Wan, K. | Search bioRxiv

bioRxiv2018

Large scale changes in host methylation patterns induced by IncA/C plasmid transformation in Vibrio cholerae

DNA methylation is a central epigenetic modification and has diverse biological functions in eukaryotic and prokaryotic organisms alike. The IncA/C plasmid genomes are approximately 150kb in length and harbour three methylase genes, two of which demonstrate cytosine specificity. Transformation of the Vibrio cholerae strain C6706 with the IncA/C plasmid pVC211 resulted in a significant relabelling of the methylation patterns on the host chromosomes. The new methylation patterns induced by transformation with IncA/C plasmid were accepted by the restriction enzymes of the hosts restriction modification (RM) system. These data uncover a novel mechanism by which plasmids can be compatible with a hosts RM system and suggest a possible reason that plasmids of the IncA/C family are broad-host-range.\n\nAuthor summaryAntibiotic resistance of bacteria is a growing serious problem worldwidely and the horizontal transfer of multi-drug resistance genes mediated by plasmids within and between species of bacteria is the main reason. In the researches of multi-drug resistance of Vibrio cholerae, I have isolated several IncA/C plasmids. What impressed me most is their ability to accumulate the resistant genes. Moreover, they can transfer with high frequency and are stable in several bacterial species. There are at least three Tra regions on the IncA/C plasmid which containing components of the Type 4 Secretion System and are important for conjugative transfer of plasmids. So the horizontal transfer ability of IncA/C plasmids is reasonable. There are three methylase genes on the small genome of IncA/C plasmids, which demonstrate cytosine specificity and are seldom in bacteria. Their modification target and roles are interesting. Here, we analysed the methylation profiles of the host V. choerae induced by the plasmid pVC211 and found that they were completely changed. In addition to replicons, this may be a novel mechanism that plasmid cross the barrier of the hosts RM system and become broad-host range. Changing the activity of methylase in IncA/C plasmids may be a new way to affect the stability of IncA/C plasmids to eliminate these multidrug-resistant plasmids from bacteria.

microbiology↗

bioRxiv2018

Low nutrient levels reduce the fitness cost of MexCD-OprJ efflux pump overexpression in ciprofloxacin-resistant Pseudomonas aeruginosa

The long-term persistence of antibiotic resistance in the environment is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, is usually associated with a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persists in environments such as drinking and source water in which antibiotic selective pressure may be very low or even absent. Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacin-resistant mutants revealed that the fitness cost of ciprofloxacin resistance (strains cip_1, cip_2, and cip_3) significantly decreased (P < 0.05) under low-nutrient (0.5 mg/l total organic carbon (TOC)) relative to high-nutrient (500 mg/l TOC) conditions. Mechanisms underlying this fitness cost were analyzed. MexD gene expression in resistant bacteria (cip_3 strain) was significantly lower (P < 0.05) in low-nutrient conditions, with 10 mg/l TOC (8.01 {+/-} 0.82-fold), than in high-nutrient conditions, with 500 mg/l TOC (48.89 {+/-} 4.16-fold). Moreover, rpoS gene expression in resistant bacteria (1.36 {+/-} 0.13-fold) was significantly lower (P < 0.05) than that in the wild-type strain (2.78 {+/-} 0.29-fold) under low-nutrient conditions (10 mg/l TOC), suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller (P < 0.05) in low-nutrient conditions (5 and 0.5 mg/l TOC). These results suggest that nutrient levels are a key factor in determining the persistence and spread of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.\n\nImportanceThe widespread of antibiotic resistance has led to an increasing concern about the environmental and public health risks. Mechanisms associated with antibiotic resistance including efflux pumps often increase bacterial fitness cost. Our study showed that the fitness cost of ciprofloxacin resistance conferred by overexpression of MexCD-OprJ efflux pump significantly decreased under low-nutrient relative to high-nutrient conditions. The significance of our research is to reveal that nutrient levels are key factor in determining the persistence of antibiotic resistance conferred by efflux pumps under conditions with trace amounts or no antibiotics, which can be mediated by some mechanisms including MexD gene expression, SOURs differences, and rpoS gene regulation.

microbiology↗