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Pathogenic bacteria

Disease-causing bacteria

Top 10 Pathogenic bacteria related articles

  (Redirected from Bacterial infections)
Bacterial infection
Clostridium tetani is a pathogenic bacterium that causes tetanus
Commensals vs pathogens mechanism. Mechanisms underlying the inflammation in COPD. Airway epithelium has complex structure: consists of at least seven diverse cell types interacting with each other by means of tight junctions. Moreover, epithelial calls can deliver the signals into the underlying tissues taking part in the mechanisms of innate and adaptive immune defence. The key transmitters of the signals are dendritic cells. Once pathogenic bacterium (e.g., S. pneumoniae, P. aeruginosa) has activated particular pattern recognition receptors on/in epithelial cells, the proinflammatory signaling pathways are activated. This results mainly in IL-1, IL-6 and IL-8 production. These cytokines induce the chemotaxis to the site of infection in its target cells (e.g., neutrophils, dendritic cells and macrophages). On the other hand, representatives of standard microbiota cause only weak signaling preventing the inflammation. The mechanism of distinguishing between harmless and harmful bacteria on the molecular as well as on physiological levels is not completely understood.

Pathogenic bacteria are bacteria that can cause disease.[1] This article deals with human pathogenic bacteria. Although most bacteria are harmless or often beneficial, some are pathogenic, with the number of species estimated as fewer than a hundred that are seen to cause infectious diseases in humans.[2] By contrast, several thousand species exist in the human digestive system.

One of the bacterial diseases with the highest disease burden is tuberculosis, caused by Mycobacterium tuberculosis bacteria, which kills about 2 million people a year, mostly in sub-Saharan Africa. Pathogenic bacteria contribute to other globally important diseases, such as pneumonia, which can be caused by bacteria such as Streptococcus and Pseudomonas, and foodborne illnesses, which can be caused by bacteria such as Shigella, Campylobacter, and Salmonella. Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis, and leprosy. Pathogenic bacteria are also the cause of high infant mortality rates in developing countries.[3]

Koch's postulates are the standard to establish a causative relationship between a microbe and a disease.

Pathogenic bacteria Intro articles: 16


Each species has specific effect and causes symptoms in people who are infected. Some, if not most people who are infected with a pathogenic bacteria do not have symptoms. Immunocompromised individuals are more susceptible to pathogenic bacteria.

Pathogenic susceptibility

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

An abscess caused by opportunistic S. aureus bacteria.

Streptococcus and Staphylococcus are part of the normal skin microbiota and typically reside on healthy skin or in the nasopharangeal region. Yet these species can potentially initiate skin infections. They are also able to cause sepsis, pneumonia or meningitis. These infections can become quite serious creating a systemic inflammatory response resulting in massive vasodilation, shock, and death.[4]

Other bacteria are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis. Examples of these opportunistic pathogens include Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium.[5][6]


Obligate intracellular parasites (e.g. Chlamydophila, Ehrlichia, Rickettsia) have the ability to only grow and replicate inside other cells. Even these intracellular infections may be asymptomatic, requiring an incubation period. An example of this is Rickettsia which causes typhus. Another causes Rocky Mountain spotted fever.

Chlamydia is a phylum of intracellular parasites. These pathogens can cause pneumonia or urinary tract infection and may be involved in coronary heart disease.[7]

Other groups of intracellular bacterial pathogens include Salmonella, Neisseria, Brucella, Mycobacterium, Nocardia, Listeria, Francisella, Legionella, and Yersinia pestis. These can exist intracellularly, but can exist outside of host cells.

Infections in specific tissue

Bacterial pathogens often cause infection in specific areas of the body. Others are generalists.

Pathogenic bacteria Diseases articles: 73

Mechanisms of damage

The symptoms of disease appear as pathogenic bacteria damage host tissues or interfere with their function. The bacteria can damage host cells directly. They can also cause damage indirectly by provoking an immune response that inadvertently damages host cells.[16]


Once pathogens attach to host cells, they can cause direct damage as the pathogens use the host cell for nutrients and produce waste products.[17] For example, Streptococcus mutans, a component of dental plaque, metabolizes dietary sugar and produces acid as a waste product. The acid decalcifies the tooth surface to cause dental caries.[18] However, toxins produced by bacteria cause most of the direct damage to host cells.[17]

Toxin production

Protein structure of Botulinum toxin 3BTA

Endotoxins are the lipid portions of lipopolysaccharides that are part of the outer membrane of the cell wall of gram-negative bacteria. Endotoxins are released when the bacteria lyses, which is why after antibiotic treatment, symptoms can worsen at first as the bacteria are killed and they release their endotoxins. Exotoxins are secreted into the surrounding medium or released when the bacteria die and the cell wall breaks apart.[19]


An excessive or inappropriate immune response triggered by an infection may damage host cells.[1]

Pathogenic bacteria Mechanisms of damage articles: 7

Survival in host


Iron is required for humans, as well as the growth of most bacteria. To obtain free iron, some pathogens secrete proteins called siderophores, which take the iron away from iron-transport proteins by binding to the iron even more tightly. Once the iron-siderophore complex is formed, it is taken up by siderophore receptors on the bacterial surface and then that iron is brought into the bacterium.[19]

Overview of "Siderophores" article


Typically identification is done by growing the organism in a wide range of cultures which can take up to 48 hours. The growth is then visually or genomically identified. The cultured organism is then subjected to various assays to observe reactions to help further identify species and strain.[20]


Bacterial infections may be treated with antibiotics, which are classified as bacteriocidal if they kill bacteria or bacteriostatic if they just prevent bacterial growth. There are many types of antibiotics and each class inhibits a process that is different in the pathogen from that found in the host. For example, the antibiotics chloramphenicol and tetracyclin inhibit the bacterial ribosome but not the structurally different eukaryotic ribosome, so they exhibit selective toxicity.[21] Antibiotics are used both in treating human disease and in intensive farming to promote animal growth. Both uses may be contributing to the rapid development of antibiotic resistance in bacterial populations.[22] Phage therapy can also be used to treat certain bacterial infections.[23]

Pathogenic bacteria Treatment articles: 10


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. Surgical and dental instruments are also sterilized to prevent infection by bacteria. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection. Bacteria in food are killed by cooking to temperatures above 73 °C (163 °F).

Pathogenic bacteria Prevention articles: 4

List of genera and microscopy features

Many genera contain pathogenic bacterial species. They often possess characteristics that help to classify and organize them into groups. The following is a partial listing.

Genus Species Gram staining Shape Oxygen requirement Intra/Extracellular
Bacillus[24] Positive Rods Facultative anaerobic Extracellular
Bartonella[24] Negative Rods Aerobic Facultative intracellular
Bordetella[24] Negative Small coccobacilli Aerobic Extracellular
Borrelia[24] Negative, stains poorly spirochete Anaerobic Extracellular
Brucella[24] Negative coccobacilli Aerobic Intracellular
Campylobacter[24] Negative spiral rods[27]
coccoid in older cultures[27]
Microaerophilic[27] extracellular
Chlamydia and Chlamydophila[24] (not Gram-stained) Small, round, ovoid Facultative or strictly aerobic Obligate intracellular
Clostridium[24] Positive Large, blunt-ended rods Obligate anaerobic extracellular
Corynebacterium[24] Positive (unevenly) bacilli Mostly facultative anaerobic extracellular
Enterococcus[26][30] Positive Cocci Facultative Anaerobic extracellular
Escherichia[3][26][31] Negative Bacillus Facultative anaerobic extracellular or intracellular
Francisella[24] Negative coccobacillus strictly aerobic Facultative intracellular
Haemophilus Negative coccobacilli to long and slender filaments extracellular
Helicobacter Negative Spiral rod Microaerophile extracellular
Legionella[24] Negative, stains poorly cocobacilli aerobic facultative intracellular
Leptospira[26][34] Negative, stains poorly Spirochete Strictly aerobic extracellular
Listeria[24] Positive, darkly Slender, short rods Facultative Anaerobic facultative intracellular
Mycobacterium[24] (none) Long, slender rods aerobic intracellular
Mycoplasma[24] (none) 'fried egg' appearance, no cell wall Mostly facultative anaerobic; M. pneumoniae strictly aerobic extracellular
Neisseria[26][35] Negative Kidney bean-shaped aerobic Gonococcus: facultative intracellular
N. meningitidis
: extracellular
Pseudomonas[26][36] Negative rods Obligate aerobic extracellular
Rickettsia[24] Negative, stains poorly Small, rod-like coccobacillary Aerobic Obligate intracellular
Salmonella[24] Negative Bacillus shape Facultative anaerobica Facultative intracellular
Shigella[26][37] Negative rods Facultative anaerobic extracellular
Staphylococcus[3] Positive, darkly Round cocci Facultative anaerobic extracellular, facultative intracellular
Streptococcus[24] Positive ovoid to spherical Facultative anaerobic extracellular
Treponema[24] Negative, stains poorly Spirochete Aerobic extracellular
Ureaplasma[3] Stains poorly[38] indistinct, 'fried egg' appearance, no cell wall anaerobic extracellular
Vibrio[26][39] Negative Spiral with single polar flagellum Facultative anaerobic extracellular
Yersinia[26][40] Negative, bipolarly Small rods Facultative Anaerobe Intracellular

Pathogenic bacteria List of genera and microscopy features articles: 76

List of species and clinical characteristics

This is description of the more common genera and species presented with their clinical characteristics and treatments.

Species of human pathogenic bacteria
Species Transmission Diseases Treatment Prevention
Actinomyces israelii Oral flora[41] Actinomycosis:[41] painful abscesses in the mouth, lungs,[42][43] or gastrointestinal tract.[28] Prolonged penicillin G and drainage[41]
Bacillus anthracis

Contact with cattle, sheep, goats and horses[44]
Spores enter through inhalation or through abrasions[26]

Anthrax: pulmonary, gastrointestinal and/or cutaneous symptoms.[41]

In early infection:[45]


Anthrax vaccine[26]
Autoclaving of equipment[26]

Bacteroides fragilis Gut flora[41] Abscesses in gastrointestinal tract, pelvic cavity and lungs[41] metronidazole[41] Wound care[47]

Aspiration prevention[47]

Bordetella pertussis

Contact with respiratory droplets expelled by infected human hosts.[26]

Whooping cough[26][41]
Secondary bacterial pneumonia[26]

Macrolides[26] such as erythromycin,[26][41] before paroxysmal stage[41]

Pertussis vaccine,[26][41] such as in DPT vaccine[26][41]

Borrelia B. burgdorferi[26][41]

B. garinii[26]
B. afzelii[26]

Ixodes hard ticks
Reservoir in mice, other small mammals, and birds[48]

Lyme disease[49][50]

Doxycycline for adults, amoxicillin for children, ceftriaxone for neurological involvement[49]

Wearing clothing that limits skin exposure to ticks.[26]
Insect repellent.[26]
Avoid areas where ticks are found.[26]

B. recurrentis[51]

and others[note 1]

Pediculus humanus corporis body louse (B. recurrentis only) and Ornithodoros soft ticks[51] Relapsing fever Penicillin, tetracycline, doxycycline[52] Avoid areas where ticks are found[51]

Better access to washing facilities[51]
Reduce crowding[51]

Brucella B. abortus

B. canis
B. melitensis
B. suis

Direct contact with infected animal[26]
Oral, by ingestion of unpasteurized milk or milk products[26]

Brucellosis: mainly fever, muscular pain and night sweats

or gentamicin[26]

Campylobacter jejuni

Fecal-oral from animals (mammals and fowl)[26][41]
Uncooked meat (especially poultry)[26][41]
Contaminated water[26]

Treat symptoms[26]
Fluoroquinolone[41] such as ciprofloxacin[26] in severe cases[26]

Good hygiene[26]
Avoiding contaminated water[26]
Pasteurizing milk and milk products[26]
Cooking meat (especially poultry)[26]

Chlamydia C. pneumoniae

Respiratory droplets[26][41]

Atypical pneumonia[41]


C. trachomatis

vaginal sex[26]
oral sex[26]
anal sex[26] Vertical from mother to newborn(ICN)[26]
Direct or contaminated surfaces and flies (trachoma)[26]

Neonatal conjunctivitis[26][41]
Neonatal pneumonia[26][41]
Nongonococcal urethritis (NGU)[26][41]
Pelvic inflammatory disease[26][41]
Lymphogranuloma venereum (LGV)[26][41]

(adults)[41] Doxycycline[26][41]
(infants and pregnant women)[41]

Erythromycin or silver nitrate in newborn's eyes[26]
Safe sex[26]

Chlamydophila psittaci Inhalation of dust with secretions or feces from birds (e.g. parrots) Psittacosis, mainly atypical pneumonia


Clostridium C. botulinum Spores from soil,[26][41] persevere in canned food, smoked fish and honey[41]

Botulism: Mainly muscle weakness and paralysis[41]

Hyperbaric oxygen[41]
Mechanical ventilation[41]

Proper food preservation techniques

C. difficile

Gut flora,[26][41] overgrowing when other flora is depleted[26]

Pseudomembranous colitis[26][41]

Discontinuing responsible antibiotic[26][41]
Vancomycin or metronidazole if severe[26][41]

Fecal bacteriotherapy
C. perfringens

Spores in soil[26][41]
Vaginal flora and gut flora[26]

Anaerobic cellulitis[26][41]
Gas gangrene[26][41] Acute food poisoning[26][41]

Gas gangrene:

Debridement or amputation[26][41]
Hyperbaric medicine[26][41]
High doses of doxycycline[26] or penicillin G[26][41] and clindamycin[41]
Food poisoning: Supportive care is sufficient[26]

Appropriate food handling[26]
C. tetani

Spores in soil, skin penetration through wounds[26][41]

Tetanus: muscle spasms[53]

Tetanus immune globulin[26][41] Sedatives[26]
Muscle relaxants[26]
Mechanical ventilation[26][41]
Penicillin or metronidazole[41]

Tetanus vaccine (such as in the DPT vaccine)[26]

Corynebacterium diphtheriae

respiratory droplets
part of human flora

Diphtheria: Fever, sore throat and neck swelling, potentially narrowing airways.[54]

Horse serum antitoxin

DPT vaccine

Ehrlichia E. canis[41]

E. chaffeensis[41]

Dog tick[41] Ehrlichiosis:[41] headache, muscle aches, and fatigue
Enterococcus E. faecalis

E. faecium

Part of gut flora,[41] opportunistic or entering through GI tract or urinary system wounds[26]

Bacterial endocarditis,[41] biliary tract infections,[41] urinary tract infections[41]

Ampicillin (combined with aminoglycoside in endocarditis)[41] Vancomycin[26]

No vaccine Hand washing and other nosocomial prevention

Escherichia E. coli (generally) UTI:[26]

(resistance-tests are required first)



  • Antibiotics above shorten duration
  • Electrolyte and fluid replacement
(no vaccine or preventive drug)[26]
Enterotoxigenic E. coli (ETEC)
Enteropathogenic E. coli
  • Diarrhea in infants[26]
Enteroinvasive E.coli (EIEC)
Enterohemorrhagic (EHEC), including E. coli O157:H7
  • Reservoir in cattle[26]
Francisella tularensis
  • vector-borne by arthropods[26]
  • Infected wild or domestic animals, birds or house pets[26]
Tularemia: Fever, ulceration at entry site and/or lymphadenopathy.[56] Can cause severe pneumonia.[56]
  • Avoiding insect vectors[26]
  • Precautions when handling wild animals or animal products[26]
Haemophilus influenzae
  • Droplet contact[26]
  • Human flora of e.g. upper respiratory tract[26]

(resistance-tests are required first)

Helicobacter pylori
  • Colonizing stomach[26]
  • Unclear person-to-person transmission[26]
(No vaccine or preventive drug)[26]
Klebsiella pneumoniae
Legionella pneumophila (no vaccine or preventive drug)[26]

Heating water[26]

Leptospira species
  • Food and water contaminated by urine from infected wild or domestic animals. Leptospira survives for weeks in fresh water and moist soil.[26]
Vaccine not widely used[26]

Prevention of exposure[26]

Listeria monocytogenes
(no vaccine)[26]
  • Proper food preparation and handling[26]
Mycobacterium M. leprae
  • Prolonged human-human contact, e.g. through exudates from skin lesions to abrasion of other person[26]
Tuberculoid form:

Lepromatous form:

M. tuberculosis

(difficult, see Tuberculosis treatment for more details)[26]

Standard "short" course:[26]

Mycoplasma pneumoniae
Neisseria N. gonorrhoeae
Uncomplicated gonorrhea:[26]

Ophthalmia neonatorum:

(No vaccine)[26]
N. meningitidis
Pseudomonas aeruginosa Opportunistic;[41] Infects damaged tissues or people with immunodeficiency.[26] Pseudomonas infection:[26] (no vaccine)[26]
Nocardia asteroides In soil[41] Nocardiosis:[41] Pneumonia, endocarditis, keratitis, neurological or lymphocutaneous infection TMP/SMX[41]
Rickettsia rickettsii (no preventive drug or approved vaccine)[26]
Salmonella S typhi
Other Salmonella species

e.g. S. typhimurium[26]

  • Fecal-oral[26]
  • Food contaminated by fowl[26] (e.g. uncooked eggs)[41] or turtles[41]
(No vaccine or preventive drug)[26]
  • Proper sewage disposal[26]
  • Food preparation[26]
  • Good personal hygiene[26]
Shigella S. sonnei[26]

S. dysenteriae[41]