Lecture 10: Sepsis & Meningitis Flashcards
Streptococcus pneumoniae and Neisseria meningitidis
Sometimes the terms bacteraemia and septicaemia are used interchangeably. There are not quite the same though. What is meant by the term ‘bacteremia’?
The spread of local infection to distant organs, through the bloodstream. Often considered a transient state.
What is haemoatogenous spread?
The spread of bacteria within the blood. Can be asymptomatic. This is the route of dissemination.
Sometimes the terms bacteraemia and septicaemia are used interchangeably. There are not quite the same though. What is meant by the term ‘septacaemia’?
Presence of bacteria or toxins in the blood. Body is responding to this presence.
What does the term ‘sepsis’ refer to?
Blood infection that results in a more vigorous immune response, body immune system is now dysregulated. Very high grade fever, increased heart rate and increased respiration rate.
What is septic shock?
Endothelial cells lining the vasculature lose integrity, leading to leaky blood vessels. Blood coalesces under skin, organs lose integrity - they are not getting nutrients and oxygen.
What is encephalitis?
Inflammation of brain tissue.
What is meningitis?
Meningitis is the inflammation of the meningeal membranes, which surround the central nervous system (CNS).
What are the two most common causes of meningitis?
Bacteria and viruses, with viral meningitis being the most common.
How does viral meningitis generally compare to bacterial meningitis in severity?
Viral meningitis is often self-resolving and has a much lower fatality rate than bacterial meningitis.
Why is meningitis difficult to diagnose?
Its symptoms are often non-specific, making it hard to distinguish from other illnesses.
What are some common symptoms of meningitis?
Fever, headache, stiff neck, photophobia, and vomiting.
What are two specific clinical signs associated with meningitis?
Kernig’s Sign and Brudzinski’s Sign.
What are the three meningeal membranes?
Pia mater, arachnoid mater, and dura mater.
Which meningeal membrane is the innermost and highly vascularised?
The pia mater.
What is the function of the arachnoid mater?
It links to the pia mater by processes and contains cerebrospinal fluid (CSF).
What is the structure and function of the dura mater?
It is very fibrous and thick, sitting just beneath the skull bone to provide protection.
Describe Streptococcus pneumoniae in terms of gram staining, arrangement, oxygen requirements, catalase and haemolysis.
Gram-Positive, Catalase negative bacteria that commonly arrangem in pairs. They are faculatative anaerobes and they are alpha-haemolytic (partial haemolysis of erythrocytes).
How does Streptococcus pneumoniae cause meningitis?
It invades the bloodstream from the nasopharynx, leading to bacteraemia, which coexists with meningitis.
What age groups are most affected by Streptococcus pneumoniae meningitis?
It is bimodal, primarily affecting children under 3 and adults over 45.
How does Streptococcus pneumoniae meningitis compare to Neisseria meningitidis meningitis?
It is the most virulent form of bacterial meningitis, with higher mortality rates than Neisseria meningitidis.
What is pneumolysin and what is its role in virulence?
Pneumolysin is a toxin that binds to cholesterol in cell membranes, forming pores and causing cell damage.
How does the pneumococcal vaccine work?
The vaccine is based on capsular polysaccharide, stimulating a primary immune response to the 13 most common capsule types.
What is unique about Neisseria meningitidis compared to other Neisseria species?
It is the only species that produces a capsule.
What is the Gram stain and arrangement of Neisseria meningitidis?
It is Gram-negative and often arranges in pairs (diplococci).
What is the only known host of Neisseria meningitidis?
Humans.
How is Neisseria meningitidis transmitted?
By aerosol.
There are around 12 serogroups of Neisseria meningitidis exist, how many are of major concern?
5 are of major concern, accounting for ~90% of infections.
What role do pili play in Neisseria meningitidis infection?
Pili allow receptor-specific attachment to non-ciliated cells of the nasopharynx.
Why is the capsule important for Neisseria meningitidis?
It protects the bacteria against phagocytosis.
How does Neisseria meningitidis evade the immune system?
By down-modulating its capsule and producing IgA proteases.
What is the significance of LPS release in Neisseria meningitidis?
It is released in bleb form, triggering a dysregulated cytokine storm response.
How is Neisseria meningitidis diagnosed?
By cerebrospinal fluid (CSF) analysis.
How effective are antibiotics against Neisseria meningitidis?
It has very little antibiotic resistance, making swift treatment essential.
Why are vaccines targeting the Neisseria meningitidis capsule effective?
The pathogen requires its capsule to survive in the host.
Why has vaccinating against serogroup B been challenging?
The Bexsero vaccine is now available, but its long-term effectiveness is still being assessed.
What is an endemic disease?
A disease that is maintained in a population without external input, occurring at a constant but relatively high rate.
What is an epidemic?
A disease that appears as new cases in a population at a rate that exceeds what is expected during a given period.
