Strain typing and antimicrobial susceptibility of Salmonella enterica Albany isolates from duck farms in South Korea

Abstract

Salmonella enterica is distributed worldwide and is a common cause of bacterial food poisoning in humans and a serious public health problem. Although duck meat consumption has recently increased in Korea, studies on the epidemiological relationship between S. enterica contamination in duck farms are scarce. Salmonella enterica serovar Albany isolates recovered from duck farms were analyzed using two typing methods - IR Biotyper® (IRBT) and multilocus variable-number tandem repeat analysis (MLVA). The clustering results were compared with the epidemiological survey findings and the antimicrobial resistance profiles. From April 2019 to October 2020, 20 individual feces per farm from 5-6-week-old ducks were collected repeatedly from 105 duck farms. Salmonella spp. isolated from duck feces were identified using PCR and multilocus sequence typing to investigate the prevalence and distribution of the Salmonella serovars. The prevalence of S. enterica was 19%, and S. enterica Albany was the predominantly recovered isolate. The S. enterica Albany isolates underwent antimicrobial susceptibility testing to determine the minimum inhibitory concentration. MLVA and IRBT methods established relatedness and diversity among the S. enterica Albany isolates. Multidrug-resistant S. enterica Albany was distributed in all the farms. Antimicrobial resistance profiles reflected the duck farm characteristics and isolates recovered from the same farm showed an identical profile. Isolates repeatedly recovered from the same farm also showed identical IRBT clusters and MLVA groups. These findings suggest that the isolates remained on the duck farm and re-infected new duck flocks. Thus, proper cleaning and disinfection is required before the farms are repopulated.

Keywords: Antimicrobial resistance; Duck; Epidemiological survey; Salmonella enterica Albany; Typing method.

Fig. 1

Prevalence and distribution of Salmonella serovars on duck farms. Positive rates of Salmonella spp. ranged from 0 to 100% in duck farms (A). A total of 11 serovars were detected, of which S. enterica Albany was the most common. The list includes farms where the same serotype was repeatedly recovered from existing and new duck flocks (asterisks) (B).

Fig. 2

Isolates of Salmonella enterica Albany repeatedly recovered from the same farm indicated identical antimicrobial resistance profiles (A1, FIS-SXT-NAL; A2, FIS-SXT-NAL-CIP; A3, FIS-SXT-NAL-AMP; A4, FIS-SXT-NAL-STR; A6, FIS-SXT-NAL-CIP-AMP-CHL; A7, FIS-SXT-NAL-AMP-CHL-TET; A9, FIS-SXT-NAL-CIP-AMP-CHL-TET). A5, A8, A10, and A11 antimicrobial resistance profiles had one isolate each and were not represented. Two or more isolates from 24 farms had identical antimicrobial resistance profiles.

Fig. 3

Dendrogram clustered using IRBT for 94 Salmonella enterica Albany isolates. The vertical line represents the cutoff value (0.126), and all isolates were classified into 16 clusters via IRBT. For ease of reading, clusters composed of more than two isolates are shaded in orange; two isolates are shaded in yellow; single isolates are shaded in green.

Fig. 4

Assessment of 2D scatter plot for 94 isolates of PCA using IRBT. The target was the farms. Isolates delimited using ellipses show the same farm, and points within the ellipse were located close together. Some farms overlap, but non-overlapping farms were distinguished in the spectra.

Fig. 5

Assessment of 2D scatter plot for 94 isolates of PCA using IRBT. The target was the MLVA groups. Isolates delimited using lines show the identical MLVA groups (M1, M3, and M4). These groups did not overlap, and a distinction was made in the spectra.

Fig. 6

Comparison of strain typing results and antimicrobial resistance profiles. The typing results of MLVA (A) and IRBT (B) for the 94 isolates did not consistently correspond with the antimicrobial resistance profiles. The isolates recovered from the same duck farms showed identical MLVA results, IRBT findings, and antimicrobial resistance profiles. M2 and M5 groups had one isolate each and were not represented (C).