INTRODUCTION

Acinetobacterspecies are gram-negative, non-fermentative, immobile aerobe coccobacilli. They form translucent, opaque, convex colonies 0.5-2 mm in diameter on a blood agar plate in 24 hours. They exhibit natural resistance to several antibiotics because of their intrinsic resistance mechanism; therefore, it is difficult to treat outbreaks of health care-associated infections. Acinetobacter species are prevalent, and exist on the skin flora of healthy people, hospital staff and the hospital environment. Despite the low virulence of the bacteria, they may cause opportunistic infections in patients with underlying disease, newborn babies, and in the elderly. The intensive care unit (ICU) is where patients in poor general condition are followed up and invasive devices are frequently applied. Approximately 25% of health care-associated infections develop in ICUs[1,2]. However, it is known that the resistance rates of the infections in ICUs are higher[3]. A large number of antibiotic-resistant Acinetobacter outbreaks have been reported in many ICUs[4,5,6]. Because the antibiotic resistance rates vary between hospitals, is important to ascertain the bacterial resistance status for each hospital in order to select the appropriate antibiotics for empiric therapy. In this study, it was aimed to determine the antibiotic resistance rates of Acinetobacter strains isolated from clinical specimens of ICU patients and the distribution of these ratios during the period 2008-2011.

Materials and Methods

A prospective and active surveillance was performed among patients treated in a state hospital ICU between 2008 and 2011. The diagnosis of health care-associated infection was based on the Centers for Disease Control and Prevention (CDC) criteria[7]. A total of 320 Acinetobacter spp. isolated from the patients who had health care-associated infection in the ICU and the antibiotic resistance of the isolates were investigated in the study. The samples were inoculated on 5% sheep blood agar and EMB agar. The identification and antibiotic susceptibility tests were performed using the BD Phoenix 100 system, BD Phoenix NMIC/ID-82 Id+ADT (Becton Dickinson, Belgium). Strains defined as Acinetobacter spp. were evaluated for resistance to antimicrobials. Statistical analysis was performed with the Statistical Package for the Social Sciences (SPSS) for Windows (SPSS Inc., Chicago, IL, USA) program and the non-parametric chi-square test.

Results

A total of 320 Acinetobacter strains were isolated (Table 1); 245 (76.5%) of the strains were identified as A. baumannii, 40 (12.5%) as A. lwoffii and 35 (10.9%) were other Acinetobacter spp. with respect to the distribution of the species obtained according to clinical specimens, 40% were from tracheal aspirate, 22.5% from sputum, 10% from blood, 18.1% from wound, 7.1% from urine, and 2% from other samples (Table 2). We determined the antibiotic resistance rates for a four-year average as follows: 93.4% for ceftazidime, 93.2% for cefepime, 93.1% for ceftriaxone, 92.6% for ciprofloxacin, 91.4% for gentamicin, 89.4% for ampicillin-sulbactam, 88.9% for piperacillin-tazobactam, 88.9% for amikacin, 84.5% for tetracycline, 87.9% for trimethoprim-sulfamethoxazole, 68.5% for meropenem, 67.6% for cefoperazone-sulbactam, 65.8% for imipenem, 37% for tobramycin, 2.5% for colistin, and 10% for tigecycline (Figure 1). The annual distribution of these ratios is shown in Table 3. When the resistance rates were compared between 2008 and 2011, significant increases were observed for imipenem (p

DISCUSSION

The broad-spectrum antibiotic application leads to the emergence of resistant microorganisms in ICUs related to high rates of infection. Aging, immune suppression, surgery, invasive procedures, antibiotic use, and long-term hospitalization are the risk factors for these resistant bacterial infections. The most common species of Acinetobacter that cause health care-associated infections are A. baumannii[8]. We also determined that A. baumannii (76.5%) was the most frequently isolated strain (Table 1). Acinetobacter species may lead to sepsis, pneumonia, urinary tract infections, wound infections, meningitis, and surgical site infections in ICU patients. Although studies vary, the respiratory tract and blood samples are the most frequently isolated samples of Acinetobacter[1,9,10,11]. As shown in Table 2, tracheal aspirate culture was the most frequently examined sample in our study, followed by sputum (22.5%), wound (18.1%), blood (10%), urine (7.1%), and other (2.1%) cultures. Multi-drug resistant (MDR) Acinetobacter are an important cause of morbidity and mortality in hospitalized patients in the ICU[12]. In our country, in the many studies investigating antibiotic resistance among Acinetobacter strains that cause infections in ICU patients, the resistance ratios were determined as follows: 15-100% for cephalosporins, 65-100% for quinolones, 39-100% for aminoglycosides, 61-100% for penicillins, 68-100% for trimethoprim-sulfamethoxazole, 22-92% for tobramycin, and 0-90% for carbapenems (Table 4)[3,9,13,14,15,16,17,18,19,20]. There may be different rates of resistance according to hospitals or years. Due to their constitution of cephalosporinase, 3rd generation cephalosporins have low efficiency against Acinetobacter. Colistin resistance was detected as zero for A. baumannii in a study involving 19 centers in Spain; however, it was reported in a study performed in Turkey as 6% in 2009 and 5% in 2010[21,22]. In the same study, resistance to tigecycline was found as 13.7%[21]. We found resistance to colistin as 2.5% and to tigecycline as 10% in our study. In our study, colistin was found to be the most effective antimicrobial agent against Acinetobacter spp. In recent years, colistin has been used as a therapeutic agent because of these MDR strains. Widespread use of this antibiotic increases the resistance rates to colistin. When the resistance rates were compared between 2008 and 2011, significant increases were observed for imipenem (p[23]. Tobramycin has not been available in our country since 2006. Since it has not been used for treatment, the resistance rates to this antibiotic are decreasing. For the treatment of severe Acinetobacter infections, combination therapy should be applied by considering antibiotic sensitivity tests. The best approach is combinations of carbapenem, colistin, rifampin, and ampicillin-sulbactam[8]. It is determined that MDR strains cause infections in ICU patients. These infections increase the cost of treatment, morbidity and mortality. Accurate empirical treatment of these patients will be lifesaving. Management of these infections is very difficult because of MDR, including to carbapenems. For empirical therapy, it is important to know the frequent pathogens and their antibiotic resistance, which vary in each hospital.