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Amino Acid Substitutions in Putative Selectivity Filter Regions III and IV in KdpA Alter Ion Selectivity of the KdpFABC Complex from Escherichia coli. Jessica Bertrand, 2004.When grown under conditions of potassium limitation or high osmolality, Escherichia coli synthesizes the K+-translocating KdpFABC complex . The KdpA subunit, which has sequence homology to potassium channels of the KcsA type, has been shown to be important for potassium binding and transport . Replacement of the glycine residues in KdpA at positions 345 and 470, members of putative selectivity filter regions III and IV, alters the ion selectivity of the KdpFABC complex . Reactivity of Platelia Aspergillus Galactomannan Antigen with Piperacillin-Tazobactam: Clinical Implications Based on Achievable Concentrations in Serum. Nina Singh, 2004.The possible reactivities of commonly used antibiotics of fungal, nonfungal, and nonmicrobial or synthetic sources with the Platelia Aspergillus galactomannan assay were assessed . For drugs that tested positive, the minimal concentration of the antibiotic in serum that yielded a positive test (index, >0.5) was determined . At undiluted concentrations, piperacillin and multiple lots of piperacillin-tazobactam tested positive, whereas amoxicillin, ampicillin-sulbactam, nafcillin, cefazolin, ceftazidime, erythromycin, gentamicin, and levofloxacin tested negative . All three lots of piperacillin-tazobactam and all bags within each lot tested positive, with a mean index value of 5.168 . At achievable concentrations in serum, however, only one of three lots of piperacillin-tazobactam yielded a positive test . Concentrations of 75, 150, and 300 µg/ml of serum tested positive with the Platelia Aspergillus enzyme immunoassay, whereas lower concentrations, mimicking the trough levels, tested negative . Thus, while achievable serum piperacillin-tazobactam concentrations may potentially result in a positive test for galactomannan, the timing of the collection of serum samples from patients may influence the test results, with reactivity being less likely in samples collected at trough levels or prior to the administration of a dose of the antibiotic .
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