Background: Resistance of Acinetobacter baumannii to carbapenems is a rising problem. Colistin and Tigecycline provided a new hope for the treatment of infections caused by carbapenem resistant A. baumannii.
Aim of the work: The current study aimed at assessment of Carbapenem resistant Acinetobacter baumannii among its clinical isolates as well as the in vitro activity of Tigecycline and Colistin against these resistant strains at Sohag University Hospital.
Material and Methods: This study was conducted from June to December 2015 on a total of 53 Acinetobacter baumannii isolates collected from 600 different clinical specimens in the infection control unit laboratory of Sohag University Hospital and identified by the Vitek- 2 colorimetric compact system (bioMérieux, France). All isolates were tested for their susceptibility to the commonly used antibiotics by disc diffusion method and the diameters of the inhibition zones were interpreted according to Clinical Laboratory Standards Institute(CLSI) guidelines, Imipenem resistant isolates were further tested for metallo- β-lactamase (MBL) production by Imipenem-EDTA double disc synergy test and the MBL producers were further tested for the presence of blaIMP and blaVIM genes coding for MBL production by polymerase chain reaction(PCR), finally in vitro susceptibility of carbapenem resistant A. baumannii to Tigecycline and Colistin was tested using disc diffusion method and E test, respectively.
Results: Carbapenem resistance rate in A. baumannii isolates was found to be 41/53(77.35%) as tested by Imipenem discs and the resistance rates for other antibiotics were found to be as following: Gentamicin 47/53(88.67%), Amikacin 35/53 (66.03%), Cefotaxime 53/53 (100%), Cefepime 38/53 (71.69%), Ceftazidime
50/53 (94.33%), Ciprofloxacin 53/53 (100%), Trimethoprim - sulfamethoxazole 48/53 (90.65%), Aztreonam 51/53 (96.22%) according to Imipenem-EDTA double disc synergy test MBL was produced by 27/41(65.85%) isolates of the 41 imipenem resistant A. baumannii isolates among them blaVIM gene was detected in 16/27(59.25%) but blaIMP failed to be detected in any of them by duplex PCR technique. All the Carbapenem resistant A. baumannii isolates were sensitive to Colistin, According to CLSI guidelines, as no CLSI interpretive criteria have been approved for in vitro testing of Tigecycline activity against Acinetobacter spp. Therefore, the Tigecycline disc diffusion results were interpreted according to Jones
criteria where resistance rate for Tigecycline among isolated carbapenem resistant A. baumannii was found to be 1/41 (2.4%).
Conclusion: The Present study concluded that carbapenem resistance is common among Acinetobacter baumannii isolates in Sohag University Hospital, as regards in vitro activity of Tigecycline & Colistin against carbapenem resistant A. baumannii, all of them were sensitive to Colistin and rarely resistant to Tigecycline. It should be noted that there is a need for regular surveillance for emergence of resistance to these two antimicrobial agents as they are rare limited options for treating infections caused by this bacterium.