Enterobacterales

The order Enterobacterales comprises Gram-negative, non-spore-forming, aerobic/facultative anaerobic, partly motile, partly immotile rod-shaped bacteria. According to the phylogenetic system, Enterobacterales belong to the class Gammaproteobacteria in the phylum Proteobacteria.

Classification of the most important families in human pathology (Adeolu M et al. 2016). In the order Enterobacterales, the following family are taxonomically grouped since 2o16:

• Enterobacteriaceae with the genera:Escherichia, Citrobacter, Enterobacter, Klebsiella, Leclercia, Raoultella, Salmonella, Shigella. and others.
• Yersiniaceae with the genera: Yersinia, Rahnella, Rouxiella, Serratia, and others.
• Hafniaceae with the genera: Hafnia, Edwardsiella, and others.
• Morganellaceaewith the genera Morganella, Proteus, Providencia, etc.
• Erwiniaceae with the genera Erwinia, Pantoea, Phaseolibacter, Tatumella, and others.
• Pectobacteriaceaewith the genera Dickeya, Lonsdalea, Sodalis, etc.
• Budviciaceae with the genera: Budvicia, Leminorella, Pragia, and others.

About half of all nosocomial infections are caused by bacteria of the order Enterobacterales. With Escherichia coli and the coliform bacteria, the most important indicator bacteria belong to this order. Like all Gram-negative bacteria, the Endobacterales are endotoxin producers. Endotoxin is a lipopolysaccharide of the outer bacterial membrane that is released when the bacteria decay (in vivo and in vitro). When washed into the bloodstream, it acts as one of the most effective PAMPS capable of stimulating cell receptors with activation of a cytokine cascade through which, if unchecked reactivity can cause cytokine shock.

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All Enterobacterales show growth on simple solid as well as in liquid culture media. However, their differentiation is not possible either microscopically or by means of culture morphology. They are classically differentiated on the basis of various patterns of metabolic activity. The differentiation is classically based on different metabolic patterns, which are tested as biochemical reactions in the "coloured series". A very important metabolic performance is the question of the presence of the enzyme beta-galactosidase, which catalyses the degradation of lactose. Lactose-negative enterobacterales are suspect in terms of pathogenicity and need to be further differentiated.

For many microbiological questions, the assessment of the lactose cleavage ability is sufficient. Spies designated in this way are referred to as "coliform bacteria" (Hof H et al. 2016).

Another reliable differentiation method is MALDI-TOP mass spectrometry, which has the advantage that results are available in minutes.

Further differentiation is possible in order to perform species or serovar differentiation within the individual genera. This is done by determining the following antigen structures:

• O antigen: surface antigens, thermostable lipopolysaccharides in the bacterial cell wall
• Ha antigen: flagellar antigens, thermolabile flagellin proteins
• F antigens: fimbrial antigens, fimbrial proteins important in the process of adherence.
• K-antigens: capsular antigens, polysaccharides which are attached to the surface of the bacteria in encapsulated Enterobacteriales.
• OMP antigens: outer membrane proteins that act as porins that ensure the permeability of substances through the lipid bilayer.

1. Adeolu M et al. (2016)Genome-based phylogeny and taxonomy of the 'Enterobacteriales': proposal forEnterobacterales ord. nov. divided into the families Enterobacteriaceae, Erwiniaceae fam. nov., Pectobacteriaceae fam. nov.,Yersiniaceae fam. nov., Hafniaceae fam. nov., Morganellaceae fam. nov., and Budviciaceae fam. nov.. International Journal of Systematic and Evolutionary Microbiology 66:5575-559