Flashcards in Microbiology 2 Deck (63)
In terms of normal nasopharyngeal flora, what 5 bacteria are found in normal flora of the pharynx?
1) Streptococcus pyogenes (group A)
2) Haemophilus influenzae
3) Streptococcus pneumoniae
4) Neisseria meningitidis
5) Staph. aureus
What 2 bacteria make up vaginal flora pre puberty?
1) Skin flora
2) Lower GI flora - mainly e.coli
What 3 bacteria make up vaginal flora post puberty and why does it change?
Glycogen produced due to circulating oestrogens
1) Lactobacillus spp. lactobacillus acidophilus
Above ferments glycogen maintaining a ph of 3 and preventing overgrowth of other species
2) Skin flora
3) A few C.albicans
What is characteristic of the stomach and small intestine which inhibits bacterial growth, what 2 bacteria make up the flora here?
- Low gastric pH inhibits bacterial growth
- Predominantly aerobic bacteria
1) Acid-tolerant lactobacilli
2) H. Pylori
Counts increase daily, few or no anaerobes
What percentage of bacteria that make up the colon flora are anaerobes?
Which 3 anaerobes make up 96-99% of the colon flora?
1) Bacteroides spp
2) Clostridium spp
3) Bifidobacteria spp
What 5 aerobic bacteria are found in the colon flora, they are all types of what bacteria?
1) Escherichia coli
2) Klebsiella spp
3) Enterobacter spp
4) Proteus spp
5) Citrobacter spp
All enteric gram-negative bacilli
How many organisms per gram and how many species have been found in the colon flora?
10^9 - 10^10 organisms/gram
At least 400 species identified
Give the 3 main benefits of normal flora?
1) Synthesis and excretion of vitamins - vitamins K and B12 secreted by enteric bacteria
2) Colonisation resistance - environmental manipulation (lowering pH) and producing antibacterial agents (colicins, bacteriocins, fatty acids, metabolic waste products)
3) Induction of cross reactive Ab - may have a protective effect
Give 6 conditions/diseases caused by normal flora?
2) Inflammatory bowel disease
4) Metabolic disorders such as diabetes
6) Infection - particularly C diff
What is the main risk factor for C Diff infection, why and how does the disease present?
1) Usually happens in people >60 yrs
2) Main risk factor is Abx treatment
3) Perturbation of normal colonic microflora allows C Diff overgrowth
4) Leads to toxin production
5) Diarrhoea, pseudomembranous colitis
What has faecal transplants been used to treat?
What 6 diseases has it been suggested that faecal transplants may be useful for?
2) Chronic fatigue syndrome (ME)
3) Ideopathic thrombotic purpura
4) Ulcerative colitis
What are the 3 pathological mechanisms linked to normal flora?
1) Overgrowth - excessive growth at normal sight
2) Translocation - presence at abnormal sight (spread from one surface to another or inoculation into a normally sterile sight)
3) Cross infection
Give an example of a disease caused by overgrowth of normal flora and why?
1) Vaginal thrush
2) Treated with broad spectrum Abx, inhibition of colonisation resistance
3) Develop vaginal itch with a creamy discharge
Give an example of a disease caused by translocation of normal flora from one surface to another?
URTI - infects eye
Give an example of a disease caused by translocation of normal flora - through inoculation into a normally sterile sight?
1) Intravascular catheter infection
Skin flora inoculated into blood
Give an example of a disease caused by cross infection?
MRSA from nose infects lungs causing pneumonia - uncommon cause
Give 9 clinical conditions caused by normal flora?
5) Dental caries
6) Peridontal disease
9) Urogenital infections
What is pathogenicity and what are the 4 requirements for pathogenicity?
The capacity of a micro-organism to cause an infection
2) Establishment in or a host
3) Harmful effects
4) Persistence (cant just be in contact with host for a short amount of time)
How is harm mediated in an infection?
Harm is often mediated by the host response rather than the pathogen itself - its the collateral damage to human tissue from destruction of the pathogen that causes the harm
What are the 6 components of the chain of infection?
1) Pathogenic organism (of sufficient virulence and in adequate numbers to cause disease)
2) Reservoir or source that allows the organism to survive and multiply
3) Mode of exit from the source
4) Mode of transmission from the source to the host
5) Portal of entry through which the pathogen can enter the host
6) Susceptible (ie. non-immune) host
What is virulence defined as?
Interchangeable with pathogenicity
Virulence is sometimes defined as the degree to which a micro-organism is able to cause disease
How does virulence and pathogenicity enable us to distinguish between s. aureus and streptococcus mutans?
Both are pathogenic
S aureus is more virulent that stretococcus mutans as it causes disease much more rapidly
What is meant by the LD50 and ID50 of a pathogen?
LD50 - Lethal dose - the dose of bacteria which would cause death in 50% of people infected
ID50 - infectious dose - the dose of bacteria which would cause infection in 50% of the people it came into contact with
What is colonisation and how is it facilitated?
Becoming maintained on or in the host
Facilitated by a receptor-ligand interaction (microbial ligand and host cell surface receptor)
What is infectivity?
The ability of a microorganism to become established in or on a host
Give the ligand receptor interaction of E coli?
P fimbriae : glycolipids on human uroepithelial cells
Give the ligand receptor interaction of S. pyogenes?
Protein-F : fibronectin (large multifunctional glycoprotein found in connective tissue, on cell surfaces and in various body fluids)