Age-related susceptibility of mice to ocular challenge with Pseudomonas aeruginosa exotoxin A.

We studied the responses of mice to ocular challenge with purified exotoxin A from Pseudomonas aeruginosa in 5-, 10-, 16-, 21-, and 30-day-old animals. In the absence of trauma, injection of 3 to 6 microgram of exotoxin per mouse beneath the fused eyelids of 5-day-old Swiss-Webster mice resulted in death of all animals within 24 h. Administration of 1.5, 0.75, and 0.375 microgram of exotoxin per mouse resulted in 24-h mortality rates of 50, 22, and 20%, respectively. Additional deaths were recorded throughout the next 4 days. Similar lethality results were obtained with 10-day-old animals that received equivalent amounts of exotoxin beneath the fused eyelid and in these experiments, the 72-h 50% lethal dose was 0.49 microgram of exotoxin per mouse. Mice that were 16 and 21 days old, whose eyelids were open, each received from 0.375 to 15 microgram of exotoxin topically applied to the surface of a wounded cornea. Cataracts were observed within 1 week in both groups, and none of the animals that received the higher concentrations of toxin died. Young adult (30-day-old) animals also received from 1.8 to 15 microgram of exotoxin topically on the surfaces of wounded corneas. Corneal swelling and slight opacity were observed at 24 h and within 1 month; 80% of these mice had cataracts of the ocular lens.