Bacteriology: Staphylococci and Streptococci

Staphylococci

• Staphylococcus aureus is a gram-positive bacterium that stains purple
• Typically spherical in shape, it is organized in clusters
• Stained purple in Gram stain
• It can cause skin infections, severe coughs, and production of sputum and pus
• S. aureus are found in wounds, clinical infections of respiratory or urinary tracts, and can be spread through direct and indirect contact
• Its size ranges from 0.5 to 1.5 micrometers in diameter
• Non-motile
• It is sensitive to penicillin and develops resistance very quickly
• It grows well on selective media (mannitol-salt agar) or non-selective media
• Forms yellow and smooth colonies
• It is oxygen-rich as it needs oxygen for survival

Streptococci

• Streptococcus pneumoniae is a gram-positive cocci that appears in chains
• It is sensitive to penicillin, erythromycin, and ampicillin
• It stains purple but older colonies stain purple
• They are non-motile and do not have flagella
• They are hemolytic and grow on blood agar forming grey-white colonies
• The bacteria can cause a variety of illnesses, such as pneumonia, bacterial meningitis, otitis media, bacteremia, and endocarditis
• It is transmitted through direct person-to-person contact.
• Alpha-hemolytic Streptococcus pneumonia strains are sensitive to optochin
• Beta-hemolytic streptococci can cause serious infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome

Corynebacterium

• Corynebacterium diphtheriae is a gram-positive bacterium that are typically rod or cylindrical shaped
• They are sensitive to penicillin
• It shows very limited motility
• Grows well on blood agar (tellurite blood agar)
• It produces small, smooth, opaque, creamy colonies
• Causes diphtheria disease, a respiratory illness that is characterized by a thick, gray membrane that forms in the throat
• The bacteria is commonly found in the respiratory tract and on the skin
• It also causes wound infection
• Transmission occurs through the respiratory droplets

Enterococci

• Enterococcus faecalis and Enterococcus faecium are gram-positive cocci in spherical shapes
• These bacteria are gram-positive and stain purple in a Gram stain
• Non-motile
• Sensitive to ampicillin, vancomycin, and gentamicin
• Commonly found in faeces
• They are also sensitive to antibiotics, such as ampicillin, vancomycin, and gentamicin
• Can be transmitted through fecal-oral route
• Found on nutrient agar

Listeria

• Listeria innocua and Listeria ivanovii are gram-positive rods that are short and appear small
• They are sensitive to ampicillin and penicillin
• Gram-positive bacteria form purple colonies during Gram staining
• Most species are non-motile
• Usually found in raw milk, contaminated vegetables, and other foodstuffs
• Causes listeriosis
• Transmission is through eating food contaminated with bacteria
• It grows in Müller-Hinton agar.
• It is a facultative anaerobe, meaning it can grow in the presence or absence of oxygen
• Most commonly known for causing food poisoning

Clinical Manifestations Caused by Staphylococcus aureus and Other Bacteria Mentioned

• Staphylococcus aureus:
  • Inflammation of a hair follicle
  • Non-bullous impetigo
  • Severe soft tissue infection
  • Endocarditis
  • Bacteremia
  • Septicemia
  • Urinary tract infections
  • Neonatal sepsis
  • Loss of balance
  • Stiff neck
  • Muscle aches
  • Fever
• Streptococcus pneumoniae:
  • Pneumonia
  • Meningitis
  • Otitis media
  • Bacteremia
  • Endocarditis
• Corynebacterium diphtheriae:
  • Diphtheria
  • Wound infection
• Enterococci:
  • Endocarditis
  • Urinary tract infection
  • Bacteremia
  • Sepsis
• Listeria:
  • Listeriosis
  • Food Poisoning
  • Weight loss
  • Diarrhea
  • Abdominal pain
  • Joint pain
  • Lymphadenitis
  • Skin hyperpigmentation

This quiz covers the essential characteristics of Staphylococcus aureus and Streptococcus pneumoniae, exploring their gram-positive nature, shapes, growth conditions, and clinical significance. Understand their roles in infections and their susceptibility to antibiotics.