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You are here: Home / Archives for E. coli

Heterotrophic Plate Count: What is HPC and when is the right time to use it?

Lyn Gandham

Heterotrophs are a group of microorganisms (bacteria, moulds and yeasts) that use organic carbon sources to grow and can be found in all types of water. In fact, the majority of bacteria found in drinking water systems are considered heterotrophs. Heterotrophic plate count (HPC) is a method that measures colony formation on culture media of heterotrophic bacteria in drinking water. Thus the HPC test (also known as Standard Plate Count) can be used to measure the overall bacteriological quality of drinking water in public, semi-public and private water systems.

The Limitations of HPC:

hpc plate count
Bacteria count

As stated by the Health Canada guidelines on HPC testing, “HPC results are not an indicator of water safety and, as such, should not be used as an indicator of potential adverse human health effects.” The World Health Organization (WHO) states that methods such as coliform testing are better indicators than HPC to test the sanitary conditions of water.

The HPC method does not indicate the specific heterotrophic bacteria present or their sources. Instead, HPC testing indicates the culturable organisms present, which could be as low as 1% of the total bacteria present. There are several factors that affect the genera of bacteria and their level of presence recovered by HPC. These factors include the type of medium used to grow the bacteria, what temperature is used for incubation, how long the plates are incubated, where the water sample was collected, the time of year and the age of the sample. It is also important to note that the concentrations and types of bacteria that are recovered at the same sampling location can vary over time.

Typically high levels of HPC bacteria in a distribution or plumbing system result from bacterial regrowth where bacteria that resisted treatment grow or those that were injured during treatment recover.

How do we interpret HPC results?

For HPC, regulations set out by Health Canada are followed under the Canadian Drinking Water Quality Guidelines: “No maximum acceptable concentration (MAC) is specified for heterotrophic plate count (HPC) bacteria in water supplied by public, semi-public, or private drinking water systems. Instead, increases in HPC concentrations above baseline levels are considered undesirable.”

In other words, sudden increases in HPC above levels typically seen may indicate a change in the quality of raw water or, that bacterial regrowth has occurred in the distribution system or plumbing. When steady increases of HPC are seen over time, this indicates a gradual decline in raw water quality.

As stated by the National Primary Drinking Water Regulations established by the U.S. EPA a “lower concentration of heterotrophic bacteria in the drinking water is linked to a better maintenance of the treatment and distribution systems.” According to these regulations, treatment techniques should aim to control HPC concentrations in surface waters and groundwaters influenced by surface waters to less than 500 CFU/mL (using standard methods). Note: “This is not a health-based standard, but reflects the concern that at concentrations above 500 CFU/mL, heterotrophic bacteria can interfere with some total coliform and E. coli recovery methods.”

Importance of HPC counts:

High HPC counts indicate ideal conditions for bacterial regrowth and should be corrected. Bacterial regrowth can lead to pipe corrosion, encourage slime growth, increase the need for disinfectants, cause foul-tasting water, and harbour secondary respiratory pathogens (ex. Legionella). Thus, HPC can be used as a marker for the underlying causes of some aesthetic problems (WHO, 2002).

Does having a positive HPC results mean the overall water quality is poor?

No, not necessarily.

Unlike other indicators, such as Escherichia coli or total coliforms, low concentrations of HPC organisms will still be present after drinking water treatment. In general, water utilities can achieve heterotrophic bacteria concentrations of 10 colony-forming units (CFU) per millilitre or less in finished water.

What are the health effects associated with HPC levels?

At an international meeting of experts in Geneva, Switzerland, it was concluded that heterotrophic bacteria in drinking water is not a health concern to the general public. However, some bacteria present in a heterotrophic population are opportunistic pathogens that could infect individuals with weakened immune systems.

“Heterotrophic bacteria belonging to the following genera have been associated with opportunistic infections: Acinetobacter, Aeromonas, Chryseobacterium (Flavobacterium), Klebsiella, Legionella, Moraxella, Mycobacterium, Serratia, Pseudomonas, and Xanthomonas. These organisms have been mainly associated with nosocomial (hospital acquired) infections, including wound infections, urinary tract infections, post-operative infections, respiratory infections, and infections in burn patients.”

What methods can be used to measure HPC?

There are 3 methods used for routine testing of heterotrophic bacteria:

  1. Pour plate method (least desirable method because embedded colonies are slower growing and microaerobic environment is not ideal for growth and, bacteria could undergo heat shock during plating).
  2. Spread plate method (heat shock is eliminated by using solidified agar but only a small volume (0.1-0.5 mL) can be tested).
  3. Membrane filtration method (most flexible method because volumes upto 10L can be tested, heat shock is eliminated by membrane filter, and  it is ideal for HPC less than 10 CFU/mL but multiple dilutions may be required to count colonies on filter).

Here at MBL, we use membrane filtration to measure heterotrophic plate count. If you need to determine the level of heterotrophic bacteria, fecal coliforms, E.coli, total coliforms, Legionella or other type of bacteria in water call our Mississauga office at 905-290-9101 or our Burnaby office at 604-435-6555 or,  our toll free number at 1-866-813-0648.

References:

Health Canada (1996) Guidelines for Canadian Drinking Water Quality, 6th edn. Minister of Public Works and Government Services Canada, Ottawa, Ontario

Heterotrophic plate counts and drinking-water safety: The significance of HPCs for water quality and the human health. Edited by J. Bartram, J. Cotruvo, M.Exner, C. Fricker, A. Glasmacher. 

Guidelines for Canadian Drinking Water Quality: Guideline Technical Document: Heterotrophic Plate Count (Prepared by the Federal-Provincial-Territorial Committee on Drinking Water of the Federal-Provincial-Territorial Committee on Health and the Environment (February 2006).  

For access to the BC Drinking Water Protection Act and the BC Drinking Water Protection Regulation, please refer to the following website: http://www.health.gov.bc.ca/protect/dw_index.html

Guidance on the Use of Heterotrophic Plate Counts in Canadian Drinking Water Supplies (Document for Public Comment Prepared by the Federal-Provincial-Territorial Committee on Drinking Water – Consultation period ended May 27, 2011).

US EPA (1989) 40 CFR Parts 141 and 142 Drinking Water; National Primary Drinking Water Rules and Regulations; filtration, disinfection; turbidity, Giardia lamblia, viruses, Legionella, and heterotrophic bacteria; final rule. US Environmental Protection Agency. Fed. Regist. 54(124), 27486–27541.

US EPA (2001) National Primary Drinking Water Standards. EPA 816-F-01-007, March, US Environmental Protection Agency, Washington, DC (www.epa.gov/safewater).

Filed Under: Bacteria Tagged With: Acinetobacter, Aeromonas, Bacteria, Chryseobacterium, coliform, E. coli, Flavobacterium, Heterotrophic Plate Count, hpc, Klebsiella, Legionella, Moraxella, Mycobacterium, Pseudomonas, Serratia, Xanthomonas

Can Mold, Yeast, and Non-specific Bacteria Cause Bladder Problems?

Jackson Kung'u

Question: I love your blog and hope you can answer this mold question.

I worked at a beauty salon for 1 1/2 years. I started to have back to back urinary tract infections (Escherichia coli). I’ve had these infections a couple of times in my 40+ years on earth but nothing like I was experiencing this time around. It felt like someone lined my bladder with vicks vapor rub and added some pins. The antibiotics I was prescribed made the pain worse. A client of mine (she came every week and spent a long time under the dryer) was experiencing the same thing. About 2 weeks after the bladder pain started, I started having difficulty breathing (I was diagnosed with moderate lung obstruction) and I was placed on an inhaler. I then noticed a fungal rash on my arms I had to treat with Monistat (it cleared up in 6 days). My symptoms started in early June after a flood in the shop which I suspect could have caused mold growth. Dehumidifiers were bought in and ran all day for a couple of days. By August I had to leave because it was just too difficult to breath, take a flight of stairs etc. My urologist couldn’t find the cause of the pain and an internal view of my bladder found nothing. Can mold, yeast, and non-specific bacteria found in these reports cause bladder problems? The pain got significantly better a week after I left. The pain went away completely after about 2 months away from the salon.

The owner decided to have an air quality test for mold done because a girl that rented the room prior to me complained of breathing difficulties only when she was at work. I attached the mold report for you to look at.

Thanks!

Answer: Escherichia coli (E. coli in short) is a bacterium commonly found in the lower digestive tract of warm-blooded animals including humans. Most E. coli strains are harmless, but some strains, such as serotype O157:H7, can cause serious food poisoning. E. coli is also a common cause of urinary tract infections. Infection occurs when E. coli from the digestive tract find their way into the urethra and begin to multiply. The bacterium can move to the bladder and multiply there causing infection of the bladder. I have looked at the lab report that you had attached. The molds reported are unlikely to cause infection. A possible fungal infection of the bladder especially when one has been using antibiotics is Candida infection (candidiasis). Candida can infect other areas of the body including the mouth, throat, skin, scalp, genitals, fingers, nails, bronchi, lungs, and the gastrointestinal tract.

Filed Under: Bacteria, Fungi, Indoor Air Quality, MBL Answers Tagged With: Bacteria, bacterium, candida, E. coli, Yeast

Is There a Difference Between Total Microbe Test and Total Coliform Test?

Jackson Kung'u

Question: Is there a difference between total microbe test and a total coliform test. What do the following results mean as far as safe drinking water is concerned, (5-10)(10-20)(400-500) (800-1000) Colony forming units(CFUs) of aerobic bacteria?

Thank you.

Answer: There is a difference between total microbes test and total coliform test. The former is a non-specific test for everything including the coliforms (if they are present). This test is commonly referred to as Heterotrophic Plate Count (HPC) or Total Aerobic Plate Count. HPC does not give an indication of the types of organisms present or their sources. The total coliform test is designed to detect bacteria belonging to the coliform group.

I am not sure whether the results above were CFUs per litre or per 100 mL. Assuming these were per 100 mL of water the first set of results would be considered insignificant provided coliforms were not present. The second two sets of results suggests the water is either not properly treated or is getting contaminated after treatment.

Below are the Health Canada Microbiological Guidelines for Canadian Drinking Water Quality.

Guidelines for microbiological parameters

Currently available detection methods do not allow for the routine analysis of all microorganisms that could be present in inadequately treated drinking water. Instead, microbiological quality is determined by testing drinking water for Escherichia coli, a bacterium that is always present in the intestines of humans and other animals and whose presence in drinking water would indicate faecal contamination of the water.

Bacteriological guidelines

Escherichia coli

The maximum acceptable concentration (MAC) of Escherichia coli in public, semi-public, and private drinking water systems is none detectable per 100 mL.

Testing for E. coli should be carried out in all drinking water systems. The number, frequency, and location of samples for E. coli testing will vary according to the type and size of the system and jurisdictional requirements.

Total coliforms

The MAC of total coliforms in water leaving a treatment plant in a public system and throughout semi-public and private supply systems is none detectable per 100 mL.

For distribution systems in public supplies where fewer than 10 samples are collected in a given sampling period, no sample should contain total coliform bacteria. In distribution systems where greater than 10 samples are collected in a given sampling period, no consecutive samples from the same site or not more than 10% of samples should show the presence of total coliform bacteria.

Testing for total coliforms should be carried out in all drinking water systems. The number, frequency, and location of samples for total coliform testing will vary according to the type and size of the system and jurisdictional requirements.

Heterotrophic plate count

No MAC is specified for heterotrophic plate count (HPC) bacteria in water supplied by public, semipublic, or private drinking water systems. Instead, increases in HPC concentrations above baseline levels are considered undesirable.

Emerging pathogens

No MAC for current or emerging bacterial waterborne pathogens has been established. Current bacterial waterborne pathogens include those that have been previously linked to gastrointestinal illness in human populations. Emerging bacterial waterborne pathogens include, but are not limited to, Legionella, Mycobacterium avium complex, Aeromonas hydrophila, and Helicobacter pylori.

Protozoa

Although Giardia and Cryptosporidium can be responsible for severe and, in some cases, fatal gastrointestinal illness, it is not possible to establish MACs for these protozoa in drinking water at this time. Routine methods available for the detection of cysts and oocysts suffer from low recovery rates and do not provide any information on their viability or human infectivity. Nevertheless, until better monitoring data and information on the viability and infectivity of cysts and oocysts present in drinking water are available, measures should be implemented to reduce the risk of illness as much as possible. If the presence of viable, human-infectious cysts or oocysts is known or suspected in source waters, or if Giardia or Cryptosporidium has been responsible for past waterborne outbreaks in a community, a treatment and distribution regime and a watershed or wellhead protection plan (where feasible) or other measures known to reduce the risk of illness should be implemented. Treatment technologies in place should achieve at least a 3-log reduction in and/or inactivation of cysts and oocysts, unless source water quality requires a greater log reduction and/or inactivation.

Viruses

Although enteric viruses can be responsible for severe and, in some cases, fatal illnesses, it is not possible to establish MACs for enteric viruses in drinking water at this time. Treatment technologies and watershed or wellhead protection measures known to reduce the risk of waterborne outbreaks should be implemented and maintained if source water is subject to faecal contamination or if enteric viruses have been responsible for past waterborne outbreaks. Where treatment is required, treatment technologies should achieve at least a 4-log reduction and/or inactivation of viruses.

For more details on Canadian Guidelines for drinking water click Guidelines for Canadian Drinking Water Quality.

Filed Under: MBL Answers, Water Testing Tagged With: bacterium, Drinking Water Quality, E. coli, Heterotrophic Plate Count, hpc, Total Aerobic Plate Count, Total coliforms

Health Hazards in Pools, Hot Tubs and Spas

Jackson Kung'u

Pools, hot tubs and spas occasionally get contaminated with harmful bacteria such as E. coli, Legionella pneumophila, Pseudomonas aeruginosa, Mycobacterium avium, Streptococcus and Salmonella. These bacteria are known to cause serious diseases in humans such as infection of the skin, eyes, ears, hair follicles, intestines and urinary tract.

More serious illnesses are the Legionaires’ Disease and Pontiac Fever acquired from inhaling airborne Legionella cells. This occurs when Legionella becomes airborne by way of aerosol mists produced in spas and hot tubs.

Legionella bacteria are able to survive in low temperatures, but thrive at temperatures between 20oC and 45oC. Legionella cannot survive at temperatures of 60oC and above.

Filed Under: Bacteria, Water Testing Tagged With: E. coli, Legionaires Disease, Legionella, Mycobacterium avium, pontiac fever, Pseudomonas aeruginosa, Salmonella, Streptococcus

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