Fourier-Transform Infrared Spectroscopic Analysis Is a Powerful Tool for Studying the Dynamic Changes in Staphylococcus aureus Small-Colony Variants

Abstract

Infections due to small-colony variants (SCVs) of Staphylococcus aureus in patients with chronic and recurrent infections are an emerging problem; however, studies with this subpopulation are hampered by the fact that SCVs may exhibit unstable phenotypes, making them difficult to study, particularly in broth media. In this study, two S. aureus sets comprising the (i) normal and the (ii) SCV phenotype (clonal with normal phenotype) recovered from clinical specimens, as well as (iii) corresponding site-directed mutants displaying the SCV phenotype (knockout of hemB) and (iv) their complemented mutants were examined by Fouriertransform infrared (FTIR) spectroscopy. Phenotypes were defined on solid and in broth media. Using firstderivative infrared spectra to calculate spectral distances, hierarchical clustering based on spectral information resulted in a dendrogram with clear discrimination between SCV and normal phenotypes. The SCVs gave an FTIR fingerprint that was easily recognizable and that was much closer to other SCVs than to their parent strains. This technique offers for the first time a noninvasive approach to investigate dynamic processes of reversion of SCVs to the normal phenotype and vice versa. Thus, FTIR spectroscopy allowed a rapid and reproducible tool for the examination of different subpopulations of S. aureus on solid and in broth media for diagnostic and research purposes.

Small colony variants of Staphylococcus aureus — review

“…JB1), the majority of colonies of SCV phenotype are unstable and revert to normal phenotype by compensatory mutations (Tuchscherr et al 2010;Becker et al 2006;Lånnergard et al 2008). Stability of SCV phenotype was studied using different culture media, atmospheres and temperature as described above.…”

Clinical Significance and Pathogenesis of Staphylococcal Small Colony Variants in Persistent Infections

“…Aberrant growth curve courses might be indicative of those events but are coupled with waste of time and experimental efforts. To overcome these drawbacks, Fourier transform infrared (FTIR) spectroscopy was shown to offer a real-time readout tool to study the nature of SCVs under liquid culture conditions (127). Analysis of FTIR-generated spectra of SCVs and their parental strains resulted in a clear discrimination between both phenotypes; thus, it is possible to ensure and monitor the SCV phenotype by a fast, direct, and noninvasive approach.…”

Staphylococcus aureus small colony variants: a challenge to microbiologists and clinicians

“…Since clinical SCVs often exhibit an unstable phenotype, Fourier-transform infrared spectroscopy has been used to investigate the phase variation from SCV phenotype into the normal phenotype and vice versa [13]. Indeed, this non-invasive technique offered a rapid, reliable and nondestructive approach to trace directly the process of reversion from the normal phenotype into the SCV phenotype and vice versa.…”