Burn infection caused by pathogenic bacteria is one of the most common hospital problems worldwide, particularly in developing countries ¹ . Fire leads to skin destruction and simultaneous suppression of both humoral and cellular immune system subsequently resulting burn infection ² . Complications of burn infection are responsible for more than 70% of death cases among inpatients with burns ³ . These infections mainly caused by multi-drug resistant gram-negative and gram-positive bacteria such as Pseudomonas aeruginosa ( P. aeruginosa), Klebsiella pneumoniae ( K.pneumoniae) and Staphylococcus aureus ( S.aureus) ^{4, 5} . Non-sterile burns halls and duration of patients stay in hospital in addition to the surface area of burned skin, are the most important factors related to the increase of persistent and multiplication of pathogenic bacteria in the burned areas ^{6, 7} . Multi-drug resistant (MDR) bacteria is one of the most common pathogens causing burn infection in hospitalized patients worldwide ^{8, 9} . These pathogens are resisting to at least three different classes of antimicrobials such as, penicillin’s, beta-lactams, cephems, 3rd and 4th generation cephalosporins, aminoglycosides, tetracyclines and quinolones, and is becoming one of the most dangerous health issues in hospitals ¹⁰ . In addition, extended-spectrum β-lactamase (ESBL)-producing bacteria are considered as a potent pathogens due to it their resistance to a wide range of antimicrobials like, cefotaxime, ceftriaxone and ceftazidime, that lead to difficulty in the treatment of most infections such as burn infection and urinary tract infection ^{11, 12} . Burn infection is characterized by difficult healing due to administration of unsuitable treatment, long stays in hospital and the contaminates of hospital environments lead to the emergence of new multi-drug resistant bacterial isolates causing dangerous complications such as, bacteremia, septicemia and death ^{13, 14} . Therefore, we must pay attention to all safety standards in hospitals, especially in burns wards through sterilization, performing antimicrobial susceptibility test on all pathogenic bacteria isolated from burn infections, and keeping the burned skin in sterile conditions to prevent the emergence of these pathogens. According to the above, the aim of this work was to investigate of the prevalence of multi-drug resistant bacteria and extended-spectrum β-lactamase-producing bacteria isolated from inpatients with burn infection in Al-Najaf central hospital in Al-Najaf City, Iraq over three years, from January 2015 to December 2017 to increase our understanding of the most prominent bacteria and their resistance to different antimicrobials to prevent the emergence of these isolates in the future.

Of the 295 burn swabs, 513 different bacterial strains were isolated, 335 isolates (65.3%) were gram negative bacteria and 178 isolates (34.7%) were gram positive bacteria ( Figure 1). Pseudomonas aeruginosa was one of the most common bacteria causing burn infection, 142 isolates (27.6%), followed by methicillin resistant S.aureus 106 isolates (20.6%), K. pneumoniae 93 isolates (18.2%), methicillin sensitive S.aureus 72 isolates (14.1%), E.coli 51 isolates (10%), A.baumannii 32 isolates (6.2%) and S.typhi 17 isolates (3.3%). 323 different bacterial strains (63%) were isolated from patients with burn infection who stayed in hospital for 15 days ( Table 1). Out of total 513 bacterial isolates, 122 (23.8%) were isolated as single growth, while 391(76.2%) were isolated as mixed growth ( Table 2). According to the results of antimicrobial susceptibility tests, most bacterial isolates were resistant to most antimicrobials with high percentages. Out of the 513 bacterial isolates, only 33 isolates (6.40%) were resistant to imipenem 10µg. The results of antimicrobials susceptibility test and overall resistant of 513 bacterial strains to 14 antimicrobials are shown in Table 3 and Figure 2. Of the total 513 bacterial isolates, 464 isolates (90.4%) were MDR, 20 isolates (14%) were XDR and 17 isolates (3.3%) were PDR ( Table 4). Pseudomonas aeruginosa was the most common MDR-bacteria, 130 strains (91.5%), while 4 strains (2.8%) were XDR and 8 strains (5.6%) were PDR. All resistant types of all bacterial isolates are shown in Table 4. According to MDDST, Pseudomonas aeruginosa was the most common ESBL-producing bacteria 51 isolates (35.9%) ( Figure 3) followed by K.pneumoniae 21 isolates (2.6%), while, no strain of S.typhi was ESBL. All ESBL- producing gram negative bacteria are shown in Figure 4.

Burn infection is one of the most serious problems in hospitals caused by different pathogens that infect most patients who stay in hospitals for prolonged periods. In this study, 513 different bacterial strains were isolated from 295 swabs of hospitalized patients with burn infections over the three years. Gram negative bacteria were responsible for more than half of infections while gram positive bacteria accounted for 34.7% of overall bacterial isolates. Pseudomonas aeruginosa was the most common bacteria, accounting for 27.6% of total isolates. These results are in agreement with previous studies ^{20– 23} . Pseudomonas aeruginosa is one of the most important pathogens causing different infections such as bacteremia and burn infections ²⁴ . This pathogen is well adapted to the hospital environments due to biofilm formation that provides long survival advantages for the pathogen, and effectively prevent eradication by the host immune system or antimicrobial drug treatment ²⁵ . Pseudomonas aeruginosa has become responsible for more than 70% of mortality in burn patients ^{26, 27} . The results of this study showed that MRSA was the second most common bacteria isolated from patients with burn infection, 106 isolates (20.6%) of total bacterial isolates, while, MSSA was the most 4 ^th common pathogen with 72 isolates (14.1%). These results are similar with many previous studies ^{28, 29} . Staphylococcus aureus is the most common bacteria causing both hospital and community associated infections, including bacteremia, pneumonia and burn infection ³⁰ . Hospital-associated MRSA accounts for a high proportion of hospitalized infected with S.aureus ³¹ . As compare with different bacteria that cause burn infection in hospitalized patients, MRSA-infections is associated with higher morbidity and mortality ³² . Klebsiella pneumoniae was the most 3 ^rd common bacteria isolated from burn infection in this study with, 93 isolates (18.2%). This result is similar to past studies ^{33, 34} . Klebsiella pneumoniae is an opportunistic pathogen which causes serious infections like, urinary tract infection, pneumonia, burn infection, and soft tissue infections in compromised and hospitalized patients. It has number of virulence factors such as a capsule that enable this pathogen to colonize and provides phagocytosis resistance ^{35, 36} . The results of this study showed that Escherichia coli, A.baumannii and S.typhi were prevalent in different percentages, 10%, 6.2% 3.3%, respectively. Our results are similar with some previous studies ^{37– 39} . On the other hand, the results of the current study proved that there was a positive relationship between a longer stay in hospital and the high prevalence of pathogenic bacteria causing burn infections. Contaminated burning wards and duration of patients stay in hospital, in addition to the size of surface area of burned skin are the most important reasons to increase of persistent and multiplication of pathogenic bacteria in the burned areas ⁴⁰ . There are a number of factors that influence the emergence of infection in burns patient including; prolonged hospital stays, contamination of burns wards, nature of burn injury itself, as well as intensive diagnostic and therapeutic procedures ^{41, 42} . Some studies suggested that burn infection is the most common type of infection, while, others studies reports show it to be bacteremia and pneumonia ^{43, 44} . In this study, most pathogenic bacteria isolated from burn infection were highly resistant to most antimicrobials, especially against beta-lactams and 3rd generation cephalosporins., All pathogenic bacteria were MDR with high percentages and most of them were XDR,. P. aeruginosa was the most common PDR- bacteria followed by MRSA and A.baumannii. These results are similar with many previous studies ^{5, 45– 47} . Biofilm formation by microorganisms is one of the most important mechanisms in antimicrobials resistant, consisting of the irreversible assemblage of bacterial cells associated with a surface and enclosed in matrix of polysaccharides material ⁴⁸ . Biofilms are regarding as a major factor contribution to many chronic inflammatory diseases such as burn infection due to enabling bacteria to colonize the burned skin, altering growth rate and allowing genes to be transcribed that provide these pathogens to high resistance to antimicrobials and host immune system. The overuse and unsuitability of different antimicrobials to treat burn infections has led to the emergence of new MDR, XDR and PDR-bacterial strains that are able to resistant a wide range of many antimicrobials such as aminoglycosides, beta-lactams, cephalosporins, streptomycin and tetracycline ^{49, 50} . Burn infection in hospitalized patients caused by MDR, XDR and PDR-gram negative and gram positive bacteria such as; P. aeruginosa, K. pneumoniae, MRSA, MSSA and A.baumannii may lead to delays in burn healing, graft lose, as well as development of sepsis and death; therefore, determination of the risk factors for these pathogens infections is essential for infection control ⁴⁷ . The results of this study showed that P. aeruginosa and K. pneumoniae were the most common ESBL-producing gram negative bacteria followed by A.baumannii and E.coli while there was no any strain of ESBL- S.typhi. These results are similar to previous studies ^{1, 51, 52} . Infections caused by ESBL-producing gram negative bacteria are associated with an increase of health care costs, morbidity and mortality ^{53, 54} . Extended spectrum beta-lactamases (ESBLs) have been reported as one of the most important hospital-acquired infections such as burn infection and bacteremia ^{9, 55} . Most bacteria harboring ESBLs are usually resistant to beta-lactam antibiotics and other classes of antimicrobials ⁵⁶ . These enzymes are carried in and transferred from bacteria to bacteria by plasmids ^{57, 58} . The most important steps to ensure the safety of patients with burn infections are: to control the spread of ESBL-producing bacteria, isolation of colonized patients in sterile wards, and continuously performing antimicrobial sensitivity tests ⁵⁹ .

There was a high incidence of MDR-bacteria causing burn infections in Al-Najaf hospital in Al-Najaf City, Iraq. Pseudomonas aeruginosa was the most common MDR, XDR and PDR-bacteria, and the most common of ESBL-producing bacteria causing burn infection over three years followed by MRSA. Imipenem 10µg had good antibacterial activity against more than 93% of bacterial isolates. There was positive correlation between a long stay in hospital and high prevalence of pathogenic bacteria causing burn infection.

In this study, some gram negative and gram positive bacterial isolates are excluded because of the small number of isolates (less than seven isolates over the three years) such as proteus spp (5 isolates), citrobacter spp (4 isolates), enterobacter spp (6 isolates) and enterococcus spp (5 isolates). We think this small number of bacterial isolates don’t has any significant effect on the results of this study.

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Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

Dataset 1: Test results for patient swabs 10.5256/f1000research.15088.d211541 ⁶⁰