International Journal of Medical Microbiology 303 (2013) 61–69 Contents lists available at SciVerse ScienceDirect International Journal of Medical Microbiology jo u r n al hom epage: www.elsevier.com/locate/ijmm Functional variation reflects intra-strain diversity of Staphylococcus aureus small colony variants in the host–pathogen interaction Dina Hilmi a , Marijo Parcina a,b , Konrad Bode a , Jenny Ostrop a , Sabine Schuett a , Klaus Heeg a , Wilma Ziebuhr c , Olaf Sommerburg d , Isabelle Bekeredjian-Ding a,b,∗ a Department of Infectious Diseases, Medical Microbiology and Hygiene, University Hospital Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany b Institute for Medical Microbiology, Immunology and Parasitology (IMMIP), University Hospital Bonn, Sigmund-Freud-Str. 25, D-53105 Bonn, Germany c Institute for Molecular Infection Biology, University of Wuerzburg, Josef-Schneider-Str. 2, D-97080 Wuerzburg, Germany d Department of Pediatrics, University Hospital Heidelberg, Im Neuenheimer Feld 430, D-69120 Heidelberg, Germany a r t i c l e i n f o Article history: Received 19 August 2012 Received in revised form 26 November 2012 Accepted 2 December 2012 Keywords: Staphylococcus aureus Small colony variants Intrastrain variability Biofilm TLR2 Protein A a b s t r a c t It is well acknowledged that genetic variation accounts for the intra-species variability in Staphylococ- cus aureus isolates. Similarly, deficiency in DNA repair and the resulting increase in genomic mutations determine intra-strain variability in S. aureus small colony variants (SCV). The aim of this study was to investigate whether intra-strain diversity would be associated with an alteration of the host–pathogen interaction. To this end, biofilm formation and immune stimulatory capacity were compared in consec- utive SCV isolates originating from a single patient. Despite the relatedness of the isolates, the results revealed significant differences in biofilm formation and immune stimulation determined by Toll-like receptor-2 (TLR2) activity. Variation in the extent of biofilm production could be attributed to differ- ences in the expression of protein A (SpA) and agrA. TLR2 activity only partially correlated with these parameters. Although transiently increased functional activity correlated with clinical remission and was abrogated in MRSA superinfection, we can only speculate that changes in the SCV phenotype reflect alterations in the microbial environment and/or treatment. Taken together, our study provides in vivo evidence for the functional consequences of intra-strain variation in S. aureus. © 2013 Elsevier GmbH. All rights reserved. Introduction Staphylococcus aureus is a versatile microbe that causes severe infections, but can also colonize the respiratory mucosa in the absence of disease manifestation. These contrasting scenarios result from differential regulation of the host–pathogen inter- action that is governed by the expression of virulence factors and the quality and intensity of the host immune response elicited. S. aureus is further renown for its superb adaptation to the human host, to certain niches, i.e. the nasal atrium, to the hospital environment, and to antimicrobial therapy. A clas- sic example for this host adaptation is the formation of small colony variants (SCV). These slowly growing and metabolically deficient staphylococcus isolates are commonly cultured from patients with chronic infections such as osteomyelitis, endocardi- tis, or cystic fibrosis (Kahl et al., 2003; Tuchscherr et al., 2010; ∗ Corresponding author at: Institute of Medical Microbiology, Immunology and Parasitology (IMMIP), University Hospital Bonn, Sigmund-Freud-Str. 25, D-53105 Bonn, Germany. Tel.: +49 (0)228 287 15675; fax: +49 (0)228 287 19573. E-mail address: bekeredjian-ding@uni-bonn.de (I. Bekeredjian-Ding). Proctor et al., 2006). They survive in the intracellular niche and down-regulate key cellular functions such as DNA transcription and peptidoglycan synthesis. SCV formation is further triggered by selective pressure through antibiotics and/or antimicrobial substances derived from other colonizing bacteria such as Pseu- domonas aeruginosa (Hoffman et al., 2006; Biswas et al., 2009), thus representing an efficient means to escape their bactericidal effects. The evolvement of the SCV phenotype is frequently accompa- nied by genetic mutations that stabilize the SCV phenotype and often result from hypermutability due to deficient DNA repair (Besier et al., 2008; Miller, 1996; Schaaff et al., 2003). These muta- tions confer resistance to antibiotics and changes in the nutritional requirements such as hemin, menadione, and thymidine depend- ency (Kahl et al., 1998; Gilligan et al., 1987; von Eiff et al., 1997; Proctor et al., 2006). Nevertheless, albeit mutations can accumu- late over time, the SCV phenotype is frequently instable and rapidly reverses under nutritious growth conditions. Morphological and biochemical changes may, thus, also occur within the human organ- ism, and may be triggered by acute alterations in the microbial environment, nutritional conditions, and/or the antibiotic regime. The resulting variations in the expression of virulence factors are 1438-4221/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijmm.2012.12.008