Changes in the Ultrastructure of Staphylococcus aureus Treated with Cationic Peptides and Chlorhexidine

Abstract

Antimicrobial peptides, including synthetic ones, are becoming increasingly important as a promising tool to fight multidrug-resistant bacteria. We examined the effect of cationic peptides H2N-Arg9-Phe2-C(O)NH2 and H2N-(Lys-Phe-Phe)3-Lys-C(O)NH2 on Staphylococcus aureus, which remains one of the most harmful pathogens. Antiseptic chlorhexidine served as reference preparation. We studied viability of S. aureus and examined its ultrastructure under treatment with 100 µM of R9F2 or (KFF)3K peptides or chlorhexidine using transmission electron microscopy of ultrathin sections. Bacterial cells were sampled as kinetic series starting from 1 min up to 4 h of treatment with preparations. Both peptides caused clearly visible damage of bacteria cell membrane within 1 min. Incubation of S. aureus with R9F2 or (KFF)3K peptides led to cell wall thinning, loss of cytoplasm structure, formation of mesosome-derived multimembrane structures and “decorated fibers” derived from DNA chains. The effect of R9F2 peptides on S. aureus was more severe than the effect of (KFF)3K peptides. Chlorhexidine heavily damaged the bacteria cell wall, in particular in areas of septa formation, while cytoplasm kept its structure within the observation time. Our study showed that cell membrane damage is critical for S. aureus viability; however, we believe that cell wall disorders should also be taken into account when analyzing the effects of the mechanisms of action of antimicrobial peptides (AMPs).

Sinonasal Stent Coated with Slow-Release Varnish of Chlorhexidine Has Sustained Protection against Bacterial Biofilm Growth in the Sinonasal Cavity: An In Vitro Study

“…CHX is one of the most commonly prescribed antiseptic agents in the dental field. It has a long-lasting antibacterial and antifungal activity with a broad spectrum of action [21][22][23][24], and its use is considered a safe compound, with minimal and transitory local and systemic side effects [29].…”

“…Chlorhexidine (CHX), which is selected as the active agent in this study, is a quaternary ammonium antiseptic compound, with known safety and effectivity in human mucosal membranes and has previously been tested for medical device use, including the nasopharynx [17,19,20]. In addition, CHX has broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative bacteria as well as yeasts [21][22][23][24] and has been shown to act on preformed biofilms [23].…”

Unveiling the Membrane and Cell Wall Action of Antimicrobial Cyclic Lipopeptides: Modulation of the Spectrum of Activity

“…For example, AMS NK-2, an internal fragment of mammalian NK-lysin, causes very similar morphological changes in S. aureus [35]. The formation of spherical mesosomes is also induced by gramicidin S [32], defensin [36], and cationic peptides R9F2 and (KFF)3K [37], and it is attributed to the lateral membrane expansion caused by insertion of the peptide.…”

Oxidative Stress-Mediated Antibacterial Activity of the Total Flavonoid Extracted from the Agrimonia pilosa Ledeb. in Methicillin-Resistant Staphylococcusaureus (MRSA)

“…After cocultivation for 8 h, the bacteria were collected by centrifugation (3000 rpm, 15 min, 4 • C) and washed with PBS three times. Then, the bacterial cells were fixed by 2.5% glutaraldehyde at 4 • C overnight and observed by TEM [21].…”