Listeriosis Cases and Genetic Diversity of Their L. monocytogenes Isolates in China, 2008-2019

Abstract

Listeriosis, caused by Listeria monocytogenes, is a severe food-borne infection. The nationwide surveillance in China concerning listeriosis is urgently needed. In the present study, 144 L. monocytogenes isolates were collected from the samples of blood, cerebrospinal fluid (CSF), and fetal membrane/placenta in China for 12 years from 2008 to 2019. We summarized these listeriosis patients' demographical and clinical features and outcomes. The susceptibility profile for 12 antibiotics was also determined by the broth microdilution method. Multilocus sequence typing (MLST) and serogroups of these listeria isolates were analyzed to designate epidemiological types. We enrolled 144 cases from 29 healthcare centers, including 96 maternal-neonatal infections, 33 cases of bacteremia, 13 cases of neurolisteriosis, and two cutaneous listeriosis. There were 31 (59.6%) fetal loss in 52 pregnant women and four (9.8%) neonatal death in 41 newborns. Among the 48 nonmaternal-neonatal cases, 12.5% (6/48) died, 41.7% (20/48) were female, and 64.6% (31/48) occurred in those with significant comorbidities. By MLST, the strains were distinguished into 23 individual sequence types (STs). The most prevalent ST was ST87 (49 isolates, 34.0%), followed by ST1 (18, 12.5%), ST8 (10, 6.9%), ST619 (9, 6.3%), ST7 (7, 4.9%) and ST3 (7, 4.9%). Furthermore, all L. monocytogenes isolates were uniformly susceptible to penicillin, ampicillin, and meropenem. In summary, our study highlights a high genotypic diversity of L. monocytogenes strains causing clinical listeriosis in China. Furthermore, a high prevalence of ST87 and ST1 in the listeriosis should be noted.

Keywords: Listeria monocytogenes; antibiotic resistance profile; isteriosis; multilocus sequence typing; neonatal listeriosis.

Figure 1

Distribution of infection types of 144 listeriosis cases in China between 2008 and 2019.

Figure 2

Representation of analysis and phylogeny of L. monocytogenes strains collected from patients with listeriosis in 15 cities/provinces in China. A complete picture of the phylogeny was constructed by the maximum likelihood method using seven housekeeping genes of multilocus sequence typing (MLST) of the above strains using MEGA (Version 10.0.5) and iTOL v4. from left to right: 1 Sex; 2 Age; 3 Pregnancy or not; 4 Mother/newborn (both mothers and newborns were infected in the cases of LM44, 39, 35); 5 Bacteremia; 6 Meningitis; 7 Sequence types; 8 Clonal complexes; 9 Serogroups; 10 Lineage; 11–22 MICs of 12 antibiotics (µg/ml); 23 Year of isolation of L. monocytogenes strains; 24 Adverse outcomes.

Figure 3

Risk factors of 48 nonmaternal-neonatal listeriosis cases.

Figure 4

Correlation between sequence type (ST) of L. monocytogenes strains, types as well as outcomes of patients with listeriosis. Minimum spanning tree analysis of L. monocytogenes strains conducted according to ST, demonstrating the relationships among 144 strains collected from patients with listeriosis in 15 cities/provinces. in the minimum spanning tree, the STs are displayed as circles; the size of each circle indicates the number of strains within this particular type. The founder ST was defined as that with the highest number of single-locus variants. STs varying by two alleles in their multilocus sequence typing (MLST) profiles (single-locus variants) are arranged in circles around the primary founder ST. (A) Relationship between infection types of the patients and STs of all 144 L. monocytogenes strains. (B) Relationship between outcomes of the patients and STs of all 144 L. monocytogenes strains.

Figure 5

The distribution of the Minimum inhibitory concentration (MIC) 144 clinical unique strains of L. monocytogenes for 12 antibiotics. Redline: the breakpoint for L. monocytogenes by CLSI.