Gram Positive Bacteria Classification

Gram Positive Bacteria

• Gram-positive bacteria are classified primarily by morphology (appearance) and biochemical characteristics.
• This classification only includes medically important bacteria.
• Scientific nomenclature: Italicize family, genus, and species. Capitalize the first letter of the family and genus names. Capitalize the first letter of kingdom, phylum, class, order, and suborder. All other words are lowercase.
• Binary genus-species system is used (e.g., Salmonella enterica, Escherichia coli, Staphylococcus aureus).
• Gram-positive bacteria can be cocci (spherical) or rods (elongated).
• They can be spore-forming or non-spore-forming.
• Important examples of gram-positive cocci are Streptococcus, Staphylococcus, Enterococci and Viridans streptococci.
• Important examples of gram-positive rods are Bacillus, Clostridium, Corynebacterium, and Listeria.

Classification of Medically Important Bacteria

• Bacteria are often classified based on their characteristics like morphology, spore-forming ability, and other biochemical properties.
• Gram-positive and gram-negative types are different on the basis of their cell wall characteristics.
• Examples: Streptococcus, Staphylococcus, and Enterococci are gram-positive cocci.
• Important gram-negative bacteria include Escherichia coli, Listeria, Corynebacterium.
• The study of gram-positive and gram-negative bacteria is important for understanding bacterial infections and disease processes.

Hemolytic Properties on Blood Agar

• a-hemolytic streptococci cause a change in the hemoglobin in red blood cells on blood agar, resulting in a green pigment that forms a ring around the colony.
• ẞ-hemolytic streptococci cause gross lysis (destruction) of red blood cells, showing a clear ring around the colony.
• y-hemolytic streptococci do not cause any color change or lysis (destruction) of red blood cells on blood agar.

Serological (Lancefield) Groupings

• Many streptococci have a polysaccharide in their cell wall that is antigenic (generating an immune response).
• The Lancefield scheme classifies mainly beta-hemolytic streptococci into groups A through U.
• The medically most important groups of beta-hemolytic streptococci are types A and B.

Group A B-Hemolytic Streptococci

• Streptococcus pyogenes is one of the most frequent bacterial pathogens in humans.
• Can invade intact skin or mucous membranes.
• A small inoculum (amount) is enough for infection.
• Some strains cause post-infectious sequelae (e.g., rheumatic fever and acute glomerulonephritis).

Streptococcus pneumoniae

• Gram-positive, nonmotile, encapsulated cocci (pairs).
• They are lancet-shaped.
• Common cause of pneumonia, otitis media, meningitis, and bacteremia/sepsis.

Enterococci

• Important species are E. faecalis and E. faecium.
• These bacteria can be y, β, or nonhemolytic.

Viridans Streptococci

• A group of streptococci found in the mouth.
• S. mutans and other species cause dental caries.
• Can cause subacute bacterial endocarditis in patients with abnormal or damaged heart valves.

Gram-positive rods

• The slides provide information on various gram-positive rods such as Bacillus, Corynebacterium, and Listeria.
• The slides describe characteristics like morphology, growth conditions needed, and diseases caused by each species.

Clostridia

• Anaerobic gram-positive rods of medical importance.
• C. perfringens causes histotoxic infections (myonecrosis) and food poisoning.
• C. difficile causes pseudomembranous colitis.
• C. tetani causes tetanus.
• C. botulinum causes botulism

Staphylococcus

• Staphylococcus aureus is one of the most virulent species.
• Common cause of bacterial and food poisoning.
• Staphylococcus epidermidis causes prosthetic implant infections.
• Staphylococcus saprophyticus causes urinary tract infections.

Coagulase-Negative Staphylococci

• S. epidermidis and S. saprophyticus are important causes of common CNS infections, and frequently found in hospital settings and are linked with the infections from implanted devices and catheters.

(Other information)

• Information on diseases, diagnosis, and treatment is provided in the slides, but this has been compiled into summary form.