A note on gentamicin susceptibility testing: the validity of the MS-2 system and Rosco Neosensitabs agar diffusion

The MS-2 automated system was compared with Rosco Neosensitabs agar diffusion for the gentamicin susceptibility of a group of 267 organisms isolated from clinical material. With Rosco Neosensitabs agar diffusion agreement with reference minimal inhibitory concentrations was 98.5%, while with the MS-2 system it was 100% if calcium and magnesium-supplemented MS-2 broth was used.     

Comparison of disc diffusion, Etest and agar dilution for susceptibility testing of colistin against Enterobacteriaceae

Aims: In this study, we compared different methods of colistin susceptibility testing, disc diffusion, agar dilution and Etest using a set of Enterobacteriaceae isolates that included colistin‐resistant strains. Methods and results: Susceptibility of 200 clinical isolates of Enterobacteriaceae to colistin was tested to compare agar dilution (reference method), disc diffusion (50 and 10 μg) and Etest. MICs (minimum inhibitory concentrations) were interpreted using the criteria established by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Colistin exhibited excellent activity against Escherichia coli and E. cloacae (MIC₉₀ = 0·5 mg l^?1). In contrast, colistin was less active against Klebsiella pneumoniae (MIC₉₀ = 16 mg l^?1). Resistance rates varied from 0% in E. coli to 1·8% in E. cloacae and 13% in K. pneumoniae. High rates of very major errors were observed in the disc diffusion test using either the criteria of the Comité de l’antibiogramme de la Société Française de Microbiologie (CA‐SFM) or the criteria of the Clinical and Laboratory Standards Institute (CLSI), respectively, 3·5 and 2·5%. When the criteria of Gales et al. were applied, the number of very major errors was reduced to one (0·5%). The Etest showed good concordance with agar dilution method. Conclusion: Disc susceptibility testing methods are unreliable on detecting colistin resistance. MIC should be determined to confirm the susceptibility results by disc diffusion. Significance and Impact of the study: We recommend the determination of MIC by Etest for all multidrug‐resistant Enterobacteriaceae when colistin is required for the treatment.     

常见皮肤癣菌体外药物敏感试验的研究

目的比较液基稀释法和纸片扩散法对临床常见皮肤癣菌的体外药物敏感性。方法应用Rosco纸片扩散法和微量液基法（参考美国国家实验室标准委员会NCCLS推荐的M38-P方案修改方案）测定临床分离的40株皮肤癣菌（包括红色毛癣菌、须癣毛癣菌、犬小孢子菌及絮状表皮癣菌）对两性霉素B、伊曲康唑、氟康唑和特比萘芬的体外药物敏感性。结果应用Rosco纸片扩散法,大部分菌株在7—9d时可读到清晰的结果。Rosco纸片扩散法和微量液基法结果中,特比萘芬、伊曲康唑和两性霉素B一致性较好,氟康唑较差。结论Rosco纸片扩散法操作简单,可选择用于皮肤癣菌对某些抗真菌药的药敏试验。     

Influence of the culture medium on antibiotic susceptibility testing of food-associated lactic acid bacteria with the agar overlay disc diffusion method

AIMS: To investigate the influence of the culture medium on antibiotic susceptibility testing of food-associated lactic acid bacteria (LAB) with the agar overlay disc diffusion (DD) method. METHOD: The antibiotic resistance profile of 39 food-associated lactobacilli and enterococci was determined with the agar overlay DD method using a defined medium (i.e. Iso-sensitest agar; ISA) or an undefined medium (i.e. de Man, Rogosa, Sharpe or MRS agar). RESULTS: The study revealed that ampicillin discs and, although to a lesser extent, also tetracycline discs consistently produced larger zones on MRS medium compared to ISA medium. For the antibiotics gentamicin, bacitracin and erythromycin, the radius of the inhibition zones produced on MRS medium was significantly smaller in relation to ISA. For categorizing LAB isolates into resistant, intermediate and susceptible groups, it was demonstrated that major errors can occur in determining bacitracin and gentamicin resistance if MRS medium instead of ISA medium is used. On the other hand, the performance of both media was found to be equivalent for testing tetracycline resistance. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Despite the fact that MRS medium generally supports the growth of lactic acid bacteria much better than the nutrient-poor ISA medium, the present study clearly demonstrates that both media are not compatible in susceptibility testing against various classes of antibiotics. These results may stimulate future discussions on a generally recommended DD method for susceptibility testing of food LAB strains.     

A note on the determination of antibiotic susceptibility of invasive strains of Proteus by a simple agar dilution method

A method is described for testing antibiotic susceptibility of invasive and non-invasive micro-organisms in which strains are grown on small agar discs.     

A note on the determination of antibiotic susceptibility of invasive strains of Proteus by a simple agar dilution method

A method is described for testing antibiotic susceptibility of invasive and noninvasive micro-organisms in which strains are grown on small agar discs.     

Comparison of broth microdilution, Etest, and agar disk diffusion methods for antimicrobial susceptibility testing of Lactobacillus acidophilus group members

In recent years, the absence of acquired antimicrobial resistance has become an important criterion to evaluate the biosafety of lactobacilli used as industrial starter or probiotic cultures. At present, however, standards for susceptibility testing of Lactobacillus strains or approved guidelines for interpreting the test results are not available. Hence, this study was carried out to contribute to the establishment of a standardized procedure for antimicrobial susceptibility testing of lactobacilli. The results obtained by testing 104 strains of the Lactobacillus acidophilus group were compared based on broth microdilution, disk diffusion, and Etest. Except for some specific agent-related effects, agreement between MICs resulting from the broth microdilution method and the Etest was good. In addition, inhibition zone diameters determined with disk diffusion correlated well with MICs from Etest and broth microdilution.     

Quicolor: A novel system for rapid antibacterial susceptibility testing

Early determination of antibacterial susceptibility increases the success of therapy, decreases unnecessary use of antibacterials and side effects and lowers the overall healthcare costs. We have evaluated a rapid antibacterial susceptibility test, Quicolor (Salubris Inc., Massachusetts, USA), which is based on a rapid culture medium that indicates growth early by changing its colour. Quicolor proved to be a reliable rapid test for determining antibacterial susceptibility, having an overall agreement of 97.6% with the conventional CLSI sisk diffusion susceptibility test results. Between two methods overall agreement was 96.7% for Enterobacteriaceae, 96.8% for staphylococci and 94.2% for non-fermentative bacteria. There was only 0.6% major discrepancy in Enterobacteriaceae, 1.7% in staphylococci and 0.9% in non-fermentative bacteria. Since the test provides results in 3.5–6 h, it can provide the means to choose the right treatment regimen the same day the infectious agent is isolated.     

A note on the diffusion drag forces

A formal derivation of the expression for the diffusion drag force is given. The expression involves the coefficient of diffusion of the solute through the solvent and the coefficient of diffusion which the solute would posses if it diffused through itself in the form of a gas, in the absence of the solvent.     

A note on the diffusion of electrolytes in cells

A somewhat simpler solution is given to the problem previously discussed by R. R. Williamson relating to the diffusion of a metabolized electrolyte whose ions have different mobilities.     

Comparison of disk diffusion test and Etest for voriconazole and fluconazole susceptibility testing

The distribution for voriconazole and fluconazole susceptibility was determined by Etest and disk diffusion test in 143 clinical isolates. The majority of the strains of Aspergillus spp., Candida krusei, C. inconspicua, C norvegensis and Saccharomyces cerevisiae displayed resistance or decreased susceptibility to fluconazole in contrast to voriconazole. The absolute categorical agreement for voriconazole and fluconazole susceptibility results by the disk method and Etest was 90.5 and 74.8 % respectively. The error rate bounding analysis showed only 0.7 % of false susceptible results ( very major error) with voriconazole, but 2.8 % with fluconazole. Fluconazole can be used as a surrogate factor to predict voriconazole susceptibility but with lower reliability for susceptible-dose dependent and resistance category, especially in Candida glabrata isolates. The results of the disk method were not substantially influenced by the composition of media (Mueller-Hinton agar vs antimycotic Sensitivity Test agar), even if with the latter the results had fewer tendencies to produce false susceptibility of C.glabrata isolates to both of the triazole drugs. Disk test as well as Etest were shown to represent suitable methods for routine evaluation of susceptibility of clinical isolates of pathogenic fungi, including aspergilli, to fluconazole and voriconazole.     

Levofloxacin susceptibility testing for Helicobacter pylori in China: comparison of E-test and disk diffusion method

Background: The aims of this study were to compare disk diffusion with E‐test method for levofloxacin susceptibility testing of Helicobacter pylori and standardized breakpoints for disk diffusion as a stable and reliable method for determining qualitative levofloxacin susceptibility. Materials and Methods: We determined the levofloxacin susceptibility of 45 H. pylori strains isolated from Chinese patients by the E‐test method. Disk diffusion was evaluated as an alternative method to determine susceptibility and compared with the E‐test results by linear regression analysis. Results: The minimum inhibitory concentration (MIC) values tested by E‐test method ranged from 0.047 to 32 μg/mL. Resistance to levofloxacin was detected in 16 (35.6%) isolates. The levofloxacin disk zone sizes obtained by disk diffusion method correlated well (r² = .877) with the MICs obtained by E‐test method. As a consequence of regression analysis, isolates with inhibition diameters <12 mm were considered resistant to levofloxacin. There was 100% agreement between the two methods for levofloxacin, applying the regression‐based breakpoints. Conclusions: The disk diffusion method is equivalent to the E‐test method for testing levofloxacin susceptibility of H. pylori strains; it is more practical and inexpensive, and it is suitable for the analysis of a small number of isolates compared with the E‐test method.     

A note on the diffusion approximation for single neuron firing problems

Summary This paper presents a well-known stochastic model used to describe the firing or discharge pattern of a single neuron in terms of various input processes, and shows how the potential level of the neuron can be given by means of a diffusion equation approximation. There is a discussion of the adequacy of this approximation, and the paper concludes with a brief discussion of first passage time problems.Supported in part by a grant from the Alfred P. Sloan Foundation to the Committee on Mathematical Biology and by a grant of the Statistical Branch, Office of Naval Research to the Department of Statistics, University of Chicago.     

A note on susceptibility of Branhamella catarrhalis to heavy metals

The susceptibility of 56 strains of Branhamella catarrhalis and ten Neisseria spp. to arsenate, silver, nickel, mercury, lead, cadmium, chromium, manganese, iron, cobalt and molybdenum was tested with an agar dilution technique. All but two strains of B. catarrhalis were resistant to multiple metal ions. There were not sufficient differences in susceptibility, however, to allow the development of a typing scheme based on resistograms. Heavy metal resistance in Branhamella was unrelated to beta-lactamase production. Neisseria spp. were more susceptible to metal ions than B. catarrhalis and this may form the basis of a simple diagnostic test.     

A note on susceptibility of Branhamella catarrhalis to heavy metals

The susceptibility of 56 strains of Branhamella catarrhalis and ten Neisseria spp. to arsenate, silver, nickel, mercury, lead, cadmium, chromium, manganese, iron, cobalt and molybdenum was tested with an agar dilution technique. All but two strains of B. catarrhalis were resistant to multiple metal ions. There were not sufficient differences in susceptibility, however, to allow the development of a typing scheme based on resistograms. Heavy metal resistance in Branhamella was unrelated to beta-lactamase production. Neisseria spp. were more susceptible to metal ions than B. catarrhalis and this may form the basis of a simple diagnostic test.     

A note on an improved molybdate agar for the selective isolation of yeasts from tropical fruits

Molybdate agar was fortified with 0.125% calcium propionate and used for routine isolation and differentiation of a variety of yeasts from mixed floras including large numbers of fungi and actinomycetes inhabiting tropical fruits. The results suggest that this technique could be usefully incorporated in yeast isolation and identification procedures.     

A note on a modified membrane-Bovis agar for the enumeration of Streptococcus bovis by membrane filtration

The effect of dilution and temperature on the antibacterial properties of potassium sorbate was determined. The time taken to kill a standard inoculum of Escherichia coli was increased considerably after either dilution of the preservative or lowering of the temperature. The value for the concentration exponent, eta, was approximately 3 and that for the temperature coefficient, Q10, was 2.3.     

A note on an improved molybdate agar for the selective isolation of yeasts from tropical fruits

R ale , V.B. & V akil , J.R. 1984. A note on an improved molybdate agar for the selective isolation of yeasts from tropical fruits. Journal of Applied Bacteriology 56 , 409–413.
Molybdate agar was fortified with 0.125% calcium propionate and used for routine isolation and differentiation of a variety of yeasts from mixed floras including large numbers of fungi and actinomycetes inhabiting tropical fruits. The results suggest that this technique could be usefully incorporated in yeast isolation and identification procedures.