|Year : 2015 | Volume
| Issue : 4 | Page : 337-341
Aerobic bacteriology of burn wound infections
Sarita Otta1, Jayant Kumar Dash2, Bichitrananda Swain3
1 National Reference Laboratory, Regional Medical Research Center, Kalinga Nagar, Bhubaneswar, Odisha, India
2 Department of Burn and Cosmetic Surgery, Institute of Medical Sciences and SUM Hospital, S'O'A University, Kalinga Nagar, Bhubaneswar, Odisha, India
3 Department of Microbiology, Institute of Medical Sciences and SUM Hospital, S'O'A University, Kalinga Nagar, Bhubaneswar, Odisha, India
|Date of Web Publication||18-Sep-2015|
HIG 5/4 Ext. Phase-1, Housing Board Colony, Chandrasekharpur, Bhubaneswar - 751 016, Odisha
Source of Support: Nil., Conflict of Interest: No.
Introduction: Burn wound infections are important cause of mortality, morbidity and prolonged hospitalization in burn patients as the causative agent is generally a multidrug resistant organism. The pattern of microbial flora infecting burn wound varies according to geographical pattern as well as with duration of hospital stay. Objective: The present study aims to identify the causative agents of burn wound infections in our hospital, to assess the change in pattern of flora in accordance to duration of wound as well as to determine the sensitivity pattern of isolates. Materials and Methods: Wound swabs from 52 patients admitted in Burn unit of IMS and SUM Hospital, Bhubaneswar were collected every 5th day during their hospital stays and were cultured. The results were interpreted according to the standard methods and antibiotic susceptibility pattern was noted. Results: The most common organism isolated was Staphylococcus aureus, that is, 20 (47.6%) while Klebsiella spp. 12 (28.6%) was the most common Gram-negative isolate. The commonest organism isolated in the 1st week of hospital stay was S. aureus (15.4%), but it was Acinetobacter spp. (22.2%) in 2nd week and coagulase negative Staphylococcus in 3rd week of hospital stay S. aureus was mostly sensitive to levofloxacin (77.8%) and netilmycin (98%). Conclusion: The pattern of bacterial flora changes according to duration of hospital stay. Effective strict isolation techniques and infection control are thus needed to decrease the occurrence of burn wound infection.
Keywords: Antibiotic resistance, bacteria, burn wounds, infection
|How to cite this article:|
Otta S, Dash JK, Swain B. Aerobic bacteriology of burn wound infections. CHRISMED J Health Res 2015;2:337-41
| Introduction|| |
Despite many advances in burn wound care, infection over the burnt area leading to septicemia still accounts for about 75% of all deaths in burn patients. Infection on burns is also an important factor in the prolongation of hospitalization and delay in skin grafting. Bacterial isolates from wounds of burn victims are known to vary with time and geographical location in every burn unit. Pathogens like Candida, Enterobacter, Acinetobacter, etc., which were quite rare in the past, are being increasingly isolated from burn wounds. Avascularity of the burnt area further places the organisms beyond the reach of host defense mechanism and systemically administered antibiotics. Thus, knowledge of the pattern of the organism prevailing on the burn wounds, would allow early management of imminent septic episodes with empirical systemic antibiotic. The present study was undertaken to establish the type of aerobic bacterial infection on burn wounds and determine the changing pattern of infection according to the duration of hospital stay.
| Materials and Methods|| |
This study was undertaken in IMS and SUM Hospital, Bhubaneswar, which is a tertiary care hospital in the capital city of Odisha. Patients admitted to the Burn unit of the hospital were included in the study. Proper history regarding the type of burn (flame, scald, electric, chemical burns) time since injury, coexisting illness or associated conditions, treatment obtained and duration of hospital stay were noted in a performa. The extent and severity of burn was examined by assessing total body surface area (TBSA) burnt as per Wallace rule of nine. Treatment protocol of the burn was established in accordance with the main international standards of treatment, including antibiotics; daily bath wound care with topical antimicrobial such as silver sulfadiazine; fluid resuscitation; nutritional support; surgical operations such as eschar excision and grafting. Basic measures of infection control such as staff hygiene, room isolation, periodic cultures from various parts of the burn unit and limitation of visitors were thoroughly maintained.
The sample was collected periodically every 5th day for microbiological study, by two sterile moistened swabs, from the most infected part of the burn wound. Wound surface culture was repeatedly performed in the similar manner to assess the changing pattern of infection following hospital stay. In each sampling procedure, the bandages were removed, the remnants of topical antimicrobial agents were scraped away by normal saline and the wounds were swabbed before washing and applying new topical antimicrobial agents.
The samples were immediately transferred to the Microbiology department avoiding any delay in transport. One of them was inoculated on 5% sheep blood agar, MacConkey agar as well as to a nutrient broth media. Second swab was used for a preparation of Gram-stain for direct examination. The inoculated plates were incubated overnight at 35°C ± 2°C and colonies obtained the following day were stained and then identified according to the standard protocol. The antibiogram of each isolate was done using Kirby-Bauer disc diffusion method on Muller Hinton agar plate according to CLSI guidelines.
The Staphylococcus isolates were tested for methicillin resistance by using 1 μg of oxacillin disc. Zone of inhibition ≤10 mm was treated as methicillin-resistant Staphylococcus.
Vancomycin resistance was detected by 30 μg vancomycin disc on a lawn culture of Staphylococcus. No zone of inhibition was designated as vancomycin-resistant and was further confirmed by detection of MIC by Hi comb MIC strips from Himedia labs.
For extended spectrum β-lactamases (ESBL) detection ceftazidime (30 μg) and ceftazidime plus clavulanic acid (30/10 μg) were placed on lawn culture of the organism on Mueller-Hinton agar and incubated overnight. Organism was considered as ESBL producer if there was a ≤;5 mm increase in diameter of ceftazidime plus clavulanic disc and that of ceftazidime disc alone.
Complete blood count, liver function tests, renal function tests, electrolyte assays were repeatedly carried out to note the presence of septicemia, dehydration and organ dysfunction. Wound was examined for the presence of infection like-erythema or cellulitis, purulent discharge, graft loss, rapid eschar separation, necrosis of small blood vessels, edema and tenderness at the wound edges. Fever >38.5°C, hypothermic or hyperthermia, hypotension, decreased urine output, and ileus suggested systemic progression of infection. Laboratory results like leukocytosis or leukopenia, thrombocytopenia, positive blood cultures, hyperglycemia also suggested an infected wound. Results of the wound culture were interpreted according to the direct smear examination of the wound swab in concordance with clinical, biochemical and hematological profile of the patient.
| Results|| |
114 swabs were collected from 52 cases. Of the total cases 22 (42.3%) were males and 30 (57.7%) were females; 36 (69.2%) had flame injury while 12 (23%) had scalds and 2 (3.9%) cases each had electrical and chemical burns. The patients ranged from 1 to 50 years of age. The TBSA of burn injury patients varied from 5% to 55%.
The number of sterile cultures was 46.15% in 1st week but 16.7%, 12.5% in 2nd and 3rd week, respectively. More than one type of organism was isolated in 4 (7.6%) cases. Of all the organisms isolated, the most common strain isolated was Staphylococcus aureus, that is, 20 (47.6%). Of all the Gram-negative bacteria isolated Klebsiella spp. was most common 12 (28.6%); followed by Pseudomonas spp. and Acinetobacter spp. 10 (23.8%) each. The most common organism isolated in the 1st week was S. aureus (15.4%), but it was Acinetobacter spp.(22.2%) in 2nd week and coagulase negative Staphylococcus (CoNS) in 3rd week [Table 1].
All the strains of S. aureus were methicillin-resistant and show very high degree of resistance to all the antibiotics used. Beta-lactam drugs were the most resistant antibiotics even when used in combination with beta-lactamase inhibitors. Most sensitive antibiotics for S. aureus were levofloxacin (77.8%) and netilmicin (98%). S. aureus was resistant to linezolid and vancomycin in 80% and 60.7%, respectively. CoNS strains were similarly mostly sensitive to aminoglycosides and fluoroquinolones. Of the total strains isolated 50% were resistant to vancomycin [Table 2]. All the vancomycin-resistant Staphylococcci when subjected to Hicomb MIC test were confirmed as intermediate sensitive to vancomycin (MIC value - 4–8 µg for S. aureus and ≤ 32 µg for CoNS).
Among the Enterobacteriaceae organisms most common isolates were Klebsiella spp. (n = 12), followed by Citrobacter spp. (n = 8), Escherichia More Details coli (n = 4) and Enterobacter spp. (n = 2). All the species show very high degree of resistance to beta-lactam antibiotics as well as their combination with beta-lactamase inhibitors. All E. coli were resistant to aminoglycosides while all other organisms showed moderately sensitive to it. Of the Klebsiella isolates 75% were resistant to imipenem, but all other species of Enterobacteriaceae remained susceptible to this antibiotic. Among Enterobacteriaceae members Klebsiella isolates (40%) were the highest ESBL producers [Table 2].
Acinetobacter isolates were mostly sensitive 80% each to levofloxacin and imipenem. Of all isolates 40% were sensitive to netilmycin while only 20% of them to amikacin. Pseudomonas spp. was most sensitive 80% each to amikacin and piperacillin-tazobactam. Of the Pseudomonas and Acinetobacter spp.isolated, 40% and 60% of those were ESBL producer respectively [Table 2].
For all the organisms beta-lactam drugs were the most resistant antibiotics. Among the aminoglycosides, netilmicin was more sensitive than amikacin while among quinolones levofloxacin was the most sensitive antibiotic [Table 2].
| Discussion|| |
Burn wound infection is the 2nd infectious complication of burn closely following pneumonia and it is the leading cause of higher mortality. The requirement of a prolonged hospital stays increases the chances of nosocomial infections in an already compromised patient. Colonization is very frequent in burn wounds. The denatured protein of the burn Escher provides nutrition for the organism. Degree of patients immunosuppression, wound local environment and virulence potential of the organism determines the further course taken up by the wound infection. Quantitative cultures which were previously advocated as the evidence of infection has now been largely abandoned as they were labor intensive and did not provide a precise evidence of infection. Hence, an accurate diagnosis of invasive burn wound infection is best determined by clinical criteria, supported when possible by histopathologic examination if the patient's condition is suspicious for this infection. Thus in this study the cultures were obtained from clinically infected ulcers to avoid the problem of detection of colonizing bacteria.
In the present study, females (57.7%) were infected more commonly than males (42.3%). The most common organism isolated is S. aureus as observed by few other workers., These findings contrast with some studies  where Pseudomonas has been reported as the most common organism. A similar study in a teaching hospital  in Odisha, finds Pseudomonas aeruginosa 87 (49.4%) as the most predominant bacterial isolate, followed by other Gram-negative Enterobacteriaceae 42 (23.9%). In this study, S. aureus and Acinetobacter baumannii isolated were only 39 (23.9%) and 8 (4.5%) respectively. Klebsiella spp. is the 2nd most common isolated organism in the study. A similar high rate of isolation of Klebsiella spp. has also been noted by Mehta et al.
Burn wound flora and antibiotic susceptibility patterns also change during the course of the patient's hospitalization. It has been said that the burnt area is sterile atfirst, but it is colonized in the 1st week by organisms from the skin appendages followed by those from the patient's endogenous flora and from the hospital environment. This changing pattern of organisms constitutes a threat to the management of such patients. Thus repeated culture of the wound is advised to provide early identification of organisms colonizing the wound; to monitor the effectiveness of current wound treatment; to guide perioperative or empiric antibiotic therapy; to detect any cross-colonizations which occur quickly so that further transmission can be prevented. In the present study although S. aureus is the predominant pathogen in the 1st week it has been replaced by Acinetobacter in the subsequent swabs. Other workers have also established Gram-positive cocci as initially prevalent and then being gradually superseded by Gram-negative bacilli.,,, As Acinetobacter spp. is a normal skin commensal, particularly in tropical areas, it is being increasingly isolated in burn wound infection.,, CoNS which are generally considered as commensals may be pathogenic when found in significant number in a clinically infected burn wound. A prolonged hospital stay and antibiotic use may have led to a significant colonization and subsequent infection by the CoNS after 15 days of stay in the present study.
Burn patients are also unique in their propensity to disperse organisms into the surrounding environment. Thus; these patients are generally infected with multidrug-resistant organisms. In our study, a large number Staphylococci isolated were methicillin resistant. Dash et al., while working on burn wound infections had shown, 59% of S. aureus to be methicillin-resistant Staphylococcus aureus (MRSA). In another study, done in this locality, authors found MRSA in 65% of cases of skin and soft-tissue infection caused by S.aureus . Such a rising pattern of MRSA is due to the empirical use of broad-spectrum antibiotics which commonly includes a third generation cephalosporin. The high percentage of MRSA also accounts for the resistance of the isolates to beta-lactam drugs. In addition to it, we encountered alarming rate of resistance of the isolates to vancomycin and linezolid, which are generally accepted as reserve drugs. Worldwide, there are reports of increasing rate of resistance to these drugs. Levofloxacin and netilmicin are the most effective drugs for treatment of Staphylococcal infections in the present study.
Gram-negative bacteria showed highest degree of susceptibility to imipenem and levofloxacin and very high resistance to cephalosporins. Acinetobacter isolates were the highest ESBL producers (60%). ESBL are plasmid-mediated TEM and SHV derived enzymes. These enzymes are capable of hydrolyzing broad spectrum antibiotics like cephalosporins, monobactams as well as are capable of showing co-resistance to other classes of antibiotics like quinolones and aminoglycosides resulting in limitation of therapeutic options. This explains the high degree of resistance showed toward the beta-lactams antibiotics in the present study. Pseudomonas spp. and Klebsiella spp. produce this enzyme in 40% cases. Other authors have found Pseudomonas to be the highest producer of ESBL. Studies in India on the different clinical condition have reported the prevalence of ESBL in the range of 58% to 68.1%.,,,
| Conclusion|| |
Burn wound infections are an important cause of mortality, morbidity and prolonged hospitalization in burn patients as the causative agent is generally a multidrug-resistant organism. In the current study, S. aureus is the most common organism followed by the Klebsiella spp. Repeated culture swabs show a change in the microflora of the wounds. The isolates are resistant to cephalosporins. Levofloxacin is most useful antibiotic for Gram-positive organism while imipenem is the most useful antibiotic for Gram-negative organisms. Effective strict isolation techniques and infection control are thus needed to decrease the occurrence of burn wound infection.
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[Table 1], [Table 2]