Antibiotic-Induced, Increased Conjugative Transfer Is Common to Diverse Naturally Occurring ESBL Plasmids in Escherichia coli

Abstract

Previously, we showed that cefotaxime (CTX) exposure increases conjugative transfer of a blaCTX–M–1 encoding IncI1 plasmid (IncI1/pST49/CTX-M-1) in Escherichia coli in a SOS-independent manner. This study aimed at investigating whether the observation was unique for that plasmid/strain/antibiotic combination or whether antibiotic-induced plasmid transfer (PT) is a more general phenomenon among plasmids in E. coli. Whole genome sequences of 25 E. coli strains were analyzed to identify different extended spectrum beta-lactamases (ESBL) plasmids enabling selection of a diverse collection of plasmids. Experiments were performed following exposure of these strains to 1/2 minimal inhibitory concentration (MIC) of CTX, ampicillin (AMP), or ciprofloxacin (CIP) before conjugation experiments. The frequency of PT was measured and compared to that of donors not exposed to antibiotics. Reverse-transcribed-quantitative real time polymerase chain reaction (RT-qPCR) was used to measure mRNA levels of five PT genes and two SOS response genes in donors exposed to antibiotics. The PT of eight strains (30.8% of strains tested) with IncI1/pST7/CTX-M-1, IncI1/pST49/CTX-M-1, IncI1/pST3/CTX-M-1, IncI1/pST293/CTX-M-1, IncI1/pST295/CTX-M-1, IncI1/pST16/CTX-M-55, and IncFII/CTX-M-14 (n = 2) plasmids was significantly increased following antibiotic exposure. CTX increased PT in all of these eight strain/plasmid combinations, AMP and CIP increased the PT in six and three strains, respectively. RT-qPCR showed that PT genes were up-regulated in the presence of the three antibiotics, whereas SOS-response genes were up-regulated only following CIP exposure. Our findings reveal that antibiotics can increase PT in E. coli strains with various ESBL plasmids. Thus, antibiotic-induced conjugative transfer of ESBL plasmids appears to be a common phenomenon in E. coli, having important implications for assessing the risks of antibiotic use.

Secondary Effects of Antibiotics on Microbial Biofilms

“…The biofilm lifestyle and the presence of antibiotics are known to induce the bacterial stress response, including the general stress response, oxidative stress response accompanied by the induction of central carbon metabolites and elevated TCA cycle intermediates, stringent response and the SOS response. The latter increases mutation rates and facilitates horizontal transfer of DNA, including antimicrobial resistance determinants ( Kohanski et al, 2010 ; Gutierrez et al, 2013 ; Belenky et al, 2015 ; Strugeon et al, 2016 ; von Wintersdorff et al, 2016 ; Gillings, 2017 ; Liu et al, 2019 ). Thus, biofilms may constitute specific foci of genetic adaptation and evolution, leading to the selection of subpopulations with a greater ability to withstand current and future antibiotic exposure.…”

Estimating plasmid conjugation rates: a new computational tool and a critical comparison of methods

“…dimensionless Plate [12] Exconjugant frequency [12] T R dimensionless Filter [23] Gene transfer frequency [23] T D dimensionless Liquid [16,24]; Filter [17,21,23] (Plasmid) transfer frequency [21]; Gene transfer frequency [23]; Conjugation frequency [16,17], Recombinant yield [24], Plasmid transfer efficiency [14] T N dimensionless Liquid [20] Conjugation frequency based on total bacterial count [20] T +D R dimensionless Liquid microcosms [25] Plasmid prevalence [25] T +D N dimensionless Soil microcosms [26] Frequency of plasmid carriage [26] T R+T dimensionless Liquid [8,25], Mouse gut [8,11] Proportion of transconjugants [11,25], Fraction of transconjugants (in recipient population) [8] log 10 T √ DR dimensionless Liquid [27] (Logarithm of) Conjugation rate [27] T DR ml CFU Filter [28] Transconjugant frequency [28] ψmax…”

“…36 In addition, this ratio is not only determined by a plasmid's conjugation rate, but also by its clonal 37 expansion [14]. As such, the resulting measurements are not a priori comparable across experimen- 38 tal conditions that could affect the growth rate, including differing nutrient conditions [20], recipient 39 species [8,12,21], temperatures [16], and (sublethal) antibiotic exposure [17]. This limits the predic-40 tive power of conjugation proficiency when expressed as a ratio of population densities [14].…”

Bacteria DNA Conjugation: from The Cellular to The Community Level

“…In parallel, antibiotics have also been recognized as signaling molecules increasing conjugative transfer although not all antibiotics can potentiate the frequency of conjugation [295][296][297][298][299][300][301][302][303]. Interestingly, when conjugation occurs in a free-antibiotics environment with a donor strain pretreated with sub-concentrations of antibiotics, conjugation frequency increased significantly [304,305].…”

“…In the literature, it is proposed that sub-MIC antibiotics treatment enhance the frequency of conjugation through an up-regulation of the tra gene expression in donors [298,[304][305][306][307]. However, in many studies, the increase of conjugation frequency was evaluated using the antibiotic which resistance gene is carried by the tested conjugative plasmid itself [295,297,298,300,301,307,308]. This approach makes it difficult to distinguish between the selection bias induce by the antibiotic on the mating population, and the actual effect on conjugation frequencies.…”