Microbial Communities: Built Environment Non-Technical Summary

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Non-Technical Summary

Humans spend most of their time inside buildings- that includes the time they spend in the hospital. Hospitals are a hub for not only sick patients, but healthcare workers and visitors. As a high-traffic area, the types of bacteria growing in a hospital are constantly fluctuating. This growth is only exacerbated by the bacteria lent to the environment by the sick patients. The conditions that impact how microbes spread in a hospital are important to understand so a patient doesn’t come down with a new disease while being treated for something unrelated. Researchers from the University of Chicago spent over a year sampling what bacteria were growing throughout a new hospital and on patients- and they found some surprising results.  When a new patient was admitted to the hospital, the bacteria of the room they were staying in quickly came to resemble the patient. This trend was most obvious on surfaces that a patient would often touch- like a bedrail. Results from DNA sequencing showed that antimicrobial resistance was also present. However, bacteria with resistances to drugs were more likely to be found on the hospital surfaces rather than living on the skin of patients or staff. Researchers also found that certain patients had fewer microbes on themselves and their surroundings. In particular, chemotherapy patients had fewer different types of microbes. This study concluded that humans are the biggest factor for what microbes are living in buildings. Further research should spend more time looking for trends in microbial transfer within hospitals and for deciding what can be done to present a healthy hospital.

Source
S. Lax, et al., Bacterial colonization and succession in a newly opened hospital. Sci. Transl. Med. 9, eaah6500, (2017), https://dx.doi.org/10.1126/scitranslmed.aah6500.

Human Microbiome

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Zachary Snelson

The Host Microbiome Regulates and Maintains Human Health: A Primer and Perspective for Non-Microbiologists

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5392374/

Summaries

General audience:

Human beings have always seen themselves as superior organisms that can operate on their own. However, would you ever think that even small parts of your body can have an entire ecosystem of microbes? Those interacting microbes can effect not just each other, but they can also have effects on the human host too. This research paper gives details on how the amount of diversity of microbes in the human microbiome can lead to adaptations against certain diseases and the changes in microbiome overtime can also help maintain the host’s development. Changes in the human host in terms of aging, diet and even what kind of environment that they are in have important roles in how the human microbiome is composed. The ongoing research over the diversity and composition of microbes on the human host can help us to further understand the molecular mechanics in disease.

The diverse variety of microbes in the human microbiome consists of not only bacteria and viruses, but also archaea and fungi as well. What kinds of benefits the microbes in the human microbiome can offer in terms of survival can range from The microbiome changes as the host ages, such as when a newborn is introduced to a foreign environment and when it eventually grows up to be an adult. When a baby is born, it can have a different structure in its microbiome depending on how it was born. For example, when born vaginally, the baby will have bacteria that helps aid in the digestion of lactose in milk products due to microbes in the vaginal cavity coming into contact with the baby during birth. Even other types of interaction with the human host can alter the microbial communities in the microbiome. In this case, the human host having a different diet can promote changes in the gut microbiota, an example such as animal products can increase the abundance of bile resistant bacteria in the gut. The human microbiome can play a crucial role in providing other benefits that can help maintain the host’s health. Such examples are the gut microbiome acting as a safeguard against cardiovascular disease, Inflammatory Bowel Syndrome, and pathogens. Cancer is also another threat to the health of the human host and negatively impact the microbiome. Changes in the gut microbiome from foreign bacteria, antibiotics, and age related symptoms can lead to the development of cancer in the human host’s gut.

Microbes in the human host that were genetically engineered have potential that can even assist with cancer prevention. It is important to help assess the advances in the diversity of microbes in the human microbiome to accommodate the emerging methods of surveillance and detection of different strains of microbes on the human body. Looking into how and why the interacting microorganisms in the human microbiome will be able to help us further understand the implication that microbes have on important medical fields such as disease management, cancer research, and even aging.

Scientists/engineers:

To emphasize the size and scale of microbes, the amount of eukaryotic cells in the human body is estimated to be 3 × 1013   and there are about 3.9 × 1013 colonizing microorganisms, in which would imply that the amount of microbes is larger than the human host. There is compelling evidence that the interaction between microorganisms in the human biome and the host is important to maintaining the individual host’s survival. The diversity of the microbiome is determined using metagenomic data. The bioinformatic results from the targeted metagenomic sequencing are available from various sources such as the Human Oral Microbiome Database, SILVA, and the Ribosomal Database Project. Prokaryotic microbes such as bacteria, archaea, fungi and even viruses like Bacteriophages play a role in the ecology and community of prokaryotes and eukaryotes in the human gut. Even eukaryotic microbes such as fungi, Protozoa, algae, and nematodes are prevalent in the skin microbiota.

The human microbiome in terms of diversity can change over time as the host develops and ages during its lifetime. When it comes to the development microbiota of babies, for instance, changes depending on the human host being exposed to a different environment over time. When the human baby is born, for instance, the microbiome can change depending on how the host is born and what types of microbes are related to those types of exposure. Babies that were born through the Cesarean section method were found to have Streptococcus spp. and other bacteria that were associated with the mother’s skin, while babies born vaginally have Lactobacillus which can aid in the digestion of milk. Aging over time can lead susceptibility to disease that correlates with changes in the immune system such as increase in inflammatory states in the gut, Lactobacillus bacteria increasing with low fat diets and oxidative stress that encourages virulence of anaerobic bacteria. The human microbiome can play a role in the health of the heart in regards to cardiovascular health, obesity and even behavior. The human microbiome, especially the gut microbiota, are vital for the metabolic potential to alter the chance of the human host having cancer. The microbiome can be changed by dysbiosis, which is the disruption of interactions between the gut flora and the human host. Smoking, foreign pathogens, and immunosenescence from aging are major factors that can disrupt the gut microbiome, and can eventually result in negative results such as tumor progression.

While evidence for the interplay is not fully understood, there have been evidence to show that microbes can affect the rate of carcinogenesis, the progression of tumors and the overall response to immunotherapy treatment. Through the co-evolution between the human host and the microbiome, the immune system is inherently modulated by microorganisms that inhabit the human host from selective pressure from invading pathogens in the environment. The applications of microbes in the gut microbiome can help provide insight on how microbes can help benefit the human host in preventing irritable bowel syndrome and In order to help improve cancer treatments, researchers will need to keep thoroughly examining the human microbiome. While there have been astounding achievements in developing the taxonomy of the human microbiome, there are still challenges in Studying the human microbiome can help us become more familiar with the genetics, biology, physiology and immunologic effects of the interacting microorganisms in the human host.

Microbial Communities of Mt. Prindle, AK — Permafrost soils!

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Sophie Weaver
Technical summary: Permafrost and microbial functional diversity

Climate change is amplified in high latitudes, making areas with discontinuous permafrost especially susceptible to thaw. With the thaw and resulting processing of previously frozen soils through microbial decomposition, increased release of CO2 and CH4 into the atmosphere will occur. Permafrost currently stores approximately twice as much carbon as is in the atmosphere, making permafrost thaw and microbial processing an important topic of research in light of climate change. These authors asked (1) how are microbial communities and their functional composition and abundance affected by permafrost thaw and (2) what environmental shifts due to permafrost thaw (i.e. vegetation) might be leading to these changes. This study was carried out in Interior Alaska, where discontinuous permafrost creates an ideal location to study the impacts of permafrost thaw on soil biogeochemical cycling. They used GeoChip analyses to measure microbial functional genes present in minimally thawed, moderately thawed, and extensively thawed permafrost soil samples. They found that microbial community functional gene abundances (especially for C and N cycling genes) were highest at the moderately thawed sites and were associated with higher vascular plant growth. They found that along the thaw progression, microbial functional gene richness declined, but microbial community diversity actually increased. These results suggest that microbial communities and vascular plant growth might be correlated due to warming soils and permafrost thaw. As permafrost thaws, microbial decomposition and nutrient cycling will likely increase in these soils, and vascular plants could benefit from this, changing the tundra landscape and vegetation and suggesting that microbial and plant communities may co-evolve.

Non-technical Summary: What’s going on below this patch of vegetation??
Every environment surrounding us contains communities of microorganisms that perform important processes. These processes cycle elements, like carbon and nitrogen, throughout the biosphere (think – water cycle but more complex!). Soils, for example, are incredibly diverse environments that not only harbor plant growth, but are also home to millions of microbes. Soils have many characteristics that help define the community of plants and microbes that will be able to live there. Some soils are located in climates that are so cold they are continuously frozen for more than two years. This extreme soil habitat is called permafrost, and has its own unique microbial communities. When we think of climate change, we often picture starving polar bears and rising sea levels, but permafrost is also damaged by warming temperatures! As permafrost thaws, the plants growing on these soils can be impacted by increasing soil moisture and temperature. Microbial communities can also change, as some microbes are better fit to survive in the new, thawed,  conditions. So what might happen to these microbes that currently live in permafrost habitats that are starting to thaw? A study in central Alaska discovered that as permafrost thaws, plant growth changes, and the amount and the function of microbial communities present also changes! These scientists discovered that microbes found in more thawed soils had more abundant genes involved in the cycling of carbon and nitrogen, meaning that these microbes were better fit to process the carbon and nitrogen available in their environment. This change in soil conditions not only caused a change in microbial community, but also impacted the growth of the plants nearby! So what does this mean for microbes? As the Earth’s temperature continues to rise, more permafrost is expected to thaw, and microbes in Alaska are going to have to adapt in order to survive in novel soil conditions or they will be replaced by other microbes that are better fit for an unfrozen soil environment. While these microbes will likely benefit from thawing permafrost, the loss of permafrost will have huge implications for climate warming and plant growth, Microbes will contribute to climate change by increasing the prevalence of greenhouse gases (carbon dioxide, methane) in the atmosphere. The importance of microbial contributions to climate change should not be underestimated!

ThingLink Cloud microbiology Technical summary

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Technical Summary:

Compared to the terrestrial, marine, and limnic environments, the microbial community is relatively unknown in the upper atmosphere (>8 km). Some attempts to measure the lower atmosphere (1 – 7 km) from the tops of mountains have been made, showing that airborne bacteria and fungi from near the ground are lofted by zephyrs and other types of air movement. Studies in the past have also shown that some plant pathogens carry genes for the ice nucleation protein inaZ. If these bacteria were present in the upper atmosphere, they would constitute a major portion of the high-altitude supermicron ice nuclei (particles 0.5 – 3 \( \mu \)m   in size that supercooled water can freeze to). Bacteria are also thought to be meaningful condensation nuclei for cloud formation at lower altitudes.

In this paper, the authors sampled air from the platform of NASA’s aircraft while they were engaged studying the upper atmosphere studying the effects of hurricanes on the upper atmosphere. They sampled ~ 8 m\(^3\) of air with an aerosol spectrometer to estimate the size and abundance of molecules followed by filtration for the sample to perform microscopic counting and qPCR analyses of the small subunit rRNA. They found that there were on average 15,000 cells per cubic meter of air. at high altitude. Most of these were bacteria which do not fall as quickly through the air as do the larger and heavier fungal cell/spores. Analysis of the 16S rRNA gene revealed the vast majority of OTUs were Alpha– and Betaproteobacteria with genera such as Afipia (alpha) and Burkholderiales (beta) making up > 70% of the total reads. Many of the OTUs were in families known to utilize 1-4 carbon molecules in their metabolism, which exist in abundance at that altitude in cloud droplets.

Sampling in the wake of hurricanes Earl and Karl showed that a large portion of the bacterial community resulted from ocean water lofted to altitude and fecal coliforms whenever the hurricane encountered human settlement. In addition, samples taken over land in transit from California, USA to Florida, USA showed that the majority of bacteria were from limnic systems. Together, this suggests that the high altitude bacterial community is primarily supplied by specimens originating in bodies of water that evaporate and are lofted by updrafts and storms.

 

Paper:  DeLeon-Rodriguez, N., Lathem, T.L., Rodriguez-R, L.M., Barazesh, J.M., Anderson, B.E., Beyersdorf, A.J., Ziemba, L.D., Bergin, M., Nenes, A. and Konstantinidis, K.T., 2013. Microbiome of the upper troposphere: species composition and prevalence, effects of tropical storms, and atmospheric implications.  Proceedings of the National Academy of Sciences,  110(7), pp.2575-2580.

Biofilms in Flexible Hoses

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General Audience Summary:

Many kitchen sinks (and shower heads), have an extendable (pull out) faucet that requires a flexible hose of some length. These hoses are made from different materials and many of the materials leach organic carbon that may facilitate bacterial growth on the surface, referred to as a biofilm, in the hose. The study evaluated different materials commonly used for these flexible hoses and the resultant biofilm growth while simulating realistic use of a kitchen sink or shower. The flexible materials evaluated included polyethylene (PEX) tubing, a silicone based pipe, a pipe with an antibacterial coating containing silver, and two types of polyvinyl chloride (PVC) pipes, one much more expensive than the other. In addition, a non-flexible PEX pipe was evaluated. It’s important to note that the water used in the testing was not chlorinated, which is common for systems that have use groundwater wells for a water source (many public water systems maintain a residual chlorine level in the distribution system).

The results indicated that the PEX tubing (both flexible and non-flexible) as well as the silicone-based pipe leached the lowest amounts of organic carbon (a food source for bacteria) and had the least amount of bacteria growth. However, the community of bacteria that did develop had overall higher numbers of pathogens such as Legionella, a type of bacteria that may cause pneumonia- or flu-like illnesses. The piping with the antibacterial coating initially had lower growth but over-time the coating was lower effective and, after 8 months, it had a similar biofilm to the other flexible pipes tested with the exception of the “cheap’ PVC pipe that had the highest overall number of bacteria present.  Based on their results, the authors suggest that pipe materials should be engineered to leach organic carbon that encourages benign bacterial growth in order to better protect the consumer from harmful pathogen development.

Technical Audience Summary:

Flexible hoses are commonly used in the last one meter (two to three feet) before a fixture at a kitchen sink or shower. Different materials leach more organic carbon which leads to greater biofilm growth in these hoses. The study evaluated different material types commonly used in household plumbing including polyethylene (PEX) (both a non-flexible and flexible pipe), silicone based piping, one with an inorganic silver-ion coating, and two types of polyvinyl chloride (PVC) pipes, one that was much more expensive and included an ash addition in the pipe material. The study examined total organic carbon leaching and biomass growth in the short term and over a longer term (8 months). A BioMig test package was used to quantify the organic carbon migration potential and biomass formation potential. Fluorescence staining was used to calculated total cell concentration (TCC). Total ATP and organic carbon (TOC) in the biofilm was also determined. DNA extraction, qPCR targeting 16S rRNA genes, and 16S rRNA amplicon sequencing was used with statistical analysis to determine the community structure of the biofilm.

The study showed that the PEX non-flexible pipe overall had the least biomass growth while the “cheap’ PVC pipe had the most. After about 8-months, the other four pipe materials (flexible PEX, silicone, silver-ion coated, and ash-PVC had similar biofilm concentrations. Overall, biofilm concentrations increased over time. The community structure varied by both material and time. The authors also found that even though the same source of water was used in all pipes, the community structures did vary between pipe types. They attributed this to the different types and amounts of organic carbon that are leached from the pipes. The pipe materials with the lowest biofilm concentration also tended to have higher amounts of opportunistic pathogens; the four genera found were Legionella, Pseudomonas, Nocardia, and Mycobacterium with Legionella being common to all samples. Six other genera were also found to be common to all samples and included Caulobacter, Bradyhizobium, Sphigomonas, Methyloversatilis, Phenylobacterium and an unclassified genera within Comamonadaceae. Based on their results, the authors suggest that pipe materials should be engineered to leach organic carbon that encourages benign bacterial growth in order to better protect the consumer from opportunistic pathogen development.

Link to Article: https://pubs.rsc.org/-/content/articlehtml/2016/ew/c6ew00016a

Citation: Proctor, Caitlin R., Marja Gachter, Stefan Kotzsch, Franziska Rolli, Romina Sigrist, Jean-Claude Walser, Frederik Hammes (2016). Biofilms in shower hoses — choice of pipe material influences bacterial growth and communities. Environmental Science: Water Research & Technology, 2016, 2, 670-682.

Microbial Communities: Invasive vs. Native Plants Non-Technical Summary

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According to this article, invasive plant species pose a threat to many ecosystems, including wetlands. Invasive plant species have been known to outcompete and take over native plant communities, reduce the amount of different native plants in an area, and alter nitrogen and carbon cycles within the environment by altering the microorganism community (microbiome). This paper focuses on the chemical and physical compositions as well as the soil microbial communities of the Cheboygan March, a freshwater wetland, in Michigan. The marsh was infested by an invasive hybrid species of plant called Typha×glauca about 30-40 years ago. Because the study area was divided into 3 stages (native plants, transitional, and only Typha×glauca), the researchers were able to establish a gradient of infestation, chemical composition, and microbial community differences. They ran chemical composition tests to determine whether this invasive plant species was altering the sediment nutrient content. To determine whether or not the microbial community composition was being altered, they ran sediment samples through DNA sequencing and Polymerase Chain Reaction (PCR: used to amplify certain sections of DNA). They also ran functional gene analysis on the samples to see if microbes were using genes associated with nitrogen uptake and cycling, an important nutrient in the environment. Overall, they found that the microbial community composition was significantly different between the native plant area and the Typha×glauca area. There were more species of bacteria in the Typha×glauca area than the native plant section. Chemically, they found a significant increase in soluble nutrients within the Typha×glauca section. They also found that the abundance of one important gene used for nitrogen cycling by microbes was higher in the Typha×glauca section than in the native area. This study proved that invasive plant species have a significant impact on sediment chemical and microbial characteristics. Invasive plants may hinder the ability for natural wetlands to rid the environment of excess nutrients, thus altering the nutrient cycles for surrounding ecosystems, but more research must be compiled to support this statement.

Citation: Angeloni, N. L., Jankowski, K. J., Tuchman, N. C., & Kelly, J. J. (2006). Effects of an invasive cattail species (Typha× glauca) on sediment nitrogen and microbial community composition in a freshwater wetland. FEMS microbiology letters, 263(1), 86-92.

Article: https://academic.oup.com/femsle/article/263/1/86/598071

 

Microbial communities article summaries

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https://www.sciencedirect.com/science/article/pii/S0168160504000820#FIG6

Prevalence of Microbial biofilms on selected fresh produce and household surfaces

Non-technical:

Do you wash your vegetables after purchasing them from the store? Do you wipe down your counter, sink, and cutting boards after every use? If not, you may want to start. A group of scientists went to the grocery store and bought carrots (bulk and bagged), tomatoes, lettuce, and mushrooms to test if there is any bacteria living on these veggies. They discovered that there was a presence of a biofilm on every vegetable they purchased. A biofilm is a thin layer on the surface of objects that is created by bacteria. The scientists also decided to test whether there were bacterial communities living on sponges, wooden cutting boards, wet and dry towels, as well as wet and dry socks. They came up with the same results; bacterial biofilms were growing on every surface. Unfortunately the scientists also concluded that not much can be done to completely sanitize your vegetables or towels. Typical detergents and soaps are not able to break through that biofilm layer and properly disinfect your veggies or linens. But there is good news; if you rinse your food with chlorine, or acidic detergents you can inhibit further growth on those surfaces.

Technical:

This paper gives the results from testing multiple surfaces in a domestic environment for the presence of biofilms and other microbial communities. They tested tomatoes, lettuce, carrots, and mushrooms from the grocery store, as well as cutting boards, sponges, wet and dry towels, and wet and dry socks. They used Cryostage scanning electron microscopy and light microscopy to detect microbes, and Alcian blue staining to expose a biofilm layer. The results revealed that there was an exopolymeric associated biofilm layer on every vegetable surface and household item, plus the results indicated a presence of fungal growth on sponges, socks, and towels. Unfortunately typical detergents and sanitizers are unable to break through that biofilm layer and kill the bacteria inside. The scientists reference literature where not even multiple chlorine rinses were able to completely sanitize these items. Rinsing with chlorine, acidic, or alkaline detergents can only decrease the viability of the organisms creating the biofilm, but not completely rid the layer. Because the biofilm on these surfaces is hard to remove, there is an increased possibility of those surfaces carrying pathogenic bacteria. The end result is that there are microbes living on most surfaces that you may encounter in everyday life.

 

Joanna Rayner, Richard Veeh, Janine Flood, Prevalence of microbial biofilms on selected fresh produce and household surfaces, International Journal of Food Microbiology, Volume 95, Issue 1, 2004, Pages 29-39, ISSN 0168-1605, https://doi.org/10.1016/j.ijfoodmicro.2004.01.019 (https://www.sciencedirect.com/science/article/pii/S0168160504000820)

Microbial Communities: Invasive vs. Native Plants Technical Summary

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A study completed in 2006 focused on the exotic plant invasion of Cheboygan Marsh, a freshwater wetland in Michigan. Previous studies have shown that the introduction of an invasive plant species can alter the microbial community and carbon or nitrogen cycling systems of that area. In this study, researchers focus on an exotic cattail plant species, which they call Typha. Chemical and physical sediment analyses were done by multiple methods to examine nitrate, ammonium, and phosphate concentrations. They also measured sediment water content and organic matter content. Microbial analysis was performed using DNA sequencing and PCR to amplify 16S rRNA. To analyze the composition of genes for denitrification (nirS and nirK), they used specific primers and 16S rRNA amplicon sequencing. Results from sediment chemical and physical analysis suggested that there was a significant increase in nitrate, ammonium, and phosphate concentrations in the Typha infested area. The microbial analysis suggested that there was a significant difference in microbial community composition between the Typha zone and the native plant zone, with the Typha zone showing more bacterial species richness. This was surprising considering the native zone had higher plant species diversity. The nirK  gene could not be amplified possibly due to inhibitory compounds blocking the PCR from working. The nirS gene was significantly more rich in the Typha zone than the native plant zone. Overall, this study found that the invasive Typha plant species could be affecting the marsh’s ability to remove certain nutrients from the water by increasing the amount of soluble nutrients put into the environment and allowing for a shift microbial community composition and denitrifying microbes.

Citation: Angeloni, N. L., Jankowski, K. J., Tuchman, N. C., & Kelly, J. J. (2006). Effects of an invasive cattail species (Typha× glauca) on sediment nitrogen and microbial community composition in a freshwater wetland. FEMS microbiology letters, 263(1), 86-92.

Article:  https://academic.oup.com/femsle/article/263/1/86/598071

Microbial Communities: Built Environment Technical Summary

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Technical Summary  

The microbiome of the built environment has implications for human health. Understanding what influences the presence, spread and colonization of microbes in the built environment is necessary for preventing disease stemming from the microbial population in homes, workplaces, and hospitals. Furthermore, the risk of hospital-acquired infections is a growing concern as effective treatments for antibiotic-resistant bacteria increases. In order to identify the risk and spread of infection in a hospital preliminary research about the hospital microbiome is required. Lax et al. conducted a longitudinal study in a newly- opened hospital. They sampled the hospital surfaces, patients and staff. Abiotic factors, such as light, temperature and humidity, were also tracked for potential influence on bacterial transmission.  Microbial communities from pre-opening and post- opening were highly distinct suggesting that human presence was highly influential of the built environment microbiome. When a patient was admitted, their skin microbiome was transferred to the surfaces in their room. Metagenomic characterization showed that antimicrobial resistance genes were more likely to be found on surfaces than skin. In this study, there were no correlations found between the abiotic factors measured and the transmission of microbes. Researchers correlated chemotherapy treatment in patients with a lower alpha diversity in the patient’s nose, hand, and bedrail. The conclusions from this study showed that patient skin is clearly a vector for the hospital microbiome.

 

Source
S. Lax, et al., Bacterial colonization and succession in a newly opened hospital. Sci. Transl. Med. 9, eaah6500, (2017), https://dx.doi.org/10.1126/scitranslmed.aah6500.

Microbial Communities: Microorganisms in Kitchen Sponges

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Microorganisms in Kitchen Sponges: Technical Summary                                               In this study conducted by ErdoÄŸrul and Erbilir they examined the presence of various microorganisms in sponges, and whether or not dishwashing detergent had an effect on eliminating the growth of organisms. They found that daily application of detergent had no effect on yeast, molds, pseudomonads, or  E. coli, but it did decrease the presence of Salmonella spp. in sponges used in a “normal’ household. They also artificially contaminated 10 sponges with  E. coli  and  S. typhimurium  and kept them in a laboratory setting. Here they found that dishwashing detergent was effective in reducing the number of both  E. coli  and  S. typhimurium  microorganisms in the sponge. The study concluded that the presence of food residue on kitchen sponges greatly reduced the effectiveness of the dishwashing detergent on preventing microbial growth. They emphasized that sponges and dishcloths should be rinsed and dried after use in order to not facilitate bacterial growth.

Microorganisms in Kitchen Sponges: Non-Technical Summary                                   Have you ever wondered what microbes live in your kitchen sponge, and if detergent actually affects these microbes at all? Well, a research team from Turkey did a study looking at how dishwashing detergent actually can kill the bacteria that live in kitchen sponges. They discovered that by applying soap to the sponge two times a day only some Salmonella spp. bacteria were killed, but the detergent had no effect on most of the yeasts, molds, and bacteria like E. Coli. They also added bacteria to some sponges that were stored in the laboratory, and here they found that the dishwashing detergent actually killed most of the bacteria. As we know most strains of E. coli are harmless, but some might cause sickness when it comes to Salmonella spp. most strains are pathogenic, but will just cause symptoms like diarrhea, fever, etc. or you might not get any symptoms at all.  Therefore, they concluded that the food that gets stuck on the sponge when it is used in the kitchen actually helps the bacteria grow, so they recommended that all sponges and dishcloths should be rinsed and dried after they have been used in order to make it harder for the bacteria to survive.

Literature Cited                                                                                                                 Erdogrul, Ö., & Erbilir, F. (2000). Microorganisms in Kitchen Sponges. Internet Journal of Food Safety, 6(Erdogrul, Ö., Erbilir, F. (2000). Microorganisms in Kitchen Sponges. Internet Journal of Food Safety, 6, 17—22.), 17—22.                                                               Link: https://www.internetjfs.org/articles/ijfsv6-4.pdf