Using Bacterial Fluorescence Imaging and Antimicrobial Stewardship to Guide Wound Management Practices: A Case Series

 The EWMA position paper⁵ lists 3 key factors that contribute to antimicrobial misuse in wound care: 1) diagnostic uncertainty (is there a bacterial infection in this wound?), 2) clinician ignorance regarding when to treat with antibiotics or clinician fear of failing to treat properly, and 3) patient demands for prescription of inappropriate antibiotics. Current best clinical practice in wound infection diagnosis relies on subjective, qualitative visual assessment of clinical signs and symptoms^7,8 with confirmation via wound sampling for microbiological analysis,⁹ which delays confirmation by several days. However, clinical studies^10-13 have shown high levels of bacteria in the absence of signs and symptoms, even in some cases of wound infection, and this is a major contributing factor to diagnostic uncertainty and to clinician fear of improper treatment.¹⁴ Real-time visualization to identify concerning levels of bacteria at the bedside could help alleviate uncertainty, instill clinician confidence, and facilitate evidence-based wound care treatment.⁵ 

Recently, bacterial fluorescence imaging has been developed and validated as a method to screen at the bedside for bacterial presence in and around wounds.^15-18 This safe, noncontact, contrast agent-free method facilitates visualization of bacteria in real time; decades of research have demonstrated that low intensity illumination with violet light is safe. The handheld imaging device emits a low-intensity violet light (405 nm) that excites the tissue and bacteria within and around a wound, leading tissues to fluoresce green while bacteria fluoresce either red or cyan, enabling immediate bacterial localization.¹⁷ Several prospective clinical trials^15-17 with this device, in which more than 120 wounds were imaged and sampled for corresponding microbiological confirmation, have demonstrated its ability to detect the most common wound pathogens (including Staphylococcus aureus, Escherichia coli, Enterobacter spp, Proteus spp, and Klebsiella pneumonia) at bacterial loads of clinical concern (≥10⁴ CFU/g, a moderate/heavy load¹⁵). Visualization of bacteria at these levels does not independently diagnose the host response of infection; the device is meant to be used in conjunction with gold standard clinical signs and symptoms, as per standard practice. Although intra- and interrater reliability was not addressed, a 60-patient, prospective, single-blind, multisite evaluation¹⁵ of this imaging device demonstrated a 100% positive predictive value of the device for detecting bacteria within and around chronic wounds, completely eliminating the acquisition of false negative samples using biopsy or curettage. A prospective, single-site, 12-patient study¹⁷ demonstrated that when the device was used to guide aspects of wound care to reduce bioburden (ie, sampling, cleaning, debridement, and antimicrobial or antibiotic selection), the rate of wound healing was significantly improved compared to standard of care (P = .017). 

This case series of 7 patients is presented to report use of real-time bacterial fluorescence imaging to guide immediate, evidence-based antibiotic decision-making and, as such, antimicrobial stewardship practices. 

Antimicrobial stewardship practices are particularly challenging to implement in the field of wound care for several reasons: 1) wound infections are frequently polymicrobial, requiring broad-spectrum antibiotic therapy; 2) many wounds experience frequent, recurrent infections, exposing patients to repeated courses of antibiotic therapy; and 3) no worldwide consensus for diagnosing infection in wounds has been achieved and most criteria for diagnosing infection are highly subjective.⁵ The advanced age of patients who typically experience chronic wounds is also a challenge due to the higher prevalence of preexisting conditions in this older population that increase risk factors for wound colonization with multidrug-resistant organisms, as shown by epidemiological and surveillance studies.¹⁹ Furthermore, the high prevalence of wounds among the elderly in long-term care facilities (ie, facilities where clinicians often are not onsite) was shown in a retrospective study of 100 patient wounds across 12 nursing homes to lead to frequent inappropriate overprescription of antibiotics in this population, with medicines often prescribed via telephone without any assessment by a clinician.²⁰ 

Antibiotics are used extensively in the treatment of chronic wounds, although rates of antibiotic prescribing in chronic wound patients vary widely depending on country, care setting, wound type, and a host of other factors. A Swedish retrospective study²¹ of 707 chronic wound care patients found 60% had received at least 1 antibiotic during a 6-month period, while a United Kingdom database search found almost 70% of chronic wound patients in Wales received at least 1 systemic antibiotic in the previous year compared with 30% of age-matched, nonwound patients.²² Data for both of these studies were collected in the year 2000 or earlier before awareness of the need for antimicrobial stewardship practices had increased. Yet results of a more recent Norwegian study²³ (2008) citing antibiotic prescription rates of 75% among 60 chronic wound patients who had not yet been referred to a wound care clinician suggest awareness efforts directed at general practitioners have been largely ineffective; after conducting thorough wound assessments, wound care clinicians agreed with the need for antibiotics in only 1 of these 60 patients (<1%). Additional studies reporting current prescription rates are required to better understand whether antimicrobial stewardship campaigns have yielded success in the wound care field.  

The diagnostic uncertainty in determining whether bacteria actually are present in a wound at clinically concerning levels and clinician fear of a poor outcome from lack of antibiotic treatment are key contributing factors to antibiotic overusage in wound care patients.⁵ Rapid diagnostic tests for the presence of bacteria, performed in conjunction with current best practices for assessment of clinical signs and symptoms of infection, have been proposed as a possible solution to these problems.⁵ 

Patients. Over a 7-week period in the summer of 2016, all Lion’s Gate Hospital, North Vancouver, British Columbia, Canada inpatient and wound care clinic outpatients who consecutively required consultation from an infectious disease specialist were prospectively included in the evaluation of the fluorescence imaging device. All wounds were assessed per standard of care for clinical signs and symptoms of infection in addition to being imaged for bacterial fluorescence. Wounds were deemed healable when factors that were impeding healing were able to be modified and optimized, as per the healable wound criteria of the Wounds Canada Best Practice Recommendations for the Prevention and Management of Wounds²⁴: the patient 1) had the physical capacity to heal, 2) was making lifestyle choices consistent with optimal wound healing, and 3) was in a system/environment that could support optimal wound healing. Each patient provided informed written consent for publication of their anonymous case information and images of their wounds in a scientific publication format. Patients who were unable to provide consent were ineligible for inclusion in this study. 

Imaging procedure. Wounds were imaged at the bedside for bacterial fluorescence by an experienced wound care clinician as part of routine wound assessments, which included standard assessments for wound healing and for clinical signs and symptoms of infection as per International Wound Infection Institute guidelines.⁷ Using the MolecuLight i:X Imaging Device (MolecuLight Inc, Toronto, Canada),¹⁵ regular white light images of the wound were acquired under standard room lighting conditions. Bacterial fluorescence images were acquired after the room was made dark by turning on the device’s violet excitation light and shining the light over the area of the wound. A range finder on the device was used to ensure all images were taken at the optimal imaging distance (8 cm to 12 cm), and a light sensor on the device indicated when the room was dark enough for fluorescence images to be acquired. 

The clinician used the bacterial fluorescence images to determine if significant levels of bioburden (≥10⁴ CFU/g) were present in wounds, as has been described previously.¹⁵ In brief, when excited by 405-nm violet light, tissues fluoresce green (collagens) and bacteria fluoresce red (porphyrin-producers, eg, S aureus) or cyan (pyoverdine-producing P aeruginosa), and specialized optical filters reveal these signals in real time on the device’s display screen.¹⁷ The device can visualize bacteria to a depth of ~1.5 mm,¹⁷ with fluorescence from surface bacteria generally appearing brighter red than subsurface bacteria that appear more blush-colored.¹⁵ This device has been approved by Health Canada and was used per its intended use for visualizing bacteria within and around wounds. 

All wounds exhibiting red or cyan fluorescence were considered to have concerning bacterial loads; swabs from regions of red or cyan fluorescence were taken using the Levine technique to confirm via standard wound care culture analysis. The level of bioburden was considered to be ≥10⁴ CFU/g (moderate/heavy growth) when imaging was positive for a red fluorescence signal,¹⁵ and the extent of bacterial burden was qualitatively assessed based on the surface area occupied by the fluorescence signal.   

When deemed appropriate, regions of bacterial fluorescence on images also were used to guide the extent and location of surgical debridement. Any change to wound management or antibiotic decision-making (eg, change of dressing, antimicrobials, or antibiotics used) as a result of the fluorescence image was electronically noted by the wound care clinician on a spreadsheet used to track the utility of the device. 

Case 1. Mr. K, an 83-year-old with ependymoma (central nervous system tissue cancer) and diminishing mobility and minimal at-home care, presented with a septic sacral ulcer. Mr. K had a past history of hypothyroidism, hypertension, mild cognitive impairment, neurogenic bladder, and seizure disorder. At the time of hospital admittance, Mr. K’s diagnosis included a large sacral pressure injury measuring 12 cm x 10 cm x 2.5 cm, osteomyelitis of the sacrum, seizure disorder, deconditioning, and aspiration pneumonia. Mr. K was taking levetiracetam, levothyroxine, perindopril, phenytoin, amlodipine, atenolol, tamsulosin, and systemic antibiotics at the time of his admission. A wound care specialist was consulted to determine whether the wound simply required cleaning and debridement or if a further course of antibiotics was warranted.  Assessment findings indicated considerable size and depth of wound, drainage, and odor. Measures employed to ensure suitable offloading also were assessed. Fluorescence images acquired of his wound revealed an extensive area of bioburden (see Figure 1; bacteria appear red on fluorescence images)  that remained after conservative surgical wound debridement of necrotic tissue. Based on these fluorescence images, the antibiotic course was continued. In addition to guiding this treatment decision, fluorescence images demonstrating the presence and location of bioburden were used to guide swab location as well as additional surgical debridement, conservatively targeted solely to the regions of red fluorescence. Mr. K’s blood cultures confirmed the presence of bacteria (Bacteroides spp), and fluorescence-guided swabs confirmed heavy growth of Morganella morganii, E coli, and Enterococcus faecalis. Due to the fragile nature of the wound tissue post debridement, the wound received packing dampened with povidine iodine for 24 hours, at which point negative pressure wound therapy (NPWT) with instillation of saline was begun. Fluorescence images acquired on day 5 of NPWT and instillation treatment showed persistent bioburden (see Figure 1) and guided additional targeted debridement of slough and necrotic tissue (sparing noncontaminated regions). Images acquired at each subsequent dressing change showed decreases in red fluorescence, demonstrating the effectiveness of the treatment. Because the low intensity violet light illumination of the device is entirely safe for clinical use per Rennie et al,¹⁵ repeat imaging sessions and high frequency of use have no known adverse effects. Six (6) weeks after hospital admittance the wound was managed with NPWT along with offloading, nutrition changes, and other modifiable patient lifestyle factors.¹⁶ At this time, the wound bed was 100% granulated with no signs of infection.   

Case 2. During her hospital stay, Ms. Z, a 93-year-old inpatient originally admitted for pneumonia, developed a pressure injury on her coccyx measuring 5 cm x 4 cm x 2.7 cm with 4 cm of undermining at 12 o’clock. Comorbidities included chronic heart failure, chronic renal failure, chronic obstructive pulmonary disease (COPD), atrial fibrillation, hypertension, and hypothyroidism. Ms. Z was taking bisoprolol, diltiazem, furosemide, levothyroxine, and warfarin at the time of admission. The pressure injury was being treated with an absorbent foam dressing and packing ribbon that was impregnated with sodium chloride. Ms. Z’s respiratory status improved and her hospitalist requested a consult with a wound care specialist to inquire about discharge/transfer from the acute ward. Bacterial fluorescence images were taken as part of wound assessment; they revealed and documented a widespread area of bioburden in and around her wound (see Figure 2A,B). Clinical assessment included periwound area of erythema of approximately 2 cm to 3 cm and minimal progress with granulation tissue. Ms. Z still required twice-daily dressing changes because considerable exudate was noted. This resulted in a consult with an infectious disease specialist, who prescribed systemic antibiotics and suspended all plans for immediate discharge. Swabs analyzed for typical culture and sensitivity later confirmed heavy growth of mixed anaerobes. In addition to antibiotic management, the wound was treated twice daily with 1-inch packing dampened with povidone iodine; 7 days later, NPWT was initiated for 2.5 weeks. Bacterial fluorescence images acquired 6 days after antibiotic initiation demonstrated antibiotic effectiveness, as noted by an absence of red fluorescence (see Figure 2C). Based on these images, no additional antibiotics were prescribed. Bioburden in the wound then was controlled with an absorbent dressing containing methylene blue and gentian violet. The wound was deemed healable provided all established, modifiable risk factors were addressed (eg, offloading, mobility, nutrition, recovery from pneumonia). At Ms. Z’s 6-month follow up, the wound was almost healed (0.5 cm x 0.5 cm x 0.5 cm). 

Case 3. Ms. U, a 63-year-old patient with lymphoma, presented to the outpatient chemotherapy unit where she was being treated with combination chemotherapy (R-CHOP) for follow-up. Known patient comorbidities included type 2 diabetes, diabetic retinopathy, dyslipidemia, hypothyroidism, and hypertension for which she was taking metformin, glibenclamide, empagliflozin, levothyroxine, and bisoprolol perindopril atorvastatin. On this visit, a sacral injury (6 cm x 6 cm, 100% slough) also was noted for which Ms. U had not been receiving treatment. A wound care specialist was consulted; standard wound assessment and bacterial fluorescence images of the wound were performed. Standard assessment did not suggest infection; however, bacterial fluorescence images verified the presence of a large region of bioburden (see Figure 3A,B) and Ms. U was admitted for treatment of her sacral injury. Swabs taken from regions of red fluorescence on images later confirmed heavy growth of S aureus and E coli. Upon Ms. U’s admission, systemic antibiotics were started immediately and she received additional measures such as fluorescence-guided surgical debridement targeting areas of red fluorescence and offloading to manage her unstageable (obscured by necrotic tissue), complex pressure injury. After 7 days of antibiotic treatment and NPWT, visualized bacterial fluorescence in the wound bed was notably decreased (see Figure 3C). Wound size increased over the following weeks due to debridement and cleaning of the necrotic region (7 cm x 6 cm x 3.5 cm), revealing the patient’s coccyx bone and prompting further antibiotic treatment for osteomyelitis. After 2 months of inpatient wound care treatment, Ms. U was transferred to a residential care setting where bioburden was controlled using a tunnelling absorbent dressing containing methylene blue and gentian violet. At the time of transfer, Ms. U’s wound was deemed healable, recognizing that healing the wound would take a minimum of 6 to 8 months. At 6 months after originally discovering the wound, it measured 2 cm x 1.3 cm x 1.5 cm with 100% granulation tissue. 

Case 4. Eighty-two (82)-year-old Ms. T was admitted to the hospital for a painful venous leg ulcer with nondemarcated edges. Her comorbidities included noninsulin-dependent diabetes, hypertension, chronic heart failure, gout, and hypothyroidism. At the time of admission, Ms. T was taking gabapentin, pantoprazole, hydromorphone, levothyroxine, hydrochlorothiazide, ferrous gluconate, amlodipine, glycopyrronium bromide (for sweating), and metformin. Her wound was treated with absorptive silicone foam and light compression. A wound care protocol for discharge and community follow-up was requested from the wound care team. Upon evaluation by the wound care specialist, traditional signs and symptoms of extensive erythema (ie, >2 cm from the wound edge) were not present, although pain was still a factor. Additionally, bacterial fluorescence images revealed an extensive area (ie, >2 cm from the wound edge) of bacterial burden (see Figure 4A,B), leading to a suspension of patient discharge, prescription of a systemic antibiotic, and a modified wound care protocol to include an antimicrobial dressing (sustained-release povidine iodine). Swabs of the region that fluoresced red/blush on bacterial fluorescence images later confirmed heavy growth of Acinetobacter baumannii. The wound was deemed healable (taking 2 to 3 months to heal), provided compression and antimicrobial dressing therapy were maintained; the wound closed within 6 weeks. 

Case 5. Ms. R was an 88-year-old with right lower leg cellulitis who presented at a wound outpatient clinic. Comorbidities included hemorrhagic stroke with no deficits, atypical seizures, hypothryodism, dyslipidemia, hypertension, and COPD. At the time of admission, Ms. R was taking pantoprazole, hydrochlorothiazide, atenolol, phenytoin, atorvastatin, levothyroxine, losartan, fluticasone (puff), citalopram, and conjugated estrogen. She had received a skin graft (11 cm x 10 cm x 0.5 cm) on the same ankle 1 year prior for squamous cell carcinoma; that wound had closed. The skin encompassing approximately 6 cm x 6 cm within the previously closed graft area was tender and had erythema and superficial splits/tears in the skin with clear exudate. At the time of presentation, Ms. R had just returned from a long overseas flight during which the previously grafted leg had become swollen and red. Standard wound assessment did not reveal any overt signs of infection; however, bacterial fluorescence images revealed blush red (subsurface) bacteria (see Figure 5A,B). These images, together with the patient’s wound history, led to a prescribed course of oral antibiotics and selection of silver-based antimicrobial dressings. Swabs later confirmed heavy growth of S aureus. Ms. R’s wound was deemed healable and closed within 3 to 4 weeks.  

Case 6. Ms. P was 64 years old with no notable past medical history. She sustained a type 3 skin tear injury of the lower leg.²⁵ Ms. P presented in the emergency room (ER) 3 weeks later when the wound had not healed; she had been treating the tear herself with over-the-counter antibiotic ointment and was only taking trazadone for sleep. She noted increasing redness and pain, but the ER physician found no other clinical signs or symptoms of infection. Ms. P was concerned about possible infection because in 3 weeks she would be travelling, prompting the physician to prescribe oral antibiotics and a consultation with a wound care specialist. Fluorescence images were acquired and demonstrated no bacterial burden in or around the wound (see Figure 6A,B). The real-time images were negative for bacterial fluorescence, so antibiotic treatment was eliminated. Loose tissue around the wound was debrided, and a silicone foam dressing was applied. Traditional wound care without any antibiotics or antimicrobial treatments lead to wound closure within 2 weeks, prior to Ms. P’s travel (see Figure 6C). 

Case 7. Mr. N was a 57-year-old with gastric cancer, hypertension, anemia, and peripheral arterial disease who was prescribed systemic antibiotics after a partial gastrectomy (wound size: 2.9 cm x 1.3 cm x 0.8 cm). Mr. N also was taking pantoprazole, almotriptan, sildenafil, and escitalopram. Several days before his hospital discharge, abdominal midline dehiscence was noted; the general surgeon initiated oral antibiotics and the wound was treated with 0.25-inch antimicrobial packing and an absorptive foam cover dressing. Mr. N returned to the ER 7 days later when he was due to conclude oral antibiotic treatment because he was concerned with increased wound drainage and the midline opening. The wound appeared to be clean and granulating with no evident odor. Fluorescence images showed no evidence of bacterial contamination (see Figure 7A,B). This information was relayed by the wound care specialist to the surgeon, and the decision was made to prescribe no further antibiotics; traditional postsurgical wound care with antimicrobial packing ribbon was continued. No microbiological cultures were obtained at this time point. At Mr. N’s 2-week follow-up with the general surgeon, the wound was virtually closed and by week 3 had closed completely. 

This 7-patient case series found that real-time bacterial fluorescence imaging facilitated evidence-based deployment of systemic antibiotics and prevented their unnecessary use. Antibiotic resistance is a growing public health crisis of global concern that can be prevented, at least in part, by antimicrobial stewardship practices, as shown by systematic reviews and meta-analysis.^4,26 The EWMA⁵ recently identified 3 possible solutions to antibiotic misuse: 1) rapid diagnostic tests for the presence of bacteria, 2) clinician education and reassurance, and 3) patient education.⁵ In this series of wound care patients, a beneficial effect of bacterial fluorescence imaging was noted on each of these 3 areas. Images assisted the clinician’s antimicrobial stewardship practices by providing evidence of bacterial presence at the bedside and by guiding clinician swabbing to regions of bioburden, optimizing wound specimens for culture before starting therapy. Two (2) wounds that lacked bacterial fluorescence on images, supported by a lack of clinical signs and symptoms of infection, reassured the clinician and patient that asymptomatic bioburden was not present and that antibiotics were not required. Five (5) wounds exhibiting widespread bacterial burden on fluorescence images were prescribed antibiotics, resulting in a noted decrease in bacterial burden on follow-up images. 

Although this case series focuses on antimicrobial stewardship, additional benefits of bacterial fluorescence imaging on wound management were observed for many of these wounds. First, fluorescence images identified wounds with asymptomatic bacterial burden and highlighted areas of concern in and around a wound that otherwise might have been overlooked, leading to more timely treatment interventions to reduce bacterial load. This was of particular interest in light of the tissue, infection/inflammation, moisture balance, edge of wound (TIME) and debridement/devitalized, infection/inflammation, moisture balance, edge of wound (DIME) guidelines²⁷ for wound bed preparation, highlighting the importance of wound edge preparation and warranting further study. 

Second, images of bacterial fluorescence also provided the clinician with a map to guide wound sampling. The optimal location to sample a wound is rarely obvious, even for highly experienced wound care clinicians; according to systematic reviews and clinician auditing studies,^28-30 wound sampling is prone to costly false negatives that can delay or entirely prevent appropriate treatment. In this study, microbiological analysis of bacterial fluorescence targeted swabs later confirmed heavy bacterial growth in 5 cases. 

Third, fluorescence images also guided the extent and location of surgical debridement in several of these patients. Images highlighting regions of bioburden enabled the clinician to target the bioburdened tissue while sparing noncontaminated tissue (ie, tissue not exhibiting bacterial fluorescence). 

Lastly, images also provided rapid feedback on the effectiveness of treatments against bacterial burden (wound cleaning, debridement, dressings, and so on). Wound care treatments require time to have an effect; without fluorescence imaging, clinicians often wait several weeks before a clear effect of treatment, such as reduction in wound size or in clinical signs and symptoms, can be determined.³¹ Wound culture results at the hospital in this study commonly take 72 hours. However, in this series of patients, the authors were able to note either the wound/symptom persistence or the reduction in visualized bacterial fluorescence pre- and postcleaning, pre- and postdebridement, and/or at the next dressing change. The wound management strategy could immediately be changed if no effect of treatment was observed. 

To the authors’ knowledge, this is the first report using this or any bacterial visualization technology to facilitate antimicrobial stewardship practices in wounds other than burns.¹⁸ Although this case series establishes the feasibility of this approach, larger studies to determine approach effectiveness on a large patient population are certainly required. Because this technology is novel and focused on bacterial detection rather than bacterial treatment, data with which to compare the current findings are limited. Other technologies that have been applied to wound care antimicrobial stewardship programs and practices are mostly advances in health information technology systems,³² advances in treatment technologies targeting bioburden (eg, reactive oxygen species³³ and gas plasma-targeting of bioburden to manage infections³⁴), and advances in topical nonantibiotic antimicrobials that can be used in lieu of systemic antibiotics when deemed appropriate.^35,36 It is likely that advances in infection diagnosis, antibiotic prescribing surveillance, and nonantibiotic treatment options, in addition to clinician and patient education, all will be required to develop comprehensive and effective antimicrobial stewardship practices in the wound care field. 

This case study describes the effective incorporation of point-of-care bacterial fluorescence imaging using a handheld device to facilitate antimicrobial stewardship practices in 7 patients with diverse wounds and comorbidities. The feasibility and potential of using real-time bacterial fluorescence imaging to guide antimicrobial stewardship practices should prompt further reliability and specificity testing as well as prospective, randomized controlled studies to evaluate the effect of this diagnostic aide on antibiotic usage and wound outcomes in a larger population. 

Dr. Rennie is an employee of MolecuLight, Inc.