Enterobacteria, Enteric Bacteria

The Enterobacteriaceae are the most common group of gram-negative rods and along with staphylococci and streptococci are among the most common bacteria that cause disease. These are gram-negative, facultatively anaerobic, rod-shaped bacteria that do not form endospores. Enterobacteria are distributed worldwide with some being saprophytes and others being plant and animal parasites. Many species are of considerable economic importance due to their pathogenic effects on agriculture and livestock.

Colonies of Gram-negative bacteria growing on MacConkey agar.
Gram-negative bacteria growing on MacConkey agar. Pink color indicates lactose fermentation

The natural habitat of gram-negative rods is intestinal tract of humans and animals. The group includes many genera (Escherichia, Salmonella Shigella, Enterobacter, Klebsiella Serratia, Proteus and others. Some enteric organisms, for example Escherichia coli, are part of the normal flora and incidentally cause disease, while others, the salmonella and shigella, are regularly pathogenic for humans.1

On the far end of the spectrum lies Yersinia pestis, the causative agent of the Black Plague, the most deadly pandemic disease of all times.2

The Enterobacteriaceae ferment a wide range of carbohydrates, possess a complex antigenic structure, and produce a variety of toxins and other virulence factors.1 Many species survive readily in nature and live freely anywhere water and minimum energy sources are available.

Pathogenic Enterobacteria

The majority of the bacterial species belonging to this family are pathogenic only in certain situations. While E.coli are normal and welcomed occupants of the intestinal flora, they can cause urinary tract infections if allowed to spread beyond the confines of the intestinal tract. However, some E.coli strains can cause intestinal disorders of varying severity. These intestinal pathogenic species are divided into subclasses (enterotoxigenic, enteroinvasive, enterohemorrhagic, and enteropathogenic) based upon their site of action, the presence of toxins, and indirectly by the symptoms they produce. A particularly frightening E.coli infection is neonatal meningitis which is caused by exposure to contaminated amniotic fluid.2

Recently, the evaluation of oncology hospital workers as potential reservoirs and disseminators of pathogenic bacteria has been described as a strategy for the prevention and control of healthcare-associated infections (HAIs). A total of 64 bacteria were isolated, including potentially pathogenic species. The most prevalent species was Enterobacter gergoviae (17%). The highest rates of resistance were observed for β-lactam , and 48% of the isolates were considered multiresistant. The significant prevalence of carriers of Enterobacteria and the profile of the isolates represents a concern.3


  1. Jawetz, Melnick, & Adelberg's medical microbiology. George F. Brooks, Janet S. Butel, Stephen A. Morse
  2. Antibacterial chemotherapeutic agents. Scott L. Dax
  3. Enterobacteriaceae isolates from the oral cavity of workers in a Brazilian oncology hospital (2015)



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