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BBB - Miscellaneous enterics

Bad Bug Book:
Foodborne Pathogenic Microorganisms and Natural Toxins Handbook
Miscellaneous enterics

A new version of the Bad Bug Book was released in 2012, below is a previous version.


1. Name of the Organism:

Miscellaneous enterics, Gram-negative genera including: Klebsiella, Enterobacter, Proteus, Citrobacter, Aerobacter, Providencia, Serratia

These rod-shaped enteric (intestinal) bacteria have been suspected of causing acute and chronic gastrointestinal disease. The organisms may be recovered from natural environments such as forests and freshwater as well as from farm produce (vegetables) where they reside as normal microflora. They may be recovered from the stools of healthy individuals with no disease symptoms. The relative proportion of pathogenic to nonpathogenic strains is unknown.

2. Nature of Acute Disease:

Gastroenteritis is name of the disease occasionally and sporadically caused by these genera.

3. Nature of Disease:

Acute gastroenteritis is characterized by two or more of the symptoms of vomiting, nausea, fever, chills, abdominal pain, and watery (dehydrating) diarrhea occurring 12-24 hours after ingestion of contaminated food or water. Chronic diarrheal disease is characterized by dysenteric symptoms: foul-smelling, mucus-containing, diarrheic stool with flatulence and abdominal distention. The chronic disease may continue for months and require antibiotic treatment.

Infectious dose--unknown. Both the acute and chronic forms of the disease are suspected to result from the elaboration of enterotoxins. These organisms may become transiently virulent by gaining mobilizeable genetic elements from other pathogens. For example, pathogenic Citrobacter freundii which elaborated a toxin identical to E. coli heat-stable toxin was isolated from the stools of ill children.

4. Diagnosis of Human Illness:

Recovery and identification methods for these organisms from food, water or diarrheal specimens are based upon the efficacy of selective media and results of microbiological and biochemical assays. The ability to produce enterotoxin(s) may be determined by cell culture assay and animal bioassays, serological methods, or genetic probes.

5. Associated Foods:

These bacteria have been recovered from dairy products, raw shellfish, and fresh raw vegetables. The organisms occur in soils used for crop production and shellfish harvesting waters and, therefore, may pose a health hazard.

6. Relative Frequency of Disease:

Acute gastrointestinal illness may occur more frequently in undeveloped areas of the world. The chronic illness is common in malnourished children living in unsanitary conditions in tropical countries.

7. Course of Disease and Complications:

Healthy individuals recover quickly and without treatment from the acute form of gastrointestinal disease. Malnourished children (1-4 years) and infants who endure chronic diarrhea soon develop structural and functional abnormalities of their intestinal tracts resulting in loss of ability to absorb nutrients. Death is not uncommon in these children and results indirectly from the chronic toxigenic effects which produce the malabsorption and malnutrition.

8. Target Populations:

All people may be susceptible to pathogenic forms of these bacteria. Protracted illness is more commonly experienced by the very young.

9. Food Analysis:

These strains are recovered by standard selective and differential isolation procedures for enteric bacteria. Biochemical and in vitro assays may be used to determine species and pathogenic potential. Not being usually thought of as human pathogens, they may easily be overlooked by the clinical microbiology laboratory.

10. Selected Outbreaks:

For more information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.

11. Education and Background Resources:

Literature references can be found at the links below.

Loci index for genome Klebsiella spp.

Enterobacter spp.

Proteus spp.

Citrobacter spp.

Providencia spp.

 Serratia spp.

Available from the GenBank Taxonomy database, which contains the names of all organisms that are represented in the genetic databases with at least one nucleotide or protein sequence.