Infections On Surfaces

Question 1

What is a surface?

Answer 1

Interface between a solid and either a liquid

or gas.

Question 2

Name some skin micro organisms

Answer 2

Viruses
– Papilloma (can be carcinogenic)
– Herpes simplex

Bacteria
Gram positive
– Staph aureus
– Coagulase negative staphylococci - All staphylococci except staph aureus
– Corynebacterium - Never cause significant disease outside a healthcare setting
Gram negative
– Enterobacteriaceae

Fungi
– Yeasts - All have small numbers of candida species,
– Dermatophytes - Multicellular fungi, live on skin, some infect hair and nails, cause athletes foot,

Parasites
– mites

Question 3

Name mucosal flora of the eye

Answer 3

Coagulase negative staphylococci, diphtheroids, saprophytic Neisseria species, viridans group streptococci

Question 4

Name mucosal flora of the nares

Answer 4

Staph aureus

Question 5

Name mucosal flora of the nasopharyngeal

Answer 5

Neisseria meningitidis (a lot of people have this but not have disease), Streptococcus pneumoniae, Haemophilus
influenzae,

Question 6

Name mucosal flora of the mouth

Answer 6

Viridans Streptococci (can get to heart), Neisseria, Veillonella, Lactobacillus, Actinomyces, Bacteroides, Capnocytophaga, Eikenella, Prevotella, fusobacteria, clostridia, propionibacteria, Candida, Geotrichum species

Question 7

NAME MUCOSAL FLORA OF THE STOMACH

Answer 7

Helicobacter - can cause peptic ulceration - treated with a week/2 of antibiotics - they are a precursor for gastric cancer or lymphoma , streptococci, staphylococci, lactobacilli,

Question 8

Name mucosal flora of the intestine

Answer 8

Bacteroides, Bifidobacterium, Eubacterium, Lactobacillus, coliforms,
aerobic and anaerobic streptococci, Clostridium, yeasts
Anaerobes in the large bowel

Question 9

NAME mucosal flora of the urethra

Answer 9

Enterobacteriaceae - gram negs, lactobacilli, diphtheroids, alpha and non-haemolytic streptococci, enterococci,
Can causeuti

Question 10

Name mucosal flora o the vagina

Answer 10

Lactobacilli - most are these. These produce lactic acid to reduce candida (which cause thrush), diphtheroids, micrococci, coagulase-negative staphylococci, Enterococcus faecalis, microaerophilic and anaerobic streptococci, mycoplasmas, ureaplasmas, yeasts

Question 11

Describe the distribution of bacteria in the human body

Answer 11

See slide for diagram

Question 12

What is the most common way of infection

Answer 12

From own microbiota - when you acquire a new strain of myth ur not immune to
• Microbiota = “commensals”
– micro-organisms carried on skin and mucosal surfaces
– normally harmless or even beneficial
– transfer to other sites can be harmful

Question 13

Name methods of transfer

Answer 13

– Invasion
• e.g. Strep pyogenes pharyngitis 
– Migration
• e.g. Escherichia coli urinary tract
infection
– Innoculation
• e.g. Coagulase negative
staphylococcus prosthetic joint
infection eg after surgery 
– Haematogenous
• e.g. viridans Strep endocarditis -

Question 14

How can viridans strep cause endocarditis

Answer 14

Viridans need to be anchored down in the mouth, some people e have congenital abnormalities of valves eg bicuspid aorti valve - significant risk of endocarditis - turbulent blood flow over the valves - that erodes the epithelial surface, any bacteria that get from mouth into blood stream (usually taken up by macrophages or in spleen), but bacteria can attach to fibronectin - grow in the heart, body causes inflammatory processes, growth of bacteria and host response

Question 15

Name extranal natural surface infections

Answer 15

– Cellulitis
– Pharyngitis
– Conjunctivitis
– Gastroenteritis
– Urinary tract
infection – Pneumonia

Question 16

Name internal natural surface infections

Answer 16

Endovascualer - endocarditis, vasculitis

• septic arthritis
• osteomyelitis
• empyema

Question 17

What are example s of prosthetic surfaces that can become infected

Answer 17

• Intravascular lines
• Peritoneal dialysis catheters
• Prosthetic joints
• Cardiac valves - artificial or derived from animals - put in when patients valves damage
• Pacing wires
• Endovascular grafts
• Ventriculo-peritoneal shunts

Question 18

What causes native alve endocarditis and prosthetic valve endocarditis >1 year post op

Answer 18

viridans Streptococci Enterococcus faecalis Staph aureus
HACEK group
Candida

Question 19

What causes prosthetic valve endocarditis <1year post op?

Answer 19

coagulase negative staphylococci

Question 20

What are ventricular-peritoneal shunts

Answer 20

A ventriculoperitoneal (VP) shunt is a medical device that relieves pressure on the brain caused by fluid accumulation.

VP shunting is a surgical procedure that primarily treats a condition called hydrocephalus. This condition occurs when excess cerebrospinal fluid (CSF) collects in the brain’s ventricles.

Drains liquid into peritoneum

Question 21

What are causative organisms of prosthetic joint infections

Answer 21

coagulase negative staphylococci - mostly this

Staphylococcus aureus

Question 22

What is cardia pacing wire endocarditis and what are the causative organisms

Answer 22

Infection of the pace maker wires

coagulase negative staphylococci Staphylococcus aureus

Question 23

What are the processes n the pathogenesis of infection a surfaces

Answer 23

• Adherence to host cells or prosthetic surface
• Biofilm formation
• Invasion and multiplication
• Host response
– Pyogenic (neutrophils -> pus)
– Granulomatous (fibroblasts, lymphocytes, macrophages -> nodular inflammatory lesions)

Question 24

What are pili/l

Answer 24

Fimbriae and pili are interchangeable terms used to designate short, hair-like structures on the surfaces of procaryotic cells. Like flagella, they are composed of protein
Bind to surface of host

Question 25

What is a biofilm

Answer 25

A biofilm is an assemblage of surface-associated microbial cells that is enclosed in an extracellular polymeric substance matrix
If we can make prosthetics that biofilms cannot get a foothold on - reduce infections on them

Question 26

What is quorum sensing

Answer 26

Quorum sensing is the regulation of gene expression in response to fluctuations in cell-population density. Quorum sensing bacteria produce and release chemical signal molecules called autoinducers that increase in concentration as a function of cell density

Question 27

What does quorum sensing control and what are the 3 principles

Answer 27

• Controls
– Sporulation 
– Biofilm formation 
– Virulence factor secretion….
• Three principles
– Signalling molecules 
– autoinducers (AI) 
– Cell surface or cytoplasmic receptors – Gene expression ->co-operative behaviours and more AI production.

Question 28

How are surface infections managed

Answer 28

Diagnosis
• Aim is to identify infecting organism and its
antimicrobial susceptibilities.
• Challenges
– Adherent organisms - difficult to get samples
– Low metabolic state/small colony variants
• Blood cultures
• Tissue/prosthetic material sonication and culture

Question 29

What is teh differential time to positivity

Answer 29

The differential time to positivity was defined as the difference in the time it took for a blood culture drawn through the central venous catheter and a culture drawn from a peripheral vein to become positive
- (from central line and peripheral. If central line bacteria grow faster, central line infection as more bacteria there - Differential time to positivity)

Question 30

How is surface infection managed in terms of treatment

Answer 30

• Treatment
• Aim:
– sterilise tissue
– reduce bioburden
• Antibacterials - only work bile bacteria is dividing - bacteria resistant if they are not going through right element of growth
• Remove prosthetic material - If a patient is frail/old and infected prostetic cannot be removed, keep them comfortable
• Surgery – resect infected material
• Challenges
– poor antibacterial penetration into biofilm
– low metabolic activity of biofilm micro-organisms
– dangers/difficulties of surgery

Question 31

How are surface infections managed in terms of prevention

Answer 31

Natural surface 
• Maintain surface integrity 
• Prevent bacterial surface
colonisation 
• Remove colonising bacteria 

Prosthetic surfaces
• Prevent contamination
• Inhibit surface colonisation
• Remove colonising bacteria