Occurrence and mechanisms of tigecycline resistance in carbapenem- and colistin-resistant Klebsiella pneumoniae in Thailand

Abstract

Tigecycline has been regarded as one of the most important last-resort antibiotics for the treatment of infections caused by extensively drug-resistant (XDR) bacteria, particularly carbapenem- and colistin-resistant Klebsiella pneumoniae (C-C-RKP). However, reports on tigecycline resistance have been growing. Overall, ~ 4000 K. pneumoniae clinical isolates were collected over a five-year period (2017-2021), in which 240 isolates of C-C-RKP were investigated. Most of these isolates (91.7%) were resistant to tigecycline. Notably, a high-risk clone of ST16 was predominantly identified, which was associated with the co-harboring of bla_NDM-1 and bla_OXA-232 genes. Their major mechanism of tigecycline resistance was the overexpression of efflux pump acrB gene and its regulator RamA, which was caused by mutations in RamR (M184V, Y59C, I141T, A28T, C99/C100 insertion), in RamR binding site (PI) of ramA gene (C139T), in MarR (S82G), and/or in AcrR (L154R, R13Q). Interestingly, four isolates of ST147 carried the mutated tet(A) efflux pump gene. To our knowledge, this is the first report on the prevalence and mechanisms of tigecycline resistance in C-C-RKP isolated from Thailand. The high incidence of tigecycline resistance observed among C-C-RKP in this study reflects an ongoing evolution of XDR bacteria against the last-resort antibiotics, which demands urgent action.

Figure 1

Dendrogram based on ERIC-PCR typing, antimicrobial susceptibility profile, resistance gene profile, and efflux pump activity of 57 C-C-RKP isolates with tigecycline MIC ranged from 4 to 8 µg/ml. The black, gray, and white color in antimicrobial susceptibility profile indicate resistant, intermediate, and susceptible phenotype to an antibiotic, respectively. ^aFold reduction of tigecycline MIC in presence of 20 µg/ml CCCP compared to absence of CCCP. ^bScreening of tigecycline resistant gene including tet(A), tet(X), and tmexCD1-toprJ1.

Figure 2

Relative expression level of (a) acrB, and (b) ramA of tigecycline high-level resistant isolates (TGC MIC > 2 µg/ml, N = 12), and tigecycline low-level resistant isolates (TGC MIC 1–2 µg/ml, N = 17). ***P = 0.0002; Mann–Whitney U test.

Figure 3

Phylogenetic analysis based on core genome single nucleotide polymorphisms (cgSNP) of 15 C-C-RKP isolates from this study (red labeled) and 76 isolates of tigecycline-resistant K. pneumoniae retrieved from NCBI database.