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

Abstract

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...

Multicenter Evaluation of the Accelerate PhenoTest BC Kit for Rapid Identification and Phenotypic Antimicrobial Susceptibility Testing Using Morphokinetic Cellular Analysis

“…The results for minocycline look promising with EA and CA greater than 92% and no VMEs. These results are similar to those recently reported by Wang et al when testing 107 CRAB isolates against the tetracyclines using Etest, disk diffusion, and Sensititre BMD methods ( 67 ). VMEs (2.8%) were higher than in the present study ( 67 ).…”

Evaluation of the Accelerate Pheno System for Identification of Acinetobacter Clinical Isolates and Minocycline Susceptibility Testing

“…In one study, which evaluated the performance of Spanish laboratories to accurately determine A. baumannii AST results, minor errors of 88.6% were observed across all systems evaluated (14). A second study demonstrated minor errors of 15% to 40% across different disk diffusion, Sensititre, and Etest methods (15).…”

Karbapeneme dirençli, çoklu ilaç direnci fenotipi gösteren Acinetobacter baumannii suşlarında polimiksin B, minosiklin, kolistin ve fosfomisin duyarlılıklarının belirlenmesi

“…Sensitivities of minocycline, polymyxin B, colistin and phosphomycin were determined according to CLSI criteria (7). For the minocycline, the zone was considered sensitive if the diameter was ≥ 16 mm, moderately sensitive between 13 and 15 mm, and resistant if ≤ 9 mm (8).…”