Pathogenic Gram-Positive and Bacilli (Listeria-Erysipelothrix)

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)

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 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)

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

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