Therapeutic & Prophylactic Evaluation of Phage Cocktail in Combating Mild & Severe Colibacillosis in Poultry

Abstract

Avian pathogenic Escherichia coli (APEC) strains cause severe respiratory and systemic illnesses, endangering global food security and avian welfare. Progressive increase in multi-drug resistant bacteria have fueled interest in the use of bacteriophages to battle bacterial illnesses in humans and animals. The present study aimed at investigating the in vivo therapeutic and prophylactic performance of a phage cocktail to combat mild and severe colibacillosis in experimentally infected chicks. Three lytic coliphages isolated from the bedding material of poultry, were characterized and combined in a 1.47×1012 PFU/ml cocktail to be administered in 14-days old APEC O1 infected chicks. The mortality was reduced from 85.72% to 0% in prophylactic phage treatment and combination therapy, whereas therapeutic phage therapy decreased mortality to 33.3% in intramuscular-treated groups. Weight-gain and feed conversion ratios were significantly better in chicks treated with phage therapy than antibiotic therapy, combination therapy and untreated controlled birds. Absence of whitish fibrinous layers around the organs of the treated chicks emphasized that the severe damage in the positive control, corresponding to the score values of 2.7, 2.5 and 2.42 in the liver, heart and lungs respectively, had been reduced to mild damage after phage therapy. However, the lowest damage was recorded in all the organs of the combination therapy with the lesion score of 0.14, 0.28 and 0.28 in the liver, lungs and heart respectively. Histopathology of all the retrieved organs, heart, liver and lungs revealed necropsied degenerated cells with vascular congestion and oedema in the infected chicks however, such severe symptoms were not present in the treatment groups. The liver of the Positive control had 91.2% percentage in tissues, which was reduced to below 50% across all treatment groups, with combination therapy having the lowest damage at 10%. Damage to the heart was 86.1% in the positive control and was significantly decreased to 7.5% with the use of combination therapy. Lung damage was reduced from a mean of 75.5% to a range from 56.3% to 6.7% across all treatment groups, with the maximum reduction in the nasal-treated group. The data indicates that delivering phages either prophylactically, therapeutically or in combination with antibiotics via intramuscular, subcutaneous and nasal route may be an effective means for controlling colibacillosis caused by APEC O1 infection and may improve survival rate, weight gain, FCR, organ and tissue damage.