Da Re, S. | bioRxiv Science

bioRxiv2022

Conjugative IncC plasmid entry triggers the SOS response and promotes effective transfer of the integrative antibiotic resistance element SGI1

The broad host range IncC plasmid family and the integrative mobilizable Salmonella Genomic Island 1 (SGI1) and its derivatives enable the spread of medically-important antibiotic resistance genes among Gram-negative pathogens. Although several aspects of the complex functional interactions between IncC plasmids and SGI1 have been recently deciphered regarding their conjugative transfer and incompatibility, the biological signal resulting in the hijacking of the conjugative plasmid by the integrative mobilizable element remains unknown. Here, we demonstrate that the conjugative entry of IncC/IncA plasmids is detected at an early stage by SGI1 through the transient activation of the SOS response, which induces the expression of the SGI1 master activators SgaDC, shown to play a crucial role in the complex biology between SGI1 and IncC plasmids. Besides, we developed an original tripartite conjugation approach to directly monitor SGI1 mobilization in a time-dependent manner following conjugative entry of IncC plasmids. Finally, we propose an updated biological model of the conjugative mobilization of the chromosomal resistance element SGI1 by IncC plasmids. IMPORTANCEAntimicrobial resistance has become a major public health issue, particularly with the increase in multidrug resistance (MDR) in both animal and human pathogenic bacteria, and with the emergence of resistance to medically important antibiotics. The spread between bacteria of successful mobile genetic elements such as conjugative plasmids and integrative elements conferring multidrug resistance is the main driving force in the dissemination of acquired antibiotic resistances among Gram-negative bacteria. Broad-host range IncC plasmids and their integrative mobilizable SGI1 counterparts contribute to the spread of critically-important resistance genes (e.g., ESBLs, and carbapenemases). A better knowledge of the complex biology of these broad-host range mobile elements will help to understand the dissemination of antimicrobial resistance genes that occurred across{gamma} -proteobacteria borders.

microbiology↗

bioRxiv2021

Microniches in biofilm depth are hot-spots for antibiotic resistance acquisition in response to in situ stress

Class 1 integrons play a major role in antibiotic resistance dissemination among Gram-negative bacteria. They are genetic platforms able to capture, exchange and express antibiotic resistance gene cassettes. The integron integrase, whose expression is regulated by the bacterial SOS response, is the key element of the integron catalyzing insertion/excision/shuffling of gene cassettes. We previously demonstrated that the basal level of integrase expression and in consequence, its activity, is increased via the starvation-induced stringent response in the biofilm population. However, biofilms are heterogeneous environments where bacteria are under various physiological states. Here we thus analyzed at the bacterial level, the SOS response and integrase expression within the biofilm, using confocal microscopy and flow cytometry. We showed that in the absence of exogenous stress, only a small number of bacteria (~ 1%) located in the depth of the biofilm induce the SOS-response leading to a high level of integrase expression, through both a stringent response-dependent and -independent manner. Our results thus indicate that few bacteria located in microniches of the biofilm depth undergo sufficient endogenous stress to promote the acquisition of antibiotic resistance, forming a reservoir of bacteria ready to rapidly resist antibiotic treatments.

microbiology↗