Session 6: Infections on Surfaces Flashcards
Basic definitions of a surface.
Interface between a solid and either liquid or gas.
What type of surfaces of the body can micro-organisms live on?
Skin
Mucosal surfaces
What are mucosal surfaces?
Conjunctival
Gastrointestinal
Respiratory
Genitourinary
Give examples of surface micro-organisms and where they can be found: Viruses
Papilloma (mouth) Herpes simplex (around mouth)
Give examples of surface micro-organisms and where they can be found: Gram positive bacteria
Staph aureus (skin) Coagulase negative staphylococci (usually skin) Corynebacterium (salivary microbiome and can also be found on skin)
Give examples of surface micro-organisms and where they can be found: Gram negative bacteria
Enterobacteriaceae (gut microbiota and urethra)
Give examples of surface micro-organisms and where they can be found: Fungi
Yeasts like Candida albicans which can be found in vagina
Dermatophytes (from dogs and cats)
Give examples of surface micro-organisms and where they can be found: Parasites
Mites like head lice, scabies, Norwegian scabies
What micro-organisms can be found in: Eye
Coagulase negative staphylococci
Diphteroids
Saprophytic Neisseria species
viridans group streptococci
What micro-organisms can be found in: Nares
Staphylococcus aureus
What micro-organisms can be found in: Mouth
Viridans Streptococci Neisseria Veillonella Lactobacillus Actinomyces Bacteroides Capnocytophaga Eikenella Prevotella Fusobacteria Clostridia Propionibacteria Candida Geotrichum species
What micro-organisms can be found in: Stomach
Helicobacter
Streptococci
Staphylococci
Lactobacilli
What micro-organisms can be found in: Intestine
Bacteroides Bifidiobacterium Eubacterium Lactobacillus Coliforms Aerobic and anaerobic streptococci Clostridium Yeasts
What micro-organisms can be found in: Urethra
Enterobacteriaceae Lactobacilli Diphtheroids Alpha and non-haemolytic streptococci Enterococci
What micro-organisms can be found in: Vagina
Lactobacilli Diphtheroids Micrococci Coagulase negative staphylococci Enterococcus faecalis Microaerophilic and anaerobic streptococci Mycoplasmas Ureaplasmas Yeasts like Candida albicans
How do people get infected by themselves?
By commensals where a micro-organism which is normal and maybe even beneficial at one site of the body can travel to another site and be harmful.
An example is staph aureus getting somewhere else than skin and do harm.
Give four examples of how people get infected by themselves.
Invasion like strep pyogenes pharyngitis
Migration like E. coli to UT
Innoculation like coagulase negative staphylococcus prostethic joint infection
Haematogenous via blood like viridans streptococci endocarditis
Give examples of external natural surface infections.
Cellulitis Pharyngitis Conjunctivitis Gastroenteritis UTI Pneumonia
Give examples of internal natural surface infections.
Vasculitis and endocarditis
Septic arthritis
Osteomyelitis
Empyema
Give examples of prostethic surfaces which can cause infections.
Intravascular lines like a PVK or a central venous line.
Peritoneal dialysis catheters for kidneys
Prosthetic joints like hip joints
Cardiac valves
Pacing wires like pacemaker
Endovascular grafts
Ventricle-peritoneal shunts
Give two common ways of getting endocarditis.
Native valve endocarditis where you are born with a bicuspid aortic valve
Prosthetic valve endocarditis where you have a prosthetic aortic valve
Explain why native valve endocarditis might occur.
Micro-organisms such as viridans streptococci, enterococcus faecalis, staph aureus, HACEK group or Candida albicans can cause this.
Let’s focus on viridans streptococci present in the mouth. Poor mouth hygiene or forceful brushing of teeth can lead to viridans streptococci entering the bloodstream. If you have a bicuspid aortic valve with endothelial damage fibronectin can be exposed here and the bacteria can adhere to this surface, this is because of the bicuspid valve there will be abnormal blood flow (turbulent). The bacteria can then create a biofilm here and cause endocarditis.
Explain why prosthetic valve endocarditis might occur.
Because of coagulase negative staphylococci are introduced into heart when the prosthetic valve was put in. Endocarditis may develop within a year meaning the infection might not arise shortly after but later on.
What are the most common causative organisms of prosthetic joint infections?
Coagulase negative staphylococci like S. epidermidis
Staphylococcus aureus
What are the most common causative organisms of cardiac pacing wire endocarditis?
Coagulase negative staphylococci like S. epidermidis
Staphylococcus aureus
Explain the pathogenesis of infection at surfaces.
Adherence of the micro-organisms to host cell surface or prosthetic surface.
A biofilm is formed by the micro-organism secreting extracellular matrix and a micro-colony.
There is invasion and multiplication by the biofilm making it into a macrocolony.
This can cause a host response which might not be favourable.
Give examples of host responses to pathogenesis where a biofilm is formed.
In case of a pyogenic micro-organism neutrophils will try to fight it and eventually form pus.
In case if it is granulomatous -> fibroblasts, lymphocytes and macrophages will cause a nodular inflammatory lesion.
What is quorum sensing?
The communication of bacteria between each other.
What does quorum sensing control?
Sporulation of micro-organism
Biofilm formation
Virulence factor secretion
What are the three principles involved in quorum sensing?
Signalling molecules like autoinducers
Cell surface or cytoplasmic receptors
Gene expression to form more autoinducers.
How do you make a diagnosis of surface infections?
Usually you take blood cultures in order to make a correct diagnosis and identify the infecting organism.
Sonication is also possible
How do you treat surface infections?
Sterilise tissue
Antibiotics
If it doesn’t work you might have to remove the surface which is infected with the biofilm like removing the prosthetic or in worst case scenario remove the bicuspid valve and make a prosthetic aortic valve
Why might antibiotics not be effective in treating biofilms?
Because the matrix of the biofilm restricts penetration and diffusion of antimicrobials
Bacteria within the biofilm can also secrete beta-lactamases into surrounding environment and increase expression of multi-drug resistance efflux pumps.
The quorum-sensing system along with different concentration gradients of nutrients, oxygen and metabolic waste products can cause antibiotic tolerance and resistance.
