Letter to the Editor: An unusual microorganism, Aerococcus viridans, causing endocarditis and aortic valvular obstruction due to a huge vegetation

Dear Editor,

I read with interest the case report by Çalık and co-workers concerning a patient with endocarditis that did not respond to seemingly adequate antibiotic treatment. The authors typed the causative organism with an API test strip as Aerococcus viridans and discuss this organism.[1]

A. viridans was described in 1953[2] and additional aerococcal species including Aerococcus urinae[3] and Aerococcus sanguinicola[4] have been defined since then. A. viridans and A. sanguinicola have similar biochemical properties5 but A. sanguinicola seem to be more commonly isolated from infected patients than A. viridans.[6, Senneby et al. in preparation]. Importantly, the API system used by Çalık et al. fails to recognize A. sanguinicola and misclassifies this species as A. viridans.[6] Thus, it is possible that the organism causing the infection described by Çalık et al. is not A. viridans but instead A. sanguinicola. This potential misidentification may have occurred in many cases where A. viridans was identified only on the basis of the API or Vitek2 systems. Since biochemical typing of aerococci is difficult, 16S rRNA gene PCR and sequencing would be helpful to clarify the bacterial aetiology in this interesting case.