Detection and evaluation of the antimicrobial activity of Micrococcin P1 isolated from commensal and environmental staphylococcal isolates against MRSA

BACKGROUND

Bacteriocins (of different origins) have been proposed as promising alternatives to face antimicrobial resistance-associated health problems. Isolates of the Staphylococcus genus are well-known bacteriocin producers, especially coagulase-negative species.

METHODS

Twenty-eight bacteriocin-producing staphylococcal isolates were selected from a previous study for in-depth characterisation. The antimicrobial activities (AA) of the producing isolates were studied by the spot-on-lawn method and their crude cell-free supernatants (CFS) and butanol extracts (BT) were evaluated by agar diffusion assays against six indicator bacteria, including multidrug-resistant and zoonotic isolates (such as Listeria monocytogenes or methicillin-resistant Staphylococcus aureus [MRSA]).

RESULTS

Six bacteriocin-producing isolates showed AA in their CFS, whereas all staphylococcal BT extracts inhibited at least one of the tested indicator bacteria. Micrococcin P1 (MP1) bacteriocin was detected by mass spectrometry in four producing isolates: Staphylococcus aureus-C5802, Staphylococcus hominis-C5835, Staphylococcus sciuri-X3041, and -X3011. Growth curves performed with CFS and BT extracts of the four MP1 producers revealed a strong AA profile against MRSA and Listeria monocytogenes, even when considerably diluted. Moreover, synergism between the BT extract of MP1-producing Staphylococcus sciuri-X3041 and several antibiotics against an MRSA indicator was observed: BT-clindamycin (> 80%) and BT-oxacillin (30%) combinations. For the BT-chloramphenicol combination, synergism and near synergism values were observed in 37% of the combinations. Competition studies revealed potent inhibitory effects of the MP1-producing isolates against the MRSA indicator.

CONCLUSION

These results help to identify Staphylococcus isolates or their bacteriocins as interesting candidates for potential future applications.

Pyrazole-Based Water-Soluble Dendrimer Nanoparticles as a Potential New Agent against Staphylococci

Although the antimicrobial potency of the pyrazole nucleus is widely reported, the antimicrobial effects of the 2-(4-bromo-3,5-diphenyl-pyrazol-1-yl)-ethanol (BBB4), found to be active against several other conditions, have never been investigated. Considering the worldwide need for new antimicrobial agents, we thought it noteworthy to assess the minimum inhibitory concentration (MICs) of BBB4 but, due to its scarce water-solubility, unequivocal determinations were tricky. To obtain more reliable MICs and to obtain a substance also potentially applicable in vivo, we recently prepared water-soluble, BBB4-loaded dendrimer nanoparticles (BBB4-G4K NPs), which proved to have physicochemical properties suitable for clinical application. Here, with the aim of developing a new antibacterial agent based on BBB4, the BBB4-G4K NPs were tested on several strains of different species of the Staphylococcus genus. Very low MICs (1.5–3.0 µM), 15.5–124.3-fold lower than those of the free BBB4, were observed against several isolates of S. aureus and S. epidermidis, the most pathogenic species of this genus, regardless of their resistance patterns to antibiotics. Aiming at hypothesizing a clinical use of BBB4-G4K NPs for staphylococcal skin infections, cytotoxicity experiments on human keratinocytes were performed; it was found that the nano-manipulated BBB4 released from BBB4-G4K NPs (LD₅₀ 138.6 µM) was 2.5-fold less cytotoxic than the untreated BBB4 (55.9 µM). Due to its physicochemical and biological properties, BBB4-G4K NPs could be considered as a promising novel therapeutic option against the very frequent staphylococcal skin infections.