Abstract
Simple SummarySalmonella Gallinarum causes fowl typhoid in all ages of chickens, which results in economic loss of commercial chicken farms. The disease has been eradicated in many developed countries, but is still prevalent in Korea. In this study, we investigated virulence and genetic variation of S. Gallinarum from Korea, between 2014 and 2018. The results indicated that virulence was increased, which was associated with genetic change over time. Therefore, surveillance of genetic change associated with virulence increase is necessary for monitoring of S. Gallinarum isolates for dissemination.Salmonella Gallinarum is a Gram-negative bacteria that causes fowl typhoid, a septicemic disease with high morbidity and mortality that affects all ages of chickens. Although vaccines and antimicrobials have been used nationwide to eradicate the disease, the malady is still prevalent in Korea. In this study, we investigated the virulence and genetic variation of 116 S. Gallinarum isolates from laying hens between 2014 and 2018. A total of 116 isolates were divided into five Gallinarum Sequence Types (GST) through clustered regularly interspaced short palindromic repeats (CRISPR) subtyping method. The GSTs displayed changes over time. The 116 isolates showed no difference in virulence gene distribution, but the polyproline linker (PPL) length of the SpvB, one of the virulence factors of Salmonella spp., served as an indicator of S. Gallinarum pathogenicity. The most prevalent PPL length was 22 prolines (37.9%). The shortest PPL length (19 prolines) was found only in isolates from 2014 and 2015. However, the longest PPL length of 24 prolines appeared in 2018. This study indicates that PPLs of S. Gallinarum in Korea tend to lengthen over time, so the pathogenic potency of the bacteria is increasing. Moreover, the transition of GST was associated with PPL length extension over time. These results indicate that surveillance of changing GST and PPL length are necessary in the monitoring of S. Gallinarum isolates.
Highlights
Fowl typhoid (FT), caused by Salmonella enterica subsp. enterica serovar Gallinarum biovarGallinarum
These results indicate that surveillance of changing Gallinarum Sequence Types (GST) and polyproline linker (PPL) length are necessary in the monitoring of S
This study indicates that PPLs tend to lengthen over time in Korea, and it implies that the pathogenic potency of the field-isolated bacteria in Korea is increasing
Summary
Fowl typhoid (FT), caused by Salmonella enterica subsp. enterica serovar Gallinarum biovarGallinarum Gallinarum), is a host-adapted septicemic bacterial disease associated with high morbidity and mortality in all ages of poultry, and the infection of chicken has been a serious problem in. The disease has several transmission routes: through food, environment, or contaminated eggs, causing significant financial losses for farming industries. FT critically affects chicken farms economically worldwide, except for those countries that are not suffering from the disease [3]. FT has been eradicated in many developed countries, including the United States [4], Animals 2020, 10, 2346; doi:10.3390/ani10122346 www.mdpi.com/journal/animals. The policy for control and eradication of FT in Korea (similar to the National Poultry Improvement Plan in the United States) has been underway since the 1970s [5], the disease is still prevalent. Most of the commercial layer population consists of brown-shell egg layers, which are more susceptible to FT [2]; red poultry mites, which is a significant mechanical vector for transmission of FT, have spread to poultry houses nationwide [6]
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