Polymyxin susceptibility testing: time for a review

Background: Polymyxins are polycationic peptides consisting of a cyclic heptapeptide, a linear tripeptide segment and a fatty acid tail linked to the N-terminal of the tripeptide. Two commercially available polymyxins, polymyxin B and polymyxin E (colistin), are very similar structurally and microbiologically. These antibiotics were widely used to treat serious infections caused by Gram-negative bacilli until the mid-1980 when they were banned in clinical practices because of their nephrotoxicity and neurotoxicity adverse events. They are now serve as the last therapeutic option to manage life-threatening infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) bacteria, including Pseudomonas aeruginosa, Acinetobacterbaumannii, and Klebsiella pneumonia. Due to the growing menace of multi-resistant pathogens and consequently, increased need for polymyxin treatment in critically ill patients in the intensive care unit (ICU), a significant effort is required to maintain antibacterial properties of these antibiotics. Updating the susceptibility data on polymyxins, including standardization of in vitro, and defining correct breakpoints is a critical issue both for patient care and epidemiological surveillance purposes. The in vitro susceptibility testing of polymyxins is influenced by various factors, such as the lack of interpretive categories (criteria) and breakpoints, the lack of a reliable reference susceptibility method, multicomponent composition of polymyxins, poor diffusion into agar, their cationic properties, the effect of polysorbate-80, development of heteroresistance, as well as others (e.g. quality controls, the impact of medium, subcultures and storage). Conclusion: Updating the susceptibility data on polymyxins, including standardization of in vitro, and defining correct breakpoints is a critical issue both for patient care and epidemiological surveillance purposes.

کلیدواژه ها:

Colistin ، MDR ، Polymyxin B ، Susceptibility testing ، XDR