Laboratory Bacteria Testing Services

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Bacteria testing on chromogenic media

Bacteria testing on chromogenic media

Bacteria testing can determine the types and numbers (in terms of colony forming units) of bacteria present in a sample. The testing could be focused on a specific type of bacteria, medical bacteria or a broad range of environmental bacteria.

Since bacteria are present in virtually any environment, it’s important to be clear why the testing is being performed. The more specific the testing, the better and easier it is to interpret the results.

Numbers and types of bacteria that should be a cause for concern depends upon several factors, including the type of bacteria present and the type of samples. For example, there should be no indicators of fecal contamination in drinking water.

Samples and Types of Bacteria Testing Services at MBL

Air Samples for Bacteria Testing

Air samples for bacteria testing can be taken with either an RCS sampler or Andersen sampler. Air is impacted on agar media such as TSA or nutrient agar (NA). Once the samples are sent back to the lab the media is incubated at 37°C for 24-48 hours (depending on how fast the bacteria grow). Bacteria colonies are counted and reported as colony forming units (CFU) per cubic meter of air. Transfer to ID media is performed if identification to species is required. This test reveals if the air is contaminated with types of bacteria that are of healthy concern.

Surface Samples for Bacteria Testing

Surface bacterial samples may be taken with culture-swabs, wipes or contact plates. The samples may be taken from any kind of surface (dry/wet) suspected of bacterial contamination. Surface samples for bacteria testing may also be collected to assess the efficacy of antimicrobial agents. Both quantification and identification of the types of bacteria present in the sample are possible.

Well Water Samples for Bacteria Testing

Well water testing for bacterial contamination is very important. Contamination can be determined by testing for coliform bacteria that are indicators of sewage contamination. Water can also be analysed for other types of bacteria such as iron, sulfur or slime bacteria that cause blockage of plumbing systems, bad odors, discolorations and diseases.

Food Samples

Various food can be contaminated by bacteria. Food samples can be tested for bacteria to monitor, detect and/or identify bacterial contamination. Tests can be performed for Total Plate (Aerobic/Anaerobic) Counts, Total Coliform, Salmonella, Shigella, Pseudomonads, Staphlococcus, Bacillus, and even Yeasts and Molds.

Metalworking Fluids (MWFs) Samples

Metalworking fluids (MWFs) are neat oils or water-based fluids used during the machining and shaping of metals to provide lubrication and cooling. Impurities in the coolant encourage microbial growth including various types of bacteria. These organisms directly degrade the coolant resulting in the splitting of emulsions, decreased pH, increased corrosion, and loss of lubricating ability. Microbial contamination of MWFs may also expose workers to pathogens and contribute to respiratory and skin diseases. Results of bacteria testing of MWFs are reported as CFUs/ml of the fluid.

Cosmetics & Pharmaceuticals

Cosmetics may also get contaminated with bacteria and other microorganisms. This include bacterial contamination by Gram-positive Bacilli, Staphylococcus aureus and non Escherichia coli Gram-negative organisms. Bacteria testing of cosmetics involve analyses of Gram positives or Gram negatives, Total Plate Count, Yeast and Mold Counts.

Specific Types Of Bacteria That We Test

The specific types of bacteria that we routinely test for from air, surface, and water samples are listed below. If a type of bacterium or test of your interest is not listed here, please contact us.

Coliform Analysis

Coliforms are common environmental bacteria and may be found in soil, on hands, on equipment surfaces, in water and other environments. Coliform tests, as a group, are used as an overall indication of sanitation efficiency. Most coliforms are not harmful (pathogenic), but if a coliform test indicates their presence, it is considered to be an indication of unsanitary conditions.

There are no standards for coliforms for most foods. Many product specifications are written with a zero or low tolerance for coliforms. They can be tested for water samples, swab samples, and air samples. Water samples, if the water comes from a chlorinated system, must be treated with sodium thiosulfate. Swab samples must use liquid culture swabs to preserve the sampled bacteria.

Testing can be performed for presence/absence of these bacteria in the samples with or without enumeration. For sampling information, please contact us so that we can discuss the needs of your unique situation.

Escherichia coli

Simply called E.coli, Escherichia coli is one of the main species of bacteria living in the lower intestines of mammals. Except for one strain, E. coli strain O157:H7, the bacterium is not pathogenic. E. coli are a subgroup of the coliform group discussed above. They are the most numerous coliform species and most are considered non-pathogenic (normally not able to cause illness). E.coli can be found in the intestinal tract of warm-blooded animals. The presence of E.coli in foods is considered to be an indication of fecal contamination.

Iron Bacteria

Iron bacteria are seen as nuisances, and are particularly common in systems using wells as a water source. Examples of iron bacteria include Gallionella, Sphaerotilus, Leptothrix, and Crenothrix. These aerobic, filamentous bacteria oxidize iron from a soluble ferrous (Fe2+) form to an insoluble ferric (Fe3+) form. They produce thick slime layers which can cause blockage in a plumbing system. They can also discolour water (“red water”) or cause odors and odd taste. Iron bacteria test results include estimated CFU/ml. For sampling equipment and information, please contact us.

Sulfur Bacteria

Sulfur bacteria act in a similar fashion to iron bacteria and are also commonly found in well-water systems. They also produce thick slime, usually coloured black. The odors produced by them can be described as ‘rotten eggs’. They are tested for in water samples. Results will include estimated cfu/ml. For sampling equipment and information, please contact us.

Legionella (Causative agent of Legionnaires’ Disease)

Legionella sp. can be isolated from surface water, mud and from thermally polluted lakes and streams; causative agent in Legionnaire’s Disease and Pontiac Fever. In investigations, this organism can also be found in water cooling towers, evaporative condensers, spas, respiratory therapy equipment, showers, water faucets, decorative fountains, ultrasonic mist machines and damp potting soil. More information is available on the Legionella Analysis Page.

Other Bacteriological Tests

Gram Staining & Enumeration

Depending on their wall composition, bacteria will stain as either Gram positive or Gram negative. Gram’s Stain is a widely used method of staining bacteria as an aid to their identification. The types of bacteria with walls containing small amounts of peptidoglycan and characteristically, lipopolysaccharide, are Gram-negative whereas bacteria with walls containing relatively large amounts of peptidoglycan and no lipopolysaccharide are Gram-positive. Gram-negative bacteria produce endotoxins. Endotoxins have been associated with many respiratory symptoms and complaints related to the indoor environment.

Aerobic Plate Count

The aerobic plate count (APC) indicates the level of microorganisms in a product and is an estimation of the total viable aerobic bacteria present in a sample of raw material, in-process material, or finished product. Also referred to as the Standard Plate Count (SPC), it can be used to assess the overall bacterial load of a product.

Anaerobic Plate Count (AnPC)

This test is used to determine the total number of anaerobic bacteria (i.e., bacteria requiring no oxygen) present at mesophylic temperatures (30°C-37°C). Examples of such types of bacteria include Clostridium spp. Most human bacterial pathogens are facultative anaerobes and may show up on this test as well.


Salmonella sp. occur in humans, warm and cold blooded animals, and in the environment. Bacteria in this genus are pathogenic for humans. They can cause typhoid fever, enteric infections and sepsis.


Staphylococcus organisms are commonly found in the environment. Several species of Staphylococcus are found on the skin, intestines, nasal passages, etc. of warm-blooded animals. Some species of Staphylococcus, particularly Staphylococcus aureus can be pathogenic (capable of causing illness).


Pseudomonas aeruginosa is widely distributed in soil, water and plants. It survives in hot tubs, whirlpools, contact lens solution, sinks and showers. It can cause a number of opportunistic infections including infections of the skin, external ear canal and of the eye.


Mycobacterium spp. can be isolated from water, soil and dust. They have been associated with hypersensitivity pneumonitis reactions in health spas whirlpools. In hospital environment, Mycobacterium species have also been associated with nosocomial outbreaks.

Sulfate reducing Bacteria

Sulfate reducing bacteria (SRB) are types of anaerobic bacteria that, as a part of their normal activities, generate hydrogen sulfide (H2S). This product can cause a number of significant problems. These range from “rotten egg” odors, through to the blackening of equipment, waters and slime formations, and the initiation of corrosive processes.

Slime forming bacteria

Slime-forming bacteria generally produce the thickest slime formations under aerobic (oxidative) conditions. They cause plugging of plumbing system and render the water unfit for use.

Acid Producing Bacteria (APB)

Some types of bacteria produce acidic metabolites, such as organic or inorganic acids. These bacteria are referred to as acid producing bacteria (APB). APBs can be a problem in gas transmission lines and could also be a problem in closed water systems that become anaerobic.

The acids accelerate corrosion by dissolving oxides (the passive film) from the metal surface and accelerating the cathodic reaction rate. Examples of APBs include Thiobacillus thiooxidans which produce sulfuric acid and Clostridium aceticum which produces acetic acid.

Nitrifying Bacteria

Nitrifying bacteria recycle organic nitrogenous materials from ammonium (the endpoint for the decomposition of proteins) to nitrates. Their prescence can indicate that the water may have been polluted by nitrogen-rich organics from sources such as compromised septic tanks, sewage systems, industrial and hazardous waste sites and is undergoing an aerobic form of degradation.

Denitrifying bacteria

The presence of denitrifying bacteria can indicate that the water has been polluted by nitrogen-rich organics from sources such as compromised septic tanks, sewage systems, industrial and hazardous waste sites.

If any of this information was unclear or you wanted to learn more about out laboratory testing services, please contact us by email or telephone.

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