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Results for “Disk Diffusion Antimicrobial Tests”

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PubMed1987

Impact of prolonged incubation on disk diffusion susceptibility test results for Staphylococcus aureus.

Because strains of Staphylococcus aureus that are resistant to penicillinase-resistant penicillins may be difficult to detect in the clinical laboratory, a variety of changes in methodology have been suggested to increase their detection. In 1984, the West Los Angeles Veterans Administration Medical Center experienced an increase in clinically significant strains of oxacillin-resistant S. aureus. To insure that such strains would not be missed by the disk diffusion test methods employed for routine testing, changes in methodology were insituted. These included interpreting zone diameters around oxacillin disks at 48 h of incubation. We collected 139 isolates from patients thought to have oxacillin-resistant S. aureus based on these test results and later retested the isolates using microdilution MIC testing. Only 85 isolates (61%) had microdilution oxacillin MICs of greater than or equal to 8.0 micrograms/ml, whereas 54 (39%) had oxacillin MICs of less than or equal to 2.0 micrograms/ml. A review of medical records revealed that in 1 year there were 98 patients with isolates appearing resistant by disk diffusion but not confirmed by microdilution MICs; many patients were placed in isolation and treated with specific antimicrobial agents. We conclude that incubation of oxacillin disk diffusion tests for longer than 24 h in conjunction with disregard for resistance to other classes of antimicrobial agents may result in an unacceptably high degree of false resistance results. Because the resistance of S. aureus has important therapeutic and infection control implications, it is necessary to recognize problems that may result in ambiguous or inaccurate susceptibility results.

Humans↗

PubMed2005

The prevalence and antimicrobial susceptibilities of Salmonella and Campylobacter in ducks in Taiwan.

Cloacal swabs were sampled from 100 duck farms in Taiwan between March 2000 and January 2001 for isolation and standard cultivation of Salmonella spp. and thermophilic Campylobacter spp. Salmonella spp. were isolated from 4.6% (91/2000) of ducks from 20% (20/100) of duck farms. Ten serotypes of Salmonella enterica were identified: S. Potsdam (31.9% of isolates), S. Dusseldorf (18.7%), S. Indiana (14.3%), S. Typhimurium (7.7%), S. Hadar (5.5%), S. Newport (4.4%), S. Derby (4.4%), S. Montevideo (2.2%), S. Schwarzengrund (2.2%), and S. Asinnine (1.1%). Isolation of S. Asinnine or S. Indiana from poultry had not hitherto been described in Taiwan. The salmonella isolation rate in ducklings under two weeks of age was significantly higher than the other age groups (P<0.05). Campylobacter spp. were isolated from 43.5% (1045/2400) of ducks from 92% (92/100) of duck farms. Among them, 991 isolates (94.8%) were identified as C. jejuni and 54 isolates (5.2%) as C. coli. The campylobacter isolation rate in ducklings under two weeks of age was significantly lower than other age groups (P<0.05). Antimicrobial susceptibility testing was conducted by the disk diffusion and E- test methods. The results indicated that Salmonella isolates were 100% susceptible to amikacin, amoxicillin/clavulanic acid, ceftraxone, cephalothin, ciprofloxacin, norfloxacin, ofloxacin, and polymyxin B. A markedly higher antimicrobial resistance to amoxicillin, florfenicol, flumequine, josamicin/trimethoprim, nalidixic acid, nitrofurantoin, norfloxacin, ofloxacin, polymyxin B, sulfamethoxazole/trimethoprim and tetracycline was found in campylobacter isolates.

Animals↗

PubMed1994

[Microbial drug resistance and the presence of plasmids in Salmonella strains isolated from different sources].

BACKGROUND: To establish the relationship between the presence of plasmid and their antimicrobial resistance of Salmonella strains. METHODS: We tested 171 strains of Salmonella isolated from different sources: natural waters (73 strains), food (23 strains), and from clinical samples (75 strains). The disk diffusion method was used to test the antimicrobial susceptibility of the strains to 13 drugs. Plasmid analysis were performed by agarose gel electrophoresis technique. RESULTS: Antimicrobial resistances of the strains significantly varies according to their primary isolation sources. Strains isolated from the water environment exhibited a full susceptibility to cephalothin and colistin, whilst all the strains isolated from food were sensitive to ampicillin, gentamicin, kanamycin, neomycin, tobramycin and trimethoprim-sulphamethoxazole. On the other hand, resistances to colistin, gentamicin and trimethoprim-sulphamethoxazole were not found in clinical isolates. From the 171 Salmonella strains tested, only 12.2% were sensitive to all the antimicrobials. The most frequently antibiotic resistances detected were to streptomycin (49.3%), tetracycline (33.1%) and nalidixic acid (30.7%). The percentage of strains that harboured plasmids was different depending on the source of isolation, ranging from 41.4% for water isolated, 76% for clinical isolates and 86.9% for food isolates. The relationship between antimicrobial resistance and plasmid presence is very close, since higher percentages of resistance to chloramphenicol, carbenicillin, cephalothin, kanamycin, neomycin, nalidixic acid and trimethoprim-sulphamethoxazole were obtained in strains containing plasmids. CONCLUSIONS: (a) The most frequently resistance detected in strains of Salmonella was to streptomycin (49.3% of the strains). On the other hand, only 0.6% of the strains were resistant to gentamicin. (b) Percentages of resistance to some antibiotics was higher in strains harbouring plasmids, that implies a relationship between the plasmid presence and the antibiotic resistance in Salmonella. (c) Curing of extrachromosomic elements by acridine orange showed a percentage of resistance lost greater than 70% for cephalothin, kanamycin, neomycin, and nalidixic acid. This indicates that the resistance to those antibiotics is mainly linked to plasmids. In the case of the unusual nalidixic acid-resistance, previously described in Shigella strains, suggests that are needed more studies to demonstrate the direct association between antimicrobial resistance and presence of plasmids.

Anti-Bacterial Agents↗

PubMed2006

Citrobacter infections in a tertiary care hospital in Northern India.

OBJECTIVES: This prospective study was carried out to look for the frequency of isolation of Citrobacter species from clinical specimens and study their antimicrobial susceptibility pattern. METHODS: Patients from whom Citrobacter species were isolated during routine diagnostic testing from January to December 2004 were included in the study. Isolates were identified by standard biochemical tests. Antimicrobial susceptibility testing was performed by disk diffusion method as per National Committee of Clinical Laboratory Standards (NCCLS) guidelines. RESULTS: Citrobacter species were isolated from a total of 205 patients. Infection was nosocomially acquired in 94.6% patients. One hundred eighty one (88.3%) patients had significant underlying illnesses. Culture yielded Citrobacter koseri in 185 (90.2%) and Citrobacter freundii in 20 (9.8%) patients. The distribution of isolates was as follows: urine (46.2%), respiratory tract (16.3%), blood (15.8%), pus (12.1%) and sterile body fluids (9.3%). Drug resistance was observed to be more in C. koseri as compared to C. freundii. CONCLUSIONS: Citrobacter infections are often nosocomially acquired, seen in patients with significant underlying diseases and isolates are commonly drug-resistant. Adoption of hospital infection control practices and a good antibiotic policy may prevent their spread.

Adolescent↗

PubMed2026

Genomic epidemiology of extended-spectrum beta-lactamase-producing Escherichia coli across humans, poultry and wastewater sectors in Douala, Cameroon.

BACKGROUND: The global health threat of antimicrobial resistance involves the human, animal and environmental sectors. Data from Cameroon are scarce. OBJECTIVES: This study aimed to define extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-Ec) rates and associated risk factors across the three sectors in Douala, Cameroon, and to define molecular characteristics of isolates. METHODS: From June 2022 to May 2023, we collected blood cultures from hospitalized patients, rectal swabs from healthy pregnant women, caeca from broiler chickens and environmental wastewater. Samples were screened for ESBL-Ec using CHROMAgar™ ESBL and cefotaxime-supplemented Tryptone Bile X-glucuronide agar. Antimicrobial susceptibility testing was performed by disk diffusion following EUCAST guidelines. Whole-genome sequencing was carried out using Illumina technology. RESULTS: Of 628 samples, 374 yielded ESBL-Ec. Prevalence was 54.6% (131/240) in pregnant women, 70.4% (169/240) in chickens and 93.1% (67/72) in wastewater. The proportion of ESBL-Ec among E. coli-positive-blood cultures was 9.2% (7/76). Multi-family household living was independently associated with ESBL-Ec carriage among pregnant women (adjusted odds ratio = 1.7, 95% CI 1.0-3.1, P = 0.03). High co-resistance (>70%) was observed for tetracycline, ciprofloxacin and trimethoprim/sulfamethoxazole. Sequencing of 32 isolates revealed 45 distinct resistance genes, including blaCTX-M-15 (n = 13, 40.6%), blaCTX-M-55 (n = 11, 34.4%) and last-resort antibiotic resistance genes mcr-1 and bla OXA-181. High-risk sequence types included ST131 (pregnant women) and ST10 (chickens). Notably, ST48 was shared between pregnant women and chickens, and ST155 between pregnant women and wastewater. CONCLUSION: Cross-sectoral ESBL-Ec in Douala exhibits high genomic diversity and alarming resistance. The occurrence of last-resort genes requires immediate One Health surveillance and coordinated interventions.

Journal Article↗

PubMed1998

Incidence, epidemiology and evolution of reduced susceptibility to ciprofloxacin in Neisseria gonorrhoeae in Korea.

OBJECTIVE: To verify the decrease of susceptibility to ciprofloxacin in Neisseria gonorrhoeae, determine the size of the recently reported new beta-lactamase plasmid and explain the high prevalence of penicillinase-producing Neisseria gonorrhoeae (PPNG). METHODS: Gonococci were isolated from prostitutes in Korea. Antimicrobial susceptibility was tested by NCCLS disk diffusion and agar dilution methods. Plasmid was isolated by an alkaline lysis method. Patterns of Nhel-digested genomic DNA were compared after pulsed-field gel electrophoresis (PFGE). RESULTS: The minimum inhibitory concentration of ciprofloxacin for 50% of the isolates rose from 0.015 mg/L in 1993 to 0.12 mg/L in 1996. The proportion of PPNG remained at 70% or over during the 5-year period. The size of a novel beta-lactamase plasmid, first reported in 1994, was determined to be approximately 3.2 MDa, and 48% of the PPNG isolates contained it. Twelve of 50 isolates had the same PFGE pattern and nine others another pattern. CONCLUSION: The rapid decrease of fluoroquinolone-susceptible gonococci suggests that in the near future the drug may become less useful for gonorrhea treatment. The new 3.2-MDa plasmid may have been introduced as a result of the recent increase in overseas travel. The PFGE pattern suggests that high prevalence of PPNG may be due to dissemination of a few resistant clones among the high-risk groups.

Journal Article↗

PubMed2000

Emerging antimicrobial resistance, plasmid profile and pulsed-field gel electrophoresis pattern of the endonuclease-digested genomic DNA of Neisseria gonorrhoeae.

Resistant gonococci are very prevalent in many countries, particularly in Asia. This study was conducted to determine the trend of resistance, the effect of decreasing the ciprofloxacin susceptibilities of gonococci on the prevalence of penicillinase-producing N. gonorrhoeae (PPNG), and to compare the epidemiology of strains with the previous studies. A total of 602 strains of gonococci were isolated from prostitutes in 1997-1999. Antimicrobial susceptibility was tested by NCCLS disk diffusion and agar dilution methods. For epidemiologic analysis, plasmid analysis and pulsed-field gel electrophoresis (PFGE) were performed. The proportion of PPNG remained high (79%), and the strains with decreased susceptibility to ciprofloxacin increased significantly from 67% in 1997 to 84% in 1999. Compared to our previous study, the PFGE patterns were similar, while the proportion of strain with the 3.2-MDa plasmid markedly decreased. In conclusion, a rapid increase in ciprofloxacin-nonsusceptible strains may suggest difficulties in the treatment of gonococcal infections in the near future with the drug. The recent decrease of PPNG with the 3.2-MDa plasmid may suggest that there is an epidemiological change in gonococcal infections, and the prevalence of related PFGE patterns suggests the dissemination of a few clones among the high risk populations.

DNA↗

PubMed1999

[Vancomycin-resistant enterococci in north-eastern Taiwan].

Vancomycin-resistant enterococci (VRE) is a world-wide emerging pathogen. The first confirmed VRE isolate in Taiwan was detected in 1995. After that, more and more isolates of VRE were found in western part of Taiwan. However, before this report, there was no any isolate of VRE found in eastern part of Taiwan. In December 1997 and January 1998, two cases of VRE urinary tract infection were found in two regional hospitals in north-eastern Taiwan. They had received prolonged treatment with multiple antibiotics for other infections before they got VRE infection. The isolates showed susceptibility to other antimicrobial agents by routine disk diffusion susceptibility test and these two patients were successfully treated. The VRE did not spread in those two hospitals. After further study, the 3 isolates from these two patients all had minimum inhibitory concentration of vancomycin >256 microg/mL. They all carried van A gene and the pulsed-field gel electrophoresis demonstrated they belonged to different DNA types. It was concluded that VRE appeared in north-eastern Taiwan but the strains were not from a common source.

Aged↗

PubMed2003

[In vitro sensitivity to antimicrobial agents of Haemophilus influenzae strains isolated from clinical specimens].

In-vitro activity of several antimicrobial agents were evaluated against Haemophilus influenzae (n:127) isolated from clinical specimens within the years 2000 and 2002 in a children's hospital. Antimicrobial susceptibility tests were performed by disk diffusion method according to the recommendations of the NCCLS standards and beta-lactamase activity was investigated by nitrocefin test. Resistance rates for the antibiotics were as follows: ampicillin 5.6%, trimethoprim-sulfamethoxazole (TMP/SMX) 27.5%, tetracycline 8.6%, clarithromycin 7%, chloramphenicol 4.7%. Five isolates (3.9%) were found multiple resistant. Beta-lactamase activities were detected in all of the ampicillin resistant isolates. None of the isolates were resistant to ampicillin-sulbactam, cefaclor, cefuroxime, cefprozil, cefpodoksim, cefotaxime, meropenem or ciprofloxacin. According to these results, resistance to ampicillin is low in our H. influenzae isolates compared to other European countries but resistance to TMP/SMX is very high and this finding has to be taken into account in the empirical therapy of community acquired respiratory tract infections.

Anti-Bacterial Agents↗

PubMed1988

The identification and antimicrobial susceptibility testing of Neisseria gonorrhoeae, 1980-1987. Results from the College of American Pathologists Microbiology Surveys Program.

The results of the College of American Pathologists (Skokie, III) Microbiology Surveys from 1980 through 1987 indicate subscriber laboratories have continued to improve their ability to identify and test the antimicrobial susceptibility of Neisseria gonorrhoeae. Bacteriology and Comprehensive Surveys participants correctly identified this organism more frequently (95% to 96%) than did the Basic Surveys Laboratories. Neisseria gonorrhoeae samples in mixed cultures were slightly more difficult (3% to 5% decreased accuracy) to identify. Antimicrobial susceptibility testing by the disk-diffusion and beta-lactamase tests were more accurate (98% to 99%) than minimum inhibitory concentration-dilution methods (92%). Currently, most laboratories use the commercially prepared beta-lactamase reagents and the disk-diffusion test. The National Committee for Clinical Laboratory Standards is currently standardizing methods for the susceptibility testing of several antibiotics against gonococci. The College of American Pathologists Microbiology Surveys will continue to monitor participant accuracy for the identification and resistance recognition of this epidemiologically important pathogen.

Anti-Bacterial Agents↗

PubMed2001

Scavenging of free radicals, antimicrobial, and cytotoxic activities of the Maillard reaction products of beta-lactoglobulin glycated with several sugars.

The Maillard reaction occurs during many industrial and domestic thermal treatments of foods. It is widely used because of its role in creating colors, flavors, textures, and other functional properties in foodstuffs. Proteins glycated without the use of conventional chemical reagents have improved technofunctional properties such as heat stability, emulsifying, and foaming properties. The present study was carried out to determine the extent to which this reaction can convey antioxidant, antimicrobial, or cytotoxic activities to beta-lactoglobulin (BLG) and to its tryptic and peptic hydrolysates. BLG was modified with six different sugars in solution at 60 degrees C. Antiradical properties were estimated using a radical scavenging activity test. Antimicrobial activities against different bacterial strains were studied with a diffusion disk method. Cytotoxic tests were performed using two cell lines and the 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide (MTT) rapid colorimetric assay. Glycation induced a radical scavenging activity to BLG, the intensity of which depended on the sugar used for modification. Proteins modified with ribose and arabinose showed the highest radical scavenging activities depicted by about 80 and 60% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) absorption decrease at 515 nm. No antimicrobial effect of any glycated form of BLG against Escherichia coli, Bacillus subtilis, Listeria innocua, and Streptococcus mutans was observed. The MTT test showed no enhancement of cytotoxicity by modified proteins and peptides against COS-7 and HL-60 cells. Thus, glycated proteins could be used in formulated food as functional ingredients with a radical scavenging activity able to delay deterioration due to oxidation. This use could be even more advisable considering the lack of toxicity to eukaryotic and prokaryotic cell cultures demonstrated in this work.

Animals↗

PubMed1998

Clinical microbiology laboratories do not always detect resistance of Haemophilus influenzae with disk or tablet diffusion methods. Finnish Study Group for Antimicrobial Resistance (FiRe).

The performance of disk diffusion testing of Haemophilus influenzae was evaluated in 20 laboratories. Thirteen disk-medium-breakpoint-inoculum modifications were used in Finnish clinical microbiology laboratories. The performance of various methods was evaluated by testing a susceptible control strain and one with non-beta-lactamase-mediated ampicillin resistance 10 times in 16 laboratories. Gaps in millimeters were measured between these two groups of results. The strains were separated by a gap of at least 5 mm in 8/16 laboratories testing ampicillin, in 7/15 laboratories testing cefaclor, in 5/ 16 laboratories testing cefuroxime, and in 15/16 laboratories testing trimethoprim-sulfa. Detection of ampicillin resistance was better with 2.5 microg tablets than with 10 microg disks or 33 microg tablets. For MIC-determinations, 785 isolates and their disk diffusion results were collected. None of the 12 clinical isolates with non-beta-lactamase-mediated ampicillin resistance was detected as resistant in the participating laboratories. The ampicillin and cefaclor results of the isolates were no better even when a laboratory was able to separate the control strains. Cefaclor results were unreliable because of poor disk diffusion-MIC correspondence and incoherent breakpoint references. Interlaboratory variation of the zone diameters caused false intermediate results of cefuroxime-susceptible strains. When ampicillin, cefaclor and cefuroxime were tested, the discrimination of laboratories using disks and tablets was equal, whereas the laboratories using paper disks were better able to detect trimethoprim-sulfa resistance.

Diffusion↗

PubMed2001

Nasal carriage of Streptococcus pneumoniae among children in Beijing.

OBJECTIVE: To investigate the antimicrobial susceptibility of Streptococcus pneumoniae carried in the nose among children in Beijing and the distribution of serotypes, and to analyze the risk factors for nasal carriage of penicillin non-susceptible S. pneumoniae. METHODS: A disk diffusion test was applied to detect the antimicrobial susceptibilities of S. pneumoniae to erythromycin, trimethoprim-sulfamethoxazole, chloramphenicol and tetracycline. The E test was applied to determine the minimal inhibitory concentrations of penicillin, cefuroxime, cefotaxime, augmentin and imipenem. S. pneumoniae isolates were serotyped by the Quellung reaction. RESULTS: S. pneumoniae that was resistant to penicillin or cefuroxime was not found, but S. pneumoniae intermediate resistant to penicillin and cefuroxime accounted for 8.2% and 2.1%, respectively. All of the isolates were susceptible to cefotaxime, augmentin and imipenem. S. pneumonia that was resistant to erythromycin, trimethoprim-sulfamethoxazole and tetracycline were extremely numerous, accounting for 72%, 70% and 79%, respectively. Five serotypes (19, 6, 14, 23, 17) accounted for 54.7%, and nontypables accounted for 20.6% of all the S. pneumoniae. Previous history of otitis media was a risk factor we found for nasal carriage of penicillin non-susceptible S. pneumoniae. CONCLUSIONS: Continued surveillance of the antimicrobial susceptibilities of S. pneumoniae is necessary. A larger scale investigation is needed to identify if the 7 or 9-valent conjugate pneumococcal vaccine is appropriate for Chinese children.

Child, Preschool↗

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↗

PubMedDate not supplied

Distribution of serotypes and antimicrobial resistance of Streptococcus pneumoniae in a children's hospital in Turkey.

Streptococcus pneumoniae isolates resistant to penicillin and other antibiotics have been increasing in many parts of the world. The aim of this study was to evaluate the antimicrobial susceptibilities to penicillin and other commonly used agents in 98 isolates recovered between 1997 and 1998 from clinical specimens from children, and to determine the serotypes/serogroups related to resistance. Susceptibility to penicillin was determined by E-test and disk diffusion tests were used for the other antimicrobials. Serotyping was performed on all the isolates by the quelling reaction. The rates of intermediate- and high-level resistance to penicillin were 29.6% and 2%, respectively. Overall resistance to trimethoprim-sulfamethoxazole was high (46%), of which 21% coexisted with penicillin resistance. Resistance rates to erythromycin and chloramphenicol were 5% and 1%, respectively. Five isolates were multi-drug resistant. The most frequent serotypes associated with penicillin resistance were serotypes 19, 23, 6, 9 and 15.

Anti-Bacterial Agents↗

PubMed2005

Reevaluation of Enterobacteriaceae MIC/disk diffusion zone diameter regression scattergrams for 9 beta-lactams: adjustments of breakpoints for strains producing extended spectrum beta-lactamases.

Validity of the current susceptibility breakpoint criteria for 9 beta-lactam antimicrobials and performance of proposed alternative breakpoints to improve prediction of clinical outcomes were analyzed by testing a contemporary collection of 350 Enterobacteriaceae, enriched for an overrepresentative collection of 70 (20.0%) strains producing extended-spectrum beta-lactamases (ESBLs). The majority of the strains were isolated from bloodstream infections (83.7% of the entire collection and 85.7% of the ESBL subset). The 9 beta-lactam antimicrobials analyzed were aztreonam, cefepime, cefotaxime, cefotetan, cefoxitin, ceftazidime, ceftriaxone, ceftizoxime, and cefuroxime. Reference broth microdilution MIC results were compared with those zone diameters obtained by the standardized disk diffusion test. The correlation coefficient (r) was acceptable for all antimicrobials, ranging from 0.87 (cefotetan) to 0.97 (aztreonam, cefotaxime, and ceftazidime). Using the current susceptible breakpoint criteria for Enterobacteriaceae, the intermethod categorical agreement ranged from 90.6% (cefotaxime) to 98.0% (ceftazidime). Very major (false-susceptible by disk test) and major errors (false-resistant) were nil (0.0%) for 6 of the 9 beta-lactams. Minor error rates ranged from only 0.9% (cefotetan) to 9.4% (cefotaxime). The proposed MIC breakpoint criteria (generally lower) adjusted to levels to accurately detect ESBL-producing strains and better predict clinical outcomes, also had acceptable intermethod concordance ranging from 90.6% (cefotetan) to 100.0% (ceftazidime). Remarkably, an improvement in the intermethod categorical agreement ranging from +1.7% to +8.3% was observed for 7 of the 9 antimicrobials, including the ESBL index or screening compounds (aztreonam, ceftazidime, cefotaxime, and ceftriaxone). No change in the breakpoint criteria, with removal of the intermediate category was tentatively proposed for cefoxitin and cefuroxime, resulting in an increase of the serious intermethod errors (very major and major), but the absolute intermethod agreement remained highly acceptable at 90.6% to 93.4%. Although the current breakpoint criteria remain acceptable in minimizing intermethod discords, the alternative susceptible breakpoint criteria proposed by combining pharmacokinetic/pharmacodynamic (PK/PD), microbiology MIC population analyses, and clinical success parameters possess improved intermethod agreement for the ESBL screening drugs and 5 other broad-spectrum beta-lactam compounds. The Clinical Laboratory Standards Institute (formerly, the National Committee for Clinical Laboratory Standards) should consider these changes to facilitate the detection of all Enterobacteriaceae with low PK/PD target attainment rates, therefore having the potential for suboptimal responses with usual therapeutic dosing.

Anti-Bacterial Agents↗

PubMed2001

Assessment of BMS284756 MIC and 5-microg disk diffusion quality control studies tested against seven American type culture collection strains.

BMS284756 is a novel des-fluoro(6)-quinolone with antimicrobial activity similar to recently developed fluorinated quinolones. The purpose of this investigation was to determine the appropriate disk diffusion and MIC quality control (QC) ranges for BMS284756 when used against commonly tested QC strains (M23-A2). The BMS284756 5-microg disk content was tested against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Hemophilus influenzae ATCC 49247, Streptococcus pneumoniae ATCC 49619 and Staphylococcus aureus ATCC 25923. In addition, Enterococcus faecalis ATCC 29212 and S. aureus ATCC 29213 were evaluated by the broth microdilution method. Seven laboratories tested 2 disk lots on 3 agar media or 3-4 broth lots over a 10 day period. A total of 420 zone diameter values and 210 or 280 MIC values per organism were generated. The following disk diffusion and MIC QC ranges were suggested for BMS284756 and the seven QC strains: E. coli ATCC 25922 (28-35 mm/0.004-0.016 microg/mL), E. faecalis ATCC 29212 (0.03-0.25 microg/mL), S. aureus ATCC 25923 (30-36 mm), S. aureus ATCC 29213 (0.004-0.016 microg/mL), P. aeruginosa ATCC 27853 (19-25 mm/0.5-2 microg/mL), H. influenzae ATCC 49247 (33-41 mm/0.002-0.008 microg/mL), S. pneumoniae ATCC (26-33 mm/0.016-0.06 microg/mL). The proportion of participant results observed within the proposed ranges was 97.4-98.8% and 94.6-100% for the disk diffusion and MIC tests, respectively.

Anti-Infective Agents↗

PubMed1991

Evaluation of the E test for quantitative antimicrobial susceptibility testing of Helicobacter pylori.

The Progressive Diagnostics Manufacturers epsilometer test (E test; AB Biodisk, Solna, Sweden), a quantitative variant of the disk diffusion technique, was evaluated comparatively to an agar dilution method for the antimicrobial susceptibility testing of Helicobacter pylori. A collection of 79 H. pylori clinical strains, including isolates with known resistance to various antimicrobial agents, was tested against 12 different antimicrobial agents. All strains were tested on Columbia agar supplemented with 10% horse blood. Plates were incubated at 37 degrees C in microaerobic atmosphere (5% O2, 10% CO2), and readings were done after 3 days of incubation. In general, E test MICs were easy to interpret and the correlation between MICs by the agar dilution method and the E test was good, with 86 and 99.5% of results being within, respectively, 1 and 2 log2 dilution steps in a total of 936 tests. All strains of H. pylori with documented resistance to the tested agents were detected by the E test. Thus, the E test appears to be an easy and reliable method for determination of MICs of antibiotics for H. pylori, and it may offer an interesting alternative to MIC determination by the agar dilution technique.

Drug Resistance, Microbial↗