Physiology and Antibiotic Susceptibility ofStaphylococcus aureusSmall Colony Variants

Abstract

Small colony variants (SCV) are slow-growing subpopulations with altered metabolism and reduced antibiotic susceptibility which, in the case of Staphylococcus aureus, can cause persisting and recurrent infections. We studied four SCVs and their corresponding parent strains: one clinical strain pair, one menaquinone-deficient spontaneous mutant, and two constructed mutants obtained by inactivation of hemB in S. aureus 8325-4 and COL, respectively. SCVs growing in chemically defined medium (CDM) with glucose limitation and enhanced buffering capacity were found to generate deltapsi of -120 to -140 mV, which is comparable to the parent strains. However, glucose is consumed inefficiently with small growth yields. In contrast to wild-type strains, deltapsi dropped immediately to values below -100 mV when glucose expired and other nutrients such as acetate and lactate did not allow for further growth. Accordingly, the sensitivity of SCVs toward antibiotics known to be taken up through deltapsi, such as aminoglycosides, dropped 10- to 30-fold when compared to the parent strain under routine MIC determination conditions. When growing in CDM, the susceptibility of SCVs varied according to the magnitude of deltapsi.

Reduced Vancomycin Susceptibility inStaphylococcus aureus, Including Vancomycin-Intermediate and Heterogeneous Vancomycin-Intermediate Strains: Resistance Mechanisms, Laboratory Detection, and Clinical Implications

“…The S. aureus small-colonyvariant (SCV) phenotype is a slow-growing variant with distinct characteristics including reduced pigmentation and hemolytic activity as well as altered host-pathogen interactions favoring persistent and recurrent infection (265,266). Small-colony variants of S. aureus have demonstrated reduced susceptibility to a number of antimicrobials including gentamicin, fluoroquinolones, and linezolid (16,52,264). Recently, the in vitro bactericidal activity of vancomycin against an SCV-defined hemB mutant was tested.…”

The role of small-colony variants in failure to diagnose and treat biofilm infections in orthopedics

“…Consequently, these SCVs produce very small, mostly non-pigmented, and non-hemolytic colonies on normal agar plates. Moreover, they show various other features that are atypical of S. aureus, including reduced coagulase production and increased resistance to aminoglycosides and cell wall-active antibiotics (von Eiff et al 1997, 2003a, Seifert et al 1999, Baumert et al 2002. Furthermore, the ability of these variants to persist intracellularly within non-professional phagocytes, cells other than macrophages and neutrophils, has been described , von Eiff et al 2001, Vaudaux et al 2002.…”

Physiological Characterization of a Heme-Deficient Mutant of Staphylococcus aureus by a Proteomic Approach

“…4). As described previously, lactate could not be used as an alternative carbon source after glucose consumption (2). Surprisingly, in E. coli the situation is quite different.…”

“…Supplementation of media with hemin often allows clinical SCVs to grow as rapidly as the parent strain and to exhibit a normal phenotype with regard to antibiotic susceptibility, membrane potential, and exoprotein and pigment production (2,12,14,16,23,32,35). To characterize the phenotype of a genetically defined SCV of S. aureus, a stable mutant with a mutation in in electron transport was generated by interrupting one of the heme biosynthetic genes, hemB, which is a member of the family of genes encoding enzymes of the porphyrin biosynthetic pathway (9).…”