Rapid detection of Staphylococcus aureus strains with reduced susceptibility to vancomycin by isothermal microcalorimetry - PubMed (original) (raw)

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Rapid detection of Staphylococcus aureus strains with reduced susceptibility to vancomycin by isothermal microcalorimetry

J M Entenza et al. J Clin Microbiol. 2014 Jan.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) usually harbors a vancomycin-susceptible phenotype (VSSA) but can exhibit reduced vancomycin susceptibility phenotypes that can be heterogeneous-intermediate (hVISA), intermediate (VISA), or fully resistant (VRSA). Current detection techniques (e.g., Etest and population analysis profiles [PAPs]) are slow and time-consuming. We investigated the potential of microcalorimetry to detect reduced susceptibilities to vancomycin in MRSA strains. Representative MSSA, VSSA, hVISA, VISA, and VRSA reference strains, as well as clinical isolates, were used. PAPs were performed by standard methods. Microcalorimetry was performed by inoculating 5 × 10(7) CFU of overnight cultures into 3-ml vials of brain heart infusion broth supplemented with increasing concentrations of vancomycin, and growth-related heat production was measured at 37°C. For the reference strains, no heat production was detected in the VSSA isolates at vancomycin concentrations of >3 μg/ml during the 72 h of incubation. The hVISA and VISA strains showed heat production with concentration-proportional delays of up to 6 μg/ml in 48 h and up to 12 μg/ml in 72 h, respectively. The VRSA strain showed heat production at concentrations up to 16 μg/ml in 12 h. The testing of clinical strains indicated an excellent negative predictive value, allowing us to rule out a decreased vancomycin susceptibility phenotype in <8 h of incubation. Sequential isolates from a patient undergoing vancomycin therapy showed evolving microcalorimetric profiles up to a VISA phenotype. Microcalorimetry was able to detect strains with reduced susceptibilities to vancomycin in <8 h. The measurement of bacterial heat production might represent a simple and rapid method for the detection of reduced susceptibilities to vancomycin in MRSA strains.

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Figures

FIG 1

FIG 1

Typical time-heat flow curves for the seven tested S. aureus reference strains in the presence of increasing concentrations of vancomycin (0 to 8, 12, and 16 μg/ml) recorded for up to 72 h of incubation. Shown are the vancomycin-susceptible strains S. aureus ATCC 29213 (MSSA) and S. aureus ATCC 43300 (MRSA) (A), vancomycin heterogeneous-intermediate strains S. aureus Mu3 and S. aureus PC1 (B), vancomycin homogeneous-intermediate strains S. aureus Mu50 and S. aureus PC3 (C), and vancomycin-resistant strain S. aureus SA510 (D).

FIG 2

FIG 2

Population analysis profiles of four representative invasive MRSA strains isolated from a patient with persistent MRSA colonization and invasive bacteremia episodes (see the text for details on the case report). S. aureus Mu3 and Mu50 are shown as reference hVISA and VISA strains, respectively.

FIG 3

FIG 3

Typical time-heat flow curves of four representative invasive MRSA strains isolated from a patient with persistent MRSA colonization and invasive bacteremia episodes (see the text for details on the case report) in the presence of an increasing concentration of vancomycin (0 to 8 μg/ml) recorded for up to 48 h of incubation.

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