Experimental production of dermatitis in sheep with Pseudomonas aeruginosa.

The attachment, to sheep skin, for 4 days, of control wool pads saturated with sterile culture medium which contained a bacteriostat, induced only a mild dermatitis, whereas wool pads saturated with Pseudomonas aeruginosa culture induced a subacute dermatitis characterised by scaling, microabscess formation and seropurulent exudate. Changes similar to the latter were observed in skin affected by natural fleece-rot which developed spontaneously after 7 days of artificial wetting and in which P. aeruginosa was the predominant species of bacteria. An exacerbatory, if not causal, role for this organism is suggested in the development of the dermatitis associated with fleece-rot and in the exudation of seropurulent material, a step essential in the development of body strike.

Microflora and volatile fatty acids present in inguinal pouches of the wild rabbit,Oryctolagus cuniculus, in Australia.

Contents of inguinal pouches of the wild rabbit,Oryctolagus cuniculus, have been examined for the presence of microorganisms and volatile fatty acids. A total of 245 isolates were made from 167 samples taken from 75 rabbits, and microorganisms were obtained from 93% of individuals. The most common microorganism encountered wasStaphylococcus aureus, followed by the yeastCandida kruzei. Other organisms isolated wereBacillus subtilis,Escherichia coli, andStreptococcus faecalis. Quantitative analysis of volatile fatty acids in scrapings from pouches showed considerable variation between individuals. Of the acids identified, acetic acid and isovaleric acid were the most abundant. In a liquid medium containing one of these acids, the growth of microorganisms was only slightly affected. However, growth became inhibited when these fatty acids were used in combination.

The ovipositional response of the Australian sheep blowfly, Lucilia cuprina, to fleece-rot odours.

The ovipositional response of Lucilia cuprina flies to odours emanating from fleece-rot lesions of greasy wool in which Pseudomonas aeruginosa bacteria proliferated, was studied. Fractionation of the fleece-rot odours was carried out by bubbling the volatile components through hydrochloric acid and sodium hydroxide solutions to remove basic odours and acidic odours respectively. It was found that the acidic/neutral odours of fleece-rot wool, when perfused into wet, greasy wool stimulated L. cuprina to oviposit. On the other hand, the basic/neutral odours of fleece-rot wool were virtually unattractive to the gravid fly. Similarly, the acidic/neutral odours emanating from fleece-rot lesions of clean wool from which the non-fibre components, wax, suint and epithelial debris, had been removed by scouring, were found to be unattractive to the gravid fly in choice tests.

Observations on fibre diameter variation of sheep in relation to fleece-rot and body strike susceptibility.

A comparative study of various fleece properties known to influence fleece-rot susceptibility was made in a merino flock consisting of sheep which were found to be either resistant or susceptible to fleece-rot and body strike following heavy rains. The fleece properties measured were fibre diameter, fibre diameter, fibre diameter variation, wax content, suint content, wax to suint ratio, suint pH, insoluble nitrogen content, wool colour and wettability. Fibre diameter variation, due mainly to the presence of coarse, secondary fibres in the staple, was the only fleece property which differed significantly (p less than 0.001) between resistant and susceptible animals. The coefficient of variation of fibre diameter was lowered from a mean value of 22.7 +/- 0.3% in susceptible sheep to 20.0 +/- 0.3% in resistant sheep. A causal relationship between high fibre diameter variation and fleece-rot susceptibility is suggested. Sheep with irregular fibre size may retain free moisture in the fleece for longer, and thereby become more susceptible to fleece-rot than sheep with uniform fibre diameter, other predisposing factors being equal.

Intestinal lymph and the local antibody and immunoglobulin response to infection by Trichostrongylus colubriformis in sheep.

A local antibody response occurred in the small intestine when immune sheep were challenged with the enteric nematode parasite, Trichostrongylus colubriformis. Incoming infective larvae stimulated the appearance of increased numbers of IgA-containing lymphocytes in intestinal lymph. There were increases in the populations of IgA- and IgG1-containing plasma cells in the lamina propria. This did not occur in regions of the small intestine distant to the habitat of T. colubriformis. Challenge infection in immune animals increased the titre of anti-T. colubriformis haemagglutinating antibody in serum, intestinal lymph, intestinal fluid and extracts of intestinal mucosa. Although immune intestinal lymph contains anti-T. colubriformis antibody of IgA isotype, which is presumably produced in intestinal lamina propria, it failed to transfer passive immunity against the parasite. This result, however, does not exclude the possibility that IgA-antibody responses are important in protective immunity against T. colubriformis.

The significance of certain skin characters of sheep in resistance and susceptibility to fleece-rot and body strike.

Micro-anatomical differences in skin structure associated with resistance and susceptibility of sheep to fleece-rot and body strike were identified, and found to be of similar magnitude in 2 genetically divergent flocks of medium-woolled Merino ewes. Susceptible sheep were characterised by smaller follicle groups, resulting in higher densities of follicle populations with greater concentrations of the primary follicles (and sudoriferous glands) than in the resistant sheep. From these smaller follicle groups of susceptible sheep, thicker wool fibres grew than were found in the resistant sheep. The significance of these findings is discussed in relation to the pathogenesis of fleece-rot and body strike of sheep, and the value of the measured skin characters as a method for identifying resistant sheep.

An in-vitro technique for studying fleece-rot and fly strike in sheep.

Fleece-rot was experimentally induced in-vitro by wetting and incubating Merino wool samples embedded in serum-agar. Gravid Lucilia cuprina were readily-attracted to these wool culture plates to oviposit. Where serum was freely available to newly-hatched larvae, fly strike and larval development ensued. Using this technique, fleece-rot and oviposition were found to be markedly influenced by the availability of protein and by bacterial activity, particularly that of Pseudomonas spp. The results indicated that odours emanating from wool culture plates containing the latter species played an important role in oviposition. Furthermore, these events varied according to the type of fleece selected, and could be prevented by the addition of a bactericide.

The changes in protein concentration and bacteria of fleece and skin during the development of fleece-rot and body strike in sheep.

The sequence of events in the development of fleece-rot and body strike in sheep is described. When sheep were wetted by rain, vast increases in the numbers on microorganisms on the fleece and skin surface occured. Frequently, only one bacterial genus, Pseudomonas, proliferated and produced a bacteriostat to inhibit the growth of other resident flora. The development of fleece-rot lesions was characterised by a sudden substantial increase od soluble protein, presumably plasma protein, onto the skin surface. Pseudomonas spp proliferated on the skin surface and frequently produced extracellular, green pigment. First instar blowfly larvae were observed subsequently in such lesions.

IgG1 and IgG2 immunoglobulins to Bacteroides (Fusiformis) nodosus protease in infected and immunized sheep.

Sheep experimentally infected with foot rot developed antibodies that neutralized the proteolytic activity of Bacteroides nodosus culture filtrates in vitro. Similar antibody activity developed in sheep vaccinated against foot rot. In both cases the antibody was initially only associated with the IgG2 fraction of serum, but with time there was an increase in the proportion associated with IgG1. A subsidiary protein peak devoid of antiprotease activity was observed in elution profiles of affected and vaccinated sheep.