Gram Positive Bacteria

Gram Positive Bacteria

Actinobacteria

  • High GC nucleotide content.

  • If GC content > 50% = Actinobacteria

  • Examples include Mycobacterium sp., Corynebacterium sp., Propionibacterium sp., and Streptomyces sp.

  • Mycolic acids found in Mycobacterium sp., similar structure to fungi.

  • Mycobacterium smegmatis has a doubling time of 5 hours, slow absorption of nutrients and waste elimination.

Firmicutes

  • Low GC nucleotide content.

  • If GC content < 50% = Firmicutes

  • Example: If G = 30%, then GC content = 60%.

Immune Response to Infection

  • Infectors target macrophages and dendritic cells, leading to infections in up to 50% of organisms.

  • Granuloma formation involves macrophage cells that cannot eliminate M. tuberculosis.

  • Two modes of leprosy exist.

Corynebacterium sp.

  • Pleomorphic with palisade arrangement.

  • Associated with secondary infections, can cause deep and erosive ulcers (cutaneous diphtheria).

Propionibacterium sp.

  • Anaerobic (do not require oxygen).

Streptomyces sp.

  • Non-pathogenic and produces numerous antibiotics.

Pathogenic Firmicutes

  • Clostridium sp. (endospore-forming), Staphylococcus sp., Bacillus sp., and Streptococcus sp. are pathogenic.

  • Non-pathogenic examples include Lactobacillus sp.

Bacillus sp.

  • Aerobic (requires O2) and anaerobic species are often catalase positive/negative.

  • Spores can cause vegetative cells to swell, centrally placed endospores.

  • Bacillus anthracis causes anthrax; lethal factor causes self-lysis in macrophages, and edema factor releases liquid that inhibits macrophages.

Pulmonary Anthrax

  • Highly lethal; linked to Bacillus cereus, transmitted via contaminated food (milk, cheese, rice, pasta, chicken).

  • Clinical manifestations include brain abscesses, meningitis, endophthalmitis, respiratory infections, endocarditis, hepatitis, and gastrointestinal diseases.

Bacillus Subtilis and Bacillus Megaterium

  • Neither are pathogenic; referenced for their substantial industrial applications.

  • Model organism for gram-positive rod bacteria; used in endospore staining in microbiology courses.

Clostridium sp.

Clostridium perfringens

  • Causes myonecrosis (muscle cell death).

  • Non-penetrative; treatment may involve hyperbaric oxygen therapy.

Clostridium botulinum

  • Produces botulinum toxin, inhibiting muscle contraction.

  • Risky in respiratory muscle infections.

Clostridium tetani

  • Causes tetanus by preventing neuronal inhibitory functions, resulting in sustained muscle contraction.

Clostridium difficile

  • Capable of surviving antibiotics and growing rapidly.

Listeria sp.

  • Fecal-oral route of transmission; ingested cells use actin for intracellular movement, can affect fetuses.

Staphylococcus sp.

  • Includes S. aureus (gold) and S. epidermidis (white), commonly alive on skin.

  • Folliculitis characterized by inflammation of follicles.

  • MRSA (Methicillin-resistant Staphylococcus aureus) is a significant medical concern.

Enterococcus sp.

  • Associated with dysbiosis (overpopulation), allowing cellular translocation.

Mycoplasma sp.

  • Lack cell walls, small size (0.3-0.5 μm), and very limited metabolic activity; filterable by 0.22 μm pore size filters.