Worm Breeder's Gazette 13(2): 25 (February 1, 1994)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Nematodes, including many parasitic species, live in environments with a high content of microbial organisms. Some of these serve as food, but free-living nematodes are also known to be susceptible to microbial attack, which will affect their abundance and ecology. There is, however, very little known about the anti-microbial defense systems of nematodes. Whilst there is some information on cellular defense mechanisms, nothing of which we are aware has been reported on non-cellular (humoral) factors.
A difficulty in examining anti-microbial activity in nematodes is the small size of most species and the fact that many are bacterial feeders so that it would be difficult to discriminate between anti-microbial factors related to their feeding and any present in their tissues or the fluid which bathes them. As a starter, therefore, we have carried out some simple assays for anti-bacterial activity on the pseudocoelomic fluid (PCF) of Ascaris as a plentiful source of material. We looked for inhibition of bacterial growth on nutrient agar surrounding filter paper discs impregnated with, or wells in agar filled with, PCF. Susceptibility to PCF varied substantially from one species of bacteria to another (see below), and all of the highly susceptible species were Gram positive. The factor(s) involved were stable at 65°C for at least 80 min, although there is about 50% loss of activity following heating in a 100°C water bath for 10 minutes. There was still the possibility that the anti-bacterial activity was due to contaminating antibiotics from the host's food or gut commensals, or metabolic products of the worm such as the small branched chain fatty acids which Ascaris excretes in abundance. We found, however, that dialysis did not diminish the titre of the anti-bacterial factor(s).
So it seems that nematodes may have humoral factors to defend themselves against invasive pathogens, but whether this extends to rapid quantitative and qualitative changes in the anti-bacterial activity of PCF following infection (as happens in the haemolymph of insects) remains to be seen. If such a system does exist, then we have probably only picked up resting levels of anti-bacterial factors, and not detected as broad a spectrum of anti-bacterial activity as might exist. In the meantime, we hear tales of some free-living soil nematodes having apparently harmless fluorescent bacteria in their pseudocoelom and those whose surfaces are cleaned of adherent bacteria by soil protozoa, but we have found nothing in the C. elegans literature on bacterial infection or anti-microbial factors. It would be valuable to obtain a species of bacterium which is pathogenic to C. elegans which might induce an increase in the titre of any antibacterial activity found in a filtered homogenate of the worm.