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High Prevalence of Phenotypic Resistance to Colistin, Tigecycline and Netilmicin in a Region with no History of Colistin Administration in Nigeria by Theophilus K. Udeani, Uchenna I. Ugah

Background: Colistin is currently used as a last line antibiotic for the treatment of extensively drug-resistant Gram-negative bacteria. The widespread dissemination of ESBL-producing and carbapenem-resistant Gram-negative bacteria necessitated the re-introduction of colistin which was initially abandoned as a result of high toxicities. This study aimed at determining the epidemiology of Enterobacteriaceae isolates that are resistant to colistin, tigecycline, and netilmicin and the risk factors that may contribute to the resistance observed within Southeastern Nigeria.
Methods: A total of 400 participants who came to the hospitals for various reasons and suspected to have bacterial infections were enrolled in this study. Phenotypic resistance to colistin was detected using broth microdilution technique on cation - adjusted Mueller-Hinton broth while resistance to colistin and netilmicin was detected using the Kirby-Bauer disk diffusion method using tigecycline disk (10 µg) and netilmicin disk (30 µg). Risk factors were determined by the administration of questionnaires to the participants.
Results: Our study found an overall high prevalence of colistin - resistant Enterobacteriaceae (45.8%) and a high prevalence for colistin and tigecycline (22.2%) and colistin and netilmicin (31.7%) resistant isolates. Among the risk factors that contribute to colistin, non-completion of antibiotics was found to be more significant (p = 0.039 and an odds ratio of 0.324 - 0.972 at 95% confidence interval).
Conclusions: Our finding is significant in that colistin resistance was determined to be present among populations that have not been exposed to colistin therapy.

DOI: 10.7754/Clin.Lab.2020.200405