Transportation Affects Gut Microbiome of Laboratory Mice


Experimental controls are at the center of every quality experiment, and understanding the causes of microbiome variability is key to controlling for microbiome-related effects. Researchers that utilize murine models attempt to control for possible microbiome variability by ordering mice from the same vendor, using littermate controls, and employing co-housing strategies1. Given the ongoing research reproducibility crisis, it is vital to understand potential factors that contribute to microbiome variation in research mice and how best to control for these confounding factors2.

Effects of Transportation on Mouse Physiology

The transportation of laboratory mice from provider to recipient is a stressful process for research animals. Some affected characteristics include:

  • Behavior
  • Weight gain or loss
  • Eating and drinking frequency
  • Immune system function
  • Hormone levels
Tests in mice have shown that their levels of glucocorticoids and catecholamines remain abnormal for up to 48 hours after being received at their new destination. This, compounding with any additional stressors, can induce immunosuppression making the mice more vulnerable to infections3. Since these issues are all well-documented, most model providers therefore recommend at least 72 hours post-arrival to allow for mice to return to their normal physiological states prior to beginning any experiments. However, less information has been published on the effects of transportation on the mouse microbiome4.

Microbiome Disruptions During and After Shipping

Currently, there is limited published information on how transportation can alter the composition of the mouse gut microbiome. Certain studies have shown that moving mice from a specific pathogen-free (SPF) status facility to a different health status facility within the same institution resulted in a shift of the bacteria present in the mouse gut for up to five days5.

A study published in 2018 in Frontiers Microbiology tested the effects of shipping C57BL/6 and BALB/c mice from a model provider to two different facilities at the recipient institution and sampled fecal pellets to determine the effects on the composition of the microbiome.

Fecal samples were collected at multiple times to establish the microbiome profile prior to transport, after arriving at the facility, and at intermittent time points after. When analyzing the samples from pre-shipment and arrival, it was determined that the relative abundance of operational taxonomic units (OTUs) present in each sample were different. In this instance, OTUs are used to categorize different bacterial species based on a 97% sequence similarity as determined by 16S rRNA gene sequencing. The genera initially present in very low percentage abundance pre-shipping were seen to either disappear or decrease even further upon shipping. However, the more abundant genera present initially did not experience as much variation in their abundance.

Aside from the stress of shipping, a decrease in some of the rare OTUs present could be attributed to the transition of a primary food source such as chow to gel packs during shipment. These decreases in rare OTUs allowed for the increase of the more abundant genera, leading to a less rich, but more even, community of microbes in the gut. Upon analysis of all the samples, the researchers determined that the most stable period for the mouse gut microbiome is between seven and forty-eight days post-arrival. After this time, the composition of the microbiome did show some changes, which the authors attribute to a periodic shift characteristic of rodents6.

For researchers that want to control for potential variability in the mouse gut microbiome, monitoring of the OTUs present upon arrival and throughout their acclimation period is essential. Additionally, fecal pellet collection and sample sequencing throughout a study are invaluable for confirming the continued presence or absence of specific bacterial species7.

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References:
1. Franklin, C. L.; Ericsson, A. C. Microbiota and Reproducibility of Rodent Models. Lab Anim. (NY). 2017, 46 (4), 114-122.
2. Baker, M. 1,500 Scientists Lift the Lid on Reproducibility. Nature 2016, 533 (7604), 452-454.
3. Landi, M. S.; Kreider, J. W.; Lang, C. M.; Bullock, L. P. Effects of Shipping on the Immune Function in Mice. Am. J. Vet. Res. 1982, 43 (9), 1654-1657.
4. Obernier, J. A.; Baldwin, R. L. Establishing an Appropriate Period of Acclimatization Following Transportation of Laboratory Animals. ILAR J. 2006, 47 (4), 364-369.
5. Ma, B. W.; Bokulich, N. A.; Castillo, P. A.; Kananurak, A.; Underwood, M. A.; Mills, D. A.; Bevins, C. L. Routine Habitat Change: A Source of Unrecognized Transient Alteration of Intestinal Microbiota in Laboratory Mice. PLoS One 2012, 7 (10), e47416.
6. Hoy, Y. E.; Bik, E. M.; Lawley, T. D.; Holmes, S. P.; Monack, D. M.; Theriot, J. A.; Relman, D. A. Variation in Taxonomic Composition of the Fecal Microbiota in an Inbred Mouse Strain across Individuals and Time. PLoS One 2015, 10 (11), 1-17.
7. Montonye, D. R.; Ericsson, A. C.; Busi, S. B.; Lutz, C.; Wardwell, K.; Franklin, C. L. Acclimation and Institutionalization of the Mouse Microbiota Following Transportation. Front. Microbiol. 2018, 9 (MAY), 1-13.