Microbiology- Causes of Infection Flashcards
Define the agents that can cause infections?
- Viruses
- Bacteria
- Fungi
- Parasites
- Prions
Name a few facts about viruses?
Smaller than cellular organisms Metabolically inert Simple structure Need living host cells to replicate >1/100th size of bacteria too small to see with light microscope Different shapes Infect animals, plants and bacteria (bacteriophages)
What are the three properties on viral replication?
Viruses contain genetic material but no organelles
They rely on their host’s organelles / systems to reproduce
They use surface protein(s) to bind to a cell, insert their genetic material into it
Why do viruses infect hosts for different lengths of time?
Some can stay dormant in host – with symptoms re-appearing months or years later
What are the three examples viruses can lay dormant and appear later on in life?
Chickenpox virus- can lay dormant for decades, emerging to cause shingles
Hepatitis C virus- causes chronic liver infection over years
Rhinovirus - infects hosts for days, causing a cold
Give facts on bacteria?
Unicellular organisms
Cell membrane
Cell wall
No nucleus
Genetic material is DNA but not bounded by a membrane
Reproduce asexually
Some move using flagella and attach via fimbriae
What colour does gram +ve bacteria stain?
G+ve stain purple
What colour does gram -ve bacteria stain?
G –ve stain pink
Give 4 examples of bacterial diseases?
Meningococcal sepsis
Bacterial endocarditis
Cellulitis
Streptococcal throat infection
Define fungi?
Kingdom of their own
Eukaryotes
Cell membrane, cell wall, nucleus and cytoplasmic structures
Reproduce sexually and asexually
What is dimorphic fungi?
Diamorphic fungi (can switch between types)
What is the difference between yeast and mould?
Yeast is the infection and mould is the reproducing stage.
Give examples of yeast infections?
Mild infections
thrush, athletes foot, ringworm
Severe infections–In the Immunocompromised
Cryptococcal meningitis in HIV patients•Invasive candida in ICU–Or Immune competent
What are the different types of parasites?
Ectoparasites–live outside body Fleas, Ticks Endoparasites–Iive inside body Worms Epiparasites–a parasite which lives on another parasite Malaria (mosquito)
What are the two general classes of human parasites?
Unicellular organisms-
Protozoa
Worms- Helminths
What is giardia?
Cause bloody diarrhoea
Caught from drinking infected water
May be seen in stool under a light microsope
Cyst form aids survival + spread
What are the different types of helminth worms?
Cestodes (tapeworms) Segmented, flat Trematodes (flukes) Unsegmented, flat Nematodes (round worms) Cylindrical, have digestive tract with lips, teeth and anus
What does cestodes cause?
Tapeworms–Fish, pork, beef tapeworms Cause variety of disease: –Malabsorption –Malnutrition in chronic disease –Cysts in muscle or brain
What does nematodes cause?
Round worms Biggest of helminth family –Huge burden of disease worldwide –Diarhoea / malabsorption Problems often caused because worms are not “usual” human parasites–E.g. Elephantiasis
Define prions?
Smallest infective agents known
Proteinaceous Infectious particles
Lack nucleic acid - not a ‘living organism’
Proteins fold abnormally and accumulate, mainly in neural tissue
They are very difficult to destroy
Concerns over cleaning surgical instruments
What are the different types of prion diseases?
CJD- fatal, degenerative neurological disease
–Affects 1 in a million people each year
–Transmitted through contaminated human growth hormone, surgical instruments and corneal grafts
•Variant CJD- typically occurs in young adults
•BSE- occurs in cattle
•Scrapie- occurs in sheep
•Kuru- similar to vCJD, –occurred in Papua New Guinea in 1950s–thought to be spread by cannibalism
What are the growth requirements for microorganisms to reproduce?
Nutrient provide the necessary elements such as carbon, hydrogen, oxygen and nitrogen (CHON)
Microbes are very successful in obtaining nutrients from variety of sources. This helps them inhabit all possible environments
Growth and reproduction require synthesising new molecules.
Energy is needed to build those molecules.
Define the differences between anabolic and catabolic metabolism?
Catabolic pathways
Break down molecules to produce energy. (lerger substrates, smaller products)
Anabolic pathways
§Use energy to combine small molecules into macromolecules (energy+ source of elements espcially carbon)
What are the three entry of molecules into a cell?
Passive Diffusion: No energy needed. Driven by concentration gradient.
Active Transport: requires energy. Requires recepters and work even against concentration gradient.
Group Translocation: less energy, involved phosphorylation of the molecule.
What affect does temperature have on growth?
Temperature affect protein structure and fluidity of the cytoplasm and the cytoplasmic membrane.
Minimum growth temperature: lowest temperature that a given organism can carry out its metabolic activities
Maximum growth temperature
Optimum growth temperature: temperature at which metabolic activity is at its peak and thus growth rate is the highest.
define water activity Aw?
Water activity (Aw): the vapour pressure of a sample divided by that of pure water at the same temperature.
How does the pH affect growth?
PH effect: High or low PH inhibit microbial growth except for few!
Acidic conditions are body defense mechanism e.g. stomach and vagina (via fermentation by normal flora)
Acidophiles can tolerate acidic conditions. Some are obligate acidophiles
Alkalinophile lives in alkaline media like soil and alkaline water (e.g. Vibrio cholerae).
In both, interacellular PH is near normal
Define the different O2 requirements ?
Obligate aerobes: requires O2 for energy production (respiration)
Anaerobes : do not use O2 for energy production
Facultative Anaerobes: can survive with or without O2 Microaerophiles: can tolerate oxygen levels from 2-10% (limited ability to detoxify hydrogen peroxide and superoxide radicals)
Aerotolerant: Anaerobes but have some enzymes that detoxify oxygen’s poisonous forms.
Classification of Organisms Based on O2 Requirements
