Virginiamycin S1

The Streptomyces virginiae gamma-butyrolactone autoregulator virginiae butanolide is a low-molecular-weight Streptomyces hormone eliciting virginiamycin biosynthesis through its binding to the specific receptor protein, BarA. Immediately downstream of barA lies barB, the transcription of which is tightly repressed by BarA in the absence of virginiae butanolide and derepressed in its presence. Thus, BarB is next to BarA on the virginiae butanolide-BarA signaling cascade. An in-frame 279-bp deletion was introduced into the barB allele, which rendered it inactive by eliminating the majority of the coding region, including the helix-turn-helix DNA-binding motif. No significant change was observed with the Delta barB mutant with respect to the timing or amount of virginiae butanolide production, or the morphological differentiation on solid media, indicating that barB neither participates in virginiae butanolide biosynthesis nor in cytodifferentiation. In contrast, analysis of virginiamycin production in the Delta barB mutant revealed that production of both virginiamycin M(1) and virginiamycin S occurred immediately after virginiae butanolide production, 2-3 h earlier than in the wild-type strain, indicating that BarB participates in the temporal retardation of virginiamycin production after virginiae butanolide inactivates the repressor function of BarA. RT-PCR analysis of the transcription of several genes surrounding barA-barB by the Delta barB mutant indicated that BarB plays a negative regulatory role, directly or indirectly, in the transcription of barZ, vmsR, and orf5 located upstream of barB.

Quinupristin and dalfopristin are relatively large molecules that are unlikely to be excreted into breastmilk in large amounts or to be absorbed orally by the breastfeeding infant.[1] However, since no information is available on the use of quinupristin and dalfopristin during breastfeeding, an alternate drug may be preferred, especially while nursing a newborn or preterm infant.

Antibiotics are used in ethanol production to discourage the growth of bacteria that would result in lower ethanol content and a lower quality product. A survey conducted by the FDA (FY 2010 Nationwide Survey of Distillers Grains for Antibiotic Residues, 2009 [1]) revealed that the residues of these antibiotics can remain in the distillers grains (DG) by-product, which is used as an animal feed ingredient. The low levels of antibiotic residues in DG could be a public health concern, as they could lead to antimicrobial resistance. To enable the quantitative determination of these antibiotics (erythromycin, penicillin G, virginiamycin M1 and virginiamycin S1), we developed a sensitive LC-MS/MS method. The residues were extracted from distillers grains with a mixture of acetonitrile and buffer followed by acetonitrile. The combined extract was diluted with water and washed with hexane. An aliquot was cleaned up on an Oasis HLB solid phase extraction cartridge. Extracts were analyzed by LC-tandem mass spectrometry. The method was successfully validated using a variety of different matrices such as corn DG, corn & milo DG, and deoiled corn DG. Absolute recoveries of the analytes ranged from 53 to 106%. Accuracy ranged from 90 to 101% based on calibration by matrix standards. The limits of quantitation and relative standard deviation were all satisfactory to support future surveillance studies.