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Case Study

18-year-old Mary has just moved into the dormitory at her university. One day, her roommate finds her lying in bed under her sheets. She is complaining of fever, chills, bad headaches and a stiff neck. She is staying under the covers because the light is hurting her eyes. Her roommate calls 911 and an ambulance takes Mary to the local hospital.

The emergency room physician asks Mary about her recent vaccinations and she reports that she has not had any since she was in elementary school. The physician documents a fever of 39.2°C and low blood pressure. He sends blood and cerebral spinal fluid to the Microbiology Laboratory. She is started immediately on intravenous antibiotics. Mary’s blood and cerebral spinal fluid grow Neisseria meningitidis and she is diagnosed with meningococcal meningitis.

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Encounter: where does the organism normally reside, geographically and host wise, and what are the bacterial characteristics that leave it suited to these places of residence. How would our patient have come in contact with this bacteria?

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Geographical Location

Sub-Saharan Africa

High incidence in the meningitis belt of sub-Saharan Africa

Epidemics every 5-10 years since 1905

Serogroup A → 90% of disease cases
Serogroup X → Case incidences on the meningitis belt

Stretching from Senegal to Ethiopia

Europe

Serogroup A was considered the primary cause of invasive meningococcal disease, few cases caused by serogroup C,

before and through World War I as well as II.

Serogroup B and C increased in prevalence to surpassed serogroup A after WWI & WWII.

China, India, Nepal, Russia

Infrequent → serogroup A disease incidences.

Stephens, D. S., Greenwood, B. & Brandtzaeg, P. Epidemic meningitis, meningococcaemia, and Neisseria meningitidis. The Lancet 369, 2196–2210 (2007)

THE GLOBAL SIGNIFICANT MENINGOCOCCAL SEROGROUPS DISTRIBUTIONS AND SEROGROUP B OUTBREAKS APPEAR IN PURPLE

Climate

Most likely to occur in areas with contrasting seasons like the semi-arid savanna and grasslands.

Infection rates rise around January to May

Low absolute humidity and the dry Harmattan winter winds → cause irritation to the pharyngeal mucosa → primary site of colonization of N. meningitidis.

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Host Location

Primarily found in:

Newborns less than a year old 🡪 at highest risk of infection from N. meningitidis.
Young children
Adolescents & Young adults 🡪 relatively high carriage rate, as well as their behavior

Survival of N. meningitidis

Cannot survive for long outside host environment
Require high humidity, sufficient CO2 and approximately 34 degrees Celsius temperature
Can sustain for a short period on hard surfaces such as glass or plastics
Require iron to survive and colonize → derived from human proteins (transferrin and hemoglobin)
Bacteria cannot survive outside host due to iron deficiency
Mostly infects the human nasopharynx, acting like a commensal microorganism

Attaches to the naso- and oropharyngeal mucosa non-ciliated columnar cells via type IV pili (organelles that are surface exposed).
N. meningitidis' Ops and Opc outer membrane adhesion proteins attach to host → causes pneumonia and sinusitis

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Transmission

N. meningitides → human pathogen
Asymptomatic carriers → major source of transmission → respiratory droplets with N. meningitidis infected individuals → direct contact

Occurs through kissing, sharing utensils, coughing or sneezing, smoking → infection through mouth and nose
Usually found in high traffic areas (clubs, pubs)

Individuals vulnerable to meningococcal meningitis

Have existing respiratory tracts infections
Dry mucosal surface in the respiratory tract
Irritation due to dust particles or severe low humidity

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.meetmeningitis.com%2Ffacts-about-meningitis&psig=AOvVaw1GWbJAAp7O9OJXA_r_nkhJ&ust=1644125555169000&source=images&cd=vfe&ved=0CAwQjhxqFwoTCNj-4JDr5_UCFQAAAAAdAAAAABAa

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Patient contact rationale

Patient could have acquired meningitis due to living in a dorm has:

Exposure to large crowds where N. meningitidis has higher virulence.
Sharing of communal food or drinking sources which have been infected by carriers (via respiratory droplets)
Coughing, sneezing or kissing → leading to contact and exposure to N. meningitidis.

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Entry: what facilitates the entry of the bacteria into the human host? What are the molecular, cellular and/or physiological factors at play in the initial entry/adherence step from the point of view of the organism and the host.

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Major Adhesins

Type IV pili (Tfp) – N. meningitidis

The bacteria attaches to the non-ciliated columnar cells of the nasopharyngeal mucosa
Attachment happens via Tfp (hetero-multimeric pilin subunits formed into a helical fiber)
Tfp ligan attaches to a CD46 complement regulator and membrane cofactor that is localized in the apical surface of the human epithelial cells.
CD147 transmembrane protein(brain capillaries marker→ two immunoglobulin-like domains) bound by Tfp regulates the primary bacterial attachment.
β2-adrenoceptor (β2AR → G-protein coupled receptor) → 2^nd receptor → ‘signals’ via heterotrimeric Gs protein and β-arrestins as a response to circulating catecholamines
PilE and PilV attach to extracellular N-terminal region of β-arrestins and trigger signal transduction within the cell.

Opacity Associated Adhesion Proteins– N. meningitidis

Opacity protein A (Opa) and opacity protein C (Opc) → integral proteins of outer membrane in N. meningitidis.
Carcinoembryonic antigen-related cell-adhesion molecule (CEACAM) → recognized by Opa → facilitating cellular attachment and invasion.
Cell-surface-associated heparan sulfate proteoglycan (HSPGs) are bound by Opc.
Opc → important in invasion of endothelial cells.

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Minor Adhesins

Neisserial adhesinA (NadA):

→ Binds human epithelial cells via protein-protein interactions

Neisseria hia homologue A(NhhA):

→ Facilitate adhesion to epithelial cells by binding to HSPGs and laminin

Adhesion and penetration protein (App):

→ Bacterial adhesion to epithelial cells, as well as bacterial colonization and spreading

Meningococcal serine protease A (MspA)

→ Adheres to human brain microvascular endothelial cells

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Host Defenses and Bacterial Evasions

N. meningitidis enter nasopharynx → attachment to epithelium → evasion of mucus and use of major and minor adhesions to bypass innate immune response.
N. meningitidis capsules containing sialic acid →commonly found in host system → evades immune response.
α-chain structures of meningococcal LOS like human l/I antigens → thus allowing bacteria to evade immune response.
Once in blood, bacterial PAMPS are identified by host PRRs → resulting in cytokine & chemokine release → preventing further spread by use of inflammation, macrophages and immune cells.
Environmental barriers such as irritated respiratory pathways due to dust, low humidity → conditions that make hosts more prone to infection.
Hosts that are affected by other existing infections → more prone to N. meningitidis infection due to weaker mucosal defenses.

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Multiplication and Spread: does the organism remain extracellular or do they enter into cells and what are the molecular and cellular determinants of these events. Do the bacteria remain at the entry site or do they spread beyond the initial site i.e. are there secondary sites of infection and why do the bacteria hone in on these particular secondary sites.

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From the Nasopharynx to the Bloodstream

Tfp recruits the B2-adrenergic receptor to induce plaque formation
ERM proteins facilitate the binding of N. meningitidis with CD44 and ICAM-1 through the binding of the host plasma membrane and actin of the pathogen
HSPG is bound by Opa and Opc resulting in the bacterium being internalized.
Internalized bacterium accumulates in the phagocytic vacuoles of epithelial cells.
The pathogen is released in the tight junction where they access the bloodstream via use of extracellular proteins (fibronectin and vitronectin).
Proximity of capillaries (leaky blood vessels) to mucosal epithelial cells provide the bacteria ability to enter bloodstream.

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From the CNS to the Blood Brain Barrier and Further

Entering the bloodstream → N. meningitidis can functionally spread to various other parts of the body.
N. meningitidis is commonly a blood-brain barrier (BBB) crossing bacterium → the line of entry:

After approaching the BBB, the bacteria creates a cortical plaque that utilizes Tfp to adhere CD147.
Recruitment of B2-adrenoreceptor to initiate plaque formation and B-arresting that allow actin polymerization occurs. A junction is formed between the bacteria and endothelial cells by the recruitment of the Par3/Par6/PKCz complex
This plaque basically facilitates the pathogen to cross the BBB and enter the subarachnoid space that has leakey interendothelial passageways that let the bacteria travel into the cerebrospinal fluid.
The bacteria will then infect the rest of the CNS due to the lack of Igs and component proteins that can stop the spread through the CSF→ causing sepsis and bacterial meningitis.

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Bacterial Damage: do the bacteria cause any direct damage to the host (or is the damage fully attributable to the host response, as indicated below) and, if so, what is the nature of the bacterial damage. Can it be linked to any of the signs and symptoms in this case?

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Meningococcal Septicaemia

N. meningitidis invades bloodstream. 8-25% patients are asymptomatic and the disease is caused indirectly through the host’s response to the infection.
Rapid proliferation of bacteria in blood circulation → high meningococcal endotoxins.
N. meningitidis outer membrane contains endotoxins (LOS→lipopolysaccharides).
N. meningitidis releases endotoxins by blebbing → causes binding to lipopolysaccharide binding proteins where they are transported by immune cells (macrophages, etc.).
The resulting inflammatory response after immune cells react to the LOS causes release of cytokines and chemokines and reactive oxygen species → all of which lead to shock and multiorgan failure.

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Purpura Fulminans

Purpura Fulminans resulting from meningococcal septicaemia.
A life threatening condition → mortality rate greater than 50%.
Can be identified by hemorrhagic infarction of the skin resulting from coagulation abnormalities→ direct damage to the host.
The pathogen is able to utilize the following processes to debilitate the host:
Production of Thrombin: thrombin is able to cleave fibrinogen to fibrin → making it essential in coagulation.
Inhibition of Anticoagulant Pathways: N. meningitidis inhibits the preventative anticoagulation pathway which causes uncontrolled downregulation of thrombomodulin (essential in controlling thrombin activation).
Inhibition of Fibrinolysis: fibrinolysis allows for fibrin clots to be destroyed, however, meningococcal septicaemia through N. meningitidis results in LOS causing monocytes to produce PA-1 that disrupts this negative regulation pathway of thrombin activation.

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Meningococcal Meningitis

N. meningitidis breaches the blood-brain barrier and enters the subarachnoid space, resulting in inflammation of the meninges.
This inflammation in the brain and increased intracranial pressure is as a result of increase in LOS.
LOS interact with TLR4 that mount an immune response along with proinflammatory cytokines (IL-10 and TNF-a) which cause increased blood flow and cerebral oedema → high intracranial pressure.
There are characteristic fevers, headaches, chills, neck stiffness and pain associated with meningococcal meningitis.
These symptoms can be identified with what is observed for Mary’s condition.