Time-dependent hormetic effects of polypeptide antibiotics and two antibacterial agents contribute to time-dependent cross-phenomena of their binary mixtures.

Polypeptide antibiotics (PPAs), silver nanoparticles (plural) (AgNP) and quorum sensing inhibitors (QSIs) are considered to be the ideal antibiotic substitutes. Due to the great potential for the combined use of these antibacterial agents, it is necessary to evaluate their joint effects. In this study, the joint toxic actions for the binary mixtures of PPA + PPA, PPA + AgNP, and PPA + QSI were judged via the independent action (IA) model based on the individual and combined toxicity of test agents to the bioluminescence of Aliivibrio fischeri during 24 h. It was observed that the single agents (PPAs, AgNP, and QSI) and the binary mixtures (PPA + PPA, PPA + AgNP, and PPA + QSI) all triggered the time-dependent hormetic effects on the bioluminescence, where the maximum stimulatory rate, the median effective concentration, and the occurrence of hormesis varied with the increase of time. While bacitracin triggered the maximum stimulatory rate (266.98 % at 8 h) among the single agents, the mixture of capreomycin sulfate and 2-Pyrrolidinone induced the maximum stimulatory rate (262.21 % at 4 h) among the binary mixtures. The cross-phenomenon that the dose-response curve of mixture crossed the corresponding IA curve was observed in all treatments, which also varied with time, exhibiting that the joint toxic actions and corresponding intensities possessed dose- and time-dependent features. Furthermore, three kinds of binary mixtures resulted in three different variation tendencies for the time-dependent cross-phenomena. Mechanistic speculation indicated that test agents possessed the stimulatory modes of action (MOAs) at low-dose and inhibitory MOAs at high-dose to induce the hormetic effects, and the interplays between these MOAs varied with time to trigger the time-dependent cross-phenomenon. This study provides the reference data for the joint effects of PPAs and typical antibacterial agents, which will benefit the application of hormesis in the exploration of time-dependent cross-phenomenon and promote the future development of environmental risk assessment of pollutant mixtures.

Dose-dependent joint resistance action of antibacterial mixtures in their hormetic effects on bacterial resistance based on concentration addition model.

The judgment of joint resistance action is significant for evaluating the resistance risk of antibacterial mixture. Using bacterial mutation frequency (MF) and conjugative transfer frequency (CTF) to respectively characterize the bacterial endogenous and exogenous resistance, mutation unit and conjugative transfer unit have been proposed to judge the joint resistance action of antibacterial mixture at a certain dose. However, these methods could not evaluate the antibacterial mixture's joint resistance action at a larger concentration-range. In this study, the concentration addition for bacterial resistance (CA-BR) approach was used to judge the joint resistance actions between kanamycin sulfate (KAN) and some other typical antibacterial agents, including sulfonamides (SAs), sulfonamide potentiators (SAPs), and silver antibacterial compounds (SACs). Through comparing the hormetic dose-response curves of the binary mixtures on the MF (or CTF) in Escherichia coli (E. coli) and the corresponding CA-BR curves calculated from the hormetic dose-responses of the single agents, the joint resistance actions between KAN and other agents were judged to exhibit dose-dependent feature: with the increase of mixture concentration, the joint mutation actions between KAN and SAs (or SAPs) were fixed at synergism, and the joint mutation actions between KAN and SACs varied from antagonism to synergism; the joint conjugative transfer actions between KAN and other agents changed from antagonism to synergism. Mechanistic explanation suggested that the heterogeneous pattern of joint resistance action had a close relationship with the interplays among the agents' modes of action, and meanwhile was significantly influenced by their joint survival pressure on E. coli. This study reveals the dose-dependent feature for the joint resistance action of antibacterial mixture and highlights the importance of exposure concentration, which will benefit clarifying the resistance risk of antibacterial mixture in the environment.

A simple judgment method for joint action of antibacterial agents on bacterial resistance.

The severe pollution of bacterial resistance induced by the wide and even indiscriminate use of antibacterial agents has posed serious threats to human health and ecological safety. Furthermore, the combined effects of antibacterial agents have a closer relationship with the pollution of bacterial resistance than single antibacterial agent. However, there is little information regarding how multiple antibacterial agents interplay to induce bacterial resistance. Here, we developed a simple judgment method with five basic procedures for the joint action of antibacterial agents on bacterial resistance, involving toxicity determination, mutation frequency determination, conjugative transfer frequency determination, dose-response relationship fitting, key parameters obtaining, and joint resistance action judgment. This proposed approach was validated through investigating the joint resistance action between silver nanoparticle (AgNP) and 1-pyrrolidino-1-cyclohexene (1P1C, a kind of quorum sensing inhibitors). According to the procedures, the mutation unit and conjugative transfer unit for the AgNP-1P1C mixture were calculated to be 64.27 and 5.10, respectively, indicating the antagonism for their joint resistance action. This method can not only benefit the mechanistic explanation for how mixed antibacterial agents stimulate the bacterial resistance, but also guide the environmental risk assessment and clinical use of combined antibacterial agents in the related fields. • We present a novel method to judge the joint resistance action of antibacterial agents, taking the emergence and dissemination of antibiotic resistance genes into account. • Toxicity determination can help to design the mixtures of antibacterial agents and confirm the appropriate test concentration range of antibacterial agents used in mutation frequency and conjugative transfer frequency determination. • The mutation unit and conjugative transfer unit were proposed according to the toxic unit in the judgment of joint toxic action.

Direct binding of ESCRT protein Chm7 to phosphatidic acid-rich membranes at nuclear envelope herniations.

Mechanisms that control nuclear membrane remodeling are essential to maintain the integrity of the nucleus but remain to be fully defined. Here, we identify a phosphatidic acid (PA)-binding capacity in the nuclear envelope (NE)-specific ESCRT, Chm7, in budding yeast. Chm7's interaction with PA-rich membranes is mediated through a conserved hydrophobic stretch of amino acids, which confers recruitment to the NE in a manner that is independent of but required for Chm7's interaction with the LAP2-emerin-MAN1 (LEM) domain protein Heh1 (LEM2). Consistent with the functional importance of PA binding, mutation of this region abrogates recruitment of Chm7 to membranes and abolishes Chm7 function in the context of NE herniations that form during defective nuclear pore complex (NPC) biogenesis. In fact, we show that a PA sensor specifically accumulates within these NE herniations. We suggest that local control of PA metabolism is important for ensuring productive NE remodeling and that its dysregulation may contribute to pathologies associated with defective NPC assembly.