Plastics and the microbiome: impacts and solutions.

Global plastic production has increased exponentially since manufacturing commenced in the 1950's, including polymer types infused with diverse additives and fillers. While the negative impacts of plastics are widely reported, particularly on marine vertebrates, impacts on microbial life remain poorly understood. Plastics impact microbiomes directly, exerting toxic effects, providing supplemental carbon sources and acting as rafts for microbial colonisation and dispersal. Indirect consequences include increased environmental shading, altered compositions of host communities and disruption of host organism or community health, hormone balances and immune responses. The isolation and application of plastic-degrading microbes are of substantial interest yet little evidence supports the microbial biodegradation of most high molecular weight synthetic polymers. Over 400 microbial species have been presumptively identified as capable of plastic degradation, but evidence for the degradation of highly prevalent polymers including polypropylene, nylon, polystyrene and polyvinyl chloride must be treated with caution; most studies fail to differentiate losses caused by the leaching or degradation of polymer monomers, additives or fillers. Even where polymer degradation is demonstrated, such as for polyethylene terephthalate, the ability of microorganisms to degrade more highly crystalline forms of the polymer used in commercial plastics appears limited. Microbiomes frequently work in conjunction with abiotic factors such as heat and light to impact the structural integrity of polymers and accessibility to enzymatic attack. Consequently, there remains much scope for extremophile microbiomes to be explored as a source of plastic-degrading enzymes and microorganisms. We propose a best-practice workflow for isolating and reporting plastic-degrading taxa from diverse environmental microbiomes, which should include multiple lines of evidence supporting changes in polymer structure, mass loss, and detection of presumed degradation products, along with confirmation of microbial strains and enzymes (and their associated genes) responsible for high molecular weight plastic polymer degradation. Such approaches are necessary for enzymatic degraders of high molecular weight plastic polymers to be differentiated from organisms only capable of degrading the more labile carbon within predominantly amorphous plastics, plastic monomers, additives or fillers.

Evaluation of culture-based and molecular detection methods for Campylobacter in New Zealand raw cows' milk.

AIMS: This study evaluated the performance of a commercial molecular detection method (mericon Campylobacter triple kit real-time/quantitative (q)PCR) and a selective plating medium (R&F Campylobacter jejuni/Campylobacter coli Chromogenic Plating Medium (CCPM)) against a culture-based reference method (ISO 10272-1:2017 detection procedure B) for the detection of Campylobacter from raw milk enrichment broths. METHODS AND RESULTS: New Zealand raw cows' milk and Ultra-High Temperature-processed milk samples were inoculated with 50, 125 and 500 colony forming units of C. jejuni and C. coli cocktail per analytical unit. Samples were tested for Campylobacter after 0, 24- and 48 h refrigeration. ISO 10272-1:2017 proved to be a sensitive detection method (77/80 positive samples); detection only failed for some milk samples tested 48 h postinoculation. CCPM was as effective as Cefoperazone Charcoal Deoxycholate Agar for selective plating of Campylobacter raw milk enrichments (78/80 positive samples). However, the qPCR detected Campylobacter in only 42/80 samples and qPCR reaction inhibition was observed. CONCLUSIONS: The ISO 10272-1:2017 method was a more sensitive method for Campylobacter detection from raw milk than the mericon Campylobacter triple kit qPCR, and CCPM was a useful complementary medium to mCCDA where one of these media is required by the standard. SIGNIFICANCE AND IMPACT OF THE STUDY: In regions where testing is required or recommended, optimized methods for Campylobacter detection from raw milk will reduce risk to the raw milk consumer. Although molecular methods are generally touted as a rapid alternative to culture, issues with inhibition due to matrix components mean that culture-based methods might provide the most sensitive option for Campylobacter detection in raw milk. Findings also emphasize the importance of minimizing the time between milk collection and testing for Campylobacter.