Biofilms Polymicrobial Infections Flashcards
What are classical infections?
Classical infections are caused by a single organism.
Where do these organisms derive from?
These organisms are of exogenous source, meaning they are not found in our resident microbiota.
i.e. not part of normal flora
What do these organisms do once they enter the body?
These Organism colonise a susceptible host, multiply and evade host defence. They damage the host, normally by the production of protein toxin (exotoxin).
What are polymicrobial infections?
An infection associated with more than one microbe.
A mixture of one type of microorganism, e.g. different species of bacteria.
Combinations of different types of microorganism, e.g. bacteria and
viruses, bacteria and protozoa, fungi etc.
Impossible to apply Koch’s postulates to polymicrobial infections.
Give Examples of Polymicrobial infections in the oral environment.
Dental caries
Angular Cheilitis
Dental Abscesses
Denture Stomatitis - Denture stomatitis causes redness, swelling and tenderness in the mouth. While the condition is most common among denture wearers, it can affect anyone
Periodontal Disease
Give an example of a secondary infection.
In some cases an initial infection can predispose to a more serious secondary infection. We often see this in the Lung (non-sterile organ with resident microbiota).
Viral infection of Lung tissue predisposes to secondary bacterial Infection.
1918 Influenza pandemic: 50 - 100 million Majority of deaths were from bacterial pneumonia (secondary infection).
How do the lungs develop a secondary infection such as pneumonia?
Initial viral infection causes damage to lung tissue.
Tissue damage exposes basement membrane elements such as fibrinogen to which bacteria can adhere and infiltrate into the host.
Viral neuraminidase cleaves sialic acid residues on host cells, creating more bacterial binding sites (neuraminidase inhibitors reduce S. pneumoniae infiltration in experimental models).
Bronchitis or pneumonia caused by Streptococcus pneumoniae (pneumococcus), Haemophilus influenzae or S. aureus. this all leads to impaired host immune response.
How is the host immune response impaired?
Over-activity of immune system
Overproduction of inflammatory cytokines leading to infiltration of bacteria, lymphocytes, neutrophils and macrophages. Damages alveolar architecture
Secondary bacterial infection leads to more prolonged and severe clinical symptoms when compared to viral infection alone.
Bacterial invasion can lead to septicaemia. A frequent cause of death, particularly in the elderly.
What are the factors that underpin Septicaemia?
- virus
- secondary bacterial infection
- dysregulated host immune response gives rises to large quantities of cytokines also known as a cytokine storm.
How can we prevent primary viral infection and mitigate the effects of secondary infections?
Vaccinations - Immunisation with influenza vaccine reduces pneumonia and influenza hospitalisations by 52% and deaths by 70% in individuals over 65.
For primary viral disease, why shouldn’t we give antibiotics?
The current recommendation to reduce antibiotic resistance is not to use antibiotics to treat viral diseases.
However, In vulnerable populations such as the elderly and other high risk groups,
aggressive antiviral and antibacterial therapy at the first sign of influenza infection is warranted to prevent secondary bacterial infection.
What are biofilms?
Biofilms are a matrix-enclosed population of
microbes that can adhere to biotic and abiotic substrates.
Biofilms are the most prevalent manifestation of polymicrobial communities.
Present in numerous natural environments. Biofilms are complex and dynamic structures
What substrates can biofilms adhere to?
Biotic substrates that biofilms can adhere to: skin/mucosal surfaces/teeth
Abiotic substrates that biofilms can adhere to:
Dentures/acrylics/resins
Intravenous/urinary catheters
Abdominal drains, Stents
Ventilator tubes, feeding tubes
Contact lenses, Heart valves
Describe the composition of biofilms.
The composition of a biofilm changes over time from person to person, between individual substrates and tissue sites, and in response to changes in the environment.
How does biofilm develop?
Biofilm development in the oral cavity is continuous and sequential.
1. The substratum is coated with a conditioning film. The first microbes arrive (primary colonizers) these interact with the film initially through electrostatic forces of attraction and then through a more robust covalent interaction mediating through adhesins.
- These primary colonisers obtain nutrients and undergo cell division and form structures called microcolonies. These microcolonies form a substance called EPS.
- Coadhension of single cells or groups of cells or coaggregates (groups of different species microbes) these are incorporated into the growing biofilm.
- Succession occurs - the selective pressure that is imposed upon a developing population of microbes. Due to succession, the compositions of the biofilm changes over time until the equilibrium is reached, once reached this is known as the final stage which is a mature multi-species biofilm also known as the climax community.
How does the biofilm develop on the tooth?
Due to the hydroxyapatite in the tooth enamel the acquired pellicle can form. As soon as saliva contacts the teeth surface,salivary proteins adhere to the tooth surface to form acquired salivary pellicle.
Once the acquired pellicle is present it is colonised by early colonisers. Streptococcus sp occurs first. Streptococcus sp is followed by other early colonisers.
Which is followed by late colonisers such as T. forsythia and T. denticola.
These bacteria interact with one another through adhesins that they have on their surface.
