Detection of Salmonella enterica isolates producing CTX-M Cephalosporinase in U.S. livestock populations

Abstract

We report the detection of Salmonella carrying bla(CTX-M) in U.S. livestock populations. We identified 12 of 2,034 (0.6%) Salmonella isolates originating from turkeys, horses, and pigs from at least 6 U.S. states, all carrying bla(CTX-M-1), many on a pandemic sequence type 1 IncN plasmid.

Fig 1

MICs of 26 antimicrobial drugs for 13 Salmonella clinical isolates containing the bla_CTX-M genetic element (numbers of isolates are shown in the body of the figure). Broken lines represent susceptible breakpoints, and solid lines represent resistant breakpoints when available. Corresponding to the concentration listed at the top of each column (μg/ml), the included range of each antimicrobial is shown in gray. a, amikacin MICs were not determined for isolate 11-9696. b, clavulanic acid and tazobactam were included at fixed concentrations of 4 μg/ml. c, isolate 11-13665 (S. Bredeney) was resistant to cefoxitin and the β-lactamase inhibitors. d, isolate 11-13094 (Salmonella with rough serotype O:d:e,n,z15) was susceptible to gentamicin. e, isolates 11-13094 (Salmonella with rough serotype O:d:e,n,z15) and 11-104 (S. Ouakam) were susceptible to kanamycin and streptomycin. f, the 5 S. Anatum isolates were resistant to chloramphenicol, tetracycline, and trimethoprim-sulfamethoxazole. g, the 5 isolates susceptible to sulfisoxazole were the S. Ouakam isolates except 11-9696.

Fig 2

(A) Plasmid content of 13 Salmonella clinical isolates containing the bla_CTX-M genetic element originally submitted to the NVSL for serotyping. Lanes: 1, BAC-Tracker supercoiled DNA ladder; 2, 11-13049; 3, 11-13094; 4, 11-13665; 5, 11-13933; 6, 11-104; 7, 11-2362; 8, 11-2945; 9, 11-2946; 10, 11-3665; 11, 11-4809; 12, 11-4872; 13, 11-6604; 14, 11-9696; 15, control plasmid DNA containing bla_CMY-2; 16, BAC-Tracker supercoiled DNA ladder. (B) Southern blot hybridization using CTX-M probe of plasmid content of 13 Salmonella clinical isolates containing the bla_CTX-M genetic element originally submitted to the NVSL for serotyping. Lanes: 1, BAC-Tracker supercoiled DNA ladder; 2, 11-13049; 3, 11-13094; 4, 11-13665; 5, 11-13933; 6, 11-104; 7, 11-2362; 8, 11-2945; 9, 11-2946; 10, 11-3665; 11, 11-4809; 12, 11-4872; 13, 11-6604; 14, 11-9696; 15, control plasmid DNA containing bla_CMY-2; 16, BAC-Tracker supercoiled DNA ladder.

Fig 3

(A) Dendrographic analysis of XbaI PFGE data for five Salmonella serovar Anatum clinical isolates containing the bla_CTX-M genetic element. (B) Dendrographic analysis of XbaI PFGE data for six Salmonella serovar Ouakam clinical isolates containing the bla_CTX-M genetic element.