1. Pathogenic Gram-Positive and Bacilli (Listeria-Erysipelothrix)

2. Listeria Gram-positive non-spore-forming, aerobic coccobacillus
Found in soil, water, mammals, birds, fish, and insects
Enters body in contaminated food and drink
Listeria produces no toxins or enzymes
Listeria monocytogenes is the pathogenic species
Virulence is directly related to the bacteria’s ability to live within cells (listeriolysin O forms pores in the phagosome before it fuses with the lysosome)

6. Figure 19.17

7. Listeriosis Affects many wild and domestic animals as well as man
In adults, the disease is meningoencephalitis & bacteremia especially in immunosuppressed (diabetics, pregnant females, elderly)
Perinatal infection (may be intrauterine) is granulomatosis infantiseptica
Early onset disease: intrauterine sepsis and death
Late onset disease: meningitis (0-3 wks)

8. Diagnosis
Diagnosis
Presence of the bacteria in the cerebrospinal fluid
Rarely seen by Gram-staining because so few Listeria cells are required to produce disease
Cold enrichment
Characteristic tumbling motility at room temperature
Grows on ordinary media but prefers serum, blood or glucose media
Cold agglutinins in blood (human and sheep RBCs)

10. Treatment and Prevention
Most antimicrobial drugs eg.penicillin, erythromycin inhibit Listeria
Prevention
Difficult because the organism is ubiquitous
At risk individuals should avoid undercooked vegetables, unpasteurized milk, undercooked meat, and all soft cheeses

11. Erysipelothrix rhusiopathiae
Gram positive slender, non-motile rods occuring singly and in chains
Microaerophilic
Cause human erysipeloid
Infection through skin abrasions after contact with contaminated fish, shelfish, meat & poultry
Severe pain and swelling of a finger or part of the hand (without fever) with purple discolouration of the affected area.
It is considered an occupational hazard for those who handle infected animals or fish

12. Diagnosis
Isolation from skin biopsy in glucose broth