Lecture 40: Post Operative Complications: Healthcare Associated Infections

Question 1

What are Biofilms

Answer 1

Biofilm is microbial community of cells that attach to a substrate or interface or to each other, embedded in a matrix of extracellular polymeric substance.

These commonly occur on the surfaces of devices (e.g. plastic, titanium) that we implant into people.

These are h ard to treat

Question 2

Factors for Pathogenesis of Device-Associated Infections are ____, _____, _____

Answer 2

Factors for Pathogenesis of Device-Associated Infections (Bacteria, Host, Device)

Question 3

Describe the Bacterial factors for pathogensis of device-associated infections

What are the most common bacteria that cause pathogenesis from device-associated infections?

What are the factors that allow them to allow them to infect?

Answer 3

Biofilm-associated microorganisms commonly isolated from selected indwelling medical devices are central venous catheters, prostetic heart valve, urinary catheter etc.

Microorganisms include:

• Gram-positives (~50-60% nosocomial bacteremic events) are mostly Staphylococcus epidermidis and S. aureus.
• Gram-negatives (~30% of all episodes of bactermia at most institutions) are mostly Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter aerogenes.
• Fungi are mostly Candida.

Most common are Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli.

Factors include:

• Non-specific (hydrophobicity, electrostatic forces)
• Adhesive proteins (MSCRAMMs)
• Polysaccharide intercellular adhesion (PIA)

Question 4

Describe the Device factors that favour bacterial adhesion causing device-associated infections

Answer 4

Device Factors That Favour Bacterial Adhesion

• For device material, PVC > Teflon, PE > PU, steel > titanium, latex > silicon
• For source of material, synthetic > biomaterial
• For surface of devices, textured > smooth, irregular > regular
• For shape of device, polymeric tubing > wire mesh

Question 5

Describe the Fhost factors that favour device-associated infections

Answer 5

Host tissue can affect bacterial adherence to the device, e.g. host-tissue ligands (fibronectin).

In addition, host immune response also plays a role.

Question 6

What are some problems with biofilm-associated bacteria?

Answer 6

• Antibiotics hard to reach bacteria deeper in biofilm
• Change of phenotype (different gene expression)
• Change of cell surface properties (increased antibiotics tolerance).
• Slower growth rate is more resistant to antibiotics
• Persister cells (specialised survivor cells that are resistant to antibiotics)
• Difficult to determine antibiotic resistance (cannot do standard dilution tests)
• Blood tests might be negative for bacteraemia after antibiotic treatment, but bacteria/biofilm might still be present.

Question 7

What are some prevention strategies to device-associated infections?

Answer 7

• Reconsider r_equirement for the device._
• Handwashing before and after touching the device.
• Place the device appropriately under aseptic conditions (avoid femoral site)
• Monitor devices carefully for signs of infection
• Remove unnecessary devices.
• Reduce central venous catheter infection by 66%.

Question 8

What are the Likely Source And Mode Of Transmission For Clostridium Difficile

Answer 8

Clostridium difficile is part of the normal flora of the GI tract (carriage rates is 5% in community; 20% in hospital)

It spreads from person to person within hospital ward:

• Diarrhoea (contaminates the environment)
• Long lived bacterial endospores

Persons Most At Risk

• Hospital patients receiving antibiotics
  
  • Beta lactams and clindamycin especially
  • Fluoroquinolones (epidemic strain)
• Longer than 1 week in hospital (time to become colonised)
• Other treatments that disrupt the colonic flora (removes competition, allows C. difficile to grow)

Question 9

What are the colonisation factors for Clostridium Difficile and the likely route for colonisation?

Answer 9

1. Antibiotics reduce numbers of major genera of non-endospore forming anaerobes in the colon.
2. C. difficile grows to high numbers, where it produces toxins.
3. C. difficile may be sensitive to the antibiotics but survive as _endospores and out-compete other specie_s, when treatment is stopped.

Endospores (Right Figure)

Endospores are only produced by species of Bacillus and Clostridium

• It is a dormant, survival structure and not reproductive.
• Endospore formation for survival in hospital environment

Summary

• C. difficile is part of the colonic flora
• Major defence by other bacteria of the colonic microbiota, which is removed by broad spectrum antibiotic treatment
• Damage due to combined effect of toxins A and B
• Pseudomembranous colitis

Question 10

What are C.difficile endospores killed and not killed by?

Answer 10

Killed By

• Heat by autoclaving (121 for 15min)
• Chemicals (need to be sporicidal and expose for a certain period of time)

Not Killed By

• Heat by pasteurisation (72 for 15s)
• Antibiotics (resistant as cells are dormant)
• Oxygen (C. difficile are obligate anaerobes)

Question 11

What are the bacterial virulence factors in C.Difficile?

Answer 11

Bacterial virulence factors, including toxin A and toxin B cause the damage.

Question 12

How do Toxin A and Toxin B of C.difficile cause damage?

Answer 12

Toxin A and toxin B have three major domains, including a catalytically active N-terminal domain, a centrally located translocation domain and a C-terminal receptor binding domain.

These toxins are monoglucosyltransferases and have similar substrate specificity. They catalyze transfer of a glucose moiety onto Rho family GTPases inside their target cells.

• The toxins are endocytosed
• Glucosylation of Rho GTPases by toxins A and B locks these proteins into an inactive conformation, thereby blocking all downstream signaling pathways in the cell.
• This results in disruption of the actin cytoskeleton, c_ell rounding_ and eventually apoptosis and death of the intoxicated cell.
• The epithelium barrier loses its integrity and the toxins and other bacteria from the lumen start entering the submucosa and cause inflammation
• There is also less water absoption, and more water flow through the colon = diarrhoea.
• If things get worse, (increased mucous, white cells). there is a pseudomembrane (ulcertation) where the submucosa used to be.
• After some time, there may be a severe inflammation, this colon my perforate therefore need surgical intervention (Toxic Megacolon)

Question 13

Describe the Diagnostic tests for C.difficile

Answer 13

Early diagnosis is important for effective treatment.

Diagnostic test uses unformed stool from:

• Suspected C. difficile-associated disease (CDAD), all patients with diarrhoea hospitalised for 72+ hours
• All patients with potentially infective diarrhoea persisting for 48+ hours that is negative for common enteropathogens.

Using the samples, antibody based assays are performed for (1) toxins; (2) glutamate dehydrogenase (GDH) (common cell associated antigen by C. difficile).

• If GDH positive or toxin negative, samples are tested by PCR for toxin genes (more sensitive), and are reported if positive.
  
  • For Gram-positive rod, presence of C. difficile may not be diagnostic, many individuals carry this bacterium. Next step would be culture (anaerobically) for epidemiology and identification of hypervirulent ribotype 027.

Patients are very likely to have a raised WBC count .

Question 14

How do you treat someone with C.Difficile?

Answer 14

Treatment(s)

• Discontinue implicated antibiotic (clindamycin), which is often enough in mild cases.
• Treat with anti-C. difficile antibiotic, including IV metronidazole and oral vancomycin
• Support fluid loss/pain
• _Restoration of microflora/probiotic_s (faecal transplants?)

Question 15

What should you be thinking about in this case?

A 64 year old woman is recovering in hospital following surgery.

Her post-operative care was complicated by a wound infection treated by a seven day course of oral clindamycin.

Three days later she developed increased frequency of bowel movements, changing over the course of a few days to explosive, watery, bloodless diarrhoea.

Answer 15

An infection with Clostridium difficile is suspected as symptoms are similar to two further cases diagnosed yesterday.

Our patient is 64 yr old woman, presenting with symptoms of diarrhoea

At risk due to:

• Hospitalised > 1 week
• Clindamycin for 1 week, course has finished
• C. difficile growth in place of colon flora?
• Toxin production?