Category:Gram Negative Anaerobic Bacteria

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Introduction

This group includes Gram negative, anaerobic bacteria. They are excreted in faeces and survive short periods in environment. They can cause opportunistic infections with facultative anaerobes. Non-specific infections include; wound infections, cellulitis, abscesses, oral infections and peritonitis. Specific infections include; liver abscesses in cattle, Calf Diphtheria and footrot in sheep. They may be required to produce swine dysentery.

Pathogenic Organisms

Pathogenic gram negative anaerobic bacteria that are of interest to vets include:

• Bacteroides fragillis
• Dichelobacter nodosus
• Fusobacterium necrophorum

Pathogenesis and pathogenicity

The bacteria cause pathology by the invasion of damaged tissues. They replicate at low or negative reduction potentials and produce superoxide dismutase, allowing survival in oxygenated tissues until conditions are appropriate.

Tissue necrosis and multiplication of facultative anaerobes allows anaerobic conditions for growth of facultative anaerobes. Most infections are mixed with the synergistic relationship between bacteria, e.g. between Fusobacterium necrophorum and Arcanobacter pyogenes and between F. necrophorum and Dichelobacter nodosus in ruminant pedal lesions.

Diagnosis

To diagnose bacterial infection, direct samples can be taken from lesions and discharges and cultured in anaerobic conditions with hydrogen and 10% carbon dioxide. They require enriched media for growth, for example enriched blood agar supplemented with 5-10% ruminant red cells, yeast extract, vitamin K and haemin. The media must have been pre-reduced. The colonies have a foetid or putrid odour. Antibiotic sensitivity, biochemical tests and gas liquid chromatography can be used for more accurate identification.