New antibiotics for antibiotic-resistant bacteria

The need for new antibiotics to effectively treat antibiotic-resistant infections remains unfulfilled. Despite the well-publicised concern over this issue, only two novel antibiotic classes have been introduced in the past 20 years alongside several new agents of existing classes. Accordingly, the current antibiotic armoury remains inadequate to meet the challenges posed by resistance today. More worryingly, there are very few new agents being developed that can be expected to replace existing antibiotics that succumb to the rising tide of resistance

Uniformity of Glycyl Bridge Lengths in the Mature Cell Walls of Fem Mutants of Methicillin-Resistant Staphylococcus aureus

Peptidoglycan (PG) composition in intact cells of methicillin-resistant Staphylococcus aureus (MRSA) and its isogenic Fem mutants has been characterized by measuring the glycine content of PG bridge structures by solid-state nuclear magnetic resonance (NMR). The glycine content estimated from integrated intensities (rather than peak heights) in the cell walls of whole cells was increased by approximately 30% for the FemA mutant and was reduced by 25% for the FemB mutant relative to expected values for homogeneous structures. In contrast, the expected compositions were observed in isolated cell walls of the same mutants. For FemA mutant whole cells, the increase was due to the presence of triglycyl bridge PG units (confirmed directly by mass spectrometric analysis), which constituted 10% of the total PG. These species were coalesced in some sort of a lattice or aggregate with spatial proximity to other PG bridges. This result suggests that the triglycyl-bridged PG units form a PG-like structure that is not incorporated into the mature cell wall

Staphylococcus aureus NfrA (SA0367) Is a Flavin Mononucleotide-Dependent NADPH Oxidase Involved in Oxidative Stress Response

The NfrA protein, a putative essential oxidoreductase in the soil bacterium Bacillus subtilis, is induced under heat shock and oxidative stress conditions. In order to characterize the function of an homologous NfrA protein in Staphylococcus aureus, an nfrA deletion strain was constructed, the protein was purified, the enzymatic activity was determined, and the transcriptional regulation was investigated. The experiments revealed that NfrA is not essential in S. aureus. The purified protein oxidized NADPH but not NADH, producing NADP in the presence of flavin mononucleotide, suggesting that NfrA is an NADPH oxidase in S. aureus. In addition, the NfrA enzyme showed nitroreductase activity and weak disulfide reductase activity. Transcription was strongly induced by ethanol, diamide, and nitrofurantoin. Hydrogen peroxide induced nfrA transcription only at high concentrations. The expression of nfrA was independent of the alternative sigma factor σ(B). Furthermore, the transcriptional start site was determined, which allowed identification of a PerR box homologous sequence upstream of the nfrA promoter. The observations presented here suggest that NfrA is a nonessential NADPH oxidoreductase which may play a role in the oxidative stress response of S. aureus, especially in keeping thiol-disulfide stress in balance

In Vitro and In Vivo Validation of ligA and tarI as Essential Targets in Staphylococcus aureus▿

A conditional expression system has been developed using the isopropyl-β-d-thiogalactopyranoside (IPTG)-inducible Pspac promoter to validate essential genes of Staphylococcus aureus in vivo. The system has been applied to prove the essentiality of ligA and to evaluate the function of tarI, which was found to be essential in vitro but not in vivo