A 6-year surveillance of antimicrobial resistance patterns of Acinetobacter baumannii bacteremia isolates from a tertiary care hospital in Saudi Arabia during 2005–2010

M ultidrug resistance (MDR) of Acinetobacter baumannii increasingly jeopardizes the health care setting leading to substantial mortality and morbidity globally. During the past decade, entirely resistant A. baumannii strains presented a real challenge to clinicians and posed difficulties in therapy (1, 2). MDR of A. baumannii associated infections, with adverse clinical outcomes involving the respiratory tract, blood, soft tissues, urinary tract, and central nervous system, significantly increases the outlay of the infirmary. Being Gram-negative coccobacilli and an obligate aerobe, A. baumannii causes both communityand hospital-acquired infection outbreaks in intensive care units especially in countries with tropical climates (3, 4). Of particular concern, we sought to reveal the status of antimicrobial resistance in A. baumannii bacteremia isolates, the trends and relative frequency of multidrug resistance pattern and also the underlying clinical condition among patients with A. baumannii bacteremia at Riyadh Military hospital, Saudi Arabia, from January 2005 to December 2010. Our retrospective study was conducted at Riyadh military Hospital, Riyadh, Saudi Arabia, which is a tertiary health care center with a capacity of 1,200 beds. Identification of the microorganism was done using the microbiology laboratory protocol, and those nonrepetitive clinical cultures that showed positive for A. baumannii during a 5-year period from January 2005 to December 2010 were included in the study. Blood cultures were performed using the BACTEC 9,240 system (Becton Dickinson Sparks, MD, USA). A total of 380 A. baumannii blood isolates were identified in blood cultures between January 2005 and December 2010 and confirmed by API 20 NE (bioMerieux Inc., France). Isolation and identification was followed by antibiotic typing of these 380 blood isolates by MicroScan WalkAway (Dade Behring Inc., West Sacramento, CA, USA) according to manufacturer specifications. Antibiotic patterns were determined in accordance with CLSI guidelines. The antimicrobial agents used in this study were amikacin (AK), ampicillin sulbactam (AM S), cetazidime (CFZ), ceftriaxone (CFN), ciprofloxacin (CIP), gentamicin (GEN), meropenem (MERO), netilmicin (NET), piperacillin/tazobactam (PT), trimethoprim/ sulfamethoxazole (TM-SXT), and tetracycline (TET). Intermediately, susceptible strains were considered to be resistant. All laboratory testing was performed according to manufacturer specifications for that instrument in accordance with practices recommended by CLSI. Multidrug resistant A. baumannii (MDR-AB) is classically recognized and defined if it is resistant to three or more classes of antibiotics. Statistical analysis was done using a t-test, and PB0.05 was considered significant. Table 1 depicts the resistance profiles of all the cases and consequently the fluctuations in the susceptibility patterns during the study years. Table 2 describes the frequency of A. baumannii isolation from blood during the year 2005 2010 and also the preponderance of MDR-AB during these retrospective years. Resistance to most potent drugs for A. baumannii associated infections, namely AK, CFN, and MERO firmly increased to 50, 71, and 55% during the year 2009 from 21, 42, and 12%, respectively during year the 2005. Resistance to AM-S fluctuated in these years maximizing in the year 2009 to 60%, and similarly the resistance rates to CIP (60%) and GEN (55%) attained peak values during the year 2009. It was noted that there has been a steady increase in the resistance rates of A. baumannii isolates, thereby increasing the relative frequency of MDR-AB strains. The number of A. baumannii isolated from blood culture increased considerably from 49 to 110 in the period 2005 2010. Moreover, MDR-AB-associated infections endangered the hospital settings by their significant predominance in ICU as 76 and 75% in 2006 and 2008, respectively. A substantial increase in MDR-AB strains is horrendous since MDR-AB were significantly isolated from ICU patients (5). Apart from being MDR, the steady increase in resistance rates of these bacteriemic isolates to MERO is certainly noteworthy as it reflects the probability of a nosocomial outbreak of carbapenamresistant clones of A. baumannii. The number of cases of MDR-AB isolated from non-ICU patients in the years 2005 and 2009 were 12 [63%] and 9 [75%], respectively, which was higher than that isolated from ICU patients in the same years (7 [37%]) and 3 [25%], respectively). Moreover, the MDR rate was 63% in 2005 whereas 72% in 2009, thus prevailing antimicrobial resistance pattern Libyan Journal of Medicine