Anaerobic Organisms: Spore and Non-Spore Formers

Anaerobic Organisms: Spore and Non-Spore Formers

• Anaerobic organisms thrive in environments lacking oxygen.
• They obtain energy through fermentation or anaerobic respiration, using alternative electron acceptors.
• These organisms are found in various environments including soil, water, and the human gut.
• Aerobic organisms require oxygen for metabolic processes.

Oxygen Requirements of Bacteria

• Obligate anaerobes: These bacteria only grow in the complete absence of oxygen.
• Facultative anaerobes: These bacteria can grow with or without oxygen.
• Aerotolerant anaerobes: These organisms can tolerate oxygen but do not use it for metabolism.
• Microaerophiles: These organisms grow best in the presence of lower amounts of oxygen.
• Aerobes: Require oxygen to survive.

Differences Between Aerobic and Anaerobic Organisms

• Oxygen Requirements: Aerobic organisms require oxygen for survival, while anaerobes do not.
• Energy Production: Aerobes use oxygen to generate energy while anaerobes rely on other processes like fermentation.
• Metabolic Pathways: Aerobes use oxidative phosphorylation, while anaerobes use fermentation.
• Sensitivity to Oxygen: Anaerobes can be inhibited or even killed by the presence of oxygen.

Anaerobic Classification

• Non-spore forming anaerobes: Gram-negative bacilli (Bacteroides) and Gram-positive bacilli (Lactobacillus).
• Spore forming anaerobes: Gram-positive bacilli (e.g., Clostridium spp.).

Non-Spore Forming Anaerobes

• Bacteroides: A group of gram-negative bacteria frequently found in the human gut and associated with infections of the digestive system. They are normally inhabitants of the bowel, vagina, and mouth.
• Fusobacterium: Gram-negative anaerobic bacilli often implicated in periodontal disease and other oral infections.
• Peptostreptococcus: Anaerobic cocci frequently part of the human microbiome, particularly in the gastrointestinal tract and oral cavity.

Bacteroides Species

• Gram-negative, anaerobic bacteria commonly found in the gastrointestinal tract.
• Generally commensal, playing a role in gut health.
• Some species can become opportunistic pathogens causing infections in various body parts.

Bacterial Infections Caused By Bacteroids

• Intraabdominal infections
• Post-operative wound infections
• Puerperal sepsis
• Periodontitis
• Lung abscess

Anaerobic Gram-positive Bacilli (Lactobacillus)

• Gram-positive, non-motile bacilli arranged in chains.
• Found in oral cavity, intestines, vagina, milk, and milk products.
• Benefits include acidogenic, aciduric, protective low pH in normal female adults, and used as a probiotic.
• Lactobacilli infections are linked to dental caries.

Actinomyces

• Gram-positive, branching bacilli; Some species are anaerobic, some microaerophilic.
• Actinomyces israelii causes actinomycosis (abscess).
• Forms mycelial masses.

Sulphur Granules

• Sulphur granules are produced by Actinomyces and can be cultured on blood agar for 10 days to identify spider colonies.

Spore-forming Anaerobes

• Spore-forming anaerobic bacteria produce dormant, highly resistant structures called spores.
• Spores can survive harsh environments like heat, desiccation, and disinfectants.
• When conditions are favorable, spores germinate, producing vegetative bacteria.
• Vegetative bacteria can cause infections

Anaerobic Spore-forming Gram-positive Bacilli (Genus Clostridium)

• Clostridia are anaerobic, spore-forming Gram-positive bacteria.
• Natural habitat includes the intestinal tracts of humans and animals, as well as soil and water.
• Cl. tetani causes tetanus.
• Cl. perfingens causes gas gangrene and food poisoning.

Tetanus

• Caused by Clostridium tetani.
• Gram-positive, anaerobic bacteria.
• Motile, non-capsulated, have drumstick-shaped terminal spores.
• Found in soil and intestinal tracts.
• Grows in cooked meat mediums and produces thin films.
• Produces a toxin ("tetanus exotoxin") that causes the disease and impacts nerve function.

Laboratory Diagnosis of Anaerobic Infections

• Specimens (e.g., wound exudate) are collected.
• Prepared slides are Gram-stained to detect bacteria shape.
• Laboratory media like Robertson Cooked Meat Medium are used for culture.
• Other diagnostic tests include detecting hemolysis, motility, and gelatin liquefaction.

Specimen Collection and Transport

• Proper techniques to prevent contamination and maintain anaerobic conditions are crucial.
• Use of specialized transport media (e.g., GasPak jars).
• Specimens need to be delivered promptly to the laboratory to avoid spoilage.

Antimicrobial Resistance

• Anaerobic bacteria can develop resistance to antibiotics, leading to more difficult-to-treat infections.
• Factors contributing to resistance are overprescription, misuse of antibiotics, and inherent traits.
• Resistance can be spread through agricultural practices and animal husbandry.

Difficulty in Specimen Collection

• Anaerobic bacteria are sensitive to oxygen.