Factors That Affect Transfer of the IncI1 β-Lactam Resistance Plasmid pESBL-283 between E. coli Strains

Abstract

The spread of antibiotic resistant bacteria worldwide presents a major health threat to human health care that results in therapy failure and increasing costs. The transfer of resistance conferring plasmids by conjugation is a major route by which resistance genes disseminate at the intra- and interspecies level. High similarities between resistance genes identified in foodborne and hospital-acquired pathogens suggest transmission of resistance conferring and transferrable mobile elements through the food chain, either as part of intact strains, or through transfer of plasmids from foodborne to human strains. To study the factors that affect the rate of plasmid transfer, the transmission of an extended-spectrum β-lactamase (ESBL) plasmid from a foodborne Escherichia coli strain to the β-lactam sensitive E. coli MG1655 strain was documented as a function of simulated environmental factors. The foodborne E. coli isolate used as donor carried a CTX-M-1 harboring IncI1 plasmid that confers resistance to β-lactam antibiotics. Cell density, energy availability and growth rate were identified as factors that affect plasmid transfer efficiency. Transfer rates were highest in the absence of the antibiotic, with almost every acceptor cell picking up the plasmid. Raising the antibiotic concentrations above the minimum inhibitory concentration (MIC) resulted in reduced transfer rates, but also selected for the plasmid carrying donor and recombinant strains. Based on the mutational pattern of transconjugant cells, a common mechanism is proposed which compensates for fitness costs due to plasmid carriage by reducing other cell functions. Reducing potential fitness costs due to maintenance and expression of the plasmid could contribute to persistence of resistance genes in the environment even without antibiotic pressure. Taken together, the results identify factors that drive the spread and persistence of resistance conferring plasmids in natural isolates and shows how these can contribute to transmission of resistance genes through the food chain.

Antibiotics as a selective driver for conjugation dynamics

“…2b, we measured conjugation efficiency for five additional native self-transmissible conjugative systems, including the native F plasmid, RP4, R388, R6K, and pESBL283 42 (Fig. 2d i–v, Fig.…”

Growth phase‐dependent control of R27 conjugation is mediated by the interplay between the plasmid‐encoded regulatory circuit TrhR/TrhY‐HtdA and the cAMP regulon

“…pSLT conjugation does not decline in the stationary phase and traJ expression is inhibited by H‐NS in both the logarithmic and stationary phases of growth (Camacho et al ., ). Growth rate and nutrient levels also affect IncP and IncI1 plasmids transfer efficiency, although the regulatory mechanism remains unknown (Fox et al ., ; Händel et al ., ). Moreover, active growth is required for efficient plasmid transfer, which may account for the limited plasmid spread detected in slow‐growing cells during biofilm formation (Merkey et al ., ).…”

Physicochemical Factors That Favor Conjugation of an Antibiotic Resistant Plasmid in Non-growing Bacterial Cultures in the Absence and Presence of Antibiotics

“…Rarely are the same methods used by investigators to assess conjugation. For example, some studies have chosen to shake cultures (Zhang et al, 2013 ; Händel et al, 2015 ), while other studies have chosen not to shake cultures (Hayashi et al, 1988 ; Fernandez-Astorga et al, 1992 ; Muela et al, 1994 ; Beuls et al, 2012 ; Sandegren et al, 2012 ; Lopatkin et al, 2016 ). Some studies have examined conjugation in liquid cultures (Barr et al, 1986 ; Fernandez-Astorga et al, 1992 ; Sandegren et al, 2012 ; Zhang et al, 2013 ; Schuurmans et al, 2014 ; Händel et al, 2015 ; Lopatkin et al, 2016 ), while others have examined conjugation using the filter plate method (Kim et al, 2014 ; Jutkina et al, 2016 , 2018 ; Moller et al, 2017 ).…”

“…For example, some studies have chosen to shake cultures (Zhang et al, 2013 ; Händel et al, 2015 ), while other studies have chosen not to shake cultures (Hayashi et al, 1988 ; Fernandez-Astorga et al, 1992 ; Muela et al, 1994 ; Beuls et al, 2012 ; Sandegren et al, 2012 ; Lopatkin et al, 2016 ). Some studies have examined conjugation in liquid cultures (Barr et al, 1986 ; Fernandez-Astorga et al, 1992 ; Sandegren et al, 2012 ; Zhang et al, 2013 ; Schuurmans et al, 2014 ; Händel et al, 2015 ; Lopatkin et al, 2016 ), while others have examined conjugation using the filter plate method (Kim et al, 2014 ; Jutkina et al, 2016 , 2018 ; Moller et al, 2017 ). Many studies have examined conjugation at 37°C (Khalil and Gealt, 1987 ; Hayashi et al, 1988 ; Fernandez-Astorga et al, 1992 ; Sandegren et al, 2012 ; Zhang et al, 2013 ; Moller et al, 2017 ), while many other investigators have utilized other temperatures for their experiments (Fernandez-Astorga et al, 1992 ; Muela et al, 1994 ; Beuls et al, 2012 ; Jutkina et al, 2016 ; Lopatkin et al, 2016 ; p. 74; Jutkina et al, 2018 ).…”

“…One area of methodological agreement appears to be the use of growing bacterial cultures in conjugation experiments. There is good evidence that conjugation increases with bacterial growth (Muela et al, 1994 ; Schuurmans et al, 2014 ; Händel et al, 2015 ; Lopatkin et al, 2016 ) and the vast majority of conjugation studies are conducted on growing bacterial populations or populations exposed to growth media during conjugation (e.g., Barr et al, 1986 ; Hayashi et al, 1988 ; Fernandez-Astorga et al, 1992 ; Beaber et al, 2004 ; Beuls et al, 2012 ; Sandegren et al, 2012 ; Zhang et al, 2013 ; Kim et al, 2014 ; Schuurmans et al, 2014 ; Händel et al, 2015 ; Jutkina et al, 2016 , 2018 ; Lopatkin et al, 2016 ; Matsumoto et al, 2016 ; Moller et al, 2017 ). However, just because conjugation has been shown to increase with bacterial growth does not mean that it does not occur in non-growing bacteria.…”