Escherichia hermanii: Introduction, Classification, Pathogenecity, Lab Diagnosis, Treatment, and Keynotes

Introduction of Escherichia hermanii

Escherichia hermannii is a gram-negative rod. This bacterium belongs to the family of Enterobacteriaceae. It was first described in 1982. It had been previously known as enteric group 11 of Escherichia coli but was later reclassified as a distinct species in the genus, Escherichia after identifying special genomic features that allowed differentiation from E. coli. In the Clinical Microbiology Laboratory, E. hermannii can be isolated from E. coli having the production of a specific yellow pigment as shown below picture. It is responsible only for rare cases of human infections which are supposed to be mostly a co-infector in polymicrobial infections and it is not considered truly pathogenic. Although, there is evidence of the pathogenicity of this organism, which seems to be able to cause infections even in immunocompetent, and non-predisposed individuals causing bacteremia, urinary tract, and central nervous system infections.

Escherichia hermanii colony morphology on MacConkey agar
Fig. Escherichia hermanii colony morphology on MacConkey agar-Medium indicator has faded the yellow pigment of this organism but still shows the pigment expression.

Classiication of Escherichia hermanii

  • Domain: Bacteria
  • Phylum: Pseudomonadota
  • Class: Gammaproteobacteria
  • Order: Enterobacterales
  • Family: Enterobacteriaceae
  • Genus: Escherichia
  • Species: E. hermannii
  • Binomial name: Escherichia hermannii

Pathogenicity of Escherichia hermanii

  • Bacteremia
  • Urinary tract infections (UTIs)
  • Central nervous system infection
  • Gastrointestinal infections
  • Peritonitis (abdominal cavity infection)
  • Conjunctivitis
  • Skin and soft tissue infection (SSTI)

Laboratory Diagnosis of Escherichia hermanii

Biochemical tests of E. hermannii

Gram Negative Rods of E. hermannii in Gram Staining of Culture
Fig. Gram Negative Rods of E. hermannii in Gram Staining of Culture (Mag.4000X)
  • Motility -Positive (+)
  • Pigment -Positive (+)
  • Catalase production -Positive (+)
  • Oxidase fermentation -Positive (+)
  • Indole-Positive (+)
  • Methyl Red-Positive (+)
  • Voges-proskauer -Negative (-)
  • Citrate -Negative (-)
  • Urease -Negative (-)
  • H2S Production -Negative (-)
  • Oxidase -Negative (-)
  • Deoxyribonuclease -Negative (-)
  • Lysine decarboxylase -Negative (-)
  • Ornithine decarboxylase -Positive (+)
  • Arginine dihydrolase -Negative (-)
  • Aesculine hydrolysis- d
  • Sucrose- d
  • Melibiose -Negative (-)
  • D-sorbitol -Negative (-)
  • Mucate -Positive (+)
  • KCN -Positive (+)
  • Gelatine -Negative (-)
  • Lactose-d
  • Phenylalanine deaminase -Negative (-)
  • D-mannitol -Positive (+)
  • Dulcitol- (-)
  • Salicin- d
  • Adonitol -Negative (-)
  • Raffinose- d
  • L-rhamnose -Positive (+)
  • Malonate -Negative (-)
  • Jordan tartrate- d
  • Lipase -Negative (-)
  • ONPG -Positive (+)
  • D-glucose gas production -Positive (+)
  • D-xylose -Positive (+)
  • Maltose -Positive (+)
  • Cellobiose -Positive (+)
  • D-glucose acid production -Positive (+)
  • Nitrate reductase -Positive (+)
  • Glycerol -Negative (-)
  • Acetate utilization – (+)
  • L-arabinose -Positive (+)
  • Myo-inositol -Negative (-)
  • D-Mannose -Positive (+)
  • Trehalose -Positive (+)
  • Alpha Methyl glucoside -Negative (-)

Keynotes
Positive (+): 90-100% Positive
Negative (-): 0-10% positive
(+): 76-89% positive
(-): 11-25% positive
d: 26-75% positive
v: strain instability

Urine Culture & Sensitivity Test Report-Positive showing Escherichia hermannii and its antimicrobial susceptibility testing (AST)  pattern
Report: Urine Culture & Sensitivity Test Report-Positive showing Escherichia hermannii and its antimicrobial susceptibility testing (AST) pattern

Treatment

Cephalosporins and aminoglycosides are the most common antibiotics used for the treatment of Escherichia hermannii-causing infections.

Keynotes on Escherichia hermanii

  • There are also available case reports regarding bloodstream infection by Escherichia hermannii in a neonate and E. hermannii as the sole cause of osteomyelitis in a patient with an open tibial shaft fracture.
  • A case report suggests that E. hermanni viscous materials contained mannose-rich exopolysaccharides contributing to its pathogenicity.

E. hermanii in BD™ Tryptic Soy Broth (TSB) wet mount microscopy

E. hermanii in BD™ Tryptic Soy Broth (TSB) wet mount microscopy
Fig. E. hermanii in BD™ Tryptic Soy Broth (TSB) wet mount microscopy

Escherichia hermannii in Wet Mount Microscopy

Video: E. hermannii in Wet Mount Microscopy at a magnification of 1600X

Bibliography

  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6473853/
  • bioinfo.bisr.res.in/cgi-bin/project/docter/get_details.cgi
  • https://en.wikipedia.org/wiki/Escherichia_hermannii
  • https://www.jcdr.net/article_fulltext.asp?id=8304
  • https://casereports.bmj.com/content/12/11/e231206
  • https://academic.oup.com/femspd/article/59/3/456/497186
  • https://journals.asm.org/doi/10.1128/JCM.01119-08

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