GRAM POSITIVE BACILLI/RODS
CORYNEBACTERIUM DIPHTHERIAE
Characteristics
-Gram positive, non-sporing, non-motile rods.
-In gram stained films, cells arranged as ‘Chinese letters’ showing irregular
staining or granular formation are characteristic
-Non-fastidious,but growth enhanced by inspissated serum (Loeffler medium)
-Capable of aerobic and anaerobic respiration
Lab Identification
Grows on Blood Agar (BA) but Identification aided by blood tellurite
(characteristic black colonies form within 48 hrs at 35℃
Catalase and Nitrate positive
Toxin production demonstrated by Elek test
Diseases
Toxigenic strains of C. Diptheriae cause Diptheria. Focus of infection may be the
throat or the skin
Spread through aerosol
Pathogenesis
Toxin blocks protein synthesis of the host cells by inactivating an elongation factor
GENUS BACILLUS
Two species of medical Importance: B. anthracis and B. cerus
BACILLUS ANTHRACIS
Characteristics
, Large gram positive spore forming encapsulated rods. Spores form only after the
organism is shed from the body. Respires aerobically
Laboratory ID
In body fluid smears, the capsule can be stained with polychrome methylene blue
(McFadyean reaction). This is diagnostic of B. anthracis
Non fastidious and grows well on simple media
Characteristic colonies (Medusa head) are related to chaining of the long rods
Non hemolytic on BA
Growth in CO2 encourages formation of capsule and smooth colonies
Diseases
Anthrax is a zoonosis and humans are infected by contact with infected hides and
bone. Infection acquired when spores enter abrasions on the skin or are inhaled
Intestinal and respiratory anthrax is rare in humans but the potential lethal effect
can be used in biological warfare
Pathogenesis
Capsule is antiphagocytic
Produces a heat labile exotoxin
BACILLUS CERUS
Characteristics
Large Gram –positive spore-forming rod. Similar to B. anthracis except most are
motile and non-capsulated. Respires aerobically.
Lab ID
Non-fastidious. Hemolytic on horse and sheep BA. Lecithinase production and
inability to utilize mannitol used to distinguish features on specially designed
selective medium
CORYNEBACTERIUM DIPHTHERIAE
Characteristics
-Gram positive, non-sporing, non-motile rods.
-In gram stained films, cells arranged as ‘Chinese letters’ showing irregular
staining or granular formation are characteristic
-Non-fastidious,but growth enhanced by inspissated serum (Loeffler medium)
-Capable of aerobic and anaerobic respiration
Lab Identification
Grows on Blood Agar (BA) but Identification aided by blood tellurite
(characteristic black colonies form within 48 hrs at 35℃
Catalase and Nitrate positive
Toxin production demonstrated by Elek test
Diseases
Toxigenic strains of C. Diptheriae cause Diptheria. Focus of infection may be the
throat or the skin
Spread through aerosol
Pathogenesis
Toxin blocks protein synthesis of the host cells by inactivating an elongation factor
GENUS BACILLUS
Two species of medical Importance: B. anthracis and B. cerus
BACILLUS ANTHRACIS
Characteristics
, Large gram positive spore forming encapsulated rods. Spores form only after the
organism is shed from the body. Respires aerobically
Laboratory ID
In body fluid smears, the capsule can be stained with polychrome methylene blue
(McFadyean reaction). This is diagnostic of B. anthracis
Non fastidious and grows well on simple media
Characteristic colonies (Medusa head) are related to chaining of the long rods
Non hemolytic on BA
Growth in CO2 encourages formation of capsule and smooth colonies
Diseases
Anthrax is a zoonosis and humans are infected by contact with infected hides and
bone. Infection acquired when spores enter abrasions on the skin or are inhaled
Intestinal and respiratory anthrax is rare in humans but the potential lethal effect
can be used in biological warfare
Pathogenesis
Capsule is antiphagocytic
Produces a heat labile exotoxin
BACILLUS CERUS
Characteristics
Large Gram –positive spore-forming rod. Similar to B. anthracis except most are
motile and non-capsulated. Respires aerobically.
Lab ID
Non-fastidious. Hemolytic on horse and sheep BA. Lecithinase production and
inability to utilize mannitol used to distinguish features on specially designed
selective medium
