Colistin, once infrequently used due to nephrotoxicity, has gained popularity in combating multidrug-resistant (MDR) infections. The mobile colistin resistance (mcr) gene, initially identified in China, has since spread globally, raising concerns about antimicrobial resistance (AMR) dissemination, particularly in regions with agricultural colistin use. While surveillance in wealthy regions is common, data on mcr prevalence in Africa is scarce.
Key Findings
Prevalence of mcr in Nigeria:
- A retrospective survey of 4907 rectal swabs from mothers and neonates in Nigeria revealed mcr carriage in 1% of samples.
- mcr genes were found in various bacterial species, predominantly Enterobacter spp., along with Shigella, E. coli, and Klebsiella quasipneumoniae.
- The majority (90%) of mcr genes identified were mcr-10, with a smaller proportion of mcr-1 and mcr-9.
Widespread Diversity and Distribution:
- Phylogenetic analysis showed intraspecies diversity of colistin-resistant Enterobacter, indicating a diverse reservoir within the microbiota of women and neonates.
- Detected mcr genes were found on plasmids, suggesting potential dissemination within the microbiota and surrounding environments.
Early Acquisition and Transmission:
- Neonates, including those with sepsis, were found to carry mcr-positive Gram-negative bacteria (GNB), suggesting early acquisition.
- Potential routes of transmission include maternal vertical transmission, community exposure, and environmental contamination.
Potential Agricultural Origins:
- Despite limited clinical colistin use in Nigeria, the presence of mcr suggests possible agricultural usage, supported by reports of European colistin imports for agricultural purposes.
Laboratory Observations:
- Microbial growth rates following colistin broth enrichment were consistent with previous studies, maximizing mcr recovery.
- Sequential sub-MIC exposure led to the emergence of colistin-resistant phenotypes, indicating the importance of surveillance for capturing resistant populations.
Methods
Sample Collection and Processing:
- 4907 rectal swabs from mothers and neonates across three hospital sites in Nigeria were retrospectively screened for mcr.
- Samples were enriched in colistin broth and subjected to phenotypic and genotypic characterization of bacterial isolates carrying mcr genes.
Genomic Analysis:
- Phylogenetic analysis was conducted to assess intraspecies diversity and distribution of colistin-resistant Enterobacter.
- Long-read sequencing was performed to characterize the genetic context of mcr genes.
Limitations:
- Lack of colistin susceptible isolates due to laboratory approach.
- Variable sample sizes across sites, affecting the interpretation of prevalence data.
- Absence of data on maternal HIV status and other immune-compromising conditions that may influence AMR carriage.
Conclusion
The study highlights the presence of mcr genes in Nigeria, indicating potential agricultural origins and early acquisition in neonates. The diverse reservoir of colistin-resistant bacteria underscores the importance of ongoing surveillance, particularly in vulnerable populations. These findings suggest a need for comprehensive AMR monitoring and control strategies in Africa, considering both clinical and agricultural sectors.
Link to the article : https://tinyurl.com/mbujvftr
