Molecular Basis of Azithromycin-Resistant Pseudomonas aeruginosa Biofilms

Abstract

Pseudomonas aeruginosa biofilms are extremely recalcitrant to antibiotic treatment. Treatment of cystic fibrosis patients with azithromycin (AZM) has shown promise. We used DNA microarrays to identify differentially expressed transcripts in developing P. aeruginosa biofilms exposed to 2 g/ml AZM. We report that transcripts for multiple restriction-nodulation-cell division (RND) efflux pumps, known to be involved in planktonic antibiotic resistance, and transcripts involved in type III secretion were upregulated in the resistant biofilms that developed in the presence of AZM. Interestingly, the MexAB-OprM and MexCD-OprJ efflux pumps, but not type III secretion, appear to be integral to biofilm formation in the presence of AZM, as evidenced by the fact that a mutant deleted in both mexAB-oprM and mexCD-oprJ was unable to form a biofilm in the presence of AZM. A mutant deleted in type III secretion was still able to form biofilms in the presence of drug. Furthermore, single mexAB-oprM-and mexCD-oprJ-null mutants were able to form a biofilm in the presence of drug, indicating that either of the pumps can confer resistance to AZM during biofilm development. In contrast to planktonically grown cells, where no mexC expression was detectable regardless of the presence of AZM, biofilms exhibited induction of mexC expression from the outset of their formation, but only in the presence of AZM. mexA, which is constitutively expressed in planktonic cells, was uniformly expressed in biofilms regardless of the presence of AZM. These data indicate that the MexCD-OprJ pump acts as a biofilm-specific mechanism for AZM resistance.

Biofilms: A Survival and Resistance Mechanism of Microorganisms

“…In contrast to these results, resistance to azithromycin is associated pumps MexAB-OprM and MexCD-OprJ to biofilm resistance mechanisms in P. aeruginosa (Gillis et al, 2005) and PA1874-1887 pump that is expressed at high level in both biofilms and planktonic cells (Zhang & Mah, 2008). Although the results are still inconclusive, have proposed the use of anti-inhibitor drugs efflux pumps (EPI) as potential anti-biofilm treatment have been well tolerated in humans (Kvist et al, 2008).…”

Adaptive and Mutational Resistance: Role of Porins and Efflux Pumps in Drug Resistance

“…For this reason, Pamp et al (194) strongly recommended the use of combined therapy for the treatment of biofilm-related infections. Also, Gillis et al (74) described the importance of the MexAB-OprM and MexCDOprJ efflux pumps for the growth of P. aeruginosa biofilms in the presence of the macrolide azithromycin. Thus, while mexABoprM showed constitutive expression independently of antibiotic exposure, mexCD-oprJ overexpression was dependent on azithromycin.…”

Screening of Class 1 and Class 2 Integrons in Clinical Isolates of Pseudomonas aeruginosa Collected from Seven Hospitals in Turkey: A Multicenter Study

“…Pseudomonas aeruginosa (P. aeruginosa) is a ubiquitous, Gram-negative, opportunistic organism. This organism can cause various infections such as hospital-acquired pneumonia and fulminant sepsis especially in immunocompromised hosts [2][3][4]. P. aeruginosa can also cause urinary tract infections.…”