Gram Positive bacteria

Gram Positives

• Gram-positive bacteria have a thick peptidoglycan layer in their cell walls.
• This layer is responsible for their ability to retain the crystal violet dye during a Gram stain.
• They exhibit diverse shapes and appearances, including spherical (cocci), rod-shaped (bacilli), and filamentous forms. 
• Examples of Gram-positive bacteria, including their characteristics, appear in the following presentation slides.

Classifying Prokaryotes

• There are two domains: bacteria and archaea
• Bacteria are further classified into:
• Gram-negative
• Enteric Bacteria
• Non-enteric Bacteria
• Gram-positive
• Bacillota
•  Actinomycetota

Learning Objectives

• The objectives outline the identification and classification of bacteria, focusing on Gram-positive characteristics and examples.

Gram Positive vs. Gram Negative

• Gram-positive bacteria have a thin layer of peptidoglycan and a large periplasmic space.
• Gram-negative bacteria have a thick layer of peptidoglycan and a small or no periplasmic space, an outer membrane, and lipopolysaccharides.

Phylum Bacillota (Firmicutes)

• This phylum includes bacteria with low GC content.
• Many species are obligate or facultative anaerobes.
• These bacteria are a vital part of the human gut microbiome.
• Their presence can decrease with age and might be associated with obesity.

Order Lactobacillales

• This order comprises bacteria with low GC content and are generally acid-tolerant bacilli or cocci.
• They include members like Streptococcus and Lactobacillus, known for their role in lactic acid production and their use in food production (e.g., yogurt, cheese, wine)
• Certain Streptococcus species can cause diseases.

Streptococcus

• Streptococcus are commensal or pathogenic bacteria.
• These bacteria can cause various infections like strep throat, pink eye, meningitis, endocarditis, and necrotising fasciitis caused by Streptococcus pyrogenes.
• They're also found in some cheeses like Emmenthal.

Lactobacillus

• Lactobacillus are commensal bacteria found in the mouth, stomach, gut, and vagina.
• They're known for their probiotic properties, competing with pathogens.
• They help prevent cavities in the mouth, though they do produce acid.
• They're used in food production (sourdough, kimchi, beer) and other products.

Order Bacillales

• This order includes bacteria common in soil, including anaerobic and facultative aerobic bacteria.
• Spore-forming types are present.

Staphylococcus aureus

• Staphylococcus aureus is found in 25% of the population.
• It's an opportunistic pathogen causing various infections, including hospital-acquired infections, and diseases like toxic shock syndrome, endocarditis, pneumonia, and scalded skin syndrome.
• It's also a common cause of food poisoning.

S. aureus Virulence Factors

• Staphylococcus aureus has many virulence factors, including protein A, capsule, toxins (enterotoxin, endotoxin), and enzymes (hemolysins, coagulase, staphylokinase) that contribute to its pathogenicity.
• Resistance to antibiotics (like methicillin-resistant S. aureus - MRSA) is a significant concern.

Bacillus thuringiensis

• This species is a natural insecticide producing crystal proteins.
• The toxins are safe for plants and the environment.
• It's used to control pests like blackfly larvae and is a component of genetically modified (GM) crops.

Bacillus anthracis

• Bacillus anthracis causes anthrax.
• This pathogen exhibits three main disease forms: cutaneous (low mortality), pulmonary (very high mortality), and gastrointestinal (moderate mortality) presentations.
• The pathogen can be weaponized.

Order Clostridiales

• This order comprises anaerobic bacteria, mostly non-pathogenic.
• Some pathogenic species like Clostridium botulinum, Clostridium perfringens, Clostridium difficile, and Clostridium tetani cause diseases.
• Several species play crucial roles in cellulose digestion in ruminant animals.

Clostridium botulinum

• Clostridium botulinum is implicated in botulism, a food poisoning caused by the toxin it produces.
• This toxin blocks nerve signals that control muscles, resulting in muscle weakness and potentially paralysis.
• Botulinum toxin, a potent neurotoxin, has some medical applications, including the treatment or amelioration of muscle spasticity and in cosmetic procedures, known as Botox.

Phylum Actinomycetota (Actinobacteria)

• This phylum comprises bacteria, including terrestrial and aquatic species that are important for soil processes.
• Many species are characterized by high GC content and nitrogen fixation.
• A significant number are associated with human illness.

Streptomyces

• Streptomyces is a large genus within the phylum, known for forming spores and producing antibiotics and other bioactive compounds.
• Streptomyces is often found in soil, characterized by a distinct earthy smell attributed to the compound geosmin.
• Streptomyces are a source of important antibiotics and other substances.

Mycobacterium

• Genera within this phylum are not Gram stainable.
• Mycobacterium tuberculosis causes tuberculosis and Mycobacterium leprae causes leprosy, both impacting peripheral nerves.
• Both are slow-growing pathogens.