EFFECTS OF HYPERCAPNIC HYPOXIA ON THE CLEARANCE OF VIBRIO PARAHAEMOLYTICUS IN THE BLUE CRAB, CALLINECTES SAPIDUS

Holman, J. D., K. G. Burnett, L. E. Burnett. 2004. Effects of hypercapnic hypoxia on the clearance of Vibrio parahaemolyticus in the Atlantic blue crab, Callinectes sapidus. Biol. Bull. 206:188-196.

ABSTRACT
The blue crab, Callinectes sapidus, encounters both hypoxia and bacterial infections in its natural environment. We propose that acute exposure to hypercapnic (elevated CO₂) hypoxia (HH) alters the crab’s ability to clear a pathogenic strain of the bacterium Vibrio parahaemolyticus. Adult male crabs were held in normoxia (well-aerated) or HH water and challenged with Vibrio (2.5x10⁴/g) to achieve a circulating concentration of 10⁵ bacteria/mL. 1 mm injecting and sampling ports were drilled in the carapace over the ventricle and pericardium, respectively, and covered with a layer of latex rubber. Vibrio was injected directly into the heart to allow immediate and rapid distribution of the bacterium. Hemolymph was sampled from the pericardium. Injecting and sampling were done without removing the crabs from the water. HH was induced within 30 min and maintained at Po₂=30 torr, Pco₂=14 torr, and pH=6.7–7.1 for 45, 75, and 240 min prior to injecting Vibrio. Hemolymph bacteria (colony forming units=CFU) were counted before injection and 10, 20, and 40 min after. Crabs with detectable infections prior to treatment were not used. Hemocytes were counted 24 h before and 10 min and 2 h after injection. Sham injections of saline revealed no change in bacteria or hemocyte counts. Vibrio caused hemocytes to decline from 64x10⁶/mL to 24x10⁶/mL in normoxia. Similar declines occurred in all groups. Vibrio was nearly cleared within 1 h in all groups. HH treatment reduced the rate of Vibrio clearance. Normoxic crabs had significantly lower Vibrio at 10 min (427 CFU/mL) than HH 75 min crabs (3255 CFU/mL). NSF–REU 99-35204-8555.