Some pathogens invade only the surface epithelium, skin or mucous membrane, but many travel more deeply, spreading through the tissues and disseminating by the lymphatic and blood streams.

For hitherto unknown pathogens, Koch's postulates are the standard to establish a causative relationship between a microbe and a disease.

[7] Some pathogenic bacteria cause disease under certain conditions, such as entry through the skin via a cut, through sexual activity or through compromised immune function.

[9] Other bacteria are opportunistic pathogens and cause disease mainly in people with immunosuppression or cystic fibrosis.

[12] Other groups of intracellular bacterial pathogens include Salmonella, Neisseria, Brucella, Mycobacterium, Nocardia, Listeria, Francisella, Legionella, and Yersinia pestis.

[23] For example, Streptococcus mutans, a component of dental plaque, metabolizes dietary sugar and produces acid as a waste product.

[24] Endotoxins are the lipid portions of lipopolysaccharides that are part of the outer membrane of the cell wall of gram-negative bacteria.

To avoid competition with host cells for glucose which is the main energy source used by human cells, many pathogens including the respiratory pathogen Haemophilus influenzae specialise in using other carbon sources such as lactate that are abundant in the human body [26] Typically identification is done by growing the organism in a wide range of cultures which can take up to 48 hours.

[30] Infections can be prevented by antiseptic measures such as sterilizing the skin prior to piercing it with the needle of a syringe and by proper care of indwelling catheters.

Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection.

Contact with cattle, sheep, goats and horses[51] Spores enter through inhalation or through abrasions[33] Anthrax: pulmonary, gastrointestinal and/or cutaneous symptoms.

[48] Penicillin Doxycycline Ciprofloxacin Raxibacumab[53] Anthrax vaccine[33] Autoclaving of equipment[33] Aspiration prevention[54] Contact with respiratory droplets expelled by infected human hosts.

[33] Whooping cough[33][48] Secondary bacterial pneumonia[33] Pertussis vaccine,[33][48] such as in DPT vaccine[33][48] B. garinii[33] B. afzelii[33] Ixodes hard ticks Reservoir in mice, other small mammals, and birds[55] Lyme disease[56][57] Doxycycline for adults, amoxicillin for children, ceftriaxone for neurological involvement[56] Wearing clothing that limits skin exposure to ticks.

[33] and others[note 1] Better access to washing facilities[58] Reduce crowding[58] Pesticides[58] B. canis B. melitensis B. suis Direct contact with infected animal[33] Oral, by ingestion of unpasteurized milk or milk products[33] Brucellosis: mainly fever, muscular pain and night sweats doxycycline[33] streptomycin or gentamicin[33] Fecal–oral from animals (mammals and fowl)[33][48] Uncooked meat (especially poultry)[33][48] Contaminated water[33] Treat symptoms[33] Fluoroquinolone[48] such as ciprofloxacin[33] in severe cases[33] Good hygiene[33] Avoiding contaminated water[33] Pasteurizing milk and milk products[33] Cooking meat (especially poultry)[33] Respiratory droplets[33][48] Doxycycline[33][48] Erythromycin[33][48] vaginal sex[33] oral sex[33] anal sex[33] Vertical from mother to newborn(ICN)[33] Direct or contaminated surfaces and flies (trachoma)[33] Trachoma[33][48] Neonatal conjunctivitis[33][48] Neonatal pneumonia[33][48] Nongonococcal urethritis (NGU)[33][48] Urethritis[33][48] Pelvic inflammatory disease[33][48] Epididymitis[33][48] Prostatitis[33][48] Lymphogranuloma venereum (LGV)[33][48] Erythromycin[33][48] (adults)[48] Doxycycline[33][48] (infants and pregnant women)[48] Erythromycin or silver nitrate in newborn's eyes[33] Safe sex[33] Abstinence[33] Tetracycline[33] Doxycycline[33] Erythromycin[33] Botulism: Mainly muscle weakness and paralysis[48] Antitoxin[33][48] Penicillin[48] Hyperbaric oxygen[48] Mechanical ventilation[48] Proper food preservation techniques Gut flora,[33][48] overgrowing when other flora is depleted[33] Pseudomembranous colitis[33][48] Discontinuing responsible antibiotic[33][48] Vancomycin or metronidazole if severe[33][48] Spores in soil[33][48] Vaginal flora and gut flora[33] Anaerobic cellulitis[33][48] Gas gangrene[33][48] Acute food poisoning[33][48] Debridement or amputation[33][48] Hyperbaric medicine[33][48] High doses of doxycycline[33] or penicillin G[33][48] and clindamycin[48] Food poisoning: Supportive care is sufficient[33] Spores in soil, skin penetration through wounds[33][48] Tetanus: muscle spasms[60] Tetanus immune globulin[33][48] Sedatives[33] Muscle relaxants[33] Mechanical ventilation[33][48] Penicillin or metronidazole[48] Tetanus vaccine (such as in the DPT vaccine)[33] respiratory droplets part of human flora Diphtheria: Fever, sore throat and neck swelling, potentially narrowing airways.

[61] Horse serum antitoxin Erythromycin Penicillin DPT vaccine E. chaffeensis[48] E. faecium Part of gut flora,[48] opportunistic or entering through GI tract or urinary system wounds[33] Bacterial endocarditis,[48] biliary tract infections,[48] urinary tract infections[48] Ampicillin (combined with aminoglycoside in endocarditis)[48] Vancomycin[33] No vaccine Hand washing and other nosocomial prevention (resistance-tests are required first) Meningitis:[33] Diarrhea:[33] (resistance-tests are required first) Heating water[33] Prevention of exposure[33] Lepromatous form: (difficult, see Tuberculosis treatment for more details)[33] Standard "short" course:[33] Ophthalmia neonatorum: e.g. S. typhimurium[33] S. dysenteriae[48] Of the 59 species listed in the table with their clinical characteristics, 11 species (or 19%) are known to be capable of natural genetic transformation.

[81] The pathogenic bacteria able to carry out natural genetic transformation (of those listed in the table) are Campylobacter jejuni, Enterococcus faecalis, Haemophilus influenzae, Helicobacter pylori, Klebsiella pneumoniae, Legionella pneumophila, Neisseria gonorrhoeae, Neisseria meningitidis, Staphylococcus aureus, Streptococcus pneumoniae and Vibrio cholerae.