Antimicrobial Susceptibility Testing of Antimicrobial Peptides Requires New and Standardized Testing Structures

Abstract

The need for optimized as well as standardized test systems of novel antimicrobial peptides (AMPs) was discussed by experts in the field at the International Meeting on Antimicrobial Peptides (IMAP) 2017 and the 2019 Gordon Research Conference (GRC) on Antimicrobial Peptides, and a survey related to this topic was circulated to participants to collate opinions. The survey included questions ranging from the relevance of susceptibility testing for understanding the mode of action of AMPs, to the importance of optimization and a degree of standardization of test methods and their clinical relevance. Based on the survey results, suggestions for future improvements in the research field are made.

An ultrasensitive microfluidic approach reveals correlations between the physico-chemical and biological activity of experimental peptide antibiotics

“…Therefore, these peptide therapeutics will need to be carefully evaluated in pre-clinical models like those presented in this work to help design appropriate treatment strategies. More generally, our results add to the growing body of evidence that show some of the challenges associated with quantifying the activity of peptide-based therapeutics 16 , 21 . However, given the new strategy shown here and also complementary tools being developed elsewhere 21 , it is hoped that these difficulties can be quantified and addressed at an early stage of development, facilitating the efficient clinical translation of this promising category of therapeutics.…”

“…However, the clinical translation of peptide antimicrobials has suffered from a lack of suitable assays to characterize their efficacy 16 . Standard bulk techniques such as Minimum Inhibitory Concentration (MIC) assays fail to uncover heterogeneities in drug activity within a population of genetically identical cells.…”

“…A recent study by the Stella group confirmed a strong inoculum effect on the MICs of a range of antimicrobial peptides, which led the authors to question the utility of standard cellular screening assays for the field 21 . Other researchers have also identified a need for “new and standardized testing structures” to facilitate the translation of peptide antimicrobials from the bench to the clinic 16 . In their comprehensive review on the subject, Mercer et al list a range of factors that can additionally influence the activity of AMPs, such as media composition, diluents, additives, the pH and ionic strength of test solutions, the presence of metal ions, amongst others 22 ; these all need careful consideration during the development of standardized testing protocols.…”

The role of metal binding in the function of the human salivary antimicrobial peptide histatin-5

“…Like other cationic AMPs, the antimicrobial activity of Hst5 relies on initial electrostatic binding of the peptide to microbial surface proteins or membranes 11,21 . Such interactions are suppressed by salts and high ionic strength buffers 11,14,[22][23][24][25][26] . To lower the ionic strength in our experiments, phosphate was replaced with Mops.…”

Taxonomic bias in AMP prediction of invertebrate peptides

“…Although our current study addresses in silico prediction of antimicrobial activity in (invertebrate) peptides based on amino acid sequence, some of the details we have discussed are connected to the recent aspiration to improve upon currently used methodological standards of (pre)clinical testing of AMPs (such as in antimicrobial susceptibility testing, e.g. see 29,30 ). Indeed, more reliable and robust in silico prediction tools utilizing modern algorithms and ever larger data sets undoubtedly require standardization of quality of data.…”