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        Knowledge for the CommonWealth

Water and Wastewater Microbiology

Crop and Soil Environmental News, February 2001

Charles Hagedorn, Professor
Extension Specialist, Water Quality


The information is divided into three parts as listed below. Much detailed information on water and wastewater microbiology is available on-line at Virginia Tech and other locations, and this material is based heavily on these electronic resources. Many links to the appropriate pages are provided below. All PDF files have been prepared by the author and contain no computer viruses. (


  1. Pathogens and Diseases
  2. Indicators and Detection
  3. Trends and New Research


Pathogens and the Fecal-Oral Route ( Pathogens and diseases spread by the fecal-oral route (waterborne diseases) can be caused by bacteria (salmonellosis, typhoid fever, and cholera), viruses (viral gastroenteritis, and hepatitis A), and protozoa (amoebic dysentery and cryptosporidiosis). Many pathogenic bacteria, viruses, and protozoa are passed from one host to the next by the "fecal-oral route" of transmission, and water usually serves as the carrier for these organisms. Of particular concern are bacterial pathogens such as Salmonella, Shigella, diarrheagenic Escherichia coli (including E. coli 0157:H7), Campylobacter and Vibrio. Many viruses can be transmitted by water, including poliovirus, rotaviruses, Norwalk viruses, and hepatitis A and E viruses. Protozoan pathogens that can be transmitted by water include Giardia and Cryptosporidium.

Bacterial Pathogens - "The Big 5"
Salmonella - salmonellosis
S. typhimurium - typhoid fever
Shigella - shigellosis
Enterotoxigenic E. coli (ETEC) - diarrhea
Vibrio cholerae - cholera
Camplyobacter jejuni - gastroenteritis

Viral Pathogens - Over 120 enteric viruses, all pathogenic to humans, low minimum infectious dose
Hepatitis A - hepatitis
Norwalk-like agents - gastroenteritis
Virus-like 27 nanometer particles - gastroenteritis
Rotavirus - gastroenteritis

Protozoal Pathogens - "The Big 3" in Temperate Zone Countries
Cryptosporidium parvum - cryptosporidiosis
Giardia lamblia - giardisis
Entamoeba histolytica - amoebic dysentery

Different pathogens can be transmitted by a variety of sources. For example, Giardia and Cryptosporidium outbreaks are often associated with cattle, and E. coli 0157:H7 outbreaks are usually tied to beef products. Giardia is also spread by deer (backpacker's disease), and Canada geese feces have been found to contain Cryptosporidium, Giardia, and Campylobacter. Salmonellosis is commonly associated with hogs (as well as Vibrio), poultry, and waterfowl, and Campylobacter is widespread in poultry and waterfowl. Most viral gastroenteritis is caused by contact with human feces. All of these organisms pose a risk to human public health.

Disease Outbreaks Today ( Waterborne Diseases and the fecal-oral route
      Worldwide - 250 million cases, 10 million deaths
      U.S. - 30-40 outbreaks/yr, 10,000 cases total (these are averages, range is much wider)
            Onsite: Average of 10-12 outbreaks/yr, 2,500 cases (no reporting required)
            Community: 10-15 outbreaks/yr, 5,000 cases (reporting is mandatory, CDC)
            Recreational: 10-12 outbreaks/yr, 2,000 cases (no reporting required)
      Why so low in the U.S.?
            Community wastewater treatment
            Standards for onsite systems
            Treatment of drinking water
            Mandatory nationwide vaccination programs

With filtering and chlorinating of public water supplies, drinking water in the U.S. is among the cleanest in the world. These practices, combined with proper sewage treatment and immunization have virtually eliminated diseases such as typhoid fever, cholera, and polio in the U.S. (but these diseases are still common in many other parts of the world). There are some 30-40 outbreaks of waterborne disease and roughly 10,000 cases of illness from these outbreaks in the U.S. each year. This is less than 10% of the number of out breaks that occurred some 40 years ago, before the development of public water and sewer systems. There are some 10 to 20 outbreaks yearly with roughly 2,000 cases of illness associated with recreational water use.

Who is at Risk?

Roughly one-half of the current outbreaks and one-third of the illnesses mentioned above are from contamination in well water. Seepage or overflow from improperly functioning septic systems has been cited as the most common cause of well water contamination. Reporting outbreaks and illnesses of waterborne disease in non-community water sources and recreational waters is voluntary, so nobody knows how many disease outbreaks caused by contaminated well water or by recreational exposure to contaminated water there really are.


( Non-pathogenic bacteria such as total and fecal coliforms, and the enterococci - fecal streptococci are used as indicators, because they indicate that fecal pollution has occurred, and that microbial pathogens might be present.

Total Coliforms
Escherichia, Enterobacter, Klebsiella, Citrobacter

Fecal Coliforms
Escherichia, Klebsiella, Citrobacter (60% to 90% of total coliforms are fecal coliforms) 90%+ of fecal coliforms are Escherichia (usually E. coli) (

Presence-Absence Test (

Most-Probable Number (

Membrane Filtration (

The "Fecal Streptococci" Enterococcus - 18 species, all enteric (
Streptococcus - 40+ species, 8-10 enteric

Membrane Filtration (


The Future There have been numerous out breaks where the tested waters were coliform negative. Clearly, improvement in pathogen detection will require methods that focus on other microbes as indicators.

Virus Detection (coliphages?

Protozoal Detection? (a DNA probe?

Bacterial Source Tracking

The total maximum daily load (TMDL) initiative currently being implemented in the U.S. will result in the identification of waters that contain fecal bacteria of different origins, such as human, wildlife, and livestock. Correct source identification will allow development of BMPs that target actual sources, rather than estimated ones.

Source Tracking Webpage:

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