Spreading Factors of Mycoplasma alligatoris , a Flesh-Eating Mycoplasma

Abstract

ABSTRACT Mycoplasma alligatoris causes lethal invasive disease of alligators and caimans. A homolog of the nagH gene, encoding a hyaluronidase secreted by Clostridium perfringens , and a C . perfringens hyaluronidase nagI or nagK pseudogene were discovered in the M . alligatoris genome. The nagH gene was detected by PCR in the closest relative of M . alligatoris , Mycoplasma crocodyli , but not in 40 other species representing the Mycoplasma hominis , Mycoplasma pneumoniae , and Spiroplasma phylogenetic clusters. The hyaluronidase activity in the cellular fraction of M . alligatoris and M . crocodyli SP4 broth cultures was equivalent to 10 −16 U of Streptomyces hyalurolyticus hyaluronidase CFU −1 . Negligible activity was present in the cell-free supernatant fraction. No chondroitinase activity was detected. There is also a novel homolog of the nanI gene, which encodes a sialidase secreted by C . perfringens , in the M . alligatoris genome. The signature YRIP and SXDXGXTW motifs and catalytic residues of the clostridial sialidase are conserved in the mycoplasmal gene, but the leader sequence necessary for its secretion by C . perfringens is absent. The gene was not detected by PCR in any other mycoplasma. Potent cell-associated sialidase activity was present in M . alligatoris colonies on agar but not in the cell-free supernatants of broth cultures or in M . crocodyli . The presence of hyaluronidase and sialidase in M . alligatoris is consistent with the rapid invasiveness and necrotizing effects of this organism, and the lack of sialidase in M . crocodyli is consistent with its comparatively attenuated virulence. This genetic and biochemical evidence suggests that the spreading factors hyaluronidase and sialidase, a combination unprecedented in mycoplasmas, are the basis of the virulence of M . alligatoris .