Since “clean” now goes beyond simply removing dirt, it is critical that cleaning business owners and technicians know what they are really getting into. And this means a mini-biology lesson.

In Chapter One: Of Men and Microbes of Modern Cleaning: The Evolution of Chemical Free Cleaning, the authors do just that—give a little biology review of bacteria and the Gram dye stain used to group different bacteria, as well as viruses and their many forms. The list presented below is certainly not exhaustive, but it covers the main threats to residents and to the cleaning technicians who encounter them as they work to remove contaminants from a home.

Here’s a quick review of what’s important to know about bacteria and viruses:

Common Bacteria:  micro-organisms (can’t see them) which exist primarily to recycle nutrients in our natural environment and our human bodies. The vast majority of bacteria are either harmless to or actually beneficial to human health as part of our immune and digestive systems. Relatively few are pathogenic (make us sick) and need to be eliminated on a regular basis from our environment.

Gram-negative bacteria: found living on our skin; don’t dry out easily so they live longer; most of the bacteria that make us sick is Gram-negative—like strep, staph, listeria

Gram-positive bacteria: found mostly in our intestines; dry out easily so they like to live in water; can thrive and be spread when you don’t dry your hands thoroughly after washing; common Gram-positive bacteria are e. Coli and salmonella

Gram-Negative Bacteria

Escherichia Coli –Some strains of E. coli are found naturally in human and animal digestive tracts. Our own E. coli doesn’t make us sick because our immune system recognizes it. Other strains of E. coli, such as the newsworthy O157 strain can cause a severe and bloody diarrhea. The most common cause of acute kidney failure in children, hemolytic uremic syndrome (HUS), is caused by E. coli O157:H7 and related bacteria.

Pseudomonas aeruginosa –Naturally found in soil, water and on surfaces of some plants and animals, these bacteria have become a particular problem in hospitals and nursing homes. It can cause infections of the urinary tract, lungs, skin, soft tissue, bones and joints, gastrointestinal systems as well as a variety of systemic infections.

Salmonella –These bacteria reside in the digestive tracts of cattle and poultry. Salmonella is the second most common source of food-borne illness after E. coli. It can cause mild to severe nausea, vomiting, abdominal cramps, fever, headache and diarrhea. It can invade the bloodstream and cause life threatening infections in those with poor health or weakened immune systems.

Campylobacter –Naturally found in water, fecal matter, raw chicken and meat, C. jejuni is the most common bacterial cause of diarrhea worldwide. Causes fever, diarrhea and abdominal cramps. Guillian-Barre syndrome can be caused by Campylobacter infection.

Shigella –These bacteria are found in fecal matter. Flies also transmit it by feeding on feces and then landing on human food. Shigella can cause bacterial dysentery (bloody, mucous diarrhea). Poor hygiene causes this bacterium to be easily passed from person to person.

Legionella – Found in warm, stagnant water, cooling towers, evaporative condensers of large air-conditioning systems, whirlpool spas, hot water tanks and certain other plumbing systems. It causes Legionnaire’s Disease, which can be fatal.

Serratia marcesans – commonly found in soil, water, plants, and animals. Has the ability to produce red pigmentation. This bacterium can be pathogenic to immune compromised individuals in whom it can cause pneumonia and urinary tract infections. Responsible for the pinkish-red “mold” found in toilets, the grout of tubs/showers, and shower heads.

Gram-Positive Bacteria

Staphylococcus – Found in human noses, wounds and cuts as well as in improperly stored or processed foods. Staphylococcus aureus can grow in some foods and produce a toxin that causes intense vomiting. An especially virulent form has acquired the namesake MRSA (Methicillin or, now, Multi-Drug Resistant Staphylococcus Aureus), which has become increasingly problematic in hospitals, nursing homes and day care centers.

Streptococcus – Part of normal animal flora. Group A is very pathogenic to humans and includes “strep throat,” scarlet and rheumatic fever, toxic shock syndrome and necrotizing fasciitis (“flesh eating disease”). Group B causes pneumonia.

Listeria –Naturally found in soil and water. It is also found in processed foods such as luncheon meats and hot dogs, raw vegetables, soft cheeses, and other dairy products. Since it is not easily controlled through refrigeration, it is currently considered the most deadly agent in our food supply. Listeria can cause nausea, vomiting, diarrhea, encephalitis, miscarriages in animals and humans, as well as other non-abdominal problems.

Clostridium – Found in poorly processed, acidic canned foods. Can transform into a tough endospore which can survive tough environments for a long period of time. The bacterium can grow in some foods and produce a powerful payalytic toxin. Can cause botulism, tetanus, diarrhea, and gangrene.

Bacillus –Commonly found in soil, Bacillus forms very tough endospores. When B. anthracis spore is inhaled or enters through an open wound, it can be lethal. B. cereus is found in many types of foods and produces a toxin after ingestion which makes people sick.

Mycobacterium tuberculosis –This type of bacteria has a waxy cell membrane, which means it can’t really be classified as a Gram-positive or a Gram-negative bacterium. The tuberculosis bacteria can survive for long periods outside a host, especially when shielded by a coating of sputum or pus. These bacteria can live on dust and surfaces for months, which is the reason transmission is usually through the air.

Common Viruses: smaller than bacteria, viruses live and thrive inside of living organism but die quickly outside of them. But like bacteria, there are viruses that assist the human immune system and those that attack it. Below are some of the harmful viruses which can be killed and removed using Chemical Free Cleaning.

Rotavirus – Can cause severe diarrhea in infants and children. This virus is usually transmitted by poor hygiene after bathroom use, also known as the “oral-fecal route.” It is a top concern in day care settings.

Norovirus –A type of Norwalk and an extremely common cause of foodborne illness in the US. It causes vomiting, watery diarrhea, abdominal cramps, nausea, and low grade fever. The most common complication is dehydration. This virus is transmitted through the oral-fecal route, through direct consumption of contaminated food or water as well as by person-to-person contact.

Influenza H5N1 (“Bird Flu”) — Highly contagious among birds and may cross over to infect humans.

Influenza H1N1 (“Swine Flu”) – Source of the 2009-2010 pandemic. The World Health Organization reports about 18,450 people died, including many pregnant women and young people.

Coronavirus – Can cause the common cold and SARS (Severe Acute Respiratory Syndrome). Causes both upper and lower respiratory infections, colds and gastroenteritis.

Rhinovirus — Can cause colds and flu with cough, sore throat, runny nose, fever, and upper respiratory tract infection. It is transmitted by aerosol droplets and via contaminated surfaces.

Adenovirus – causes severe respiratory illnesses, gastroenteritis, conjunctivitis, bladder infection, and rash illnesses. There are more than 50 types of adenoviruses that can affect humans. Those with immature, aging, or compromised immune systems are most likely to experience severe symptoms.

Hepatitis – an inflammation of the liver, specifically caused by an infection from viruses (A, B, or C). Hepatitis A is acquired by poor hygiene situations and takes three months to run its course. Hepatitis B and C are chronic diseases acquired by sexual contact, the sharing of IV needles, or through contact with blood from an infected person.

HIV – the virus that causes Acquired Immune Deficiency Syndrome (AIDS), a condition that causes the immune system to fail. This leads to life threatening, opportunistic infections. HIV is often caused by sexual contact with an infected person or via contact with the blood or body fluids of an infected person.

Hantavirus – a virus spread by rodents that is similar to the flu. It is found in the urine and feces of deer mice and bats, but does not make the carrier animal sick. The respiratory disease is not passed between humans, only by exposure to dust or soil contaminated with deer mouse urine and feces.


Cryptosporidium – A microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are known as “Crypto.” The parasite is protected by an outer shell that allows it to survive outside the body for a long period of time and makes it very tolerant of chlorine disinfection. It is commonly transmitted by drinking and recreational water, and is one of the most frequent causes of parasitic waterborne diseases in the US. The most common symptom of Crypto is watery diarrhea.

Giardia – A microscopic parasite that causes the diarrheal illness known as Giardiasias. Giardia is found on surfaces or in soil, food, or water that has been contaminated with feces from infected animals and humans. Giardia, like Cryptosporidium, is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection. Drinking water and recreational water are the most common methods of transmission. Symptoms include diarrhea, nausea and abdominal cramps.

Toxoplasma gondii – Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. Cats are the definitive host of the parasite, but it is also found in many species of animals and birds. Human infection can result from eating raw or undercooked lamb, pork or beef and from carelessly handling cat litter which can lead to accidental consumption of infectious particles. Symptoms include enlarged lymph nodes in the head and neck, headache, mild illness and fever, muscle pain and sore throat. The infection may also be passed from an infected mother to her baby through the placenta, which can damage the baby’s eyes, nervous system, skin and ears.

Fungi and Yeast:

Candida – a yeast that is part of the normal human body flora. Can overpopulate and produce yeast infections (candidiasis) in women, and oral thrush in children and immunocompromised adults.

Penicillium – A ubiquitous soil fungi that prefers cool, moderate climates. It produces penicillin and is one of the most common fungi in the world.

Aspergillus – Common in the environment and a major contaminant of fruits, vegetables, and peanuts. Produces spores commonly found in indoor and outdoor air. Some strains are linked to cancer of the liver. Others can cause fever, cough and chest pain. Aspergillus niger is the black household mold found on bathroom tubs, tile and grout.

Histoplasma – found in the soil in many parts on North and South America. Growth is enhanced by the presence of bird and bat excreta. Can cause Histoplasmosis with fever, cough and chest pain.

Trichophyton (Causes “Athlete’s Foot”or Tinea pedis) – Found in soil and on skin. Invades the skin, hair and nails of humans.

Stachybotrus (“Black Mold” or “Toxic Mold”) – found in water-compromised buildings. It can cause respiratory irritation and other health complaints such as chronic fatigue, headaches, and fever as well as eye, mouth and nose irritation, sneezing, rashes, chronic coughing, nausea, vomiting, and bleeding in the lungs and nose.