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Indian J Med Sci. 2011 Jan;65(1):18-25. doi: 10.4103/0019-5359.103161.

Carbapenem resistance and phenotypic detection of carbapenemases in clinical isolates of Acinetobacter baumannii.

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Department of Microbiology, Punjab Institute of Medical Sciences, Jalandhar, Punjab, India.



Multidrug-resistant Acinetobacter baumannii (MDR-Ab) reported worldwide has become one of the most difficult nosocomially acquired Gram-negative pathogens to control and treat. The clinical utility of carbapenems is under threat with the emergence of acquired carbapenemases, particularly Ambler class B metallo-lactamases (MBL). Because of the global increase in the occurrence and dissemination of MBLs, early detection is critical. This study was undertaken to detect resistance to carbapenems in clinical isolates of A. baumannii from hospitalized patients by both disk-diffusion and minimum inhibitory concentration (MIC) methods and to assess the rate of carbapenemase and MBL production among the isolates.


A. baumannii were identified from various clinical samples and antibiotic susceptibility profile was determined by the standard disk-diffusion method. Meropenem-resistant strains were tested further by agar dilution MIC for meropenem. Resistant isolates were screened for carbapenemase production by the modified Hodge test and positive isolates were further checked for metallo-β-lacatmase production by the EDTA disk synergy test.


42 isolates (31.81%) showed resistance to meropenem by the disk diffusion method. 47.6% were carbapenemase positive by the modified Hodge test and 19% were MBL producers phenotypically by the EDTA disc synergy test (EDS). These meropenem-resistant isolates were resistant to most of the other antibiotics tested. These 42 isolates were recovered mostly from patients admitted to intensive care units. Four isolates of the A. baumannii complex were pan drug resistant and showed resistance to even tigecycline and polymyxin B.


Carbapenem resistance has been increasingly reported, necessitating their detection. This study reports simple, carbapenemase, and MBL detection method that can be easily incorporated into the daily routine of a clinical laboratory.

[Indexed for MEDLINE]

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