The isolation and identification of bacteria from wounds

A non-contact device for fast screening of wound infections

Screening for wound infection relies on the expertise of the provider. Clinical diagnosis of infections based on wound swab/biopsy results often takes a few days and may not assess the full wound. There is a need for a non-invasive tool that can quickly and accurately diagnose wound infection. Leukocyte esterase strips are used to identify various infectious diseases. However, it is not clear whether infected wounds also have elevated leukocyte esterase activities as compared with non-infected wounds. To achieve the objective, a device was developed to detect elevated leukocyte esterase activities in wounds by measuring wound exudates adsorbed onto wound dressings in 3 minutes. The efficacy of the device in assessing leukocyte esterase activities across various chronic wounds was tested. Such measurements were unaffected by the type of underlying wound dressing. By correlating the device outputs with clinical adjudication of infection, we found that this device had high positive predictive values for diagnosing wound infection in a wide variety of chronic wounds. In addition, a positive device output increases the probability of detecting infected wounds, while the negative device output reduces the probability of detecting infected wounds. This rapid non-contact and disposable diagnostic tool may serve as a rapid and accurate indication of infection in the chronic wound.

Imaging in Chronic Wound Diagnostics

Significance: Chronic wounds affect millions of patients worldwide, placing a huge burden on health care resources. Although significant progress has been made in the development of wound treatments, very few advances have been made in wound diagnosis. Recent Advances: Standard imaging methods like computed tomography, single-photon emission computed tomography, magnetic resonance imaging, terahertz imaging, and ultrasound imaging have been widely employed in wound diagnostics. A number of noninvasive optical imaging modalities like optical coherence tomography, near-infrared spectroscopy, laser Doppler imaging, spatial frequency domain imaging, digital camera imaging, and thermal and fluorescence imaging have emerged over the years. Critical Issues: While standard diagnostic wound imaging modalities provide valuable information, they cannot account for dynamic changes in the wound environment. In addition, they lack the capability to predict the healing outcome. Thus, there remains a pressing need for more efficient methods that can not only indicate the current state of the wound but also help determine whether the wound is on track to heal normally. Future Directions: Many imaging probes have been fabricated and shown to provide real-time assessment of tissue microenvironment and inflammatory responses in vivo. These probes have been demonstrated to noninvasively detect various changes in the wound environment, which include tissue pH, reactive oxygen species, fibrin deposition, matrix metalloproteinase production, and macrophage accumulation. This review summarizes the creation of these probes and their potential implications in wound monitoring.

Matrix metalloproteinases: The sculptors of chronic cutaneous wounds

Cutaneous wound healing is a complex mechanism with multiple processes orchestrating harmoniously for structural and functional restoration of the damaged tissue. Chronic non-healing wounds plagued with infection create a major healthcare burden and is one of the most frustrating clinical problems. Chronic wounds are manifested by prolonged inflammation, defective re-epithelialization and haphazard remodeling. Matrix metalloproteinases (MMPs) are zinc dependent enzymes that play cardinal functions in wound healing. Understanding the pathological events mediated by MMPs during wound healing may pave way in identifying novel drug targets for chronic wounds. Here, we discuss the functions and skewed regulation of different MMPs during infection and chronic tissue repair. This review also points out the potential of MMPs and their inhibitors as therapeutic agents in treating chronic wounds during distinct phases of the wound healing. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Is a wound swab for microbiological analysis supportive in the clinical assessment of infection of a chronic wound?

AIM

To determine whether bacteriological analysis of a wound swab is supportive in the clinical assessment of infection of a chronic wound.

METHODS

Patients attending an outpatient wound clinic who had endured a chronic wound for more than 3 weeks were clinically assessed for infection. In addition, standardized wound swabs were taken according to the Levine technique and the microbiological findings of the swabs compared with the clinical assessment of the wounds.

RESULTS

There was no significant relationship between the clinical assessments of the chronic wounds and the qualitative or quantitative bacteriological results of the swabs.

CONCLUSION

Microbiological analysis of wound swabs taken from chronic wounds to support clinical assessment of the wounds is waste of time and money. It may be preferable to assess chronic wounds clinically, however, validation studies of these signs and symptoms are needed.

Sample procurement for cultures of infected wounds: a systematic review

OBJECTIVE

Identifying the responsible pathogen is required in order to select optimum antimicrobial therapy for infected wounds, but the best techniques to use remain the subject of debate. Our aim was to assess the evidence on the value of wound swabs compared with biopsies.

METHOD

We conducted a systematic literature review with the terms 'wound infection', 'wound swab', 'wound swab technique', 'wound biopsy', 'wound culture', 'wound swab comparison', 'Levine swab technique', 'microbiological technique', 'specimen handling', 'bacterial load', 'perioperative care', 'swab', and 'culture'. We examined yields in identifying relevant pathogens, summarised salient features of qualifying studies, and defined knowledge gaps and endpoints that future studies should address.

RESULTS

Studies have been inconsistent, lacking specificity regarding wound types, clinical features, and sampling methods. We found moderate quality evidence that punch biopsies provide qualitative and quantitative information about the bacterial load and tissue reaction with nearly 100% sensitivity, 90% specificity and 95% accuracy for predicting wound closure. Biopsies are relatively invasive, costly, require skilled operators, and potentially exacerbate infection. Needle aspiration samples a limited portion and may enter uninfected tissue and extend infection. Wound swabs are minimally invasive, easier to perform and widely employed in clinical practice, but techniques vary. In comparative studies, the Levine technique was superior to the Z-swab techniques, and biopsies were more sensitive for antibiotic-resistant wounds than Levine or Levine-like swabs, suggesting that swabs may be useful for initial wound monitoring, but biopsies are preferred when antibiotic resistance is suspected.

CONCLUSION

The Levine swab is superior to the Z-swab technique and may be useful for initial wound monitoring, but quantitative biopsies are preferred for evaluation of antibiotic-resistant wounds and to monitor the response to treatment. There is limited evidence on the role of wound swabs for detecting wound colonisation versus infection and the impact of culture-guided therapy on such clinical outcomes as eradication of infection and accelerated healing. Future studies should specify patient populations, wound types, sampling protocols, and outcomes based on culture yield and treatment results, using rigorous statistical methodology.

Swab versus biopsy for the diagnosis of chronic infected wounds

OBJECTIVE

The goal of this review was to investigate the usefulness of a wound swab (using the Levine or Z technique) in comparison with a biopsy as a reliable method for the diagnosis of a chronic wound infection.

METHOD

A literature review using the electronic databases PubMed, CINAHL, and MEDLINE were searched by strategy. A total of 6 articles fulfilled the inclusion criteria.

MAIN RESULTS

The Levine technique detects more organisms in acute wounds, as well as in chronic wounds, than the Z technique. Comparing both with the biopsy as criterion standard, the diagnostic accuracy to diagnose a chronic wound infection by the Levine technique was higher in comparison to the Z technique. At a threshold of 3.7 × 10(4) microorganisms per swab, the Levine technique had a sensitivity of 0.90, a specificity of 57%, and a positive predictive value and negative predictive value of 0.77 and 0.91, respectively. Description of the method of swab taking was diverse and not uniform.

DISCUSSION

Only a few studies in the literature compare wound swabs with biopsies for the diagnosis of chronic infected wounds. Until now, the Levine technique has been considered as the most reliable and valid method, but there is an urgent need for a well-designed study with a sufficient number of patients to optimize the diagnostic accuracy of chronic infected wounds.

CONCLUSION

The best sampling technique for taking a swab has not yet been identified and validated. Until then, the authors recommend the Levine technique.

Bacterial isolates from infected wounds and their antibiotic susceptibility pattern: some remarks about wound infection

Wound infection plays an important role in the development of chronicity, delaying wound healing. This study aimed to identify the bacterial pathogens present in infected wounds and characterise their resistance profile to the most common antibiotics used in therapy. Three hundred and twelve wound swab samples were collected from 213 patients and analysed for the identification of microorganisms and for the determination of their antibiotic susceptibility. Patients with diverse type of wounds were included in this retrospective study, carried out from March to September 2012. A total of 28 species were isolated from 217 infected wounds. The most common bacterial species detected was Staphylococcus aureus (37%), followed by Pseudomonas aeruginosa (17%), Proteus mirabilis (10%), Escherichia coli (6%) and Corynebacterium spp. (5%). Polymicrobial infection was found in 59 (27·1%) of the samples and was mainly constituted with two species. The most common association was S. aureus/P. aeruginosa. All Gram-positives were susceptible to vancomycin and linezolid. Gram-negatives showed quite high resistance to the majority of antibiotics, being amikacin the most active against these bacteria. This study is mostly oriented to health care practitioners who deal with wound management, making them aware about the importance of wound infection and helping them to choose the adequate treatment options to control microbial infection in wounds.

Best technique for obtaining wound cultures

Infection is a major impairment in delayed and nonhealing chronic wounds. Cultures of chronic wounds are not routinely performed unless there is a clinical suspicion of infection. The culture is then indicated to identify the causative organism and to guide antibiotic therapy, systematically and topically. The deep tissue biopsy is regarded as the gold standard for identification of wound bioburden and clinical infection. However, controversy persists among practitioners as to the relevancy of doing cultures and the technique to use. This article will explore the various techniques used in clinical practice to obtain cultures for diagnosing wound infections.

The clinical efficacy of two semi-quantitative wound-swabbing techniques in identifying the causative organism(s) in infected cutaneous wounds

A prospective randomised controlled trial of two paired wound-swabbing techniques (Levine versus Z) was conducted to establish which method was more effective in determining the presence of bacteria in clinically infected wounds. The Levine technique involves rotating the wound swab over a 1-cm(2) area of the wound; the Z technique involves rotating the swab between the fingers in a zigzag fashion across the wound without touching the wound edge. Fifty patients were recruited into the study with acute (42%) and chronic wounds (58%). Overall, the Levine technique detected significantly more organisms than the Z technique (P≤ 0· 001). When acute and chronic wounds were analysed separately, the Levine technique again detected more organisms in both acute (P≤ 0· 001) and chronic wounds (P≤ 0· 001). We conclude that the Levine technique is superior to the Z technique and this result may be because of the Levine technique's ability to express fluid from the wound bed and thereby sampling a greater concentration of microorganisms from both the surface and slightly below the surface of the wound.

Assessing bacterial burden in wounds: comparing clinical observation and wound swabs

A randomised controlled trial (RCT) was conducted to compare the efficacy of nanocrystalline silver and cadexomer iodine dressings in healing chronic lower leg ulcers. The relationships between wound swab culture results and nurses' clinical assessments of critical colonisation, and between bacterial burden and healing rate, were also examined. There were 281 individuals with leg ulcers recruited. The bacterial burden of wounds was assessed using semi-quantitative wound swabs collected at baseline and intervals during the study. The study found no relationship between the nurses' clinical assessments and bacterial burden as identified from wound swabs in the wounds. A significant difference in wound healing was found with the use of nanocrystalline silver as compared to cadexomer iodine in the first 2 weeks of treatment when nil or low levels of leukocytes, gram positive bacilli, gram positive cocci or gram negative cocci were reported. This study has raised a number of questions regarding the need for further investigation into methods of assessing wound bacterial burden as well as the impact of wound biofilms on wound assessment and treatment.

Sternal wound infections: improvements made to reduce rates

Wound infections from surgical sites account for 15% of all healthcare-associated infections (National Institute for Health and Clinical Excellence (NICE), 2008). There is evidence that the care provided before and after the operation is paramount to minimize the risk of surgical site infection. Sternal wound infections lengthen hospital stays (or prompt readmission) and carry a high mortality rate. In August 2009 a Manchester Hospital discovered a cluster of three patients with sternal wound infections. A review of clinical data for patients having cardiac surgery from 1 December 2008 and 9 October 2009 revealed an increased incidence of patients with sternal wound infections. The data did not reveal a significant problem, but one that should be kept under observation. During the investigation no single pathogen had been identified as responsible and no obvious source of environmental infection was identified. Implementing additional infection prevention and control practices helped the hospital team to improve the care given to patients. A host of factors, ranging from providing more information on wound care to patients, improving audit scores, and adhering to NICE guidelines, contributed to the reduction in this type of surgical site infection.

Foot burns: Epidemiology and management

This is a retrospective study of the epidemiology and management of isolated foot burns presenting to the Welsh Centre for Burns from January 1998 to December 2002. A total of 289 were treated of which 233 were included in this study. Approximately 40% were in the paediatric age group and the gender distribution varied dramatically for adults and children. In the adult group the male:female ratio was 3.5:1, however in the paediatric group the male:female ratio was more equal (1.6:1). Scald burns (65%) formed the largest group in children and scald (35%) and chemical burns (32%) in adults. Foot burns have a complication rate of 18% and prolonged hospital stay. Complications include hypertrophic scarring, graft loss/delayed healing and wound infection. Although isolated foot burns represent a small body surface area, over half require treatment as in patients to allow for initial aggressive conservative management of elevation and regular wound cleansing to avoid complications. This study suggests a protocol for the initial acute management of foot burns. This protocol states immediate referral of all foot burns to a burn centre, admission of these burns for 24-48 h for elevation, regular wound cleansing with change of dressings and prophylactic antibiotics.

Are routine peritoneal fluid cultures during appendicectomy justified?

BACKGROUND

To determine the impact of obtaining routine peritoneal fluid cultures during appendicectomy, on the treatment and the clinical outcomes.

METHODS

The case notes of 137 consecutive patients having appendicectomy, selected from the microbiology database over a period of 1 year were reviewed. The microorganisms in peritoneal cultures, selection of antibiotics and clinical outcomes were recorded. Patients were subdivided into two groups; group I: uncomplicated appendicitis and group II: complicated appendicitis.

RESULTS

The study included 137 patients with a median age of 19 years. Cultures were obtained from 79.5% of patients (group I: 67/84, group II: 42/53). Cultures were positive in 28.3% (19/67) patients in group I and 69% (29/ 42) in group II. Wound infection (5.6%), prolonged ileus (7.5%) and intra-abdominal abscess (3.7%) were the recorded complications in group II. Antibiotics were modified in 3 out of 109 patients.

CONCLUSION

Intra-operative peritoneal cultures during appendicectomy do not significantly contribute towards patient management.

Exploratory Analysis of the Bacteriological Status of Post-irradiation Wounds and Its Relationship to Healing

AIMS

To investigate the bacteriological status of post-irradiation wounds and its relationship to wound healing in patients with nasopharyngeal cancer.

MATERIALS AND METHODS

One hundred and forty-six nasopharyngeal cancer patients with post-irradiation wounds on one or both sides of the neck were studied prospectively. Swabs were taken from the wounds at the initial study visit for bacteriological examination. A further swab for culture was taken when possible signs of infection developed. Wound healing was assessed on alternate days with respect to wound condition, the presence of clinical infection and healing time.

RESULTS

The results showed that most of the post-irradiation wounds were colonised with bacteria. This was not associated with clinical signs of infection in any instance. There was no association between wound healing time and the presence of organisms, the identity of organisms, the number of species of organisms, or the use of antibiotics.

CONCLUSIONS

The presence of bacteria in post-irradiation wounds, in the absence of clinical signs of wound infection, is not a barrier to wound healing. Oncology practitioners should recognise the unique features of radiation-induced wounds and skin reactions with confidence and provide appropriate treatment as needed.

Surgical wound benchmark tool and best practice guidelines

Surgical wounds that heal by primary intention are expected to heal without complication (Watret and White, 2001). Patients are frequently subjected to a variety of treatment regimens, often based on individual practitioners' preferences. This article discusses how one acute hospital trust developed a multidisciplinary approach to devise best practice guidelines. This was achieved through consensus and expertise of a working party, and a clinical practice benchmark tool for patients with surgical wounds to standardize and ensure the implementation of evidence-based practice. Clinical practice benchmarking is "a process through which best practice is identified and continuous improvement pursued though comparison and sharing" (Department of Health (DoH), 1999). The work has led to the development of a standardized assessment and documentation tool, which the working party hopes will be used trust-wide. In addition, ward staff are encouraged to undertake the benchmark process as a method of identifying areas where the use of this tool would ensure that standards of care could be improved.

Infection control: validity and reliability in wound swabbing

Wound infection is initially identified by the recognition of clinical signs and symptoms such as pus and cellulitis. Wounds are, however, cultured in order to establish the causative organism and ensure appropriate treatment. A 'gold standard' method for wound sampling has not been established although the literature details wound swabbing and looks at the variations in practice within this method. A number of procedural issues are raised which prompt the need for further study to eliminate these variables and reach consensus as to how to achieve a meaningful result, thereby increasing the validity and reliability.

Metronidazole gel in managing malodorous fungating wounds

Historically, the incidence of fungating wounds is not well documented. This article looks at the limited up-to-date information on the impact and incidence of fungating wounds in the UK. As fungating wounds generally signal palliative care and rarely heal, the ability to manage their unpleasant symptoms is increasingly important. One of the most distressing symptoms identified by patients is malodour; therefore, this article will review the limited research available on the use of metronidazole preparations to manage malodorous wounds.

Investigating the bacterial barrier properties of four contemporary wound dressings

The ability of four wound dressings (CombiDERM, Allevyn Hydrocellular, Tegaderm and Tielle) to resist penetration of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis and Pseudomonas aeruginosa was investigated in vitro using a dedicated test apparatus. With the exception of Tielle, each dressing prevented bacterial transmission over an 11-day challenge period. When both the wound contact surface and the external surface of Tielle were directly challenged with a bacterial suspension, penetration of the dressing was observed within three to five days. The breakdown of its outer membrane could explain the inability of Tielle to maintain a barrier to the passage of the test bacteria used in this wound model. On the basis of these data, CombiDERM, Allevyn Hydrocellular and Tegaderm dressings may facilitate infection control by acting as a physical barrier to the transmission of potentially pathogenic and antibiotic-resistant wound bacteria. However, further research is urgently required to determine whether or not the same results are observed in clinical practice.

Assessment of infection in diabetic foot ulcers

Typical signs of infection in diabetic foot ulcers are often absent or late. This literature review outlines the factors practitioners must take into account when assessing for and managing such infections.

Applying the principles of infection control to wound care

Human skin in healthy adults is inhospitable organisms. A wound may occur from any accidental or deliberate trauma that breaks the surface of the skin. Once this line of defence is broken there is a risk of infection. All soft tissue injuries, whether chronic, traumatic or surgical, involve the same basic biochemical and cellular processes. This article looks at the risk factors associated with healing of such wounds. The principles of asepsis, wound cleansing agents, choice of dressings and the taking of wound swabs are considered.

Swab taking

Experienced clinicians offer top tips to guide practice on specific wound-care issues.

Swabs and other sampling techniques

This study explores the absorptive capacity of standard cotton wool-tipped swabs in vitro and in vivo. An alternative wound exudate sampling technique using small filter paper discs is also briefly examined. Results showed a poor uniformity of fluid absorption by swabs and a limited correlation of wound exudate quantities in relation to visual estimates and size of wound. It was found, however, that swabs reliably removed material from a wound surface. The filter paper technique appeared to offer no advantages.