Pitfalls of polymyxin antimicrobial susceptibility testing of Pseudomonas aeruginosa isolated from cystic fibrosis patients

Hogardt, Michael; Schmoldt, Sabine; Götzfried, Monika; Adler, Kristin; Heesemann, Jürgen

doi:10.1093/jac/dkh470

Cited by 63 publications

(47 citation statements)

References 8 publications

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“…In contrast, only 15% of laboratories use AD or BMD for testing colistin. Numerous studies have demonstrated very good agreement between AD and BMD (4,6,20,21), with the exception of P. aeruginosa isolated from cystic fibrosis patients, in whom AD might have more readily detected colistin resistance (5,6). Among the 6 methods used in our study, we found the greatest EA between TDS (83%) and BMD-T, and between AD (80%) and BMD-T ( Table 2).…”

Section: Discussionsupporting

confidence: 59%

“…More recent data suggest that this is also true for contemporary Pseudomonas aeruginosa isolates. Up to 32% of VMEs have been observed by DD testing compared to reference MICs obtained using either broth or agar dilution reference methods (4)(5)(6)(7)(8). The Clinical and Laboratory Standards Institute (CLSI) provides DD breakpoints for P. aeruginosa (9) but not for any other GNB, and one manufacturer of colistin disks (BBL, BD Diagnostic Systems, Sparks, MD) suggests that any DD zone in the susceptible range be confirmed by a method that yields an MIC (Sensi-Disc antimicrobial susceptibility test disc package insert, no.…”

mentioning

confidence: 99%

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Colistin MIC Variability by Method for Contemporary Clinical Isolates of Multidrug-Resistant Gram-Negative Bacilli

2013

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In vitro evaluation of colistin susceptibility is fraught with complications, due in part to the inherent cationic properties of colistin. In addition, no reference method has been defined against which to compare the results of colistin susceptibility testing. This study systematically evaluated the available methods for colistin MIC testing in two phases. In phase I, colistin MICs were determined in 107 fresh clinical isolates of multidrug-resistant (MDR) Gram-negative bacilli (GNB) by broth microdilution with polysorbate 80 (BMD-T), broth macrodilution (TDS), and the Etest. In phase II, 50 of these isolates, 10 of which were colistin resistant, were tested in parallel using BMD-T, TDS, agar dilution, broth microdilution without polysorbate 80 (BMD), and the TREK Gram-negative extra MIC format (GNXF) Sensititre. The Etest was also performed on these 50 isolates using Mueller-Hinton agar (MHA) from three different manufacturers. Colistin MIC results obtained from the five methods were compared to the MIC results obtained using BMD-T, the method that enables the highest nominal concentration of colistin in the test medium. Essential agreement ranged from 34% (BMD) to 83% (TDS), whereas categorical agreement was >90% for all methods except for BMD, which was 88%. Very major errors (VMEs) (i.e., false susceptibility) for the Etest were found in 47 to 53% of the resistant isolates, depending on the manufacturer of the MHA that was used. In contrast, VMEs were found for 10% (n ‫؍‬ 1) of the resistant isolates by BMD and 0% of the isolates by the TDS, agar dilution, and Sensititre methods. Based on these data, we urge clinical laboratories to be aware of the variable results that can occur when using different methods for colistin MIC testing and, in particular, to use caution with the Etest.

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Section: Discussionsupporting

confidence: 59%

mentioning

confidence: 99%

Colistin MIC Variability by Method for Contemporary Clinical Isolates of Multidrug-Resistant Gram-Negative Bacilli

2013

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“…Several studies have shown nearly complete agreement in the susceptibility results for polymyxin B and those for colistin, particularly when colistin sulfate was used (41,49,55,130,153,179). In one report, the MICs of colistin were slightly higher than those of polymyxin B using agar dilution, although the categorical agreement was very good when the 4-g/ml breakpoint was used (73). Taken together, the data suggest that susceptibility to one agent should nearly always imply susceptibility to the other.…”

Section: Susceptibility Testing Methodologymentioning

confidence: 98%

“…Several recent studies compared these two methods (15,55,73,111). Although MICs tended to be slightly higher using agar dilution, in general, a very good correlation between the two methods was seen using CLSI methodology (15,55,111).…”

Section: Susceptibility Testing Methodologymentioning

confidence: 99%

“…Although MICs tended to be slightly higher using agar dilution, in general, a very good correlation between the two methods was seen using CLSI methodology (15,55,111). One study demonstrated a poor correlation, although results were improved when broth MICs were read after 48 h and a susceptibility breakpoint of 4 g/ml was used (73). Those findings may be related to the large number of P. aeruginosa isolates from cystic fibrosis patients included, which frequently have MICs near the susceptibility breakpoints of 2 to 4 g/ml.…”

Section: Susceptibility Testing Methodologymentioning

confidence: 99%

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Polymyxins Revisited

et al. 2008

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SUMMARY The global emergence of multidrug-resistant gram-negative bacilli has spurred a renewed interest in polymyxins. Once discarded due to concerns regarding nephrotoxicity and neurotoxicity, polymyxins now hold an important role in the antibiotic armamentarium. However, more reliable information is needed to determine the optimal dosing of these agents. Also, unanswered questions regarding in vitro testing remain, including questions regarding the reliability of automated systems and the establishment of appropriate breakpoints for defining susceptibility. Most contemporary clinical studies examining the use of these agents have involved patients with infections due to multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii strains. It has been reassuring that polymyxin therapy for resistant bacteria has resulted in clinical responses and toxicity rates similar to those for carbapenem therapy for susceptible isolates. While most surveillance studies demonstrated high rates of susceptibility, several reports noted the emergence of polymyxin-resistant nosocomial pathogens. Polymyxins have assumed an important antibiotic niche for therapy for hospital-acquired infections; further studies defining the optimal use of these agents will likely extend the duration of their clinical usefulness.

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Susceptibility Testing of the Polymyxins: Where Are We Now?

Humphries

2014

Pharmacotherapy

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Antimicrobial susceptibility testing for the polymyxins-colistin and polymyxin B-is fraught with technical challenges. Key among these is the propensity of the polymyxins to adsorb to polystyrene, a material often used for in vitro minimum inhibitory concentration testing devices. This effect may be mitigated by the addition of a surfactant such as polysorbate 80; however, concern exists that polysorbate 80 may act synergistically with the polymyxins and artificially lower minimum inhibitory concentrations. Furthermore, the polymyxins diffuse poorly through agar, compromising the performance of both disk diffusion and Etest methods. Very few peer-reviewed studies have investigated in vitro susceptibility test methods for the polymyxins, and it is clear that an in vitro test that reliably predicts the activity of the polymyxins in vivo has yet to be defined. This review describes the methods available and challenges associated with susceptibility testing of colistin and polymyxin B and discusses the current breakpoints for both agents.

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Pitfalls of polymyxin antimicrobial susceptibility testing of Pseudomonas aeruginosa isolated from cystic fibrosis patients

Cited by 63 publications

References 8 publications

Colistin MIC Variability by Method for Contemporary Clinical Isolates of Multidrug-Resistant Gram-Negative Bacilli

Colistin MIC Variability by Method for Contemporary Clinical Isolates of Multidrug-Resistant Gram-Negative Bacilli

Polymyxins Revisited

Susceptibility Testing of the Polymyxins: Where Are We Now?

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