Liquid Chromatographic Method for Determination of Iodine in Milk: Collaborative Study

Nine laboratories participated in an AOAC International/ International Dairy Federation collaborative study on a liquid chromatographic (LC) method for determination of iodine in milk. Liquid milk is passed through a 25 000 MW membrane filter to remove protein and insoluble material. Iodine (in the form of iodide) in the clear filtrate is separated by reversed-phase ion-pair LC and is detected electrochemically. Participants analyzed 2 commercial pasteurized whole milks and 5 nonfat dry milk powders in blind duplicate. Each sample was tested in duplicate on 2 days. Repeatability and reproducibility standard deviations (sr and SR, respectively) and repeatability and reproducibility relative standard deviations (RSDr and RSDR, respectively) for determinations of iodine in whole milk (mean recovery, 86.7%) were as follows: sr, 22 μg/L; SR, 22 μg/L; RSDr, 8.2%; and RSDR, 8.3%. For powdered milk (mean recovery, 91 %), the values were as follows: sr, 0.14 μg/g; SR, 0.22 μg/g; RSDr, 9.0%; and RSDR, 12.7%. The method was adopted first action by AOAC International.

A novel framework to compare the effectiveness of β-lactamase inhibitors against extended-spectrum β-lactamase-producing Enterobacteriaceae

OBJECTIVES

Extended-spectrum β-lactamases (ESBLs) present a serious challenge in the treatment of Gram-negative bacterial infections. ESBLs mediate resistance to most β-lactams, which may be reversed with the addition of an active β-lactamase inhibitor (such as tazobactam, relebactam and avibactam). However, various ESBLs may exhibit different susceptibilities to these inhibitors, which could impact efficacy. We proposed a framework for comparing the efficacy of these inhibitors when combined with the same β-lactam.

METHODS

Three clinical isolates of Klebsiella pneumoniae harbouring CTX-M-15 and one Escherichia coli isolate with SHV-12 were examined. Piperacillin MICs were determined by broth dilution using escalating concentrations of tazobactam, relebactam and avibactam. The resulting MICs were characterized as response to inhibitor concentrations using an inhibitory sigmoid E_max model. Using the best-fit parameter values, the model was conditioned with fluctuating inhibitor concentrations to simulate instantaneous MIC_i profiles for each isolate-inhibitor pair. Using a simulated exposure of 4 g piperacillin every 8 h, %fT > MIC_i was estimated for each piperacillin/inhibitor combination. A hollowfibre infection model was subsequently used to validate the predicted effectiveness of selected combinations.

RESULTS

In all scenarios, piperacillin MIC reductions were well characterized with increasing inhibitor concentrations. As predicted by %fT > MIC_i, combining piperacillin with avibactam (61.4%-73.6%) was found to be superior to tazobactam (13.5%-44.5%) for suppressing bacterial growth over time.

CONCLUSION

We illustrated a practical approach to compare the performance of different inhibitors. This platform may be used clinically to identify the optimal pairing of various β-lactams and β-lactamase inhibitors for individual isolates producing ESBLs.