Development and Validation of a UPLC-MS/MS Method to Monitor Cephapirin Excretion in Dairy Cows following Intramammary Infusion

Cephapirin, a cephalosporin antibiotic, is used by the majority of dairy farms in the US. Fecal and urinary excretion of cephapirin could introduce this compound into the environment when manure is land applied as fertilizer, and may cause development of bacterial resistance to antibiotics critical for human health. The environmental loading of cephapirin by the livestock industry remains un-assessed, largely due to a lack of appropriate analytical methods. Therefore, this study aimed to develop and validate a cephapirin quantification method to capture the temporal pattern of cephapirin excretion in dairy cows following intramammary infusion. The method includes an extraction with phosphate buffer and methanol, solid-phase extraction (SPE) clean-up, and quantification using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The LOQ values of the developed method were 4.02 µg kg⁻¹ and 0.96 µg L⁻¹ for feces and urine, respectively. This robust method recovered >60% and >80% cephapirin from spiked blank fecal and urine samples, respectively, with acceptable intra- and inter-day variation (<10%). Using this method, we detected trace amounts (µg kg⁻¹) of cephapirin in dairy cow feces, and cephapirin in urine was detected at very high concentrations (133 to 480 µg L⁻¹). Cephapirin was primarily excreted via urine and its urinary excretion was influenced by day (P = 0.03). Peak excretion (2.69 mg) was on day 1 following intramammary infusion and decreased sharply thereafter (0.19, 0.19, 0.08, and 0.17 mg on day 2, 3, 4, and 5, respectively) reflecting a quadratic pattern of excretion (Quadratic: P = 0.03). The described method for quantification of cephapirin in bovine feces and urine is sensitive, accurate, and robust and allowed to monitor the pattern of cephapirin excretion in dairy cows. This data will help develop manure segregation and treatment methods to minimize the risk of antibiotic loading to the environment from dairy farms.     

Toll-like receptor 4 deficiency: Smaller infarcts,but nogain in function

Backgound  

It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT).     

Reproductive synchrony,parental investment,and the evolutionary dynamics of sexual selection

Computer simulations showed that reproductive synchrony in the greater investing sex can evolve as a strategy for increasing the investment of mates. The potential for synchrony to increase in frequency for this reason decreased with (a) increasing population size, (b) decreasing importance of synchrony-enforced investment, (c) increasing variance in quality among members of the lesser investing sex, and (d) decreasing male: female sex ratio. By reducing the payoffs to desertion, synchrony may result in the evolution of uniquely effective forms of parental care by the lesser investing sex, making desertion unprofitable regardless of the availability of potential mates. Thus relative levels of optimal parental investment are subject to change through the action of sexual selection itself.     

Discrimination between aminoacyl groups on su+ 7 tRNA by elongation factor Tu

The su⁺7 nonsense suppressor of Escherichia coli is a mutant tRNA^Trp that can be aminoacylated with either tryptophan or glutamine. We have compared the ternary complexes of glutaminyl and tryptophanyl-su⁺7 tRNA with elongation factor Tu and GTP. Glutaminyl-su⁺7 tRNA binds more strongly than tryptophanyl-su⁺7 tRNA to EF Tu · GTP. The greatest distinction between the two species of the tRNA is seen in their dissociation rates from the complex, which differ by as much as fivefold. The distinction is affected by pH values around neutrality. These results show that EF Tu can distinguish between two aminoacyl-tRNAs which differ only in the aminoacyl group. The implications for the unusual amino acid specificity of su⁺7 tRNA are discussed.