Coagulase testing was used to identify most (78%) S. aureus; rapid oxidase testing, to
identify most (75%) P. aeruginosa; and Lancefield typing, to identify Streptococcus pyogenes
and group C Streptococcus species. The majority of P. acnes were identified using rapid catalase
and rapid indole testing; MALDI-TOF MS was performed on a single isolate, and 16S
rRNA gene PCR/sequencing, on 2 isolates. 16S rRNA gene PCR/sequencing was performed
on 24 other isolates, mostly for the identification of anaerobic organisms.
Table 3 shows the ratio of isolates classified as “pathogens” versus “contaminants”.
The profile of organisms classified as pathogens differed from that of those classified as
contaminants. S. aureus accounted for 208 isolates (204 pathogens and 4 indeterminate
cases) and was always associated with PJI. Similarly, S. caprae was always associated
with PJI. S. epidermidis was equally distributed between pathogens and contaminants
(17% and 19%, respectively; P = .3). A similar observation was noted for S. lugdunensis,
whereas all other CoNS species accounted for 0.7% and 21% of pathogens and