Meet Your Bacteria: The Hidden Communities that Live in Your Gut and Other Organs

Fleming's Accidental Discovery

The discovery of penicillin by Alexander Fleming, physician, biologist, pharmacologist and botanist, was quite accidental. After returning home from a brief holiday with his family in 1928, Fleming discovered that a petri plate where he had been growing Staphylococcus bacteria, in order to study them in greater detail, had been contaminated by a fungus. (He was well known for keeping an untidy laboratory.) None of the bacteria were growing where the fungus had grown on the plate, but, more interestingly, they were not growing even close to it. The colonies closest to the fungus were even smaller than those further away. The fungus was Penicillium notatum, and the antimicrobial substance that it was producing was penicillin.

Staphylococcus Aureus, first documented 1884

What: One of many Staphylococcus strains that populate the skin.

Where: A normal inhabitant of skin, nose, mouth and throat, but one that can be a devil when excited.

How: If the skin is broken, Staphylococcus aureus can start growing in the epidermal layer of the skin close to the point of entry, causing infections such as impetigo, boils and conjunctivitis or styes in the eye. S. aureus is also a cause of food poisoning. Growing on food, it releases an enterotoxin, a toxin that when eaten causes violent vomiting and diarrhea, thus ensuring the bacteria's spread to another unsuspecting host.

Propionibacterium Acnes, first documented 1902

What: Despite its implied role in the development of types of acne, this is a commensal bacterium, part of our normal healthy skin flora.

Where: This bacteria colonizes the sebaceous glands all over the skin, but particularly the face and upper back, and makes enzymes that degrade the fats within sebum.

How: The free fatty acids that are released both help S. acnes' adherence to the skin and contribute to the acidic pH of the skin surface.

Case notes: Many of the common pathogenic bacteria such as Staphylococcus aureus and Streptococcus pyogenes are inhibited by an acidic pH. A pH of around 5.0 is just right for our helpful bacteria and there are steps you can take to maintain that (see page 68).

Staphylococcus Epidermidis, first documented 1884

What:S. epidermidis is the most commonly isolated bacteria on human skin. It is definitely one to encourage, but only if it's in the right place.

Where: Found all over the skin so not a species that you can specifically promote, just one to celebrate when it is in a good mood.

How: It has a secret weapon, an enzyme that inhibits the growth of skin pathogens such as Staphylococcus aureus and some of the Streptococcus species, both of which cause infections. And cross talk between Staphylococcus epidermidis and skin cells helps skin cell survival and repair during infections.

Case notes: Beware — this is an opportunistic pathogen. In people with a weakened immune system, it can cause infections, for example in catheters or artificial heart valves.

Pseudomonas Aeruginosa, first documented 1882

What:P. aeruginosa is a free-living bacterium usually found in soil and water.

How:P. aeruginosa is a highly skilled opportunistic pathogen which exploits a break in our defenses to initiate an infection. It almost never infects undamaged areas, yet there is hardly any site in the body that it cannot infect, given the chance. In the eye, P. aeruginosa causes conjunctivitis; elsewhere it is responsible for respiratory, gastrointestinal and urinary tract infections.

Where: It can grow anywhere, favoring moist places and having very basic nutritional requirements. The wet surface of the eye is perfect.

Case notes:P. aeruginosa is a tough cookie, resistant to many antiseptics and antibiotics. It is one of the most successful bad bacteria we know.

Escherichia Coli, first documented 1885

What:Escherichia coli is a commensal gut bacteria. Most strains are harmless but some can cause disease, including urinary tract infections and food poisoning.

Where: The incubation period for food poisoning caused by E. coli is typically one to eight days. The symptoms of cramps and diarrhea usually last for a few days to a week.

How: Most cases of E. coli food poisoning from the 0157 strain, which produces a toxin known as Shiga toxin, occur after eating undercooked beef (particularly ground beef) or drinking unpasteurized milk.

Case notes: Antibiotics are used for most E. coli infections, except in the case of E. coli 0157 where they can aggravate symptoms and increase the chance of developing a more severe illness known as hemolytic-uremic syndrome. E. coli bacteria can also cause infections outside the intestine if it is torn or damaged, for example by an injury or a disease such as inflammatory bowel disease (IBD).