E. D. Heller

Enhancement of natural killer cell activity by Marek's disease vaccines 1

Vaccination against Mareks disease with herpesvirus of turkeys (HVT) has been reported to cause increased natural killer (NK) cell activity as detected in vitro against LSCC-RP9 target cells. The effect of vaccination with SB-1 (a nononcogenic chicken herpesvirus), HVT and the HVT/SB-1 combination on NK cell activation was compared in Mareks disease susceptible (P-2) and resistant (N-2) chickens. Birds were vaccinated at 7 days of age and NK cell activity was measured between 3 and 42 days after vaccination. Both SB-1 and HVT caused a significant increase in NK cell-induced specific release. The increase was similar in N-2 and P-2 chickens for either HVT or SB-1, while the combined vaccine induced a significantly higher increase in N-2 compared to P-2 birds. The maximal effect of vaccination on NK cells was detected at 7 days after vaccination. In contrast with the results in young birds, vaccination of birds between 31 and 45 days of age caused either no effect or a suppression rather than an enhancement in NK cell activity.

Passive immunisation of chicks against Escherichia coli

At hatching, the level of maternal antibody to E. coli in chicks, measured by ELISA was found to be 55 to 62% of that of the hen. It declined to an undetected level at 21 days of age. A sonicated experimental vaccine when given with a Freunds complete adjuvant to breeder hens produced the highest antibody titres and which were maintained for at least 160 days (end of the experiment) as well as providing the progeny protection. Progeny of hens with high antibody titre challenged with the homologous bacteria at 7 and 14 days of age exhibited total resistance, while those challenged at 21, 34 and 45 days of age, when antibody titres were undetectable, still showed 30 to 40% higher resistance than the control group. The results indicated a correlation between the hens antibody titre and percentage of survival of her progeny. Challenged progeny with a heterologous strain exhibited no protection. Hens which were vaccinated with a bivalent vaccine gave rise to chicks which were protected against both serotypes.

Short heat stress as an immunostimulant in chicks

The effect of 1 hour exposure of seven 1-week-old chicks to heat stress (41.5-42.5 degrees ) on their antibody titre after antigenic stimulation with E.coli bacteria was assessed. Exposure to heat 24 or 96 hours after immunisation resulted in a significant increase in antibody titres while heat treatment 42 or 72 hours after vaccination caused a non-significant increase in antibody titres. Heat exposure for 2 hours, 24, 48, 72 or 96 hours after immunisation either with E. coli or sheep red cells (SRBC) resulted in significantly increased antibody titres. When a number of antibody forming cells (against SRBC) in the spleens were tested, heat treated chicks showed no significant increase compared with the non-treated group. Heat-exposed chicks phagocytised Staphylococcus aureus bacteria (as measured by their disappearance from the blood) more rapidly than the non-treated group.

Vaccination of turkey poults against pathogenic Escherichia coli

A vaccine made of bacterial membranes which form vesicles has been developed in our laboratory and found to be effective in protecting chickens against challenge with pathogenic E. coli. In the present study we monitored maternal anti-5. coli antibody in turkey poults and found that although at hatch the antibody titre was relatively high, it decreased gradually to a low level by 14 days of age and remained low up to 31 days of age. Both intramuscular and subcutaneous vaccination with membrane vesicles (MV) resulted in increased antibody titres. Poults with high antibody titres could survive challenge with the pathogenic bacteria. Serum from vaccinated poults reduced E. coli bacterial growth rate when added to the growth medium at a high concentration, whereas serum from non-vaccinated poults did not. Lymphocytes from vaccinated poults responded with an increased rate of blastogenesis when MV was added to the cultures. Lymphocytes from non-vaccinated poults were not stimulated to blastogenesis. We concluded that MV can be used as a vaccine to render poults resistant to E. coli by evoking antibody production, stimulating the bacterial-lysis activity of complement, stimulating T cells to proliferate and stimulating cytotoxic T cells involved in disease resistance.

Marek's disease vaccines cause temporary U-lymphocyte dysfunction and reduced resistance to infection in chicks

One-day-old chicks were vaccinated with one of the commercially used vaccines [herpes virus of turkeys (HVT), bivalent HVT+SB1 or Rispens] and the immune response and resistance to infection evaluated. A temporary depletion of B-lymphocyte activity of varying intensity was found, as demonstrated by a diminished response to a B-lymphocyte-specific mitogen in vitro, and by decreased antibody production to BSA in vivo. Of the three vaccines tested, the bivalent vaccine (HVT+SB1) and Rispens were the most damaging. A temporary decreased resistance to pathogenic E coli infection in vaccinated chicks was observed.

Relationship between resistance to complement, virulence and outer membrane protein patterns in pathogenic Escherichia coli O2 isolates

To establish a possible relationship between resistance to complement, virulence and outer membrane protein banding patterns, ten E. coli O2 strains isolated from chickens with colibacillosis were studied for: (1) resistance to the bactericidal effect of complement by a quantitative microtiter method, (2) virulence, as determined by chicken lethality test, and (3) outer membrane protein banding patterns yielded by SDS-polyacrylamide gel electrophoresis. The ten isolates were classified into three groups: (1) Group 1, consisting of four isolates showed: (a) high resistance to complement, (b) high virulence, and (c) different pattern between 35 and 40 kDa with a weak peptide band at 35 kDa. (2) Group 2, consisting of one isolate showed: (a) high resistance to complement, (b) low virulence, and (c) a weak peptide band at 35 kDa. (3) Group 3, consisting of five isolates showed: (a) low resistance to complement, (b) low virulence, and (c) identical OMP pattern between 35 and 40 kDa exhibiting a strong peptide band at 35 kDa. The results suggest that high resistance to complement may be necessary but no sufficient for virulence and that OMP banding patterns may be a marker for virulence.

The effect of apramycin on colonization of pathogenic Escherichia coli in the intestinal tract of chicks.

Summary The purpose of the present study was to examine the effect of apramycin sulphate on the colonization of pathogenic E. coli in the intestines of chicks. Apramycin treatment (0.5g/l in the drinking water) of 3‐to 5‐week‐old Leghorn chicks for 24 or 48 hours resulted in a reduction, to an undetectable level, in the number of coliforms in the digestive tract for at least the first 24 h. Per os inoculation of E. coli (02:K1) after 24 to 48 h of treatment resulted in a significant decrease in colony forming units (cfu) in the digestive tract of the treated chicks. Food deprivation from the time of inoculation did not significantly change the results. However, food and water deprivation caused bacteraemia in a number of the control chicks but not in the treated chicks. Comparison of the level of protection between Leghorn and broiler (Anak strain) chicks revealed that there was a significantly higher (P<0.05) level of bacteraemia in the broiler than in the Leghorn chicks. Chicks treated with 0.25 g/l or 0.125 g/l apramycin for 24 or 48 h before E. coli inoculation showed significantly lower cfu in the colon and caecum than untreated control chicks, but significantly higher cfu were found in the colon than in chicks treated with 0.5 g/l apramycin. Although in vitro preincubation of apramycin with ileum cells did not decrease the percentage of cells to which the bacteria adhered, the number of bacteria adhered per cell decreased significantly. Taken together, our in vitro and in vivo results show that apramycin is effective against E. coli by preventing colonization of the gut by the bacteria, which could lead to a reduction of colibacillosis in poultry.

Adherence-associated characteristics and pathogenicity of Escherichia coli from avian colibacillosis.

Escherichia coli isolates from avian colibacillosis were examined for adherence-associated characteristics and post-colonisation pathogenicity. The adherence-associated characteristics studied included expression of pili, ability to partition with a hydrophobic phase, and ability to bind to Biosilon plastic polar-surfaced microcarriers. None of the adherence-associated characteristics correlated absolutely with post-colonisation pathogenicity, and thus in vitro tests for these adherence-associated characteristics cannot be used to predict whether any given E. coli avian colibacillosis isolate will exhibit post-colonisation pathogenicity. The isolation of strain BT7 from avian colibacillosis, a piliated E. coli strain which binds to Biosilon polar-surfaced plastic microcarriers, but is not pathogenic, is reported.