Ceftriaxone Resistance of Nontyphoidal Salmonella entericaIsolates in Northern Taiwan Attributable to Production of CTX-M-14 and CMY-2 ß-Lactamases

ABSTRACTAmong 3,027 nontyphoidal Salmonella entericaisolates identified between January 1999 and December 2002 in a medical center in northern Taiwan, 31 were resistant to the extended-spectrum cephalosporin ceftriaxone (1.02% [31/3,027]), including 2 in 1999 (0.36% [2/549]), 13 in 2000 (1.49% [13/870]), 7 in 2001 (0.78% [7/893]), and 9 in 2002 (1.26% [9/715]). Sixteen of these isolates belonged to Salmonellaserogroup B, nine belonged to serogroup C, four belonged to serogroup D, and two belonged to serogroup E. The majority were from stool cultures. The mechanism of resistance was investigated for eight isolates, including three S. entericaserovar Typhimurium, one S. entericaserovar Wagenia, one S. entericaserovar Senftenberg, one S. entericaserovar Derby, one S. entericaserovar Panama, and one S. entericaserovar Duesseldorf isolate. All eight patients from whom these isolates were recovered had community-acquired infections. All eight isolates were resistant to ampicillin, ceftriaxone, and cefotaxime but susceptible to imipenem and ciprofloxacin. Ceftriaxone resistance was due to the production of the CMY-2 AmpC ß-lactamase by seven isolates and the CTX-M-14 ß-lactamase by the remaining isolate. Both ß-lactamase genes were carried on conjugative plasmids. In a 2.5-kb region encompassing the blaCMY-2gene, at nucleotide 49 upstream of the start codon of blaCMY-2, three of the seven blaCMY-2-positive isolates had an A nucleotide and four had a G nucleotide. In conclusion, the ceftriaxone resistance of nontyphoidal Salmonellaisolates in our hospital was attributed to the CTX-M-14 and CMY-2 ß-lactamases.