Session 6: Infections on Surfaces

Question 1

Basic definitions of a surface.

Answer 1

Interface between a solid and either liquid or gas.

Question 2

What type of surfaces of the body can micro-organisms live on?

Answer 2

Skin

Mucosal surfaces

Question 3

What are mucosal surfaces?

Answer 3

Conjunctival
Gastrointestinal
Respiratory
Genitourinary

Question 4

Give examples of surface micro-organisms and where they can be found: Viruses

Answer 4

Papilloma (mouth)
Herpes simplex (around mouth)

Question 5

Give examples of surface micro-organisms and where they can be found: Gram positive bacteria

Answer 5

Staph aureus (skin)
Coagulase negative staphylococci (usually skin)
Corynebacterium (salivary microbiome and can also be found on skin)

Question 6

Give examples of surface micro-organisms and where they can be found: Gram negative bacteria

Answer 6

Enterobacteriaceae (gut microbiota and urethra)

Question 7

Give examples of surface micro-organisms and where they can be found: Fungi

Answer 7

Yeasts like Candida albicans which can be found in vagina

Dermatophytes (from dogs and cats)

Question 8

Give examples of surface micro-organisms and where they can be found: Parasites

Answer 8

Mites like head lice, scabies, Norwegian scabies

Question 9

What micro-organisms can be found in: Eye

Answer 9

Coagulase negative staphylococci
Diphteroids
Saprophytic Neisseria species
viridans group streptococci

Question 10

What micro-organisms can be found in: Nares

Answer 10

Staphylococcus aureus

Question 11

What micro-organisms can be found in: Mouth

Answer 11

Viridans Streptococci
Neisseria
Veillonella
Lactobacillus
Actinomyces
Bacteroides
Capnocytophaga
Eikenella
Prevotella
Fusobacteria
Clostridia
Propionibacteria
Candida
Geotrichum species

Question 12

What micro-organisms can be found in: Stomach

Answer 12

Helicobacter
Streptococci
Staphylococci
Lactobacilli

Question 13

What micro-organisms can be found in: Intestine

Answer 13

Bacteroides
Bifidiobacterium
Eubacterium
Lactobacillus
Coliforms
Aerobic and anaerobic streptococci
Clostridium
Yeasts

Question 14

What micro-organisms can be found in: Urethra

Answer 14

Enterobacteriaceae
Lactobacilli
Diphtheroids
Alpha and non-haemolytic streptococci
Enterococci

Question 15

What micro-organisms can be found in: Vagina

Answer 15

Lactobacilli
Diphtheroids
Micrococci
Coagulase negative staphylococci
Enterococcus faecalis
Microaerophilic and anaerobic streptococci
Mycoplasmas
Ureaplasmas
Yeasts like Candida albicans

Question 16

How do people get infected by themselves?

Answer 16

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.

Question 17

Give four examples of how people get infected by themselves.

Answer 17

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

Question 18

Give examples of external natural surface infections.

Answer 18

Cellulitis
Pharyngitis
Conjunctivitis
Gastroenteritis
UTI
Pneumonia

Question 19

Give examples of internal natural surface infections.

Answer 19

Vasculitis and endocarditis
Septic arthritis
Osteomyelitis
Empyema

Question 20

Give examples of prostethic surfaces which can cause infections.

Answer 20

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

Question 21

Give two common ways of getting endocarditis.

Answer 21

Native valve endocarditis where you are born with a bicuspid aortic valve

Prosthetic valve endocarditis where you have a prosthetic aortic valve

Question 22

Explain why native valve endocarditis might occur.

Answer 22

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.

Question 23

Explain why prosthetic valve endocarditis might occur.

Answer 23

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.

Question 24

What are the most common causative organisms of prosthetic joint infections?

Answer 24

Coagulase negative staphylococci like S. epidermidis

Staphylococcus aureus

Question 25

What are the most common causative organisms of cardiac pacing wire endocarditis?

Answer 25

Coagulase negative staphylococci like S. epidermidis

Staphylococcus aureus

Question 26

Explain the pathogenesis of infection at surfaces.

Answer 26

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.

Question 27

Give examples of host responses to pathogenesis where a biofilm is formed.

Answer 27

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.

Question 28

What is quorum sensing?

Answer 28

The communication of bacteria between each other.

Question 29

What does quorum sensing control?

Answer 29

Sporulation of micro-organism
Biofilm formation
Virulence factor secretion

Question 30

What are the three principles involved in quorum sensing?

Answer 30

Signalling molecules like autoinducers
Cell surface or cytoplasmic receptors
Gene expression to form more autoinducers.

Question 31

How do you make a diagnosis of surface infections?

Answer 31

Usually you take blood cultures in order to make a correct diagnosis and identify the infecting organism.
Sonication is also possible

Question 32

How do you treat surface infections?

Answer 32

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

Question 33

Why might antibiotics not be effective in treating biofilms?

Answer 33

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.