Antibiotic resistant nosocomial infections are becoming serious health care problem in ICU and other areas of hospital care, leading to high rate of morbidity and mortality [6, 21]. The epidemiological and antimicrobial resistance profiles of NIs showed variations among hospitals around the globe. Many of the infections are caused by bacteria that are resistant to multiple antibiotics [21, 22]. This study showed the proportion of NIs due to two MDR non-fermentative gram negative bacilli among patients hospitalized in different wards of a referral hospital.
In the present study, 8.4% of patients were infected with nosocomial MDR A.baumanii and P.aeruginosa. This indicated that MDR A.baumanii and P.aeruginosa infections are the major health problem in the clinical area in Ethiopia. High patient load, overcrowding, poor infrastructure, poor infection control practices of the hospital and differences in trained medical staﬀ for aseptic procedures might be the possible explanations. This finding was coherent with reports in Tikur Anbessa Hospital, Ethiopia (8.12%) , Uganda (7.39%) , Morocco (7 - 8%) , Italy (9.3%)  and Gaza city (6.9%) . However, it was higher compared to reports from Hiwot Fana Hospital, Ethiopia (0.5%) , Gabon (5.7%) , China (0.78%)  and Indonesia (3.5%) . In contrast, the overall nosocomial MDR A. baumannii and P.aeruginosa infections in the present study was lower than studies done in Nigeria (12.5%)  and Ghana (23.5%) . This might be due to variation in sample size, clinical site of infection, age of patients, hospital setting, duration of hospitalization, patients exposure to high risk devices or surgical procedures, microbiological methods employed for detection and screening of MDR resistant strains.
In this study, the proportion of nosocomial MDR A.baumanii and P.aeruginosa surgical site infection (6.3%) was comparable with reports from Tikur Anbessa Hospital (6.6%), Ethiopia  and Ghana (8.5%) . However, it was lower than studies from Nigeria (11.1%) , Morocco (70.9%) , Southeast China (28.5%) , Heraklion (20.1%) , Pakistan (19.5%) . This could be the difference in age of study participants as the present study included any age groups of patients, type of surgery and handling of surgical equipments.
The proportion of nosocomial urinary tract infection linked with MDR A.baumanii and P.aeruginosa (8.3%) isolates in the present study was consistent with a study conducted in Kenya (9%) . However, it was lower than studies in Morroco (52.83%) , Nigeria (12.5%) , Gabon (26%) , USA (16%) , Indonesia (16.5%) , Pakistan (32%) . In contrast, the proportion of MDR nosocomial UTI in the present study was lower than a study in Vietnam (4%) . This could be due to differences among study participants interms of age, catheterization and hospitalization.
The prevailing proportion of nosocomial BSI in this study (8.9%) was comparable with studies done in Nigeria (8.6%)  and USA (10%). However, it was higher than studies from Indonesia (3.5%)  and Pakistan (2.4%) . In contrast, it was lower than reports from Morocco (70.3%) , Gabon (20%) , Southeast China (46.1%)  and Tunis (48%) . The observed difference might be due to non-sustainable infection control practices in hospitals, difference in use of invasive medical devices and procedures, hospital type and diverse nature of study participants.
In this study, the proportion of nosocomial MDR A.baumannii infection (3.8%) was in agreement with studies conducted in Uganda (2.39%) , Ghana (4%)  and Gabon (5.7%) . However, it was lower compared with findings from Sodo Ethiopia (15.3%) , Morocco (7%) , Gaza city (6.9%)  and Thailand (17.3 %) . In contrast, it was higher than findings from Uganda (0.95%), Italy (0.52%)  and China (0.42%) .The variations in this report might be due to host, microbial and environmental factors.
The proportion of nosocomial MDR P.aeruginosa infection (4.6%) in the present study was comparable with a study in Uganda (5%) . However, it was lower than findings from other parts of Ethiopia (11.1% - 66.7%) [15, 22, 27, 40], Ghana (19.5%) , Morocco (8%) , India (76.8%) , Thailand (9.6%)  and Italy (8.7%) . In contrast, it was higher compared to a study in China (0.36%) . The variations in this report might be due to host, microbial and environmental factors.
In this study all isolates of MDR P.aeruginosa were resistant for ampicillin and amoxacillin-clavulanic acid. This was consistent with reports from Tikur Anbessa hospital, Ethiopia (22) and Southeast China  where 87.5% and 100% resistance levels against ampecillin and amoxacillin-clavulanic acid, respectively were noticed. In this study, all isolates of P. aeruginosa revealed 100% resistance against piperacillin. This was significantly higher than studies from Italy (25%) , Vietnam (17.7%) , Southeast China (12%) , Turkey (28.7%)  and Taiwan (66.8%) .This might be associated with differences in the number of MDR strains of P.aeruginosa and patient type. The frustrating level of resistance against piperacillin antibiotic is an alarm for treatment to be guided with antimicrobial susceptibility testing hence so far, piperacillin was not prescribed in the study area (FHRH).
In this study, high levels of resistance to cephalosporins (cefotaxime (63.6%) and ceftazidime (100%)) were obtained against P.aeruginosa isolates. This was coherent with studies in Uganda , India  and Taiwan  where 71 - 77% resistance against ceftazidime reported. Moreover, 70.8% and 92.8% level of resistance against cefotaxime documented in Sodo, Ethiopia  and Southeast China , respectively. On the other hand, low level of resistance against ceftazidime reported in Tikur Anbessa Hospital (12.5%) and Sodo, Ethiopia (29.1%) [15, 22], Italy (31%)  and Vietnam (22.1%) . The highest level of resistance against third generation cephalosporins might be linked with excessive use, mis and inappropriate use of these antibiotics in the study hospital that drives selective pressure and emergence of MDR.
In the present study, P.aeruginosa isolates showed 45.5% levels of resistance against meropenem. This was coherent with studies in Sodo, Ethiopia (41.7%) , Southeast China (36.6%) , India (54%)  and Vietnam (40%) . However, higher level of resistance against meropenem was documented in Taiwan (73.2%) , Pakistan (86.4%)  and Saudi (81.8%) .The relatively lower proportion resistance against meropenem in the present study might be due to the absence of meropenem prescription practice for patients in the study hospital. In contrast, lower level of resistance against meropenem was reported in Uganda (14%)  and Turkey (20.4%) .This could be due to variation in the availability of meropenem in each localities, prescription difference, misuse and inappropriate use of antibiotics.
In this study, all isolates of MDR A. baumannii were resistance against ampicillin. This was parallel with studies conducted in Tikur Anbessa Hospital (88.2%), Ethiopia  and Southeast China (100%) . Moreover, high level (88.9%) of MDR A. baumannii isolates resistance to amoxacillin clavulanic acid in the present study was comparable with earlier studies in Nigeria  and Southeast China , where all isolates of A. baumannii were resistant against amoxacillin- clavulanic acid.
In this study all isolates of A. baumannii were resistant to piperacillin. This was comparable with studies conducted in Morocco (75 - 95%) [24, 41], Southeast Asia (83.7%)  and Italy (81) . In present study, A. baumannii isolates revealed 77.8% and 88.9% resistance against ceftazidime and cefotaxime, respectively. The finding was comparable with studies done in Tikur Anbessa Hospital , Morocco , Tanzania , Southeast China , Italy  and Vietnam , where resistance against ceftazidime and cefotaxime reported in 71 - 97.1% and 54.4—100% of isolates, respectively.
In the present study, 33.3% of A.baumanii isolates showed resistance against meropenem. The finding was relatively similar with studies conducted in Sodo, Ethiopia , Tanzania  and Nigeria  where, 30.2% - 40% resistance rate against meropenem reported. However, in Vietnam  and Saudi , resistance against meropenem were reported in 40 and 90.5% of A.baumanii isolates, respectively
The resistance level of MDR isolates of A. baumannii to ciprofloxacin (44.5%) in the present study was lower than studies done in Tikur Anbessa Hospital (70.6%) and Sodo Ethiopia (88.4%) [15, 22], Uganda (78%) , Morocco (78–80%) , Nigeria (100%) , Southeast China (89.6%)  and Italy (84%) .The low resistance rate against ciprofloxacin and meropenem in the present study might be due to the high price and unavailability of the drugs in the hospital.
In this study, all isolates of A. baumannii were MDR (100%). This finding was consistent with studies conducted in Sodo, Ethiopia (81.4%) , Tanzania (100%)  and Ghana (100%) . However, it was higher than reports from Uganda (40%) , Morocco (77.5%) , Pakistan (22.7%) , Saudi Arabia (71.8%)  and Italy (54%) .
In the present study, all isolates of P. aeruginosa were MDR (100%) which is comparable with earlier studies in Sodo, Ethiopia (83.3%) , Ghana (100%)  and India (76.8%) . However, it was significantly higher than earlier studies in Uganda (38%) , Saudi Arabia (28.2%)  and Italy (20%) . The overall MDR proportion of A.baumanii and P.aeruginosa isolates in the study area is very alarming and needs urgent intervention and strict adherence to infection control practices to contain them.
The high MDR proportion observed in two non-fermenter gram negative bacilli in this study is probably related to the contaminations and cross transmission of this bacteria from hospital environment , hands of healthcare workers, frequent use of broad spectrum antibiotics, inherent resistance nature to many antimicrobial agents and the ability of pathogens persist in the environment, and on medical devices for a long period of time . Moreover, intrinsic nature of the bacteria, high prescription practice of common antibiotics and third generation cephalosporins and use of drugs outside the hospital might contribute for the high resistance rate of A. baumannii and P. aeruginosa different classes of antibiotics.
The highest proportion of nosocomial infection due to MDR non-fermentative gram negative bacilli infection among the lower age groups in the present study is consistent with earlier studies elsewhere [28, 50, 51]. On the other hand, in the present study all NIs observed among patients with intravenous catheterization. The rate of nosocomial infections was also significantly higher among patients who had prolonged time of operation than their counter parts. This was consistent with previous study in Tikur Anbessa Hospital, Ethiopia (22) and India . This might be due to the high rate of exposure of patients to the two MDR pathogens from the hospital environment, health care professionals, multiple invasive device and cross-contamination among patient’s procedures.
This study was limited to participants admitted in hospital but nosocomial infection that arose after discharge was not detected.