Gram-positive anaerobic cocci. Identification and clinical relevance

PhD ceremony: Ms. A.C.M. Veloo, 14.45 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Gram-positive anaerobic cocci. Identification and clinical relevance

Promotor(s): prof. J.E. Degener

Faculty: Medical Sciences

Gram-positive anaerobic cocci (GPAC) are part of the normal microbiota and account for about one third of all the anaerobes recovered from clinical material. For their identification commercial systems based on enzymatic tests can be used. We validated two systems, Vitek ANC card and Rapid ID 32A. Two most commonly encountered GPAC, Finegoldia magna and Parvimonas micra, were correctly identified. However, a third commonly encountered GPAC, Peptoniphilus harei, was constantly mis-identified as Peptoniphilus asaccharolyticus. Until recently the relevance of this species was unknown, but molecular methods showed that this species is more abundant as assumed. We used several methods to improve the identification of GPAC. Species-specific 16S rRNA based probes were designed, in order to identify them by fluorescent in situ hybridisation. A database was constructed to identify GPAC using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). Both methods gave satisfactory results, when compared to 16S rRNA sequencing. Consequently, an antibiotic resistance study was performed. This revealed a difference in antibiotic resistance between the different species of GPAC, not observed before. The most encountered GPAC, F. magna, had the highest resistance rate. A review of the literature on F. magna revealed that this species is capable of producing several virulence factors and that it is associated with a specific site of infection, for example bacterial vaginosis. It can be concluded that it is important to identify GPAC properly and define their importance in infection and their susceptibility to antimicrobial agents.