The Stringent Response Promotes Antibiotic Resistance Dissemination by Regulating Integron Integrase Expression in Biofilms.

Emilie Strugeon,Marie-Cécile Ploy,Valentin Tilloy,Sandra Da Re,Julian E Davies

doi:10.1128/mbio.00868-16

Abstract

ABSTRACTClass 1 integrons are genetic systems that enable bacteria to capture and express gene cassettes. These integrons, when isolated in clinical contexts, most often carry antibiotic resistance gene cassettes. They play a major role in the dissemination of antibiotic resistance among Gram-negative bacteria. The key element of integrons is the integrase, which allows gene cassettes to be acquired and shuffled. Planktonic culture experiments have shown that integrase expression is regulated by the bacterial SOS response. In natural settings, however, bacteria generally live in biofilms, which are characterized by strong antibiotic resilience and by increased expression of stress-related genes. Here, we report that under biofilm conditions, the stringent response, which is induced upon starvation, (i) increases basal integrase and SOS regulon gene expression via induction of the SOS response and (ii) exerts biofilm-specific regulation of the integrase via the Lon protease. This indicates that biofilm environments favor integron-mediated acquisition of antibiotic resistance and other adaptive functions encoded by gene cassettes.

Highlights

Antibacterial drugs are one of the most important therapeutic advances in medical history, but bacterial resistance has increased dramatically over the last decade
The V. cholerae integron integrase (IntIA, formerly called IntI4) was shown to be controlled by cyclic AMP receptor protein (CRP)-dependent regulation [19]. All of these regulatory mechanisms have been extensively studied in planktonic culture, whereas in natural settings, bacteria mostly live in biofilms
In agreement with Bernier et al, who showed that the SOS response is gradually induced in aging static biofilm culture in minimal medium [28], we found that both the SOS response and class 1 integron integrase expression were induced more than twofold in 24-h continuous biofilm culture in LB medium compared to their expression level in planktonic culture

Summary

Introduction

Antibacterial drugs are one of the most important therapeutic advances in medical history, but bacterial resistance has increased dramatically over the last decade. The V. cholerae integron integrase (IntIA, formerly called IntI4) was shown to be controlled by cyclic AMP (cAMP) receptor protein (CRP)-dependent regulation [19] All of these regulatory mechanisms have been extensively studied in planktonic culture, whereas in natural settings, bacteria mostly live in biofilms. Biofilms are highly heterogeneous environments with local gradients of nutrients, pH, oxygen tension, etc., creating microniches of distinct bacterial subpopulations that experience and adapt to various stresses [29, 30] Another characteristic explaining the survival of biofilm bacteria during antibiotic exposure is that biofilms facilitate the transfer of mobile genetic elements and, the spread of antibiotic resistance between bacteria [31,32,33,34]. It has been shown that various environments where bacteria live in complex biofilms contain large numbers of integrons displaying a huge variety of gene cassettes [35,36,37]

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