Lecture 22: Micro-organisms in Health: Normal microbiota Flashcards
How many human cells does the average 70kg human have?
30 trillion human cells
How many bacterial cells does the average 70kg human have?
39 trillion bacterial cells
what varies at different sites of the body?
Organism density
What areas harbour fewer organisms?
Dry, exposed areas of skin
What area harbours more organisms on the body?
‘moist’ or protected areas of skin such as armpits, the groin area or between the toes.
Where is organism density greatest in the body?
oral cavities and colon
What is normal flora/ normal microbiota?
Organisms found in a given location in a state of health
What is colonisation?
Establishment at a site in the body
What is microbiota?
All the organisms in a given community
What is microbiome?
All the genes present within the microbiota
What is symbiosis?
Two or more organisms co-exist in close physical association.
What is the relationship between the human ‘host’ and normal flora described as?
Symbiotic
What is infection?
Infection is the presence of microorganisms causing damage to body tissues, usually in the presence of acute inflammation (pain, swelling, redness, heat and loss of function)
What is mutualism?
Both organisms benefit from symbiosis
What is neutralism?
Neither organism derives benefit or harm
What is commensalism?
One organism benefits, the other derives neither benefit nor harm
What is parasitism?
One organism (parasite) benefits at the expense of the other (host)
What is Dysbiosis?
Shift in microbiota which is representative of a disease state
Pathobiont (cause harm under certain circumstances)
Give an example of mutualism?
Nitrogen fixing bacteria and legumes
What type of flora are found in non-sterile sites?
Have normal flora
What type of flora are found in sterile sites?
No normal flora
What are characteristics of non- sterile sites?
Exposed to the environment
- Directly
- Indirectly
No mechanism in place to maintain sterility
During pregnancy, till when is sterility maintained?
Until birth
When does the acquisition of normal flora begin?
At birth
What produces differences in normal flora at the beginning of life?
Caesarean vs birth canal
Breast vs bottle feeding
What type of flora is acquired from birth?
Predominantly bifidobacteria and lactobacillus. Bottle-fed more Enterobacteriacea.
Name some non-sterile sites?
Skin
Vagina
Conjunctiva
Nasopharynx
Vagina
GI tract
How are sterile sites maintained?
- Sterility maintained by surface cleaning
- Open to the environment e.g. lower respiratory tract - Sterility maintained by barriers (allow uni-directional flow)
- Adjacent to non-sterile sites e.g. upper genital tract protected by the cervix - Sterility maintained by physical separation from non-sterile sites
- Closed cavities e.g. pleural cavity, peritoneal cavity, spinal cord and meninges
How do you collect Blood cultures/CSF/ Pleural fluid?
obtained by passing a needle through the skin into the relevant ‘sterile’ site. Potential for contamination with skin organisms
How do you collect a sputum sample?
obtained by expectoration of lower airways secretions (‘sterile site’) through the upper airway (‘non-sterile site’) – risk of contamination
How do you collect a urine sample?
obtained by passing urine from the bladder/upper urinary tract (‘sterile site’) via the terminal urethra (‘non-sterile site’). Risk of contamination reduced by collecting Mid Stream Urine (MSU) sample
What are microenvironments?
Different sites, Within sites
What is tissue tropism?
Propensity for a particular organism to grow in a particular habitat
Factors that influence what organisms colonise what areas?
Moisture
Temperature
pH
O2 availability
Nature of surface
Characteristics of skin?
Variable temperature
Dry
Subject to abrasion
Aerobic environment
Nutrient-poor
Skin surface components
Name 3 types of skin flora?
- Coagulase-negative staphylococci (Staphylococcus epidermis)
- Staphylococcus aureus (esp. in nasal carriers)
- Cutibacterium acnes (Propionibacterium acnes)
what bacteria may be similar to bacteria in an orifice?
The bacteria on the skin near any body orifice
Characteristics of gingival crevice?
Constant temperature
Moist
Few physical challenges (toothbrush)
Anaerobic environment
Bathed in nutrients
Mucosal surface components
Where are higher proportions of Actinomyces found: Teeth or soft tissue?
Teeth
Is the microenvironment of the gingival crevice similar to the microenvironment of the tongue and saliva?
No.
The microenvironment of the gingival crevice differs greatly from the bacteria present on the tongue and again form those present within saliva
Give 3 examples of mouth flora?
Viridans/oral streptococci
Anaerobes
Red complex bacteria
Give 5 examples of Red complex bacteria?
Porphyromonas gingivalis
Tannerella forsythia
Treponema denticola
Aggregatibacter actinomycetemcomitans,
Prevotella intermedia
How does flora of the mouth benefit from the host?
By gaining nutrients
What does flora of the mouth provide the host with?
Essential vitamins that are synthesised by bacterial species.
What can established normal flora of the mouth prevent?
Colonisation of pathogenic flora.
What are the consequences of overgrowth of oral sreptococci?
- Biofilms on teeth
- Conversion of sugar to lactic acid
Damages enamel and erodes the tooth
What are the 2 sites of Nasopharyngeal flora?
Nostrils
Pharynx
What are the types of bacteria found in the nostrils?
Skin flora
S.aureus
What are the types of bacteria found in the Pharynx?
Respiratory and other pathogens
- Streptococcus pyogenes (group A)
- Haemophilus influenzae
- Streptococcus pneumoniae
- Neisseria meningitidis 7-34% in UK university
students1
- Staphyloccus aureus
What can be a consequence of damage to the respiratory tract epithelium?
If respiratory tract epithelium becomes damaged, these species can cause infections in the lower respiratory tract.
E.g. Bronchitis, pneumonia
What type of flora is found in pre-puberty vagia?
Skin flora
Lower GI flora
Mainly E. coli
What type of flora is found in post-puberty vagina?
Lactobacillus spp. Lactobacillus acidophilus
Skin flora
A few C. albicans
What is produced post puberty due to circulating oestrogens?
Glycogen
How is low pH beneficial in the vagina?
Low pH beneficial in preventing infection by opportunistic pathogens e.g. overgrowth of C. albicans – causing Thrush
What does low gastric pH inhibit?
Bacterial growth
What type of bacteria is found in the GI tract (Stomach and small intestine)?
Predominantly aerobic bacteria
- acid-tolerant Lactobacilli
- Helicobacter pylori
Few or no anaerobes
How does H. Pylori cause a gastric ulcer?
H. pylori can survive the highly acidic nature of the stomach by producing urease to convert urea into ammonia and carbon dioxide.
What percent of the population is H. Pylori found in?
30 - 50%
What percent of people with H. Pylori colonised to develop ulcers?
less than 20%
How many species have been identified in the large intestine?
At least 400
What percent of flora in the large intestine are anaerobes?
95-99%
What other type of flora is found in the large intestine aside from Anaerobes?
Aerobic bacteria
(Enteric Gram-negative bacilli)
What prevents overgrowth of pathogens in the large intestine?
Colonisation resistance by normal gut microflora prevents overgrowth of pathogens. Notably the hospital acquired infection Clostridium difficile
When are changes in healthy microbiota in hospital likely to occur?
The process usually begins around day 4 of admission; this is why after 4 days of admission the antibiotics for hospital acquiredinfections change. It is not because the severity of the illness isdifferent.
What are the benefits of normal flora to metabolism?
Synthesis secondary metabolites/vitamins
e.g. vitamins K and B12 secreted by enteric bacteria
Fermenting unused energy substrates (SCFA)
What are the benefits of normal flora to colonisation resistance?
Environmental manipulation
e.g. low pH
Antibacterial agents
e.g. colicins, bacteriocins, fatty acids, metabolic waste products
