Week 4 - Bacterial infections

Question 1

What are systemic infections?

Answer 1

1. Infections that occupy the:
   a) Cardiovascular system and/or
   b) Lymphatic vessels

Question 2

What is septicaemia?

Answer 2

1. Any microbial infection of the blood causing illness (e.g. virus, bacteria, fungi)
2. Bacteraemia refers to bacterial septicaemia
   a) Bacteria are rapidly multiplying and so can cause quick infection if they enter a dangerous site
   b) Bacteraemia more often caused by Gram negative bacteria and the associated disease is usually more severe
3. Toxaemia is an infection/pathology caused by bacteria releasing toxins into blood
   a) A result of septicaemia
   b) Symptoms vary within toxin and bacterial type

Question 3

What is lymphangitis?

Answer 3

1. An infection and inflammation of the lymphatic vessels

Question 4

What are the signs and symptoms of septicaemia?

Answer 4

1. Fever over 38 degrees Celsius
2. Shortness of breath which is associated in increase in respiration
3. Increased heart rate > 90 bpm
4. As infection becomes more severe; chills, nausea, vomiting, abdominal pain, diarrhoea, malaise, changes in mental status (e.g. confusion and anxiety)
5. Small haemorrhagic lesions (petechiae) may appear in bacterial septicaemia

Question 5

What is sepsis?

Answer 5

1. Progression of septicaemia to septic shock
   a) Extremely low blood pressure due to vasodilation (doesn’t respond to fluid replacement)
2. Signs and symptoms:
   a) Decrease in body temperature and urine
   b) Aberrant blood clotting, clots in organs
   c) Tissue death (gangrene), organ failure, shock, death
   d) Mortality can exceed 50%, depending on bacterium + overall health of patient

Question 6

Who is most affected by septicaemia?

Answer 6

1. Older adults
2. Young children
3. Those with weakened immune systems (e.g. HIV, cancer, chemotherapy recipients, those already sick, burns patients etc)
4. Immunocompetent adults (healthy) rarely have septicaemia

Question 7

How are we infected with septicaemia?

Answer 7

1. Mostly as opportunistic infections
   a) Healthcare acquired - via surgery (e.g. catheter, implant)
   b) Community acquired - via infections from injury and wounds (e.g. drug use, skin and soft tissue injuries, mouth ulcers/gum injury, neonates at birth)
2. Also through zoonosis - infections from animals to humans (e.g. veterinarians, zoo keepers, pet owners etc)

Question 8

What are the virulence factors for bacteraemia?

Answer 8

1. Capsule - resist phagocytosis/hide from IR/stick cells
2. Fimbriae for attachment
3. Modify phagocytosis - adapt phagosome, live intracellularly
4. Promote bacterial metabolism - use sidrophores to acquire host cell iron
5. Produce toxins - activate and hyperstimulate IR (toxaemia)

Question 9

What is the pathogenesis of bacteraemia?

Answer 9

1. Primary bacterial infection e.g. intestines, kidney, lungs, skin, urinary tract, mouth
   a) Peritoneal inflammation
   b) Appendicitis
   c) UTI
   d) Pyelonephritis
   e) Pneumonia
   f) Cellulitis
   g) Gingivitis
2. Infection spreads to blood to cause bacteraemia and possible sepsis (host response)
3. Leaking blood vessels causes infection to spread to cause complications at other sterile sites/organs leading to organ damage and dysfunction
   a) Meningitis
   b) Osteomyelitis
   c) Endocarditis

Question 10

What is the diagnosis of bacteraemia?

Answer 10

1. First by signs and symptoms
2. Second by bacterial ID - Blood culture
   a) Taken under sterile conditions from 2 different venesections incubated (aerobic and anaerobically) with medium for growth - same organism must grow to be conclusive of bacteraemia
   b) 2-3 days incubation on average (some longer)
   c) Major problem can be contamination from skin NF when sampling
3. Gram stain from growth of blood and BC
4. Inoculation to Agar
5. Biochemical tests
6. Nucleic acid detection - PCR, mass spectrophotometry
7. Antibiotic sensitivity testing

Question 11

What is the treatment of systemic infections?

Answer 11

1. Essential to treat patient early to improve chances of survival
   a) Antibiotics via IV
   b) Requires large volumes of intravenous fluids
   c) Attend to primary infection where possible

Question 12

What are central nervous infections?

Answer 12

1. A blood infection that crosses the blood-brain barrier and infects CNS
2. Usually blood-borne or sometimes infectious agents invading via peripheral nerves
3. Brain and spinal cord are protected from mechanical pressure or deformation by enclosure in rigid containers, the skull and vertebral column, which also act as barriers to the spread of infection
   a) Blood vessels and nerves that traverse the walls of the skull and vertebral column are the main routes of invasion
4. Local invasion from infected ears or sinuses, local injury, or congenital defects such as spina bifida, also occurs, while invasion from the olfactory trace leading to meningitis is rare

Question 13

How does blood-borne invasion take place in CNS?

Answer 13

1. Blood-brain barrier to cause encephalitis
2. Blood-CSF barrier to cause meningitis
3. Microbes can traverse these barriers by:
   a) Growing across, infecting the cells that comprise the barrier
   b) Being passively transported across in intracellular vacuoles
   c) Being carried across by infected white blood cells
4. Once infection has reached the meninges and CSF, the brain substance can in turn be invaded if the infection crosses the pia
5. Pathological consequences of CNS infection depend upon the microorganism
6. Bacteria cause more rapidly evolving pathological changes with local responses to bacterial antigens and toxins play an important part

Question 14

What is meningitis?

Answer 14

1. Acute bacterial meningitis is a life-threatening infection needing urgent specific treatment
2. Bacterial meningitis is more severe, but less common, than viral meningitis and may be caused by a variety of agents
3. Treatment and preventative strategies differ depending on the bacterial type and strain