Plant and animal pathogens

• what is a parasite?

  • organism that lives in or on another living thing, causing harm to the host
• what role do vectors play?

  carry pathogens from one organism to another e.g. mosquito
• how might bacteria be classified into shape?

  • rod shaped (bacilli)
  • spherical (cocci)
  • comma shape (vibrios)
  • spiralled (spirilla)
  • corkscrew (spirochaetes)
• how might bacteria be classified using Gram staining?

  • by their cell wall - two main types of bacterial cell walls have different structures and react differently with Gram staining
  • Gram positive bacteria - purple/blue under light microscope
  • Gram negative bacteria - red under light microscope
  • this is helpful as you can see which type of cell wall affects how bacteria reacts with antibiotics
• why is gram-staining classification useful for the treatment of disease?

  helps identify which antibiotic will be affective depending on the type of cell wall of the bacteria
• which type of bacteria are more susceptible to penicillin-based antibiotics?

  • Gram-positive - thicker layer of cell wall of peptidoglycan which is easier to disrupt, penicillin causes punctures in cell wall
• what is the basic structure of a virus?

  • 0.02-0.3 micro meters in diameter
  • smaller than bacterium
  • some genetic material (DNA or RNA) surrounded by protein
• how do viruses replicate themselves?

  • invade living cells, where virus genetic material takes over biochemistry of host cell to make more viruses
  • reproduce rapidly and evolve by developing adaptations to their host, making them successful pathogens
• what is bacteriophage?

  • viruses that attack bacteria
  • takes over bacterial cells and use them to replicate, destroying bacteria at the same time
• what are positives of using bacteriophages?

  • specific to certain bacteria - once gone they die
  • less side affects
  • can mutate to stop immune system destroying them
• what are negatives of using bacteriophages?

  • still in experimentation
  • could evolve and attack good bacteria/human cells
  • immune system may try to destroy before they've done their job
• what are fungi?

  eukaryotic organisms that are often multi-cellular, although the yeasts which cause human diseases such as thrush are single-celled
• how do most fungi feed?

  • can't photosynthesise
  • digest their food extracellularly before absorbing nutrients
  • many are saprophytes meaning they feed on dead and decaying matter
  • some are parasitic, feeding on living plants and animals
• how can fungi cause disease?

  • fungal injections affect leaves of plants, stopping them photosynthesising and so can quickly kill the plant
• • fungi produce millions of spores which can spread a huge distance through water and air
• how do protocista cause disease?

  • they use people or animals as their host organism
  • may need a vector to transfer them to their hosts
  • may enter body directly through polluted water
• how do viruses directly damage hosts?

  • take over cell metabolism
  • genetic material gets into host cell and is inserted into host DNA
  • virus uses host cell to make new viruses, which burst out of cell, destroying it and spreading to other cells
• how do protoctista damage host cells directly?

  • some take over cell and break them open
  • do not take over genetic material of cell
  • digest and use cell contents as they reproduce e.g. malaria
• how does fungi directly damage host cells?

  • digest living cells destroying them
  • combined with response of the body to the damage caused by fungus gives the symptoms
  • produce toxins which affect host cell and cause disease
• how do bacteria damage host cells?

  • produce toxins that poison or damage host cells causing disease
  • toxins break down cell membranes
  • damage or inactivate enzymes
  • interfere with host cell genetic material so cells can't divide
• what is tuberculosis?

  • bacterial
  • infects humans, cows, pigs, badgers and deer
  • damages and destroys lung tissue and suppresses immune system
  • curable by antibiotics and preventable by improving living standards and vaccination
• what is bacterial meningitis?

  • bacterial
  • infects the brain (protective membranes on surface of the brain) which can spread causing septicaemia (blood poisoning) and rapid death
  • blotchy/red/purple rash when a glass is pressed against it and doesn't disappear (symptom of septicaemia)
  • affects children/teenagers
  • cured by antibiotics (if delivered early) and vaccines can protect against some forms of meningitis
• what is ring rot?

  • bacterial
  • damages leaves, tubers and fruit (plants only)
  • disease of potatoes, tomatoes and aubergines caused by Gram positive bacterium
  • no cure, once infected a field can't grow potatoes again for at least 2 years
• what is HIV/AIDS?

  • virus
  • targets T helper cells in immune system
  • infects human and non-human primates
  • gradually destroys immune system so affected people are open to other infections, such as TB and pneumonia as well as other types of cancer
  • passed by person to person (bodily fluid, unprotected sex, shared needles, mothers to child during pregnancy)
  • no vaccine, no cure
  • anti-retroviral drugs help slow progress of disease
• what is influenza?

  • virus
  • infects ciliated epithelial cells in gas exchange system - kills them leaving airways open to severe secondary infection (e.g. pneumonia, flu)
• what is Tobacco mosaic virus?

  • virus
  • tobacco plants and tomatoes, peppers, cucumber
  • damages leaves, flowers and fruits
  • stunts growth
  • reduces yield
  • almost total crop loss
  • resistant crop strains available but no cure
• what is malaria?

  • protocista
  • spreads by bites of infected mosquitos (vector)
  • makes people weak and vulnerable to other infections
  • no vaccine and limited cures
  • preventing measures - control vector (use mosquito nets, window/door screens and wear long sleeves to prevent biting)
• what is potato/tomato late blight?

  • fungal
  • infects potato’s and tomato’s
  • hyphae penetrate host cells
  • destroy leaves, tubers and fruits
  • crop damage
  • no cure but resistant strains, careful management and chemical treatments can reduce infection risk
• what is black sigatoka?

  • fungal
  • attacks and destroys banana leaves
  • hyphae penetrate and digest cells
  • turns leaves black
  • reduces yield
  • resistant strands being developed - fungicides can help control spread
  • no cure
• what is ringworm?

  • fungal
  • infects mammals (cattle, dogs, cats, humans)
  • grey-white, crusty, infectious, circular areas of skin (not damaging)
  • anti fungal creams are effective cure
• what is athletes foot?

  • fungal
  • infects humans
  • grows on and digests warm, moist skin between toes
  • cracking and scaling which is itchy and may become sore
  • anti-fungal creams are and effective cure