There are many species of bacteria. The mere presence of bacteria is different than infection and disease caused by bacteria.
Staphylococcus lives harmlessly on the surface of the skin, and causes little concern when there. Some species of E. Coli live as normal flora in the gut ( while there are outside species of E. Coli enteritis that are very harmful if they got inside) Remember- we do not live in sterile conditions, but as a co-existing part of nature.Bacterial disease begins when the bacteria get past our protective barriers and into locations they should not be. Barriers include skin, nasal mucosa,tears,gut walls stomach acid and then the immune system.
Examples would be Staphylococcus entering a break in the skin, multiplying, and causing cellulitis. If the invasion continued to spread into the bloodstream, this would be a very serious infection known as sepsis, potentially life threatening. Drinking contaminated watercan lead to an organism called Shigella breaching the gut wall causing GI disease. Eating contaminated coulf present an alien variant of E. Coli enterotoxic into the gut causing severe food poisoning.
Why can’t our bodies fight off bacterial infections without the need for antibiotics?
Our bodies do fight off bacterial infections on their own. They do it all the time. Most of the time they do it so well that we’re not even aware of it.
The bacterias that make you sick and are treated with antibiotics are particularly nasty ones that have overgrown and it’s taking your immune system a lot of work to fight off. Antibiotics give your immune system an advantage, to put it simply.
We do this in part to shorten the duration of certain illnesses but also to reduce the risks of complications, secondary infections and death. In example, strep throat is a pretty common childhood illness. If untreated it can turn quickly into rheumatic fever which damages the heart and can lead to serious problems later in life. A simple skin infection once red, swollen and causing fever can quickly turn septic and lead to death if untreated. Bacterial pneumonia can lead to lung damage and death. Urinary tract infections can end up in the kidneys where the illness can cause some very severe and painful symptoms, once in the kidneys, if left untreated a simple uti can turn into sepsis and death. A dental abcess can move to your sinus and brain and kill you. Absolutely all of these things can happen to otherwise healthy adults, with strong immune systems.
Yes, humans as a species survived without antibiotics, but the life expectancy was much lower prior to antibiotic intervention. Many people died from what are now treatable illnesses and people question the veracity of antibiotics simply because they’ve never seen how sick someone can get from certain common infections if left untreated.
How do antibiotics “know” where to fight bacteria during an infection? There are 9 bacteria per human cell in our body, why are those not killed?
In general, when antibiotics are given internally (by oral administration, injection or infusion), they circulate throughout your body. But they (like all drugs) don’t perfuse all tissues equally well – they tend to accumulate in some tissues and organs, and not in others. Generally speaking, the liver, kidney, heart and brain are the best-perfused tissues. Lung, gut and skin are often the hardest tissues in which to achieve killing doses of antibiotics. This is especially true if the infected tissue has formed an abscess. Diabetic foot and leg ulcers are notoriously unresponsive to systemic antibiotic treatment because of poor peripheral circulation.
Some antibiotics, like vancomycin, are particularly poor at penetrating skin, lung and gut tissues. Antibiotics that are fat-soluble (like rifampicin and metronidazole) are better at penetrating capillary beds that have tight junctions, such as in the spinal cord. Some drugs (like clindamycin) are better at getting into cells, and thus are preferred for intracellular infections, such as those caused by Salmonella or Mycobacteria (TB).
No antibiotic can be effective unless it actually gets to the infecting bacteria. Antibiotics that are effective against an organism in a test tube might well fail clinically for just this reason. The site of infection is thus a factor in choosing the most effective antibiotic treatment.
Antibiotics, like other drugs, home in on a particular molecular target, preferably to the exclusion of all others. They do this principally by having a shape and electrical charge distribution that is complementary to that the target, and by displacing water, thereby increasing entropy. Human cells are exposed to antibiotics, but are not killed because they don’t contain the proper molecular target. The antibiotic molecules collide with human molecules but bounce off harmlessly. When they collide with bacterial molecules, they stick, and thus interfere with their function.The image below shows penicillin binding to its target, the bacterial enzyme which cross-links polymers in the bacterial cell wall. Penicillin is the purple blob in the center.
Animals don’t have cell walls or cell wall enzymes and so are unaffected by penicillins.Antibiotics are selective in attacking bacterial proteins vs human ones, but they are much less selective in which bacteria they attack – they do not just attack the pathogenic ones, but the “good” bacteria as well. Some consequences of killing good bacteria are well known – increased risk of C. difficile diarrhea, for example. Others, such as increased risk of obesity, diabetes, asthma and gut inflammatory diseases are just beginning to be appreciated. Antibiotic developers have traditionally tried to formulate antibiotics to have the widest spectrum possible, as this would create the largest markets for their products. However, the drawbacks to this approach are beginning to be realized. Some narrow-spectrum antibiotics such as Dificid have now reached the market, but in general, the poor economics of narrow-spectrum antibiotics has discouraged their development.