Abstract

Clostridium perfringens, an anaerobic Gram-positive bacterium known to be a common pathogen in humans, domestic animals and in wildlife, is the primary cause of clostridial enteric disease in domestic animals. C. perfringens can lead to both clinical and subclinical disease in poultry. Due to the diminished use of growth-promoting antibiotics in the European Union, C. perfringens associated necrotic enteritis and subclinical diseases have become serious threats to poultry health. The objectives of this PhD project were to learn how C. perfringens causes necrotic enteritis in broilers. The genetic diversity of C. perfringens in a wider perspective was also determined. It is of great importance that the plasmid-borne toxin genes are stable, both when the bacteria are transported to the laboratory and at the laboratory, in order that toxin typing of C. perfringens isolates should be accurate. Our results demonstrate that the plasmid encoded genes cpb1, cpb2 and etx are indeed stable under normal laboratory conditions and under conditions normally applying during transportation. Pulsed-field gel electrophoresis (PFGE) was used to explore the genetic relatedness of C. perfringens. The genetic diversity was found to be wide among C. perfringens isolates from different animal species, from food poisoning outbreaks and sewage sludge. Epidemiologically related isolates showed a close genetic similarity, as expected, while isolates with no obvious epidemiological relationship were genetically not so similar. Furthermore, sequence comparison of the cpb2 gene revealed two genetically different populations. The genetic relatedness of C. perfringens isolates from a broiler flock affected by mild necrotic enteritis (NE) was investigated by PFGE. Generally, a low genetic relatedness was found among C. perfringens isolates from these broilers affected by either mild or severe NE. The uniform susceptibility to narasin indicated that the substance can still be used to control clostridiosis, and that development of the resistance observed is slow. In this study C. perfringens also showed a low degree of resistance to most other antimicrobials tested. The exception was the high degree of tetracycline resistance found in C. perfringens in Swedish broilers.