The Antibiotic Resistance Profiles of Bacterial Strains Isolated from Patients with Hospital-Acquired Bloodstream and Urinary Tract Infections

Treatment of nosocomial infections is becoming difficult due to the increasing trend of antibiotics resistance. Current knowledge on antibiotic resistance pattern is essential for appropriate therapy. We aimed to evaluate antibiotic resistance profiles in nosocomial bloodstream and urinary tract pathogens. A total of 129 blood stream and 300 urinary tract positive samples were obtained from patients referring to Besat hospital over a two-year period (2009 and 2010). Antibiotic sensitivity was ascertained using the Kirby-Bauer disk diffusion technique according to CLSI guidelines. Patient's data such as gender and age were recorded. The ratio of gram-negative to gram-positive bacteria in BSIs was 1.6 : 1. The most prevalent BSI pathogen was Coagulase-Negative Staphylococci (CoNS). The highest resistance rate of CoNS was against penicillin (91.1%) followed by ampicillin (75.6%), and the lowest rate was against vancomycin (4.4%). Escherichia coli was the most prevalent pathogen isolated from urinary tract infections (UTIs). Ratio of gram-negative to gram-positive bacteria was 3.2 : 1. The highest resistance rate of E. coli isolates was against nalidixic acid (57.7%). The present study showed that CoNS and E. coli are the most common causative agents of nosocomial BSIs and UTIs, and control of infection needs to be addressed in both antibiotic prescription and general hygiene.


Introduction
Nosocomial or hospital-acquired infections are defined as infections which are acquired during the hospital stay. Nosocomial infections are usually defined as infections that are identified at least 48-72 hours following admission to health institutions [1]. Nosocomial infections are also important public health problems in developing countries as well as in developed countries [2]. The most frequent types of nosocomial infections are urinary tract infection (UTI), surgical-wound infection, pneumonia, and bloodstream infection (BSI) [3]. BSIs are responsible for approximately 10-30% of the cases [4]. UTI is the presence of bacteria in the urine (bacteriuria) and defined as the growth of a single pathogen of >10 5 colony-forming units/mL from properly collected mid-stream urine specimens [5]. The common bacterial pathogens present in the BSIs and UTIs are Staphylococcus aureus, Coagulase-Negative Staphylococci (CoNS), Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterobacter spp., Enterococcus spp., and Acinetobacter spp. [6]. As the result of extensive uses of antimicrobial agents, nosocomial pathogens have shifted away from easily treatable bacteria towards more resistant bacteria. This change is important problem for nosocomial infection control and prevention [7]. Area-specific monitoring studies aimed to gain knowledge about type of pathogens and antimicrobial resistance patterns can optimize treatment and decrease mortality rates [8,9]. In Iran, broad-spectrum antibiotics are commonly used in the hospitals, and there is limited data on antibiotic resistance. The present study was  aimed to ascertain the resistance patterns of the most common bacterial isolates from hospital-acquired bloodstream and urinary tract infections over a two-year period.  [10,11]. Multimicrobial growth on culture media was excluded. Nonrepetitive positive cultures were recruited for study. In UTI suspected patients, the midstream specimens of urine were taken following the recommendations of Kass [12]. The plates were incubated in aerobic atmosphere at 37 • C for 24-48 hrs. Presence of more than 10 5 (cfu/mL) bacteria signified as UTI. Isolated bacteria were microbiologically identified with standard biochemical identification methods [13,14].

Discussion
Nosocomial infections occur worldwide and affect both developed and developing countries [16]. Many of these infections are associated with microorganisms that are resistant to antibiotics and can easily spread by hospital personnel [17]. Guidelines for antibiotic therapy can be helpful for clinicians to select more appropriate antibiotics for effective treatment and prevent the development of drug resistance. This study shows the distribution of antibiotic resistance pattern of bacterial species isolated from patients with nosocomial BSI or UTI at a hospital in Tehran, Iran. This study revealed that 129 (10.7%) out of 1200 bloodstream samples which were obtained from nosocomial BSI suspected patients were positive. Of the 129 patients, 61 (47.3%) were females and 68 (52.7%) were males (P > 0.05). The CoNS (34.8%) and E. coli (29.4%) were the most prevalent microorganisms that have been isolated. Similar findings have been observed in Turkey and in a Children's Medical Center, Iran [18,19]. A study in Brazil revealed the predominance of S. aureus (14%) followed by CoNS (12.6%) and Klebsiella (12%) [20]. In several studies, CoNS followed by S. aureus comprised the most prevalent bacteria isolated from BSIs [21][22][23]. In our study, gram-negative bacteria were more regularly involved in nosocomial BSI than grampositive bacteria (P < 0.05). This finding is in accordance with the results of recent studies [24]. Based on our data, the highest resistance rate of the CoNS was against penicillin followed by ampicillin and oxacillin (Table 1). Oxacillinresistant staphylococcus spp. are an increasing global problem in nosocomial infections [25][26][27]. Oxacillin-resistant strains show the high level of resistance to penicillin, cephalosporins, and other beta-lactams like imipenem. In the present study, 62% of the isolated CoNS were oxacillin resistant with the high rates of resistance to penicillin, cephalothin, and imipenem (100%, 100%, and 62%, resp.). E. coli strains which were isolated from BSI patients had the highest resistance rates to tetracycline and ampicillin (63.2%), which is similar to the recent study from Ireland [28]. In the present study, the E. coli strains which were isolated from BSI patients showed a resistance rate of 47.4% to ciprofloxacin which is consistent with the other studies from Iran [29,30]. In our study, the 8.5% of microorganisms which were isolated from nosocomial BSI patients were Acinetobacter spp. The Acinetobacter spp. isolates showed the highest resistance rate to cephalothin (81.8%) followed by cotrimoxazole and gentamicin (63.6%) ( Table 1). Reports of Acinetobacter spp. bacteremia are increasing, especially from Asian countries and neighboring countries of Iran such as Iraq, Kuwait, Turkey, and Afghanistan [31][32][33]. A recent surveillance study from Iran reported that Acinetobacter spp. were the most frequently isolated bacteria in the hospital and communityacquired BSIs (32%) followed by E. coli (13.7%) and Klebsiella sp. (12%), respectively [28]. In the present study, vancomycin was the most effective antibiotic against CoNS (95.6% susceptible) and S. aureus (100% susceptible). This is in agreement with another study performed in Iran [34]. In our study, statistical analysis showed a significant correlation between nosocomial UTI prevalence and gender (P < 0.05). It has been extensively reported that adult women have a higher prevalence of UTI than men because of anatomic and physical situations [35,36].
The present study indicates that E. coli is still the most common cause of nosocomial UTI. This finding is consistent with the other studies from Iran and other countries [35,37,38]. The highest resistance rate of E. coli isolate which was obtained from urine samples was against nalidixic acid followed by cotrimoxazole, ciprofloxacin, and ampicillin, respectively ( Table 2). These results were predictable because these antibiotics have been used as a long time in our hospital. In this study, amikacin and imipenem had the widest coverage against E. coli isolates (97.5%). In a recent surveillance study in Iran authors reported that the highest resistance rate of E. coli isolates which were obtained from various clinical specimens at 11 hospitals was against tetracycline followed by amoxicillin and penicillin, respectively [39].
The rate of nosocomial UTI is determined by the interactions of several factors such as primary disease and its severity, duration of hospitalization and treatment, and invasive interventions like use of urinary catheters; Moreover, the incidence of nosocomial UTI has been increasing and its treatment has become more complicated because of the pathogens with increasing resistance to antibiotics [40,41].

Conclusion
It is concluded that in our hospital gram-negative bacteria were more frequently involved in nosocomial BSI than grampositive bacteria. CoNS and E. coli were the most common isolated bacteria from blood cultures and included the 64% of total isolates. Vancomycin was the most effective antibiotic against gram-positive bacteria, and gentamicin, amikacin, and imipenem are proposed for treatment of nosocomial UTI caused by Gram-negative bacteria. E. coli was the most common cause of nosocomial UTI in our hospital and imipenem and aminoglycosides (gentamicin, amikacin) were the most effective antibiotics against this infection. Finally, to reduce the incidence of nosocomial infections, the appropriate use of antibiotics according to the standard antimicrobial susceptibility tests is proposed.