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Performance Testing
Published in Marc B. Brown, Adrian C. Williams, The Art and Science of Dermal Formulation Development, 2019
Marc B. Brown, Adrian C. Williams
An advance on the relatively simple modified zone of inhibition assays are infected skin models. These rely on the ability to grow and culture the organisms on the skin, and to accurately recover and quantify the viable organisms after treatment. Typical organisms used (but not exclusively) are yeasts such as C. albicans or P. ovale, dermatophytes such as T. rubrum or T. mentagrophytes, or bacteria such as P. acne, S. aureus (including MRSA), P. aeruginosa, and S. epidermis. In these models, an organism (bacteria, yeast, or fungi) most relevant and causative of the infection is artificially introduced under controlled conditions and growth is controlled. The location of the infection within the skin is also controlled, for example, superficial or on the underside of the stratum corneum, epidermis, or dermis, such that the position of the organism within the skin closely resembles that of the clinical presentation. In addition, and if appropriate, the barrier properties of the diseased skin itself can be replicated. The ability of the drug or formulation to exert its antimicrobial effect is then assessed using the measurement of a biological marker in the form of ATP, a direct indicator of cell viability, PCR, or direct viable counts. This model also allows the use of living ex vivo skin to explore the effects of an infection and consequent inflammatory responses for multimodal mechanistic studies.
Azithromycin in the treatment of rectogenital Chlamydia trachomatis infections: end of an era?
Published in Expert Review of Anti-infective Therapy, 2021
Margaret R. Hammerschlag, Roopali Sharma
The epidemiology of rectal infection in women without a history of anal intercourse is not clear. A number of explanations have been offered including nucleic acid contamination from the vagina during toileting as the majority of these data have been based on NAAT testing. However, studies have documented rectal C. trachomatis infection by culture and by a viability PCR that detects mRNA [16,17]. The presence of high rectal viable C. trachomatis loads in women is felt to represent ongoing infection, not the presence of remnant DNA from dead organisms or contamination form an active vaginal infection [16,17]. The clinical impact of rectal infection in women is not known. The majority of these rectal infections are asymptomatic. Currently, routine screening of women for rectal C. trachomatis is not recommended if they do not provide a history of anal intercourse. It is not known if the presence of rectal infection in women impacts treatment of vaginal infection, sexual transmission, or clinical sequelae including pelvic inflammatory disease.
Review of Chlamydia trachomatis viability methods: assessing the clinical diagnostic impact of NAAT positive results
Published in Expert Review of Molecular Diagnostics, 2018
Kevin J. H. Janssen, Jeanne A. M. C. Dirks, Nicole H. T. M. Dukers-Muijrers, Christian J. P. A. Hoebe, Petra F. G. Wolffs
NAATs are known to amplify the targeted nucleic acids without discriminating between DNA originating from viable or dead bacteria. However, implementation of membrane-impermeable DNA intercalating dyes (e.g. propidium monoazide; PMA) as a sample preparation step before conducting NAAT has shown to be a promising approach for the selective detection of viable bacteria. In this approach, called viability-PCR (V-PCR), the distinction between viable and dead bacteria is based on membrane integrity. V-PCR consists of incubating the sample with a DNA intercalating dye which can only pass compromised membranes. Upon photoactivation, the DNA intercalating dye irreversibly binds to the exposed DNA, which in turn prevents amplification by PCR [65–67]. Subsequently, the observed difference in bacterial load between the PMA treated and untreated sample correlates with the bacterial viability in the original sample. The amount of dead bacteria is greater with increasing differences in the observed cycle of quantification values (Cq).