Cleaning products and bacterial ecologies

A few months ago, our participants conducted their second attempt at bacterial mapping. 

Their experiment explored how different cleaning methods affected the bacterial communities found on their kitchen surfaces. They tested eight different methods for cleaning kitchen surfaces: washing up liquid, warm water, anti-bacterial surface cleaner, bleach, environmentally-friendly detergent, vinegar, special cloths, and even a probiotic cleaner. They swabbed the surfaces before cleaning them; they swabbed the cloths they used in cleaning; and they swabbed the surfaces afterwards. The swabs were then taken to the lab, and prepared for sequencing. 

This graphic shows combined data from 26 separate cleaning product experiments. Each experiment swabbed a surface before cleaning, swabbed the cloth used for cleaning (using one of eight possible products), and swabbed the surface again after cleaning.

This graphic shows combined data from 26 separate cleaning product experiments. Each experiment swabbed a surface before cleaning, swabbed the cloth used for cleaning (using one of eight possible products), and swabbed the surface again after cleaning.

The results from the 16S sequencing are tricky to interpret. First, the method doesn't distinguish between "live" and "dead" DNA - so the swabs done after cleaning don't tell you if the bacterial DNA represents live bacteria or not. And second, there is some controversy amongst microbiologists about whether sequencing "reads" can be interpreted as proxies for bacterial abundance. 

This graphic shows the data from an individual household. Each household tested two products.

This graphic shows the data from an individual household. Each household tested two products.

Nevertheless, the patterns found are pretty interesting. The bacterial communities found on kitchen surfaces after cleaning tend to look an awful lot like either: (i) the community found before cleaning, (ii) the community found on the cloth used to do the cleaning; or (iii) a mix of the two. And they don't look anything like some other surfaces we swabbed as controls, which is reassuring. Also, if the abundance measures are to be believed, most of the cleaning techniques lead to very little reduction in bacterial abundance (although for those products that work by killing bacteria rather than removing them, the DNA found may well represent dead bacteria).

This graphic aggregates the 26 experiments according to which cleaning product was used. The number at the top of each column represents how many households tested this method - which was their own choice.

We met to discuss these findings last week - and a big thanks are due to Adam Hardgrave from the Food Standards Agency who came along to help us interpret the data!