Gram (+) Rods

• Small pleomorphic rods with clubbed ends

• Palisade or “chinese letter” arrangement

• Metachromatic granules (stain red-purple with methylene blue)

• Tinsdale agar - black colonies due to tellurite hydrolysis

• Elek test - determines toxin production by the isolate in vitro

Key characteristics of Corynebacterium Diphtheriae

Why use Loeffler’s stain?

Enhances development of metachromatic granules in C. diphtheriae (Pallisade arrangement may be seen)

Exotoxin production by only lysogenic organisms carrying a…

B phage

C. diphtheriae produces (—) on tonsils, uvula, or soft pallate

pseudomembrane

C. diphtheriae causes…

diphtheria

• Small colonies with narrow zone of beta hemolysis

• Catalase (+)

• Tumbling motility; “umbrella” motility in SIM at room temperature but NOT 37^oC

• Bile esculine (+)

Key characteristics of Listeria monocytogenes

Which organism causes neonatal meningitis and sepsis; sepsis in immunocompromised hosts?

L. monocytogenes

I’m (—) cold temp’s my game

Umbrella motility brings me fame

I’m a gram positive rod and hemolytic

Kills babe in utero after mom gets sick

From eating dairy or processed meat

Or veggies not exposed to hear

Listeria

• Non-motile

• Catalase (-)

• “Test tube brush” growth in gelatin; H₂S positive in TSI

Key characteristics of Erysipelothrix

What organism has an occupational infection for fisherman, butchers, veterinarians and rose growers?

Erysipelothrix

• Large, ground glass colonies

• Some beta hemolysis (but not B. anthracis)

• Catalase (+)

• Large gram (+) to variable rods in chains with spores

Key characteristics of Bacillus sp. (Sporeformers)

• Very long chains (“bamboo shoots”)

• “Medusa head” colonies

• Non-motile, non-hemolytic

• Anthrax - cutaneous, pulmonary, or gastrointestinal

B. anthracis

Organism that causes food poisoning due to preformed toxin - “fried rice”

B. cereus

Gram positive rod that is catalase (-) and H₂S in TSI:

Erysipelothrix

How to distinguish Listeria?

• Bile esculin (+)

• Beta hemolysis

How to distinguish Corynebacterium?

• Esculin (-)

• H₂S (-) in TSI

How to distinguish Bacillus?

Contain endospores on Gram stain ?