BIOCHEMICAL INVESTIGATIONS OF BIOGROUPS AND SUBSPECIES OF MORGANELLA-MORGANII

We determined the subspecies and biogroup designations for 73 strains of Morganella morganii principally recovered from routine clinical spe cimens. On the basis of trehalose fermentation, 90% of all strains wer e identified as M. morganii subsp, morganii (trehalose negative), whit e the remaining 10% were designated M. morganii subsp, sibonii (trehal ose positive). Using three tests (ornithine decarboxylase [ODC] and ly sine decarboxylase [LDC] activities and susceptibility to tetracycline ), we determined the biogroup designations for these 73 strains, Four of the seven recognized biogroups within the genus Morganella were fou nd in the study, with biogroup A (ODC positive [ODC+], LDC negative [L DC(-)]) predominating (78%); all M. morganii subsp. sibonii strains we re found to belong to biogroup G (ODC+, LDC(-)). Rapid glycerol fermen tation (24 h) was linked to nonmotility and biogroup B strains (ODC+, LDC(+)), LDC activity but not tetracycline resistance appeared to be a ssociated with the possession of a 40- to 45-MDa plasmid, The use of t hree commercial systems (API ZYM, API 50 CH, and Biolog GN) failed to detect any new biochemical tests useful for subspecies identification, with the possible exception of L-phenylalanine utilization as a sole carbon source in the Biolog GN system, No Morganella strain was found to invade either HEp-2 or Vero cell lines, but four of seven M. morgan ii subsp, morganii strains were cytotoxic on sheets of both cells. Thi s cytotoxic activity appeared to correlate with the rapid expression o f beta-hemolytic activity.