INTRODUCTION
One of the main problems in trauma wards of hospitals is burn wound infections, which are mainly caused by bacteria (1, 2). Pneumonia and blood infections such as septicemia and wound infections are the leading cause of mortality in burn patients (2). Wounds are naturally suitable for colonization of bacteria; therefore, burn patients are at great risk of life-threatening complications (3). Emergence of multidrug-resistant (MDR) strains that carry transferable plasmids, integrons, or other transferring elements is another health problem (4, 5).
Bacterial contamination of wounds could have either an endogenous (microorganisms in nasopharynx, gastrointestinal tract, and the surrounding skin) or exogenous (healthcare settings) origin (6). The prevalence of nosocomial infections caused by gram-positive bacteria, particularly MDR strains, is on the rise (7). The most commonly isolated gram-positive bacteria are Staphylococcus aureus, coagulase-negative staphylococci (CoNS), and Enterococcus spp., which are recognized as important causes of nosocomial infections in the world (8).
Enterococci, especially vancomycin-resistant enterococci (VRE) infections, are becoming common and challenging to treat. In addition, the increased incidence of methicillin-resistant S. aureus (MRSA) and contingency of vancomycin resistance highlights the need for rapid and reliable characterization of isolates and control of MRSA and VRE spread in hospitals (9-11). Due to the importance and increased rate of antibiotic resistance, it is essential to prevent or control pathogens in clinical settings (12-14). Therefore, the present study aimed to investigate the prevalence and antibiotic resistance pattern of gram-positive bacteria isolates from burn patients in the North of Iran.
 
MATERIALS AND METHODS
This retrospective cross-sectional study was performed on burn patients admitted to the Velayat burn injuries hospital in Rasht, North of Iran, from March 2017 to September 2020. The study was approved by the Ethics Committee of the Guilan University of Medical Sciences (ethical code: IR.GUMS.REC.1399.276) and was performed according to the Helsinki's declaration. Demographic and clinical information of patients who had a positive culture for a gram-positive isolate were collected.
Superficial cleaning of the wounds was performed using normal saline. Then, each sample was taken by rotating a sterile, pre-moistened swab across the wound surface of a 1 cm area in a zig-zag motion, from the center to the outside of the wound. Next, the swab was placed in an enrichment tube and transferred to the Microbiology Laboratory for testing. Briefly, each swab was plated into blood agar, mannitol salt agar, and bile esculin agar and incubated overnight at 37 °C. All culture media were purchased from Merck, Germany. Grown isolates were identified by morphological examination, followed by biochemical testing using the conventional microbiological tests (15, 16).
 
Antibiotic susceptibility testing
The antibiotic susceptibility pattern of gram-positive isolates was determined by the disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) recommendations (17). The antibiotics used were ampicillin, penicillin, cefoxitin, erythromycin, tetracycline, teicoplanin, gentamicin, ciprofloxacin, clindamycin, trimethoprim/sulfamethoxazole, and rifampin. All antibiotic disks were purchased from Oxoid, UK. The S. aureus strain ATCC 25923 was used for quality control. In addition, MDR was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories (18).
Data analysis was performed using SPSS™ software (version 21, IBM Corp., USA). The results are presented using descriptive statistics in terms of relative frequency.
 
RESULTS
During the study period, 671 bacterial cultures were obtained, of which a total of 16 gram-positive isolates were taken from burn patients. Overall, 68.7 % (11/16), 18.8% (3/16), and 12.5 % (2/16) of the isolates were CoNS, S. aureus, and Enterococcus spp., respectively. Out of the 16 culture-positive samples, 56.2% (9/16) belonged to males and 43.8% (7/16) to females.
The patients' median age was 35.3 years (age range: 2 to 76 years). The isolates were taken from the surgery ward and intensive care unit (ICU, 81.3%). Most of the isolates (93.8%) were taken from wounds. Of 16 culture positive cases, two (12.5%) patients died (Table 1).
 
Table 1. The demographic and clinical characterization of burn patients’ with bacterial infections

 
 
The antimicrobial-susceptibility patterns of the gram-positive isolates are shown in table 2. Overall, 87.5% (14/16) of isolates were MDR. The resistance pattern of CoNS showed that the highest resistance rate was against trimethoprim/sulfamethoxazole (81.8%), followed by clindamycin (72.7%), and penicillin (72.7%), whereas the lowest resistance was to gentamicin (45.4%). Enterococci isolates were almost resistant to all tested antibiotics, except ampicillin and rifampin. Moreover, 66.7% of isolates were MRSA based on the cefoxitin disk diffusion method. In S. aureus isolates, the resistance rate was highest against penicillin (100%) and lowest against gentamicin (33.3%) and rifampin (33.3%).
Table 2. The antimicrobial-susceptibility patterns of isolates taken from burn patients
 

 
 
DISCUSSION
Bacterial contamination of wounds is a serious problem, particularly in burn patients. This often has poly-microbial nature, and the presence of MDR microorganisms frequently collaborates with vigorous clinical appearance and insignificant response to antimicrobial therapy (19). Nevertheless, proper identification of pathogenic microorganisms in burn hospitals' and determining their susceptibility to commonly used antibiotics will help clinicians manage wound infection more efficiently. In the present study, CoNS and S. aureus were the most common gram-positive isolates, which is similar to findings of a study (20) but inconsistent with others (21, 22). Generally, difference in the frequency of isolates could be related to geographical location, hygiene measures, and the number of isolations. Other studies in Iran also showed that the number of nosocomial infections caused by enterococci, particularly resistant strains, is growing (23, 24).  
In 2001, the National Nosocomial Infection Surveillance System stated that the incidence of burn wound infections caused by Enterococcus was 11% (5). In this regard, our country experienced a dramatic increase in rate of antibiotic resistance for enterococci (21). This is an alarming issue for the healthcare system (25). In the present study, we found no VRE isolate, which is similar to results of a similar study in Tehran (26). However, other studies have isolated VRE strains from burn wound infections (27, 28).That is an alarming issue for the hygiene system and medical healthcare (26). What found no VRE isolate in our study, which is similar to findings of Heidari et al. (25) and in contrast with some previous studies (27, 28). These discrepancies could be due to the difference in geographical location and antibiotic prescriptions in the study area.
In a study conducted by Chirife et al., S. aureus was the most common gram-positive bacteria isolated from wound infections (29). In some countries such as Iraq, S. aureus has been  considered as a significant cause of nosocomial infection in burn patients (30). Our results demonstrated that CoNS was the most prevalent gram-positive isolate taken from burn patients.
The emergence of worldwide antibiotic resistance, particularly among nosocomial pathogens, limits the efficiency of available antibiotics for treatment of burn wound infections (20, 21, 31). The frequency of MRSA and MDR isolates in our study was significantly higher than that in other studies (32-34). This might be related to the lack of awareness in taking care of burn wounds, horizontal transmission of MDR by the healthcare staff, transferring resistance genes by mobile genetic elements, and non-adherence to the hospital guidelines. The prevalence of MDR and MRSA strains among burn patients in hospitals is alarming. However, periodic monitoring of commonly used antibiotics and susceptibility information can help to overcome the emergence of drug-resistant strains.
Retrospective studies are not without limitation. In the present study, we only studied a single referral hospital, which makes results difficult to generalize. Second, because of the study design, additional clinical information could not be provided. Despite these limitations, this study provides useful information regarding microbiological aspects of gram-positive bacterial infections among burn patients.
 
CONCLUSION
According to the results, the prevalence of MDR and MRSA isolates is alarmingly high in hospitalized burn patients. Given that a high proportion of mortalities in burn patients is because of nosocomial infections, particularly those caused by resistant strains, it is essential to conduct periodical and epidemiological studies of nosocomial diseases.
 
ACKNOWLEDGMENTS
The authors wish to thanks the Razi Clinical Research Development Unit of Guilan University of Medical Sciences for their technical support.
 
DECLARATIONS
Funding
 The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article.
 
Ethics approvals and consent to participate
The study was approved by the Ethics Committee of the Guilan University of Medical Sciences (ethical code: IR.GUMS.REC.1399.276) and was performed according to the Helsinki's declaration.
 
Conflict of interest
The authors declare that there is no conflict of interest regarding publication of this article