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Carbapenemases among Acinetobacter species isolated from NICU of a tertairy care hospital in Karachi

Fakhuruddin Indhar, Muhammad Asif Durrani, Amir Bux  ( Department of Microbiology, Basic Medical Sciences Institute, JPMC )

Muhammad Sohail  ( Department of Microbiology, University of Karachi, Karachi, Pakistan )


Objective: To determine the carbapenemases in carbapenem-resistant Acinetobacter species.
Methods: This descriptive, cross-sectional study was carried out at the Jinnah Postgraduate Medical Centre, Karachi, from March to December 2014, and comprised Acinetobacter species isolated from the clinical specimen collected from hospitalised neonates. The screening for carbapenem resistance was performed by meropenem and imipenem discs, and minimum inhibitory concentrations. SPSS 16 was used for data analysis.
Results: A total of 100 Acinetobacter isolates were included. The patients’ age ranged from 1-28 days. The main species 95(95%) was Acinetobacter calcoaceticus-baumannii complex, followed by Acinetobacter lwoffii 5(5%). The overall resistance to carbapenem was 95(95%); it was higher 100 (100%) in Acinetobacter lwoffii in comparison to Acinetobacter calcoaceticus-baumannii complex 90 (94.7%). Phenotypic characterisation revealed that 89 (93.6%) of both the species were class D carbapenemase producers, 2 (2.1%) were metallo-b-lactamases and 4 (4.2%) were non-producers.
Conclusion: Among carbapenem-resistant Acinetobacter species, the class D carbapenemases were the main mode of resistance to carbapenems.
Keywords: Acinetobacter calcoaceticus baumannii, Acinetobacter lwoffii, Carbapenem-resistant, Carbapenemase. (JPMA 67: 1547; 2017)


Acinetobacter species is found in a variety of environments such as soil, water, animals and human skin. The classification of the organism has remained under revision and currently based on deoxyribonucleic acid (DNA)-DNA hybridisation studies; four species are found closely related to each other that cannot be distinguished phenotypically. The species are collectively known as Acinetobacter calcoaceticus-baumannii complex (ABC) accounting for more than 80% of infections caused by any Acinetobacter species.1 The organism can survive for long period in different environments2,3 including hospitals and has been isolated from hospitalised patients.4 Therefore, many reports describe cross-infection between patients, particularly in case of longer stay in intensive care units (ICUs). Historically, Acinetobacter spp. have been considered health care-related pathogens, accounting for 1-3% of hospital-acquired infections, out of which 2-10% of infections occur in ICUs.5 The situation becomes grave when there is an involvement of patients with prolonged antimicrobial therapy as it results in colonisation with multidrug-resistant (MDR) strains. Indeed, Acinetobacter sp. is also included in most common and serious MDR pathogens group, ESKAPE, i.e. Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa and Enterobacter sp.5,6

Until recently, the carbapenems were considered as the last resort against the infections by Acinetobacter and were regarded as the most powerful antibiotics due to potent antibacterial activity and low toxicity. However, various mechanisms conferring to carbapenem-resistant Enterobacteriaceae (CRE) have been reported, notably through the production of carbapenemase enzymes. This recent emergence of carbapenems resistance in A. baumannii has become a global concern and has limited the choice of therapeutic agents. Non-existence of therapeutic agents with patient safety and predictable activity against A. baumannii3 is a challenge for global healthcare in general and for countries likes Pakistan in particular. Owing to poor infection control practices and illegitimate use of antibiotics, A. baumannii has now emerged as a pandrug-resistant (PDR) pathogen in Pakistani hospitals.6,7 Among carbapenemases, class D oxacillinases (OXAs) are the most common8 and less frequent are metallo-b-lactamases (MBLs).9,10

Rapid detection of carbapenemase producers provides critical information for antibiotic stewardship and swift implementation of outbreak control measures.11 In Pakistan, a limited work has been done on Acinetobacter, in general, and on carbapenemases production and carbapenem resistance, in particular. The current study was designed to determine the prevalence of carbapenemases in acinetobacter species in Pakistani hospitals. We used the RAPIDEC® CARBA NP (Biomeriux, France) first time in Pakistan for the rapid detection of carbapenemases in Acinetobacter.

Materials and Methods

This descriptive, cross-sectional study was carried out at the Department of Microbiology, Basic Medical Sciences Institute, Jinnah Postgraduate Medical Centre (JPMC), Karachi, from March to December 2014, and comprised Acinetobacter species isolated from the clinical specimen collected from hospitalised neonates. The carbapenem-resistant Acinetobacter strains were collected from neonatal intensive care unit (NICU) of the hospital.

Approval for the study was obtained from the institutional review board and informed consent was taken from each guardian. 

The sample size was calculated by OpenEpi calculator, and confidence level was set at 95% in the light of an earlier study.9

Isolates were initially identified by Gram-staining, followed by growth characterisation on blood and MacConkey agar, and analysis by standard biochemical methods including analytical profile index (API) 20NE (BioMerieux, France).

Using the Kirby-Bauer disc diffusion method, the isolates were tested for antimicrobial susceptibilities to antibiotics: piperacillin-tazobactam, ampicillin-sulbactam, cefepime, ceftazidime, ceftriaxone, meropenem, imipenem, amikacin, colistin, trimethoprim-sulfamethoxazole, tetracycline and gentamicin. The strains were classified as susceptible, intermediate or resistant according to Clinical Laboratory Standards Institute (CLSI) guidelines.12 The minimum inhibitory concentration (MIC) for all isolates to imipenem and meropenem was also determined by Etest (BioMerieux, France). Escherichia coli (ATCC 25922) was used as a quality control strain.
Carbapenemase production was confirmed

by the modified Hodge test13 (MHT) and Rapidec Carba NP(BioMerieux, France; Figure-2).

Two different b-lactamase inhibitors (ethylenediaminetetraacetic acid [EDTA] and boronic acid) were used for the evaluation of class A and B production. A double-disc synergy test protocol recommended by Song et al.14 was followed. The discs of 10mg meropenem and 400mg of phenylboronic acid (PBA) (Sigma-Aldrich, St. Louis, Missouri, United States) were placed on the inoculated plate, 15mm apart centre to centre, and incubated for 24 hours.

In combination with b-lactamase inhibitors phenotypic double disc diffusion method, temocillin 30mg disc was also used for the OXA carbapenemase detection. Interpretation of carbapenemase by phenotypic methods was modified from the interpretation of Dijk et al.15 E. coli ATCC 25922 and NCTC 13476 were used as negative and positive control, respectively.

The data was initially made on Microsoft Excel. SPSS 16 was used for data analysis. The frequencies were analysed and represented in percentages. Hypothesised percentage frequency of outcome of carbapenemases in the organism was 94±5% and the margin of error was taken as 5% at confidence level of 95%.


A total of 100 Acinetobacter isolates were included. Of them, 35(35%) were from blood samples and 65(65%) from tracheal aspirates samples. Patients' age ranged from 1 to 28 days, with 47(47%) being 1-5 days old. Moreover, 71(71%) patients had fever and 57(57%) had respiratory distress syndrome. Interestingly, 26(26%) of the patients had normal white blood cell levels but 84(84%) had elevated levels of neutrophils (>70%) and 88(88%) had elevated levels of C-reactive protein (CRP >8 mg/dl). The gestational age of 61(61%) subjects were <38 weeks.

The main species was ABC 95(95%), followed by A. lwoffii 5(5%). The isolates were tested for antibiotic sensitivity and it was found that the resistance to cefoperazone/sulbactam in Acinetobacter sp. was 100(100%), whereas the resistance to aminoglycosides, quinolones, and cephalosporins were 95(95%)-100(100%). The resistance to tetracycline was, however, 80(80%)-83(83%).

The overall resistance to carbapenem was 95(95%) but higher 05(100%) in A. lwoffii in comparison to ABC which was 90(94.7%). Phenotypic characterisation of carbapenemase revealed that 89(93.6%) of both the species produced D carbapenemase.


Acinetobacter has emerged as a significant pathogen, posing a continuous threat and challenge to the healthcare system.6,7 In addition to the severity of infections, the emergence of extensively drug-resistant (XDR) and PDR Acinetobacter species is aggravating the situation into a number of complications and deaths in hospitals. But limited data is available about crabapenem-resistant A. baumannii from Pakistan. In an earlier study, a high prevalence of MDR A. baumannii was found in healthcare facilities in Pakistan, with carbapenem resistance overriding.16 In this study, the prevalence of A. calcoaceticus baumannii was found to be higher, which is consistent with a study conducted by Kaur et al (2014).

Surveillance by the ChiNet project in China revealed that the rate of resistance of A. baumannii to the carbapenem, such as imipenem, has been doubled from 30.1% in 2006 to 62.8% in 2013.17 In Pakistan, the resistance to carbapenems in gram-negative bacteria was found to be increased by 11% from 2002 to 2012.18 In this study, 95% of Acinetobacter species were found to be PDR, which indicates resistance to all classes of antibiotics except the colistin. This resistance pattern is much higher than 75.2% in Algeria and 60.9% in China,17 whereas similar results to this study (higher resistance) was reported from Pakistan Institute of Medical Sciences (PIMS) Islamabad.3 Interestingly, in this study, all strains were found sensitive to colistin, whereas up to 50% heteroresistance to colistin has been reported globally.16

The MHT showed low sensitivity (12.6%) to detect the carbapenemases, whereas sensitivity and specificity of Rapidec Carba NP were 100%. The Rapidec Carba NP is more reliable and easy to perform test that does not need highly skilled personnel like in MHT because there is clear change in colour from red to yellow. The results of Rapidec Carba NP were confirmed by the polymerase chain reaction (PCR) using specific primers for carbapenemases at the Centre of Clinical Microbiology, Royal Free Campus, University College London, United Kingdom (UK) (data not shown).  These results are in accordance with results of an earlier study.19 The MHT have poor sensitivity and specificity to detect the carbapenemases in A.sp. because the OXA-type producer shows weak synergetic images when there is low production of carbapenemases. These findings are in accordance with those of Bonnin et al.20 Out of the 95 carbapenem-resistant Acinetobacter .spp. only two strains were positive for MBL production; both strains were A. lwoffii, whereas all carbapenem-resistant strains of A. calcoaceticus baumannii complex were negative for MBLs. The MBLs in A. baumannii have been reported globally by several studies.21-24 The common mode of resistance mechanism in the Acinetobacter .sp. was oxacillinases (Class D; 93.6%), which is in accordance with studies from Pakistan9 and other countries. The present observations showed that only 2.1% carbapenem resistance in Acinetobacter .sp. was due to MBL production, which is in contradiction of a study6 where all the Acinetobacter species were found to be MBL producers. This variation may be due to the presence of the same clone in that environment. The finding of the present study that the major mode of resistance are oxacillinases is in accordance with the findings from Pakistan.9 This emphasises the necessity and urgency to deal with the dissemination of these superbugs. We recommend that those clinical laboratories without molecular set-up can use the Rapidec Carba NP test for routine screening of carbapenemases in imipenem/meropenem-resistant Acinetobacter sp.

Previous reports have shown that carbapenem resistance among Acinetobacter species ranged from 6% to 52% in Western countries, 2% to 26% in Asian/Pacific countries25 and 74% in Egyptian intensive care units.26 Our results indicate high prevalence of carbapenems resistance (95%) in comparison to developing countries which may result from poor hygiene and ineffective infection control practices in the hospital setting. This also represents a deficiency or failure of the strict measures to control hospital-acquired infections and the potential spread of emerging resistant pathogens. The study revealed that amongst carbapenem-resistant Acinetobacter .sp. the class D carbapenemases are the main mode of resistance to carbapenems.


The study revealed that amongst Carbapenem-resistant Acinetobacter sp. the class D carbapenemases are the main mode of resistance to carbapenems and RAPIDEC CARBA NP is reliable and sensitive tool for rapid detection of carbapenemases.

Disclaimer: The Abstract was accepted and published in the ASM Microbe 2016, Organised by the American Society of Microbiology. USA.
Conflict of Interest: None.
Source of Funding: None.


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