Susceptibility profiles of nutritionally variant streptococci (NVS) recovered from invasive cases in Ontario, Canada

Abstract

Background: Both Abiotrophia spp and Granulicatella spp have been shown to cause invasive infections, including endocarditis. Historically, these organisms were commonly referred to as nutritionally variant streptococci (NVS), as they were challenging to culture and required special media supplements for growth in vitro. Current guidelines for the management of endocarditis caused by NVS suggest treating patients with beta-lactams, particularly benzylpenicillin, but data supporting this recommendation are sparse and do not differentiate antibiotic treatment between the two species. Objective: To determine susceptibility profiles of Abiotrophia spp and Granulicatella spp recovered from invasive infections. Results: Between January 2010 and June 2015, 219 clinical isolates of NVS were submitted to the Public Health Ontario Laboratory for identification and/or susceptibility testing. The majority of these isolates (162/219; 74%) were recovered from blood cultures. Granulicatella spp showed greater susceptibility to penicillin than Abiotrophia spp (65.4% versus 23.7%). On the other hand, Abiotrophia spp isolates showed greater susceptibility to third- and fourth-generation cephalosporins than Granulicatella spp. Both Abiotrophia spp and Granulicatella spp isolates were universally susceptible to vancomycin. Conclusion: The findings demonstrate that susceptibility of NVS to commonly recommended antimicrobials depends on genus with Granulicatella spp exhibiting higher susceptibility to penicillin (the commonly recommended treatment for endocarditis caused by NVS) than Abiotrophia spp. Therefore, accurate identification and routine susceptibility testing of NVS would improve effective management of patients with invasive infections.