Diseases caused by bacteria .
The most common infectious diseases, they range from minor skin infections to bubonic plague and tuberculosis . Until the mid-20th century, bacterial pneumonia was probably the leading cause of death among the elderly. Improved sanitation, vaccines , and antibiotics have all decreased the mortality rates from bacterial infections, though antibiotic-resistant strains have caused a resurgence in some illnesses. Bacteria cause disease by secreting or excreting toxins (as in botulism ), by producing toxins internally, which are released when the bacteria disintegrate (as in typhoid ), or by inducing sensitivity to their antigenic properties (as in tuberculosis). Other serious bacterial diseases include cholera , diphtheria , bacterial meningitis , and syphilis .