrosis.

We analyzed the antimicrobial susceptibilities of Haemophilus influenzae isolates from 157 sputum specimens prospectively collected from 39 cystic fibrosis (CF) patients during a 2-year study. These isolates were characterized by random amplified polymorphic DNA analysis and major outer membrane protein (MOMP) analysis to identify H. influenzae strains and MOMP variants and to assess their persistence in the respiratory tract. Among the 247 H. influenzae isolates, 16 (6.5%) produced beta-lactamase. The 231 beta-lactamase-negative isolates represented 85 H. influenzae strains, 61 MOMP variants derived from 27 of these strains, and 85 persistent isolates identical to strains or MOMP variants. All beta-lactamase-negative isolates were tested for susceptibility to ampicillin, amoxicillin-clavulanic acid, cefuroxime, cefotaxime, cefaclor, imipenem, tetracycline, and trimethoprim-sulfamethoxazole by disk diffusion testing. Eleven (13%) H. influenzae strains, 18 (30%) MOMP variants, and 30 (35%) persistent isolates were resistant to one or more of the antibiotics tested. Antimicrobial susceptibility was decreased among MOMP variants and persistent isolates compared to nonpersistent H. influenzae strains, and changes in susceptibility occurred irrespective of MOMP variation. We conclude that the decreased antimicrobial susceptibility of H. influenzae during persistence contributes to the poor eradication of H. influenzae from the respiratory tracts of CF patients.

Adolescent↗

PubMed2004

Antimicrobial resistance and resistance genes in Staphylococcus aureus strains from rabbits.

Fifty-six Staphylococcus aureus isolates recovered between 1998 and 2003 from 31 rabbit farms with and without problems of chronic staphylococcosis, were screened for resistance to enrofloxacin, erythromycin, gentamicin, lincomycin, neomycin, penicillin and tetracyclines using the agar dilution test. For penicillin, a disk diffusion test was also performed. The detection of tetP(B), tet(K), tet(L), tet(M), tet(O), tet(T), tet(W), erm(A), erm(B), erm(C) and mec(A) genes was done via a PCR assay. Four isolates showed resistance to erythromycin and lincomycin. These isolates were positive for the erm(C) gene in the PCR. Eleven strains were resistant to tetracyclines and all harboured the tet(K) gene. In the agar dilution test, five isolates showed resistance to penicillin, whereas in the disk diffusion test 12 isolates showed resistance. None of these 12 resistant isolates carried the mec(A) gene. Only one strain showed resistance to gentamicin, and all strains were susceptible to enrofloxacin and neomycin. This study demonstrates that resistance to antimicrobial agents in S. aureus isolates originating from rabbits is relatively rare compared to resistance in S. aureus isolates originating from other animals and humans.

Animals↗

PubMed1985

Evaluation of the Cobasbact automated antimicrobial susceptibility testing system.

The Cobasbact is an automated system for use in the microbiological laboratory which is capable of performing antimicrobial susceptibility tests within five hours. The performance of the Cobasbact system was evaluated using 2000 non-fastidious, facultative and aerobic clinical bacterial isolates. The standard Kirby-Bauer disk diffusion test served as reference method. For gram-positive isolates, the rate of overall full and essential agreement between Cobasbact and reference antibiograms was 90% and 95.5% respectively, for Enterobacteriaceae 91% and 95.5% and for Pseudomonas spp. 90% and 96%. Reproducibility studies yielded an essential agreement rate of 98%. On the basis of this preliminary evaluation it would seem that the Cobasbact system can rapidly produce reasonably accurate and reproducible results of antimicrobial susceptibility tests for gram-positive cocci, Enterobacteriaceae and Pseudomonas spp.

Automation↗

PubMed1985

[Validity of the ABAC II system: applicability in the hospital laboratory and verification of breakpoint concentrations in the determination of antibiotic sensitivity].

Two different sensitivity testing methods were evaluated on 183 bacterial strains of Gram-negative clinical isolates in relation to 13 antimicrobial drugs. Comparison between both methods: conventional technique of disk diffusion (Kirby-Bauer) and the automated ABAC breakpoints system, has shown a good agreement of the results (91.1%) according to several investigators. The authors analyze the role of ABAC system and its achievement in routine work of a medium bacteriological hospital laboratory.

Anti-Bacterial Agents↗

PubMed2002

Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, Etest and reference dilution methods.

Staphylococci cause one-third of all serious invasive infections in the SENTRY Antimicrobial Surveillance Program including bacteremias and lower respiratory tract infections. Staphylococci are also commensals of the skin and nasal passages; therefore, topical agents active against these organisms are valuable in preventing infections or transfer of the organisms between patients and/or health care workers. Mupirocin is a potent topical anti-staphylococcal compound, but its effectiveness has been compromised by emerging resistance. In early 2000, the SENTRY Program detected 302 mupirocin-resistant isolates (131 Staphylococcus aureus, and 171 coagulase-negative staphylococci [CoNS]) from the United States (19/25 medical centers), Canada (4/5), Latin America (3/9) and Europe (7/18). One hundred sixty-eight mupirocin-resistant and 59 susceptible isolates were tested further by reference MIC, Etest (AB BIODISK, Solna, Sweden) and disk diffusion (5-microg) methods. Mupirocin resistance rates for blood stream infections varied by geographic area: for S. aureus from 1.9 to 5.6%, and for CoNS from 12.8 to 39.9%. Using elevated mupirocin MIC results, two resistant populations were noted: low-level resistance at 8-128 microg/mL and high-level resistance at > or = 1024 microg/mL. Acceptable correlation was observed between Etest and disk diffusion results (r = 0.84) without serious intermethod interpretive errors. High-level resistant isolates had heavy growth with no visible zone around the disk; low-level resistant isolates produced hazy zones of inhibition, and susceptible strains had clear zones of inhibition at > or = 17 mm. As mupirocin resistance can be plasmid-mediated, the prudent and appropriate use of this topical agent is important to minimize the ongoing development of resistance. Local surveillance for emerging mupirocin resistance appears warranted particularly in the United States and Canada, pragmatically using a disk diffusion test screening. Where more precise data are needed, the Etest is a very accurate method for distinguishing mupirocin low-level from high-level resistance patterns.

Anti-Bacterial Agents↗

PubMed1992

Fluoroquinolone (Lomefloxacin) International Surveillance Trial: a report of 30 months of monitoring in vitro activity.

The antimicrobial activity and spectrum of lomefloxacin were assessed by standardized disk diffusion methods in 36 countries. More than 500,000 facultative organisms were tested during the first 30 months of a 3-year monitoring interval. Lomefloxacin demonstrated inhibition (zones greater than or equal to 19 mm) of greater than 90% of Enterobacteriaceae, greater than 99% of Moraxella (Branhamella) catarrhalis, greater than 98% of Haemophilus spp., and 91% of Staphylococcus aureus strains. Pseudomonas spp., especially Pseudomonas aeruginosa (18% resistance), were considered moderately susceptible, as were most strains of streptococci and enterococci. Some variation of national/regional fluoroquinolone resistance rates was observed, using lomefloxacin as an index or indicator drug, with the highest numbers of resistant strains being isolated in France. However, these data demonstrated a wide spectrum of lomefloxacin activity in all nations monitored.

Anti-Infective Agents↗

PubMedDate not supplied

Comparison of Wilkins-Chalgren medium supplemented with nicotinamide adenine dinucleotide and Haemophilus test medium for susceptibility testing of clinical Haemophilus isolates.

Haemophilus test medium (HTM) was compared with Wilkins-Chalgren agar (WCA; supplemented with 15 micrograms/ml nicotinamide adenine dinucleotide (NAD)) for antibiotic susceptibility testing of 74 clinical isolates of Haemophilus influenzae and Haemophilus parainfluenzae. The Bauer-Kirby agar disk diffusion method and the agar dilution procedure were the two tests employed. WCA + NAD and HTM yielded comparable results for the following antimicrobial drugs and drug combinations: ampicillin, amoxicillin plus clavulanic acid, ampicillin plus sulbactam, cefotaxime, cefuroxime, chloramphenicol, ciprofloxacin, and doxycycline. However, WCA + NAD slightly antagonized rifampin. Co-trimoxazole was significantly antagonized by WCA + NAD. WCA + NAD was much simpler with regard to in-house preparation, and WCA plates could be supplemented with NAD following pouring, solidification and storage of the plates simply by surface spreading the required amount of NAD with a glass spatula, thus adding considerably to laboratory flexibility. It is suggested that additional laboratories comparatively and critically examine WCA + NAD medium for antibiotic susceptibility testing of clinical Haemophilus isolates.

Culture Media↗

PubMedDate not supplied

Susceptibility testing of Pseudomonas aeruginosa by the Vitek 2 system: a comparison with Etest results.

P. aeruginona infections need accurate antimicrobial susceptibility data, as treatment mainly relies on antibiotic efficiency in debilitated patients. Vitek 2, a popular automated susceptibility testing method, was compared with Etest to assess its reliability on 150 Belgian P. aeruginonas isolates. Vitek 2 and Etest exhibited a high degree of concordance, but some discrepancies in clinical category were evident for cefepime (high minor and borderline very major error rate) and for piperacillin/tazobactam (high very major error rate). Vitek 2 appears to yield valuable information to the clinician concerning the antimicrobials amikacin, ceftazidime, ciprofloxacin and meropenem, in the setting of pseudomonas infection. For cefepime and piperacillin/tazobactam, a confirmatory testing by means of disk diffusion is worth considering.

Bacteriological Techniques↗

PubMed1980

Topical antimicrobial cream sensitivity testing.

These gratifying results have made topical antimicrobial sensitivity testing an integral part of bacteriologic monitoring of the burn wound. Presently, we use the needle extrusion test routinely on all burn patients at our center. Its selection over the other antimicrobial tests is based on technical considerations. The needle extrusion test can be completed by an experienced technician within five minutes, but the disk diffusion test and agar-well diffusion test take two and five times longer, respectively. This time saving is an important consideration when the microflora of ten or more burn patient at our center are being monitored by this test every other day. This test system may prove useful for the topical antibiotic selection for the treatment of other wounds beside the burn wound. Its potential value in these other conditions must await the results of carefully controlled clinical studies.

Anti-Bacterial Agents↗

PubMedDate not supplied

Antibiotic susceptibility of alpha- and nonhemolytic streptococci from patients and healthy adults to 24 antimicrobial drugs.

A total of 278 alpha- and nonhemolytic streptococcal isolates (patients, n = 116; healthy adults, n = 162) were examined for susceptibility to 23 and 24 antimicrobial drugs with the Bauer-Kirby agar disk diffusion and the agar dilution method, respectively. Wilkins-Chalgren medium compared favorably with sheep blood Mueller-Hinton agar, the reference medium, for 58 representative streptococcal isolates. In terms of minimal inhibitory concentrations (MICs), all 278 isolates were susceptible to teicoplanin and vancomycin. None of the isolates revealed high-level gentamicin resistance. All isolates were resistant to fusidic acid. Twelve Streptococcus mitis isolates, all from patients, were resistant to penicillin G and variably to other antibiotics. Oxacillin disks failed to predict penicillin G susceptibility. In general, patient isolates were more frequently resistant to beta-lactam antibiotics and fluoroquinolones; conversely, isolates from healthy carriers were slightly more resistant to macrolide antibiotics. Specifically, susceptibility rates were: penicillin G 79.1%, oxacillin 87.8%, ampicillin 66.9%, piperacillin 98.2%, cefoxitin 76.6%, cefuroxime 96.8%, cefotaxime 98.6%, ceftriaxone 98.6%, cefepime 98.6%, impipenem 98.2%, ciprofloxacin 59.7%, ofloxacin 89.2%, doxycycline 65.8%, tetracycline 56.8%, clindamycin 87.8%, erythromycin 59%, clarithromycin 74.9%, chloramphenicol 98.9%, cotrimoxazole 97.9%, rifampin 97.5%, and fosfomycin 2.2%. On the basis of numerous minor discrepancies between disk diffusion and agar dilution test results for certain antibiotics, it is proposed that the current NCCLS inhibition zone (diameter, mm) criteria indicative of intermediate susceptibility of alpha- and nonhemolytic streptococci be changed for the following antimicrobial drugs: ampicillin = I = 22-27 mm; ciprofloxacin = I = 16-18 mm; clindamycin = I = 15-18 mm; doxycycline = I = 17-19 mm; tetracycline = I = 17-19 mm; erythromycin = I = 14-19 mm, and cotrimoxazole = I = 11-13 mm. It is recommended to exclude both cefoxitin and doxycycline (substitute = tetracycline) disks from test batteries for non-group A, B beta-hemolytic and alpha-/nonhemolytic streptococcal isolates.

Adult↗

PubMed2005

Resistance pattern and assessment of phenicol agents' minimum inhibitory concentration in multiple drug resistant Chryseobacterium isolates from fish and aquatic habitats.

AIMS: To assess the susceptibility of Chryseobacterium isolates of fish and aquatic habitats to antimicrobial compounds. Special attention was paid to the resistance to chloramphenicol and florfenicol, a phenicol derivative recently licensed for use in veterinary medicine and fish farming. METHODS AND RESULTS: Sixty-seven Chryseobacterium spp. isolates and reference strains, originating mainly from different aquatic habitats, were tested using the disk-diffusion method. In addition, agar dilution was used for assessing minimum inhibitory concentration of chloramphenicol and florfenicol. In spite of (i) conditions that hampered properly standardized experiments and (ii) the heterogeneity of the isolates resulting in some aberrant values in diffusion, correlation between the two methods was confirmed. Most of the isolates exhibited considerable multiresistance to most antimicrobial drug families, and many were clearly resistant to phenicols. Molecular investigations conducted on 10 strains selected for high resistance to florfenicol did not establish the existence of floR or cmlA genes currently reported in the literature as responsible for florfenicol resistance. Nevertheless, when an efflux pump inhibitor, phenyl-arginin-beta-naphthylamide, was combined with diffusion tests, drug susceptibility to florfenicol was restored, suggesting that Chryseobacterium's resistance to this molecule is under the control of efflux mechanisms. CONCLUSIONS: Constitutive multiresistance to antibiotics is common in chryseobacteria isolated from the aquatic environment. Although no gene related to the floR family could be detected, efflux mechanisms could partly support the resistance to phenicols. SIGNIFICANCE AND IMPACT OF THE STUDY: These results explain the difficulty of treatment and clearly reflect the properties previously reported in Chryseobacterium isolates of human origin. Because several species have been involved in opportunistic infections in humans, the possible role of aquatic organisms as a source of infection should be considered.

Animals↗

PubMed1980

Clinical evaluation of automated antibiotic susceptibility testing with the MS-2 system.

The MS-2 (Abbott Laboratories) system for automated antimicrobial susceptibility testing was evaluated for both accuracy and general utility in our clinical laboratory. A total of 984 fresh clinical bacterial isolates (745 gram-negative, 239 gram-positive) were tested with the MS-2 system, and results were compared directly with those from a conventional agar disk diffusion method. Discrepancies between the two methods were categorized as very major, major, and minor. For gram-positive isolates, full accord (all discrepancies considered) was 91.6%, and essential accord (minor discrepancies not included) was 96.2%. With gram-negative isolates, full accord was found to be 93.9%, with essential accord of 97.9%. Aggrement as a function both of organism group and of antimicrobial agent was determined. Full accord of 90% or more was found for all major organism groups tested, with the exception of enterococci, where discrepant results between the two methods were observed. Mean test time for all isolates tested was 4.3 h. The MS-2 was found to be an accurate and highly automated instrument which required minimal technician time and was readily adaptable to work flow in our clinical laboratory.

Anti-Bacterial Agents↗

PubMed2006

Daptomycin bactericidal activity and correlation between disk and broth microdilution method results in testing of Staphylococcus aureus strains with decreased susceptibility to vancomycin.

A total of 207 Staphylococcus aureus strains, including 105 well-characterized strains with decreased susceptibility to vancomycin (17 vancomycin-intermediate S. aureus [VISA] and 88 heteroresistant VISA [hVISA] strains) and 102 wild-type methicillin-resistant S. aureus (MRSA-WT) strains were tested by reference/standardized broth microdilution and disk diffusion methods, as well as by Etest (AB BIODISK, Solna, Sweden), against daptomycin and vancomycin. The lowest concentration of antimicrobial agent that killed > or = 99.9% of the initial inoculum was defined as the minimum bactericidal concentration (MBC) endpoint, and time-kill curves were performed in selected strains to further evaluate bactericidal activity. All MRSA-WT and hVISA strains were inhibited by < or = 1 microg/ml of daptomycin, while the VISA strains showed slightly higher daptomycin MICs (range, 0.5 to 4 microg/ml). All daptomycin MBC results were at the MIC or twofold higher. In contrast, 14.7% of MRSA-WT, 69.3% of hVISA, and all VISA strains showed a vancomycin MBC/MIC ratio of > or = 32 or an MBC of > or = 16 microg/ml (tolerant). The correlation coefficients between broth microdilution and disk diffusion method results were low for daptomycin (0.07) and vancomycin (0.11). Eight (3.8%) strains (all hVISA or VISA) were "nonsusceptible" to daptomycin by broth microdilution methods but susceptible by the disk diffusion method. For vancomycin, 35 (16.9%) strains were nonsusceptible by broth microdilution methods but susceptible by disk diffusion methods. In conclusion, daptomycin was highly bactericidal against S. aureus strains, and its bactericidal activity was not affected by decreased susceptibility to vancomycin. In contrast, many (one in seven) contemporary MRSA-WT, the majority of hVISA, and all VISA strains showed vancomycin MBC/MIC ratios consistent with tolerance, a predictor of poor clinical response. Disk diffusion tests generally failed to detect strains categorized as nonsusceptible to daptomycin or vancomycin by the reference broth microdilution method or Etest, and reassessment of breakpoints should be immediately attempted for MIC methods suggested as the test of choice.

Anti-Bacterial Agents↗