Evaluation of five susceptibility test methods for detection of tobramycin resistance in a cluster of epidemiologically related Acinetobacter baumannii isolates.

Acinetobacter baumannii is a major nosocomial pathogen causing infections in critically ill patients. This organism has acquired the propensity to rapidly develop resistance to most antibiotics. At several hospitals within Cape Town, South Africa, tobramycin and colistin are frequently the only therapeutic options. Vitek2 automated susceptibility testing (AST) is used in the clinical laboratory to determine selected susceptibility profiles. The suspicion of a possible AST-related technical error when testing for susceptibility to tobramycin in A. baumannii precipitated this study. Thirty-nine A. baumannii strains isolated from clinical specimens (June to December 2006) were included in this prospective study. Tobramycin susceptibility testing results obtained by AST, disc diffusion, the epsilometer test (Etest), and agar dilution were compared to those for broth microdilution (BMD), the reference method. The tobramycin susceptibility results revealed errors in 25/39 (64%) isolates (10 very major and 15 minor errors) when AST was compared to BMD, 12/39 (31%) (2 very major and 10 minor errors) when Etest was compared to BMD, 16/39 (41%) (3 very major and 13 minor errors) when disc diffusion was compared to BMD, and 21/39 (54%) (10 very major and 11 minor errors) when agar dilution was compared to BMD. Using PCR, we detected aac(3)-IIa, which is associated with tobramycin resistance, in 21/25 of the discrepant isolates. Molecular typing (using pulsed-field gel electrophoresis and repetitive sequence-based PCR [rep-PCR]) showed that these isolates were genetically related. Clinical laboratories that routinely use the Vitek2 system should consider an alternative testing method for determining susceptibility to tobramycin.

Serine and proline-rich ligands enriched via phage-display technology show preferential binding to BCR/ABL expressing cells.

BACKGROUND AND OBJECTIVES: Despite the use of targeted therapy, chronic myelogenous leukemia (CML) currently remains incurable with drug therapy, with patients requiring life-long treatment. Developing either a vaccine to prevent the disease or another novel drug to specifically target and eradicate the CML cell will require the identification of CML-associated cell-surface markers and molecules that can bind specifically to the cell surface. In an attempt to discover peptides that bind specifically to cells in the early chronic phase of the disease, we used phage-display technology to identify heptapeptides that bind specifically to the surface of BCR/ABL-expressing fibroblasts. METHODS: An in vitro system using NIH3T3 stably transfected with pGD210 (BCR/ABL) was used as a model for the chronic phase of the disease. The cells were panned using a linear heptapeptide phage library (Ph.D 7.0) in a negative/positive panning strategy with NIH3T3 containing only the plasmid vector as the wild type control. RESULTS: We identified four novel peptides that were enriched through this technique. These peptides contained either multiple proline residues or serine/threonine-proline pairs and showed a confirmed binding preference for BCR/ABL+ fibroblasts. The peptide Y-R-A-P-W-P-P also showed a binding affinity for granulocytes from untreated CML patients. CONCLUSION: We have identified several novel peptides that can be used in future studies to identify specific CML cell-surface antigens or provide a novel drug-delivery mechanism.