Thread: Bacterial Infections

We just learned about viruses and how they harm organisms, the lytic and lysogenic cycles. We went past prokaryotes pretty fast and did not actually learn HOW they destroy or harm human tissue. I am guessing they feed, or decompose, our cells and harm us that way.

How do bacteria harm humans, and how could a bacterial infection lead to death?

Why are gram-negative bacteria "worse" than gram-positive bacteria? My hypothesis is that gram positive bacteria obsorb the antibiotics, and therefore die, while the gram-negative are anti-antibiotic.

Well that is a good hypothesis if you're in high school.

Bacterial pathogens vary greatly and it is nothing innate about they're gram stain that makes them pathogenic. It is usually how many resistant traits they have aquired that makes them dangerous.

First I'll start with Mycobacterium.

Mycobacterium are intracellular pathogens, that means they go inside the cell to cause infections. This group includes Mycobacterium tuberculae, that causes tuberculosis, and Mycobacterium leprae, which causes lepracy. As intracellular pathogens they tend to be resistant to most common antibiotics and to the human immune system because they evade most defences simply by being inside the cells.

The common Gram positive pathogens are Staphylococcus aureus, and Streptococcus pyogenes. S. aureus causes absesses and the dreaded skin eating disorder, it produces leukocydins that kill white blood cells, which is what gives it the ability to produce pussy infections. It also has the ability to produce catalases and coagulases, catalases break down peroxide which is used as a toxin by the immune system, and coagulase inhibits the inflamatory response. S. pyogenes causes strep throat, it produces a lot of proteolytic enzymes that break down tissues and has a lot of toxins to defend itself from the immune system. Now what makes these potentially fatal is that the toxins they produce can cause septic shock, also if they get into your blood they could infect your brain or heart, which will do you in quite fast. Streptococcus pneumoniae is another one that can be quite bad because it's capsule is highly immunogenic and causes inflamation that can restrict the airways.

Common diseases caused by Gram negative bacteria are typhoid, cholera, EHEC, Salmonella and other such enterobacterial infections. These can also be dangerous if they get into the blood, but usually they cause death by dehydration and weakening the immune system causing secondary infections.

Antibacterial resistance is not based on gram stain, although obviously the type of antibiotic you would use depends on the strain being targetted. Some spore forming bacteria are particularly good at avoiding antibiotics, a good example of this is Clostridium difficile (not sure if that's 1 or 2 "f"). Other bacterial strains evolve so that the antibiotic is no longer effective, or they gain a trait through conjugation (bacterial sex!) with a strain carrying a resistance plasmid. To really understand how antibiotic resistance works we would have to get into some indepth biochemistry.

So, in summary bacteria harm the human body through obstruction of vital passages like blood vessels, growth in places that can't sustain growth like your brain and heart, and production of toxins that cause your own immune system to go bad.

Hope this helped.

Most gram positives are obligate aerobes (Clostridia - which causes tetanus, botulism, and one or two other conditions - is an important exception.). Gram negatives can be facultative anaerobes. The clinical upshot of this is that gram positives will infect only those parts of your body that receive oxygen, whereas gram negatives can also infect portions of your body that do not receive oxygen. Virtually all bacterial intestinal disorders are caused by Gram negatives.

(BTW, mycobacteria are not intracellular pathogens. They are resistant to antibiotics because their cell wall contains a hydrophobic component that effectively seals them off from treatment.)

Thanks for the explaination

Originally Posted by free radical

Most gram positives are obligate aerobes (Clostridia - which causes tetanus, botulism, and one or two other conditions - is an important exception.). Gram negatives can be facultative anaerobes. The clinical upshot of this is that gram positives will infect only those parts of your body that receive oxygen, whereas gram negatives can also infect portions of your body that do not receive oxygen. Virtually all bacterial intestinal disorders are caused by Gram negatives.

(BTW, mycobacteria are not intracellular pathogens. They are resistant to antibiotics because their cell wall contains a hydrophobic component that effectively seals them off from treatment.)

Mycobacterium in general are not intracellular, but most mammalian pathogenic Mycobacterium are, and M. tuberculae and M. leprae are, in fact M. leprae is an OBLIGATE intarcellular pathogen. I know what I'm talking about. All other strains of mycobacterium are irrelevant to humans when talking about pathogenicity because they are not pathogenic. Hydophobicity would not seal them off from treatment, mostly because almost all antibiotics are hydrophobic so as to pass through the cellular membrane. They are resistant to Penicillin because they are not susceptible to cell wall destruction. They are typically treated with prokaryotic ribosome targetting antibiotics, and the treatment has to be long and in high dose because they are intracellular.

I also don't know where you get this obligate aerobe generalization from, Listeria and Bacillis are also gram positive pathogenic genera. That is a completely arbitrary generalisation. Enterococcus are another gram-positive intestinal pathogen along with the previous two genera.

Originally Posted by i_feel_tiredsleepy

I also don't know where you get this obligate aerobe generalization from, Listeria and Bacillis are also gram positive pathogenic genera. That is a completely arbitrary generalisation. Enterococcus are another gram-positive intestinal pathogen along with the previous two genera.

The "previous two" are obligate aerobes. Very few Gram positive bacteria are capable of infecting anoxic areas of the body.

Originally Posted by i_feel_tiredsleepy

Hydophobicity would not seal them off from treatment, mostly because almost all antibiotics are hydrophobic so as to pass through the cellular membrane.

Surely this is incorrect. Many antibiotics are soluble in water, thus hydrophilic, and many hydrophilic molecules pass through cellular membranes via transport.

Originally Posted by free radical

Surely this is incorrect. Many antibiotics are soluble in water, thus hydrophilic, and many hydrophilic molecules pass through cellular membranes via transport.

Um no, Listeria is a facultative anaerobe http://microbewiki.kenyon.edu/index.php/Listeria

And Bacillus are about 50/50 aerobes and facultative anaerobes. Depending on the species.

http://microbewiki.kenyon.edu/index.php/Bacillus

Edit: Sorry my internet copped out on me and I couldn't respond, and I didn't notice you editted the last bit in, and thus misquoted. Anyway, antibiotics come in both hydrophobic and hydrophilic forms, some bacteria will pick up hydrophilic antibiotics through transport, others won't. Hydrophobic antibiotics are very popular right now as more and more bacteria become resistant to the hydrophilic penicillin derivatives.