Antimicrobial activity of SMAP-29 against the Bacteroides fragilis group and clostridia.
OBJECTIVE
The cathelicidin-derived peptide SMAP-29 exerts rapid and broad-spectrum antimicrobial activity against aerobic bacteria and fungi. In this study, the effects of the peptide against the Bacteroides fragilis group, including antibiotic-resistant isolates, Clostridium perfringens and Clostridium difficile reference and clinical isolates, were investigated.


METHODS
The microbicidal activity of SMAP-29 against eight reference and 100 clinical anaerobic strains from a national collection was assessed using a microdilution susceptibility assay, and by determining the killing kinetics on selected strains. The killing mechanism was investigated further by means of a two-colour fluorescent permeabilization assay, and by scanning electron microscopy (SEM).


RESULTS
The Bacteroides fragilis group, Clostridium reference strains and most clinical isolates were inhibited in vitro by 1-2 microM (3.2-6.4 mg/L) SMAP-29, and killed by 1.5- to 2-fold higher peptide concentrations. The anaerobic bacterial cells were 90%-100% permeabilized within 2 h of exposure to bactericidal concentrations of the peptide. The SEM images of bacteria exposed to SMAP-29 provide morphological evidence that the envelope is an important target of the bactericidal activity of this peptide. These results are consistent with earlier studies indicating that SMAP-29 kills aerobic bacteria with a membranolytic mechanism, and suggest that both aerobic and anaerobic bacteria share surface features that are targeted by this peptide.


CONCLUSIONS
These studies demonstrate that the spectrum of antibacterial activity of SMAP-29 includes the B. fragilis group and Clostridium species, and encourage further investigations of the therapeutic potential of this peptide.
Arzese
Alessandra
A
Institute of Microbiology, Udine Medical School, University of Udine, p.zza S.M. Misericordia 1, 33100 Udine, Italy. alessandra.arzese@drmm.uniud.it
Skerlavaj
Barbara
B
Tomasinsig
Linda
L
Gennaro
Renato
R
Zanetti
Margherita
M
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001442:Bacteroides Infections / Q000382:microbiology; D001441:Bacteroides fragilis / Q000187:drug effects* / Q000648:ultrastructure; D001798:Blood Proteins / Q000494:pharmacology*; D054804:Cathelicidins; D002462:Cell Membrane / Q000187:drug effects; D016360:Clostridioides difficile / Q000187:drug effects* / Q000648:ultrastructure; D003015:Clostridium Infections / Q000382:microbiology; D003016:Clostridium perfringens / Q000187:drug effects* / Q000648:ultrastructure; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning
D000900:Anti-Bacterial Agents; D001798:Blood Proteins; D054804:Cathelicidins; C403305:SMAP29 protein, Ovis aries