Antimicrobial Susceptibilities of Oral Isolates of Abiotrophia and Granulicatella According to the Consensus Guidelines for Fastidious Bacteria

The genera and , previously known as nutritionally variant streptococci (NVS), are fastidious bacteria requiring vitamin B₆ analogs for growth. They are members of human normal oral microbiota, and are supposed to be one of the important pathogens for so-called "culture-negative" endocarditis. The type strains and oral isolates identified, by using both phenotypic profiles and the DNA⁻DNA hybridization method, were examined for susceptibilities to 15 antimicrobial agents including penicillin (benzylpenicillin, ampicillin, amoxicillin, and piperacillin), cephem (cefazolin, ceftazidime, ceftriaxone, and cefaclor), carbapenem (imipenem), aminoglycoside (gentamicin), macrolide (erythromycin), quinolone (ciprofloxacin), tetracycline (minocycline), glycopeptide (vancomycin), and trimethoprim-sulfamethoxazole complex. The minimum inhibitory concentration and susceptibility criterion were determined, according to the consensus guideline from the Clinical and Laboratory Standards Institute. Isolates of were susceptible to ampicillin, amoxicillin ceftriaxone, cefaclor, imipenem, ciprofloxacin, and vancomycin. Isolates of were mostly susceptible to benzylpenicillin, ampicillin, amoxicillin, cefazolin, ceftriaxone, imipenem, minocycline, and vancomycin. The susceptibility profile of was similar to that of , and the susceptibility rate was higher than that of . Although and strains are hardly distinguishable by their phenotypic characteristics, their susceptibility profiles to the antimicrobial agents were different among the species. Species-related differences in susceptibility of antibiotics should be considered in the clinical treatment for NVS related infections.