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. 2021 Jul 1;21(1):632.
doi: 10.1186/s12879-021-06340-z.

Characterization of Salmonella serotypes prevalent in asymptomatic people and patients

Haiyan Xu #  1 , Weibing Zhang #  1 , Kai Zhang #  2   3   4 , Yue Zhang  2   3   4 , Zhenyu Wang  2   3   4 , Wei Zhang  1 , Yang Li  2   3   4 , Qiuchun Li  5   6   7
Affiliations

Characterization of Salmonella serotypes prevalent in asymptomatic people and patients

Haiyan Xu et al. BMC Infect Dis. .

Abstract

Background: Infection with Salmonella enterica usually results in diarrhea, fever, and abdominal cramps, but some people become asymptomatic or chronic carrier as a source of infection for others. This study aimed to analyze the difference in serotype, antimicrobial resistance, and genetic profiles between Salmonella strains isolated from patients and those from asymptomatic people in Nantong city, China.

Methods: A total of 88 Salmonella strains were collected from patients and asymptomatic people from 2017 to 2018. Serotyping, antimicrobial susceptibility testing, and PFGE analysis were performed to analyze the characteristics of these strains.

Results: Twenty serotypes belonging to 8 serogroups were identified in the 88 Salmonella strains. S. Typhimurium remained to be the predominant serotype in strains from both patients and asymptomatic people. Among the 27 strains from patients, S. Enteritidis and S. Rissen were shown as the other two major serotypes, while S. London, S. Derby, and S. Meleagridis were demonstrated as the other significant serotypes among the 61 strains from asymptomatic people. Antimicrobial resistance testing revealed that 84.1% of strains from both resources were multi-drug resistant. PFGE displayed a highly discriminative ability to differentiate strains belonging to S. Derby, S. Typhimurium, etc., but could not efficiently differentiate serotypes like S. Enteritidis.

Conclusions: This study's results demonstrated that S. Typhimurium could cause human infection in both symptomatic and asymptomatic state; S. London, S. Derby, and S. Meleagridis usually cause asymptomatic infection, while S. Enteritidis infection mainly results in human diseases. The high multi-drug resistance rate detected in the antimicrobial resistance and diverse PFGE profiles of these strains implied that the strains were isolated from different sources, and the increased surveillance of Salmonella from both patients and asymptomatic people should be taken to control the disease.

Keywords: Antimicrobial susceptibility; Asymptomatic infection; PFGE; Salmonella.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Prevalence of Salmonella serotypes in humans. The distribution of Salmonella serotypes among 88 isolates from humans (a), including 61 isolates from asymptomatic people (b) and 27 isolates from patients (c). The B group, C group, and E group represents Salmonella serogroup B (O:4), C [C1(O:7); C2-C3(O:8)], E [E1(O:3,10); E4 (O:1,3,19)], respectively
Fig. 2
Fig. 2
Antimicrobial resistance of human Salmonella isolates. The percentage of strains with resistance to each antimicrobial agent. The “R” displayed as red column represents resistant, the “I” displayed as orange column represents intermediate, and the “S” displayed as green column represents susceptible
Fig. 3
Fig. 3
PFGE analysis of Salmonella strains. PFGE profiles and phylogenic relationship of strains belonging to C1 and C2-C3 groups (a), E1 and E4 groups (b), S. Derby (c), S. Typhimurium (d), and S. Enteritidis (e). The strains in red box were isolated from patients. The “I”, “II”, “III”, and “IV” represents the four clusters of S. Typhimurium (including S. Typhimurium monophasic variants) divided by PFGE analysis
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