780 PASTEURELLA 



Pasteurella pestis 



Isolation. — Independently by Kitasato (1894) and by Yersin (1894). 



Habitat. — Parasite of rodents and man. 



Morphology. — Small, straight, ovoid bacillus, 1*5 /< X 0-7 jx, with rounded ends and convex 

 sides ; arranged singly, in short chains, or in small groups. Shows high degree 

 of pleomorphism, especially in buboes and on 3 per cent, salt agar ; there is every 

 degree of variation in depth of staining, and clubs, shadow forms, snake-like fila- 

 ments, coccoid forms, yeast-like forms, and numerous others may be seen. Non- 

 motile. Non-sporing. In the animal body a true capsule may be formed ; in 

 culture media there is often a slimy envelope around each bacillus. Shows bipolar 

 staining, is Gram-negative, and non-acid-fast. 



Agar Plate. — 24 hours at 37° C. Very small, 0-1-0-2 mm. in diameter, round, glistening, 

 transparent, colourless, finely granular, umbonate colonies, with smooth or finely 

 granular surface and an entire or deUcately notched edge ; differentiated into a 

 raised centre and a flat periphery. 



5 days at 37° C. Larger, up to 4 mm. in diameter, with a raised, sometimes 

 ringed, nearly opaque, greyish-yellow centre and a flat or shelving, finely granular, 

 translucent, greyish-white periphery ; consistency is butyrous or viscous, emulsi- 

 fiabiUty easy ; sometimes a secondary ring of growth is seen. Variant colonies 

 occur. 



Deep Agar Shake. — 5 days at 37° C. Maximum growth at the surface ; numerous round, 

 transparent, colourless, punctiform colonies, visible with a hand lens, scattered 

 throughout the medium. 



Agar Stroke. — 24 hours at 37° C. Poor, slightly raised, translucent, greyish-yeUow, glisten- 

 ing growth, with a wavy or frosted-glass surface, and an irregularly lobate edge. 

 Growth increases very little with subsequent incubation. 



Gelatin Stab. — 7 days at 22° C. Good, filiform growth, confluent at top, discrete below, 

 extending to bottom of tube, and sometimes sending out little feathery projections 

 into medium. Surface growth is raised, 5 mm. in diameter, with a slightly lobate 

 edge. No liquefaction. 



Broth. — 24 hours at 37° C. Moderate growth ; little or no turbidity ; a floccular or pow- 

 dery deposit, not disintegrating completely on shaking. Later the flaky deposit 

 increases and may crawl up the sides of the tube ; a delicate surface pellicle often 

 forms. If butter or oil is floated on the medium, stalactites grow down from the 

 under-surface of the droplets. 



Loeffler's Serum. — 24 hours at 37° C. Fairly good, confluent growth, better than that 

 on agar. 



Horse Blood Agar Plate. — 2 days at 37° C. Colonies are similar to those on agar but show 

 less tendency to differentiation and peripheral spread. No haemolysis ; whole 

 plate is sMghtly cleared and browned. 



Potato. — 7 days at 22° C. Usually a thin layer of growth. 



MacConkey Plate. — 24 hours at 37° C Very slight, effuse, confluent growth, just visible 

 to the naked eye. Colonies disappear after 2 or 3 days, owing presumably to 

 autolysis. 



Resistance. — Fairly susceptible to inimical agencies. Killed by drying in a day or two, 

 by heat at 55° C. in 5 minutes, by 5 per cent, phenol immediately, and by 0-5 per 

 cent, phenol in 15 minutes. Agar plate cultures exposed to sun are sterilized in 

 1 to 5 hours. Cultures in the ice-chest may survive for months. 

 Metabolism. — Aerobic, facultative anaerobe. Requires low 0-R potential for initiation of 

 growth. Opt. temp. 27-28° C. ; limits - 2° to -j- 45° C. Opt. pH 7-2 ; limits 

 pH 50-9-6. Forms alkali in broth. Growth favoured slightly by serum, unin- 

 fluenced by glucose ; partly inhibited by glycerol. No haemolysis. 



