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PubMed2001

Depletion study of trimethoprim and sulphadiazine in milk and its relationship with mastitis pathogenic bacteria strains minimum inhibitory concentrations (MICs) in dairy cows.

Time-related concentrations in milk of a combination of trimethoprim-sulphadiazine (TMP-SDZ) intramammary formulated infusion and its relationship with pathogenic bacteria strains minimum inhibitory concentrations (MICs) isolated from clinical mastitis cows were analysed. The MICs study was performed for Escherichia coli, Staphylococcus aureus and Streptococcus sp. strains. The SDZ concentrations in milk were analysed using high-performance liquid chromatography (HPLC) and TMP using a microbiological assay. Ten lactating cows milked three times daily were used in the time-concentration studies of TMP-SDZ. Milk samples (approximately 20 mL) from the treated mammary quarters were taken at 6, 12, 24, 30 and 36 h after first administration. In order to define the withdrawal time, milk samples from the treated mammary quarters were taken at 24, 36, 48, 72, 84 and 96 h, after finishing the therapy. The MICs fluctuated between 1 and 8 microg/mL. Effective therapeutic concentrations lasted for 36 h when intramammary infusion was repeated three times every 12 h. No TMP was detected in milk for 24 h after finishing therapy. Milk SDZ concentrations were below 0.1 microg/mL in all treated cows after 84 h finishing therapy. At 96 h after finishing therapy, no SDZ milk concentrations were found in six animals, although four animals of the experimental group still had concentrations of 0.07 microg/mL.

Animals↗
PubMed1994

Problems in minimum inhibitory concentration determinations in coryneform organisms. Comparison of an agar dilution and the Etest.

The antimicrobial susceptibility of 159 coryneform organisms was determined by an agar dilution and Etest methods. Overall, the correlation between minimum inhibitory concentrations obtained by both techniques was good (> or = 0.09) for most antibiotics and organisms although the essential agreement ranged from 59% to 88.3%. Most organisms were equally categorized (sensitive, intermediate, or resistant) by both methods with only 0.2%, 0.4%, and 3.5% of very major, major or minor discrepancies, respectively. Such percentages dropped significantly when discrepant strains were retested. The correlation was specially good for Corynebacterium jeikeium and Corynebacterium urealyticum.

Actinomycetales↗
PubMed1998

[Minimum inhibitory concentration of amphotericin B in yeasts of medical interest].

In order to know the sensitivity of Candida and Crytococcus to amphotericin B, main drug for the treatment od systemic mycosis, it was determined the minimum inhibitory concentration (MIC) in 90 clinical isolates of Candida and Crytococcus by a micromethod for the broth dilution. According to the results, Crytococcus neoformas was more sensitive then Candida albicans (geometrical means 0.24 and 0.41 respectively). Only one resistant strain was found (CMI = 16 micrograms/mL), corresponding to the Candida krusei species. The introduction of this technique in the Mycology Laboratory of the "Pedro Kourí" Institute of Tropical Medicine will allow to establish the sensitivity patterns and to detect the possible appearance of resistance in the main species of pathogenic fungus for men in our environment.

Amphotericin B↗
PubMed2025

Estimating the association of antimicrobial resistance genes with minimum inhibitory concentration in Escherichia coli: an observational study.

BACKGROUND: Surveillance and prediction of antibiotic resistance in Escherichia coli relies on curated databases of genes and mutations. We aimed to quantify the effect of acquiring specific genetic elements on minimum inhibitory concentrations (MICs) for particular antibiotic-species combinations, addressing the current scarcity of such data in existing databases. METHODS: For this observational study, we evaluated a collection of E coli isolates with linked whole-genome sequencing and MIC data, originating from human urinary or bloodstream infections obtained from the Oxford University Hospitals National Health Service Foundation Trust in Oxfordshire, UK. We used multivariable interval regression models to estimate the change in MIC (with 95% CIs) for specific antibiotics associated with the acquisition of antibiotic resistance genes and associated mutations in the National Center for Biotechnology Information AMRFinder database, with and without an adjustment for population structure. We then tested the ability of these models to predict MIC and binary resistance or susceptibility using leave-one-out cross-validation. FINDINGS: We evaluated 2875 E coli isolates obtained during 2013-2018 and 2020. Although most ARGs and resistance mutations (89 [80%] of 111) were associated with an increased MIC, a much smaller number (27 [24%] of 111) was found to be putatively independently resistance-conferring (ie, associated with an MIC above the European Committee on Antimicrobial Susceptibility Testing breakpoint) when acquired in isolation. We found evidence of differential effects of acquired ARGs and resistance mutations between different generations of cephalosporin antibiotics and showed that sub-breakpoint variation in MIC can be linked to genetic mechanisms of resistance. 20 697 (83·3%; range 52·9-97·7 across all antibiotics) of 24 858 MICs were correctly exactly predicted and 23 677 (95·2%; 87·3-97·7) of 24 858 MICs were predicted to within one doubling dilution. INTERPRETATION: Quantitative estimates of the independent effect of the acquisition of ARGs on MIC add to the interpretability and utility of existing databases. Compared with approaches using machine learning models, the use of these estimates yields similar or better performance in the prediction of antibiotic resistance phenotype with more readily interpretable results. The methods outlined here could be readily applied to other antibiotic-pathogen combinations. FUNDING: The National Institute for Health and Care Research (NIHR) and the Medical Research Council (MRC).

Escherichia coli↗
PubMed1999

[Multicenter evaluation of broth microdilution test, BrothMIC MTB, to determine minimum inhibitory concentrations (MICs) of antimicrobial agents for Mycobacterium tuberculosis--evaluation of interlaboratory precision and interpretive compatibility with agar proportion method].

A newly developed microdilution antimycobacterial susceptibility test, BrothMIC MTB (Kyokuto Pharmaceutical Industrial Co., Ltd., Tokyo, Japan) to determine minimum inhibitory concentrations (MICs) was evaluated at multisites. The test method utilizes air-dried microplates containing serially diluted antimicrobial agents and the modified Middlebrook 7H9 broth. The eight antimycobacterial agents tested were rifampicin, isoniazid, ethambutol, streptomycin, kanamycin, levofloxacin, sparfloxacin and ciprofloxacin. The test plates were reconstituted by inoculation of 0.2 ml of cell suspensions (6 x 10(5) cells/ml) and were incubated at 36 degrees C in 5% to 10% CO2. The growth endpoints were visually read after 7-day and 10-day incubations. The reproducibility was evaluated with the four reference strains of Mycobacterium tuberculosis, and were compared with the agar proportion method described in the National Committee for Clinical Laboratory Standards (NCCLS) M24-T. Of the 1,022 testings of the reference strains, 1,020 (99.8%) of the MICs read after 7-day incubation fell within 3 log2 dilutions. The growth endpoints read after 7-day and 10-day incubations gave equal MIC ranges for the respective agents. The results obtained by the BrothMIC MTB for 93 clinical isolates of M. tuberculosis compared well with those determined by the NCCLS method with 98% to 99% agreements, except for ethambutol. According to the comparative analysis with the agar proportion method, the interpretive MIC breakpoints to discriminate between the isolates susceptible and resistant against the respective agents were proposed. In conclusion, this newly developed microdilution test for M. tuberculosis is a practical, rapid, quantitative, nonradiometric alternative for the determination of MICs in clinical mycobacteriology laboratories.

Antitubercular Agents↗
PubMed1994

Effect of beta-lactamase on minimum inhibitory concentrations of methicillin in methicillin-resistant Staphylococcus aureus.

A study was undertaken to determine whether the production of penicillin-binding protein-2' (PBP-2') and the production of beta-lactamase were related to the minimum inhibitory concentrations of methicillin (DMPPC) in various strains of methicillin-resistant Staphylococcus aureus. The amount of PBP-2' produced by the low-level resistant strain L20A was small and the strain became resistant to DMPPC as a result of inactivation of DMPPC by beta-lactamase. The largest amount of PBP-2' produced was in a moderately resistant strain L21A but the MIC was not high since the strain was not capable of producing beta-lactamase and the population of cells was heterogeneous. The amount of PBP-2' produced in the high-level resistant strain L457A was lower than that in strain L21A but the MIC was high as a result of the production of beta-lactamase. Production of PBP-2' was essential for resistance to methicillin but production of beta-lactamase had a major effect on the MIC.

Bacterial Proteins↗
PubMed1999

Marked reduction in the minimum inhibitory concentration (MIC) of beta-lactams in methicillin-resistant Staphylococcus aureus produced by epicatechin gallate, an ingredient of green tea (Camellia sinensis).

We found that epicatechin gallate, a constituent of an extract of tea leaves (green tea) markedly lowered the minimum inhibitory concentration (MIC) of oxacillin and other beta-lactams, but not of other antibacterial agents tested, in strains of methicillin-resistant Staphylococcus aureus. The antibacterial action of epicatechin gallate plus oxacillin was a bactericidal one.

Anti-Bacterial Agents↗
PubMed1990

A rapid technique for detection of resistance to chloramphenicol in Streptococcus pneumoniae and comparison with minimum inhibitory concentration and disk-diffusion methods.

Fifty-two strains of Streptococcus pneumoniae were examined for production of chloramphenicol acetyltransferase (CAT) by a rapid technique based upon induction of enzyme activity and chemical assay. This method was compared with one measuring the minimum inhibitory concentration (MIC) by agar dilution and a diffusion test with disks containing 10 micrograms, 30 micrograms and 50 micrograms of chloramphenicol. The MIC for 13 chloramphenicol-resistant strains was 16 mg/L and for 39 sensitive strains less than or equal to 4 mg/L. The chemical assay clearly distinguished resistant from sensitive strains; it was technically simple and provided results within 90 min. The distinction between sensitive and resistant bacteria in the disk diffusion assay was clearer with 10-micrograms than with 30-microgram and 50-micrograms disks. However, the chemical CAT assay, with enzyme induction, is recommended when a rapid result is required.

Bacteriological Techniques↗
PubMedDate not supplied

Prediction of bacterial susceptibility to cefpodoxime by using the ceftriaxone minimum inhibitory concentration result.

The cross-resistance or cross-susceptibility of cefpodoxime and ceftriaxone for 3700 strains of Enterobacteriaceae, oxacillin-susceptible staphylococci, Streptococcus spp., Haemophilus influenzae, Moraxella catarrhalis, and Neisseria gonorrhoeae was evaluated. With the exception of tests with Enterobacter spp. and Morganella morganii, the ceftriaxone minimum inhibitory concentration (MIC) result interpretive criteria predicted bacterial susceptibility (or resistance) to cefpodoxime with an acceptable rate of serious interpretive errors (1.5%) and an absolute categorical agreement > 92%. By using cefpodoxime interpretive criteria for ceftriaxone MICs, the interpretive errors for testing enteric bacilli were reduced from 2.1% to 1.5%.

Ceftizoxime↗
PubMed2005

Characterization and changing minimum inhibitory concentration (MIC) of Acinetobacter species from a tertiary care setup.

128 isolates of Acinetobacter species from admitted and outdoor patients were subjected to biotyping and resistotyping. Resistance phenotype analysis included nine antibiotics and two betalactam inhibitor combination drugs. In 100 strains of Acinetobacter spp. ciprofloxacin, amikacin, cefotaxime and cefepime minimum inhibitory concentration (MIC) was done by agar dilution using NCCLS 2002 criteria. In forty-nine isolates MIC level was determined by E-strip also. Extended spectrum beta lactamase (ESBL) production was detected by double disc synergy technique. Inducible beta lactamases (IBL's) were detected by disc approximation method. The relationship between biotypes and resistance phenotype was analyzed. Majority of isolates (93.75%) were from admitted patients. The biotyping revealed Acinetobacter calcoaceticus-Acinetobacter baumannii complex (87.2%) to be the predominant species and they were isolated from tracheal aspirates of patients with ventilator associated pneumonia. By Kirby Bauer disc diffusion antimicrobial sensitivity testing Acinetobacter spp. were most sensitive to the combination of drug cefoperazone-sulbactam (95.6%) followed by meropenem (94.6%), piperacillin-tazobactam (92.6%). On screening incidence of Imipenem Nonsensitive Acinetobacter spp. (INSA) was (5.4%). Acinetobacter spp. were typable by six resistance phenotypes and six biotypes. Most common (66.6%) resistant phenotype of A. calcoaceticus-A. baumannii complex was susceptible to cefoperazone-sulbactam and or meropenem and or piperacillin-tazobactam. ESBL production was seen in 6% and IBL (Inducible Beta Lactamase) production was seen in 7% of Acinetobacter spp. The MIC90 for ciprofloxacin was =256 microg/ml, cefotaxime 512 microg/ml, cefepime 512 microg/ml, and amikacin 32 microg/ml. Multidrug resistance was seen in more than 90% of A. calcoaceticus-A. baumannii complex and 20% of Acinetobacter lwoffii. Acinetobacter spp. has other emerging novel mechanism of resistance that requires continuous research. Simpler, reproducible and reliable methods of biotyping and their subsequent correlation with resistotyping are more cost effective than molecular methods, which are available only in reference laboratories.

Acinetobacter↗
PubMed2000

Increasing minimum inhibitory concentration of cefazolin for Salmonella typhi.

Cefazolin resistance was observed in the disc diffusion method of antibiotic susceptibility testing of Salmonella typhi strains isolated from January to June 1999. Eighty six multi drug resistant (MDR) isolates were studied. Of these, 46 (53.5%) were found resistant to cefazolin by the disc diffusion test. The minimum inhibitory concentration (MIC) of cefazolin was determined for the 86 isolates of S. typhi by the agar dilution method. MIC of these strains ranged from 1.0 to 64.0 micrograms/ml. In comparison, 25 MDR S. typhi strains isolated between 1994-1998 (5 per year) also tested by the same method, gave MIC values of 0.5 to 4.0 micrograms/ml. Our findings indicate a definite upward shift in MIC of cefazolin to MDR S. typhi since 1999. This needs to be monitored since the second, third and fourth generation cephalosporins are therapeutic options for typhoid fever.

Anti-Bacterial Agents↗
PubMed2026

Prediction of antimicrobial minimum inhibitory concentration from bacterial genomes using a scalable and interpretable machine learning approach.

Although machine learning models can predict antimicrobial susceptibility from bacterial whole genome sequencing (WGS), state-of-the-art approaches are computationally demanding or dependent on knowledge of genetic resistance determinants. Here, we describe an efficient data-driven approach to predicting minimum inhibitory concentration (MIC) by progressively extending and refining predictive genome segments, independent of prior knowledge of resistance determinants. Resultant models had high interpretability - known and potentially novel resistance determinants were captured. Using 762 clinical E. coli strains, 71.6% of predictions were within one dilution of the measured MIC. Models trained with this algorithm generalised better onto external data (F1 score = 0.85) compared with alternative models trained on annotated resistance determinants (F1 = 0.82) or k-mer counts (F1 = 0.74). Computational demands were low (RAM usage 23.6GB vs 38.8GB for k-mer model). These advantages represent an important advance in predicting antimicrobial susceptibility from WGS, with potential applications for clinical diagnostics, drug development, and surveillance.

Journal Article↗
PubMed1990

Minimum inhibitory concentrations and disk diffusion zone diameter for selected antibiotics against streptococci isolated from bovine intramammary infections.

The antimicrobial susceptibility to 11 antibiotics was determined of 358 streptococcal isolates representing six species was determined. All isolates were from milk samples obtained from clinical or subclinical cases of bovine mastitis. Agar disk diffusion zone diameters and minimum inhibitory concentrations were obtained for all isolates. Of the antibiotics tested that are available for mastitis therapy, cephalothin, penicillin, ampicillin, novobiocin, and erythromycin demonstrated acceptable activity against nonenterococcal streptococci, but only penicillin and ampicillin demonstrated moderate activity against Enterococcus faecalis. Enterococcus faecalis demonstrated substantial resistance to cephalothin, erythromycin, gentamicin, streptomycin, and tetracycline, while the nonenterococcal streptococci demonstrated substantial resistance to gentamicin, streptomycin, and tetracycline. Streptococcus uberis demonstrated greater antibiotic resistance than did Streptococcus dysgalactiae, while Aerococcus viridans demonstrated the greatest overall resistance of the nonenterococcal species.

Animals↗
PubMed2005

Minimum inhibitory concentrations of tulathromycin against respiratory bacterial pathogens isolated from clinical cases in European cattle and swine and variability arising from changes in in vitro methodology.

The in vitro activity of tulathromycin was evaluated against common bovine and porcine respiratory pathogens collected from outbreaks of clinical disease across eight European countries from 1998 to 2001. Minimum inhibitory concentrations (MICs) for one isolate of each bacterial species from each outbreak were determined using a broth microdilution technique. The lowest concentrations inhibiting the growth of 90% of isolates (MIC90) for tulathromycin were 2 microg/ml for Mannheimia (Pasteurella) haemolytica, 1 microg/ml for Pasteurella multocida (bovine), and 2 microg/ml for Pasteurella multocida (porcine) and ranged from 0.5 to 4 microg/ml for Histophilus somni (Haemophilus somnus) and from 4 to 16 microg/ml for Actinobacillus pleuropneumoniae. Isolates were retested in the presence of serum. The activity of tulathromycin against fastidious organisms was affected by culture conditions, and MICs were reduced in the presence of serum.

Actinobacillus pleuropneumoniae↗
PubMed2005

Comparison of disc diffusion results with minimum inhibitory concentration (MIC) values for antimicrobial susceptibility testing of Neisseria gonorrhoeae.

BACKGROUND & OBJECTIVE: objectives: As antimicrobial susceptibility testing of Neisseria gonorrhoeae provides guidance for appropriate treatment, there is a need for simple, reliable and cost-effective method for susceptibility testing. The present study was aimed to compare the results of two methods of susceptibility testing, minimum inhibitory concentration (MIC) values by E test with disc diffusion results by Australian Gonococcal Surveillance Programme (AGSP) method in N. gonorrhoeae isolates. METHODS: Susceptibility testing for ciprofloxacin, penicillin and ceftriaxone using AGSP method was carried out for 301 confirmed consecutive isolates of N. gonorrhoeae. MIC of ciprofloxacin, penicillin and ceftriaxone was determined by E test in 301, 198 and 128 isolates respectively. The results of the two methods were compared by using Kappa statistics. RESULTS: Moderate levels of agreement for ciprofloxacin (kappa=0.44) and penicillin (kappa=0.54) were observed between the two methods. For ceftriaxone, 96.1 and 0.8 per cent isolates were found to be susceptible and less sensitive respectively by both the methods and per cent agreement between the two methods was 96.9 per cent. INTERPRETATION & CONCLUSION: Both the methods were easy to perform and gave reproducible results. However, disc diffusion method was cost-effective and more feasible in routine diagnostic laboratories in developing countries like India.

Anti-Bacterial Agents↗
PubMed1994

Correlation between zeta-potential of a cell in a new cationic disinfectant solution and minimum inhibitory concentration of the disinfectant.

In the previous paper, we described the synthesis of new quaternary ammonium slats with antimicrobial activity: N-alkyl-N-2-hydroxyethyl-N,N-dimethylammonium butyl phosphate (4) and N-alkyl-N-(2-hydroxy-3-phenoxy)-propyl-N,N-dimethylammonium butyl phosphate (5). In this study, we examined the relationship between the MIC (minimum inhibitory concentration) of these new cationic disinfectants, 4 (six compounds) and 5 (three compounds), and the xi-potential against Escherichia coli in solutions of these compounds. The MIC values of these disinfectants against E. coli were highly correlated with the concentration that induced electric charge inversion (xi-potential=0) of E. coli from negative to positive.

Disinfectants↗
PubMed1994

Inoculum effects on Etests and agar dilution minimum inhibitory concentrations. Piperacillin and piperacillin-tazobactam against Staphylococcus aureus.

Inoculum effects notoriously occur with beta-lactamase-positive staphylococci in dilution susceptibility tests with substrate beta-lactams. Etests, like dilution experiments, demonstrated such effects with piperacillin and, to a lesser extent, with its tazobactam combinations. When Etests were used with the recommended inoculum of approximately 10(6) colony-forming units (CFU/plate, the minimum inhibitory concentrations (MICs) of piperacillin-tazobactam found for beta-lactamase-positive Staphylococcus aureus isolates resembled those found by agar dilution for inocula of 10(4) CFU/spot but were two- to eightfold below those found by agar dilution for inocula of 10(6) CFU/spot; MICs of piperacillin itself by Etest were about fourfold below even those found by agar dilution with inocula of 10(4) CFU/spot. Inoculum effects for beta-lactamase-negative S. aureus were minimal by both methods.

Bacteriological Techniques↗
PubMed2005

Slime production and proteinase activity of Candida species isolated from blood samples and the comparison of these activities with minimum inhibitory concentration values of antifungal agents.

Slime and proteinase activity of 54 strains consisting of 19 Candida parapsilosis and 35 C. albicans strains isolated from blood samples were investigated in this study. Ketoconazole, amphothericin B, and fluconazole susceptibility of Candida species were compared with slime production and proteinase activity of these species. For both Candida species, no correlation was detected between the slime activity and minimum inhibitory concentration (MIC) values of the three antifungal agents. For both Candida species no correlation was detected between the proteinase activity and the MIC values of amphothericin B, and fluconazole however, statistically significant difference, was determined between the proteinase activity and MIC values of ketoconazole (p = 0.007). Slime production was determined by using modified Christensen macrotube method and proteinase activity was measured by the method of Staib. Antifungal susceptibility was determined through the guidelines of National Committee for Laboratory Standards (NCCLS M27-A).

Amphotericin B↗