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MICROBIOLOGY

Pathogenic Gram-Positive and Bacilli (Listeria-Erysipelothrix)

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)

Listeria

Figure 19.17

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)

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)

Diagnosis

Treatment and Prevention

Treatment

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

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

Diagnosis

Isolation from skin biopsy in glucose broth