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ORIGINAL ARTICLE Table of Contents   
Year : 2010  |  Volume : 53  |  Issue : 2  |  Page : 290-293
Prevalence of antibiotic-resistant Acinetobacter baumannii in a 1000-bed tertiary care hospital in Tehran, Iran

1 Department of Microbiology, Reference Health Laboratories, Ministry of Health, Tehran, Iran
2 Department of Pharmaceutics, School of Pharmacy and Pharmaceutical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Vali-e-Asr Street, Niayesh Junction, P.O. Box 14155-6153, Tehran, Iran

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Date of Web Publication12-Jun-2010


Acinetobacter baumannii is a ubiquitous pathogen that has emerged as a major cause of healthcare-associated infections. Acinetobacter baumannii usually causes respiratory tract, urinary tract, blood stream and surgical site infections. They are of increasing importance because of its ability to rapidly develop resistance to the major groups of antibiotics. There are few data available on the antimicrobial susceptibility of A. baumannii in Iran. During the period of study from July 2005 to November 2006, a total of 88 strains of A. baumannii were isolated from clinical specimens obtained from patients hospitalized in an Iranian 1000-bed tertiary care hospital. Conventional bacteriological methods were used for identification of A. baumannii. Susceptibility testing was performed by the method recommended by Clinical Laboratory and Standards Institute (CLSI). The majority of isolates were from respiratory tract specimens. The organism showed high rate of resistance to ceftriaxone (90.9%), piperacillin (90.9%), ceftazidime (84.1%), amikacin (85.2%) and ciprofloxacin (90.9%). Imipenem was the most effective antibiotic against A. baumannii and the rate of resistance for imipenem was 4.5%. The second most effective antibiotic was tobramycin, and 44.3% of A. baumannii isolates were resistant to this antibiotic. In conclusion, our study showed that the rate of resistance in A. baumannii to imipenem was low. There was a significant relationship between demographic features of patients such as age, undergoing mechanical ventilation, length of hospital stay and drug resistance.

Keywords: Acinetobacter baumannii, drug resistance, nosocomial infection, imipenem

How to cite this article:
Rahbar M, Mehrgan H, Aliakbari NH. Prevalence of antibiotic-resistant Acinetobacter baumannii in a 1000-bed tertiary care hospital in Tehran, Iran. Indian J Pathol Microbiol 2010;53:290-3

How to cite this URL:
Rahbar M, Mehrgan H, Aliakbari NH. Prevalence of antibiotic-resistant Acinetobacter baumannii in a 1000-bed tertiary care hospital in Tehran, Iran. Indian J Pathol Microbiol [serial online] 2010 [cited 2021 Jun 15];53:290-3. Available from: https://www.ijpmonline.org/text.asp?2010/53/2/290/64333

   Introduction Top

Acinetobacter baumannii is an oxidase-negative and strictly aerobic gram-negative coccobacillary rod that grows at 20 to 30ΊC on usual laboratory media. [1],[2] Acinetobacter baumannii is a ubiquitous pathogen capable of causing both community and healthcare-associated infections (HAIs). It has recently emerged as a major cause of HAI because of its propensity to accumulate mechanisms of antimicrobial resistance leading to pan-drug resistance, and cause large HAI outbreaks that often involve multiple facilities. [3] This organism is responsible for 2-10% of gram-negative bacterial infections in intensive care units (ICUs) in Europe and the United States. [4]

Knowledge about A. baumannii is much less developed than knowledge about other opportunistic pathogens such as Pseudomonas aeruginosa. Difficulty for identifying this organism has led to the publication of data that are of questionable value. [3] In a previous study, we evaluated the performance of microbiology laboratories in Tehran and its districts in an external quality assurance scheme (EQAS) for detection of A. baumannii as unknown bacteria. Of 487 laboratories involved in the study, only 29.8% of them correctly identified this organism. [5] In Iran, our data on prevalence and antibiotic susceptibility pattern of A. baumannii is very limited. However, available data suggest that A. baumannii is a remarkable microorganism because of the diversity of its habitat, its various mechanisms for acquiring antimicrobial resistance, its resistance to desiccation, its propensity to cause outbreaks of infection and the complexity of its epidemiology. [3] In this study, we decided to determine prevalence of drug resistance in A. baumannii and predisposing factors for acquisition of infection caused by this organism in an Iranian 1000-bed tertiary care hospital.

   Material and Methods Top

This study was conducted at a tertiary care hospital with 1000 beds belonging to The social security organization, located in Tehran Iran. From July 2005 to November 2006, consecutive, non-duplicate nosocomial isolates of A. baumannii were collected from different specimens of patients, who were hospitalized for ≥48 h. Specimens included respiratory tube, urine, blood, wound etc.

Medical and demographic data of the patients were collected using a questionnaire. Data recorded were as follows: demographic characteristics (age, gender), underlying diseases (diabetes mellitus, chronic renal failure, cancer, hepatitis and heart conditions), presence of intravascular or urinary tract catheters, admission ward, history of intensive care unit (ICU) stay and length of stay, being on mechanical ventilation, previous antibiotic therapy, recent hospitalization and recent surgery.

Previous hospitalization was defined as admission to a hospital ward within 1 year prior to the current admission. Recent surgery was defined as any major surgical procedure performed in the operating room within the past year. Previous antibiotic therapy was defined as treatment with any antibiotics given for at least 2 days within 6 months preceding isolation of the organism.

All specimens were routinely cultured on MacConkey and blood agar plates. Blood specimens were inoculated in Trypticase Soy Broth (TSB) and sub-cultured on chocolate agar. Specimens other than urine were inoculated also on chocolate agar. All suspected colonies were identified by Gram-staining, colonial morphology, negative oxidise and other biochemical reactions. [6]

Antimicrobial susceptibility testing of the isolated organisms was performed by the disk diffusion method as recommended by clinical laboratory and standards institute (CLSI). [7] All antibiotic disks were obtained from Oxoid Ltd. (Basingstoke, UK). Briefly, a suspension of each isolate was prepared so that the turbidity was equal to 0.5 McFarland standard and then plated onto Mueller-Hinton agar. After incubation at 35ΊC for 18-24 h, diameter of inhibition zones was measured and data were reported as susceptible, intermediate and resistant. The antibiotic potency of the disks was standardized against the reference strains  Escherichia More Details coli ATCC 25922, Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853.

For statistical analysis, data were entered into a database using SPSS 11.5 for Windows (SPSS Inc., Chicago, IL). In the case of bivariate comparisons, the Pearson χ2 test was used for categorical variables. A two-tailed P-value <0.05 was considered statistically significant. For statistical purposes, in some cases, the susceptibility data were categorized as susceptible and non-susceptible (including intermediate and resistant groups). To determine confounding factors significantly associated with antibiotic resistance, quantitative variables were considered as nominal and categorized as ≤9 or >9 for days of hospital stay, ≤8 or >8 for days of ICU stay and ≤6 or >6 for days on mechanical ventilator. Theses cut-offs were chosen based on median value obtained for each variable. Age was grouped as ≤18 years old and >18 years old as A. baumannii was mostly isolated from adult patients.

   Results Top

During the study period, a total of 88 A. baumannii were isolated from various clinical specimens of patients hospitalized in different wards of Milad Hospital, Tehran, Iran. Acinetobacter baumannii isolates were frequently isolated from adult patients especially those ≥61 years olds (94.4%), males 57 (64.8%), those patients having mechanical ventilation in ICU wards and those having intravascular/urinary catheter. Demographic data of the patients are shown in [Table 1].

The results of antibiotic susceptibility testing are shown in [Table 2]. In general, susceptibility rates of A. baumannii isolates to third- and fourth-generation cephalosporins, aztreonam, fluoroquinolones, amikacin, gentamicin and trimethoprim/sulfamethoxazole (SXT) were very low. Imipenem with susceptibility rate of 95.5% proved to be the most active antibiotic against these isolates. Tobramycin with 53.4% susceptibility rate stood next.

Statistical analysis showed that ICU stay, previous ICU stay and its length and being on mechanical ventilation were confounding factors significantly associated with the acquisition of A. baumannii isolates resistant to antibiotics such as ceftazidime, cefepime, piperacillin/tazobactam, ticarcillin/clavulanic acid, fluoroquinolones, amikacin and gentamicin. Acinetobacter baumannii isolated from tracheal aspirate had also higher rates of resistance to tested antibiotics. Previous antibiotic therapy was the only risk factors for resistance to tobramycin. However, no confounding factor was found to be significantly associated with imipenem resistance.

   Discussions Top

Acinetobacter species especially A. baumannii are causing more hospital-acquired infections. This organism has been reported as the most frequent cause of respiratory tract infections, with strains being isolated from 3 to 5% of patients with nosocomial pneumonia. [8] In our study, the most isolates of A. baumannii were from tracheal tube aspiration, and mechanical ventilation was the most important risk factor for these infections.

Nosocomially acquired multidrug-resistant A. baumannii, and in particular those showing complete antibiotic resistance pose a real challenge to hospital epidemiologist. Prolonged hospitalization (especially prolonged ICU stay) and mechanical ventilation have been shown to be important risk factors for the acquisition of resistance in A. baumannii.[8],[9] The majority of patients in our hospital had extended hospitalization or ICU stay as a risk factor. Recently, the emergence and spread of antimicrobial resistance among A. baumannii in Iran has become an important challenge to Iranian healthcare workers. Unfortunately, there is a limited data available regarding drug resistance pattern of A. baumannii in our country.

With the exception of imipenem, susceptibility of A. baumannii isolates to other antibiotics was low in our hospital setting. In our study, 95.5% of the isolates were susceptible to imipenem and 53.4% to tobramycin. Carbapenems have been the drug of choice for the treatment of infections caused by A. baumannii. However, the number of isolates resistant to these antibiotics has been increased in recent years. [10],[11],[12] The lower resistance rate of A. baumannii to imipenem in our study may be due to its recent introduction, i.e. year 2001, for use in our hospital. This antibiotic is frequently used to treat infections caused by multidrug-resistant Gram-negative bacteria especially P. aeruginosa and A. baumannii. In a study conducted in Tehran hospitals, susceptibility of A. baumannii to imipenem was 49.3%. [13] Carbapenem-resistant A. baumannii has emerged in many parts of the world. The main mechanism of resistance is through the acquisition of B and D class carbapenemases. [14] Low resistance rates of A. baumannii to imipenem (about 3%) were reported from Saudi Arabia and Japan. [10],[14] In a study from Turkey, the rate of resistance in A. baumannii for imipenem was 9.6%. [15] In another study in Turkey, this rate was found to be 43.7%. [16] A study from Spain reported that 43% of A. baumannii isolates were resistant to imipenem. [17] Regional variation in resistance of A. baumannii to imipenem is related to pattern of antimicrobial use and risk factors . The important risk factors for the acquisition of imipenem-resistant A. baumannii include previous carbapenem use, longer duration of hospital stay until infection, ICU stay, urgent surgery, total parenteral nutrition, having a central venous catheter, endotracheal tube and urinary catheter or nasogastric tube. [16],[17]

In conclusion, the present study reported data on antimicrobial resistance rate of A. baumannii in an Iranian 1000-bed hospital. Acinetobacter baumannii isolates showed a high frequency of drug resistance to commonly used antibiotics. In our study, imipenem was the most effective antibiotics against A. baummannii isolates and previous use of antibiotics, longer duration of ICU stay and mechanical ventilation were the major risk factors for resistance in A. baumannii.

   Acknowledgments Top

This study was supported by grant No. 1032 awarded by research deputy of Shahid Beheshti university of medical sciences. Authors cordially express their best sincere to Ms. Mozhgan Deldari, Ms. Parisa Eslami and Ms. Fatemeh Savahelimoghaddam for their kind laboratory assistance.

   References Top

1.Hall GS. Non-fermenting and miscellaneous gram-negative bacilli. In: Mahon CR, Lehman DC, Manuselis G, editors. Textbook of Diagnostic Microbiology. 3 rd ed. Philadelphia: WB Saunders; 2007. p. 564-85.  Back to cited text no. 1      
2.Montefour K, Frieden J, Hurst S, Helmich C, Headley D, Martin M, Boyle DA. Acinetobacter baumannii: An emerging multidrug-resistant pathogen in critical care. Crit Care Nurse 2008;28:15-25.   Back to cited text no. 2  [PUBMED]  [FULLTEXT]  
3.Fournier PE, Richet H. The epidemiology and control of Acinetobacter baumannii in health care facilities. Clin Infect Dis 2006;42:692-9.   Back to cited text no. 3  [PUBMED]  [FULLTEXT]  
4.Richet H, Fournier PE. Nosocomial infections caused by Acinetobacter baumannii: A major threat worldwide. Infect Control Hosp Epidemiol 2006;27:645-6.   Back to cited text no. 4  [PUBMED]  [FULLTEXT]  
5.Abbassi M, Rahbar M, Hekmat Yazdi S, Rashed Marandi F, Sabourian R, Saremi M. Evaluation of the 10 th External Quality Assessment Scheme results in clinical microbiology laboratories in Tehran and districts. East Mediter Health J 2006;12:310-5.  Back to cited text no. 5      
6.Forbes BA, Sahm DF, Weissfeld AS, editors. Bailey and Scott's Diagnostic Microbiology, 10 th ed. St. Louis: MO, Mosby; 1998.  Back to cited text no. 6      
7.National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing. Fourteenth informational supplement. Document M100-S14. Wayne, PA: NCCLS, 2004.  Back to cited text no. 7      
8.Rahbar M, Hajia M. Detection and quantitation of the etiologic agents of ventilator-associated pneumonia in endotracheal tube aspirates from patients in Iran. Infect Control Hosp Epidemiol 2006;27:884-5.  Back to cited text no. 8  [PUBMED]  [FULLTEXT]  
9.Mahgoub S, Ahmed J, Glatt AE. Completely resistant Acinetobacter baumannii strains. Infect Control Hosp Epidemiol 2002;23:477-9.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]  
10.Al-Tawfiq JA, Mohandhas TX. Prevalence of antimicrobial resistance in Acinetobacter calcoaceticus-baumannii complex in a Saudi Arabian hospital. Infect Control Hosp Epidemiol 2007;28:870-2.   Back to cited text no. 10  [PUBMED]  [FULLTEXT]  
11.Gootz TD, Marra A. Acinetobacter baumannii: an emerging multidrug-resistant threat. Expert Rev Anti Infect Ther 2008;6:309-25.  Back to cited text no. 11  [PUBMED]  [FULLTEXT]  
12.Perez F, Endimiani A, Bonomo RA. Why are we afraid of Acinetobacter baumannii? Expert Rev Anti Infect Ther 2008;6:269-71.   Back to cited text no. 12  [PUBMED]  [FULLTEXT]  
13.Feizabadi MM, Fathollahzadeh B, Taherikalani M, Rasoolinejad M, Sadeghifard N, Aligholi M, Soroush S, Mohammadi-Yegane S. Antimicrobial susceptibility patterns and distribution of blaOXA genes among Acinetobacter spp. isolated from patients at Tehran hospitals. Jpn J Infect Dis 2008;61:274-8.   Back to cited text no. 13  [PUBMED]  [FULLTEXT]  
14.Ishii Y, Alba J, Kimura S, Yamaguchi K. Evaluation of antimicrobial activity of beta-lactam antibiotics by E-test against clinical isolates from 100 medical centers in Japan (2004). Diagn Microbiol Infect Dis 2006;55:143-8.  Back to cited text no. 14  [PUBMED]  [FULLTEXT]  
15.Karsligil T, Balci I, Zer Y. Antibacterial sensitivity of Acinetobacter strains isolated from nosocomial infections. J Int Med Res 2004;32:436-41.  Back to cited text no. 15  [PUBMED]  [FULLTEXT]  
16.Baran G, Erbay A, Bodur H, Ongόrό P, Akinci E, Balaban N, Cevik MA. Risk factors for nosocomial imipenem-resistant Acinetobacter baumannii infections. Int J Infect Dis 2008;12:16-21.   Back to cited text no. 16      
17.Cisneros JM, Rodrνguez-Baρo J, Fernαndez-Cuenca F, Ribera A, Vila J, Pascual A, et al. Risk-factors for the acquisition of imipenem-resistant Acinetobacter baumannii in Spain: A nationwide study. Clin Microbiol Infect 2005;11:874-9.  Back to cited text no. 17      

Correspondence Address:
Mohammad Rahbar
Department of Microbiology, Reference Health Laboratories, Ministry of Health, Tehran
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Source of Support: Supported by grant No. 1032 awarded by research deputy of Shahid Beheshti university of medical sciences, Conflict of Interest: None

DOI: 10.4103/0377-4929.64333

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