UK researchers identify novel A. baumannii mutation

A 50-year-old woman returning from travels in Eygpt tested positive for the first documented resistant strain of Acinetobacter baumannii linked to a GES carbapenemase mutation in the United Kingdom.

“GES is a carbapenemase which if present, means that the only options open for treatment are colistin and tigecycline. However if the A. baumannii has outer membrane permeability loss or efficient efflux pumps then even the efficacy of these alternative therapies may be significantly reduced,” Mandy Wootton, PhD, a specialist in the antimicrobial chemotherapy unit at University Hospital Wales in Cardiff, United Kingdom told Infectious Disease News during a poster presentation at the American Academy of Microbiology’s 49^th Interscience Conferences on Antimicrobials and Chemotherapy.

Wootton and colleagues determined that A. baumannii isolated from the patient’s sputum was susceptible only to colistin, with Etests revealing resistance to imipenem, meropenem, ertapenem, ceftazidime, tigecycline and aztreonam (Azactam).

The GES-12 sequence in this strain of A. baumannii consists of an A694G mutation resulting in an amino acid change from Thr232Ala. The researchers believe that Thr232Ala is tied to carbapenemase activity due to its close proximity to Ser70 antibody, which plays a key role interacting with betalactam carboxyl moiety.

“In the future we are going to attempt to purify the GES enzyme and perform some kinetic studies to determine its precise acitivity against all carbapenems,” Wootton said.

GES enzyme has previously been reported in Klebsiella pneumoniae and A. baumannii in several countries including Brazil, France, Greece, Japan and Korea. This importation of A. baumannii from Egypt emphasizes the need to establish global surveillance networks, according to the researchers. – by Nicole Blazek

For more information:

Wootton M. #C1-097b. Interscience Conference on Antimicrobial Agents and Chemotherapy; San Francisco: Sept. 11-15, 2009.