Distribution and expression of the Ade multidrug efflux systems inAcinetobacter baumanniiclinical isolates

One hundred Acinetobacter baumannii clinical isolates were examined for inhibitory effect of reserpine and carbonyl cyanide m-chlorophenylhydrazone (CCCP) on the antimicrobial susceptibility and expression of 4 resistant–nodulation–cell division (RND)-type multidrug efflux systems, including AdeABC, AdeDE, AdeIJK, and AdeFGH, using RT-PCR. Ten A. baumannii isolates expressing AdeABC, AdeIJK, or AdeFGH were randomly selected for determination of transcription level and regulatory mutations. While all the isolates were resistant to multiple drugs, the reserpine and CCCP experiment showed that the multidrug resistance phenotype in most A. baumannii isolates was associated with efflux pumps. Most isolates expressed at least one of the RND-type efflux pumps tested (97%). AdeIJK expression was most common (97%), but none of the isolates produced AdeDE. Fifty-two percent of the A. baumannii isolates simultaneously produced up to 3 RND-type efflux systems (i.e., AdeABC, AdeFGH, and AdeIJK). No good correlation between the expression of RND-type efflux pumps and the type of antimicrobial resistance was observed. Overexpression of AdeABC, AdeIJK, and AdeFGH was not always related to the presence of mutations in their corresponding regulatory genes. This study highlights (i) the universal presence of the RND-type efflux pumps with variable levels of expression level among the A. baumannii in this collection and (ii) the complexity of their regulation of expression.

Download Full-text

Determination of imipenem efflux-mediated resistance in Acinetobacter spp., using an efflux pump inhibitor

Iranian Journal of Microbiology ◽

10.18502/ijm.v11i5.1954 ◽

2019 ◽

Author(s):

Ghazale Amiri ◽

Maryam Abbasi Shaye ◽

Masoumeh Bahreini ◽

Asghar Mafinezhad ◽

Kiarash Ghazvini ◽

...

Keyword(s):

Efflux Pump ◽

Efflux Pumps ◽

Diffusion Method ◽

Efflux Pump Inhibitor ◽

Acinetobacter Species ◽

Fold Reduction ◽

Carbonyl Cyanide ◽

Acinetobacter Spp

Background and Objectives: In recent years, reports of Acinetobacter strains resistant to all known antibiotics have caused a great concern in medical communities. Overexpression of efflux pumps is one of the major causes of resistance in bacteria. The aim of this study was to investigate the role of efflux pumps in conferring resistance to imipenem in clinically important Acinetobacter spp; Acinetobacter baumannii and Acinetobacter lwoffii. Materials and Methods: A total number of 46 clinical Acinetobacter isolates, including 33 A. baumannii and 13 A. lwoffii isolates, previously collected from Shahid Kamyab and Ghaem hospitals of Mashhad, Iran were used in this study. Imipenem susceptibility testing was carried out by the disc diffusion method. Imipenem minimum inhibitory concentration (MIC) for resistant Acinetobacter isolates were determined both in the presence and absence of the efflux pumps inhibitor, carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Results: Resistance to imipenem was observed in 38 isolates including 30 A. baumannii and 8 A. lwoffii isolates. Experiments in the presence of CCCP showed a 2 to 16384 fold reduction in imipenem MICs in 14 A. baumannii and 2 A. lwoffii isolates. Conclusion: The results obtained showed high levels of resistance to imipenem and contribution of efflux pumps in conferring resistance in both Acinetobacter species in this study. Moreover, imipenem efflux mediated resistance highlights the importance of this mechanism not only in A. baumannii but also in non-baumannii Acinetobacter Spp. which have been neglected in antibiotic resistance studies.

Download Full-text