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 ~  Abstract
 ~ Introduction
 ~ Patients and Methods
 ~ Results
 ~ Discussion
 ~  References
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  Table of Contents  
Year : 2013  |  Volume : 31  |  Issue : 1  |  Page : 60-63

Analysis of carbapenem-resistant Acinetobacter from a tertiary care setting in North India

Department of Microbiology, KG Medical University, Lucknow, Uttar Pradesh, India

Date of Submission21-May-2012
Date of Acceptance17-Aug-2012
Date of Web Publication15-Mar-2013

Correspondence Address:
J Agarwal
Department of Microbiology, KG Medical University, Lucknow, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0255-0857.108724

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 ~ Abstract 

Multidrug-resistant (MDR) Acinetobacter baumannii is a worldwide concern as cause of serious nosocomial infections. We analysed 140 non-duplicate Acinetobacter sp. isolates from hospitalised patients in a tertiary care centre; 87% were MDR and 20% (28/140) meropenem resistant. Metallo-β-lactamase was produced by 16 of these, detected by ethylene-diamine-tetra-acetic acid disc synergy test. AmpC β-lactamase and efflux pump were present in 17 and 4 of the meropenem-resistant Acinetobacter, respectively. 9/16 MBL-positive isolates carried genes for carbapenem resistance as shown by polymerase chain reaction.

Keywords: Acinetobacter baumannii, carbapenemases, nosocomial pathogen, metallo-β-lactamase,multidrug-resistant Acinetobacter

How to cite this article:
Sinha N, Agarwal J, Srivastava S, Singh M. Analysis of carbapenem-resistant Acinetobacter from a tertiary care setting in North India. Indian J Med Microbiol 2013;31:60-3

How to cite this URL:
Sinha N, Agarwal J, Srivastava S, Singh M. Analysis of carbapenem-resistant Acinetobacter from a tertiary care setting in North India. Indian J Med Microbiol [serial online] 2013 [cited 2021 Jan 26];31:60-3. Available from:

 ~ Introduction Top

Increasing incidence of Acinetobacter sp. causing serious nosocomial infections in hospital intensive care units are being reported worldwide. Most frequently encountered species is A. baumannii and it is commonly associated with infections, such as bacteremia, urinary tract infection, meningitis, skin and soft tissue infections and pneumonia with high mortality rate of 30-75% in hospitalised patients. [1] These strains are proficient in acquiring resistance determinants and are well accustomed to survive for prolonged periods in hospital environment. Acquired resistance mechanisms can act synergistically and integrate genes encoding antibiotic-inactivating enzymes, efflux pumps, ribosomal binding site mutations and down regulation of porin channels on the cell membrane giving rise to multidrug-resistant (MDR) isolates. [2]

Because of frequent resistance to commonly used antibiotics, carbapenems have become important for managing Acinetobacter infections. However, their effectiveness is being increasingly compromised due to enzymatic modification of antibiotic molecules especially by carbapenemases and expression of efflux pumps. Acquired carbapenemases can be either metallo-β-lactamases (MBLs) such as VIM and IMP, or non-MBL. MBL genes are mostly detected in class integrons' structures and these integrons are detected in a high proportion of Acinetobacter isolates. [3] This study assesses the prevalent mechanisms of resistance for meropenem among Acinetobacter sp. isolated from a tertiary care setup.

 ~ Patients and Methods Top

It was a prospective observational study and all clinical specimens referred for bacteriological cultures from patients of all age groups and both sexes admitted in a tertiary care teaching hospital from August 2010 to July 2011 were included. The specimens comprised urine, blood, sputum, pus, cerebrospinal fluids, body fluids, drain fluid, swabs (vaginal, pus, wound, etc.) endotracheal aspirate, etc., Bacterial isolates were identified using standard methods. [4] Antimicrobial susceptibility of Acinetobacter isolates was done using Kirby Bauer disc diffusion method according to Clinical Laboratory Standards Institute (CLSI) guidelines. [5] Antibiotic discs were obtained from HIMEDIA, Mumbai, India. Meropenem resistance was used as the indication for carbapenemase production. MDR was defined as previously described. [6] Acinetobacter isolates resistant to meropenem on disc diffusion test were tested for minimal inhibitory concentration (MIC) by agar dilution method. [5] Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 25923 were used as controls. Meropenem powder was obtained from Glaxo Smithkline Pvt. Ltd. Mumbai, India. Meropenem-resistant Acinetobacter was screened for presence of MBLs by Modified Hodge test (MHT) and ethylene-diamine-tetra-acetic acid (EDTA) disc synergy test (EDST) as described by Lee et al.[7] Presence of AmpC β-lactamase was detected by previously described method. [8] To test for efflux pump, MIC assay by agar dilution method for meropenem was performed in Müller-Hinton agar plates with and without 25 and 50 μg/ml reserpine (HIMEDIA, Mumbai, India). [9] The presence of blaIMP-1 , blaIMP-2 , blaVIM-1 and blaVIM-2 was detected by PCR in all meropenem-resistant Acinetobacter sp., using published protocol. [10]

 ~ Results Top

During the study period, a total of 9756 samples were received from which 140 Acinetobacter sp. were isolated (non-repetitive). Acinetobacter baumannii was the predominant species (92.14%), while Acinetobacter lwoffii (6.42%) and Acinetobacter haemolyticus (1.42%) were also isolated. Maximum number of Acinetobacter isolates were from pus (37.14%, 52/140) followed by blood (22.85%, 32/140) and urine (13.57%, 19/140). Highest percentage of Acinetobacter was isolated from intensive care unit (ICU) (22.14%) followed by paediatrics (20.71%), neurosurgery (15.71%) and general surgery wards (12.85%). Resistance pattern of Acinetobacter revealed that 87% were resistant to third-generation cephalosporins, aminoglycosides and quinolones, indicating high prevalence of MDR [Table 1]. A total of 28 meropenem-resistant Acinetobacter were detected on disc diffusion method and all were MDR. MIC for meropenem for these isolates ranged between 8 and 64 μg/ml. EDST detected MBL production in 16/28 Acinetobacter sp., whereas MHT did not pick even single MBL producer in this study. AmpC β-lactamase was found in 17 Acinetobacter sp., in 7 it was associated with either a positive EDST or efflux pump [Table 2]. In our study, nine Acinetobacter isolates carried blaIMP1 gene and two of these also carried blaVIM-1 . In addition, one isolate had blaVIM-2 gene. None carried blaIMP2 gene. All these 10 PCR positive isolates were EDST positive for presence of MBL.
Table 1: Antimicrobial sensitivity pattern of Acinetobacter sp.(n = 40)

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Table 2: Profile of meropenem-resistant Acinetobacter isolates (n = 8)

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 ~ Discussion Top

Reports on carbapenemase-producing Acinetobacter isolates are on rise globally due to increased carbapenem usage and selection pressure. [2],[6],[11] In this study, of the 140 Acinetobacter isolated, 28/140 (20.0%) were meropenem resistant by disc diffusion method and MIC. Highest number of Acinetobacter isolates were from ICU (22.14%; 31/140). A. baumannii has a tendency towards cross-transmission, particularly in ICUs where numerous outbreaks are reported. [1] While combination of β-lactam drug with β-lactamase inhibitor (cefoperazone/sulbactam) showed better results as reported previously, [6] 87% were MDR [Table 1]. This is of grave concern because treatment options become limited. [2]

We found EDST to be better than MHT for detection of MBL in Acinetobacter, a finding also reported previously. [8] CLSI [5] recommends MHT for detection of carbapenemases activity in enterobacteriaceae only. AmpC β-lactamase when present along with 'decreased membrane permeability' is capable of conferring carbapenem resistance. [12] In this study, however, AmpC alone was present in 10/28 meropenem-resistant isolates; we have not looked at the porin deficiency in these isolates, and that could be a limitation of our study. Noyal et al.[8] and Sinha and Srinivasa [9] have also reported 67.4% and 42.9%, respectively, of carbapenem-resistant Acinetobacter isolates to be carrying AmpC β-lactamase alone and have suggested its role as a contributing factor for meropenem resistance. Efflux pump was present in 4/28 isolates, always accompanied with another mechanism, and these isolates showed high resistance to meropenem (MIC between 32 and 64 μg/ml), a finding mentioned by Esterly et al.[2] Among various MBL encoding genes thus far, blaIMP appears to be the most clinically relevant due to its ability to spread among other major pathogens. [13] In this study, blaIMP1 gene was most frequently carried by meropenem-resistant isolates, also reported by others from Indian subcontinent. [14]

Overall incidence of Acinetobacter as a nosocomial pathogen in our setup is low but they are predominantly multidrug resistant. Antimicrobial susceptibility of Acinetobacter seems to vary considerably among countries, centres, and even among different wards of the same hospital; therefore, local surveillance studies are needed for deciding the most appropriate therapy. The occurrence of an MBL-positive isolate poses not only a remedial trouble but also a serious concern for infection control management. Since there are multiple mechanisms that affect carbapenem resistance in Acinetobacter sp.; for the development of novel therapeutic strategies, it is crucial to understand the interplay of various resistant mechanisms.

 ~ References Top

1.Bergogne-Bérézin E, Towner KJ. Acinetobacter spp. as nosocomial pathogens: Microbiological, clinical, and epidemiological features. Clin Microbiol Rev 1996;9:148-65.  Back to cited text no. 1
2.Esterly J, Richardson CL, Eltoukhy NS, Qi C, Scheetz MH. Genetic mechanisms of antimicrobial resistance of Acinetobacter baumannii (February). Ann Pharmacother 2011;45:218-28.  Back to cited text no. 2
3.Seward RJ. Detection of integrons in worldwide nosocomial isolates of Acinetobacter spp. Clin Microbiol Infect 1999;5:308-18.  Back to cited text no. 3
4.Collee JG, Miles RS, Watt B. Identification of bacteria. In: Collee JG, Fraser AG, Marmion BP, Simmons A, editors. Practical Medical Microbiology. 14 th ed., vol. 2. Singapore: Churchill Livingstone Publishers, Longman; 2003. p. 131-49.  Back to cited text no. 4
5.Clinical Laboratory Standards Institute (CLSI) guidelines. Performance standards for antimicrobial susceptibility testing: Twentieth informational supplement. CLSI Document M100-S20. Wayne, PA: Clinical and Laboratory Standards Institute; 2010.  Back to cited text no. 5
6.Taneja N, Singh G, Singh M, Sharma M. Emergence of tigecycline and colistin resistant Acinetobacter baumanii in patients with complicated urinary tract infections in north India. Indian J Med Res 2011;133:681-4.  Back to cited text no. 6
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7.Lee K, Chong Y, Shin HB, Kim YA, Yong D, Yum JH. Modified Hodge and EDTA-disk synergy tests to screen metallo-beta-lactamase-producing strains of Pseudomonas and Acinetobacter species. Clin Microbiol Infect 2001;7:88-91.  Back to cited text no. 7
8.Noyal MJ, Menezes GA, Harish BN, Sujatha S, Parija SC. Simple screening tests for detection of carbapenemases in clinical isolates of nonfermentative Gram-negative bacteria. Indian J Med Res 2009;129:707-12.  Back to cited text no. 8
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9.Sinha M, Srinivasa H. Mechanisms of resistance to carbapenems in meropenem-resistant Acinetobacter isolates from clinical samples. Indian J Med Microbiol 2007;25:121-5.  Back to cited text no. 9
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10.Gutiérrez O, Juan C, Cercenado E, Navarro F, Bouza E, Coll P, et al. Molecular epidemiology and mechanisms of carbapenem resistance in Pseudomonas aeruginosa isolates from Spanish hospitals. Antimicrob Agents Chemother 2007;51:4329-35.  Back to cited text no. 10
11.Goel N, Wattal C, Oberoi JK, Raveendran R, Datta S, Prasad KJ. Trend analysis of antimicrobial consumption and development of resistance in non-fermenters in a tertiary care hospital in Delhi, India. J Antimicrob Chemother 2011;66:1625-30.  Back to cited text no. 11
12.Davin-Regli A, Bolla JM, James CE, Lavigne JP, Chevalier J, Garnotel E, et al. Membrane permeability and regulation of drug "influx and efflux" in enterobacterial pathogens. Curr Drug Targets 2008;9:750-9.  Back to cited text no. 12
13.Da Silva GJ, Correia M, Vital C, Ribeiro G, Sousa JC, Leitão R, et al. Molecular characterization of bla (IMP-5), a new integron-borne metallo-beta-lactamase gene from an Acinetobacter baumannii nosocomial isolate in Portugal. FEMS Microbiol Lett 2002;215:33-9.  Back to cited text no. 13
14.Azim A, Dwivedi M, Rao PB, Baronia AK, Singh RK, Prasad KN, et al. Epidemiology of bacterial colonization at intensive care unit admission with emphasis on extended-spectrum beta-lactamase-and metallo-beta-lactamase-producing Gram-negative bacteria-An Indian experience. J Med Microbiol 2010;59:955-60.  Back to cited text no. 14


  [Table 1], [Table 2]

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