Influence of a changed care environment on bacterial colonization of burn wounds

Burn Unit Design-The Missing Link for Quality and Safety

The relationship between infrastructure, technology, model of care, and human resources influences patient outcomes and safety, staff productivity and satisfaction, retention of personnel, and treatment and social costs. This concept underpins the need for evidence-based design and has been widely adopted to inform hospital infrastructure planning. The aim of this review is to establish evidence-based, universally applicable key features of a burn unit that support function in a comprehensive patient-centered model of care. A literature search in medical, architectural, and engineering databases was conducted. Burn associations' guidelines and relevant articles published in English, between 1990 and 2020, were included, and the available evidence is summarized in the review. Few studies have been published on burn unit design in the past 30 years. Most of them focus on the role of design in infection control and prevention and consist primarily of descriptive or observational reports, opportunistic historical cohort studies, and reviews. The evidence available in the literature is not sufficient to create a definitive infrastructure guideline to inform burn unit design, and there are considerable difficulties in creating evidence that will be widely applicable. In the absence of a strong evidence base, consensus guidelines on burn unit infrastructure should be developed, to help healthcare providers, architects, and engineers make informed decisions, when designing new or renovated facilities.

The evaluation of nasal mupirocin to prevent Staphylococcus aureus burn wound colonization in routine clinical practice

BACKGROUND

Staphylococcus aureus wound colonization frequently occurs in patients with burns and can cause impaired wound healing. Nasal mupirocin application may contribute to the reduction of burn wound colonization of endogenous origin, whereas colonization by the exogenous route can be reduced by blocking cross-infection from other sources. In this study we evaluated whether the implementation of routine treatment of patients and burn center personnel using nasal mupirocin ointment reduces S. aureus burn wound colonization.

METHODS

We composed three study groups, consisting of a control period (Control), a mupirocin period (MUP), in which patients with burns were all receiving nasal mupirocin at admission, and a mupirocin+personnel period (MUP+P), in which we also screened the burn center personnel and decolonized S. aureus carriers by nasal mupirocin.

RESULTS

The patients who carried S. aureus in their nose and did not have S. aureus burn wound colonization at admission were considered as patients susceptible for the use of nasal mupirocin. In these patients, the S. aureus burn wound colonization rate was the same in all study groups. S. aureus nasal carriage was a significant independent risk factor for burn wound colonization (OR: 3.3; 95% CI: 1.4-7.6) when analyzed within the three study groups.

CONCLUSION

Although S. aureus carriage is a significant risk factor for developing burn wound colonization, the routine use of nasal mupirocin did not contribute to a reduction of burn wound colonization.

Antibacterial efficacy of silver-impregnated polyelectrolyte multilayers immobilized on a biological dressing in a murine wound infection model

OBJECTIVE

To investigate the antibacterial effect of augmenting a biological dressing with polymer films containing silver nanoparticles.

BACKGROUND

Biological dressings, such as Biobrane, are commonly used for treating partial-thickness wounds and burn injuries. Biological dressings have several advantages over traditional wound dressings. However, as many as 19% of wounds treated with Biobrane become infected, and, once infected, the Biobrane must be removed and a traditional dressing approach should be employed. Silver is a commonly used antimicrobial in wound care products, but current technology uses cytotoxic concentrations of silver in these dressings. We have developed a novel and facile technology that allows immobilization of bioactive molecules on the surfaces of soft materials, demonstrated here by augmentation of Biobrane with nanoparticulate silver. Surfaces modified with nanometer-thick polyelectrolyte multilayers (PEMs) impregnated with silver nanoparticles have been shown previously to result in in vitro antibacterial activity against Staphylococcus epidermidis at loadings of silver that are noncytotoxic.

METHODS

We demonstrated that silver-impregnated PEMs can be nondestructively immobilized onto the surface of Biobrane (Biobrane-Ag) and determined the in vitro antibacterial activity of Biobrane-Ag with Staphylococcus aureus. In this study, we used an in vivo wound infection model in mice induced by topical inoculation of S aureus onto full-thickness 6-mm diameter wounds. After 72 hours, bacterial quantification was performed.

RESULTS

Wounds treated with Biobrane-Ag had significantly (P < 0.001) fewer colony-forming units than wounds treated with unmodified Biobrane (more than 4 log10 difference).

CONCLUSIONS

The results of our study indicate that immobilizing silver-impregnated PEMs on the wound-contact surface of Biobrane significantly reduces bacterial bioburden in full-thickness murine skin wounds. Further research will investigate whether this construct can be considered for human use.

The role of nasal carriage in Staphylococcus aureus burn wound colonization

Thermal injury destroys the physical skin barrier that normally prevents invasion of microorganisms. This and concomitant depression of local and systemic host cellular and humoral immune responses are important factors that contribute to colonization and infection of the burn wound. One of the most common burn wound pathogens is Staphylococcus aureus. Staphylococcus aureus is both a human commensal and a frequent cause of infections leading to mild to life-threatening diseases. Despite a variety of infection control measures, for example patient cohorting and contact precaution at burn centres, S. aureus is still frequently encountered in burn wounds. Colonization with S. aureus has been associated with delayed wound healing, increased need for surgical interventions, and prolonged length of stay at burn centres. In this minireview, we focus on S. aureus nasal carriage in relation to S. aureus burn wound colonization and subsequent infection, and its impact on strategies for infection control.

Prevention of Staphylococcus aureus burn wound colonization by nasal mupirocin

BACKGROUND

There are two important routes for the transmission of Staphylococcus aureus to the burn wound. In the endogenous route, patients naturally carrying S. aureus colonize their own wounds, whereas in the exogenous route burn wounds are cross-infected from other sources. In this study we evaluated the effect of blocking the endogenous route on S. aureus burn wound colonization by mupirocin application in the nose of patients at the time of admission.

METHODS

From September 2000 to January 2002 all patients with burns admitted to a single dedicated Burn Centre received nasal mupirocin upon admission. This period was compared to two control periods (C1: July 1999 to July 2000 and C2: January 2002 to January 2003) for S. aureus burn wound colonization. The colonization risk was analysed, adjusting for confounding, with Cox proportional hazard regression.

RESULTS

A total of 98 patients did not have S. aureus burn wound colonization at the time of admission and were, thus, considered at risk for S. aureus acquisition during their stay. As compared to C1, the relative risk of acquiring S. aureus in their wound was 0.48 (95% CI: 0.24-0.97) in the mupirocin period and 0.55 (95% CI: 0.28-1.1) during the C2 period. S. aureus nasal/pharyngeal colonization was a significant independent risk factor for wound colonization (RR: 2.3; 95% CI: 1.2-4.2).

CONCLUSION

Nasal mupirocin may contribute to risk reduction of S. aureus wound colonization in patients with burns.

Lymph invasion route of bacteria and endotoxin and CD4+/CD8+ T cells ratio changes of draining lymph node of burn infection wound

The aim of this study was to determine the lymphatic invasion route of bacteria and endotoxin of burn wounds infected by Pseudomonas aeruginosa and moreover, the effect of P. aeruginosa infection of the burn wound on the draining lymph node and lymph fluid. Male Wistar rats were subjected to unilateral hind limb burn+wound infected by P. aeruginosa (infection limbs group) and contralateral hind limb burn alone (burn limbs group). On hours 6, 24 and 72 after infection, rats were killed, the common iliac lymph nodes (CILN) was collected for the culture of P. aeruginosa. Lymph fluid in the efferent lymph trunk of CILN was collected for the measurement of endotoxin by the Limulus Amebocyte Lysate test. Lymph fluid tumor necrosis factor-alpha (TNF-alpha) concentration was measured by enzyme-linked immunosorbent assay (ELISA). The CD4+/CD8+ T cells ratio of CILN was subjected to flow cytometry analysis. The results showed bacteria invasion incidence, endotoxin and TNF-alpha concentrations were significantly higher in the infection limb group when compared to the burn limb group (P<0.01). The CD4+/CD8+ T cell ratio was significantly lower on post-burn wound infection hours 72 (P<0.05). This study provides evidence that bacteria and endotoxin of burn wound infected by P. aeruginosa invade draining lymph node and lymph fluid. P. aeruginosa infection of the burn wound can increase TNF-alpha level of the draining lymph fluid and decrease CD4+/CD8+ T cells ratio of the draining lymph node.

Prevalence of toxin producing strains of Staphylococcus aureus in a pediatric burns unit

The aims of the study were to determine the sites in a pediatric burns unit that were contaminated with Staphylococcus aureus. Samples from the environment in bedrooms and the common room were taken monthly for 6 months using blood agar for total counts and Baird-Parker agar for S. aureus. The air was sampled using an air-sampling device and settle plates. Hard and soft surfaces including bed, blanket, sofa, chair, taps, bathtub, soft toys, locker and cupboard in the same rooms were sampled using contact plates. Swabs were taken from staff monthly for 3 months. S. aureus isolates were tested for production of enterotoxins A-D and toxic shock syndrome toxin-1 using a reverse passive latex agglutination test. The results showed that S. aureus was recovered more frequently using settle plates than using the air sampler. All surfaces sampled were contaminated with S. aureus and contamination was greatest in frequently occupied rooms. A variety of toxin producing isolates were found with enterotoxin C isolates, either alone or in combination with TSST-1 (toxic shock syndrome toxin-1) dominant. The staff were transiently colonised with S. aureus strains with a different toxin production pattern. The results show that airborne transmission may be a route for infection by S. aureus and is responsible for contaminating the environment.

Aerobic bacterial isolates from burn wound infections and their antibiograms--a five-year study

A retrospective study of major aerobic bacterial isolates from pus/wound swabs taken from patients admitted to the burn unit at Govt. Medical College Hospital, Chandigarh, India, over a period of 5 years (June 1997-May 2002) was undertaken. The study was carried out to determine the bacterial profile and antimicrobial susceptibility of the isolates and to describe the change in trends over the study period. The pus/wound swabs yielded very high culture positivity (96%) for 665 total isolates. Pseudomonas aeruginosa was found to be most common isolate (59%) followed by Staphylococcus aureus (17.9%), Acinetobacter spp. (7.2%), Klebsiella spp. (3.9%), Enterobacter spp. (3.9%), Proteus spp. (3.3%) and others (4.8%). Although P. aeruginosa continued to remain the predominant isolate over the five years, a constant and significant increase in the incidence of Acinetobacter spp. was found. Amikacin was found to be the most effective drug against gram negative bacteria, however, resistance to it was significantly increased over 5 years. For S. aureus and P. aeruginosa netilmicin and piperacillin were found to be the most effective drugs. Most of the isolates showed high level resistance to antimicrobial agents.

Molecular epidemiology of Staphylococcus aureus colonization in a burn center

The aim of this study was to investigate carriage of Staphylococcus aureus by patients and health care workers (HCW) and to define the genetic relationship of S. aureus strains isolated from burn wounds. At admission, 19/55 (34.5%) patients carried S. aureus in their nose and/or throat. Of this group, 95% subsequently colonized their burn wounds with S. aureus. Molecular analysis showed that in 78% of these cases the burn-wound colonizing strain was identical to the strain carried at admission. Importantly, 23/36 (64%) patients who did not carry S. aureus at admission also developed burn-wound colonization. In this group, three dominant genotypes were identified as colonizing strains of burn wounds. These clones represented also the majority (59%) of S. aureus strains cultured from the nose and/or throat of health care workers and patients. If patients were admitted to one of the Intensive Care rooms burn wounds of non-carriers were not colonized with S. aureus as long as they remained in such isolation. Only patients who carried S. aureus at admission developed burn-wound colonization with that genotype they carried in the nose or throat. Both carriage in patients and health care workers and auto-infection play a crucial role in (cross-) colonization events.

Bacteriology of burns at the Queen Elizabeth Central Hospital, Blantyre, Malawi

A retrospective study to determine the bacterial profile and antibiotic susceptibility pattern of burn isolates at the Queen Elizabeth Central Hospital (QECH), Blantyre, Malawi was undertaken. While a total of 1825 burn patients were admitted to the hospital over a 6-year period (January 1994 to December 1999) only 317 (17.4%) specimens selected from as many patients were processed. One hundred and seventy (170/53.6%) specimens yielded single while the rest (147/46.4%) had multiple isolates giving a total of 535 bacterial isolates. Of this number, 236 (44.1%) were Gram-negatives and 299 (55.9%), Gram-positives. Among the Gram-negatives, Pseudomonas aeruginosa, Proteus mirabilis, Coliforms/Escherichia coli and Klebsiella pneumoniae were the most common accounting for 94.1% while in the Gram-positive group, staphylococcal and streptococcal spp. predominated (100%). However, the three most common isolates were Staphylococcus aureus (37.6%), P. aeruginosa (22.4%) and beta-haemolytic streptococci (13.6%). While S. aureus and beta-haemolytic streptococci were most susceptible to penicillin (33.3 and 64.4% susceptibility, respectively), gentamycin appeared most effective against P. aeruginosa (53.3%). A general broad-spectrum resistance to panels of antibiotics used in the study was however observed among the bacterial isolates. From these results, S. aureus, P. aeruginosa, streptococcal spp., P. mirabilis, Coliforms and K. pneumoniae representing 96.4% of all isolates were the most common in the Burns Unit.

Expression of the soxR gene of Pseudomonas aeruginosa is inducible during infection of burn wounds in mice and is required to cause efficient bacteremia

Burn wounds are prone to infection by Pseudomonas aeruginosa, which is an opportunistic pathogen causing various human diseases. During infection, the bacterium senses environmental changes and regulates the expression of genes appropriate for survival. A purine-auxotrophic mutant of P. aeruginosa was unable to replicate efficiently on burn wounds, suggesting that burn wounds are purine-deficient environments. An in vivo expression technology based on purEK gene expression was applied to the burned mouse infection model to isolate P. aeruginosa genes that are specifically induced during infection. Four such in vivo-inducible (ivi) genetic loci were identified, including the gene for a superoxide response regulator (soxR), the gene for a malate synthase G homologue (glcG), an antisense transcript of a putative regulator responding to copper (copR), and an uncharacterized genetic locus. SoxR of Escherichia coli is known to regulate genes involved in protecting the bacterium against oxidative stress. The expression of soxR was proven to be highly inducible during the infection of burned mice and also inducible by treatment with paraquat, which is a redox-cycling reagent generating intracellular superoxide. The SoxR protein functions as an autorepressor in the absence of paraquat, whereas in the presence of paraquat, this autorepression is diminished. Furthermore, a soxR null mutant was shown to be much more sensitive than wild-type P. aeruginosa to macrophage-mediated killing. In support of this observation, a soxR null mutant exhibited a significant delay in causing systemic infections in the burned mice. Since most mortality in burn patients is caused by systemic infection, the defect in the ability to cause efficient bacteremia in burned mice suggests an important role of the soxR gene in the infection of burn wounds.