Fungus Among Us: The Human Body’s Many Bugs

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We’re more bacteria than we are human.  It may sound like some nightmarish work of science fiction, but it’s true: the millions of bacterial cells found within one human body could fill a half-gallon jug!  Each of us is one big playground for all kinds of germs and fungi. Bodily bacteria can help and harm, with some performing essential actions – like helping us process food – and others occasionally mutating to make us ill.

Mouth Bugs: Treponema denticola

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This nasty little bacterium is present in all human mouths, but when allowed to get out of control through spotty oral hygiene, it can cause some major damage to the gums. It’s highly specialized to thrive in the dark, moist spaces between the teeth and gums, turning them into little germ colonies. T. denticola is related to Treponema pallidum, the nasty bacteria that give people syphilis.

Mouth Bugs: Porphyromonas gingivalis

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Periodontal disease isn’t pretty – and neither is Porphyromonas gingivalis, the main bacterium that causes it. Not only does P. gingivalis cause infections, it also causes much of the antibiotic resistance seen today. It actually kicks the beneficial bacteria off your teeth and takes their place, eventually disengaging the gums from the teeth if allowed to get out of hand.

Mouth Bugs: Veillonella

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Not only is the parasitic bacterium genus Veillonella found in the mouth, it’s in our respiratory and digestive tracts as well. It’s a normal element in the complex web of bacteria that exists within all of us, and though some organisms – like Veillonella alcalescens – are associated with disease, most actually help us out. Veillonella is believed to slow the development of dental cavities by converting the acidic products of other bacteria into less acidic products.

Stomach Bugs: Helicobacter pylori

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Stomach acid is strong – so strong, that no bacteria can survive inside it except for a single exceptionally hardy species called Helicobacter pylori. Scientists believe this germ evolved to penetrate and colonize the mucus lining of the stomach, where it can cause a number of gastrointestinal diseases like peptic ulcers and gastritis.  About two-thirds of the world’s population is infected with this bacterium, but it’s usually asymptomatic.

Intestinal Bugs: Bacteroides fragilis

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Considering that bacteria make up 60% of the dry mass in human feces, it’s no wonder we find the thought of intestinal germs so disgusting. But the fact is, gut flora – including bacteria and fungi – perform so many beneficial activities in our gastrointestinal tract, they’re sometimes called a “forgotten organ”.  They play a huge role in the human immune system and help our bodies break down carbohydrates.

But as with all human flora, some intestinal bugs are beneficial and some are harmful. One of the most common types of bacteria found in our guts is Bacteroides fragilis, which typically help our bodies by producing vitamin K and competing with pathogenic bacteria that cause disease.

But then along comes escherichia coli like the bad influence it is, and suddenly B. fragilis teams up with it and starts working against our bodies, causing infection.

Intestinal Bugs: Escherichia coli

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E. coli is among the most well-known intestinal bugs we can get, because it’s one of the most destructive – but only when certain strains are present. We all have E. coli colonizing our bodies at any given time, but some strains develop virulent traits that suddenly start working against the host. The genetic elements that separate harmless E. coli from the kind that makes us violently ill are so subtle, they’re only detectable at the molecular level.

Nonpathogenic E. coli strain Nissle 1917 is so helpful, it’s used as a probiotic in medicine, but virulent strains – typically transmitted to humans from dairy and beef cattle by eating food contaminated with feces – can be fatal.

Intestinal Bugs: Candida albicans

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Candida albicans is found in the body of nearly every healthy individual and is kept under control by a strong immune system, but when it gets out of balance, it can be disastrous.

Usually unicellular, C. albicans transforms into an invasive multicellular form when prompted by certain environmental cues in the bodily areas where it lives, which can include the skin, mouth, vagina, rectum, lower bowel and esophagus. Most people know the resulting condition –candidiasis – as a ‘yeast infection’.

This isn’t just an uncomfortably itchy situation; in some immunosuppressed individuals like those infected with the AIDS virus, it can enter the bloodstream and cause serious infection of vital organs like the heart.

Skin Bugs: Malassezia

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Another type of yeast, Malassezia, is responsible for itchy scalps. M. globosa and M. restricta populate the oiliest areas of our body, causing dandruff and seborrhoeic dermatitis. Each of our heads can hold up to ten million specimens of M. globosa. Other species of Malassezia, like M. pachydermatis, are more frequently found on animal skin but can be transmitted to people by our canine companions.

Skin Bugs: Staphylococcus

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The word ‘staph’ strikes horror in the hearts of many, especially given the recent outbreak of deadly MRSA (Methicillin-resistant Staphylococcus aureus). S. aureus is the strain most often responsible for dangerous health issues and is usually transmitted in the form of food poisoning or through skin contact with another person’s infected wound.

Another form of staph is far more common, making its home on our skin.  S. epidermidis is typically harmless, but every now and then it can invade the body through medical devices or foreign objects like catheters, shunts, pacemakers and breast implants and cause infections of the blood, eyes and urinary tract.

Skin Bugs: Propionibacterium acnes

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It’s been blamed on chocolate and french fries, but the real cause of acne is a complex combo of hormones, dead skin, oil and bacteria. Namely, P. acnes. Though nobody really knows what causes acne to affect one sebaceous gland over another, we do know that P. acnes lives on the fatty acids in our pores and overgrows when the pore becomes blocked, spilling bacteria like staph onto the skin and causing a lesion. It can be killed with benzyol peroxide and many natural antibacterial preparations like clove oil, but put down the tetracycline: P. acnes is becoming resistant to it.

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