Retrospective analysis of Vitek ® 2 performance compared to manual broth micro-dilution for colistin susceptibility testing of Acinetobacter baumannii complex isolates in South Africa.

The manual broth micro-dilution (mBMD) is the recommended reference method for colistin minimum inhibitory concentration determination; however, it is not as readily available in South Africa as the Vitek ® 2. This retrospective study compared the performance of Vitek ® 2 against mBMD in determining the colistin minimum inhibitory concentration of 337 extensively drug-resistant Acinetobacter baumannii complex isolates. Vitek ® 2 yielded a categorical agreement of 89%, an essential agreement of 56%, a major error rate of 8% and a very major error rate of 55%. The Vitek ® 2 is not an alternative to mBMD for colistin susceptibility testing.