Staphylococcus and Streptococcus: Characteristics and Infections

Staphylococcus

• Easily develops antimicrobial resistance
• Gram-positive cocci
• Catalase-positive
• Facultative anaerobes
• Not demanding in their nutritional requirements
• Grow in normal media
• Some pathogenic species are generally opportunistic pathogens, commensals
• Important in animal and human infections

Natural Habitat

Widespread in nature; found on human and animal skin, surfaces of objects, air, soil, water, and milk.

S. aureus

Main pathogen associated with infections; colonizes nasal passages and pharynx.

S. epidermidis

Produces skin lesions, wound infections; microbiota found in the skin, respiratory tract, and gastrointestinal tract.

S. saprophyticus

Associated with urinary tract infections.

Immunogens

• Polysaccharide A (specific for S. aureus)
  • Antiphagocytic
  • Antiplatelet
  • Activator of NK cells
• Polysaccharide B (specific for S. epidermidis)
• Teichoic Acids
  • Ribitol teichoic acids (S. aureus and S. epidermidis)
  • Glycerol teichoic acids (S. saprophyticus)

Streptococcus

Gram-positive, spherical or ovoid, which divides into a single plane to form pairs or chains of variable length.

• Sensitive to changes in pH
• Optimum development: 37°C
• Develop poorly in common media, depending on the quality of peptones used
• Addition of blood is beneficial for growth

Treatment and Prevention

Penicillins, cephalosporins, macrolides, quinolones. The 23-valent pneumococcal polysaccharide vaccine provides an immune response.

Hemolysin

Low molecular weight protein that causes lysis of erythrocytes by producing pores in the plasma membrane.

Streptococcus pneumoniae

• Gram-positive cocci, diplococcus
• α-hemolytic
• Optochin sensitive
• Cells surrounded by a capsule
• Habitat: upper airway
• Does not produce spores or flagella
• Aerobic or facultative anaerobic

Capsule

Virulence factor of pneumococci; inhibits phagocytosis and allows them to multiply in host tissues.

Substance C

Polysaccharide found in the bacterial cell wall. Common antigen for all types of pneumococci. Formed by:

• Antigen F: Located on the outer surface of the membrane. Has an inhibitory effect on the autolytic enzymes of the bacteria.
• Antigen F: Protein similar to that found in Streptococcus pyogenes, but antibodies against these antigens do not confer protection.

Streptococcus agalactiae

The only species carrying the group B antigen. Associated with cases of septicemia, pneumonia, and meningitis in newborns (intrapartum prophylaxis). Found in the vaginal microbiota, urethra, gastrointestinal tract, and respiratory system of humans.

• Grow well in nutrient-enriched media
• Buttery-looking colonies and produce β-hemolysis

The disease in children younger than 7 days is called early-onset disease.

The one shown between 1 week and 3 months of life is considered late-onset disease.

The risk of disease is higher in pregnant women than in men or non-pregnant women.

Urinary tract infection, endometritis, and wound infections are common manifestations in pregnant women.

Neonatal Sepsis

The newborn acquires the infection from the birth canal of a colonized mother.

Early-Onset Neonatal Disease

Symptoms of the disease appear during the first week of life. Characterized by bacteremia, pneumonia, or meningitis (pulmonary involvement is seen).

Late-Onset Neonatal Disease

The disease has an exogenous origin. The event is predominantly bacteremia with meningitis.