CHRONIC PROSTHETIC HIP INFECTION CAUSED BY A SMALL-COLONY VARIANT OF ESCHERICHIA-COLI

From two different specimens of a chronic prosthetic hip infection tak en at an interval of 2 months a slow-growing gram-negative bacterium w as isolated in pure culture. The strain grew with the typical features of a small-colony variant (SCV). 16S rRNA sequencing identified the b acterium as Escherichia coli. Biochemical characterization demonstrate d multiple phenotypic alterations of a mutant carrying a defect in the heme biosynthetic pathway (Hem(-)): (i) catalase and nitrate reductas e reactions were both negative, (ii) a negative benzidine reaction dem onstrated the lack of heme-containing cytochromes, and (iii) growth st imulation under anaerobic conditions as well as gentamicin resistance indicated defective aerobic respiration. PCR and Southern hybridizatio n demonstrated that the mutation of the SCV of E. coli was localized i n the hemB gene and,vas most likely due to a deletion of the hemB gene . On blood agar plates revertants mere recognized growing as normal-si zed colonies between the dominant small colonies of the strain. Feedin g experiments indicated that the revertants hut not the small colonies were permeable for hemin. A strong antibody response against the infe cting SCV of E. coli was found. To oar knowledge, this is the first re port of a Hem- E. coli strain as the etiological agent of a chronic ba cterial infection.