Wound infection occurs when the balance of microorganisms in a wound is disrupted.

- Leads to an overwhelmed host response and impaired wound healing
(International Wound Infection Institute, 2022)

Wound bed preparation is a fundamental concept in wound care management.

o Aims to create an optimal healing environment
o Identifying signs of infection and intervening promptly helps prevent healing
delays

Risk Factors
Individual or Host Risk Factors
 Host factors that influence the development of wound infection are systemic and multifactorial and encompass many variables.

 Poorly controlled diabetes
 Age
 Peripheral neuropathy
 Malnutrition
 Compromised immune system
 Cardiac disease
 Respiratory disease
 Radiation or chemotherapy
 Poor compliance with treatment plan
 Medications

Wound Risk Factors

Wound type also contributes to infection risk.
o Acute wounds have different risk factors for infection than chronic wounds. o Risk factors include:

Acute Wounds
 Contaminated or
dirty wounds
 Traumatic injuries
 Operative factors
such as prolonged
surgery
Chronic Wounds
 Duration
 Size
 Anatomical location
near a site of
potential
contamination
Acute and Chronic
 Foreign body
presence
 Impaired tissue
perfusion
 Increased exudate

Environmental Risk Factors

 Unclean environments
 Contaminated surfaces
 Poor air quality
 Inadequate hand hygiene
 Crowded living conditions
 Improper waste disposal

Bacteria

 A wound is a break in the skin.
o Allows both normal and harmful organisms to enter the body
 A warm, low-oxygen, and moist environment supports bacterial survival.
o Increases the risk of infection
 Bacteria are classified as prokaryotes.
o Single-celled organisms lacking a nucleus
o Have a cell wall and membrane, which are targets for antibacterial compounds
o Identified and described based on their characteristics (Shultz & Weir, 2022):
 Shape
 Gram stain
 Oxygen needs
 Mode of growth

Bacteria SHAPE:

Various shapes of bacteria affect their:
o Pathogenicity
o Environmental interaction
o Surface adhesion
o Immune evasion
o Antibiotic resistance
 Three primary shapes and their characteristics:

Cocci ; Bacilli ; Spirilla

Cocci

 Spherical bacteria
 Often found in clusters or chains (e.g. Staphylococcus aureus)
 A common cause of wound infections

Bacilli

Rod-shaped bacteria that infect wounds, causing complications (e.g.,
Escherichia coli)

Spirilla

 Spiral-shaped bacteria
 Known for their corkscrew motion, which aids their mobility (e.g.
Helicobacter pylori)

Gram Stain
 Classifies bacteria as gram-positive or gram-negative based on cell wall structure, aiding
diagnosis and guiding antibiotic treatment (MedlinePlus, 2023)
 Results are usually complete within a few hours of the lab receiving the specimen.
 Developed by Hans Christian Gram in 1884
 The process involves:

o First, staining bacteria with crystal violet dye
o Then, iodine (which forms a complex with the dye)
o Next, a decolorizer is applied
o Finally, a counterstain is applied

 Results interpretation:
o Gram-Positive Bacteria

 Retain crystal violet-iodine complex
 Appear purple under a microscope are termed Gram-positive
 Examples include Staphylococcus and Streptococcus

 Results interpretation:

o Gram-Negative Bacteria

 Lose the initial stain
 Assume the counterstain
 Appear red or pink under a microscope
 Examples include Escherichia coli and Pseudomonas

Aerobic Bacteria

 Thrive in environments with oxygen (e.g., on the skin or in superficial wounds)
 Common aerobic bacteria include:
o Staphylococcus aureus
o Pseudomonas aeruginosa

Anaerobic Bacteria

 Does not need oxygen and may even die in its presence
 Thrives in deeper tissues or areas with poor blood supply and low oxygen levels
 May be found in:
o Deep puncture wounds
o Abscesses
o Gas gangrene
o Necrotizing infections

 Examples of anaerobic bacteria are:

o Clostridium perfringens
o Bacteroides species

Modes of Growth
 Bacteria grow in two primary modes

Planktonic & Biofilm

Planktonic

 Free-floating
 Single cells that move independently in liquid environments
 More susceptible to antibiotics and the immune system because they lack
protective barriers

Biofilm

 Transition from planktonic bacteria
 Produce an extracellular matrix that acts as a shield
 Resilient to treatment

Biofilm
 Biofilms are (Shultz & Weir, 2022):

o Polymicrobial complex communities
o Protected by an extracellular matrix that they create
o Able to adhere to surfaces with this matrix

Formation

 Consists of five distinct steps (Ascenzioni et al., 2021):

Initial Attachment ; Irreversible Attachment ; Maturation I ; Maturation II ; Dispersion

Initial Attachment

 Free-floating microorganisms attach themselves to a surface
 Often reversible

Irreversible Attachment

 Microorganisms produce extracellular polymeric substances (EPS)
 Firmly adhere to the surface

Maturation I

 Biofilm grows through cell division
 Recruits other microorganisms
 Forms microcolonies

Maturation II

 Develop a complex three-dimensional structure
 Has channels for nutrient and waste flow

Dispersion

 Cells or clusters detach from the biofilm
 Colonize new areas
 Spreads and forms new biofilms

Implications
 Implications of biofilm on wound healing include:

Matrix Synthesis ; Healing Impact ; Resistance

Matrix Synthesis

 Extracellular matrix acts as a shield
 Blocks antibiotics and the immune system
 Makes bacteria more resilient

Healing Impact

 Impedes healing by attaching to the wound surface
 Makes them problematic and difficult to remove
 Allows bacteria to persist

Resistance

 Bacteria are more resistant to treatments and the body’s defenses
 Leads to chronic infections and delayed healing

Challenges
 Biofilms are present in nearly 60% of hard-to-heal wounds.

o Even when eliminated, repopulate within several hours (Darvishi et al., 2021)
SWM Module 08: Preparing the Wound Bed – Infection
Prevention and Management
© 2025 Relias LLC. All rights reserved. Page | 5
 Standard methods cannot culture them.
o Resistant to host defenses
o Develop genetic resistance to antibiotics
 Bacteria within biofilms communicate and coordinate their activities (quorum sensing).
o Enhances their survival and resistance
 Biofilms can only be detected by electron microscopy and confocal laser scanning.
o Cannot be seen by the naked eye (Swoboda, 2022)
 If a biofilm is present, diagnosis is unaided by additional cultures, tissue biopsies, or
swab cultures.

Indicators

 Failure of appropriate antibiotic therapy
 Recalcitrance to an appropriate antimicrobial therapy
 Recurrence of delayed healing when antibiotic treatment ceases
 Increased exudate or moisture
 Poor or friable granulation tissue
 Low levels of erythema or chronic inflammation

Management
 Involves a combined approach of:

o Debridement to remove the biofilm
o Application of topical antimicrobial agents to prevent reformation and infection

Management

 Wound hygiene is essential in managing biofilms and preventing reformation (Murphy etal., 2019)

o Cleansing
o Debridement
o Refashioning the wound edge
o Applying biofilm prevention measures

Bacterial Load Effects
 High bacterial load in the wound can:

o Lead to infections by particularly aggressive bacteria
 Especially prevalent in individuals with weakened immune systems
o Significantly delay the healing process

Bacterial Load Effects
 Excessive growth of bacteria complicates wound healing by:

o Competing with healthy cells for oxygen
o Reducing the amount of oxygen available to repair injured cells
o Disrupting or destroying normal cellular functions within the wound
o Forming delicate, easily damaged, and friable granulation

 Staphylococcus
 Pseudomonas
 Group B Streptococcus
 Escherichia coli
 Enterococcus faecalis

 Some of the most common pathogenic bacteria found in wounds (Leonard, 2024):

Staphylococcus, or Staph
 Frequent culprits in wound infections, particularly:

Staphylococcus aureus ; Methicillin-resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus

 About 33% of adults carry Staphylococcus aureus bacteria on their skin
or in nasal cavities.
 It is a normal component of the skin's microbiome (commonly found in
healthy individuals without causing disease).

Methicillin-resistant Staphylococcus aureus (MRSA)

 Approximately 2% of adults carry MRSA.
 Prevalence can be higher in certain populations (Centers for Disease
Control and Prevention [CDC], 2024a).

Particularly noted for its ability to become antibiotic-resistant.
o Makes infections like MRSA challenging to treat (CDC, 2024a; Mayo Clinic,
2024)

Staphylococcus aureus

 Another common bacterium found in wounds
 When problematic, it exhibits distinct signs and symptoms:
o A green color exudate
o Sweet, fruity, or pungent odor
 Often associated with hydrotherapy and respiratory equipment
o Necessitates strict infection control practices to prevent cross-contamination

Pseudomonas Aeruginosa

Group B Streptococcus (GBS) or Streptococcus Agalactiae

 Highly invasive bacterium that causes severe infections (e.g., osteomyelitis)
 Can cause infection even with a lower bacterial load
o Particularly dangerous for older adults with comorbid conditions
o Poses a considerable risk of severe outcomes
 Treatment typically involves intravenous antibiotics like penicillin or vancomycin upon detection.
o Treatment irrespective of the number of microorganisms present

Escherichia Coli (E. Coli)

 A normal inhabitant of the intestines
o Helps with digestion and maintaining gut health
 When ingested through contaminated food or water, it can cause significant gastrointestinal infections.
 A common cause of wound infections, particularly when contaminated with fecal matter
 Hygiene and proper wound care are critical in preventing these infections

 One of the most common pathogens causing wound infections
 Gram-positive coccus
 Typically found in the gastrointestinal tract
 Has developed resistance to many commonly prescribed antibiotics
o Resistant to vancomycin (i.e., VRE)
o Challenging to treat (Infection Cycle, 2023)
 Prevention through hygiene and proper wound care

Enterococcus faecalis (E. faecalis)

Bioburden Overview

Skin is a barrier against microorganisms

o Any break can allow pathogens to enter

Bioburden Overview

Infection is a common wound complication, with risk varying by:

o Wound type
o Location
o Individual's health status

Bioburden Overview

When an acute wound heals without incident, the physical barrier is re-established.

When they do not heal properly, they can become chronic or hard-to-heal
wounds at higher risk for infection.

Bioburden Overview

 Bioburden

is the degree or load of microorganisms contaminating a wound (Shultz &
Weir, 2022).

Bioburden Overview

 All chronic wounds have some level of ___, which may affect the _____ process.

All chronic wounds have some level of bacteria, which may affect the healing process.

Bioburden Overview

___ is the degree or load of microorganisms contaminating a wound (Shultz &
Weir, 2022).

Bioburden

Bioburden Overview

Impact of bacteria depends on:

o Number of bacteria present
o Virulence of bacteria
o Type of bacteria
o Host’s resistance

Stages of Bioburden
Bioburden indicates ____ presence and helps validate the need for _____
dressings.

Bioburden indicates bacterial presence and helps validate the need for antimicrobial dressings.

Stages of bioburden progression are:

o Contamination
o Colonization
o Local infection
o Spreading infection
o Systemic infection

Contamination Phase
 Contamination:

Presence of non-replicating bacteria on the wound surface without a
host response
o Normal and does not imply infection or an active disease process

Contamination Phase

Characteristics of this stage:

o Microbial Presence

o Non-Invasive

o Clinical Symptoms

o Healing Process

Contamination Phase

o Microbial Presence
 Microorganisms are introduced to the wound from:

 Surrounding environment
 Skin flora
 Other sources

Contamination Phase

Non-Invasive

 Contaminating microorganisms do not invade or harm tissue.
 Removed by the body's natural defenses

Contamination Phase

Clinical Symptoms

 No clinical signs of infection are present.
 Microorganisms do not adversely affect the wound.

Contamination Phase

Healing Process

 Contaminants do not interfere with the healing process.
 The wound can continue to heal as expected without additional
intervention for infection.

Colonization
 When bacteria multiply and attach to the wound surface, the dynamics change.

o Wound is considered colonized.

Colonization

o Microbial Presence

 Bacteria and other microorganisms are present and proliferating on the
wound surface but not invading deeper tissues.
 They are not causing any damage or symptoms.

Colonization

o Host Response

 There is no host response.
 Does not invade the deeper tissues

Colonization

o Clinical Symptoms

 No clinical signs of infection are present.

Colonization

Healing Process

 The presence of microorganisms during colonization does not interfere
significantly with the healing process.
 Wound can still progress toward healing without complications.

Local Infection
 Bacteria compete with the body’s healing process

Causes subtle clinical signs

Local Infection

o Microbial Presence

 Microorganisms multiply more aggressively within the wound.
 Reaches a critical level that competes with the body's healing processes

Local Infection

o Host Response

 Microorganisms invade underlying soft tissues enough to cause a host
response.

Local Infection

o Clinical Symptoms

 Hypergranulation
 Bleeding
 Friable granulation
 New or increasing pain
 Purulent exudate
 Odor
 Local warmth

Local Infection

o Healing Process

 The presence of bacteria interrupts the healing process

Spreading Infection

 Spreading infection occurs when the microbes multiply and spread into the surrounding tissue.
o If not managed appropriately, it can quickly progress to a systemic infection.

Spreading Infection - Characteristics of spreading infection:
o Microbial Presence

 Enough microbes are present in the wound.
 Multiply and spread beyond the initial wound area

Spreading Infection - Characteristics of spreading infection:

Host Response

 Bacteria and other microorganisms invade the surrounding tissues.
 Indicates the body's local defenses are overwhelmed

Spreading Infection - Characteristics of spreading infection:

Clinical Symptoms

 Extending induration
 Edema
 Purulent exudate
 Crepitus
 Lymphangitis

Spreading Infection - Characteristics of spreading infection:

Healing Process

 Significantly delayed due to impaired blood flow, tissue necrosis, and
increased inflammation