Genetic profile mutation rpoB in clinical isolate of rifampicin-resistant Staphylococcus aureus

Staphylococcus aureus is one of the bacteria which causes nosocomial infection. Methicillin-Resistant Staphylococcus Aureus eradication using antibiotics combined with rifampicin has shown good results, whereas, adjuvant rifampicin has long been hypothesized to improve the outcome of S. aureus infection treatment. Resistant-rifampicin S. aureus mutates in rpoB gene at some codons. This study was conducted to identify the mutation of rpoB gene in S. aureus which was resistant toward rifampicin.

In this study, isolates collected in the Microbiology Laboratory of Dr. Seotomo Surabaya Hospital during May-September 2019. Then, the dilution method was carried out to determine the minimum inhibition concentration for resistant-rifampicin and dilution to determine the inhibition zone diameter. After that, DNA extraction was carried out from rifampicin-susceptible isolates as a control and resistant-rifampicin isolates followed by identification of rpoB gene mutations by Polymerase Chain Reaction (PCR) and sequencing.

There were nine isolates studied. They were four resistant-rifampicin isolates and four susceptible-rifampicin isolates. In four rifampicin-resistant isolates, the most frequent mutations that occurred was His-481 codon (75%) followed by the Ile-527 codon (25%). Rifampicin-susceptible isolates mutated in Pro-475 and Asn-474 codons. One rifampicin-resistant isolate had two mutations in codons Ile-527 and Asn-474.

The type of mutation that causes the most rifampicin resistance was a missense mutation. The susceptible-rifampicin isolate experienced silent mutations. There was a relation between the type of missense mutation of rpoB gene and rifampin resistance.