A selective antibiotic for Lyme disease.

Lyme disease is on the rise. Caused by a spirochete Borreliella burgdorferi, it affects an estimated 500,000 people in the United States alone. The antibiotics currently used to treat Lyme disease are broad spectrum, damage the microbiome, and select for resistance in non-target bacteria. We therefore sought to identify a compound acting selectively against B. burgdorferi. A screen of soil micro-organisms revealed a compound highly selective against spirochetes, including B. burgdorferi. Unexpectedly, this compound was determined to be hygromycin A, a known antimicrobial produced by Streptomyces hygroscopicus. Hygromycin A targets the ribosomes and is taken up by B. burgdorferi, explaining its selectivity. Hygromycin A cleared the B. burgdorferi infection in mice, including animals that ingested the compound in a bait, and was less disruptive to the fecal microbiome than clinically relevant antibiotics. This selective antibiotic holds the promise of providing a better therapeutic for Lyme disease and eradicating it in the environment.

Nonstable Staphylococcus aureus Small-Colony Variants Are Induced by Low pH and Sensitized to Antimicrobial Therapy by Phagolysosomal Alkalinization.

BACKGROUND: Staphylococcus aureus-infected patients treated with antibiotics that are effective in vitro often experience relapse of infection because the bacteria hide in privileged locations. These locations include abscesses and host cells, which contain low-pH compartments and are sites from which nonstable S. aureus small-colony variants (SCVs) are frequently recovered. METHODS: We assessed the effect of low pH on S. aureus colony phenotype and bacterial growth, using in vitro and in vivo models of long-term infection. RESULTS: We showed that low pH induced nonstable SCVs and nonreplicating persisters that are capable of regrowth. Within host cells, S. aureus was located in phagolysosomes, a low-pH compartment. Therapeutic neutralization of phagolysosomal pH with ammonium chloride, bafilomycin A1, or the antimalaria drug chloroquine reduced SCVs in infected host cells. In a systemic mouse infection model, treatment with chloroquine also reduced SCVs. CONCLUSIONS: Our results show that the acidic environment favors formation of nonstable SCVs, which reflect the SCVs found in clinics. They also provide evidence that treatment with alkalinizing agents, together with antibiotics, may provide a novel translational strategy for eradicating persisting intracellular reservoirs of staphylococci. This approach may also be extended to other intracellular bacteria.

Reactive oxygen species-inducible ECF σ factors of Bradyrhizobium japonicum.

Extracytoplasmic function (ECF) σ factors control the transcription of genes involved in different cellular functions, such as stress responses, metal homeostasis, virulence-related traits, and cell envelope structure. The genome of Bradyrhizobium japonicum, the nitrogen-fixing soybean endosymbiont, encodes 17 putative ECF σ factors belonging to nine different ECF σ factor families. The genes for two of them, ecfQ (bll1028) and ecfF (blr3038), are highly induced in response to the reactive oxygen species hydrogen peroxide (H(2)O(2)) and singlet oxygen ((1)O(2)). The ecfF gene is followed by the predicted anti-σ factor gene osrA (blr3039). Mutants lacking EcfQ, EcfF plus OsrA, OsrA alone, or both σ factors plus OsrA were phenotypically characterized. While the symbiotic properties of all mutants were indistinguishable from the wild type, they showed increased sensitivity to singlet oxygen under free-living conditions. Possible target genes of EcfQ and EcfF were determined by microarray analyses, and candidate genes were compared with the H(2)O(2)-responsive regulon. These experiments disclosed that the two σ factors control rather small and, for the most part, distinct sets of genes, with about half of the genes representing 13% of the members of H(2)O(2)-responsive regulon. To get more insight into transcriptional regulation of both σ factors, the 5' ends of ecfQ and ecfF mRNA were determined. The presence of conserved sequence motifs in the promoter region of ecfQ and genes encoding EcfQ-like σ factors in related α-proteobacteria suggests regulation via a yet unknown transcription factor. By contrast, we have evidence that ecfF is autoregulated by transcription from an EcfF-dependent consensus promoter, and its product is negatively regulated via protein-protein interaction with OsrA. Conserved cysteine residues 129 and 179 of OsrA are required for normal function of OsrA. Cysteine 179 is essential for release of EcfF from an EcfF-OsrA complex upon H(2)O(2) stress while cysteine 129 is possibly needed for EcfF-OsrA interaction.