Clinical Microbiology 2 Flashcards
Describe the treatment regimen used for TB
6 month course of combination antituberculent therapy;
- Rifampicin - Bacteriocidal to slow replicating organisms in necrotic foci
- Isoniazid - Bacteriocidal to fast growing mycobacteria
- Pyrazinasmide - Bacteriocidal even against slow growing mycobactria intracellularly
- Ethambutol - Bacteriocidal against slow growing mycobacteria
NB: P+E removed after 4 months
Describe the structure of a granuloma
Central caseous necrosis surrounded by epithelioid macrophages, which are in turn surrounded by lymphocytes
What is the common cold?
Most colds are caused by the Rhinovirus (RNA virus) but can also be caused by corona viruses (RNA viruses)
What is pharyngitis?
An inflammatory condition of the pharynx and/or tonsils. It is common in children and teenagers but tends to resolve in 3-7. The most common cause is the adenovirus (DNA virus)
What is croup?
A distinctive cough that occurs in children which is caused most often by the parainfluenza virus which causes inflammation of the larynx
What is bronchiolitis?
A common viral LRTI in children that causes a runny nose, dry wheezy cough and difficulty breathing. It is caused by the Respiratory Syncytial Virus (RSV) which causes the bronchioles to become inflamed and plugged with mucus
Describe the classification of the influenza virus
A - Can cause epidemics and pandemics
B - Will not cause a pandemic
C - Causes a mild infection
Further categorised by Haemagglutinin and Neuraminidase e.g. H1N1
What is antigenic drift?
In antigenic drift of the influenza virus there are continuous point mutations in the haemagglutinin receptor that is used to bind to human cells
Describe the vaccination used for influenza
2 types;
- Inactivated;
- 2 A types
- 1 B type
- Live; nasal spray for children
What is antigenic shift?
The process by which influenza pandemics occur;
1) Animal containing the virus can infect an intermediate host which passes on to humans
2) A mixture of genetic material of viruses in multiple species is passed on to humans
3) A strain from an animal that is passed directly on to a human
Describe the CURB65 tool used in pneumonia
C - Confusion U - Urea >7 R - Respiratory rate >30 B - BP; diastolic <90 65 - Age 65+
If the patient has 2 or more points then they are likely to have severe pneumonia
Describe the SIRS criteria used to assess a patient for sepsis
- Temperature 38°C
- Heart Rate >90bpm
- Respiratory Rate >20/min
- White Blood Cells 12
If the patient has two or more points then they have sepsis
What are the most common congenital infections?
T - Toxoplasma O - Other (syphillis, HIV, chickenpox etc.) R - Rubella C - Cytomegalovirus H - Herpes Simplex
Describe passive immunisation
Transmission of immunoglobulins .g. hepatits immunoglobulins. However this is a short term immunisation so lifelong immunity does not occur
Describe active immunity
Transmission of the antigen to allow the body to develop its own life long immunity
What are live attenuated vaccines?
e.g. Polio
Contains a version of the living microbe which has been weakened so that it cannot cause disease. Weakened by growing inside a chicken embryo so that the microbe is adapted to dividing in chicken cells
What are the advantages and disadvantages of live vaccines?
Advantages;
- Closest to natural infection so strongest immune response
- Life long immunity after 1 or 2 doses
Disadvantages;
- Could become virulent
- Cannot be given to the immunosuppressed
What are inactivated vaccines?
e.g. Influenza
Contains a microbe which has been inactivated by chemicals (e.g. formaldehyde), heat or radiation. This destroys the genetic material therefore preventing it from being able to replicate
What are the advantages and disadvantages of inactivated vaccines?
Advantages; - Cannot revert to virulent form - Can be used in immunosuppressed - Easy to store Disadvantages; - Elicits weaker immune response - Life long immunity is not always achieved so boosters may be required
What are toxoid vaccines?
e.g. Tetanus
In some infections, it is not the bacteria that causes infection, but the toxins it produces. These toxins can be inactivated using heat, chemicals or radiation
What are the advantages and disadvantages of toxoid vaccines?
Advantages; - Toxoids cannot become virulent - Easy to store - Individual cannot infect others Disadvantages; - Requires adjuvants and boosters - Local reactions at injection sites
What are subunit vaccines?
e.g. Hepatitis
A subunit contains only the antigens of the microbe that is being vaccinated against. Some vaccines may only contain a specific region of the antigen
What are the advantages and disadvantages of subunit vaccines?
Advantages; - Antigens cannot become virulent and cause disease - Easy to store - Individual cannot infect others - Can determine whether the person has been vaccinated Disadvantages; - Requires adjuvants and booster doses - Local reactions at the injection site
What are conjugate vaccines?
e.g. Haemophilus Influenza Type B
Some bacteria possess a polysaccharide coat which disguises its antigens from the immature immune system. A conjugate vaccine contains carrier proteins that are attached to polysaccharides to allow the immune system to recognise them
What are the advantages and disadvantages of conjugate vaccines?
Advantages; - Cannot become virulent and cause disease - Easy to store - Individual being vaccinated cannot infect others Disadvantages; - Requires adjuvants and booster doses - Local reactions at injection site - Expensive
What is gonorrhoea?
A gram negative, intracellular diplococci
Describe the T spot test
1) Blood sample is centrifuged
2) The middle layer is comprised of Peripheral Blood Mononuclear Cells
3) The sample is diluted and added to wells coated with IFN-γ antibodies
4) Wells are incubated
5) TB codes for proteins; 2 of which are used to challenge the T-cells in the blood
6) If challenged, T cells release IFN-γ
7) When washed with substrate solution the wells have spots at the bottom
Describe the classification of chlamydia
Types D to K cause genital chlamydia, however there are also L types which can cause LGV; an infection of the lymphatics which can lead to many symptoms such as rectocolitis
What treatments are used for chlamydia?
Genital chlamydia - Azithromycin
LGV - 3 weeks of doxycycline
Describe the natural history of syphilis infection
1) Exposure
2) Primary lesion - Chancre (3 weeks)
3) Secondary lesion - Rash (8-16 weeks)
4) Latent syphilis
5) Tertiary syphilis - CVS, neurological etc. (10-40 years)
Describe the treatment used for syphilis
Intra-gluteal injection of Bicillin
Describe the treatment of HSV
Acyclovir - A 5 days course of treatment which requires 5 tablets a day
What is Chronic Granulomatous Disease?
An inherited disorder which tends to be X-linked. This causes a defect in the gene coding for NADPH oxidase and so the patient will have few oxygen radicals and defective intracellular killing. This leads to recurrent bacterial and fungal infections
What are the three phases of infection following a solid organ transplantation?
<1 month - Surgical Infection e.g. E. Coli
1-6 months - Opportunistic Infections e.g. Aspergillus
6 months - Community acquired infection e.g. pneumococcus, listeria, salmonella
Describe the treatment used for neutropenic sepsis
- Pipericillin
- Tazobactam
- Gentamicin
What is Varicella Zoster?
A herpes virus that causes chicken pox and in the elderly it will cause shingles. In the immunocomprimised it may disseminate e.g. to the eCNS
What is Cytomegalovirus?
A herpes virus which causes a mild illness that may be asymptomatic or glandular fever. In the immunocomprimised this infection will be far more severe with increased risk of bacterial infection
What is Epstein Barr Virus?
A herpes virus that causes infectious mononucleosis in most patients, however in the immunocomprimised, malignant disease can arise
What are adenoviruses?
Adenoviruses are a huge family of viruses that can cause a wide range of complications in the immunocomprimised including hepatitis, nephritis and colitis
What are polyomaviruses?
Around 90% of people will have polyomavirus lying dormant in their urinary tract and kidney, however this doesn’t become a problem until we are immunocomprimised, at which point it may cause haemolytic cystitis
What are the two main types of immunodeficiency?
Primary - (Congenital) Resulting from genetic defects which are inherited
Secondary - (Acquired) As a result of other diseases or conditions
What are the main types of primary immunodeficiency?
- Humoral defect (50%) - B Cells and antibodies
- Combined humoral and cellular immunodeficiencies (20%) - B and T cells
- Cell mediated defect (10%) - T cells
- Phagocytic dysfunction (18%) - Granulocytes
- Complement deficiency (2%)
What are humoral defects? (Immunodeficiency)
A lack of antibodies e.g.
- IgA deficiency
- Hyper IgM syndrome
What are cell mediated defects? (Immunodeficiency)
T cells fail to provide sufficient signals to the B cells e.g.
- Severe Combined Immunodeficiencies (SCID) - A mutation in the cytokine receptors. This causes the T cells and NK cells to fail which means the B cells cannot efficiently produce antibodies
What are phagocytic defects? (Immunodeficiency)
A problem with the number and or functioning of the phagocytes e.g.
- Chronic Granulomatous Disease
