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You are here: Home / Archives for Acinetobacter

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

Seed Pathogen Testing

Jackson Kung'u

Question: Hello, I represent a very important agro-industrial group in Mexico. We have several roles such as wheat mills, fruit, and vegetable processing.

Right now we have a situation in one of our facilities that we want to resolve. We have a hydroponic greenhouse where we produce lettuce, mainly 3 different varieties (Boston, Lollobionda, Lollorosa). We have had several problems in the production of lettuce. We did some analysis and we have found that the root cause of the problem is in the seed.

This seed comes from Holland, and the seed is encapsulated by some material that is supposed to protect the naked seed and improve the shelf life. In our studies we have found that the encapsulation material is contaminated with some fungal pathogens and bacteria, so this is why we are requesting your support.

In a research institute in Mexico they found in the encapsulation material the following fungal pathogens and bacteria:

– Fusarium
– Verticillium
– Acremonium
– Phythium
– Aspergillus
– Stenotrophomonas
– Acinetobacter
– Bacillus cereus

So we want to confirm with your labs if these microorganisms are present in the seed or in the encapsulation material. So we need to know if your labs are able to do this analysis, the cost of the analysis and how much time you think this will take. If by some reason MBL are not able to do this kind of analysis, could you recommend some laboratory that could help us with this request.

I’ll wait for your comments, thanks and best regards.
Answer: We can you determine the fungal and bacterial pathogens present in the seeds and the encapsulation material. However, since this material is coming from outside of Canada, an import permit from the Canadian Food Inspection Agency (CFIA) would be required. We would suggest you use a lab in Mexico for this kind of testing.

Filed Under: Fungi Tagged With: Acinetobacter, Acremonium, Aspergillus, Bacillus, Fusarium, Phythium, pthogen, seed, seeds, Stenotrophomonas, Verticillium

Airborne Bacteria In Indoor Environments

Jackson Kung'u

Significance Of Airborne Bacteria In Indoor Environments

Indoor airborne bacteria have not received as much publicity as the mould. Are indoor airborne bacteria of health significance?

Read more below….

Bacteria are found virtually in every environment including the hot springs, deep-sea hydrothermal vents, glaciers, swamps, and mines! Some heat-loving bacteria (hyperthermophiles) thrive best above 176 °F (80 °C) whereas the psychrophiles (cold-loving) can survive far below 0 °C.

In indoor environments bacteria are present in air and on surfaces. High levels of bacteria concentration indoors is an indication of high occupancy rate, poor ventilation, or poor building maintenance. Similar to mould, some bacteria are associated with water-damaged building materials.

Significance Of Airborne Bacteria

While bacteria do not receive as much publicity as mould when it comes to indoor air quality, they are a health hazard. Some are serious human pathogens and others especially the gram negative bacteria produce toxic compounds (endotoxins) from the outer membrane of their cell wall. Endotoxins may have a role in sick building syndrome.

Indoor airborne bacteria can loosely be categorized into bacterial pathogens and environmental bacteria associated with water-damaged building materials. Bacterial pathogens are capable of causing severe diseases in humans if inhaled, ingested or if they come into contact with the skin. The most important airborne bacterial infections in indoor environments are tuberculosis, nosocomial pneumonia, and legionellosis. These infections are primarily acquired through inhalation of the causative agents.

Environmental bacteria generally associated with mouldy building materials include Acinetobacter, Bacillus, Flavobacterium, Nocardia, Streptomyces, and Thermomonospora. Also associated with water-damaged material are the filamentous bacteria, the Actinomycetes. Some airborne bacteria such as Staphylococcus spp and Micrococcus spp are dispersed into the air from human skin, oral and nasal surfaces, and hair. These bacteria are associated with nosocomial infections in health care facilities.

 

Sampling For Airborne Bacteria

Bacteria Colonies On TSA Agar MediaThe commonly used sampling method for airborne bacteria is the impaction of air onto agar media using volumetric samplers such as Andersen, SAS, or RCS. Samples can also be collected by impingement into liquid media. However, for routine air quality monitoring agar based sampling is recommended. Trypticase soy agar (TSA) media is usually used when sampling for bacteria. It is important to select a medium suitable for growth of the target organism, for example when sampling for some specific bacteria such as Legionella. Sampling time depends on the sampler used but generally not more than 10 minutes. Shorter times are recommended in heavily contaminated areas. Samples are kept cool and shipped for overnight delivery to the laboratory for incubation and identification of the dominant species.

References

    1. Chin, S. Yang, Patricia A. Heinsohn (Editors). Sampling and analysis of indoor microorganisms. 2007. John Wiley & Sons, Inc.(ISBN-13:978-0-471-73093-4
    2. Flannigan, B., R.A. Samson, and J.D. Miller (Editors). Microorganisms in home and indoor work environments: diversity, health impacts, investigation and control. 2001. London, UK: Taylor & Francis (ISBN: 0-415-26800-1).
    3. Wanner, H-U, AP Verhoeff, A Colombi, B Flannigan, S Gravesen, A Mouilleseux, A Nevalainen, J Papadakis, and K Seidel. 1993. Biological Particles in Indoor Environments. Indoor Air Quality and Its Impact On Man. Brussels: Commission of the European Communities. Report No. 12.

 

For more information on indoor airborne bacteria, please visit http://www.moldbacteria.com/ or call 905-290-9101.

Filed Under: Bacteria, Indoor Air Quality Tagged With: Acinetobacter, airborne bacteria, Bacillus, endotoxins, Flavobacterium, Nocardia, Streptomyces, Thermomonospora

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