Pathology - Infectious Disease Flashcards
Gram positive bacteria have what kind of cell wall?
Gram positive bacteria have a cell wall outside a single phospholipid bilayer.
Gram negative bacteria have what kind of cell wall?
Gram negative bacteria have a cell wall sandwiched between phospholipid bilayers.
Most bacteria in the body are where? And of what kind?
Most bacteria (10 to the 14) are anaerobes in the GI tract.
Which specific receptors does HIV bind to on lymphocytes?
CD4 and CXCR4 on helper T cells.
What is “quorum sensing”?
The phenomena of communities of bacteria coordinating the secretion of autoinducer peptides that turn on specific genes in the population.
It is a method of bacterial virulence.
How to bacteria adhere to host cells?
Bacterial adhesins and pili are mechanisms by which bacteria adhere. N. gonorrhoea varies its pilus to escape immune clearance.
What is an endotoxin?
Endotoxins are LPS components of cell walls of G- bacteria with a variable CHO chain. Whilst low doses induce a productive inflammatory response, high doses can lead to shock, DIC, and ARDS.
What is an exotoxin?
Proteins secreted by the bacterium which effect a pathological response. They have 4 broad categories…
Elaborate on the different categories of exotoxin:
- Enzymes. Eg protease produced by S. aureus.
- Toxins that alter intracellular pathways. Eg AB toxins produced by Bacillus anthracis
- Neurotoxins. Eg neurotransmitter blockade in botulism and tetanus.
- Superantigens. These stimulate very large numbers of T cells leading to massive cytokines release. Eg Staph and TSS.
Which pathogens are associated with B cell immunodeficiency?
S. pneumoniae H. influenzae S. aureus Rotavirus Enterovirus
Which pathogens are associated with T cell immunodeficiency?
Intracellular pathogens.
Which pathogens are associated with complement deficiencies?
S. pneumoniae
H. influenzae
N. meningitidis
Which pathogens are associated with neutropenia?
S. aureus
Gram negative infections
Fungi.
Measles:
- Type of virus
- Transmission and Distribution
- Clinical manifestations
- Immune response
- RNA Polymyxovirus
- Transmitted via respiratory droplets, starts at respiratory epithelium then spreads via lymph systematically.
- Causes croup, pneumonia, diarrhoea, keratitis, encephalitis, and (hypersensitivity) rash.
- Antibody-mediated immunity protects against re-infection
Mumps:
- Type of virus
- Transmission and Distribution
- Clinical manifestations
- Paramyxovirus
- Spreads via respiratory droplets then to lymph then haematogenously.
- Infects salivary glands, tested, ovaries, pancreas, CNS.
Poliovirus:
- Type of virus
- Transmission and Distribution
- Clinical manifestations
- Immune response
- Spherical, unencapsulated RNA enterovirus.
- Transmitted via faecal-oral route and multiplies in intestinal mucosa then systematically or via retrograde neuronal travel.
- Invades CNS in 1% replicating in motor neutrons in spinal cord or brainstem.
- Attaches to CD155
Ebola:
- Type of virus
- Transmission
- Clinical manifestations
- Enveloped RNA virus, part of the viral haemorrhagic fevers family
- Transmission occurs via infected animals.
- Haemorrhage is mediated through endothelial damage and platelet dysfunction. Also causes profound cytokine release.
What is the most common opportunistic viral pathogen in AIDS?
How might it manifest in immune compromised patients?
CMV may manifest as a life threatening colitis or pneumonitis, hepatitis, chorioretinitis, and meningoencephalitis.
How does CMV cause immune suppression?
CMV can infect dendritic cells and cause transient but severe immune suppression.
Which 2 cancers is EBV associated with?
B-cell lymphoma and Burkitt’s lymphoma.
Adherence proteins, invasive enzymes, haemolysins, exfoliative toxins, enterotoxins, and super antigens are all virulence factors of..?
Staphylococcus aureus.
Which bacterial species colonises the female genital tract and can cause chorioamnionitis in pregnancy?
Streptococcus agalacticae (GBS)
Can also cause neonatal sepsis and meningitis!
Capsules that resist phagocytosis, M proteins which inhibit complement activation, exotoxins, and pneumolysin are all virulence factors of..?
Streptococcus species.
S. pyogenes has the exotoxin and M protein.
Apart from Necrotising fasciitis, streptococcal infections are characterised by what?
Diffuse interstitial neutrophilic infiltrates with minimal host tissue destruction.
Diphtheria:
- Type of bacteria
- Transmission.
- Clinical manifestations
- Gram positive rod with clubbed ends
- Passes in aerosol or through skin exudate
- Causes life threatening disease via AB exotoxin which blocks host cell protein synthesis.
Listeriosis:
- Type of bacteria
- Transmission.
- Clinical manifestations
- Gram positive, facultative IC bacillus
- Food borne
- Causes sepsis and meningitis in elderly, immune suppressed, and placental infections in pregnant women
Neisseria meningitidis:
- Type of bacteria
- Transmission.
- Clinical manifestations
- Gram negative diplococci
- Colonise the oropharynx, pathological species are those not previously encountered by immune system.
- Causes bacterial meningitis
Adhesive pili which undergo genetic recombination, OPA proteins, and an anti-phagocytic capsule are virulence factors of..?
Neisseria gonorrhoea.
What are the virulence factors of Pseudomonas aeruginosa?
Gram negative bacillus
Endotoxin
Exotoxin A similar to Diphtheria’s
Pili and adherence proteins
Phopholipase C which lyses RBS and surfactant, and elastase that degrades IgG and ECM
Iron containing compounds which are toxic to endothelial cells
Diagnosis of TB can be made by:
Identifying AFB in sputum or tissue
Culture from sputum or tissue
PCR (highly sensitive)
What type of bacteria is Syphillis?
Treponema pallidum is a gram negative spirochete with flagellum. It has an outer sheath membrane which may mask it from the immune system.
What are the common causative organisms in head and neck abscesses?
Prevotella and Porphyromonas are the usually anaerobes, while S. aureus and S. pyogenes are the typical facultative aerobes.
What are the common causative organisms in abdominal abscesses?
Bacteroides fragilis and Peptostreptococcus and Clostridium are the common anaerobes.
Typically mixed with a facultative E. coli.
What are the common causative organisms in female genital tract abscesses?
Prevotella as the anaerobe
Facultative E. coli or GBS.
Which organisms produce gas gangrene?
Clostridium perfringins and septicum. These species may also cause food poisoning, and small bowel infection in neutropenic patients.
What are the characteristics of gas gangrene?
Marked edema Necrosis of tissue Gas bubbles Haemolysis Thrombosis WITH MINIMAL INFLAMMATION!
How does Clostridium tetani neurotoxin work?
Blocks the release GABA
How does Botulism toxin work?
Blocks the release of Ach.
Sphingomyelinase and phospholipase are both produced by which species?
Both are components or activities of alpha-toxin. One of 14 toxins secreted by Clostridium perfringins!
Name the 2 glucosyl transferase toxins secreted by C. diff:
Toxin A - stimulates chemokines
Toxin B - causes cytopathic effect and is the toxin tested for in stool specs.
What type of bacteria is Chlamydia trachomatis?
A small, obligate intracellular gram negative bacteria.
Rickettsial infections:
- Type of bacteria
- Transmission.
- Clinical manifestations
Rickettsial infections are gram negative bacilli transmitted by arthropods.
They primarily infect endothelial cells causing swelling, thrombosis, and necrosis. Epidemic typhus is spread by body lice. (Haemorrhagic) Rocky Mountain spotted fever is spread by dog ticks.
Adhesins
Invasive enzymes
Catalases
Adenosine which blocks neutrophil function
And biofilm formation are virulence factors for which organism?
Candida albicans
Which patients are affected by Cryptococcus neoformans?
Rarely, healthy individuals will form a solitary granuloma after C. neoformans infection.
Typically affects immune suppressed patient with AIDS, polyendocrinopathies, steroids, malignancies, leukaemia.
What sort of lesions does Cryptococcus neoformans produce?
In immune suppressed patients, lesions involve the brain, creating soap bubble cysts occasionally with no inflammatory response.
What is aspergillosis?
What diseases can it cause?
An ubiquitous mould transmitted by airborne conida. It causes allergy in normal patients and severe sinusitis, pneumonia, or invasive disease in immune compromised hosts.
What are the main virulence factors for A. fumigatus?
Adhesion to surfactant, albumin, and the ECM.
Antioxidant defences
Phospholipases, proteases, and aflatoxin.
What gives rise to P. falciparum’s greater pathogenicity?
- Affects erythrocytes of any age
- Causes clumping
- Induces high levels of cytokines
- Constantly changes surface proteins
Life cycle of malaria?
- Sporozoite get into blood. Attach to hepatocytes via thrombospondin and properdin receptors. Mature into schizonts.
- Schizonts multiply rapidly, merozoites are released from lysed hepatocyte.
- Merozoites bind to RBC via glycophorin, undergo development.
- Trophozoites divide to form schizonts that form new merozoites.
- Some trophozoites become gametes for further infection.
What causes Hydatid disease?
How to the cysts develop?
Ingestion of food contaminated by dog or fox faeces. The faeces contain the eggs of Echinoccocus granulosus.
Eggs hatch in the duodenum and invade the liver, lungs, or bones, where they form cysts.
Where does Schistosomiasis originate from?
How to they infect humans?
Fresh water snails.
Larvae penetrate human skin, migrate through vasculature and settle in the pelvic or portal systems.
How does Schistosomiasis escape humans?
By shedding eggs which disseminate and use inflammatory response to penetrate mucosa into bladder or bowel.
Urinary schistosomiasis is associated with?
Bladder SCC.
Lesions in which negligible polymorph infiltration accompanies extensive tissue injury include:
Clostridial myositis
Cryptococcus neoformans meningitis
Tuberculous lymphadenitis.
What is pneumocystis carinii?
A fungal infection which causes extra cellular infection of the lung in immune compromised patients.
There is generally no recognisable inflammatory response.
