Abstract
The increasing numbers of infections caused by multidrug-resistant (MDR) pathogens highlight the urgent need for new alternatives to conventional antibiotics. Antimicrobial peptides have the potential to be promising alternatives to antibiotics because of their effective bactericidal activity and highly selective toxicity. The present study was conducted to investigate the antibacterial, antibiofilm, and anti-adhesion activities of different CTP peptides (CTP: the original hybrid peptide cathelicidin 2 (1-13)-thymopentin (TP5); CTP-NH2: C-terminal amidated derivative of cathelicidin 2 (1-13)-TP5; CTPQ: glutamine added at the C-terminus of cathelicidin 2 (1-13)-TP5) by determining the minimal inhibitory concentrations (MICs), minimal bactericidal concentrations (MBCs), propidium iodide uptake, and analysis by scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy). The results showed that CTPs had broad-spectrum antibacterial activity against different gram-positive and gram-negative bacteria, with MICs against the tested strains varying from 2 to 64 μg/mL. CTPs at the MBC (2 × MIC 64 μg/mL) showed strong bactericidal effects on a standard methicillin-resistant Staphylococcus aureus strain ATCC 43300 after co-incubation for 6 h through disruption of the bacterial membrane. In addition, CTPs at 2 × MIC also displayed effective inhibition activity of several S. aureus strains with a 40–90% decrease in biofilm formation by killing the bacteria embedded in the biofilms. CTPs had low cytotoxicity on the intestinal porcine epithelial cell line (IPEC-J2) and could significantly decrease the rate of adhesion of S. aureus ATCC 43300 on IPEC-J2 cells. The current study proved that CTPs have effective antibacterial, antibiofilm, and anti-adhesion activities. Overall, this study contributes to our understanding of the possible antibacterial and antibiofilm mechanisms of CTPs, which might be an effective anti-MDR drug candidate.
Highlights
Antibiotics were once considered the most effective anti-infective drugs, the abuse of antibiotics has provoked the development of drug-resistant (DR) and multidrugresistant (MDR) pathogens
Dead cells in all of the CTP-treated biofilms increased after peptide treatment. These results indicated that all CTPs could inhibit biofilm formation by S. aureus via membrane destruction of cells embedded in the biofilm
Our results indicated that the addition of glutamine at the C-terminal of CTP could improve the antibacterial effects of CTP against P. aeruginosa ATCC 27853 and P. aeruginosa
Summary
Antibiotics were once considered the most effective anti-infective drugs, the abuse of antibiotics has provoked the development of drug-resistant (DR) and multidrugresistant (MDR) pathogens. Among such pathogens, Staphylococcus aureus is a grampositive pathogen that causes biofilm-associated infections, including pulmonary, urinary, and skin infections [1]. During the course of the disease, the adhesion of pathogens to epithelial cells is an essential first step for the pathogens to survive and colonize the gastrointestinal tract [10]. It is important to find safe and effective antibiotic substitutes with antibacterial, antibiofilm, and anti-adhesion activities. Among a variety of candidates, antimicrobial peptides (AMPs), with positively charged and hydrophobic residues, have the potential to be promising alternatives to antibiotics [11,12]
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