Some lantibiotics are active at single nanomolar levels against particular targets and several lantibiotics inhibit drug–resistant Gram positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) [1, 2]. Lantibiotics QNZ are highly stable, resistance is rare and activity can be enhanced through

genetic alteration and, thus, they are considered to be viable alternatives to traditional antibiotics [1]. Lacticin 3147 inhibits many Gram positive pathogens including Listeria monocytogenes, Staphylococcus aureus and Clostridium difficile as well as a variety of streptococci, enterococci and mycobacteria [8–10]. However, to date, the inhibition Epoxomicin purchase of Gram negative species by lacticin 3147 has not been reported. This is most often attributed to the presence of the outer membrane, which prevents access of the lantibiotic to the cytoplasmic membrane. There are many potential benefits associated

with identifying antibiotics that function synergistically with lacticin 3147. While antibiotic resistance has become a major obstacle, significant resistance to lacticin 3147 has yet to be reported and thus the use of antibiotic-lacticin 3147 combinations may prevent/overcome the emergence of resistance. Furthermore, certain antibiotic-lacticin 3147 combinations may allow for a broader range of species to be targeted. Here we assess the impact of combining lacticin 3147 with a variety of clinical antibiotics and establish that lacticin 3147 exhibits synergistic activity in combination with either polymyxin B or polymyxin E. Results Sensitivity of bacteria to lacticin 3147 and antibiotics in combination To determine whether lacticin 3147 could work synergistically with a variety

of clinically GW786034 cell line utilised antibiotics, we used antibiotic disc assays to assess the potency of individual antibiotics (cefotaxime, novobiocin, cefoperazone, teicoplanin, ceftazidime, cefaclor, cephradine, cefaclor (30 μg), bacitracin, imipenem, fusidic acid (10 μg), penicillin G (5 μg), oxacillin (1 μg), colistin sulphate (polymyxin E) (25 μg) and polymyxin B (300 U)), Mirabegron in the presence and absence of lacticin 3147. It was evident that lacticin 3147 had the ability to enhance the activity of a number of the antibiotics tested (data not shown) but the benefits of combining lacticin 3147 with polymyxin B or polymyxin E were particularly obvious (Figure 1). In the case of the representative Gram positive and negative strains, E. faecium DO and E. coli EC101, the diameters of the zones of inhibition were increased by over 180% and by over 121%, respectively. Indeed, in the case of E. faecium DO, combining sub-inhibitory concentrations of the individual antimicrobials resulted in the formation of a zone of clearing (Figure 1).