| dc.description.abstract | Application of antibiotics with concentrations lower than the minimal inhibitory concentration (MIC) is widely believed to be the main reason for antibiotic resistance development. This work aims to provide more understanding on this phenomenon. Pure strain of Pseudomonas aeruginosa ATCC 9027 was serially exposed to Moxifloxacin below its MIC for 14 days then cultured for another 12 days without antibiotics. After 14 days of serial exposures, MOX-MIC increased 128 times from 1 mg/L to 128 mg/L. When the obtained MOX- resistant strain was cultured continuously in antibiotic- free media for 12 days, interestingly the MIC of MOX still remained high indicating that in vitro MOX-resistance development was irreversible (MOX-MIC: 128mg/L). Furthermore, the in vitro-produced MOX-resistant and revertant strains became cross-resistant to five other FQs and also resistant to other unrelated antibiotics. DNA of naïve P. aeruginosa and the selected strains (MOX-resistant P. aeruginosa) after exposure was extracted and analyzed for detecting key mutations in the quinolone resistance-determining region (QRDR) of parC gene as well as the efflux regulatory genes, nfxB and mexT (nfxC) which are known to be associated with Moxifloxacin resistance. Sequencing results showed no mutation in parC gene. Similarly, mexT sequencing analysis displayed no nucleotide changes. Interestingly nucleotide sequencing of nfxB gene has shown that nfxB of MOX-resistant and MOX-revertant strains had 100-bp- nucleotide deletion. When checking with insert sequence database, we proposed that this sequence is probably one type of insert sequences in Pseudomonas aeruginosa which interferes with gene expression regulation. This probably affects the nfxB expression leading to drug resistance. However, this hypothesis is yet to be elucidated.
Key words: Moxifloxacin, minimal inhibitory concentration (MIC), antibiotic resistance mechanisms, serial exposure, Pseudomonas aeruginosa , parC, nfxB, mexT. | en_US |
