Influence of inoculum size on comparative susceptibilities of penicillinase-positive and -negative Neisseria gonorrhoeae to 31 antimicrobial agents

Hall, Wendell H.; Opfer, B J

doi:10.1128/aac.26.2.192

Cited by 10 publications

(5 citation statements)

References 19 publications

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“…The comparability of Etest and agar dilution observed in this study, has also been observed elsewhere, particularly for cephalosporins [ 21 – 23 ]. MIC differences in our study could be due to agar media and inoculum size differences as established previously [ 24 , 25 ], along with varying levels of comparability between different disk diffusion methods and agar dilution and/or Etests [ 26 – 30 ]. Identified agar media differences in this study (data not shown) in general agree with data presented from other studies, including that cephalosporin MICs were generally slightly higher from agar dilution with GC agar compared with Etests [ 21 – 23 ], MICs from Etests with chocolate agar were higher [ 31 ], as well as differing MIC variation depending upon which media was used for agar dilution [ 32 , 33 ].…”

Section: Discussionmentioning

confidence: 89%

Ten years of external quality assessment (EQA) of Neisseria gonorrhoeae antimicrobial susceptibility testing in Europe elucidate high reliability of data

et al. 2019

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BackgroundConfidence in any diagnostic and antimicrobial susceptibility testing data is provided by appropriate and regular quality assurance (QA) procedures. In Europe, the European Gonococcal Antimicrobial Susceptibility Programme (Euro-GASP) has been monitoring the antimicrobial susceptibility in Neisseria gonorrhoeae since 2004. Euro-GASP includes an external quality assessment (EQA) scheme as an essential component for a quality-assured laboratory-based surveillance programme. Participation in the EQA scheme enables any problems with the performed antimicrobial susceptibility testing to be identified and addressed, feeds into the curricula of laboratory training organised by the Euro-GASP network, and assesses the capacity of individual laboratories to detect emerging new, rare and increasing antimicrobial resistance phenotypes. Participant performance in the Euro-GASP EQA scheme over a 10 year period (2007 to 2016, no EQA in 2013) was evaluated.MethodsAntimicrobial susceptibility category and MIC results from the first 5 years (2007–2011) of the Euro-GASP EQA were compared with the latter 5 years (2012–2016). These time periods were selected to assess the impact of the 2012 European Union case definitions for the reporting of antimicrobial susceptibility.ResultsAntimicrobial susceptibility category agreement in each year was ≥91%. Discrepancies in susceptibility categories were generally because the MICs for EQA panel isolates were on or very close to the susceptibility or resistance breakpoints. A high proportion of isolates tested over the 10 years were within one (≥90%) or two (≥97%) MIC log2 dilutions of the modal MIC, respectively. The most common method used was Etest on GC agar base. There was a shift to using breakpoints published by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in the latter 5 years, however overall impact on the validity of results was limited, as the percentage categorical agreement and MIC concordance changed very little between the two five-year periods.ConclusionsThe high level of comparability of results in this EQA scheme indicates that high quality data are produced by the Euro-GASP participants and gives confidence in susceptibility and resistance data generated by laboratories performing decentralised testing.

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Section: Discussionmentioning

confidence: 89%

Ten years of external quality assessment (EQA) of Neisseria gonorrhoeae antimicrobial susceptibility testing in Europe elucidate high reliability of data

et al. 2019

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“…It is well known from in-vitro studies that a high density of /Mactamase producing bacteria diminishes the effect of /Mactam antibiotics (inoculum effect). The concentration of bacterial /Mactamases probably correlates with the density of the bacterial inoculum (Sabath et al, 1975;Eng, Smith & Cherubin, 1984;Hall & Opfer, 1984).…”

Section: Discussionmentioning

confidence: 99%

The impact of the pre-treatment interval on antimicrobial efficacy in a biological model

Gerber

Greter

Segessenmann

et al. 1993

Journal of Antimicrobial Chemotherapy

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The impact of pre-treatment intervals on the antipseudomonal efficacy of gentamicin, ticarcillin and ceftazidime was studied in an experimental thigh infection model in normal and granulocytopenic mice. Human-equivalent doses were used for simulating human pharmacokinetic profiles of the two study 0-lactam drugs. A lethal inoculum of a virulent strain of Pseudomonas aeruginosa was injected into the thigh muscle. Treatment was started at various post-infection intervals. Antimicrobial efficacy was assessed by determinations of surviving organisms at the site of infection, and plasma drug concentrations were determined in the same mice. The age of infection had a substantial impact on antipseudomonal efficacy of the three study drugs even though high, brief supra-MIC concentrations of gentamicin and persistent supra-MIC concentrations of the /Mactam drugs were obtained. A pre-treatment interval of six or more hours abolished the bactericidal effect of all three study drugs despite accumulation of the drugs to multiple-MBC plasma concentrations. We believe that the impact of pre-treatment intervals on antimicrobial efficacy is of paramount importance for the interpretation of antimicrobial activity studies in experimental models of infection, although the mechanisms remain to be elucidated.

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“…Hall and Opfer have also found that inoculum size had little influence on MICs for penicillinase-negative N. gonorrhoeae (2). The National Committee for Clinical Laboratory Standards (7) recommends that an inoculum of 104 be delivered to the antibiotic-containing plates in agar dilution tests.…”

Section: Discussionmentioning

confidence: 98%

Effects of different media and methods of inoculum preparation on results of antimicrobial susceptibility testing of Neisseria gonorrhoeae by agar dilution

Dillon

Tostowaryk

Pauzé

1987

Antimicrob Agents Chemother

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The effects of two methods of inoculum preparation (the opacity standard method and a template method) and three different types of media on the penicillin, tetracycline, spectinomycin, and erythromycin MICs for 191 non-penicillinase-producing, 49 penicillinase-producing, and 5 tetracycline-resistant isolates of Neisseria gonorrhoeae were evaluated. Three World Health Organization reference strains (HI, V, and VII) were similarly evaluated. Inoculum preparation method did not significantly alter the MIC (i.e., within a twofold dilution) of either susceptible or chromosomaHly resistant non-penicillinase-producing isolates; MICs achieved by the template method were slightly higher, but these differences were not significant. However, with penicillinase-producing and tetracycline-resistant isolates, the template method, which delivered 104 CFU, produced unequivocal MICs (denoting clinical resistance) which were significantly higher than MICs observed with the opacity standard method (inoculum, 103 CFU). With penicillin-, spectinomycin-, and erythromycincontaining medium, addition of hemoglobin to the medium produced lower, though not significantly different, MICs with all isolates as compared with MICs on medium without hemoglobin. Media supplemented with hemoglobin produced higher tetracycline MICs with all isolates, which were significantly different (greater than twofold) from MICs on the same hemoglobin-free media. Changes in auxotype did not alter overall observations concerning the effects of different media and inocula on MICs.MIC testing methods recommended for most microorganisms are not generally applicable to Neisseria gonorrhoeae (7, 10). The international method recommended for gonococcal antimicrobial susceptibility testing by agar dilution differs in several respects from methods suggested by other groups, such as the National Committee for Clinical Laboratory Standards (7, 10). None of these methods have undergone rigorous methodological analysis. As a result of these conflicting and untested recommendations, considerable variation in the methods used for gonococcal susceptibility testing exists. For example, although supplementation of media with hemoglobin is recommended, in practice, several types of media, with and without hemoglobin, are commonly used (9,10,11,13

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Influence of inoculum size on comparative susceptibilities of penicillinase-positive and -negative Neisseria gonorrhoeae to 31 antimicrobial agents

Cited by 10 publications

References 19 publications

Ten years of external quality assessment (EQA) of Neisseria gonorrhoeae antimicrobial susceptibility testing in Europe elucidate high reliability of data

Ten years of external quality assessment (EQA) of Neisseria gonorrhoeae antimicrobial susceptibility testing in Europe elucidate high reliability of data

The impact of the pre-treatment interval on antimicrobial efficacy in a biological model

Effects of different media and methods of inoculum preparation on results of antimicrobial susceptibility testing of Neisseria gonorrhoeae by agar dilution

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