Red Fluorescence of Peptostreptococcus Micros Grown Adjacent to Porphyromonas Gingivalis

Objective: Intense red fluorescence was found from Peptostreptococcus micros grown adjacent to Porphyromonas gingivalis, when studying red plaque fluorescence (van der Veen et al, 2006 DOI:10.1159/000095655). Red fluorescence of P. micros was not reported earlier. This study aimed at further investigating red fluorescence of P. micros and P. gingivalis grown together.

Method: P. micros (dsmz 20468) and six P. gingivalis strains (HG66, HG91, HG18442, HG102543, W50 and K1A kgp knockout mutant (kgp::erm) of W50 (Aduse-Opoku et al. Microbiology 2000;146: 1933-1940)) were grown alone or combined on BHI and CBA plates (both containing 5µg/ml hemine and 1µg/ml menadione) anaerobically (10%CO₂) at 37 ^oC for 24, 72 and 144 hours. Plates were photographed normally and for fluorescence (405 nm excitation, >520nm emission).

Results: None of the species showed pigmentation or fluorescence on the BHI plates at any time. On CBA plates P. micros and K1A appeared beige and all other P. gingivalis strains were black pigmented. P. micros showed little red fluorescence after 24 hrs and vague to bright green fluorescence after 72 and 144 hrs, respectively. P. gingivalis W50 and HG66 showed some red fluorescence after 144 hrs growth. After 24hrs red fluorescence was seen for P. micros together with any of the P. gingivalis strains regardless of their distance. After 72 and 144 hrs, intense red fluorescence was seen from P. micros for all P. gingivalis strains except K1A, but only when in proximity.

Conclusion: P. micros on CBA can fluoresce red and green, depending on incubation time. Red fluorescence of P. micros is enhanced and seen after longer incubation times when in close proximity to P. gingivalis, except for strain K1A which cannot produce µ-oxo bishaem-containing pigment. Interactions with µ-oxo bishaem-containing pigment and/or influence on growth of P. micros are a possible cause.