VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

RESISTANCE, ANTIGENS AND TOXINS

Resistance

• Rickettsiae are readily inactivated by physical and chemical agents.
• Rickettsiae can lose their viability in storage due to loss of their intercellular ATP pool and several coenzymes.
• They can be preserved in skimmed milk or a suspending medium containing sucrose, K, Po4 and glutamate (SPG) medium.
• Coxiella burnetti is relatively resistant to physical and chemical agents.
• In dried tick faeces and in wool, it survives for a year or more at 4⁰C and in meat for atleast a month.
• Holding method of pasteurisaton is not effective, but the flash method is effetive.
• Rickettsiae are susceptible to tetracycline and chloramphenicol.
• Penicillin and sulphonamides are ineffective. Sulphonamides may actually enhance the growth of rickettsiae.

Antigens and toxins

• Atleat 3 types of antigens have been demonstrated
  • Group specific soluble antigen
  • Species specific antigen
  • Alkaline stable polysaccharide- found in some rickettsiae and in some strains of Proteus organism.
• The sharing of antigens between rickettsiae and Proteus is the basis for the Weil-Felix reaction used for the diagnosis of rickettsial infections by the demonstration of agglutinins to Proteus strains OX19, Ox2 and OX k.
• Coxiella burnetti is the only rickettsiae to exhibit phase variation. Fresh isolates are in Phase I.
• They become Phase II on repeated passage in yolk sac but reversion to phase I take place by passaging in guinea pigs.
• Phase II cells are autoagglutinable. Phase I activity is attributed to a surfcace CHO antigen.
• Phae I immunogen is more powerful than Phase II and elicits high titre antibodies.
• Q fever sera react with other rickettsial antigens or with Proteus.
• The toxins have not been isolated and identified. Haemolysins are produced by some typhus rickettsiae.
• Rickettsiae contains (endotoxin like) LPS. They are different from true endotoxins of Gram-negative bacteria.