Aerococcal infections - from bedside to bench and back

Sammanfattning: The genus Aerococcus comprises eight species of Gram-positive cocci. The incidence and the clinical importance of aerococcal infections have been underestimated in the past, due to species identification difficulties. In our first study, we evaluated the usefulness of MALDI-TOF MS as a species identification method for aerococci and found that it had a high sensitivity and specificity. Two population-based studies on aerococcal bacteriuria were performed after MALDI-TOF MS was implemented in the clinical microbiology laboratory. A. urinae and A. sanguinicola were more common than previously thought and grew in almost 1 % of all urine samples. The patients were of old age and gender was almost equally distributed between men and women. Almost 80 % of the patients had symptoms of a urinary tract infection in one of the studies. Several antibiotics, including nitrofurantoin and amoxicillin, could serve as treatment options. Resistance against ciprofloxacin was recorded, especially in A. sanguinicola isolates. In a retrospective population-based study on aerococcal bacteremia, 77 cases were identified during a three-year period (A. urinae n=49, A. sanguinicola n=13, A. viridans n=14 and A. christensenii n=1). The A. urinae and A. sanguinicola patients were old (median age >80 years), predominately of male gender and underlying urological diseases were common. A majority of the A. urinae and A. sanguinicola patients had severe sepsis. Five patients with A. urinae bacteremia were diagnosed with infective endocarditis. A. viridans seemed to be a contaminant in most cases. The aerococcal isolates were sensitive to betalactam antibiotics and vancomycin. Two studies were conducted regarding virulence mechanisms. We demonstrated that A. sanguinicola isolates produced biofilms and induced platelet aggregation, two potentially important virulence mechanisms. A. urinae isolates were subjected to masspectrometry-based proteomics and whole genome sequencing. Two cell wall-anchored proteins with LPXTG-motifs (denoted Asp proteins) quantitatively dominated the surface and genes encoding these proteins were localized in a conserved locus on the aerococcal chromosome. It is of interest to determine the function of the Asp proteins to create a better understanding of how A. urinae cause infection.