Why is microbiology testing for dietary and nutritional items necessary, and what does it entail?

Good manufacturing practices (GMP)-produced nonsterile nutritional and dietary goods must be free of “objectionable microorganisms.” Microbial contaminants known as objectionable microorganisms have the potential to compromise product safety, contingent on the type of microorganism, quantity of organisms, dose form, intended usage, and patient population. Put another way, any germs that pose a risk to the user’s health or that could develop in the product must be eliminated or kept out of it. Additionally, microorganisms are undesirable if they compromise the stability of the product or jeopardize the integrity of the container-closure system.

Only microorganisms that pose a risk to the specific product are to be checked for; nonsterile nutritional and dietary items are not supposed to be examined for the presence of all harmful germs. The tests for Salmonella, Clostridium, Escherichia coli, and Staphylococcus aureus will be discussed in this article. In microbiology testing, the most frequent threats to food and nutritional goods are Salmonella, Clostridium, Escherichia coli, and Staphylococcus aureus.

How are food and nutritional supplements tested for microbes?

Ten grams or ten milliliters of the dietary or nutritional supplement are used for each of the tests listed below. For the first incubation of the samples, combine 10 grams or 10 milliliters of the sample with 100 milliliters of Fluid Soybean–Casein Digest Medium (FSCD). To create a cross-crossed pattern of isolated colonies, the loop should be streaked across the surface of each plate in four different directions if a plated media is being tested. It should be noted that in order to prevent mechanical harm to the microorganisms, mixing must be done while gently shaking. Escherichia coli dilutions that are suitable for controls

(ATCC No. 8739), Salmonella typhimurium (ATCC No. 13311), and Staphylococcus aureus (ATCC1 No. 6538) will be employed.

Microbiology testing for the presence or absence of Staphylococcus aureus.

FSCD broth is cultured for 18 to 24 hours at 30° to 35°C in order to test for S. aureus. The surface of one or more of the Vogel–Johnson Agar Medium (VJ Agar), Mannitol–Salt–Agar Medium (MS-Agar), or Baird-Parker Agar Medium (BP Agar) is then streaked with a loopful of FSCD. After that, agar Petri plates are covered, turned upside down, and incubated for 24 to 48 hours at 30 to 35 degrees Celsius. Following that, the agar plates are inspected in accordance with the guidelines in Table 1 below. The test samples satisfy the criteria for the absence of Staphylococcus aureus if none of the agar plates have colonies with the traits listed in Table 1. Conduct a coagulase test if colonies that are indicative of S. aureus are found. Transfer the representative S. aureus colonies to other tubes with 0.5 milliliters (mL) of horse, rabbit, or other mammalian plasma in order to perform a coagulase test. The tubes should be incubated at 37°C in a water bath. After three hours of incubation, and thereafter at appropriate intervals for up to twenty-four hours, check the tubes for coagulation. Staphylococcus aureus is not present in the examined item if there is no coagulase response. For the coagulation experiment, be careful to include both positive and negative S. aureus controls.

Microbiology testing for the presence of Salmonella.

For 18 to 24 hours, FSCD broth is incubated at 30° to 35°C. Pipette a 1-mL aliquot into 10 mL of Rappaport Vassiliadis Salmonella Enrichment Broth following FSCD incubation. After that, combine the samples and incubate them for a further 18 to 24 hours at 30° to 35°C. After that, streak a loopful of each of the Rappaport Vassiliadis Salmonella Enrichment Broth and FSCD incubation media onto separate surfaces of one or more Hektoen Enteric Agar Medium (HE Agar), Xylose–Lysine–Desoxycholate–Agar Medium (XLDC-Agar), and Brilliant Green Agar Medium (BG-Agar). Agar Petri plates should then be covered, inverted, and incubated for 24 to 48 hours at 30° to 35°C. Next, use the guidelines in Table 2 below to inspect the agar plates. The test samples satisfy the Salmonella absence criterion if none of the colonies exhibit Salmonella traits. Colonies suspected of being Salmonella are moved to a slant of Triple Sugar–Iron–Agar Medium (TSI) using an inoculating wire if they exhibit the traits listed in Table 2. In order to transmit the colonies, the wire is stabbed well below the surface once the colonies have been streaked across the slant’s surface. The slant is streaked and then incubated for 24 to 48 hours at 30° to 35°C. The test specimens satisfy the criteria for the absence of Salmonella if the tubes do not have yellow acid butts and red alkaline slants (with or without the butts becoming blackened due to the generation of hydrogen sulfide).

Microbiology testing for the presence or absence of Escherichia coli.

The FSCD broth is incubated for 18 to 24 hours at 30° to 35°C in order to test for E. coli. Pipette a 1-mL aliquot of FSCD into a container with 10 mL of MacConkey Broth after the FSCD has been incubated. After that, combine the samples of MacConkey Broth and incubate them for 24 to 48 hours at 42° to 44°C. After that, streak a loopful of each of the MacConkey Broth and FSCD incubation media onto the MacConkey Agar Medium (MC Agar) surfaces. Then, incubate the agar for 18 to 24 hours at 30° to 35°C. After that, look at the infected MC Agar plates and use the features listed in Table 3 below to interpret the results. Test specimens satisfy the criteria for the absence of Escherichia coli if none of the colonies exhibit the traits of E. coli that have been documented. Using an inoculating loop, colonies thought to be E. coli that exhibit the traits listed in Table 3 are moved (one at a time) to the surface of a plate containing Levine Eosin–Methylene Blue–Agar Medium (LEMB-Agar). Each LEMB-Agar plate’s surface should be divided into quadrants if a large number of questionable colonies are transferred. An alternative, suspected E. coli colony will be introduced into each quadrant. Following inoculation, LEMB-Agar plates are covered, turned upside down, and incubated for 24 to 48 hours at 30° to 35°C. The test specimens satisfy the criteria for the absence of Escherichia coli if none of the cultivated colonies show the distinctive metallic sheen under reflected light and none of them look blue-black under transmitted light.

Microbiology testing for the presence for absence of Clostridium species

Divide the FSCD test preparation into two equal parts. Transfer 10 mL of each component of FSCD (heated and unheated) into different containers with 100 mL of Reinforced Medium for Clostridium after heating one to 80°C for ten minutes and quickly cooling it down. After that, incubate the containers for 48 hours at 35° to 37°C in an anaerobic environment. Following incubation, subculture each specimen on Columbia Agar Medium (with gentamicin) and continue to incubate for 48 hours at the same temperature and anaerobic conditions. Lastly, look at the agar plates using Table 4 below. If there is no evidence of Clostridium microbe development, the test samples satisfy the Clostridium absence criterion. Each individual colony should be subcultured on Columbia Agar Medium if Clostridium growth is observed. After that, incubate the agar plates independently for 48 hours at 35° to 37°C in both aerobic and anaerobic settings. Clostridium is present when only anaerobic growth of gram-positive bacteria occurs, along with an unfavorable catalase reaction. Individual colonies should be moved to glass slides in order to conduct the catalase test. A drop of diluted hydrogen peroxide solution is then applied. If no gas bubbles form, the catalase test is negative. The test specimens may satisfy the criteria for the absence of Clostridium if they show a catalase reaction or are able to grow in aerobic environments.

Retests To verify a questionable finding, retests may be conducted. Ten grams of a food or nutritional supplement are used in conventional tests. It is advised that a retest be conducted using a 25-gram sample of the dietary supplement or nutritional product, following the identical protocols as previously mentioned but accounting for the greater specimen size.

In Brief

Only bacteria that pose a risk to the user’s safety or the individual product’s deterioration need to be checked in dietary and nutritional supplements. The tests to check for Salmonella, Clostridium, Escherichia coli, and Staphylococcus aureus are covered in this article. The most frequent microbiological threats to food and nutritional goods are Salmonella, Clostridium, Escherichia coli, and Staphylococcus aureus. Make sure you pick a contract testing company that can assist you with microbiological testing for your particular product demands if you’re wanting to outsource the microbiology testing for your dietary and nutritional supplements.