A recent study published in Engineering has examined the spread and epidemiology of tmexCD1-toprJ1-positive Klebsiella pneumoniae, an antibiotic-resistant bacterium that is raising concerns for public health worldwide. The research was conducted by a group of scientists from several Chinese institutions and used whole-genome sequencing to analyze strains found in humans, animals, food, and the environment.
The researchers discovered that these tmexCD1-toprJ1-positive strains, which are resistant to tigecycline—a critical antibiotic—are most often found in Klebsiella pneumoniae from chicken feces in China. However, the presence of these resistant strains has also been detected in other countries such as Japan, Vietnam, and Kenya. According to the study, most of these bacteria are resistant to almost all available antimicrobials, including colistin. The resistance rate to colistin was reported at 42.13%.
Phylogenetic analysis indicated that the tmexCD1-toprJ1 gene cluster is mainly carried by plasmids with a narrow host range specific to Klebsiella species. This could restrict its ability to move between different bacterial species. Nevertheless, there were cases where the gene cluster had been acquired by broad-host-range plasmids, increasing the risk of wider dissemination. The study also noted that this resistance gene cluster has appeared in hypervirulent carbapenem-resistant K. pneumoniae (hvCRKP) strains known for causing serious infections in hospitals.
One significant finding from the research was a marked decline in tmexCD1-toprJ1-positive strains among food animals and humans in China after antibiotics were no longer used as growth promoters in animal feed starting in 2020. This suggests that policies aimed at reducing antibiotic use can help control the spread of resistance genes. The frequent use of tetracyclines in chicken farming appears to be linked with higher detection rates of tmexCD1-toprJ1, indicating that targeted actions within poultry production could help curb further spread.
Genomic analysis revealed various genetic environments around the tmexCD1-toprJ1 gene cluster, with one type—characterized by insertion sequences like IS26—being most common and likely aiding gene mobility and spread. Specific plasmid types such as IncFIB(Mar)-IncHI1B and IncFIB(K)-IncHI1B were identified as important carriers for this resistance gene.
The study concluded: "The findings of this study emphasize the need for continuous monitoring of tmexCD1-toprJ1 across different ecological niches and the enforcement of strict antimicrobial policies in animal husbandry." It added: "The global spread of tmexCD1-toprJ1-positive Klebsiella pneumoniae poses a significant challenge to the treatment of infections caused by multidrug-resistant bacteria, highlighting the importance of a One Health approach to address the growing threat of antimicrobial resistance."
