Microbiology Flashcards
What is meant by an akaryote?
Without a nucleus
What percentage of cells within the body are human body cells?
10%
What is the difference between human commensal flora and human microbiota?
Theyre the same thing
What is the human microbiota made up of?
Mostly bacteria, but some fungi and protists aswell
Are viruses considered part of human microbiota?
No, as dont have a cellular structure and all they can achieve outside of a host cell is infection of another host cell
In what 2 ways can viruses persist in the body?
1) As latent infections
2) Persistent sub-clinical infections
Microbiota varies depending on anatomical site - what microbiota tends to be found on the teeth and what on the tongue?
Teeth - Streptococcus mutans
Tongue and other soft tissues of the mouth - Streptococcus salivarius
Which microbiota is responsible for dental caries, in which people are they most common?
Streptococcus mutans - microbiota found on the teeth
Common in people with a diet high in sugar
What 2 terms are used to describe microorganisms which may cause disease?
Virulent or pathogenic
Which vitamin would we require a constant supply of in the absence of gut commensal flora?
Vitamin K
What is Koch’s Postulates?
Criteria used to decide if a microorganism caused disease
What are Koch’s 4 postulates?
1) The causative organism must be isolated from every individual suffering from the disease in question
2) The causative organism must be cultivated artificially in pure culture
3) When the causative organism is inoculated from the pure culture, they typical symptoms of the infection must result
4) The causative organism must be recoverable from individuals who are infected experimentally
What extra postulate would possibly be added to Koch’s postulates in modern day?
Ab to be raised against the causative organism in natural cases and in organisms infected artficially
What are Koch’s postulates for genes? 6
1) The gene encoding the trait should be present and transcribed/translated in virulent strain
2) The gene encoding the trait of interest should not be present or should be silent in a strain that does not cause disease
3) Disruption of the gene in a virulent strain should result in formation of a strain which is incapable of causing disease
4) Introduction of the gene into a strain that previously did not cause disease should transform the strain into one that does cause disease (NB. some virulence traits may require the expression of more than one gene)
5) The gene must be expressed during infection
6) Ab raised against the gene product or the appropriate cell-mediated immunity should protect experimental subjects against disease
What are the 4 problems with Koch’s postulates?
1) Difficulty of isolating the causative agent
2) Impossible to grow some pathogens in artificial culture
3) Ethical objections
4) Animal models not sufficient
Name one microorganism which can be difficult to isolate, what does it cause?
Mycobacterium tuberculosis, causes TB is very difficult to isolate
Name 2 pathogenic microorganisms which cannot be grown in artificial culture, what do they cause?
1) Mycobacterium leprae - causes leprosy, cannot be grown in artificial culture except in the foot of the 9 banded armadillo
2) Treponema pallidum causes syphillis
What do viruses consist of?
A nucleic acid core wrapped in a protein coat - some are enveloped and some are naked
Do viruses have DNA or RNA core?
Either but not both
Why are retroviruses unusual in terms of their action upon infection?
Contain an RNA copy of a genome but on infection of host cell a cDNA copy is made using reverse transcriptase which is then incorporated into the host cell DNA
What is the name of the units that make up the protein coat surrounding viruses?
Capsomeres
What is the name of the class of viruses which attacks bacteria?
Bacteriophage
What is the name of viruses which infect plants?
Viroids
What (in prevailing opinion) causes spongiform encephalopathies?
Infectious proteins known as prions
Are all fungi, prokaryotes, eukaryotes or akaryotes?
Eukaryotes
What is chitin?
Polymer of N-acetyl glucosamine that is found in the cell walls of the majority of fungi
Other than fungi what other organisms is chitin found in the cell walls of?
Exoskeleton or arthropods
What are moulds?
Fungi that grow in mats of tiny filaments known as hyphae that form mats called mycelia
What is the difference between aseptate hyphae and septate hyphae?
Hyphae may or may not be seperated into compartments by cross walls known as septa
Septate hyphae tend to be more advanced fungi than aseptate hyphae
What are unicellular fungi known as?
Yeasts
Are moulds multicellular or unicellular organisms?
Multicellular
What is the most common yeast?
Saccharomyces cerevisiae - bakers or brewer’s yeast
How do yeasts grow?
By budding of daughter cells from mother cells
What is the most common yeast infection and what is it caused by?
Thrush - caused by candida albicans
Give 2 examples of infections caused by moulds are they serious?
Superficial infections - ringworm and athletes foot
In immune compromised individuals they can cause much more serious infections but these are rare
What are pseudomycelia?
Yeasts can develop into these under certain conditions
What are protists?
Unicellular eukaryotes
Can infect any human tissue and cause a variety of diseases
What are the 4 classes of protists?
1) Apicomlxa (formerly sporozoa)
2) Flagellate protista
3) Ciliate protista
4) Amoebae
Name 7 infections caused by protists?
1) Toxoplasmosis
2) Amoebic meningitis
3) Malaria
4) Trypanosomiasis
5) Leishmaniasis
6) Amoebic dysentery
7) Diarrhoea
Chronic persistent diarrhoea caused by what organisms is associated with the onset of AIDS?
Cryptosporidium spp.
or Giardia intestinalis
Name a protist which causes vaginal infections, what are the symptoms, can men be carriers?
Trichomonas vaginalis
Foul-smelling vaginal discharge
Men can be asymptomatic carriers, although this protist can cause balanitis
Is Pneumocystis jiroveci a protist or fungus?
For many years considered to be a protist now known to be a fungus
Are bacteria prokaryotes or eukaryotes, why?
Prokaryotes- lack a membrane bound nucleus
What 4 shapes can bacteria be?
1) Round - cocci
2) Rod-shaped - bacilli
3) Comma shaped
4) Spiral shaped
(Most are round or rod shaped)
What is the fundamental difference between gram negative and gram positive bacteria?
Gram positive - thick peptidoglycan layer (interlinked sugar molecules with both D and L amino acids) also containing teichoic and teichuronic acids
Gram negative - very thin peptidoglycan layer, with an extra complex outer membrane
What colours do gram positive and gram negative go in the gram test?
Gram positive - retain crystal violet
Gram negative - counterstain pink or red
What is the structure of the outer membrane of gram-negative bacteria, how does this contribute to disease?
Inner leaflet is a normal lipid layer
Outer leaflet containing lipopolysaccharide
Contains a complex lipid known as lipid A which acts as an endotoxin and is responsible for the symptoms of Gram-negative shock
On which kind of bacteria are fimbraie found? What are they used for?
Found on gram negative bacteria
Used for adhesion to surfaces
On which kind of bacteria are sex pili found, what are they used for?
Gram negative - exchange material through conjugation
Some bacteria are enclosed within a capsule, how does this aid them?
Protects them from being killed, even within phagocytes
Other than fimbraie what else do some bacteria do to help them adhere to surfaces?
Produce slime
How is streptococcus mutans adapted to be able to form plaque which leads to dental caries?
Produces slime which enables it to stick to the surface of teeth
Also allows other microorganisms to stick to the teeth
The acid produced by metabolism of sugars in the diet then etches the surface of the tooth to which the bacteria are stuck initiating dental caries
Name a bacteria that causes infections associated with metal or plastic implanted devices and how its adapted to do so?
Coagulase negative staphylococci
Live on the skin
Some strains produce a slime that enables them to stick to plastics
Can all bacteria produce endospores? What do they enable?
No, only a few species of bacteria can produce endospores, resist a range of hazardous environments and protect against heat, radiation and desiccation
Give the different methods of person to person infection? 6
1) Airbourne - droplets
2) Faecal-oral
3) Sexually transmitted
4) Direct inoculation - eg. IDUs
5) Animals - malaria
6) Inanimate objects
Give 5 diseases spread by the faecal oral route (by drinking water contaminated with human faeces)?
1) Typhoid
2) Cholera
3) Dysentery
4) Hepatitis A
5) Poliomyelitis
Why are the pathogens that cause STIs considered to be vulnerable?
They rapidly die when exposed to conditions outside of the body
In order to spread they require the most intimate of human contact
Malaria is spread by what animal and is caused by what microorganism?
Female anopheles mosquito
Protists of the genus Plasmodium
What are zoo noses? Give an example?
Animals are reservoirs for bacteria such as Salmonella enterica, infections caused by such organisms are known as zoo noses
What are inanimate objects that can act as vectors for disease known as?
Fomites
What does control of infection involve?
Identifying the mode of spread
Interrupting the cycle of infection, replication and spread
What are traits used to complete the cycle of infection frequently known as?
Virulence factors
Why are intoxication illnesses such as tetanus, botulism or ergotism unusual?
The sufferer does not need to encounter the live microorganism because disease results from exposure to the toxin rather than a living microorganism
Give 4 main mechanisms through which bacteria cause disease?
1) Production of structures that enable the microorganism to attach to the surface at which they cause disease
2) Production of one or more toxins - endotoxins or exotoxins
3) Production of aggressins
4) Initiating undesirable consequences of host defences
Why can soluble pathogenic antigens that combine with antibodies to produce circulating immune complex be a problem?
Can become trapped in blood vessels compromising their function
Glomerulonephritis can result from circulating immune complexes after infection by what microorganism?
Streptococcus Pyogenes
What does rheumatic fever result from?
Immunological cross reactions between human tissue antigens and antigens on Streptococcus pyogenes. Ab raised against the bacterial Ag cross react with human Ag causing autoimmune disease
What is the tubercle?
Characteristic lesion of TB, has a major component of giant cells made from the fusion of several macrophages
How many microbial cells does your human body harbour?
10^14
Which part of your body contains the highest number of microbial cells?
Colon
What is the definition of normal flora?
Organisms found in a given location in a state of health
What is meant by colonisation?
Establishment at a sight in the body
What is meant by symbiosis?
Two or more organisms co-exist in close physical association
What are the 4 types of symbiosis and what is meant by each?
1) Mutualism - both organisms benefit from symbiosis
2) Neutralism - neither organism derives benefit or harm
3) Commensalism - one organism benefits, the other derives neither benefit or harm
4) Parasitism - one organism benefits at the expense of the other
What is the difference non-sterile and sterile sights?
Non-sterile sights - have normal flora
Sterile sights - have no normal flora
What characterises a non-sterile sight?
Exposed to the environment either directly or indirectly
No mechanism in place to maintain sterility
Name 5 non-sterile sights?
1) Conjuctiva
2) Nasopharynx
3) GI tract
4) Vagina
5) Skin
When does aquisition of normal flora begin?
Until birth sterility is maintained throughout
Aquisition of normal flora begins at birth
Differences are evident in caesarean vs. birth canal and breast fed vs. bottle fed
What are the predominant differences in the normal flora of breast fed vs bottle fed babies?
Breast fed - bifidobacteria and lactobacillus
Bottle-fed - Enterobacteriacea
Through which 3 mechanisms is sterility maintained in sterile sights, and in which kind of sights does each tend to occur?
1) Sterility maintained by surface cleaning - in sights open to the environment
2) Sterility maintained by barriers which allow uni-directional flow - in sights adjacent to non-sterile sights
3) Sterility maintained by physical separation from non-sterile sights - eg. closed cavities
Give an example of a sterile sight maintained by surface cleaning?
1) Lower respiratory tract
Give 3 examples of sterile sights maintained by barriers allowing uni-directional flow, and what these barriers are?
1) Upper genital tract - barrier = cervix
2) Urinary tract - barrier = urethra
3) Middle ear - barrier = eustachian tube
Give 3 examples of sterile sights in which sterility is maintained by physical separation?
1) Plural cavity
2) Peritoneal cavity
3) Spinal cord and meninges
What is meant by microenvironments?
Different sites within sites
What is meant by tissue tropism?
Propensity for a particular organism to grow in a particular part of the body
What are the 5 physical variables of different sites of normal flora?
1) Moisture
2) Temperature
3) pH
4) O2 availability
5) Nature of surface
What are the 6 physical properties of the skin that make it a relatively inhospitable environment for microbiota?
1) Variable temperature
2) Dry
3) Subject to abrasion
4) Aerobic environment
5) Nutrient - poor
6) Skin surface components
What are the 6 physical properties of a gingival crevice in terms of as a site for microbiota?
1) Constant temperature
2) Moist
3) Few physical challenges (toothbrush)
4) Anaerobic environment
5) Bathed in nutrients
6) Mucosal surface components
What should be noted about the type of bacteria on skin close to an orifice?
It is likely to be similar to the bacteria in that orifice
What 3 bacteria make up the majority of skin flora?
1) Coagulase-negative staphylococci (staphylococcus epidermis)
2) Staphylococcus aureus (esp. in nasal cavities)
3) Propionibacterium species (propionibacterium acnes)
How can normal mouth flora benefit us in terms of infection?
Mouth is exposed to a wide range of bacteria and established normal flora can prevent colonisation of pathogenic flora
Overgrowth of what normal mouth flora can lead to tooth erosion and how?
Overgrowth of oral streptococci leads to biofilms on teeth, convert sugars to lactic acid which damages enamel and erodes teeth
What are the 2 main components of normal mouth flora?
1) Viridans/ oral streptococci
2) Anaerobes
In terms of nasopharyngeal flora, what 2 bacteria and mainly found in the nostrils?
1) Skin flora
2) Staph aureus (20% - nose is main carrier sight)
