Invasive and cytotoxic P. aeruginosa strains were isolated
in approximately equal proportion from human clinical cases
of ulcerative keratitis.35 A significant relationship was present
between P. aeruginosa phenotype and patient age, with cytotoxic
strains associated with patients 50 years of age and
invasive strains associated with patients 50 years of age.35
The authors of that report suggested impairment of immune
function with age might reduce the host’s ability to respond to
intracellular pathogens, increasing the prevalence of invasive
strains in older individuals. Similar to humans with P. aeruginosa
ulcerative keratitis, a significant correlation between age
and phenotype was found in the ulcerative keratitis group of
the present study, with invasive strains associated with older
dogs and cytotoxic strains with younger dogs. This finding may