Suitability of MC‑Media Pad® for Hygiene Monitoring

This study shows that the MC Media Pad® is suitable for a range of hygiene monitoring applications.

The study focused on usage of MC‑Media Pad® in passive air, personnel and surface monitoring in comparison to standard test methods.

The MC‑Media Pad® is designed as a convenient method for rapid routine testing of microbial contamination in food and beverage samples throughout production, from raw materials to finished products. The MC‑Media Pad® solution is composed of a series of ready‑to‑use pads for total count and specific detection and enumeration of indicator organisms.

Each MC‑Media Pad® consists of a fabric pad coated with a dedicated culture media formulation, placed on an adhesive support with a transparent gas-permeable cover (Figure 1). The MC‑Media Pad® has been specifically developed for the testing of 1 mL samples.

Description of MC‑Media Pad®

Figure 1: Description of MC‑Media Pad®

 

Table 1: Typical incubation conditions for MC‑Media Pad®

MC‑Media Pad® Incubation time Incubation temperature
Rapid Aerobic Count (RA) 24 - 48 hours 35 ± 1 °C
E. coli /Coliform (EC) 24 ± 2 hours 35 ± 1 °C
Yeast & Mold (YM) 48 - 72 hours 25 ± 1 °C

Control of microbial contamination in the food processing environment is a fundamental part of HACCP or HARPC programs under FSMA. Standard procedures include active and passive air monitoring, as well as surface and personnel control using either swabbing techniques or agar devices.

This study was carried out to investigate if MC‑Media Pad® can be used as a replacement for agar media, which are traditionally used as settle plates in passive air monitoring, or for pour or spread plate methods after swabbing surfaces.

Passive air monitoring

90mm settle plates with TSA and/or SDA are used for passive air monitoring. They are exposed to the air for a specific amount of time to collect airborne bacteria or fungi, which may settle onto food contact surfaces. In a side by side test, MC‑Media Pad® RA (Rapid Aerobic Count) and MC‑Media Pad® Yeast & Mold versus TSA and SDA settle plates respectively were used in parallel. The test runs were performed twice, in environments with both higher and lower levels of contamination.

Test procedure

Four test runs with 20 MC‑Media Pad® solutions (Type RA for total aerobic counts and YM for yeast and mold count) and 20 settle plates (TSA for total count and SDA for yeast and mold count) each in a side by side study were performed in two different standard laboratories. The cover films of the MC‑Media Pad® tests were opened and the pads, as well as the bottom side of the cover films, were exposed for 3 hours to the ambient air (see Figure 2). The settle plates were exposed without the lid to the air in a side by side pattern for the same amount of time. After exposure, the settle plates were closed with their lids, and the MC‑Media Pad® tests were humidified by adding 1 mL of sterile water and the cover films were returned to the pads. Finally, total aerobic count samples were incubated at 35 ± 1 °C for up to 48 hours, and yeast and mold count samples were incubated for up to 7 days at 25 ± 1 °C. The colonies were counted after 24 and 48 hours for total count measurements and after 2, 3 and 7 days for yeast and mold detection.

 Exposition of an opened MC‑Media Pad® for passive air
sampling

Figure 2: Exposition of an opened MC‑Media Pad® for passive air sampling.

 

Results and discussion

All test runs for settle plates, as well as for MC‑Media Pad® tests, resulted in consistent counting results with low variances for all 20 replicates per device in the dedicated environment.

Figure 3 below demonstrates an example of colonies on MC‑Media Pad® tests and Settle Plates after passive air sampling, each media pair (RA and TSA, Y&M and SDA) were subjected to the same sampling and incubation conditions.

Exposition of an opened MC‑Media Pad® for passive air sampling

Figure 3: Colonies on MC‑Media Pad® and Settle plates after passive air monitoring and incubation.

 

The total aerobic counts as well as yeast and mold counts show good comparability for each of the the 20 replicates in the side by side test for both TSA/ SDA plates and MC‑Media Pad® Rapid Aerobic Count and Yeast & Mold (see Figures 4 and 5). In addition, the level of airborne contamination, meaning a lower or higher contamination grade of the two test environments was well reflected by both methods.

In total count measurements, the MC‑Media Pad® did not show significant differences after 24 hours or 48 hours of incubation.

With regards to incubation time for yeast and molds, the MC‑Media Pad® did not show significant differences between 3 and 7 days incubation, whereas on SDA settle plates the counts increased after prolonged incubation up to 7 days for low contamination levels.

Total aerobic count in 2 different sampling environments

Figure 4: Total aerobic count in 2 different sampling environments after 48 hours incubation using TSA settle plates and MC‑Media Pad® Rapid Aerobic Count

 

Yeast and mold counts in 2 different sampling environments

Figure 5: Yeast and mold counts in 2 different sampling environments after 3 days incubation

 

Overall, the colony count of a single sample does not give an indication of the cleanliness of the environment. In general, air monitoring should be performed on a regular basis at the same critical control points. The comparison of data over a period (e.g. monthly, quarterly) will help to monitor changes in the cleanliness level of the food producing environment.

From the obtained data, it can be concluded that MC‑Media Pad® is suitable for passive air monitoring. To achieve consistent trending data, you should maintain the same sampling procedure and sampling device for trend analysis of defined critical control points.

 

Personnel monitoring (e.g. direct fingerprint)

Fingerprints are often part of the hygiene monitoring of personnel to avoid cross contamination between production areas, or from personnel to food. To check the suitability of MC‑Media Pad® for personnel monitoring, direct fingerprints were performed on MC‑Media Pad® (types RA, EC/CC and YM).

Direct fingerprint on a pre-moistened MC-Media Pad® testFigure 6: Direct fingerprint on a pre-moistened MC-Media Pad® test
Test procedures

The cover film of MC‑Media Pad® was opened, and 1 mL of sterile water was dispensed on the center of the media pad. The cover film was closed and maintained at room temperature for 15 minutes to be moistened. The cover film was then opened and a fingertip of a test person or alternatively a glove finger (pre-inoculated with test strains) was slightly pressed on the moistened pad surface (Figure 6). After closing the cover film, the pads were incubated as indicated in Table 1. Finally, the colonies were counted.

Results and discussion

This test was carried out to demonstrate the recovery of microorganisms from finger or glove prints. The results of the pure fingerprint test showed colonies on the various MC‑Media Pad® tests. The highest number of CFU (59) on the RA pads were obtained after 48 hours of incubation. Very low counts, mainly pinpoint colonies were detected on MC‑Media Pad® E. Coli / Coliform as well as on MC‑Media Pad® Yeast and Mold. In both cases, the maximum incubation time, indicated in Table 1, is required to detect the colonies. The pre-inoculated glove fingerprints showed clear growth of the chosen test strains on the dedicated media pads as shown in Figure 7. These results indicate that MC‑Media Pad® tests can be used for direct fingerprint testing.

Selected microorganisms grown after glove print

Figure 7: Selected microorganisms grown after glove print on various MC‑Media Pad® tests

Surface monitoring of dry surfaces (swab test)

Swabs are a well-known device for microbial monitoring of surfaces. Pre-moistened swabs are used for monitoring of dry surfaces, whereas dry swabs are used for wet surfaces. The overall swabbing efficacy is impacted by several parameters like the absorbing capacity of the swab tips, the release of collected microorganisms from the swab tips and finally by the growth performance of the microorganisms in the appropriate culture media.

The material of the swab and the swabbing procedure have significant influence on the recovery rates (Moore and Griffith). In this study, we did not investigate the efficacy of the chosen swab type for removal or release of microorganisms, but instead we investigated the overall recovery rate of microorganisms from a dry surface using MC‑Media Pad® instead of typical 90 mm agar media.

The recovery rates are calculated as follows: Recovery Rate (%) = CFUtest A or B x 100 / CFUcontrol

Test procedures

Table 3: Procedure of Swab Method A.

Swab Method A Reference of viable microorganisms
(triplicate samples) (triplicate samples)
Stainless steel coupons are inoculated with 100 uL bacterial suspension (coupons in triplicate)
Coupons dried for 3 hours in a safety cabinet (blower off)
Stainless steel surface of coupon was swabbed in a zig-zag pattern Stainless steel coupon was overlaid with molten TSA/SDA (like pour plate method)
Swab was transferred to 2 mL Letheen Broth and vortexed for approx. 30 seconds  
1 mL of Letheen Broth was transferred onto a dry MC‑Media Pad®  
Samples are incubated as indicated in Table 1
Colonies were counted, and average of triplicate determined (CFUtestA) Colonies were counted, and average of triplicate determined (CFUcontrol)

 

Test procedure for determination of the recovery rates using MC‑Media Pad®

Figure 8: Test procedure for determination of the recovery rates using MC‑Media Pad® as an alternative to pour plates (Swab Method A):

Results and discussion

The recovery rates of 1 mL of the swab rinsing solution transferred to the MC‑Media Pad® ranged from 38% for E. coli to 124% for S. aureus compared to the viable CFU on the stainless steel surface (see Figure 9).

Compared to the original inoculum, the recovery rates for the tested microorganisms are within a range which corresponds to the variances reported by Moore and Griffith.

Low recovery rates compared to the original inoculum for the stainless steel coupon are mainly influenced by the high variance of the death rate during drying of the microorganisms on the surface. Therefore, we determine the viable microorganisms on the stainlesssteel surface after drying by an agar overlay method as a 100% control (except for spores of A. brasiliensis).

The recovery rates for the different test strains and MC‑Media Pad® types are shown in Figure 9. For surface monitoring using swabs in combination with MC‑Media Pad® (Swab method A), it can be concluded, that the recovery rates are comparable to previously reported ranges. In the present study design, a cotton swab was used, which provides the highest recovery rates when vortexed in Letheen Broth and 1 mL of the Broth is then transferred to the MC‑Media Pad®.

Recovery rates of different stainless steel surfaces

Figure 9: Recovery rates of different test strains from stainless steel surfaces using swab method A (see Table 3)

 

Examples of MC-Media Pads®

Figure 10: Examples of MC‑Media Pad® used for transfer of 1 mL swab dilution broth

 

Summary and conclusion

The MC‑Media Pad® is suitable for hygiene monitoring applications, e.g. passive air sampling, personnel and surface monitoring.

The results generated in this study are comparable with standard reference methods. In addition to their suitability for hygiene monitoring, the MC‑Media Pad® provides some benefits in terms of color-coding, handling, time to results for yeast and molds in 48 hours and improved read-out using chromogenic substances / specific dyes to allow fast and convenient control of microbial contamination.

If you would like to be contacted by a specialist or to request further information on our hygiene monitoring solutions, fill out this request form.

 

Reference

  1. Moore G; Griffith C (2007): Journal of Applied Microbiology 103; 1090-1103

 

Materials