Bacteria or mold
fungus, bacteria (sometimes) and virus. :)
They can make you sick, some can kill you and can give you infections.
helpful microorganisms help our bodies proceed health
Examples of bacteria pathogenic for a human are:§ Staphylococcus aureus, causing skin infections, pneumonia, infection of the heart valves, etc.§ Streptococcus pyogenes, causing "strep throat",...