CLASSIFICATION OF BACTERIA 51 



strongly aerobic (except for some species of Actinomyces and the 

 genera Fusiformis and Leptotrichia) and oxidative. Growth on 

 culture media often slow; some genera show mold-like colonies. 



FAMILY I. Actinomycetacece. Filamentous forms often branched 

 and sometimes forming mycelia. Conidia sometimes present. 

 Some species parasitic. 



Genus 1 . Actinobacillus. Filament formation, resembling strep- 

 tobacilli. In lesions no mycelium formed, but at peripheries finger- 

 shaped branched cells are visible. Gram-negative. Not acid-fast. 

 Type species, Act. Lignieresi. 



Genus 2. Leptotrichia. Thick, long, straight or curved threads, 

 unbranched, frequently clubbed at one end and tapering to the other. 

 Gram-positive when young. Threads fragment into short, thick 

 rods. Anaerobic or facultative. Non-motile. Filaments sometimes 

 granular. No aerial hyphse or conidia. Parasites or facultative 

 parasites. Type species, Lep. buccalis. 



Genus 3. Actinomyces. Organism growing in form of a much- 

 branched mycelium which may break up into segments that func- 

 tion as conidia. Sometimes parasitic, with clubbed ends of radiating 

 threads conspicuous in lesions in animal body. Some species are 

 micro-aerophilic or anaerobic. Non-motile. Type species, Act. 

 boms Harz. 



Genus 4. Erysipelothrix . Rod-shaped organisms with a ten- 

 dency to the formation of long filaments which may show branching. 

 The filaments may also thicken and show characteristic granules. 

 No spores. Non-motile. Gram-positive. Do not produce acid. 

 Micro-aerophilic. Usually parasitic. Type species, Bacillus 

 rhusiopathice suis Kitt 1893; Mycobacterium rhusiopathice Chester 

 1901; Erysipelothrix porci Rosenbach 1909, the causal organism of 

 swine erysipelas. 



FAMILY II. Mycobdcteriacece. Parasitic forms. Rod-shaped, 

 frequently irregular in form but rarely filamentous and with only 

 slight and occasional branching. Often stain unevenly (showing 

 variations in staining reaction within the cell). No conidia. 



Genus 1. Mycobacterium. Slender rods which are stained with 

 difficulty, but when once stained are acid-fast. Cells sometimes 

 show swollen, clavate, or cuneate forms, and occasionally even- 

 branched cells. Non-motile. Gram-positive. No endospores. 

 Growth on media slow. Aerobic. Several species pathogenic to 

 animals. Type species, Mycobacterium tuberculosis. 



Genus 2. Corynebacterium. Slender, often slightly curved, rods 

 with tendency to club and pointed forms, branching cells reported 

 in old cultures. Barred uneven staining. Not acid-fast. Gram- 

 positive. Non-motile. Aerobic. No endospores. Some pathogenic 

 species produce a powerful exotoxin. Characteristic snapping 

 motion is exhibited when cells divide. Type species, Cornynebac- 

 terium diphtheria. 



