Infection is a frequent complication of burn injury. It is responsible for 75% of deaths in patients who sustain burns [1] . The increased risk of infection associated with burns is due to a number of factors. Two important factors are severe immunosuppression and loss of the skin barrier [1] [2] . When the skin barrier is lost, a burn wound is created. The burn wound is a good environment for microorganism growth because it is moist and contains necrotic tissues [3] - [5] . As a result, it becomes colonized rapidly by the skin flora, the bacteria that are usually present in the sweat glands and hair follicles.

The respiratory and gastrointestinal tracts can become additional sources of microorganisms. Invasive procedures, such as endotracheal intubation, invasive central venous or arterial lines, and urinary catheterization also increase the chances of infection [6] . Furthermore, organisms present in the hospital environment may be spread to the patient by health workers [3] [7] [8] .

The pattern of bacterial isolates and antibiotic sensitivity is not constant, but changes with time. Understanding the periodic variation of isolated microorganisms and their antibiotic sensitivity helps in selecting the appropriate antimicrobial therapy before culture and sensitivity are reported [2] [9] . It also aids the design of antibiotics protocols.

The changing population patterns of microorganisms and their antibiotic sensitivities have become more complicated in recent years by the rise of antibiotic resistant microorganisms. The genus Acinetobacter has become a major problem in many burn units globally. Unfortunately, there are no new antibiotics to combat these resistant microorganisms. As a result, older, abandoned antibiotics have again become important in the management of antibiotic resistant microbes [10] .

This report describes changes in the distribution of bacterial populations and their antibiotic sensitivity over 12 years at Khoula hospital burns unit. Khoula hospital is a tertiary care hospital and the burns unit is the only tertiary care burns unit in Sultanate of Oman.

The study was retrospective over 12 years and included all patients who were admitted to the Khoula Hospital burns unit from 01.01.2003 to 31.12.2014 and had positive cultures. The laboratory data were obtained from the computerised hospital medical record system [Al-Shifa Healthcare Information System] and the demographic data were obtained from burns unit records. Swab cultures, biopsy cultures, blood cultures, line cultures, secretion cultures and urine cultures were included. Patient demographic data and bacteriology reports of various cultures and their antibiotic sensitivities were reviewed. The data were entered into a spreadsheet and analysed using the Microsoft Office Excel 2007 program. We scored the presence of bacteria cultured from each patient during their visit. For example, if the patient had three consecutive positive swabs for a particular type of bacteria it was counted as one. The twelve-year period was divided into four three-year periods: 2003-2005, 2006- 2008, 2009-2011 and 2012-2014. The number of admissions per year during the period of study was similar (mean/year: 191.25). The study was conducted with the approval of the hospital ethics committee.

P. aeruginosa, S. aureus and MRSA are the most commonly isolated microorganisms worldwide [9] [11] - [18] . This pattern of distribution appears to be constant and does not change over time. In a review of 50 years of isolates, S. aureus and P. aeruginosa were the most commonly isolated organisms [5] . This is a global phenomenon and the pattern in our burns unit was not different.

On the other hand, there has been a sharp rise in Acinetobacter isolation over recent years. Acinetobacter was rarely isolated before 1970 [5] . In older reports, Acinetobacter either did not grow at all [19] , or was isolated but its presence was not that significant. Acinetobacter is now recognized as a microorganism that is isolated early in hospitalization [20] [21] . Furthermore, a recent report named Acinetobacter baumannii as the most prevalent organism in a tropical burn unit [22] . We also found that Acinetobacter became the most prevalent isolate in the last three years of the study and the fourth most common isolate overall. Acinetobacter has become resistant to most common antibiotics, also referred to as multi-drug resistant (MDR). This has a negative impact on burn patients as treating infection and septicaemia is very difficult in the presence of MDR Acinetobacter. Empirical antibiotic therapy should consider the growing prevalence of such MDR organisms.

There is a global rise in antibiotic resistance [23] - [26] . In our burns unit, we found that Acinetobacter was resistant to almost all of the antibiotics available except colistin. According to some reports, Acinetobacter demonstrated high sensitivity to carbapenems [9] [27] . Such was the case in our unit until 2005, after which the resistance of Acinetobacter to carbapenems increased to more than 90%.

Another organism isolated increasingly is K. pneumoniae. Unfortunately, it shows increasing resistance to most antibiotics now, including the carbapenems. In the US, K. pneumoniae resistance to carbapenems began in late 1990s [28] ; in our unit, the resistance appeared in 2012.

Bacterial sensitivity to antibiotics varies according to the organism, the antibiotic used and time. MRSA was reported by some centres to be resistant to vancomycin [25] [29] . Fortunately, MRSA susceptibility to vancomycin remained at nearly 100% in our unit. In fact, MRSA demonstrated increasing susceptibility to many antibiotics over the study period.

We also found increasing susceptibility to antibiotics in other organisms like Klebsiella species, and P. aeruginosa. Similar findings regarding Pseudomonas aeruginosa sensitivity were reported previously by other centres [26] . On the other hand, other investigators found increasing resistance of P. aeruginosa to antibiotics [13] . In our unit, MDR Pseudomonas aeruginosa is still a rare occurrence.

The infection control measures taken by our hospital, and the burns unit in particular, to control MDR Acinetobacter and MRSA are: strict hand hygiene; screening of the patients at the referring hospital and after arrival to the burns unit; strict isolation of colonized and infected cases; protective aprons, masks and gloves when staff are in contact with the patients; restricting the visitors to two per day; and regular auditing and rounds by the infection control nurse.

Despite infection control measures, the control of MDR Acinetobacter is difficult. Burns patients require prolonged hospital stays and some require prolonged ventilation as well as indwelling lines and catheters. The immunity of these patients is depressed and their wound recovery is slow. All of these factors increase the risk of infection. As might be expected, the majority of mortalities in our unit have MDR Acinetobacter growth.

The rise in MDR organisms is a global phenomenon. There is a need for new antibiotics to control such organisms. We observed in this review that microorganisms were sensitive to antibiotics that have been out of use for a long time.

In our hospital burns units, P. aeruginosa remains the most commonly isolated organism overall, followed by S. aureus and MRSA. Multidrug resistant Acinetobacter prevalence is increasing and colistin remains the only antibiotic that is effective against it. Enterobacteria, carbapenem-resistant, were isolated occasionally suggesting their growing prevalence. Although certain organisms demonstrate increasing resistance to antibiotics, other organisms display increasing sensitivity. MRSA is highly sensitive to vancomycin and shows a progressive rise in sensitivity to a number of antibiotics.

All authors declare that they have no conflict of interest.

The authors would like to thank Ishaq Ali Al-Aghbari (hospital statistician) and Shakeel Ahammed (IT Department) for helping in data analysis and retrieval.

Said Saud Al-Busaidi,Zainab Said Al-Hashimy,Adel Mohamed Hashish,Sheikh Mohammad Ashik Iqbal Faruquee,Hassan Ahmed Hamouda,Ahmed Osama Abdulhamed,Fawzi Mohamed Abdul-Aleem, (2016) 12 Years Analysis of Bacterial Isolates and Their Antibiotics Sensitivity in a Tertiary Care Burns Unit. Modern Plastic Surgery,06,11-19. doi: 10.4236/mps.2016.63003