Effects of Cations and PH on Antimicrobial Activity of Thanatin and s-Thanatin Against Escherichia coli ATCC25922 and B. subtilis ATCC 21332

Oligo-acyl-lysyls (OAKs) are synthetic mimics of host defense peptides known to exert antibacterial activity both in cultures and in animal models of disease. Here, we investigated how environmental conditions (temperature, pH, and ionic strength) affect the antibacterial properties of an octamer derivative, C 12 K-7␣ 8 . Data obtained with representative bacteria, including the Gram-negative bacterium Escherichia coli and the Gram-positive bacteria Listeria monocytogenes and Staphylococcus aureus, showed that OAK's potency was proportionally affected by pH changes and subsided essentially throughout a wide range of salt concentrations and temperature values, whereas antistaphyloccocal activity was relatively more vulnerable. It was rather the mode of action that was most susceptible to the environmental changes. Thus, OAK's bactericidal effect was limited to a growth-inhibitory effect under acidic pH, low temperatures, or high salt concentrations, whereas basic pH or high temperatures have enhanced the bactericidal kinetics. Properties of binding to model phospholipid membranes provided evidence that correlated the differential modes of action with variable binding affinities. Interestingly, combination of the optimal incubation conditions resulted in a remarkable increase in potency, as expressed by a 16-to 32-fold reduction in the MIC value and by much faster bactericidal rates (>99% death induced within minutes versus hours) compared with the standard incubation conditions. Collectively, the data suggest that OAKs might be useful in developing design strategies for robust antimicrobial peptides that are able to affect a pathogen's viability under a large spectrum of incubation conditions. Host defense peptides (HDPs) are ever-present components of the innate immune system across all organisms (25, 60). These molecules have been widely studied for their vast range of activities, such as antimicrobial, antitumor, mitogenic, and chemical signaling properties (7,22,42,59). Nevertheless, a number of disadvantages, including toxicity, poor bioavailability, and/or high production costs, continue to compromise their potential uses, especially as systemic drugs (6, 22). Also, despite the fact that these compounds have been investigated for over 2 decades, their mechanism of action is not fully understood. Namely, many HDPs are believed to exert antibacterial activity by disrupting the integrity of the cell wall and/or the plasma membrane (16,25,54), whereas others were proposed to hamper intracellular functions (4, 48). While, this nonspecific multitarget mode of action seems likely to significantly prevent the emergence of resistance (36, 59) and indeed significantly accounts for both scientific and applicative widespread interests in these peptides, new innovative tools are needed to shed light onto fine mechanistic details of this complex antimicrobial system.Various synthetic mimics using a small number of building blocks are able to capture the essential antimicrobial properties of HDPs while overcoming some of ...

Section: Discussioncontrasting

confidence: 44%

Experimental Conditions That Enhance Potency of an Antibacterial Oligo-Acyl-Lysyl

Goldfeder

Zaknoon

Mor

2010

“…(Ca 2ϩ and Mg 2ϩ ) might compromise the antimicrobial activity of natural antimicrobial peptides (25)(26)(27). In this study, LL37 showed high sensitivity to Na ϩ , Ca 2ϩ , and Mg 2ϩ for P. aeruginosa.…”

Section: Figmentioning

confidence: 83%

Bactericidal Efficiency and Modes of Action of the Novel Antimicrobial Peptide T9W against Pseudomonas aeruginosa

Zhu

Shan

et al. 2015

The antipseudomonal efficiency and mechanism of action of a novel engineered antimicrobial peptide, T9W, were evaluated in this study. T9W displayed high activity, with a lethal concentration (LC) of 1 to 4 M against Pseudomonas aeruginosa, including against ciprofloxacin-, gentamicin-, and ceftazidime-resistant strains, even in the presence of 50 to 300 mM NaCl, 1 to 5 mM Ca 2؉ , or 0.5 to 2 mM Mg 2؉ . The time-kill curve (TKC) analysis demonstrated concentration-dependent activity, with T9W achieving complete killing in less than 30 min at 1؋ LC and in less than 5 min at 4؋ LC. Combination TKC analyses additionally demonstrated a synergistic effect with ciprofloxacin and gentamicin. The selectivity of T9W was further supported by its ability to specifically eliminate P. aeruginosa in a coculture with macrophages without toxicity to the mammalian cells. The results from fluorescent measurement indicated that T9W bound to lipopolysaccharide (LPS) and induced P. aeruginosa membrane depolarization, and microscopic observations and flow cytometry further indicated that T9W targeted the P. aeruginosa cell membrane and disrupted cytoplasmic membrane integrity, thereby causing cellular content release leading to cell death. This study revealed the potential usefulness of T9W as a novel antimicrobial agent against P. aeruginosa.

“…The influence of pH on CAMP activity has also been examined for a small number of peptides (24,26,27,32). Impacts on CAMP activity due to a change in pH can occur directly, by affecting the charge-charge interactions involved in the initial binding step, or indirectly via a change in the ionic strength of the solution.…”

Section: Discussionmentioning

confidence: 99%

“…A number of studies have looked at the effects of pH or salt concentration on the ability of CAMPs to kill microorganisms (24,25). In most cases, only a narrow range of different pHs or salt concentrations were sampled, although a few studies have been more comprehensive (26,27). It is well known that higher salt concentrations often interfere with CAMP activity (25,28,29), but some CAMPs from marine organisms have been found to tolerate salt concentrations up to 450 mM (30).…”

mentioning

confidence: 99%

pH Dependence of Microbe Sterilization by Cationic Antimicrobial Peptides

Walkenhorst

Klein

et al. 2013

We recently described a family of cationic antimicrobial peptides (CAMPs) selected from a combinatorial library that exhibited potent, broad-spectrum activity at neutral pH and low ionic strength. To further delimit the utility and activity profiles of these peptides, we investigated the effects of solution conditions, such as pH and ionic strength, on the efficacy of the peptide antimicrobials against a panel of microorganisms. Peptide minimum sterilizing concentrations (MSCs) varied linearly with pH for each subtype within our family of CAMPs for all organisms tested. The peptides were much less effective against Gram-negative bacteria at high pH, consistent with a decrease in net positive charge on the peptides. A similar trend was observed for the fungus Candida albicans. Surprisingly, the opposite pH trend was observed with the Gram-positive Staphylococcus aureus. In addition, an additive ionic strength effect was observed with increasing buffer strengths at identical pH values. The extreme difference in the observed pH behavior between Gram-negative and Gram-positive organisms is attributed to the presence of native charged molecules in the much thicker peptidoglycan layer of the Gram-positive organism. The novel species-specific effects of pH observed here have important implications for applications using CAMPs and for the design of novel CAMPs.