Emergence and Dissemination of mcr-Carrying Clinically Relevant Salmonella Typhimurium Monophasic Clone ST34

Area of Science:

• Microbiology
• Public Health
• Genetics

Background:

• Antibiotic resistance in bacteria is a critical global health concern.
• The Salmonella Typhimurium monophasic sequence type 34 (ST34) clone exhibits rapid dissemination and resistance to multiple antimicrobials.
• Emerging infections caused by mobile colistin resistance (mcr)-carrying, colistin-resistant ST34 isolates are of increasing global concern.

Purpose of the Study:

• To provide an updated overview of emerging infections caused by mcr-carrying, colistin-resistant ST34 isolates.
• To analyze the global dissemination patterns of these resistant isolates.
• To assess their virulence-associated efficacy and potential as a pandemic clone.

Main Methods:

• Review and synthesis of existing data on mcr-carrying ST34 isolates.
• Analysis of geographical distribution and prevalence rates.
• Investigation of resistance gene locations (plasmid types) and co-occurrence of virulence and heavy metal resistance genes.

Main Results:

• Higher rates of mcr-1-positive ST34 observed in children in China, indicating a significant threat.
• ST34 isolates carrying mcr-1 genes frequently found in animals and food products, suggesting foodborne transmission.
• Co-emergence of multidrug resistance, virulence factors, and heavy metal resistance genes in ST34 isolates challenges therapeutic options.
• mcr-1, mcr-3, and mcr-5 genes detected in ST34 isolates across multiple countries, often on IncHI2, IncI2, and IncX4 plasmids.

Conclusions:

• mcr-carrying Salmonella Typhimurium ST34 isolates represent a growing threat with potential for pandemic spread.
• Foodborne transmission plays a crucial role in the dissemination of mcr-1.
• Urgent need for rapid detection and active surveillance across various settings (community, hospital, animal, food, environment).