9 The host-parasite relationship Flashcards
Metagenomics is study of host microbiome. Which includes host flora and genetic material. Microbiome is a consequence of different body areas which hare exposed to external environment.
Studied through DNA sequencing, and comparing to known databses.
When is microbiome acquired?
What factors influence this?
Rapidly during/ after birth
Age
Nutrition - e.g breast/ bottle fed
Environment
Immunodeficiency
Skin - exposed dry areas are not good for bacteria growth.
Moist areas (axillae/ scalp, toes/ perineum) support larger populations.
What are common skin commensals?
Staph epidermidis
Staph aureus
Anaerobic diptherioids - proprionibacterium acnes. Live in hair follices/ sebaceous glands. Diptherioids are all corynnebacterium which are usually non-pathogenic
Candida
What are common commensals in mouth/ teeth and nose?
Majority are anaerobes
Strep pyogenes Strep mutans - dental caries Staph Diptherioids Gram neg cocci - neisseria meningiditis
Staph/strep/ neisseria potentially pathogenic
What are common commensals in pharynx/ trachea
Respiratory tract normally quite sterile despite large intake of organisms by breathing
Streptococci Staphylocci Anaerobes Neisseria Diptherioids
PCP if immunocompromised
Stomach acid normally kills most bacteria
What bacteria can live in the stomach
Helicobacter pylori
Streptococci
What are common commensals in small and large intesitne
Streptococci
Lactobacilli
Bacterioides
Clostridium
E. Coli
enterobacteriaceae
What are common commensals of urethral tract
What are common commensals of vagina
Usually lightly colonoised
Staoh epidermidis
Strep faecalis
Diptherioids
Vagina before puberty - as above
After puberty - lactobacilli predominate, fermenting glycogen for maintenance of acid pH, preventing overgrowth of other organisms. Candida can overgrow. Trichomonas vaginalis can be present in healthy individuals
How are microbiota beneficial to host/ preventing other pathogens growing?
Skin bacteria produce fatty acids, prevent other species growing
Gut bacteria release bacteriocins/ colicins which prevent other species growing
Vaginal lactobacilli maintian acid environment which prevent other species gorwing
Sheer number of bacteria present in intestine prevent other species growing
Evidence gut bacteria produce B vitamins, and vitamin K, which are valuable if diet is deficient.
Antigenic stimulation provided by intestinal flora helps ensure normal development of immune system
Disease is not inevtiable outcome between microrganisms and humans
What are three broad species of symbiosis?
Microbes can change their relationship depending on changing factors , and can become harmful. e.g Bacteriodes, E. coli staph aureus
Commensalism - shelter and food. Bacterioides ferment digested food, but does not cause harm
Mutualism - reciprocal benefit. Bacterioides in rumen of cattle - metabolise host food to fatty acid and gas. Fatty acids used by host
Parasitism - unilateral benefit. Entamoeba histolytica feeds on gut mucosa causing ulcers and dysentery. All pathogens are parasites. Parasitism not limited to protozoa/ worms
Many organisms are parasitic. Evolution has conferred this benefit, as parasite can focus on replication, as resources are provided by host.
Viruses are completely dependent on host for all metabolic needs - obligate parasites
Why do some parasites have very specific hosts?
What are disadvantages of parasitism?
Specific binding proteins
Some parasites have complex regulatory pathways, and requiring signalling while in host. If cycle in host is complex, host can regulate/ slow replication
Parasites may die outside of host. Several have mechanisms to survive - virus particles, bacterial spores, protozoan cysts, worm eggs
Host may control replication - so not in control of replication cycle.
Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies
Elicit minimal immune response
Evade effects of response
Elicit minimal immune response - HSV has long latent period
Evade effects of response - Mycobacterium survive unharmed in granulomas
Social and behavioural changes effects infectious diseases.
What are the results of changes below:
Altered environment e.g air conditioning
Changes in food production and food handling
Routine use of antibiotics
Routine use of immunosuppressive therapy
Altered environment e.g air conditioning - legionella
Changes in food production and food handling - drug resistant bacteria. Inadequate cooking allows listeria/ salmonella to enter body
Routine use of antibiotics - MRSA
Routine use of immunosuppressive therapy - opportunistic infections - pseudomonas, candida, pneumocystis
Social and behavioural changes effect infectious diseases
What are the results of changes below:
Altered sexual habits
Breakdown of filtration systems, overuse of limited water supplies
Altered sexual habits - gonorrhoea, genital herpes, AIDS
Breakdown of filtration systems, overuse of limited water supplies - transmission of animal infection leading to diarrhoeal disease - cryptosporidioisis, giardiasis, leptospirosis
Social and behavioural changes effect infectious diseases
What are the results of changes below:
Increase in ownership of pets
Increased frequency of journeys to tropical and subtropical countries
Increase in ownership of pets - toxoplasma, toxocara, chlamydia, salmonella
Increased frequency of journeys to tropical and subtropical countries - exposure to vectors malaria
Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies
Depresss host’s response
Antigenic change
Depresss host’s response - HIV destrys T cells, malaria decreases immune response
Antigenic change - viruses, spirochaetes, trypanosomes - change antigens so host responnse is ineffective
Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies
Rapid replication
Survival in weakly responsive individuals
Rapid replication - viruses, bacteria, protozoa - producing acute infections before recovery and immunity
Survival in weakly responsive individuals - genetic heterogeneity in host populations means some hosts wont be able to provide immune response
What are Strep pyogenes (GAS) sequale?
Rheumatic fever
glomerulonephritis
Cell wall has M proteins - over 150 exist
M1/ M3 associated rheumatic fever
M12/ M49 associated with glomerulonephritis
During primary infection, antibodies develop against M proteins. These cross-react with with basement membrane of glomerulus, or myocardium
55 year old suffered abdominal trauma/ splenectomy 10 years ago, presents with fever, cough, SOB. Diagnosed CAP. Third infection this year
What is most likely organism?
S pneumoniae H Influenzae S aureus K pneumoniae Pseudomonas
H influenzae
Splenectomy increases risk of streptococci, haemophilus, neisseria meningitidis
Spleen normally removes circulating bacteria through phagocytic filter mechanism, and producing antibodies when splenic B cells become activated
Most other methods of removing bacteria require opsonisation. Bacteria that have capsules are not well opsonised, as capsules prevent antibody attachment to bacterial cell wall. However, spleen is good at removing these normally
28 year odl IVDU present severe diplopia. Then develops difficulty swallowing, slurred speech, and descening symmetrical weakness.
What is next stage of management?
IV botulinum anti-toxin
Surgical debridement of any abscesses. Can release more toxin, so should be performed following anti-toxin administration
IV benzylpenicillin
Botulinum toxin A-G exist, but human disease usually caused by A, B, E. Binds to receptors in presynaptic membrane of neuromuscular junction, resulting in muscle weakness.
