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Environmental Microbiology Section

We assist environmental health officials and public health epidemiologists in investigating environmental samples that may cause illness in the general public.

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One of the most significant tests performed by the laboratory is for the detection of antibiotic drug residues in milk. Appreciable amounts of antibiotics are administered to control diseases in dairy cattle. Unfortunately, sometimes these antibiotics can enter the milk supply. The presence of antibiotic residues in milk could cause allergic reactions, affect starter cultures or create an environment favorable for resistant bacteria.

This program, which became effective around 1995, permits the dairy industry and the state regulatory groups, New Mexico Department of Agriculture, to maintain the program. The involvement of the FDA includes quarterly monitors, which necessitate each state submitting 5 load samples to a regional FDA laboratory, where samples are checked for the beta-lactams, as well as tetracyclines, sulfonamides and chloramphenicol. Milk that is confirmed positive with antibiotics is destroyed and not used for production of other milk products.


In November 1999, the State of New Mexico adopted Chapter Five of EPA's "Manual for the Certification of Laboratories Analyzing Drinking Water: Criteria and Procedures" Fourth Edition (EPA 815-B-97-001) as both the technical manual and checklist for the State.

Bacterial Contamination

In spite of strict EPA regulations governing the bacterial quality of water supplies, there is still some water systems around the state that fail to meet these regulations. The contamination of private water supplies is also a common problem in New Mexico as well as around the nation.

Health Risks from Contaminated Wells

Coliform bacteria are excreted from the intestinal tracts of some warm-blooded animals. They are generally harmless, but serve as an indicator that other more dangerous organisms may be present. Water contaminated with coliform bacteria often contains pathogenic (disease-causing) bacteria and ingesting it can cause vomiting and/or diarrhea.

The EPA has adopted total coliform content as the standard used to gauge water quality. Laboratory tests do not differentiate between pathogenic and non-pathogenic bacteria. Therefore, any water supply contaminated with coliform bacteria is considered unsafe for consumption.

Water Sample Analysis

A laboratory analysis of water from a water supply is a very valuable tool in the evaluation of water supplies. A single water test is not enough to guarantee that a well is safe to drink from. A sample that indicates no bacterial growth only indicates that the water was safe at the time of sampling. Intervening events such as heavy rainfall, a failed sewage system contamination through back siphonage, a chemical spill, or a broken water line may have rendered the water supply to change. Water quality is also dependent on other factors, such as proper well construction and location, groundwater table, soil formation and other geological and mechanical factors. It is recommended that a water analysis be performed whenever repairs or alterations are made to the water supply system or when possible contamination of the well is suspected.

Water Sampling Procedures

Sterile polypropylene water sample bottles are available from the Scientific Laboratory Division. Only containers prepared by the SLD Media Prep unit will be accepted for testing.

Instructions for collecting water samples are as follows:

  1. Choose a clean non-leaking tap without aerators, strainers or attachments. Water samples should not be collected from outside hydrants, leaky faucets, or faucets with aerators or faucet filters still attached. These circumstances may result in a false positive test result when in fact the water is safe.
  2. Flush cold water tap 3 to 5 minutes before collecting sample. Carefully remove the cap and fill bottle to the shoulder line without touching the lip of the bottle to tap rim. DO NOT RINSE OUT BOTTLE. Replace cap and secure tightly.
  3. Identify sample and fill out a sample form (SLD#521--Microbiological Water Report) for each sample to be submitted for testing. Complete all information requested on the form.

The New Mexico Regulations that govern water supplies states that any public water system containing the presence of coliforms is not in compliance with Safe Drinking Water Standards. Systems with the presence of fecal coliforms are considered an immediate danger and water should be boiled for three minutes or more before consuming.

Water samples containing noncoliform bacteria are considered invalid samples, since the presence of excessive bacteria may inhibit the growth of coliforms. Although, these circumstances may indicate a need to disinfect the water supply, a commonly found problem is that a kitchen faucet with a swivel joint may have been used. It is recommended that another water sample be taken from a different tap within the house or system. If the results remain the same, then that is a good indication that the problem may be a contaminated water supply.

If it is determined that coliforms are absent, please remember that this is an indication of the safety of your water at the time that this sample was collected. It does not guarantee that your water will remain that way. The water should be retested following any repairs or maintenance to the lines.

Treatment for a Contaminated Water Supply

Treating a coliform contamination is relatively simple and inexpensive. The most common method known is shock chlorination. Chlorine is a universal disinfection agent used in water supplies. Its availability is found in many forms, the two most commonly used are calcium hypochlorite (dry chlorine) and sodium hypochlorite (household bleach). Dry chlorine contains about 65% calcium hypochlorite, while household bleach contains about 5.25% sodium hypochlorite.

Microbiological Drinking Water Laboratory Certification Program

The Department of Health Scientific Laboratory Division administers the State of New Mexico Microbiological Drinking Water Laboratory Certification Program. If you have any questions about the program, either in general such as how your lab can get certified, or specific technical questions like if you can report numbers of coliforms when using MMO-MUG, please contact the Certifying Authority or Laboratory Evaluation Officer.

Certifying Authority

Nicole Espinoza 505-383-9127

Laboratory Evaluation Officer (LEO)

Erica Swanson 505-383- 9120


Please read our Instructions for Food Samples for full details on how to collect, handle, and transport samples to us.