Gas gangrene- causative agents, Virulence factors, Pathogenesis, Clinical features, Laboratory diagnosis, Treatment, Prevention and Control

Gas gangrene:

Gas gangrene is also known as clostridial myonecrosis. It becomes prominent during First World War. Clostridium perfinges is the primary causative agent which contaminates the open wound and causes tissue necrosis.

Clostridial wound infection is of three types.

Simple contamination: when Clostridium present in injured tissue but without evidence of infection. Such contamination is simple and common. The wound heals by first intention without sequels.
Clostridial cellulitis: It is characterized by fowl, seropurulent infection of depth of wound without muscle involvement.
Clostridial myonecrosis: it is characterized by infection of muscle and severe toxemia.

Clostridium perfinges, C. novyi, C. septicum, C. histolytica, C. sordelli, C. bifermentaus
Anaerobic Streptococci
Streptococcus aureus
Vibrio vulnificus
Bacteroides
Pseudomonas aeruginosa
coli
Klebsiella pneumonae

Alpha (α)-toxin: it is a lecithinase which split lecithin present in cell membrane into phosphorylcholine and diglyceride. It is produced by Clostridium perfingens type A
Beta (β)-toxin: it necrotizing lethal toxin
Epsilon (ε)- toxin: it is a permease
Iota (η) toxin: it is lethal necrotizing toxin
Hyaluronidase: it digest hyaluronic acid
Collagenase: It digest collagen fibre of sub cutaneous tissue
θ-toxin: it has hemolytic and necrotizing effects
DNase: it digest nucleotide
Enterotoxin: it induce enteric gastroenteritis

Clostridium cannot multiply and produce disease in normal tissue because of high oxidation-reduction potential of circulating blood and tissue which is more than necessary for growth of anaerobic bacteria.
The central factor that allows anaerobes to grow in wound is tissue anoxia.
Facultative organisms such as coli, Proteus, that may be present in wound which reduce the oxidation-reduction potential facilitating the growth of anaerobic bacteria like Clostridium.
Once the infection is established in immune-compromised host, toxin produced by the organism lead to weakening of host defense.
The pathogenesis of perfinges type A is associated with production toxins, hyaluronidsea and collagenase.
Collagenase damage the unaffected muscle, that supply the aminoacids and peptide for bacterial growth.
The speed of infection is facilitated by hyaluronidase produced by perfinges and other bacteria present in wound.

Hydrogen- 5.9%

Carbondioxide- 3.4%

Nitrogen- 74.5%,

Oxygen- 16.1%

Pain: Pain develops early in the region of wound and increases in intensity with progressive swelling and edema
fever
The wound is edematous, tender and exudate profuse serous discharge
Blisters with foul-smelling discharge
Gas bubble: bubbles of gas appear in discharge, crepitus may become evident in tissue and skin become white and marbled
pale skin that quickly turns gray, dark red, purple, or black
excessive sweating
The pulse rate increases
Moderate pyrexia
Vomiting
The blood pressure falls and peripheral venous collapse often make venipuncture impossible
Profoundly toxemic and shocked
Patient collapse, but remain mentally alert and anxious
The syndrome terminates with sudden death due to circulatory failure.

Specimen: wound exudates, pus, tissue

1. Smear preparation and Microscopy: gram positive spore forming rod on Gram staining

2. Serology: Rapid immunological test for identification of Clostridial products in wound exudates. Such as ELISA

3. Inhibition test: A specific sialidase inhibition test give result in 2-6 hours

Skin culture on BA: to test for the presence of Clostridium perfringens and other bacteria
Cooked meat Agar: gas bubble due to H2S production

5. Haematological test: blood tests shows an abnormally high WBCs count, which can indicate an infection

6. Nagler reaction

7. Biochemical tests: Catalase +ve, Oxidase +ve

8. Imaging: routine X-ray, (MRI) or arteriogram etc to visualize tissues and check for the presence of gas

9. Surgery: to evaluate the spread of gas gangrene within the body

Maintain proper Hygiene
Early and adequate cleaning of contaminated wound and cover with bandage together with antimicrobial drugs
Toxoid vaccine
Maintain healthy habits
Avoiding tobacco products
Control blood sugar level