The effects of early exposure of cellulitis-associated Escherichia coli in 1-day-old broiler chickens.

Two experiments were performed to test the effect of various field strains of Escherichia coli of cellulitis origin. In the first experiment, 1-day-old broiler chicks were challenged with one of two E. coli field strains using inoculation routes including oral gavage, swabbing of the navel and subcutaneous injection. No cellulitis lesions were produced, although the birds experienced high levels of septicemia/toxemia, characteristic of colibacillosis. The birds that received the E. coli by subcutaneous injection experienced the highest rate of mortality, while those that were challenged by gavage and those that had their navels swabbed experienced lesser rates of mortality. Birds in the second experiment were challenged at 1 day of age with one of three field strains of cellulitis-origin E. coli administered alone or in combination (1:1), which were serially diluted prior to subcutaneous injection. No significant differences in body weight, mortality or cellulitis rates were associated with specific isolates given; however, significant differences were seen with mortality and cellulitis rates according to the dilution of bacteria given. A linear effect was also noted with body weight at 3 weeks, again correlating to the dilution of bacteria that the chicks received.

The influence of Escherichia coli strains from different sources and the age of broiler chickens on the development of cellulitis.

In two experiments, broilers were challenged with one of several field strains of Escherichia coli to determine whether the source of the E. coli and age of the bird at time of inoculation affected the development of cellulitis lesions. In the first experiment, birds inoculated at 52 days of age with E. coli of faecal, airsacculitis and cellulitis origin exhibited a cellulitis lesion incidence of 47.5, 25 and 77.5%, respectively. This study confirms earlier observations that E. coli strains isolated from cellulitis lesions express a higher propensity for producing these same lesions than other strains, including those associated with airsacculitis. In the second experiment, birds were inoculated at 4, 7, 10, 16, 28, and 52 days of age with an E. coli strain of cellulitis origin and necropsied 2 days post-infection. The resulting incidence of cellulitis ranged from 20% (day 7) to 95% (days 16 and 28), indicating that cellulitis can develop in any age of bird, although the lesions were frequently associated with other manifestations of colibacillosis (perihepatitis, pericarditis, airsacculitis) in birds challenged from 4 to 16 days of age.

The association of various isolates of Escherichia coli from the United States with induced cellulitis and colibacillosis in young broiler chickens.

An experiment was conducted to observe the effects of 10 different avian Escherichia coli isolates in 3-day post-hatch broiler chicks after subcutaneous administration. Isolates were originally obtained from various avian sources throughout the US. Chicks were injected subcutaneously on the ventral surface and necropsied at 7-day intervals for 3 weeks. Cellulitis was produced in all treatments receiving E. coli of cellulitis origin, with the highest incidence occurring 2 weeks post-infection in birds that received an isolate recovered in a previous challenge experiment. Cellulitis was also observed at week 1 post-infection in a small percentage of the birds in two of the treatments receiving E. coli of enteric origin, although lesions disappeared from the group after week 1 post-infection. Septicaemia was the most frequent sequel to challenge and occurred regardless of which isolate was injected. Chicks exposed to cellulitis origin isolates developed septicaemia more frequently than birds challenged with E. coli of non-cellulitis origin. The data implies that cellulitis is unlikely to occur early in the bird's life, since young birds exposed to E. coli frequently develop septicaemia.

Evaluation of scratches as an essential element in the development of avian cellulitis in broiler chickens.

Currently, the published cellulitis models do not adequately address the actual pathogenesis as seen in the commercial broiler industry. In this model, small dermal scratches were made on the skin of broiler chickens, which were then placed on litter seeded with avian cellulitis-associated Escherichia coli. The research confirms scratches are required for the induction of avian cellulitis. The research also confirms that "type I" cellulitis lesions or those previously thought to be due to hatchery-borne infections can be induced with scratches. The described methods provide a realistic model for cellulitis development that will improve the reliability of prophylactic and therapeutic-regimen efficacy testing data, thereby providing information more directly useful to the commercial broiler industry.

Scratches as a component in the pathogenesis of avian cellulitis in broiler chickens exposed to cellulitis origin Escherichia coli isolates collected from different regions of the US.

Cellulitis was induced in broiler chickens in two experiments. Birds were placed on used pine-shaving litter at day of hatch and raised to 28 days of age, at which time one-half the birds in each pen were scratched and the litter was treated with either one of seven cellulitis origin Escherichia coli (collected from various locations in the US) or sterile saline. Although minor differences could be detected in the association of specific regional isolates with differing rates of cellulitis, all isolates were capable of inducing cellulitis in a preponderance of the scratched birds. These same isolates were not capable of producing cellulitis in birds that were not scratched by design, confirming the importance of scratches in the pathogenesis of cellulitis. Those birds in the unscratched groups placed on litter inoculated with either a cellulitis E. coli isolate (EC-AR1) or sterile saline that did develop cellulitis lesions showed the remnants of healed scratches which had occurred naturally during the course of the growout, again providing evidence as to the importance of scratches in the development of cellulitis.