This serological study examined 10 strains of flagellated, gram-positive marine cocci to determine their taxonomic position. Previous researchers had proposed these organisms belong to the genus Planococcus based on guanine-cytosine (GC) content and cell wall composition, rather than the genus Micrococcus where they were traditionally placed. Using agglutination and double-diffusion agar gel techniques, the author tested the flagellated strains against immune sera from Staphylococcus aureus, S. epidermidis, and Micrococcus species. The strains showed no significant serological relationship to staphylococci or micrococci, confirming they are antigenically distinct from these genera. However, the 10 flagellated strains themselves formed a heterogeneous group. Notably, strain CCM 316 differed clearly from others, while CCM 1849 and CCM 2069 appeared serologically identical. These findings supported the taxonomic reclassification of the flagellated cocci into Planococcus and demonstrated antigenic variation within the group that correlated partially with GC content groupings but not with other biochemical characteristics.

Key findings

• The 10 flagellated marine cocci strains showed no serological relationship to Staphylococcus aureus, S. epidermidis, or Micrococcus species, supporting their reclassification into genus Planococcus
• The flagellated strains constitute a serologically heterogeneous group, with strain CCM 316 being antigenically distinct from the others
• Strains CCM 1849 and CCM 2069 were serologically identical or very similar to each other
• Antigenic variation among the strains correlated with GC content groupings but not with other biochemical characteristics
• Cell wall preparations produced few of the precipitin lines observed with whole bacterial suspensions, indicating surface antigens are primarily involved in the serological reactions