Infection Flashcards
List the 5 categories of micro-organisms that cause infection.
Bacteria, virus, fungi, parasites, prions
List 4 sterile sites.
Blood, CSF, lung, bladder
List 4 non-sterile sites
skin, nasopharynx, urethra, gut
list 4 methods for collection of bacteria
mid-stream urine, sputum, throat swab, wound swab, faeces, blood culture, CSF
Describe tests used for diagnosis of bacterial infections.
gram staining and microscopy, culture (non-selective or selective)
Name a type of non-selective media.
Blood agar (show yellow staph aureus) and chocolate agar (i.e enriched medias)
Name a type of selective media.
MacConkey’s (grow gram negative and inhibit gram positive)
Name a sensitive test for the diagnosis of bacterial infection.
Culture (microscopy is not sensitive)
What is ZN stain/auramine used for?
Mycobacteria
What are the 4 main methods used to identify a virus?
- Molecular methods (e.g real-time PCR)
- Antigen detection
- Serology
- Electron microscopy (rarely used now)
What are the diagnostic principles in parasitology?
- Microscopy (parasite, cysts or ova in faeces or blood films for malaria)
- Serology sometimes useful e.g when parasite in deep tissue
- Culture rarely possible
What colour is a gram positive stain?
Purple
What colour is a gram negative stain?
Pink
What shape are cocci?
Spherical
Which bacterial cell wall contains more peptidoglycan?
Gram positive bacteria
Which bacterial cell wall contains lipopolysaccharides?
Gram negative bacteria
What is the function of penicillin binding proteins?
Essential for cell wall synthesis by forming cross-links and also illicit a strong immune response.
How many chromosomes does a typical bacterial cell have?
One single chromosome (no nucleus)
Plasmid = extra chromosomal entities, involved in gene transfer (conjugation).
Describe the capsule.
A virulence factor which helps bacteria to survive the host environment by preventing phagocytosis and desiccation.
What is the function of flagella and describe the 4 different types?
Motility of bacteria.
Monotrichous, Amphitrichous, Lophotricous, Peritrichous
Describe a bacteriophage.
Virus that infects and replicates within a bacterium.
When are spores formed?
When no nutrients are available and adverse environmental conditions exist (ensuring survival of bacterium through periods of stress)
What is the genus and species of Staphylococcus aureus?
Staphylococcus = genus Aureus = species
Describe how bacteria replicate and create genetic variation.
Binary fission (asexual reproduction) - transformation, transduction and conjugation. Produces identical progeny.
Name the three main groups of parasites.
- Protozoa
- Helminths
- Arthropods
Give an example of a protozoa.
Malaria (human and arthropod phases)
- mosquito - sporozoite - liver to mature - merozite - invade RBC - take up by mosquito
Give two extra examples of protozoa.
- Amoebae ( amoebic dysentery)
2. Flagellates
Name the three main types of helminths and provide an example of each.
- Nermatodes (round worms) e.g Ascaris Lumbricoides
- Cestodes (tapeworms) e.g Echinococcus
- Termatodes (flat worms) e.g schistosomiasis
Give examples of Arthropods
- Lice
- Ticks
- Mice
Describe the common diseases caused by enteric parasites.
Helminth infections (Ascaris Lumbricoides, Echinococcus, Schistosomiasis)
Describe the common blood-borne/vector-borne parasites.
Protozoa infections (Malaria, Chagas, Leishmanaiasis, Toxoplasmosis, Trypanosomiasis)
Define parasite.
An organism that lives within another organism and gets food at the expense of the host. Simple organisms however, more complex than bacteria.
Explain the structure of fungi.
- Lacks chlorophyl
- Forms spores
- Cell wall contains polysaccharides (chitin or glycan)
- Membrane contains ergosterol
Describe the 3 major types of fungi.
- Moulds - Zygomycetes e.g Aspergillus
- Yeasts - Astromycetes e.g Candida
- Mushrooms - Basidomycetes e.g Cryptococcus
Name three fatal systemic diseases caused by fungi acting as opportunistic pathogens.
- Candida (infect deep organs e.g after surgery or burns)
- Aspergillus (infect deep organs and strongly angioinvasive e.g after chemo)
- Cryptococcosis (pulmonary cryptococcosis or meningitis)
Give examples of dermatophytic fungal infections (non-fatal)
E.g by microsporum, tricophytob causing athletes foot, thrush, pityriasis versicolour
Describe host factors that contribute to pathogenicity of fungal infections.
- Warm and moist micro-environments.
- Broad-spectrum antibacterial agents
- Immunosuppression by iatrogenic causes, disease processes OR a combination of both.
Describe the diagnostic methods for detecting fungi.
- Direct detection (histopathology, high-res CT)
- Direct smear
- Growth on selective media
- Serology
- Fungal antigen detection
- PCR
- Culture for normal sterile sites
What is the route of administration for anti-fungal drugs?
IV, topical or oral (static or cidal)
What is the function of Polyenes?
Anti-fungals - target membrane
Give two example of a polyenes.
Amphotericin B and Nystatin
What is the function of Azoles?
Anti-fungal - targets sterols
Give an example of an azalea.
fluconazole, clotrimazole
What is the function of Echinocandins?
Anti-fungal - targets cell wall e.g anidulafungin
Name the 3 main anti-fungal agents.
Polyenes, Azoles, Echinocandins
What is the function of Flucytosine?
Anti-fungal - targets DNA synthesis (used in combination with one of the three main anti-fungals)
How are viruses classified?
According to: vision shape, presence/absence of envelope, genome structure, mode of replication
Describe the characterisation of viruses.
Small, non-cellular, icosahedral, obligate intracellular pathogens, tissue tropism
List 5 of the main viruses.
- Hepatitis B and C - chronic infection, hepatocellular carcinoma, blood-borne, sexual or vertical transmission.
- HIV - chronic infection, blood-borne, sexual or vertical transmission, causes lymphadenopathy
- Measles - long-term immunity, airborne, respiratory conditions
- HPV - transformation , cervical, anal and oesophageal cancers.
- Herpes simplex - viral latency, oncogenic potential e.g Herpes simplex 8 causes Kaposi’s sarcoma, close-contact transmission.
What does a virus use to reproduce?
Virion associated polymerase
Describe the 4 steps of virus replication.
- Entry
- Replication
- Latency
- Shedding
What can cause recombination and generation of a new strain?
Transmission of novel virus to humans or co-infection of humans and animal/bird strains in one organsim.
What is the pro for having a virus that only replicates in humans?
Easier to eradicate
Describe the 4 consequences of viral infection.
Clearance, Chronic Infection, latent infection, transformation
Explain viral latency.
Following primary infection, some viruses lie dormant and full viral genome retained in host with expression restricted. Reactivation may occur (risk in immunocompromised)
Describe how virus have oncogenic potential.
- Increase cell proliferation
- Prevent apoptosis
- ROS mediated damage
What cancer can EBV cause?
Burkitt’s lymphoma
What cancer can Herpes 8 cause?
Kaposi’s sarcoma
What cancer can HPV cause?
Cervical cancer
What cancer can Hep B and C cause?
Hepatocellular carcinoma
How do anti-virals function?
Virtuistic and not virucidal (stop viral replication)
What are the indications for anti-virals?
Prophylaxis, pre-emptive therapy, overt disease, suppressive therapy
How do you prevent viral infections?
immunisation, anti-natal screening, blood/tissue/organ screening, infection prevention and control procedures, prophylactic treatment post-exposure.
Define pathogen.
An organism which CAUSES disease.
Define commensal.
An organism which is part of the NORMAL FLORA.
Describe features of viral pathogenesis.
Cell destruction e.g death of CD4 cells by HIV, virus-induced changes to cellular gene expression
List the cells involved in the innate immune system.
Natural killer cells, macrophages and polymorphs (eosinophil, neutrophil, basophil)
List the cells involved in acquired immunity.
Humoral (antibodies - mostly bacterial infections) or cell mediated (T cells - mostly viral infections), B lymphocytes differentiate to plasma cells.
Define colonisation.
Bacteria grow on body sites without causing infection.
Define latent.
The ability of pathogenic virus to lie dormant.
Define asymptomatic disease.
Carrier of disease infection, no symptoms. Also known as ‘sub-clinical infection’.
Define the features of clinical infection.
Inflammation, pain, pyrexia, tachycardia, riggers, high WBC count, high CRP.
Define pathogenicity.
The CAPACITY of an organism to cause infection.
Define infectivity.
Ability to become established.
Define virulence.
Ability to cause harmful effects once established.
Describe exotoxins and give an example.
Released extracellularly by micro-organisms e.g tetanus
Describe enterotoxins and give an example.
Exotoxin which act on GI tract e.g cholera.
Describe endotoxin.
Part of gram negative cell wall - lipopolysaccharide e.g Neisseria meningitides.
Describe the sites of viral entry.
Skin, conjunctiva, respiratory tract, urogenital tract, alimentary tract, capillary, arthropod.
Describe features of acute inflammation.
Localised to specific site, development of viraemia with widespread infection of tissue e.g influenza A, enterovirus.
Define antigenic drift.
Minor changes over time to generate antigenic variants.
Define antigenic shift.
Abrupt major changes, non-human hosts play a key role.
Name the two main types of gram positive cocci and describe shape.
Staphylococci (clusters) & Streptococci (chains)
Name the gram positive, anaerobic, spore-forming bacilli.
Clostridium species
What test is used to distinguish between staphylococci?
Coagulase test (positive = staph aureus, negative = staph epidermis)
What test is used to distinguish between streptococci?
Haemolysis (alpha/partial = strep pneumonia, GREEN and beta/complete = step progenies)
Name two gram positive bacteria used in biological warfare.
Clostridium botulinum and bacillus anthrax.
Name a gram negative cocci.
N.gonorrhoea and N.meningitidis
Name the gram negative cocco-bacilli.
Haemophilus influenza.
Name a curved gram negative bacilli
Campylobacter, vibrio and helicobacter species.
What distinguishes gram negative aerobic bacilli?
Lactose fermenters (E.coli) or non-lactose fermenters (pseudomonas and salmonella spp)
Name a gram negative anaerobic bacilli.
Bacteriodes (part of normal colonic flora, causes intra-abdominal abscess which needs draining)
Give two examples of an acid and alcohol fast bacilli.
Mycobacterium Tuberculosis and Mycobacterium Leprae
Give an example of a spirochaetes.
Treponema (syphillis), borrelia and leptospirosis.
Give an example of miscellaneous.
Chlamydia
Describe the principles of active immunisation.
Natural (exposure/infection) and artificial (vaccine - antigen stimulates response, with memory and specificity)
Describe the principles of passive immunisation.
Natural (using neonatal Fc receptor) and artificial (snake/spider bites etc, hypogammaglobulinaemia infusion of gamma globulins to decrease infection, specificity but no memory)
Name the three types of vaccines available.
- Conventional (killed whole e.g polio or attenuated e.g BCG)
- Subunit (purified Ag e.g HPV)
- Toxoid (modified toxin e.g Tetanus)
Define vaccination.
The administration of antigenic material to stimulate an individual’s immune response to develop adaptive immunity to a pathogen.
Describe temporary contra-indications to vaccine.
Febrile illness and pregnancy
Describe permanent contra-indications to vaccine.
Allergy and immunocompromised
Describe herd immunity.
Decreased risk to unvaccinated individuals due to vaccination schedules where the majority of people are vaccinated and less likely to carry the infection.
At what age does the childhood vaccination schedule begin?
2 months (DTP, polio, haemophilia influenza B, strep pneumonia and rotavirus)
What are the non-routine vaccinations at birth?
BCG and Hep B.
List 5 vaccines that may need to be given to travellers.
Hep A, typhoid cholera, yellow fever, Japanese encephalitis, rabies
What can an ELISA be used for?
Measure antigen or antibody in serum.
What type of organisms are resistant to phagocytosis?
Capsulated organisms e.g pneumococcus.
Name an organism which is resistant to chlorination.
Cryptosporidium parvum (filtration needs to be carried out).
What are the outcomes of colonisation and clinical infection determined by?
Host immune system and virulence factors.
Does the differing ribosomes of mammalian and bacterial cells allow selective toxicity?
Yes.
Do third generation cephalosporins (eg, ceftazidime) have better anti-staphylococcal activity than the earlier cephalosporins?
No. First generation do.
Does piperacillin have an extended spectrum and active against Pseudomonas species?
Yes
Do bacterial exotoxins act as virulence factors?
Yes
What are microglial cells?
Specialised macrophages occurring in the brain.
