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Volume 49, Number 1, February 2016

Development of ceftriaxone resistance in Salmonella enterica serotype Oranienburg during therapy for bacteremia 


Wei-Chiun Yang, Oi-Wa Chan, Tsu-Lan Wu, Chyi-Liang Chen, Lin-Hui Su, Cheng-Hsun Chiu


 

Corresponding author:

Lin-Hui Su
Corresponding author. Department of Medical Biotechnology and Laboratory Science, Chang Gung University College of Medicine, 259, Wen-Hwa First Road, Kweishan 333, Taoyuan, Taiwan.

Cheng-Hsun Chiu
Corresponding author. Division of Pediatric Infectious Diseases, Department of Pediatrics, Chang Gung Children's Hospital, 5 Fu-Hsin Street, Kweishan 333, Taoyuan, Taiwan. 



 

Background and purpose: 

The majority of nontyphoid Salmonella infection is identified in children. When an invasive or severe Salmonella infection is encountered, ceftriaxone is recommended for such patients. A 2-year-old girl was hospitalized for the treatment of Salmonella bacteremia and discharged with standard ceftriaxone treatment. She was readmitted to the hospital after 2 days due to the recurrence of the Salmonella bacteremia. The study aimed to unveil the mechanism for the relapse. 



 

Methods:

Six isolates (4 blood and 2 stool) were recovered from the patient, with the last two blood isolates being ceftriaxone-resistant. Pulsed-field gel electrophoresis was used for genotyping. Ceftriaxone resistance genes and transferability of the resistance plasmid were examined by molecular methods. 



 

Results:

All isolates were identified as Salmonella enterica serotype Oranienburg. Five isolates demonstrated almost identical electrophoresis patterns, except that in the two ceftriaxone-resistant isolates an extra band (>100 kb) was noted. A blaCMY-2 gene, carried by a 120-kb conjugative IncI1 plasmid of the sequence type 53, was identified in the two ceftriaxone-resistant isolates. Transfer of the resistance plasmid from one blood isolate to Escherichia coli J53 resulted in the increase of ceftriaxone minimum inhibitory concentration from 0.125 μg/mL to 32 μg/mL in the recipient. 



 

Conclusion:

Ceftriaxone is the standard therapeutic choice for invasive or serious Salmonella infections in children. Pediatricians should be aware of the possibility of resistance development during therapy, especially in areas with a widespread of ceftriaxone resistance genes that are carried by a self-transferrable plasmid, such as the blaCMY-2-carrying IncI1 plasmid identified herein. 



 

Key words:

Ceftriaxone resistance, IncI1 plasmid, Relapse bacteremia, Salmonella enterica serotype Oranienburg