The expression levels of baeS and baeR in ABtc increased 3.19 and 2.64-fold, respectively, this website compared with the wild-type strain, whereas those in ABhl1 only increased 1.93 and 1.39-fold, respectively (Figure 3B). Overall, the combination of the qRT-PCR results with the MIC assay above suggest that both
BaeSR and AdeAB are involved in the tigecycline resistance of A. baumannii. Dinaciclib Figure 3 Transcript levels of the adeA , adeB , baeR , and baeS genes in A. baumannii strains. ABtc and ABhl1 are laboratory-induced and clinically isolated tigecycline-resistant strains, respectively. The corresponding tigecycline minimum inhibitory concentrations (MICs) of ATCC 17978, ABtc, and ABhl1 were 0.5, 256, and 16 μg/mL, respectively. Gene expression was detected by quantitative real-time PCR (qRT-PCR). (A) qRT-PCR showed that the expression levels of adeB in ABtc and ABhl1 were 216- and 53-fold higher than those in the wild-type strain, respectively. The adeA1 expression levels in ABtc and ABhl1 were 99- and 22-fold higher than those in the wild-type strain, respectively, whereas the adeA2 expression levels in ABtc and ABhl1 were 134- and 25-fold higher. (B) The expression PF299 molecular weight levels of baeS and baeR in ABtc increased 3.19 and 2.64 times, respectively, compared
with the wild-type strain, whereas those in ABhl1 only increased 1.93 and 1.39 times, respectively. 16S rRNA gene was used as a control. The results are displayed as the means ± SD from four independent experiments. *, P < 0.05; **, P < 0.01. Influence of the BaeSR TCS on adeAB efflux pump expression To understand whether baeR influenced the tigecycline MIC by affecting the adeAB efflux pump gene, the expression of adeA1, adeA2, and adeB in ATCC 17978, AB1026, AB1027, and AB1028 was analyzed by qRT-PCR. The expression levels of adeB, adeA1, and adeA2 in AB1028 were approximately 2.9-, 2.1-, and 3-fold higher, respectively, than those in ATCC 17978, while the deletion of baeR from
the wild-type strain decreased the expression levels of these three pump genes by 68.3%, 67.3%, and 73.5%, respectively mafosfamide (Figure 4A). The decreased expression of the pump genes can be partially restored by baeR reconstitution (Figure 4A). To determine the impact of baeR deletion on adeR expression, RT-PCR was also performed. No differences in adeR expression were observed between AB1026 and the wild-type strain (data not shown). Overall, these findings suggest that BaeR upregulates the expression of adeAB genes. Figure 4 Transcript levels of the adeA and adeB genes in different strains of A. baumannii . AB1026, AB1027, and AB1028 are the baeR deletion mutant, baeR reconstitution, and wild-type with baeR overexpression strains, respectively. ABTcm is the baeR deletion mutant of ABtc, which was a laboratory-induced tigecycline-resistant strain. The relative expression of adeB, adeA1, and adeA2 was determined by qRT-PCR.