Editor’s note: In January 2013, Volume 4 of the successful PDA-DHI technical book series, Encyclopedia of Rapid Microbiological Methods, was released. In this review, long-time proponent of rapid methods and editor of the encyclopedia, Dr. Michael J. Miller, provides an expert synopsis of the book’s relevant and timely content.

Volume 4 of the Encyclopedia of Rapid Microbiological Methods engages readers with an excellent introduction by Dr. Bryan Riley, New Drug Microbiology Staff at the Food and Drug Administration’s (FDA’s) Center for Drug Evaluation and Research, and the Agency’s expert on rapid method technologies. Dr. Riley explains that modern approaches to process control — including Process Analytical Technology (PAT) — require the availability of results in real time (or at least close to real time) to enable the operator to immediately use the test results and intervene if necessary to make process-optimizing decisions and adjustments. Although real-time results are only currently available for a limited category of microbiological tests, there are many microbiological methods that are significantly more rapid than the traditional test methods. 

Dr. Riley continues, offering that the rapid methods available today vary a great deal in their mechanisms of operation. Some of these methods, he notes, still rely on a period of microbial growth using traditional media, but reduce their time to result by using an alternate method of microbial detection. Other rapid methods do away with growth entirely and utilize a stain or inherent microbial auto fluorescence to detect microorganisms; even down to the level of a single microbial cell. Furthermore, some of the available methods are quantitative, some are qualitative, and vary in their time to result (from real-time to several days) but all of these methods seem to have found a niche in the pharmaceutical microbiologist’s arsenal.
Current rapid microbiological test methods are now able to start providing some of the advantages long enjoyed by industry colleagues in clinical and food microbiology labs. Pharmaceutical microbiologists would be well served by considering which of their samples would provide a benefit with a more rapid result, then assessing the current alternate microbiological methods to see if any of them fit their needs.

Featuring up-to-the-minute advances and details regarding quality control and choosing appropriate methods, Volume 4 covers future-use scenarios, current and emerging technologies, mass spectrometry, genotypic methods for identification, new case studies and application of USP and other guidelines. The book offers valuable assessments and reviews of environmental monitoring, validation, sterility testing, Mycoplasma testing, and the application of rapid microbiological methods as they relate to both bio-processing, product-specific method advances and regulatory considerations.
For instance, guidance on the application of modern microbial methods is covered in Chapter 1, which discusses the Quality Control testing of probiotics, including master and working cell banks, release and stability testing, and viable cell counts. It also details identification and strain typing, absence of bacterial pathogens, antibiotic resistance, adherence to the intestinal wall and acid and bile resistance.

Aligning RMM to suit

Considerations when aligning a rapid microbiological method to suit an end-user’s particular needs is reviewed in Chapter 2. Topics range from the drivers for rapid methods, time savings, same-day results, sample compatibility and automation, to using a qualitative method as a screening tool, validation, identification, integration with LIMS and other data management platforms, as well as false positives, false negatives and detection limits.
In Chapter 3, a close look is taken at the future of rapid and automated microbial identification systems. Here the Encyclopedia provides an overview of technologies based on the growth of microorganisms, the detection of cellular components, optical spectroscopy, nucleic acid amplification and MEMS. Included are examples outlining the utilization of biochemical and carbohydrate substrates, fatty acid analysis, MALDI-TOF and SELDI-TOF mass spectrometry, FT-IR, elastic and inelastic light scattering, ribotyping, PCR, microfluidics and microarrays.

A more detailed case study in Chapter 4 covers the use of MALDI-TOF mass spectrometry for the identification of microorganisms. Discussions on sample preparation, OQ, PQ, accuracy, precision, robustness and computer validation are also covered. In Chapter 5, another case study on microbial identification focuses on genotypic methods, amplification of DNA, automation and validation (accuracy, precision, robustness and specificity). A discussion of the new method’s ability to comply with GMP principles is covered as well.

A review of workflow/applications for a rapid growth-based microbial identification system are reviewed by its supplier in Chapter 6. The chapter’s contributor also provides validation considerations, as well as an overview of enhancements to the supplier’s existing technology.

New growth-based method
A case study of a new growth-based rapid microbiological method that detects the presence of specific organisms and provides an estimation of viable cell count is provided in Chapter 7. The chapter thoroughly covers sample preparation, assay workflow, and the method’s applicability to a wide-range of microorganisms. Additionally, data from a validation case study, inclusivity and exclusivity testing, and a comparison to USP <61> for aerobic counts, yeast and mold, and Gram-negative bile tolerant microorganisms also provide readers valuable insight into the viability and efficacy of this new method.

An evaluation of a relatively new growth-based rapid method that utilizes a membrane filtration workflow coupled with a viability staining technique is featured in a revealing end-user case study in Chapter 8. The chapter’s author provides a review of the technology and evaluates the method’s results. This is followed by a discussion of the system’s applicability when it comes to monitoring mammalian cell cultures, as well as additional benefits the method can offer to biopharmaceutical processors.