Ohio Microbiology Program - Laboratory Capabilities

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Indicator bacteria are routinely measured by means of membrane-filtration or liquid broth most-probable number techniques. Find out more about the analytical methods used for standard bacterial indicators.

 

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INDICATOR BACTERIA CULTURE METHODS

Indicator bacteria are routinely measured by means of membrane-filtration or liquid broth most-probable number techniques.

  • Total coliforms, fecal coliforms, and Escherichia coli (E. coli) are in the total-coliform group.
  1. Total coliforms are found in animal wastes, soils, on vegetation, and in industrial wastes.
  2. Fecal coliforms are total coliforms that are able to grow at elevated temperatures and are often, but not always, associated with fecal contamination. 
  3. E. coli is one species in the fecal-coliform group, is a natural inhabitant of the gastrointestinal tract of warmblooded animals, and is used to provide direct evidence of fecal contamination.
  • Enterococci are a group of bacteria that have a different shape (the cells are round) and survival characteristics than total coliforms.  They are generally associated with fecal contamination.
  • Clostridium perfringens (C. perfringens) is a spore-forming bacterium that is present in human and animal wastes, but in lower concentrations than standard bacterial indicators. Because spores are resistant to environmental stress, they may be useful surrogates for other stress-resistant pathogens.

 

ACTINOMYCETES AND CYANOBACTERIA

The OWML analyzes samples for other types of bacteria that are not indicator bacteria.  

  • Actinomycetes are not fecal organisms.  They are a group of bacteria with fungal-type morphology and are nuisance organisms in water and wastewater treatment processes.  Most actinomycetes form chemicals which impart an earthy-musty odor to public water supplies.
  • Cyanobacteria are a group of bacteria capable of photosynthesis.  Some strains are capable of producing cyanotoxins which are harmful to humans and animals.   This toxin production along with the resultant green, blue-green, or brown colored water and mats are referred to as cyanobacterial harmful algal blooms (cyanoHABs), although cyanobacteria are not technically algae.

 

COLIPHAGE

Coliphage are viral indicators that infect and replicate in coliform bacteria, primarily E. coli.  The OWML analyzes water samples by use of two USEPA-approved coliphage methods—the two step enrichment procedure (presence or absence results) and the single-agar layer procedure (quantitative results).

 

PROTOZOAN PATHOGENS

Cryptosporidium and Giardia are widely distributed in the aquatic environment and are the principal protozoan pathogens that affect the public health acceptability of waters in the United States.  Both produce environmentally resistant forms (oocysts and cysts) that allow for their extended survival in water.  The OWML analyzes water samples for Cryptosporidium and Giardia by use of the USEPA-approved Filtration/IMS/FA method.

 

MICROBIAL SOURCE TRACKING METHODS

A wide range of techniques are available in the emerging field of microbial source tracking (MST) to help identify sources of fecal contamination.  Which methods are chosen for a study depend on the study objectives, the number of potential contamination sources, and the funds available; most often, multiple source tracking tools are needed.  At the present time, the OWML routinely analyzes samples by use of three MST techniques, only a small part of the source tracking toolbox.

 

MI METHODS

  • Antibiotic resistance methods
  • Bacterial pathogens
  • Next generation sequencing