High Concentrations of Manganese in Mueller-Hinton Agar Increase MICs of Tigecycline Determined by Etest

Fernández-Mazarrasa, Carlos; Mazarrasa, Olav; Calvo, Jorge; Arco, Asunción del; Martínez-Martínez, Luis

doi:10.1128/jcm.02464-08

Cited by 59 publications

(50 citation statements)

References 12 publications

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“…This resulted from high minor error rates (19.6 to 37.4% for minocycline and 23.4 to 63.6% for tigecycline), most of which represented a shift from the susceptible category to the intermediate category (or the corresponding categories for tigecycline). This phenomenon has been well documented for tigecycline (23,24) and more recently for minocycline as well (8). Many of these minor errors could be attributed to incremental MIC differences afforded by the granularity of Etest readings, i.e., a shift from 4 g/ml (reference) to 6 g/ml (Etest) for minocycline and from 2 g/ml (reference) to 3 g/ml (Etest) for tigecycline.…”

Section: Discussionmentioning

confidence: 83%

Comparison of Minocycline Susceptibility Testing Methods for Carbapenem-Resistant Acinetobacter baumannii

et al. 2016

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cTreatment options for infections due to carbapenem-resistant Acinetobacter baumannii are extremely limited. Minocycline is a semisynthetic tetracycline derivative with activity against this pathogen. This study compared susceptibility testing methods that are used in clinical microbiology laboratories (Etest, disk diffusion, and Sensititre broth microdilution methods) for testing of minocycline, tigecycline, and doxycycline against 107 carbapenem-resistant A. baumannii clinical isolates. Susceptibility rates determined with the standard broth microdilution method using cation-adjusted Mueller-Hinton (MH) broth were 77.6% for minocycline and 29% for doxycycline, and 92.5% of isolates had tigecycline MICs of <2 g/ml. Using MH agar from BD and Oxoid, susceptibility rates determined with the Etest method were 67.3% and 52.3% for minocycline, 21.5% and 18.7% for doxycycline, and 71% and 29.9% for tigecycline, respectively. With the disk diffusion method using MH agar from BD and Oxoid, susceptibility rates were 82.2% and 72.9% for minocycline and 34.6% and 34.6% for doxycycline, respectively, and rates of MICs of <2 g/ml were 46.7% and 23.4% for tigecycline. In comparison with the standard broth microdilution results, very major rates were low (ϳ2.8%) for all three drugs across the methods, but major error rates were higher (ϳ5.6%), especially with the Etest method. For minocycline, minor error rates ranged from 14% to 37.4%. For tigecycline, minor error rates ranged from 6.5% to 69.2%. The majority of minor errors were due to susceptible results being reported as intermediate. A cinetobacter baumannii has become a major health care-associated pathogen over the past 2 decades, due to its intrinsic resistance to several classes of antimicrobial agents, its propensity to acquire resistance to other drug classes, and its ability to resist desiccation in environments typically found in hospitals (1). A. baumannii causes a variety of infections, with respiratory tract infections being the most common (1). Significant clinical challenges are posed by carbapenem-resistant A. baumannii, which accounted for over 75% of A. baumannii clinical isolates tested in a recent global survey (2). Mortality rates for carbapenem-resistant A. baumannii infections may be as high as 76% (3). Treatment options for carbapenem-resistant A. baumannii infections have not been well defined but generally include polymyxins (colistin and polymyxin B), tigecycline, or sulbactam, alone or in combination with a second agent, such as rifampin or a carbapenem, with the expectation of synergistic activities (4). However, toxicity (polymyxins), suboptimal pharmacokinetics (tigecycline), and the propensity for development of resistance (sulbactam) limit these options (1).Minocycline is a semisynthetic tetracycline derivative that was introduced into clinical practice in the 1960s (5). With the recent reintroduction of an intravenous formulation of minocycline, there is increasing interest in this agent as an additional treatment option for carbapenem-resi...

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Section: Discussionmentioning

confidence: 83%

Comparison of Minocycline Susceptibility Testing Methods for Carbapenem-Resistant Acinetobacter baumannii

et al. 2016

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“…Due to poor reproducibility of its mineral content, the Mueller-Hinton medium may be unsuitable for this purpose. Whereas most commonly available test media probably have concentrations below the critical range, considerable variability in the concentration of divalent cations in Mueller-Hinton broth or agar from different manufacturers has been reported (11), and manganese concentrations in MuellerHinton agar that are well above 500 mg/liter have been found (5).…”

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confidence: 99%

Effect of Manganese in Test Media on In Vitro Susceptibility of Enterobacteriaceae and Acinetobacter baumannii to Tigecycline

et al. 2012

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cWe assessed the effect of increasing manganese concentrations in test media (0.001 to 1,024 mg/liter) on MICs of tigecycline. For both broth microdilution (BMD) and Etests, this effect was negligible for physiological concentrations, but MICs increased when concentrations exceeded 8 mg/liter. Susceptibility testing should be performed on media with standardized low manganese content.T igecycline is one of the few antimicrobial drugs that can be used to treat infections with highly resistant organisms (7,8). Several studies reported that in vitro bacterial susceptibility to tigecycline varies by test medium and condition (3,4,10,13,14), and a recent study showed that addition of manganese (Mn) to the test medium led to increased MICs of tigecycline, as determined by an Etest for Enterobacteriaceae and staphylococci. (5) Variability in Mn concentrations in standard media may thus result in falsely elevated MICs for tigecycline. A concentration-effect relationship was not established, however, and the threshold concentration of Mn below which MICs are unaffected remains unknown. Because such a threshold may depend on the test method used, we evaluated the effect of increasing manganese concentrations in the test medium on MICs, as determined by broth microdilution, Etest, and disk diffusion.The study included strains of five species of Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii, Enterobacter cloacae, and Proteus mirabilis) and Acinetobacter baumannii, which were collected and stored at Ϫ80 degrees in a prospective cohort study in 18 Dutch hospitals as described previously (15). An ATCC control strain (Table 1) was included for each species.In the first experiment, we determined the effect of increasing medium Mn concentrations on MICs, as measured by Etest (bioMérieux), and on zone diameters, as measured by disk (15 g tigecycline; Oxoid, United Kingdom) diffusion. Strains were thawed and inoculated on Columbia agar plates with 5% sheep blood and incubated for 18 to 24 h at 35°C. Subsequently, a suspension of a 0.5 McFarland standard (in 0.9% saline) was used to inoculate freshly prepared Iso-Sensitest agar plates (Oxoid, United Kingdom). The Iso-Sensitest medium has been developed specifically to overcome the variability in mineral concentrations observed in Mueller-Hinton medium and has a stable mineral content with an MnCl concentration of 2 mg/liter (2). Media were freshly prepared to avoid effects of oxygenation (1, 9) and supplemented with MnCl 2 (VWR, The Netherlands) in 2-fold serial dilutions to achieve Mn concentrations ranging between 2 mg/liter and 1,024 mg/liter. Plates were incubated for 18 to 24 h at 35°C before values were read.Because reference values for Mn concentrations in human serum (0.2 to 1.4 g/liter) (12) are substantially lower than concentrations found in standard susceptibility test media (Ն2 mg/liter), a second experiment in which the tested Mn concentration range also included physiological concentrations was performed. MICs were measured using br...

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“…Moreover, if the problem persists, even when using a new lot, the manufacturer should be contacted. Although there is no CLSI recommendation for manganese, iron, or zinc supplementation in the culture medium, diverse studies have shown that these ions can also influence the antimicrobial susceptibility tests results for other antimicrobial agents than polymyxin (13,16).…”

Section: Discussionmentioning

confidence: 99%

“…As the need for polymyxin usage increases in the clinical setting, routine microbiology laboratories must perform the polymyxin susceptibility testing under high-quality standard conditions. Since the cation composition of Mueller-Hinton agar (MHA) may vary among manufacturers and even among distinct lots of the same manufacturer (13), the aim of the present study was to determine the influence of different commercial brands of MHA for testing the polymyxin B susceptibility of A. baumannii and P. aeruginosa clinical isolates.…”

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confidence: 99%

Cation Concentration Variability of Four Distinct Mueller-Hinton Agar Brands Influences Polymyxin B Susceptibility Results

et al. 2012

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bPolymyxins have been the only alternative therapeutic option for the treatment of serious infections caused by multidrug-resistant Acinetobacter baumannii or Pseudomonas aeruginosa isolates. For this reason, it is of crucial importance that susceptibility tests provide accurate results when testing these drug-pathogen combinations. In this study, the effect of cation concentration variability found on different commercial brands of Mueller-Hinton agar (MHA) for testing polymyxin B susceptibility was evaluated. The polymyxin B susceptibilities determined using Etest and disk diffusion were compared to those determined by the CLSI reference broth microdilution method. In general, the polymyxin B MIC values were higher when determined by Etest than when determined by broth microdilution against both A. baumannii and P. aeruginosa isolates. A high very major error rate (10%) was observed, as well as a trend toward lower MICs, compared to those determined by broth microdilution when the Merck MHA was tested by Etest. Poor essential agreement rates (10 to 70%) were observed for P. aeruginosa when all MHA brands were tested by Etest. Although an excellent categorical agreement rate (100%) was seen between the disk diffusion and broth microdilution methods for P. aeruginosa, larger zones of inhibition were shown obtained using the Merck MHA. The high cation concentration variability found for the MHA brands tested correlated to the low accuracy, and discrepancies in the polymyxin B MICs were determined by Etest method, particularly for P. aeruginosa isolates.

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High Concentrations of Manganese in Mueller-Hinton Agar Increase MICs of Tigecycline Determined by Etest

Cited by 59 publications

References 12 publications

Comparison of Minocycline Susceptibility Testing Methods for Carbapenem-Resistant Acinetobacter baumannii

Comparison of Minocycline Susceptibility Testing Methods for Carbapenem-Resistant Acinetobacter baumannii

Effect of Manganese in Test Media on In Vitro Susceptibility of Enterobacteriaceae and Acinetobacter baumannii to Tigecycline

Cation Concentration Variability of Four Distinct Mueller-Hinton Agar Brands Influences Polymyxin B Susceptibility Results

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