Something smells...spongy.

The live text-chat for this problem took place on Wednesday, February 1, from 11:00 a.m. – 12:30 p.m. EST with the problem author in the "Comments" section below! Scroll down to see if your question was answered.

A 2017 scientific study from the journal Scientific Reports [1] set out to quantify the amount of bacteria living on both sanitized and uncleaned kitchen sponges. According to Markus Egert, a microbiologist involved in the study, “We found 362 different species of bacteria, and locally, the density of bacteria reached up to 45 billion per square centimeter."  Moreover, the study stated that two species of bacteria “showed significantly greater proportions in regularly sanitized sponges (compared to uncleaned sponges), thereby questioning such sanitation methods in a long-term perspective." This finding created a media frenzy, with articles appearing with alarming titles like “Your Kitchen Sponge Is Gross, and Cleaning It Isn’t Helping” [2].

But all was not as it seemed. As discussed in an interview with Michaeleen Doucleff [3], microbiologist Jennifer Quinlan was suspicious of the claims being made based on the paper, as heat (e.g., from microwaving or boiling a sponge) is well known to kill bacteria that cause food borne illness. In fact, a study from the USDA found that microwaving a sponge can decrease the concentration of bacteria by about 1 million-fold [4]. It seems that the Scientific Reports study may not have been especially careful in how its sponges were cleaned, or perhaps misinterpreted the experimental results. 

Your goal in this problem is to make a public health recommendation for how often people should sanitize or replace their sponges, based on the admittedly imperfect data you have available from the articles above. Begin by reading [4] in detail, and then address the following questions.

  1. Create a model that predicts the density of bacteria on a kitchen sponge as a function of that sponge’s age, assuming the sponge is not regularly sanitized.
  2. Modify your model to account for various sanitation routines. For example, you might consider how the bacteria density would change if the sponge was consistently microwaved at different intervals of time (daily, weekly, etc.). You can also consider different sanitation practices discussed in [4]. 
  3. Based on your models, make a public health recommendation for safe sponge use that would work for a majority of households.

Write a short (~150 words) press-release style explanation of your recommended best practices, justifying the recommendation to an educated but unfamiliar audience. 

[1] Massimiliano Cardinale, Dominik Kaiser, Tillmann Lueders, Sylvia Schnell, and Markus Egert. Microbiome analysis and confocal microscopy of used kitchen sponges reveal massive colonization by Acinetobacter, Moraxella and Chryseobacterium species. Scientific Reports, 7, 2017, pp. 5791.
[2] Lily Carollo. Your Kitchen Sponge Is Gross, and Cleaning It Isn’t Helping. August 2017. 
[3] Michaeleen Doucleff, So Your Kitchen Sponge Is A Bacteria Hotbed.  Here's What To Do. September 2017.
[4] Manan Sharma, Janet Eastridge, Cheryl Mudd. Effective household disinfection methods of kitchen sponges. 2009.
Problem Author: Dr. Kara Maki, Associate Professor at Rochester Institute of Technology