A comparison of sialic acid between different isolates of Photobacterium damselae subsp piscicida

Sialic acid was identified and compared among 40 strains of Photobacterium damselae subsp. piscicida (formerly, Pasteurella piscicida), isolated from a variety of fish species from geographically different regions. The isolates were divided into two main groups according to the molecular weight of their sialic acid. The first group comprised of 12 Japanese isolates, which contained sialic acid with a molecular weight of 22 kDa. The second group included 26 isolates from the Mediterranean region, which contained sialic acid with a molecular weight of 26 kDa. A subgroup of Group 2 (2 Mediterranean isolates) was also evident and had a sialic acid molecule of 38 kDa. The P. damselae subsp. damselae strains (ATCC33539, ATCC35083 and NCIMB2184) had 26 kDa sialic acid molecules. Three isolates representing the three different groups of P. damselae subsp. piscicida were treated with Vibrio cholerae Type III sialidase. Isolate OT97299 from Group 1 and isolate SA300695 from the subgroup were both susceptible to the sialidase, while isolate I736 from the main part of Group 2 was unaffected by the enzyme. All three isolates were susceptible to mild acid treatment.