Staphylococcus

Overview of Cocci-Shaped Bacteria
- Focuses on gram-positive and gram-negative cocci.
- Emphasizes the staphylococcus group.

Shape and Structure
- Staphylococcus bacteria have a unique appearance resembling clusters of grapes when viewed under a microscope.
Gram Staining & Normal Flora
- Classified as gram-positive bacteria.
- Many species are part of normal flora, colonizing the skin and mucous membranes.
Halo Tolerance
  - Described as halo tolerant; can survive in high-salt environments, which is significant as skin is saline.
  - Capable of thriving in low pH conditions.
  - Highly resistant to various antibiotics and environmental factors.

Classification and Characteristics
  - Name derived from the gold coloration of colonies grown on culture media (aureus = golden).
  - Preferred growth temperature is approximately $37^{ ext{°C}}$ .
  - Relatively flexible regarding oxygen requirements; prefers oxygen-rich environments but can tolerate anaerobic conditions.

Enzymatic Virulence Factors
  - Coagulase: Causes blood clotting.
  - Hyaluronidase: Dismantles and digests connective tissues.
  - Staphylokinase: Digests existing blood clots.
  - Lipase: Dismantles oils, aiding colonization on skin.
  - Penicillinase: Affords resistance to penicillin, enabling survival against this antibiotic.
Exotoxins Released
  - Various strains have different exotoxin profiles; not every strain produces all toxins.
  - Hemolysins: Lyse red blood cells.
  - Leukocidins: Destroy white blood cells.
  - Enterotoxins: Cause food poisoning via diarrhea.
  - Exfoliative Toxins: Disrupt connective tissue in skin, leading to skin detachment.
  - Toxic Shock Syndrome Toxin: Known as a superantigen; leads to systemic issues including shock.

Skin Infections
  - Predominantly cause cutaneous infections due to natural colonization.
  - Risk factors include unsanitary conditions, close quarters (e.g., military barracks), and skin damage.
  - Conditions like folliculitis, boils, and abscesses.
  - Transmission can occur through shared equipment among athletes or through skin breaks.
Bacteriuria
  - Occurs when Staphylococcus aureus enters the bloodstream.
  - Common during surgical procedures or when invasive devices are inserted.
  - Risks include endocarditis (heart infection) and rarely, osteomyelitis (bone infection).
Toxigenic Infections
  - Examples include:
    - Food Intoxication: Major cause of foodborne illnesses in the U.S.; results from toxin consumption leading to gastrointestinal symptoms.
    - Staphylococcal Scalded Skin Syndrome: Primarily affects infants; characterized by the skin resembling burns due to exfoliative toxin actions.
    - Toxic Shock Syndrome: Severe result of a Staphylococcus aerus infection leading to immune system overreaction, multi-organ failure, and potentially death. Linked to tampon use or severe septic conditions.

Resistance Overview
  - Most strains are resistant to penicillin and ampicillin.
  - Emergence of methicillin-resistant Staphylococcus aureus (MRSA), which led to the development of methicillin as a treatment, later also becoming ineffective.
  - Introduction of vancomycin as a last-resort drug; emergence of vancomycin-resistant strains.
Medical Personnel and MRSA Transmission
- Many medical staff can be carriers, particularly in nasal passages.
- Recommendations against contact with immunocompromised patients to prevent the spread.

Catalase Test
  - Distinguishes staphylococci from streptococci.
  - Positive test shows bubbling, indicating the presence of catalase enzyme.
  - All staphylococci are catalase positive; all streptococci are catalase negative.
Coagulase Test
- Assesses the ability to clot blood.
- Staphylococcus aureus is coagulase positive, while all other staphylococci are coagulase negative.

Staphylococcus epidermidis
- Commonly found on skin and mucous membranes.
- Can lead to endocarditis or bacteremia if it enters the bloodstream; significant cause of urinary tract infections (UTIs).
Staphylococcus saprophyticus
- Lives on the skin and may also be normal flora of the vagina.
- Likely cause of UTIs due to proximity of the urethra to the vagina.