Description
Clostridium species are widely distributed in nature and are also associated with humans, either as non-pathogens at a variety of anatomic locations or at infected sites. Diseases caused by members of the genus Clostridium generally fall into one of the three categories: a. non-invasive disease in which toxin(s) is responsible for all the symptoms b. invasive (histotoxic) disease in which a progressive infections process and tissue destruction occur c. purulent disease in which a closed-space mixed infection involving multiple organisms is present. Histotoxic clostridia can be isolated on egg yolk containing medium, as demonstrated by McClung and Toabe. This medium was further supplemented with additional milk and lactose to differentiate clostridia on the basis of lecithinase production, casein hydrolysis and lactose fermentation. Selectivity was obtained by the incorporation of neomycin sulphate. Subsequently, eggs were replaced by purified lecithin, to obtain an egg-free medium. This egg-free medium was further modified with reduced concentration of neomycin and additional sodium azide, which enhanced the selective properties of the medium. This refined medium was designated as Lactose Lecithin Agar, which is used for isolation and differentiation of histotoxic clostridia from clinical specimens.
