644 



PROTEUS 



of swarming consist in (a) the addition to the medium of certain narcotic drugs 

 such as chloral hydrate, morphine and sodium phenylethylbarbiturate (Kramer 

 and Koch 1931, Lode and Howard 1932) ; chloral should be employed in a final 

 concentration of 1/500-1/1000 ; this method suffers from the disadvantage that 

 many strains are relatively insensitive to the drugs used ; (6) the incorporation 

 of 5-6 per cent, alcohol in the medium (Floyd and Dack 1939) ; this method is 

 effective, but if used for the isolation of streptococci has the drawback of lysing 

 the blood in the agar and inhibiting the growth of the streptococci ; (c) the addition 

 to the medium of sodium azide in a final concentration of 1/5000-1/10,000 (Snyder 

 and Lichstein 1940, Lichstein and Snyder 1941) ; in the higher concentration 

 not only is spreading prevented, but the growth of Proteus is almost completely 

 inhibited ; the growth of streptococci is good, though the zone of haemolysis 

 around /9-lytic colonies appears green and around a-lytic colonies brown ; {d) the 

 use of 6 per cent, agar (Hay ward and Miles 1943). Swarming is also suppressed 



. / V '// 



\ V 



h 





/ 





/. 



\ - 



/ " 



Fig. 136. — Proteus vulgaris. 



From an agar culture, 24 hours, 37° C. 

 showing chiefly rod forms ( X 1000). 



Fig. 137. — Proteus vulgaris. 



From an agar culture, 48 hours, 37° C. 

 showing short rods only ( X 1000). 



on some of the media, such as Wilson and Blair's bismuth sulphite agar and Leif- 

 son's desoxycholate citrate agar, used for the isolation of the pathogenic intestinal 

 Gram-negative bacilli. According to Lominski and Lendrum (1942) some " surface 

 active agents," like the alkyl sulphates, have a strong anti-swarming power.^ 



Swarming is due essentially to the active motility of the bacilli. Non-motile 

 variants give rise to compact colonies which, according to Felix (1922), may 

 be of three types: (1) smooth, translucent, homogeneous, with an entire edge; 

 (2) granular and opaque with an irregular edge ; (3) tiny colonies, barely visible 

 to the naked eye after 24 hours. 



Observation clearly shows that swarming on an agar plate is a discontinuous 

 phenomenon. On a plate inoculated centrally and incubated at 37° C, a thin 

 layer of bacteria is present at the site of inoculation after about 4 hours. Swarming 

 then begins, and in 6 hours the breadth of the growth is 1-1-5 cm. Further progress 

 outwards ceases, but the layer of growth becomes thicker. After 8 hours swarming 

 again starts, and a fresh ring of growth appears. The alternation of swarming and 



1 Certain quinone compounds have also been found to be effective in suppressing the growth 

 of Proteus (see p. 1528). 



