Revised Reference Broth Microdilution Method for Testing Telavancin: Effect on MIC Results and Correlation with Other Testing Methodologies

Abstract

The reference broth microdilution (BMD) antimicrobial susceptibility testing method for telavancin was revised to include dimethyl sulfoxide (DMSO) as a solvent and diluent for frozen-form panel preparation, following the CLSI recommendations for water-insoluble agents. Polysorbate 80 (P-80) was also added to the test medium to minimize proven drug losses associated with binding to plastic surfaces. Four hundred sixty-two Gram-positive isolates, including a challenge set of organisms with reduced susceptibilities to comparator agents, were selected and tested using the revised method for telavancin, and the MIC results were compared with those tested by the previously established method and several Sensititre dry-form BMD panel formulations. The revised method provided MIC results 2-to 8-fold lower than the previous method when tested against staphylococci and enterococci, resulting in MIC 50 values of 0.03 to 0.06 g/ml for staphylococci and 0.03 and 0.12 g/ml for Enterococcus faecium and Enterococcus faecalis, respectively. Less-significant MIC decreases (1 to 2 log 2 dilution steps) were observed when testing streptococci in broth supplemented with blood, which showed similar MIC 50 values for both methods. However, Streptococcus pneumoniae had MIC 50 results of 0.008 and 0.03 g/ml when tested by the revised and previous methods, respectively. Highest essential agreement rates (>94.0%) were noted for one candidate dry-form panel formulation compared to the revised test. The revised BMD method provides lower MIC results for telavancin, especially when tested against staphylococci and enterococci. This is secondary to the use of DMSO for panel production and the presence of P-80, which ensure the proper telavancin testing concentration and result in a more accurate MIC determination. Moreover, earlier studies where the previous method was applied underestimated the in vitro drug potency.T elavancin is a lipoglycopeptide antibiotic with potent in vitro bactericidal activity when tested against Gram-positive bacteria, including methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA), heterogeneous VISA (hVISA), and multidrug-resistant (MDR) streptococci and enterococci (1, 2). Telavancin is approved in the United States and Canada for the treatment of patients with complicated skin and skin structure infections due to susceptible Gram-positive pathogens and in the United States and Europe for the treatment of hospital-acquired bacterial pneumonia, including ventilator-associated bacterial pneumonia (HABP/VABP) due to susceptible isolates of S. aureus (MRSA strains only in Europe), when alternative medicines are unsuitable (3).During the development of dalbavancin, also a lipoglycopeptide, the use of polysorbate 80 (P-80) (0.002%, final testing concentration) was shown to be essential for accurate MIC susceptibility testing determinations (4). Subsequent investigations for oritavancin (another lipoglycopeptide) demonstrated that the addi...

Telavancin Activity Against a Global Collection of Staphylococcus aureus Clinical Isolates (2013–2015)

“…In addition, the telavancin potency observed was at least 8-fold greater than tested comparators. These results confirm telavancin had more potent activity when compared to earlier studies [22][23][24] that underestimated the potency of the drug due to solubility and drug binding to plastic trays during susceptibility testing [20].…”

“…Isolates were tested for susceptibility by broth microdilution following CLSI guidelines [17]. Telavancin was tested by the revised method according to CLSI [18,20] and product package insert [14] using panels manufactured at JMI Laboratories (2015) or purchased from Thermo Fisher Scientific (2013-2014) (Cleveland, Ohio, USA). Quality control for MIC values were quality assured by concurrently testing S. aureus (ATCC 29213) and E. faecalis (ATCC 29212).…”

In Vitro Pharmacodynamics of Human Simulated Exposures of Telavancin against Methicillin-Susceptible and -Resistant Staphylococcus aureus with and without Prior Vancomycin Exposure

“…Notably, the MIC testing method and the susceptibility breakpoint (Յ0.125 g/ml) have changed due to the use of polysorbate 80 to prevent adherence of the drug to plastic surfaces and minimize MIC variability (11,34). Nonetheless, we utilized isolates with baseline vancomycin MICs of 2 g/ml, which may already have variable mechanisms for lower susceptibility to vancomycin, including a thickened cell wall; thus, no further increases in the MICs may be feasible with the exposures simulated in the experiment.…”

Efficacy of telavancin, a lipoglycopeptide antibiotic, in experimental models of Gram-positive infection

“…Longitudinal international surveillance of telavancin activity continues to demonstrate potent activity against these pathogens [14][15][16][17][18][19][20][21]. Broth MIC test methods for telavancin have recently been revised [22]. Representative telavancin potency against a collection of Gram-positive clinical isolates collected from US hospitals in 2011 and 2012 is provided in TABLE 1 [23].…”