We observed that PAbN increased FDG hydrolysis and leakage of fluorescein in all strains, especially in pump deletion mutants, by this new method. Since PAbN was first reported, it has been universally recognized as an efflux pump inhibitor, and the effect of PAbN on MDRP S1 was remarkably synergistic with all the agents examined in this study. In the presence of these antibiotics, the PBPs form a lethal covalent penicilloyl-enzyme complex that blocks the normal transpeptidation reaction; this finally results in bacterial death. However, Gram-negative bacteria have acquired Vorinostat HDAC inhibitor resistance to blactams mainly through three different strategies: production of a specific b-lactam hydrolase; presence of low-affinity PBPs; and active expulsion of b-lactams via efflux pumps. There is thus an urgent need to develop new antibiotics to AG-013736 overcome the challenge of bacterial resistance to existing antimicrobials. The crystal structure of PBP2a in both its apo form and complexed to b-lactams has shown that methicillin resistance is achieved through a distorted active site, which requires an energetically costly b3 strand movement to allow acylation by blactam antibiotics. One of the possibilities to overcome this intrinsic poor acylation efficiency of PBP2a is to design new blactams that have improved binding affinities due to increased noncovalent interactions between the inhibitor and the active site. On the other hand, noncovalent compounds that bind tightly to the active site without acylation might also provide highly effective inhibitors. Noncovalent inhibitors will not require the unfavorable conformational changes in the active site of PBP2a that are required for acylation, and they will hopefully also not be susceptible to b-lactamases. To date, only a few noncovalent inhibitors of PBPs have been described, and so we screened our in-house bank of compounds for potential inhibition of this important drug target. The waning prospect of an effective treatment for bacterial infections due to the emergence and spread of resistance to antibiotics in pathogens has been exacerbated by the lack of novel antibacterials being introduced to the market. An alternative and parallel approach in supporting the mitigation of the antibiotic resistance problem is to develop adjuvants that could interfere with the mechanism of resistance and hence restore the action of antibiotics. Such a strategy has been effectively employed to combat resistance to b-lactams due to b-lactamase activity. For aminoglycosides, a group of antibiotics used to treat serious nosocomial infections, the main mechanism of resistance is via the enzymatic inactivation of the drug by acetyltransferases, nucleotidyltransferases, or phosphotransferases. This implies that inhibitors of these enzymes could be exploited for the development of drug-adjuvant therapy. Among the three types of aminoglycoside-modifying enzymes, aminoglycoside phosphotransferases or kinases yield the highest levels of resistance thereby providing a rationale for focusing inhibitor development for these specific resistance factors. The investigation of APH inhibitors that target the ATP-binding pocket was facilitated by the structural similarities between the aminoglycoside resistance enzyme APH-IIIa and serine/threonine and tyrosine eukaryotic protein kinases, especially in the Nterminal lobe. It was subsequently shown that APH-IIIa can be inhibited by protein kinase inhibitors of the isoquinolinesulfonamide family and they are competitive with ATPbinding. However, APH-IIIa remains the most extensively studied due to its broad substrate spectrum.