CONTROL OF BACTERIAL-INFECTIONS IN THE HARD TICK DERMACENTOR-VARIABILIS (ACARI, IXODIDAE) - EVIDENCE FOR THE EXISTENCE OF ANTIMICROBIAL PROTEINS IN TICK HEMOLYMPH

The ability of hard ticks to prevent infection by bacteria was investi gated. During a 72-h period, virtually all Dermacentor variabilis fema les survived inoculation with Bacillus subtilis, Escherichia coil, and Staphyloccocus aureus but few survived infection with Pseudomonas aer uginosa. The hemocyte population increased to peak abundance at 48 h t o approximate to 6 times that of the uninfected controls. In contrast, the soluble hemolymph protein content decreased inversely as the hemo cytes increased. D. variabilis hemolymph was found to be constitutivel y antimicrobial (i.e., hemolymph from bacteria-naive individuals inhib ited bacterial growth). Infection with various bacterial species enhan ced this innate capability. When hemolymph fractions separated by high -pressure liquid chromatography were tested for their ability to inhib it microbial growth, activity against the gram-positive bacterium, B. subtilis, was found in 2 polar fractions. Antimicrobial activity was l ost when the fractions were incubated with protease. The least polar f raction contained 1 major protein, M-r 14.5 kDa, that comigrated with human lysozyme. This protein, tentatively identified as tick lysozyme, was abundant in bacteria-naive ticks but increased greatly (43%) foll owing challenge with B. subtilis. The identity of the other, more pola r protein is unknown. Studies to characterize these antimicrobial prot eins are planned.