Antibiotic resistant nosocomial infections are becoming serious health care problem in ICU and other areas of hospital care, increasing morbidity, mortality, length of stay, and health care costs [2, 24]. 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 [24, 25]. 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%) , 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 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 screening of MDR resistant strains.
The highest proportion of MDR non-fermentative gram negative bacilli NI infection among the lower age groups in the present study is consistent with earlier studies elsewhere in the world [29, 33, 34]. 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 (25). 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.
In this study, the proportion of nosocomial MDR A.baumanii and P.aeruginosa surgical site infection (6.3%) was comparable with previous reports from other part of Ethiopia (6.6%)  and Ghana (8.5%) . However, it was lower than studies from Southeast China (28.5%) . This could be the difference in the type of surgery, handling of surgical equipments and age of study participants as the present study included patients of any age groups.
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 Gabon (52.8%) , Indonesia (16.5%)  and USA (16%) . This could be due to differences among study participants, catheterization and hospitalization.
The prevailing proportion of nosocomial BSI in this study (8.9%) was comparable with studies done in USA (10%) . However, it was higher than studies from Indonesia (3.5%) . In contrast, lower findings were documented elsewhere in Africa (20-70.3%) [29, 38] and Southeast China (46.1%) . The observed difference might be due to non-sustainable infection control practices in hospitals, difference in use of invasive medical devices, procedures, hospital type and diverse nature of study participants.
The proportion of nosocomial MDR A.baumannii infection (3.8%) in the present study was in agreement with earlier studies conducted in Africa (2.4 - 5.7%) [26, 29, 32]. However, it was lower compared with findings from Sodo (15.3%), Ethiopia  and Gaza city (6.9%) . In contrast, it was higher than findings from previous studies in elsewhere (0.42% - 0.95%) [27, 30]. Similarly, the magnitude 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%) [8, 18, 25], Ghana (19.5%) , India (76.8%)  and Italy (8.7%) . In contrast, it was higher compared to a study in China (0.36%) .The variations might link with host, microbial and environmental factors.
In this study all isolates of MDR P.aeruginosa were resistant for ampecillin and amoxacillin-clavulanic acid. This was consistent with reports from Tikur Anbessa hospital, Ethiopia (25) and Southeast China  where 87.5% and 100% resistance rate against ampecillin and amoxacillin-clavulanic acid respectively were noticed. Moreover, all isolates of P. aeruginosa in the present study were resistant against piperacillin. This was significantly higher than studies from Italy (25%) , 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 as it 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 were documented in Sodo, Ethiopia  and Southeast China , respectively. On the other hand, low level of resistance against ceftazidime reported in other parts of Ethiopia (12.5% - 29.1%) [18, 25] and Italy (31%) . The highest level of resistance against third generation cephalosporins might be linked with excessive, mis and inappropriate use of these antibiotics in the area that drives selective pressure and emergence of MDR.
The resistance rate of P.aeruginosa isolates against meropenem (45.5%) in the present study was coherent with other studies in Ethiopia (41.7%)  and Asia (36.6% - 54%) [33, 39]. However, higher level of resistance against meropenem was documented in Taiwan (73.2%)  and Saudi (81.8%) .The relatively lower proportion resistance against meropenem in the present study might be linked with the nonexistence of meropenem prescription practice 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 ampecillin. 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.
All isolates of A. baumannii were resistant to piperacillin in the present study. This was comparable with studies conducted in Southeast Asia (83.7%)  and Italy (81) . Similarly, A. baumannii isolates also revealed 77.8% and 88.9% resistance against ceftazidime and cefotaxime, respectively which was comparable with studies done in Tanzania , Southeast China  and Italy , where resistance against ceftazidime and cefotaxime reported in 71 - 97.1% and 54.4 – 100% of isolates, respectively. Furthermore, 33.3% of A.baumanii isolates from the present findings 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 Saudi , resistance against meropenem was reported in 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 (88.4%), Ethiopia [18, 25], Uganda (78%) , 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 and P.aeruginosa were MDR (100%). This finding was consistent with studies conducted in Sodo (81.4 & 83.3%), Ethiopia , Tanzania (100%) , Ghana (100%) and India (76.8%) . However, it was higher than reports from Uganda (38 & 40%) , Saudi (28.2%) , Saudi Arabia (71.8%)  and Italy (20 & 54%) . Therefore, this very alarming MDR proportion of A.baumanii and P.aeruginosa isolates in the study area 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 these 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 longer time . Moreover, high prescription practice of common antibiotics including third generation cephalosporins and use of drugs outside the hospital might contribute for the high resistance rate of A. baumannii and P. aeruginosa to different classes of antibiotics.
This study was limited to participants admitted in hospital but nosocomial infection that arose after discharge was not detected. The single-centre nature of the study introduced local practice bias.The study also unable to demonstrate cross-transmission of pathogens and ignored the effect of duration of antibiotic therapy at individual patient level. Moreover, certain potential confounders could not be included in the analysis.
Conclusions: Alarming proportion of nosocomial MDR A. baumannii and P.aeruginosa infection obtained in the study area. All A. baumanii and P.aeruginosa isolates were resistant for at least three antibiotics representative of different classes. Therefore, urgent intervention towards nosocomial infection prevention practices required treatment of patients on care should be guided with antimicrobial susceptibility testing.