Abstract
Morganella morganii, which is often regarded as a human commensal organism, can be an opportunistic pathogen, causing a variety of clinical infections with serious morbidity and mortality. An efficient and convenient method for subtyping and identifying M. morganii strains in epidemiological surveillance and control is urgently needed. Serotyping based on bacterial surface polysaccharide antigens (O-antigen or K-antigens) is a standard subtyping method for many gram-negative bacteria. Here, through whole genome sequencing and comparative genomics analysis of 27 strains, we developed a molecular serotyping scheme based on the genetic variation of O-antigen gene clusters (O-AGC) in M. morganii, and 11 distinct O-AGC types were identified. A conventional serotyping scheme was also developed by the production of antisera and agglutination experiments, which was shown to be perfectly consistent with the molecular serotyping scheme, confirming that the variation in M. morganii O-AGC correlated with phenotypic O-antigen diversification. Furthermore, a microsphere-based suspension array (MSA) with high specificity was developed based on the specific genes within each O-AGC type. The sensitivity of MSA was determined to be 0.1 ng of genomic DNA and 103 CFU of pure culture. We further analyzed 104 M. morganii genomes available in GenBank, and an additional six novel O-AGC types were identified, indicating that the extension of this molecular serotyping scheme is convenient. Our work provides an important tool for the detection and epidemiological surveillance of M. morganii, and this method has the potential to be widely utilized, especially for bacterial genera/species without an efficient typing approach.
Highlights
Morganella morganii is a Gram-negative bacillus belonging to the Enterobacteriaceae family, and it is a common inhabitant of the environment and intestinal tracts of humans, mammals, and reptiles (Erlanger et al, 2019)
A typical LPS molecule consists of a mix of well-conserved and highly variable structural elements (Supplementary Figure 1), including (i) lipid A, a component in the outer leaflet of the outer membranes that contributes to the barrier properties of bacteria and provides a pathogen-associated molecular pattern (Simpson and Trent, 2019); (ii) the core oligosaccharide, which is relatively conserved within a species, attaches to lipid A and is involved in the stability of the outer membrane (Whitfield and Trent, 2014); and (iii) the O-antigen or O-polysaccharide (O-PS), which is composed of hypervariable oligosaccharide repeating units (O-units) composed of two to eight different monosaccharide residues or identical sugars in some bacteria (Valvano, 2003)
A molecular serotyping scheme based on sequence variations of surface polysaccharide antigen synthesis genes has been rapidly established for several bacterial species
Summary
Morganella morganii is a Gram-negative bacillus belonging to the Enterobacteriaceae family, and it is a common inhabitant of the environment and intestinal tracts of humans, mammals, and reptiles (Erlanger et al, 2019). The approach of traditional serotyping is limited by its high cost, high time and labor requirements, complicated procedures, cross-reactivity and subjective interpretation (Sumrall et al, 2020; Bian et al, 2021; Chaiden et al, 2021) To address these issues, many DNA-based serotyping methods on variant platforms targeting specific genes involved in the synthesis of surface polysaccharide antigens have been developed (Li et al, 2018, 2020; Zürn et al, 2020; Ouattara et al, 2021). A molecular serotyping scheme based on sequence variations of surface polysaccharide antigen synthesis genes has been rapidly established for several bacterial species. By sequencing and comparatively analyzing the genomes of 27 M. morganii strains from Shanghai Disease Control and Prevention, China, we established a molecular serotyping scheme for M. morganii with 11 different putative O-AGC types. Our work provides a promising and efficient tool for molecular diagnostics and epidemiological surveillance of M. morganii
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