Small Colony Variants – The Cause Of Chronic Infections

Some microorganisms are characterised by the ability to create specific morphological varieties called Small Colony Variants (SCVs). This characteristic was noted, among others, in Gram-positive cocci, mainly staphylococci, but also in Gram-negative bacilli. The properties of Small Colony Variants that differentiate them from wild-type colonies (mainly their small size) facilitate their intracellular survival (e.g. in epithelial or endothelial cells) as a result of which they can escape host immune response. In this way, SCV forms avoid the effects of complement components or antibodies. They are also characterised by resistance to antibiotics, mainly aminoglycoside or combination drugs, such as trimethoprim-sulfamethoxazole. The above features, which are important from a clinical point of view, namely small size and antibiotic resistance, make SCV one of the main causes of chronic, latent and recurrent infections which are difficult not only to diagnose, but also to treat. According to the literature, SCV of various microorganisms can be isolated from systemic infections of various organs and therefore from different clinical materials (e.g. blood, bones, soft tissues). SCV forms of Staphylococcus aureus are often isolated from patients with cystic fibrosis or osteomyelitis. The paper presents the characteristics and clinical relevance of this unique morphological form of bacteria.