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Infection and Biofilm

Infection and biofilm in Wound & Skin Care

 A wound is considered infected when microorganisms that damage local tissue and delay wound healing are present.

Infection and biofilm

Managing risk of infection

24% of HCPs believe that risk of infection is a challenge when treating wounds. 1

To minimise the risk of infection and simplify practice, it is key to have a wound bed conforming dressing that absorbs and retains the exudate and bacteria.

This section should help you to better understand wound infection, causes of infection, the role of microorganisms, the stages of infection and how to tell if a wound is infected.

Understanding Infection

A wound is considered infected when microorganisms that damage local tissue and delay wound healing are present.1

The presence of microorganisms triggers an immune response in the patient. Whether or not this response is successful depends on a balance of two things:

  • the strength of the patient’s immune system; and
  • the amount and virulence of the pathogens.

When the amount and virulence of the pathogens are too much for the patient’s immune system to handle, the wound becomes infected.2

It’s important to note that all wounds contain microorganisms, and their presence does not necessarily mean the wound is infected. Keep in mind that:

  • a wound’s bacterial status can change depending on local, environmental and systemic factors; and
  • the transition from non-infected to infected wounds is often gradual.

A wound’s microbial balance can be described as a continuum.1 There is a gradual increase in the number and virulence of microorganisms. As this occurs, the patient’s immune system responds accordingly.

The figure below shows the five stages of wound infection:

  • Contamination
  • Colonisation
  • Local infection
  • Spreading infection
  • Systemic infection

 

The Wound Infection Continuum

It can be challenging to identify infection in chronic wounds. By performing a holistic wound assessment, you can evaluate the patient’s risk of infection. That will allow you to proactively manage the wound to reduce the risk of infection.3

If you don’t have access to modern microscopy tests to identify the organism causing the infection, you can use the following approach:

  1. Check for clinical signs and symptoms.
  2. Take a wound culture to identify the causative organisms and their potential resistance to antibiotics.3

In the chart, you’ll see a list of the clinical signs and symptoms of local and systemic infections that you need to look out for when assessing the wound.2

Signs of local infection Signs of systemic infection
  • Increased pain
  • Erythema
  • Oedema
  • Local warmth
  • Increased exudate
  • Delayed healing
  • Friable granulation
  • Wound odour
  • Pocketing
  • Increased erythema
  • Pyrexia (fever)
  • Abscess / pus
  • Wound breakdown
  • Cellulitis
  • General malaise
  • Raised WBC count
  • Lymphangitis

If you suspect an infection, your immediate goal is to reduce the bioburden in the wound.3 You can do this by:

  • therapeutic cleansing of the wound at each dressing change;
  • aggressive debriding the surface substance and underlying non-viable or unhealthy tissue. This will disrupt the microbial burden and prevent biofilmfrom reoccurring;3 and
  • monitor the wound’s progress and reassess it continually to see if the wound is meeting your treatment goals. You should do this at least once a week or, optimally, at each dressing change.4

Treating specific types of infection

 If there are signs of local wound infection, you can use topical antimicrobials. If the infection is spreading beyond the wound area, you will need to use systemic antimicrobials.

If there are signs of a systemic infection, consult a physician or wound specialist immediately.

Biofilm and its role in wound infection

Biofilm, or bacterial aggregates, are microorganisms embedded in a thick, slimly barrier of sugars and proteins. This barrier shields microorganisms from a patient’s natural immune system and from many antimicrobial agents.1 Biofilm can form in a wound within 24 hours.

How do biofilm affect wound healing?

How do biofilm affect wound healing?

Biofilm are probably the most important single cause of persistent, delayed healing in wounds.2 As figure 1 illustrates, they are also thought to delay wound healing by effecting an inappropriate inflammatory response, which is ineffective, poorly orchestrated and damaging to host tissues.2

There is increasing evidence that biofilm are present in most, if not all, chronic, non-healing wounds.3 Therefore, if you diagnose that your patient has an infection in a chronic wound, it’s recommended that you follow the guidelines for preventing and managing biofilm.2

Two types of bacteria formations

Bacteria are often viewed as being single cells that multiply rapidly when in exponential growth. This is referred to as ‘planktonic form’ and relates mostly to acute infections. Bacteria can also form aggregates, or communities, of slow-growing cells – this kind of formation is referred to as ‘biofilm’. The most common biofilm formers are Staphylococcus aureus and Pseudomonas aeruginosa.2

All about Biofilm

Detecting biofilm can be challenging, due to the following factors:

  • Biofilm are microscopic structures, which are invisible to the naked eye. So you need to use a high-powered microscope to detect them.
  • In a clinical setting, the best detection method is a tissue biopsy. However, biofilm are small and unequally distributed in the wound bed. A wound may have different species of biofilm, and they are typically scattered around in small, isolated, single-species islands. That’s why they can be easy to miss.

Given the expense and time involved in tissue biopsy and microscopy, most clinician diagnose biofilm by identifying the common signs of wound infection. Some of these signs are2,4:

  • sloughy tissue
  • increased levels of exudate
  • poor granulation / friable hyper granulation
  • malodour
  • delayed healing

If a wound still shows these signs of infection after it has been managed correctly and the patient has received appropriate health support, biofilm may be present.

Try asking yourself the following questions2:

  • Have all appropriate diagnostic and therapeutic measures been followed?
  • Is the wound failing to heal as expected?
  • Does the wound show signs of local infection or inflammation?

If you answer ‘Yes’ to at least 2 of these questions, it would be clinically relevant to treat for biofilm.

How to prevent and manage biofilm

Preventing and managing biofilm is an important part of wound management. This is the case for two reasons:2

  1. biofilm are present in most chronic wounds; and
  2. the presence of biofilm is a leading cause of delayed wound healing.

One of the most important ways to avoid biofilm from forming is to reduce exudate pooling.2

How to manage biofilm

Once you’ve established that biofilm are likely present in the wound, you need to lay out an appropriate treatment strategy. For your treatment strategy to have the maximum effect, there are two basic steps you can take:2

  • do what you can to strengthen your patient’s immune system; and
  • always work in a clean environment.

The best strategy for biofilm-based wound care is the ‘clean and cover’ approach. This approach relies on:2

  • adequate debridement to disrupt biofilm; and
  • the use of antimicrobial dressings between debridement. This reduces the planktonic bacteria’s ability to re-establish biofilm.
Wound cleansing Mechanical debridement

Why: To remove non-viable tissue, debris, foreign matter and excess exudate

When: Each dressing change

How: Irrigation with a force of 4-15 psi has been demonstrated as effective and safe4

Why: To remove and disrupt biofilms and make them more susceptible to antimicrobials1

When: Each dressing change (sharp debridement as required)

How: Physical disruption with gauze or pad by gentle circular motion in the wound bed

 

Manage the gap Use topical antimicrobials Re-assess regularly

Why: Gaps may lead to exudate pooling, bacterial growth, and development of biofilms5

When: Each dressing change

How: Dressings that conform to the wound bed or wound fillers with a secondary dressing

Why: Antimicrobials such as silver have been shown to kill biofilms in vitro1

When: Directly after disruption by mechanical debridement

How: In particular, both silver and cadexomer iodine have been shown to kill biofilms

Why: To ensure wound progression and enable change oftreatment if the wound is not gealing

When: At every dressing change or at least once per week

How: Re-assess the questions presented above

Continuous re-assessment necessary

To prevent wound infection or biofilm re-formation, you need to continuously reassess the wound at every dressing change.

Remember always to refer the patient to a specialist if you observe:1

  • a less than 20% improvement in the wound area over a period of four weeks;
  • increased pain levels;
  • unexpected increase in exudate;
  • suspected infection or biofilm;
  • a decline in the patient’s health and wellbeing

Example of wound biofilm

Confocal laser scanning microscopy (CLSM)

Confocal laser scanning microscopy (CLSM)

Image 1 shows a microscopic image of biofilm (highlighted in red), with clusters often less than 1/10 mm. This results in many swabs coming back inconclusive.

Example of wound with suspected biofilm

Example of wound with suspected biofilm

You should suspect biofilm in ‘healable’ wounds, that are non-healing, if you have taken all of the appropriate measures.1

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