Introduction to Infectious Disease Flashcards
What are some mechanical lines of defence against pathogens?
Physical barriers (ex. skin)
Chemical barriers (stomach acid)
Mucus and cilia protect our respiratory tract
Urine flushes out bacteria from our urinary tract
Other bacteria are present on our skin and within our digestive system
What cells are in the innate immune system and what are their roles?
Innate Immune System:
Macrophages and monocytes (antigen-presenting cells and surveillance)
Neutrophils (defense against bacteria and fungus)
Eosinophils (defense against parasites and response to allergies)
Basophils (respond to allergies)
What cells are in the adaptive immune system?
T- and B-lymphocytes. These cells are very specific in their targeting and are able to remember pathogens via memory cells.
The adaptive immune system can also be broken into two parts:
Humoral mediated (within the serum)
Cellular mediated (within the cells)
Describe T-lymphocytes in further detail
T-lymphocytes are activated by an antigen-presenting cell (macrophages and monocytes)
Activated T-lymphocytes recruit other dormant T-lymphocytes
Activated T-lymphocytes are differentiated into the following groups:
Helper cells/CD4+ (secrete interleukins and interferons. Helper cells also stimulate CD8+ cells and production of antibodies
Cytotoxic cells/CD8+ (kill cells recognized as foreign)
Regulating cells (regulates the T-lymphocyte response)
Describe B-lymphocytes in further detail
B-lymphocytes are activated once an antigen is detected, often with help from T-lymphocytes
Activated B-lymphocytes are differentiated into two groups:
Plasma cells (secrete antibodies)
Memory cells (important in future attacks)
Antibodies bind to antigens, effectively trapping the antigen or clumping them together
What is an infection?
A response of host immune systems and person gets ill
ex. pneumonia
What is a sub-clinical infection?
A specific response in the body is evoked (antibody production), but person is not ill. The host does not become ill because the immune system is able to fight off the pathogens early
What is colonization in terms of pathogens in the body?
Presence of organism at a body site without production of disease
ex. skin wounds colonized with staph
How do pathogens cause disease?
Simple invasion of the microorganism can trigger immune responses. These immune responses can be perceived as illness
Some pathogens may elaborate toxins that can directly damage cells (it almost become more important to deal with the toxins before the pathogens themselves)
ex. Botulinum toxin, tetanus, staph aureus food poisoning
What bacteria are found in typical skin microbiota?
Diphtheroids (ex. Corynebacterium sp.)
Propionibacteria (P. acnes)
Staphylococci (especially coagulase-negative strains)
Streptococci
What bacteria are found in typical GI tract microbiota?
Bacteroides sp.
Clostridium sp.
Diphtheroids
Enterobacteriaceae (ex. E. coli, Klebsiella sp.)
Fusobacterium sp.
Streptococci (anaerobic)
What bacteria are found in typical upper respiratory tract microbiota?
Bacteroides sp.
Haemophilus sp.
Neisseria sp.
Streptococci
What bacteria are found in typical genital tract microbiota?
Corynebacterium sp.
Enterobacteriaceae sp.
Lactobacillus sp.
Mycoplasma sp.
Staphylococci
Streptococci
Is the host defence (innate and adaptive immune system) important in curing infections?
Yes, it is the most critical aspect of curing an infection
Are antibiotics always effective in treating susceptible infections?
No, especially if the immune system is not operating normally
For better efficacy, the following procedures can be used:
Drainage of abcess
Removal of dead tissue (dead tissue has no blood supply; therefore antibiotics cannot reach these tissues)
Removal of foreign bodies or prosthetic devices (infections develop on these objects and will often develop biofilms)
Decrease in immune impression therapy (ex. transplant patients have to ease off on immunosuppression drugs in order to fight off an infection, risking organ transplant rejection)
What factors weaken host defense?
Malnutrition
Extremes of age
Immune globulin deficiencies
Deficiencies in cellular immunity
Alcoholism
Diabetes
Immunosuppressive therapy (anticancer drugs, corticosteroids, transplant drugs)
Invasive procedures
What are some clinical manifestations of infection?
- non-specific symptoms (malaise, loss of appetite, headaches, myalgia, arthralgias)
- Fever (due to infection unless proven otherwise)
- White Blood Cell counts (Normal range is 5-10 10^9 cells/L, but anything over 1010^9 cells/L could be an infection)
- Other non-specific manifestations (anemia, increased ESR and C-reactive protein (CRP) values in blood work, increased procalcitonin, increased heart rate, anxiety, and confusion)
- Septic Shock (decreased BP, CO, and blood O2, decreased renal and hepatic function)
How are infections diagnosed?
- History (signs and symptoms, source of infection, likely pathogen)
- Physical Examination (will be different for each infection, but the goal is to localize the infection) ex. neck stiffness in meningitis
- Laboratory (WBC and differential, ESR and CRP, renal and hepatic function, electrolytes, microbiology(gram stain, culture and sensitivity testing) )
How are gram stains useful in determining pathogen responsible for infection?
This test can divide all bacteria into 2 main groups (gram+ and -) by colour alone. Staining also reveals the structure (cocci vs. bacillus) and it can also stain WBC (an indicator for the body’s response against an infection).
Some bacteria like the ones that cause TB do not stain well
Unfortunately, viruses are far too small to be visible or stained using this technique.
How are laboratory cultures useful in determining pathogens responsible for infection?
This is the best method for revealing the pathogen causing the infection. Gram stains cannot provide an exact species, while culture tests can.
The organism is grown in different environments and its biochemical profile is determined.
We also need to be aware of possible contamination issues
What is MALDI-TOF MS and how is it useful?
MALDI-TOF MS is a technique that vapourizes bacterial samples with laser. The ionized proteins and macromolecules are analyzed by a computer and can determine the microorganism in the sample. This technique is a version of mass spectrometry applied to biological study
How is sensitivity testing useful in treating infections?
These tests determine which antibiotics the organism is susceptible to (helps us predict resistance and prescribe accordingly)
It is based on the minimal inhibitory concentration of a given pathogen sample.
Clinically, one must take into account the site of infection and penetration of the antibiotic before prescribing any agent.
Why is immunology testing (serology) useful?
Useful when the organism cannnot be cultured or treatment has already begin
ex. Mycoplasma pneumonia is hard to grow, by we can use serology to determine pathogen from sample
What is antibody testing?
Detects precesnse of antibodies directed against the pathogen
