Bacteria differ from viruses very much. First of all, they are bigger, second of all, they represent quite self-sufficient live organisms capable of self-reproducing if corresponding feeding is available. Penetrating to a human body, certain bacteria find food and suitable conditions for reproduction, and diseases are appeared this way.
Before the XX century, the doctors' fight against bacterial infections has not differed from fighting against infection virus: all their efforts were directed at help to an organism to cope with a disease. Fortunately, the possibilities of modern medicine are significantly increased. It was due to creation of several groups of medications able to kill microbes without any significant harm to an individual. You, for sure, heard about these medications: antibiotics (Penicillin, Tetracycline, Gentamycin), sulfanilamides (Streptocide, Aethazolum, Biseptol) and etc.
Reading these words, the readers may think that bacterial infections are treated much easier, comparing to infection virus. But unfortunately, this is not like this. First of all, because bacteria show incredible adaptability and as the doctors discover new medications, new species of known bacteria refractory to these antibiotics are appeared (or probably the drugs affect bacteria for a short period of time or not very effectively.) Second of all, the same bacterial diseases, for example, pneumonia or meningitis, may be caused by hundreds different microbes and the doctors, sometimes, are not able to answer a question: “What is the reason?” and, accordingly, prescribe the correct antibiotic.
The world of bacteria is diverse, as well as the diseases caused by bacteria are various and numerous. Bacteria differ from each other in the sizes, structure, reproductive abilities. The conditions suitable for their normal existing are various. Some bacteria are round, they are named cocci (staphylococcus, pneumococcus, streptococcus, meningococcus, gonococcus,) others are oblong, they are named rods (dysenteric bacillus, pertussis and colon bacillus). Bacteria have outgrowth, flagellum, and cilium. In contrast to viruses, bacteria are not characterized by selective lesion of certain human body parts.
However, each microbe has own “preferences.” So, dysenteric bacillus is developed in the large intestine, pertussis agent is developed in the epithelium cells of the respiratory tracts, meningococcus agent is developed in the arachnoid membrane. Staphylococcus may cause an inflammatory process anywhere on the skin, in bones, in lungs, and in intestines, and etc.