Infectious Diseases By Andoh Wilson
Prevent the growth of pathogens
Stimulate the immune system to produce antibodies that cross-react with invading pathogens
Aid in digestion of cellulose in ruminants.
Produce essential nutrients
The same pathogen must be present in every case of the disease;
The pathogen must be isolated from the diseased host and grown in pure culture;
The pathogen from the pure culture must cause the disease when it is introduced into a healthy but susceptible organism.
The pathogen must be isolated from the inoculated animal and be shown to be the original organism.
Some infectious agents cannot be cultured e.g. prions
Some pathogens have non-virulent strains whose presence does not link them to a disease. E.g. non encapsulated Diplococcus pneumoniae
Acid-Fast e.g. Mycobacteria
Spherical described as cocci
Rod shaped described as bacilli
Thick peptidoglycan wall
No periplasmic space
No outer membrane (capsule)
E.g. Streptococcus pyogenes, Staphylococcus aureus, Bacillus anthracis, Clostridium tetani
Gram Positive wall
Thin peptidoglycan wall
Has periplasmic space containing different degradative enzymes such as deoxyribonucleases, -lactamases and proteases
Outer membrane containing lipid A, an endotoxin
E.g. Neisseria, Salmonella typhi, E. coli, Yersinia pestis, Vibrio cholerae
Gram Negative wall