Novel role of Acinetobacter baumannii RND efflux transporters
in mediating decreased susceptibility to biocides
Govindan Rajamohan1,2, Vijaya Bharathi Srinivasan1and Wondwossen A. Gebreyes1*
1Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA;
2Institute of Microbial Technology, Council of Scientific and Industrial Research, Sector 39A, Chandigarh, India
*Corresponding author. Tel: þ1-614-292-9559; Fax: þ1-614-292-4142; E-mail: firstname.lastname@example.org
Received 28 August 2009; returned 28 September 2009; revised 26 October 2009; accepted 4 November 2009
Objectives: Biocides and dyes are commonly employed in hospital and laboratory settings. We investigated the
biocide susceptibilities of a rapidly emerging pathogen, Acinetobacter baumannii, and the underlying molecular
mechanisms, with a primary focus on resistance–nodulation–cell division (RND) efflux systems.
Methods: Biocide susceptibilities, efflux and in vitro inactivation profiles were monitored in the presence/
absence of efflux pump inhibitors. The RND transporters encoded by adeB and adeJ were detected by PCR;
null mutants were constructed in the native host. Expression of adeB and adeJ in clinical isolates was
assayed by semi-quantitative RT–PCR.
Results: Susceptibility testing and phenotypic assays demonstrated the role of active efflux in mediating
decreased susceptibility to biocides. Inactivation of either the adeB or adeJ transporter gene led to increased
susceptibility to biocides. RT–PCR analysis exhibited increased adeB and adeJ expression in clinical isolates.
Conclusions: This is the first study demonstrating the role of efflux pumps in mediating decreased susceptibility
to disinfectants and other chemical substrates in A. baumannii.
Keywords: antimicrobial resistance, multidrug efflux, RND efflux pump
Biocides are an integral component in the practice of clinical
medicine, serving to prevent the dissemination of pathogenic
organisms in the hospital environment.1Reduced susceptibility
to biocides in bacterial species arises from various intrinsic and
acquired (such as qac genes) genetic determinants, but efflux
is increasingly implicated as a major resistance mechanism.2
An association between resistance to antibiotics and cross-
resistance to biocides has been reported for clinically important
One such important human pathogen is Acinetobacter
baumannii, a Gram-negative bacillus that causes numerous
healthcare-associated infections worldwide, with a remarkable
propensity for nosocomial cross-transmission.4Reports have
demonstrated the involvement of intrinsic and acquired resist-
ance determinants as well as efflux pumps (AdeABC and
AdeIJK) in conferring multidrug resistance.5
Despite the fact that these organisms have been linked to
hospital environment contamination,4,5to date only a few
studies have investigated the susceptibility profile of this bacillus
to structurally unrelated compounds, antiseptics and biocides.
The underlying genetic mechanisms responsible for mediating
decreased susceptibility to disinfectants in A. baumannii still
remain unknown. Prompted by the paucity of such information,
a systematic study was initiated using 86 multidrug-resistant
The biocide susceptibilities and underlying molecular mech-
anisms were investigated, with a primary focus on resistance–
nodulation–cell division (RND) efflux systems. To our knowledge,
this is the first study demonstrating the role of active extrusion
and involvement of AdeABC and AdeIJK in mediating decreased
susceptibility to biocides in A. baumannii.
Materials and methods
Bacterial strains, growth media and reagents
Eighty-six A. baumannii strains isolated during 2005–07 were obtained
from two sources, i.e. the Ohio Department of Health (n¼38) and The
Ohio State University Medical Center (n¼48).6All isolates were cultured
in Luria–Bertani (LB) agar and LB broth (Difco, Sparks, MD, USA).
MICs were determined by a broth dilution method following CLSI guide-
lines.7The concentration with no visible growth was considered the MIC.
The isolates were defined to exhibit decreased susceptibility if their MIC
was found to be ?2-fold higher than that for the A. baumannii
# The Author 2009. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
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J Antimicrob Chemother 2010; 65: 228–232
doi:10.1093/jac/dkp427 Advance publication 11 December 2009
by guest on October 27, 2015