Development of carbapenem resistance during therapy for non-typhoid Salmonella infection

Area of Science:

• Microbiology
• Infectious Diseases
• Genetics

Background:

• Multidrug-resistant Salmonella infections pose a significant global health threat.
• Carbapenems are often considered a last resort for treating severe Salmonella infections.
• Emergence of resistance to last-line antibiotics necessitates understanding resistance mechanisms.

Purpose of the Study:

• To report a case of Salmonella Typhimurium developing carbapenem resistance during treatment.
• To investigate the genetic mechanisms underlying acquired carbapenem resistance.
• To highlight the adaptability of Salmonella in developing antimicrobial resistance.

Main Methods:

• Isolating and characterizing Salmonella enterica serotype Typhimurium strains from a patient.
• Phenotypic antimicrobial susceptibility testing.
• Molecular analysis including plasmid identification and gene sequencing (blaCMY-2, Tn6092, OmpD, OmpC).

Main Results:

• The patient's Salmonella Typhimurium isolates were resistant to ceftriaxone and ciprofloxacin.
• A blaCMY-2 gene within Tn6092 on an IncI1 plasmid was identified in all isolates.
• During ertapenem treatment, the strain acquired carbapenem resistance, associated with OmpD deficiency and subsequent OmpC deficiency via gene mutation.

Conclusions:

• Salmonella Typhimurium demonstrates significant plasticity in acquiring multidrug resistance, including carbapenem resistance.
• The study highlights the rapid evolution of resistance mechanisms, involving both plasmid-mediated genes and chromosomal mutations affecting outer membrane proteins.
• Physicians must exercise caution when treating multidrug-resistant Salmonella infections due to the potential for rapid resistance development.