“Prrevallence off Escherriichiia collii serrottypes iin poullttrry and effffiicacy off a kiilllled bactterriin iin iitts prreventtiion””
Abstract
Escherichia coli infections remain one of the major causes of economic losses in poultry industry worldwide, because of greater intensification of poultry husbandry and ubiquity of pathogenic Escherichia coli in litter, dust, water and as a commensal organism in the host body. Present study was carried to find out the prevalence of E. coli serotypes associated with various disease conditions, to know their antibiogram pattern and to evaluate the efficacy of a formalin killed bacterin prepared from most predominate serotype along with adjuvant in protection from challenge.
Heart blood of birds from 115 flocks was plated on MLA which were suffering from colibacillosis, omphalitis, Chronic respiratory disease complex and Swollen head syndrome (SHS). E. coli was isolated and identified
on the basis of standard cultural and biochemical tests. E. coli isolates were sent to CRI Kasauli (H.P.) for serotyping. Serotype O78 was most predominant (40.8%), isolated from 47 out of 115 samples followed by O2, O8, O101, O9, O147, O50, O88, O53 and O89.
Serotype O78 was isolated from all the disease conditions and from all the age groups of the birds. Antibiogram pattern showed E. coli isolates were most sensitive to chloramphenicol, gentamicin, cephalexin, ciprofloxacin and resistant against oxytetracycline, doxycycline, ampicilin and erythromycin.
Most predominant serotype O78 was inactivated with 0.3% formalin and emulsified with Freund’s incomplete adjuvant. A dose of 3.8X108 CFU in 0.5 ml was infected S/C in neck.
114 day-old broiler chicken were divided into 4 groups and were maintained on broiler mash alone. Group 1 was given vaccination on 7th and 21st day. Group II was given vaccination on 14th and 28th day. Group I and Group III were challenged on 28th day and Group II and Group IV was challenged on 35th day.
Three birds from each group were euthanized at 6, 12, 18, 24, 48 and 72 hours post challenge. Gross lesion scoring, count of CFU and histopathological lesions were studied. There was no effect of vaccination on the weight gain. CFU (Log10) in blood of vaccinated groups were significantly lower (P 0.05) than unvaccinated group at all the different hours post challenge.
The pathological changes in unvaccinated and challenged birds comprised of fibrinous pericarditis, perihepatitis and airsacculitis, oedema, congestion and mononuclear cell infiltration in the alveoli of lungs. Lesion score in liver, heart and lungs was significantly different from vaccinated groups. The Indirect Haemagglutination test carried out for quantification of humoral immune response following vaccination with O78 killed bacterin revealed high titres till 45 days of age.
On the basis of macroscopic and microscopic lesion score, protective efficacy of bacterin using schedule II (vaccinated on 14th and 28th day of age) was 67-68%, which was slightly better than schedule I (vaccinated on 7th and 14th day of age) having 62-65% efficacy, so can be used for prevention of E. coli infections in broilers, however; further study trials using multiple serotypes may be carried out