MBY 161 Theme 10 - Bacterial diseases

*Still read own notes from lecture

Staphylococci

Spherical, gram positive

Identify types by producing coagulase vs not

Staphylococcus epidermidis

• Coagulase-negative

• 90% of skin normal microbiota

• Capsule

• Healthcare-associated pathogen e.g. with catheters

• Opportunistic

Staphylococcus aureus

• Carried in nasal passages of 20% of population

• Coagulase-positive

• May produce damaging toxins and cause sepsis

• MRSA strains are antibiotic-resistant

• Toxins tend to stimulate inflammatory response (causes more damage)

How Staphylococcus aureus avoids host defenses in skin

• Secretes proteins (blocks chemotaxis - avoids detection by immune system) and toxins (kill phagocytic cells)

• Lysozyme resistant

Folliculitis

Staphylococcal - infections of hair follicles

For an eyelash - called a Sty

Furuncle (boil)

Staphylococcal skin infection 

Type of abscess - localized region on pus surrounded by inflamed tissue

Carbuncle

Staphylococcal skin infection

Damage/inflammation of deep tissue from a spreading furuncle.

Body starts failing to ward off infection so other symptoms start showing 

Impetigo

Staphylococcal skin infection

Crushing (flat, nonbullous) sores

Spread by autoinoculation

Highly contagious but can be treated by antibiotics 

Common in toddlers

In newborn: Pemphigus neonatorum (often transmitted in birth process of lack of hygiene in nursery)

Scalded skin syndrome

Staphylococcal skin infection

Toxin A is localized but Toxin B causes exfoliation where skin layers peel off.

Pemphigus neonatorium 

Toxic shock syndrome (TSS)

When staphylococcal: fever, vomiting, sun-burn like rash

Untreated: shock and organ failure caused by toxin 1 (TSST-1) in the bloodstream. The toxin acts like a superantigen so the immune system is excessively activated.

Streptococcal skin infections

• Gram-positive cocci in chains

• Produce hemolysins 

• Beta-hemolytic version often causes disease 

• Differentiated into groups A to T 

Streptococcus pyogenes

• AKA Group A streptococci (GAS) - very common human pathogen 

• Produce virulence factors - Streptolysins, M proteins, capsule (hide from being flagged for phagocytosis) containing hyaluronic acid, hyalurodinase, streptokinases

Erysipelas

Caused by Streptococcus pyogenes - infects dermal layer of skin and causes local tissue destruction and sepsis

Necrotizing fasciitis

Caused by Streptococcus pyogenes - “flesh eating” disease

Exotoxin A produced acts as a superantigen (massive activation of immune system)

Streptococcal toxic shock syndrome

Similar to staphylococcal TSS but has no rash. Up to 80% mortality (particularly aggressive)

Septicemia

Acute illness due to the presence of pathogens or their toxins in the blood

Sepsis

Systemic inflammatory response syndrome (SIRS)

Inflammatory response of the immune system is causing damage

Lymphangitis

Inflamed lymph vessels

Severe sepsis

Decreased blood pressure and dysfunction of at least one organ

Septic shock

Sepsis and uncontrollable decreased blood pressure

Often multiple organ failure and death

Gram positive sepsis

• Exotoxins 

• Hospital-acquired infections

  • Enterococcus faecium 

  • Enterococcus faecalis

  • Group B streptococci - Streptococcus agalactiae (neonatal sepsis)

Gram negative sepsis

• Endotoxin shock

• Severe drop in blood pressure

• Condition can be worsened by antibiotics 

• Treatment 

  • neutralizing LPS components and inflammatory-causing cytokines

Tetanus

• Caused by Clostriudium tetani 

  • Gram positive, endospore-forming

  • Obligate anaerobe 

  • Spores present in soil/dust/animal excrement (infect wound)

• Tetanospasmin (toxin) released from dead cells 

  • enters CNS 

  • blocks relaxation pathway in muscles and causes muscle spasms 

  • muscle spasms of respiratory muscle causes death

• Treatment with tetanus immune globulin (TIG) - antitoxin

Tetanus vaccines

Contain the tetanus toxoid (DTaP) that stimulates antibodies that neutralize the toxin. Requires booster every 10 years.

Also vaccinates against Diptheria and whooping cough

Tuberculosis

• Mycobacterium tuberculosis 

  • Acid-fast rod (bacteria) transmitted human-to-human

  • Most common

• M. bovis

  • Not transmitted human-to-human - usually animal-to-human and in areas where there is close contact with cattle

• M. avium-intracellulare 

  • Complex that infects people with late-stage HIV infection

Treatment of Tuberculosis

Prolonged treatment with multiple antibiotics

MDR TB (Multi-drug resistant) and XDT TB (extensively drug resistant) strains 

BCG vaccine (live culture of avirulent M. bovis.

Staphylococcal Enterotoxicosis (food poisoning)

• Enterotoxin produced by Staphylococcus aureus not destroyed by boiling 

• Toxins are produced when organism is allowed to incubate in food - temperature abuse (long time in temp. danger zone)

Typhoid Fever

• Caused by Salmonella typhi 

• Spread only by human faeces! (reason that its associated with travel)

• Bacteria is spread throughout the body in phagocytes which release organism into the bloodstream

• Symptoms: high fever, headache, intestinal wall ulceration

• 1-3% of patients become chronic carriers and harbour the organism in the gallbladder

  • e.g. Typhoid Mary

• Vaccine was developed in 1911

• Treated with chloramphenicol, quinolones, or cephalosporins

Cholera

• Caused by Vibrio cholerae

  • Slightly curved, gram-negative rod with a single polar flagellum

  • Produces cholera toxin that causes host cells to secrete electrolytes and water (“rice water stools”)

• Associated with salty waters

• Can lose 12-20L fluid per day - causes shock, organ failure, death

• Treatment includes IV fluid replacement

• Often deadly when prevalent in countries with lack of healthcare infrastructure