出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2015/08/11 12:24:34」(JST)
Bacterial infection | |
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Clostridium tetani is a pathogenic bacterium that causes tetanus
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Classification and external resources | |
MeSH | D001424 |
Pathogenic bacteria are bacteria that can cause infection. This article deals with human pathogenic bacteria.
Although most bacteria are harmless or often beneficial, several are pathogenic. One of the bacterial diseases with the highest disease burden is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, 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.[1]
Koch's postulates are the standard to establish a causative relationship between a microbe and a disease.
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. Immuno-compromised individuals are more susceptible to pathogenic bacteria.
Some pathogenic bacteria cause disease under certain conditions, such entry through the skin via a cut, through sexual activity or an compromised immune function.
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, meningitis. These infections can become quite serious creating a systemic inflammatory response resulting in massive vasodilation, shock, and death.[2]
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.[3][4]
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 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.[5]
Other groups of intacellular bacterial pathogens include: Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, and Yersinia pestis. These can exist intracellularly, but can exist outside of host cells.
Bacterial pathogens often cause infection in specific areas of the body. Others are generalists.
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.[14]
Once pathogens attach to host cells, they can cause direct damage as the pathogens use the host cell for nutrients and produce waste products. As pathogens multiply and divide inside host cells, the cells usually rupture and the intercellular bacteria are released. Some bacteria such as E. coli, Shigella, Salmonella, and Neisseria gonorrhoeae, can induce host epithelial cells to engulf them in a process resembling phagocytosis. The pathogens can then disrupt host cells as they pass through them and be extruded from host cells by a reverse phagocytosis process, enabling them to enter other host cells. Some bacteria can also penetrate host cells by excreting enzymes and by their own motility; such penetration can can itself damage the host cell.[14]
Toxins are poisonous substances that are produced by certain microorganisms and are often the primary factor contributing to the pathogenic properties of the microorganisms. 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 at first worsen as the bacteria are killed and they release their endotoxins. Exotoxins are proteins produced inside pathogenic bacteria as part of their growth and metabolism, most common in gram positive bacteria. The exotoxins are released when the bacteria die and the cell wall breaks apart. Exotoxins are highly specific in the effects on body tissues and work by destroying particular parts of the host cell or by inhibiting certain metabolic functions. Exotoxins are among the most lethal known substances, only 1 mg of the botulinum exotoxin is enough to kill one million guinea pigs. Diseases caused this way are often caused by minute amounts of exotoxins, not by the bacteria themselves.[14]
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.[15] 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.[16] Phage therapy can also be used to treat certain bacterial infections.[17] 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).
Many genera contain pathogenic bacteria 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 |
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Bacillus[18] |
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Positive | Rods | Facultative anaerobic | Extracellular |
Bartonella[18] |
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Negative | Rods | Aerobic | Facultative intracellular |
Bordetella[18] |
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Negative | Small coccobacilli | Aerobic | Extracellular |
Borrelia[18] |
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Negative, stains poorly | spirochete | Anaerobic | Extracellular |
Brucella[18] |
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Negative | coccobacilli | Aerobic | Intracellular |
Campylobacter[18] |
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Negative | Spirochete Bacillus |
microaerophilic | extracellular |
Chlamydia and Chlamydophila[18] |
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(not Gram-stained) | Small, round, ovoid | Facultative or strictly aerobic | Obligate intracellular |
Clostridium[18] |
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Positive | Large, blunt-ended rods | Obligate anaerobic | extracellular |
Corynebacterium[18] |
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Positive (unevenly) | bacilli | Mostly facultative anaerobic | extracellular |
Enterococcus[20][22] |
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Positive | Cocci | Facultative Anaerobic | extracellular |
Escherichia[1][20][23] |
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Negative | Bacillus | Facultative anaerobic | extracellular or intracellular |
Francisella[18] |
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Negative | coccobacillus | strictly aerobic | Facultative intracellular |
Haemophilus |
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Negative | coccobacilli to long and slender filaments | extracellular | |
Helicobacter |
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Negative | Spirochete | Microaerophile | extracellular |
Legionella[18] |
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Negative, stains poorly | cocobacilli | aerobic | facultative intracellular |
Leptospira[20][26] |
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Negative, stains poorly | Spirochete | Strictly aerobic | extracellular |
Listeria[18] |
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Positive, darkly | Slender, short rods | Facultative Anaerobic | intracellular |
Mycobacterium[18] |
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(none) | Long, slender rods | aerobic | extracellular |
Mycoplasma[18] |
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(none) | 'fried egg' appearance, no cell wall | Mostly facultative anaerobic; M. pneumoniae strictly aerobic | extracellular |
Neisseria[20][27] |
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Negative | Kidney bean-shaped | aerobic | Gonococcus: facultative intracellular N. meningitidis: extracellular |
Pseudomonas[20][28] |
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Negative | rods | Obligate aerobic | extracellular |
Rickettsia[18] |
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Negative, stains poorly | Small, rod-like coccobacillary | Aerobic | Obligate intracellular |
Salmonella[18] |
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Negative | Bacillus shape | Facultative anaerobica | Facultative intracellular |
Shigella[20][29] |
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Negative | rods | Facultative anaerobic | extracellular |
Staphylococcus[1] |
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Positive, darkly | Round cocci | Facultative anaerobic | extracellular, facultative intracellular |
Streptococcus[18] |
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Positive | ovoid to spherical | Facultative anaerobic | extracellular |
Treponema[18] |
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Negative, stains poorly | Spirochete | Aerobic | extracellular |
Ureaplasma[1] |
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Stains poorly[30] | indistinct, 'fried egg' appearance, no cell wall | anaerobic | extracellular |
Vibrio[20][20][31] |
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Negative | Spiral with single polar flagellum | Facultative anaerobic | extracellular |
Yersinia[20][32] |
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Negative, bipolarly | Small rods | Facultative Anaerobe | Intracellular |
This is description of the more common genera and species presented with their clinical characteristics and treatments.
Genus | Species | Transmission | Diseases | Treatment | Prevention |
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Bacillus |
anthracis |
Contact with cattle, sheep, goats and horses[33] |
Anthrax: pulmonary, gastrointestinal and/or cutaneous symptoms.[34] |
In early infection:[35] Penicillin |
Anthrax vaccine[20] |
Bordetella |
pertussis |
Contact with respiratory droplets expelled by infected human hosts. |
Whooping cough |
Macrolide antibiotics Azithromycin |
Pertussis vaccine, DPT vaccine |
Borrelia |
burgdorferi |
Ixodes ticks |
Lyme disease |
Early stages: |
wearing clothing that limits skin exposure to ticks |
Brucella |
abortus |
Direct contact with infected animal |
Brucellosis |
doxycycline |
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Campylobacter |
jejuni |
Fecal/oral from animals (mammals and fowl) |
Acute enteritis |
treat symptoms |
Good hygiene |
Chlamydia |
pneumoniae |
Respiratory droplets |
Community-acquired respiratory infection |
Doxycycline |
None |
Chlamydia |
trachomatis |
sexual intercourse |
Nongonococcal urethritis (NGU) |
Erythromycin |
Erythromycin or silver nitrate in newborn's eyes |
Chlamydophila | psittaci | Inhalation of dust with secretions or feces from birds (e.g. parrots) | Psittacosis |
Tetracycline |
- |
Clostridium | botulinum | Spores from soil,[20][34] persevere in canned food, smoked fish and honey[34] |
Botulism: Mainly muscle weakness and paralysis[34] |
Antitoxin[20][34] |
Proper food preservation techniques |
Clostridium | difficile |
Gut flora,[20][34] overgrowing when other flora is depleted[20] |
Pseudomembranous colitis[20][34] |
Discontinuing responsible antibiotic[20][34] |
Fecal bacteriotherapy |
Clostridium | perfringens |
Spores in soil[20][34] |
Anaerobic cellulitis[20][34] |
Gas gangrene:
Debridement or amputation[20][34] |
Appropriate food handling[20] |
Clostridium | tetani |
Spores in soil, skin penetration through wounds[20][34] |
Tetanus[20] |
Tetanus immune globulin[20][34] Sedatives[20] |
Tetanus vaccine (such as in the DPT vaccine)[20] |
Corynebacterium | diptheriae |
respiratory droplets |
Diphtheria |
Horse serum antitoxin |
DPT vaccine |
Enterococcus |
faecalis |
Part of gut flora,[34] opportunistic or entering through GI tract or urinary system wounds[20] |
bacterial endocarditis[34] biliary tract infections[34] urinary tract infections[34] |
Ampicillin (combined with aminoglycoside in endocarditis)[34] Vancomycin[20] |
No vaccine Hand washing and other nosocomial prevention |
Escherichia | E. coli (generally) |
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UTI:[20]
(resistance-tests are required first)
Meningitis:[20]
Diarrhea:[20]
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(no vaccine or preventive drug)[20]
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Enterotoxigenic E. coli (ETEC) |
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Enteropathogenic E. coli |
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Enteroinvasive E.coli (EIEC) |
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Enterohemorrhagic (EHEC), including E. coli O157:H7 |
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Klebsiella | pneumoniae |
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Listeria | monocytogenes |
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(no vaccine)[20]
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Salmonella | typhi |
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Staphylococcus | aureus |
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Coagulase-positive staphylococcal infections:
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(no vaccine or preventive drug)
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epidermidis | Human flora in skin,[20][34] anterior nares[20] and mucous membranes[34] |
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None | |
saprophyticus | Part of normal vaginal flora |
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None | |
Streptococcus | agalactiae | Human flora in vagina,[20][34] urethral mucous membranes,[20] rectum[20]
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None |
pneumoniae |
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pyogenes |
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No vaccine
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viridans | Oral flora,[34] penetration through abrasions |
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Penicillin G[34] | ||
Vibrio | cholerae |
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リンク元 | 「細菌感染」「菌感染症」「細菌性感染症」「細菌感染症」 |
拡張検索 | 「Gram-negative bacterial infection」「enterobacterial infection」 |
関連記事 | 「infection」「bacterial」 |
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