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Applied and Environmental Microbiology, July 1999, p. 3015-3020, Vol. 65, No. 7
U.S. Environmental Protection
Agency1 and National Research
Council,2 National Health and Environmental
Effects Research Laboratory and Gulf Ecology Division, Gulf
Breeze, Florida 32561
Received 22 January 1999/Accepted 21 April 1999
A tetrazolium dye reduction assay was used to study factors
governing the killing of bacteria by oyster hemocytes. In vitro tests
were performed on bacterial strains by using hemocytes from oysters
collected from the same location in winter and summer. Vibrio
parahaemolyticus strains, altered in motility or colonial morphology (opaque and translucent), and Listeria
monocytogenes mutants lacking catalase, superoxide dismutase,
hemolysin, and phospholipase activities were examined in winter and
summer. Vibrio vulnificus strains, opaque and translucent
(with and without capsules), were examined only in summer. Among
V. parahaemolyticus and L. monocytogenes,
significantly (P < 0.05) higher levels of killing by
hemocytes were observed in summer than in winter. L. monocytogenes was more resistant than V. parahaemolyticus or V. vulnificus to the bactericidal
activity of hemocytes. In winter, both translucent strains of V. parahaemolyticus showed significantly (P < 0.05) higher susceptibility to killing by hemocytes than did the
wild-type opaque strain. In summer, only one of the V. parahaemolyticus translucent strains showed significantly
(P < 0.05) higher susceptibility to killing by
hemocytes than did the wild-type opaque strain. No significant
differences (P > 0.05) in killing by hemocytes were
observed between opaque (encapsulated) and translucent
(nonencapsulated) pairs of V. vulnificus. Activities of 19 hydrolytic enzymes were measured in oyster hemolymph collected in
winter and summer. Only one enzyme, esterase (C4), showed a seasonal
difference in activity (higher in winter than in summer). These results
suggest that differences existed between bacterial genera in their
ability to evade killing by oyster hemocytes, that a trait(s)
associated with the opaque phenotype may have enabled V. parahaemolyticus to evade killing by the oyster's cellular
defense, and that bactericidal activity of hemocytes was greater in
summer than in winter.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Factors Influencing In Vitro Killing of Bacteria by
Hemocytes of the Eastern Oyster (Crassostrea
virginica)
*
Corresponding author. Mailing address: U.S. EPA, 1 Sabine Island Dr., Gulf Breeze, FL 32561-5299. Phone: (850) 934-9342. Fax: (850) 934-2402. E-mail:
genthner.fred{at}epamail.epa.gov.
Contribution no. 1063 of the U.S. EPA's National Health and
Environmental Effects Research Laboratory and Gulf Ecology Division, Gulf Breeze, Fla.
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