Dissemination of extended-spectrum cephalosporin (ESC)-resistant
Salmonella is a public health concern in the egg production industry. ESC-resistant
Salmonella often acquires the
bla gene via insertion sequences (ISs). Therefore, this study aimed to assess antimicrobial resistance in
Salmonella from Japanese layer breeding chains and egg processing chains, and determine the genetic profiles of IS-like elements in ESC-resistant
Salmonella. Antimicrobial susceptibility testing was performed on 224 isolates from 49 facilities involving layer breeder farms, hatcheries, pullet-rearing farms, and layer farms in breeding chains along with egg processing chains. ESC-resistant
Salmonella strains were whole-genome sequenced. Among them, 40 (17.9%) were resistant to at least streptomycin, tetracycline, ampicillin, chloramphenicol, cefpodoxime, nalidixic acid, ciprofloxacin, and/or kanamycin despite lacking resistance to azithromycin and meropenem. Moreover, 15 were ESC-resistant
Salmonella harboring
blaCMY-2 (
Salmonella enterica serovar Ohio, n=12;
S. Braenderup, n=1; untypeable with O7:b:-, n=1) and
blaCTX-M-14 (
S. Cerro, n=1). IncA/C
2 plasmids containing IS
Ecp1, IS
26, and multiple antimicrobial resistance genes (including
blaCMY-2) were identified in
S. Ohio isolates from pullet-rearing and layer farms belonging to the same company. Chromosomal integration of partial or whole IncA/C
2 plasmids was seen with two
S. Ohio isolates via IS
Ecp1 or IS
26, respectively. Antimicrobial resistance genes such as
blaCMY-2 might be transmitted among the upper and the lower levels of layer breeding chains via the replicon type IncA/C
2 plasmids containing IS
Ecp1 and IS
26.
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