Introduction to microbiology Flashcards
What is the important of looking at a microorganism under a microscope?
Helps you to identify what microogranism is causing an infection and therefore this influences your treatment approach
What bacteria can cause pneumonia?
Asperigillus
What are the key groups of microorganisms?
bacteria (prokaryotes - biggest group), virus, fungi and parasites
2 groups of parasites - protozoa (similar to plants) and worms
Where do infections usually come from?
from ourselves = more bacterial cells than human cells - from our own flora
What are common endogenous infectious micro-organisms on the skin?
Staphylococcus aureus
Staphylococcus epidermidis
What are common endogenous infectious micro-organisms in the mouth/throat?
Viridans streptococci - can cause dental infections and also associated with endocarditis
What are common endogenous infectious micro-organisms in the gut?
Escherichia coli = aerobes
Bacteriodes species = anaerobes
What are common endogenous infectious micro-organisms in the vagina?
Lactobacilli = rarely cause infection - colonise in the vagina and protect it against infection
What is a common endogenous infectious micro-organisms in the vagina/mouth/skin?
Candida albicans - it occurs when lactobacillus is knocked out = causes thrush
Where do you catch exogenous infections?
From another person - e.g. chicken pox or from mother to child
From an animal - E.g. E.Coli 0157- carried in cow’s guts but not occurs and therefore contaminated burgers can infect us causing us to become very unwell
Vector - indirect method e.g. needle stick, beef burger Is the vector, malaria
Environment - certain organisms are just in the environment e.g. legionella can be found in water and can cause pneumonia
What is the structure of bacteria?
Prokaryotes
Single celled organisms
Divide by binary fission- divide rapidly e.g. E.coli divides every 20 mins
Single chromosome of circular DNA
Their cell wall is important for classification
Capsulated bacteria = helps to protect them
some have pili to help them adhere to surfaces
How are bacteria classified?
Shape = Cocci, Bacilli (rods), Spirochaetes (spirally), filamentous (grow in chains)
Gram stain - not all stain with this stain
Dependence on oxygen = anaerobes or aerobes
Spore formation = this function is very useful for bacteria because it means they are very resistant and can survive in the environment more easily
Metabolism - what they do to sugar filamentation
DNA sequencing e.g. of 16s- using mass spectrometry you can identify the organism in 10 minutes whereas it used to take 24 hours
What are the chemical used in gram staining?
Crystal violet
Iodine
Acetone
Neutral red
1) stain with crystal violet
2) fix with iodine
3) wash with acetone
4) counterstain with neutral red
What is the cell wall/membrane structure of gram positive and gram negative bacteria?
Almost all bacteria have a cell wall but the structure of it depends on the bacteria
Gram positive bacteria only have a thick peptidoglycan cell wall and no cell membrane
Gram negative bacteria have a thinner peptidoglycan cell wall which doesn’t bind crystal violet and they have an additional cell membrane on top of their cell wall
What are some examples of gram +ve cocci?
Staphylcocci aureus (clusters)
- round purple circles grouped together like a bunch of grapes
- about 30% of us carry it
- if it invades tissue it acts as a pathogen
- produces a golden colony on plates
Staphylcocci epidermis
- tends not to be pathogenic
- on our skin it helps to protect us from invasion
- can cause a problem though if it breaches the skin barrier e.g. central line
- it isn’t particularly nasty but it will still cause infection
Streptococci (chains)
- produce a toxin that surrounds their colony
- streptococci pneumonia = occurs in pairs and has a green clearing
What are some examples of gram +ve bacilli?
Lysteria
- associated with soft chest
- many people are not able to consume soft cheese due to this bacteria= immunosuppressed, elderly and pregnant
Clostridium = anaerobic
- large family
- difficile = infection can lead to diarrhoea
- tetani = produces tetanus toxin
- botulinum = producers botulinum = paralysis of muscles
What is an example of gram -ve bacilli?
Aerobic or anaerobic
e.g. E.coli
What are some examples of gram -ve cocci?
Nisseria
- 2 infections: meningitis and gonnorhoea
- To test for meningitis you take some CSF via lumbar puncture
Gram -ve diplococci =meningitis
Gram +ve diplococci = streptococcus pneumonia = also causes meningitis
What are some examples of bacteria that don’t stain with the gram stain?
Spirochetes e.g. syphilis
- cell wall is too thin
- identified by PCR or dark stain microscopy
Tuberculosis - use acid-fast stain
What is the key pathogen for cellulitis?
Staph. aureus, streptococcus progenis
What is the key pathogen for pneumonia?
Streptococcus pneumonias (gram +ve diplococci), Haemophilus influenza (rod)
What is the key pathogen for meningitis?
Nisseria meningitis, streptococci pneumonia
What is the key pathogen for UTI?
most commonly from gut bacteria
Occurs more often in women than men due to their shorter ureter
E.Coli - from own flora
What is the key pathogen for cholecystitis?
E.Coli
