Molecular Study of the (rpoB) Gene as a Diagnostic Tool in Acinetobacter baumannii and the Identification of the Mutations in this Gene Led to Rifampicin Resistance

Background: Rifampicins are bactericidal antibiotics that prevent the synthesis of RNA by interacting with the rpoB -gene encoded bacterial RNA polymerase beta subunit. The rpoB gene has emerged as a pivotal candidate gene for bacterial diagnostics and phylogenetic investigations. In recent years, the Acinetobacter baumannii acquired a prominent interesting as a result of their high resistance to broad spectrum of antibiotics. Objective: The current study was designed to identify the sequence of rpoB gene, the mutation led to rifampicin resistance and compared them to standard isolates in the NCBI and sensitive isolates in Iraq (local control). Materials and Methods: Three hundred samples in total were gathered from patients with various infections in Medical City Hospital during the period from July 1, 2022 to January 30, 2023. The Vitek 2 system was used to identify bacterial isolates, cultural media (blood agar, macconkey agar, chromagar TM ) and the partial sequence of the rpoB gene whereas Kirby-Bauer method was used to test antibiotic susceptibility. Results: Total genomic DNA was extracted from the most resistant (MDR) thirty bacterial isolates in order to genetically identified by PCR and sent for sequencing. PCR and DNA sequence analysis of rpoB revealed that the RIF-resistance determining region (RRDR) of the rpoB gene had been modified in at least nine of the isolates. And the 21 of the isolates with no mutation, six mutations were discovered (CAA, ATG, GGA, ACT, GCA, GAT), four of them are novel mutation G114G, T249T, A348A, and D444D (Silent mutation) identified for the first time in Iraq when compared with sensitive isolates (local control). Most A. baumannii isolates with rpoB gene mutations exhibited the rifampicin resistance in 8 isolates (88.8%), only one isolate with rpoB gene mutation was sensitive to rifampicin. Conclusion: At the end, the molecular analysis showed that rpoB gene mutations in some isolates play a significant role in rifampicin resistance, particularly if the mutation at the rpoB -binding site to rifampicin.