Vibrio fluvialis, An
Emerging Pathogen Responsible For Limp Lobster Disease In The American Lobster Ben D. Tall1, S. Fall1, M. R. Pereira1, S. R. Monday1,
M. H. Kothary1, K. A. Lampel1, L. Kornegay1,
S. K. Curtis1, F. M. Khambaty1, D. T. Chu1,
B. M. McCardell1, D. Prince2, and R. C. Bayer2 1CFSAN, US FDA, Washington, D.C. 20204 and 2University
of Maine, Orono, ME 04469. Evidence is accumulating that Vibrio fluvialis
is the etiological agent responsible for Limp Lobster Disease in Homarus
americanus (American lobster). Infection leads to a rapid onset of symptoms
such as weakness, lethargy, and slow or ineffectual responses to sensory
stimuli; death occurs within hours. We studied the pathogenic mechanisms
involved in this syndrome using 18 isolates obtained from ill lobsters
representing five closely related groups as defined by Pulsed-Field Gel
Electrophoresis (PFGE). Based on biochemical analyses, these strains appear to
embody a new biotype. Sixteen of the isolates were found to harbor a ~12-kb
plasmid. Challenge studies using lobsters in which a plasmid-positive outbreak
strain was injected via the tail hemocoel revealed that the LD50
dosage was a thousand-fold lower than that for a plasmid-negative strain. This
suggests that the 12-kb plasmid may escalate the pathogenicity of these
microorganisms in lobsters. Microorganisms recovered from experimentally
infected lobsters exhibited API 20E and PFGE profiles that were
indistinguishable from those of the outbreak challenge strain. Tissue affinity
studies demonstrated that the challenge microorganisms accumulated in heart and
mid-gut tissues, as well as in the hemolymph. In summary, these data support
the hypothesis that V. fluvialis cause Limp Lobster Disease, satisfying
Koch's postulates at the organismal and molecular level. Upon further analyses of these strains in
mammalian systems, bacteria-free culture supernatants caused Chinese hamster
ovary cells to elongate, suggesting the presence of a hitherto unknown
enterotoxin. To determine whether these microorganisms can cause disease in
warm-blooded vertebrates, suckling mice were orally challenged with either
plasmid-positive or plasmid-negative strains.
Significant accumulation of intestinal fluid was observed in mice
receiving a dose of 109 CFU/ml of either plasmid- positive or
plasmid-negative strains; however, no microorganisms were recovered from
intestinal contents in either case. These data suggest that the mechanism
resulting in fluid accumulation observed in mice differs from the disease
process observed in lobsters by requiring neither the persistence of viable
microorganisms nor the presence of the 12-kb plasmid. Our findings imply that V.
fluvialis is capable of causing diarrhea in mice and hence should be
treated as a potential mammalian pathogen. |