Emergence of plasmid-mediated colistin resistance mcr-3.5 gene in Citrobacter amalonaticus and Citrobacter sedlakii isolated from healthy individual in Thailand

Abstract

Citrobacter spp. are Gram-negative bacteria commonly found in environments and intestinal tracts of humans and animals. They are generally susceptible to third-generation cephalosporins, carbapenems and colistin. However, several antibiotic resistant genes have been increasingly reported in Citrobacter spp., which leads to the postulation that Citrobacter spp. could potentially be a reservoir for spreading of antimicrobial resistant genes. In this study, we characterized two colistin-resistant Citrobacter spp. isolated from the feces of a healthy individual in Thailand. Based on MALDI-TOF and ribosomal multilocus sequence typing, both strains were identified as Citrobacter sedlakii and Citrobacter amalonaticus. Genomic analysis and S1-nuclease pulsed field gel electrophoresis/DNA hybridization revealed that Citrobacter sedlakii and Citrobacter amalonaticus harbored mcr-3.5 gene on pSY_CS01 and pSY_CA01 plasmids, respectively. Both plasmids belonged to IncFII(pCoo) replicon type, contained the same genetic context (Tn3-IS1-ΔTnAs2-mcr-3.5-dgkA-IS91) and exhibited high transferring frequencies ranging from 1.03×10-4 - 4.6×10-4 CFU/recipient cell Escherichia coli J53. Colistin-MICs of transconjugants increased ≥ 16-fold suggesting that mcr-3.5 on these plasmids can be expressed in other species. However, beside mcr, other major antimicrobial resistant determinants in multidrug resistant Enterobacterales were not found in these two isolates. These findings indicate that mcr gene continued to evolve in the absence of antibiotics selective pressure. Our results also support the hypothesis that Citrobacter could be a reservoir for spreading of antimicrobial resistant genes. To the best of our knowledge, this is the first report that discovered human-derived Citrobacter spp. that harbored mcr but no other major antimicrobial resistant determinants. Also, this is the first report that described the presence of mcr gene in C. sedlakii and mcr-3 in C. amalonaticus.

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

“…Carbapenemase genes ( bla KPC , bla NDM , bla IMP , bla VIM , and bla OXA-48-like ) 82 and mobilized colistin resistance genes ( mcr -1 to mcr -9) were detected by multiplex PCR according to our previous studies 83 , 84 . Acquired tigecycline resistance genes including tet (X) 85 , tet (A) 86 , and tmexCD1-toprJ1 87 were screened by single-plex PCR.…”

Mobile Colistin-Resistant Gene; mcr-1, mcr-2, mcr-3 Identified in Diarrheal Pathogens among Infants, Children, and Adults in Bangladesh: Implications for the Future

“…This includes carbapenem-resistant Acinetobacter baumannii (CRAB) as well as other pathogens resistant to the new antimicrobial agents [55][56][57]. However, the use of colistin as a last resort antibiotic is greatly threatened by the rise of plasmid-borne mobile colistin resistance gene [58][59][60], spreading rapidly via horizontal gene transfer [61]. Resistance to colistin is generated by the chromosomally mediated modification of lipopolysaccharide (LPS) [62].…”

Mobile Colistin-Resistant Genes mcr-1, mcr-2, and mcr-3 Identified in Diarrheal Pathogens among Infants, Children, and Adults in Bangladesh: Implications for the Future

“…The use of colistin as an antibiotic of last resort is greatly threatened by its overuse and the associated rise of plasmid-borne mobile colistin resistance genes [ 50 , 51 , 52 ], spreading rapidly via horizontal gene transfer [ 53 ]. Resistance to colistin is generated by the chromosomally mediated modification of lipopolysaccharide (LPS) [ 54 ].…”

“…This is important in Bangladesh, given extensive colistin-resistant Escherichia coli in broiler meat and chicken feces [39][40][41] exacerbating resistance among patients to colistin in Bangladesh [42][43][44][45]. Over-the-counter dispensing of antibiotics is also common in Bangladesh and is a concern, especially when this involves 'Reserve' antibiotics [46][47][48][49] The use of colistin as an antibiotic of last resort is greatly threatened by its overuse and the associated rise of plasmid-borne mobile colistin resistance genes [50][51][52], spreading rapidly via horizontal gene transfer [53]. Resistance to colistin is generated by the chromosomally mediated modification of lipopolysaccharide (LPS) [54].…”