Species identification and antimicrobial susceptibility analysis of Acinetobacter calcoacelicus-Acinetobacter baumannii complex

Objective To identify the exact species of Acinetobacter calcoacelicus-Acinetobacter baumannii complex and determine susceptibility of the isolates to aminoglycosides and carbapenems.Methods Species identification of clinical Acinetobacter spp.was performed using VITEK 2 instrument and isolates with Acinetobacter calcoacelicus-Acinetobacter baumannii complex results were further subjected to 16S rRNA sequence analysis identification.The susceptibility of Acinetobacter baumannii isolates and Acinetobacter calcoacelicus isolates to five antibiotics (amikacin,gentamicin,tobramycin,imipenem,ertapenem) was determined using VITEK 2 instrument or by mirodilution method,and the results were analyzed.Results Totally 232 Acinetobacter spp.was involved in species identification by VITEK 2 instrument,and 195 were identified as Acinetobacter calcoacelicus-Acinetobacter baumannii complex.Further species identification of the 195 Acinetobacter baumannii by 16S sequence analysis revealed that 173 isolates were Acinetobacter baumannii and 22 isolates were Acinetobacter calcoaceticus.Susceptibility testing of the 173 Acinetobacter baumannii and 22 Acinetobacter calcoacelicus to five antibiotics (amikacin,gentamicin,tobramycin,imipenem and ertapenem) were performed using VITEK 2 and by microdilution method respectively.The results with microdilution method demonstrated that 173 Acinetobacter baumannii were resistant to the three aminoglycosides,while relatively susceptible to the two carbapenems;22 Acinetobacter calcoaceticus were susceptible to the three aminoglycosdes and two carbapenems,with susceptible rates of 77.27% 100%.As comparison to the results with microdilution method,the susceptibility results with VITEK 2 showed testing error of various degrees,with amikacin of the highest very major error rate (35.84%) in Acinetobacter baumannii susceptibility test and ertapenem of the highest major error rate (40.91%) in Acinetobacter calcoacelicus susceptibility test.Conclusion VITEK 2 has limitations in species identification of Acinetobacter spp.,and 16S rRNA sequence analysis is needed for exact identification of Acinetobacter baumannii.Acinetobacter baumannii with high resistant rate to aminoglycosides.Errors of various degrees exist for aminoglycoside/carbapenem susceptibility test against Acinetobacter baumannii/Acinetobacter calcoacelicus using VITEK 2,and broth microdilution method is needed for verification.