Surface Sampling for ISO Class 5 Primary Engineering Controls


Contact Plates and Clean-Up

In the compounding of pharmaceuticals, Primary Engineering Controls (PECs) are critical in ensuring final product integrity and public safety. Equipment such as compounding aseptic isolators (CAIs) and biological safety cabinets (BSCs) must be contamination free, and this requires diligent monitoring to maintain standards to PEC ISO 5 classification. According to USP <797> guidelines, flat interior surfaces of PECs should be sampled for microorganism contamination per your organization’s Standard Operating Procedures (SOPs) and as part of any Environmental Sampling Plan (ESP) and, to this end, contact plates are a primary tool for performing surface sampling. However, given their gelatinous nature, these devices also leave behind a residue that must be diligently removed through careful cleaning performed using prescribed tools and techniques. For a primer on both surface sampling and the most effective cleaning of your PECs, read on…

What Are Contact Plates?

Contact plates, sometimes known as RODAC (Replicate Organism Detection and Counting) plates, are an industry standard tool for retrieving microbial samples. Post-collection, they additionally serve as containers for the cultivation and count of colony-forming units (CFUs). Comprised of a round lidded dish of transparent plastic, the contact plate is filled with Tryptic Soy Agar (TSA), a gelatinous substance that is derived from red algae. As a cultivation medium, TSA is considered non-selective, and its ability to detect a large number of microorganisms makes it a popular choice. For the detection of yeasts or molds, Sabouraud Dextrose Agar (SDA) may be a preferred option as a growing medium. In addition, contact plates also contain  additives such as lecithin and polysorbate 80 which are incorporated to neutralize the antimicrobial effects of certain residues at the testing site. To offset the effects of residual disinfectants on test surfaces, other common neutralizers are histidine or sodium thiosulfate; for inactivating potential β-lactam antibiotic contamination, ephalosporinase (cephase) or penicillinase (penase) may be present in the contact plates.

How Are Contact Plates Made?

Contact plates are themselves manufactured in a cleanroom setting in a process that fills the dishes with the medium under laminar flow. After several days’ storage at room temperature, the plates undergo visual inspection for imperfections such as cracks or bubbles before being stacked, bagged, heat-sealed, and labelled, all without ever leaving the contamination-controlled environment. When plates are destined for use in grade A cleanrooms or aseptic isolators, they are also gamma-irradiated and triple bagged. The three layers of packaging allow the removal of one layer per material lock. Design and functional specifications for the plates are listed in ISO 14698.

Microbiologist inspecting petri dish, observing bacteria growth

What Are Contact Plates Used to Detect?

Contact plates are used within environmentally controlled facilities to detect the presence of Gram-positive non-spore forming bacteria such as Staphylococcus aureus, Gram-positive spore forming bacteria such as Bacillus cereus, and Gram-negative bacteria such as Pseudomonas aeruginosa. In addition, the presence of yeasts such as Candida albicans and molds such as Aspergillus brasiliensis may also be detected using these plates.

How to Use Contact Plates:

The convex surface of the contact plate is placed directly onto the surface to be tested in a rolling motion, thereby allowing any microorganisms to transfer to the agar medium. After a moment, the plate dish is lifted, sealed with a lid, and marked with the location of the area tested, date of testing, and the tester ID. Some contact plates have lockable lids that offer the option not only of on-site incubation but also of transportation under aerobic, anaerobic, or microaerophilic conditions. Per USP <797> guidelines, surface sampling using contact plates should be conducted at the end of a compounding activity but prior to disinfection of the area.


Post-Sampling Clean-Up:

Contact between the TSA and testing surface leaves behind a residue that should be thoroughly cleaned following sample retrieval. The most effective method for removal is the use of a presaturated 70%-30% IPA wiper such as SatPax®. Berkshire’s line of SatPax® wipers offers a variety of materials and different IPA saturation levels, in sterile, non-sterile, and low endotoxin formats. For cleaning an aseptic isolator, Berkshire’s EasyClean® 360 tool is ideal for use in conjunction with the SatPax® product line. Additionally, if your operators would appreciate a refresher on the use of these items when cleaning an aseptic isolator, a video is available on our website. And if you have questions about cleaning a biological safety cabinet, we have both a training video and a downloadable guide. For the full line of SatPax® products, click here.

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