The active ingredients in Chinese peony pods synergize with antibiotics to inhibit MRSA growth and biofilm formation.

Staphylococcus aureus (S. aureus) is a zoonotic pathogen that infects both humans and animals. The rapid spread of methicillin-resistant S. aureus (MRSA) and its resistance to antibiotics, along with its ability to form biofilms, poses a serious challenge to the clinical application of traditional antibiotics. Peony (Paeonia lactiflora Pall.) is a traditional Chinese medicine with multiple pharmacological effects. This study observed the strong antibacterial and antibiofilm activity of the water extract (WE) and ethyl acetate extract (EA) of Chinese peony pods against MRSA. The combination of EA and vancomycin, cefotaxime, penicillin G or methicillin showed a synergistic or additive antibacterial and antibiofilm effects on MRSA, which is closely related to the interaction of 1,2,3,4,6-penta-O-galloyl-ß-D-glucose (PG) and methyl gallate (MG). The active ingredients in peony pods have been found to increase the sensitivity of MRSA to antibiotics and demonstrate antibiofilm activity, which is mainly related to the down-regulation of global regulatory factors sarA and sigB, extracellular PIA and eDNA encoding genes icaA and cdiA, quorum sensing related genes agrA, luxS, rnaIII, hld, biofilm virulence genes psma and sspA, and genes encoding clotting factors coa and vwb, but is not related to genes that inhibit cell wall anchoring. In vivo test showed that both WE and EA were non-toxic and significantly prolonged the lifespan of G. mellonella larvae infected with MRSA. This study provides a theoretical basis for further exploration of the combined use of PG, MG and antibiotics to combat MRSA infections.

Synergistic Inhibitory Effect of Polymyxin B in Combination with Ceftazidime against Robust Biofilm Formed by Acinetobacter baumannii with Genetic Deficiency in AbaI/AbaR Quorum Sensing.

Carbapenem resistance of Acinetobacter baumannii poses challenges to public health. Biofilm contributes to the persistence of A. baumannii cells. This study was designed to investigate the genetic relationships among carbapenem resistance, polymyxin resistance, multidrug resistance, biofilm formation, and surface-associated motility and evaluate the antibiofilm effect of polymyxin in combination with other antibiotics. A total of 103 clinical A. baumannii strains were used to determine antibiotic susceptibility, biofilm formation capacity, and motility. Enterobacterial repetitive intergenic consensus (ERIC)-PCR fingerprinting was used to determine the genetic variation among strains. The distribution of 17 genes related to the resistance-nodulation-cell division (RND)-type efflux, autoinducer-receptor (AbaI/AbaR) quorum sensing, oxacillinases (OXA)-23, and insertion sequence of ISAba1 element was investigated. The representative strains were chosen to evaluate the gene transcription and the antibiofilm activity by polymyxin B (PB) in combination with merapenem, levofloxacin, and ceftazidime, respectively. ERIC-PCR-dependent fingerprints were found to be associated with carbapenem resistance and multidrug resistance. The presence of blaOXA-23 was found to correlate with genes involved in ISAba1 insertion, AbaI/AbaR quorum sensing, and AdeABC efflux. Carbapenem resistance was observed to be negatively correlated with biofilm formation and positively correlated with motility. PB in combination with ceftazidime displayed a synergistic antibiofilm effect against robust biofilm formed by an A. baumannii strain with deficiency in AbaI/AbaR quorum sensing. Our results not only clarify the genetic correlation among carbapenem resistance, biofilm formation, and pathogenicity in a certain level but also provide a theoretical basis for clinical applications of polymyxin-based combination of antibiotics in antibiofilm therapy. IMPORTANCE Deeper explorations of molecular correlation among antibiotic resistance, biofilm formation, and pathogenicity could provide novel insights that would facilitate the development of therapeutics and prevention against A. baumannii biofilm-related infections. The major finding that polymyxin B in combination with ceftazidime displayed a synergistic antibiofilm effect against robust biofilm formed by an A. baumannii strain with genetic deficiency in AbaI/AbaR quorum sensing further provides a theoretical basis for clinical applications of antibiotics in combination with quorum quenching in antibiofilm therapy.