Bacteria can be both useful and harmful to us. The bacteria can be divided into pathogens (those that cause diseases) and non-pathogens (those that do not cause any diseases). Some of the pathogens and the diseases they cause are listed here:
1. Salmonella: generally ingested through food: causes typhoid fever (S. typhi), Salmonellosis
2. Campylobacter: from contaminated water or uncooked meat: causes Enteritis (C. jejuni)
3. Escherichia coli: or E. coli: one of the major pathogens, can cause diseases through physical contact, contaminated food and water, etc. A number of strains of E. coli are pathogenic to us. : causes diarrhea, urinary tract infection, bloody diarrhea, fever, etc.
4. Streptococcus: spreads through direct physical contact or sexually (depending on the strain): causes meningitis, pneumonia, sepsis, rheumatic fever, dental cavities, etc.
There are a number of other bacterial pathogens.
Hope this helps.