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Pathogenic bacteria

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Bacterial infection
Clostridium tetani 01.png
Clostridium tetani is a pathogenic bacterium that causes tetanus
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.

Diseases[edit]

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.

Pathogenic suseptibility[edit]

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]

Intracellular[edit]

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.

Infections in specific tissue[edit]

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

Mechanisms[edit]

Nutrients[edit]

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]

Direct damage[edit]

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]

Toxin production[edit]

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]

Treatment[edit]

Main article: Antibiotics
See also overview list below

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).

List of genera of pathogenic bacteria and microscopy features[edit]

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
Bacillus[18] Positive Rods Facultative anaerobic Extracellular
Bartonella[18] Negative Rods Aerobic Facultative intracellular
Bordetella[18] Negative Small coccobacilli Aerobic Extracellular
Borrelia[18] Negative, stains poorly spirochete Anaerobic Extracellular
Brucella[18] Negative coccobacilli Aerobic Intracellular
Campylobacter[18] Negative Spirochete
Bacillus
microaerophilic extracellular
Chlamydia and Chlamydophila[18] (not Gram-stained) Small, round, ovoid Facultative or strictly aerobic Obligate intracellular
Clostridium[18] Positive Large, blunt-ended rods Obligate anaerobic extracellular
Corynebacterium[18] Positive (unevenly) bacilli Mostly facultative anaerobic extracellular
Enterococcus[20][22] Positive Cocci Facultative Anaerobic extracellular
Escherichia[20][23][1] Negative Bacillus Facultative anaerobic extracellular or intracellular
Francisella[18] Negative coccobacillus strictly aerobic Facultative intracellular
Haemophilus Negative coccobacilli to long and slender filaments extracellular
Helicobacter Negative Spirochete Microaerophile extracellular
Legionella[18] Negative, stains poorly cocobacilli aerobic facultative intracellular
Leptospira[20][26] Negative, stains poorly Spirochete Strictly aerobic extracellular
Listeria[18] Positive, darkly Slender, short rods Facultative Anaerobic intracellular
Mycobacterium[18] (none) Long, slender rods aerobic extracellular
Mycoplasma[18] (none) 'fried egg' appearance, no cell wall Mostly facultative anaerobic; M. pneumoniae strictly aerobic extracellular
Neisseria[20][27] Negative Kidney bean-shaped aerobic Gonococcus: facultative intracellular
N. meningitidis
: extracellular
Pseudomonas[20][28] Negative rods Obligate aerobic extracellular
Rickettsia[18] Negative, stains poorly Small, rod-like coccobacillary Aerobic Obligate intracellular
Salmonella[18] Negative Bacillus shape Facultative anaerobica Facultative intracellular
Shigella[20][29] Negative rods Facultative anaerobic extracellular
Staphylococcus[1] Positive, darkly Round cocci Facultative anaerobic extracellular, facultative intracellular
Streptococcus[18] Positive ovoid to spherical Facultative anaerobic extracellular
Treponema[18] Negative, stains poorly Spirochete Aerobic extracellular
Ureaplasma[1] Stains poorly[30] indistinct, 'fried egg' appearance, no cell wall anaerobic extracellular
Vibrio[20][20] [31] Negative Spiral with single polar flagellum Facultative anaerobic extracellular
Yersinia[20][32] Negative, bipolarly Small rods Facultative Anaerobe Intracellular

List of species of pathogenic bacteria and clinical characteristics[edit]

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

Species of human pathogenic bacteria[18]
Genus Species Transmission Diseases Treatment Prevention
Bacillus

anthracis

Contact with cattle, sheep, goats and horses[33]
Spores enter through inhalation or through abrasions[20]

Anthrax: pulmonary, gastrointestinal and/or cutaneous symptoms.[34]

In early infection:[35]

Penicillin
Doxycycline
Ciprofloxacin
Raxibacumab[36]

Anthrax vaccine[20]
Autoclaving of equipment[20]

Bordetella

pertussis

Contact with respiratory droplets expelled by infected human hosts.

Whooping cough
Secondary bacterial pneumonia

Macrolide antibiotics

Azithromycin
Erythromycin
Clarithromycin

Pertussis vaccine, DPT vaccine

Borrelia

burgdorferi
garinii
afzelii

Ixodes ticks
reservoir in deer, mice and other rodents

Lyme disease
Arthritis

Early stages:
cephalosporins
amoxicillin
doxycycline

wearing clothing that limits skin exposure to ticks
insect repellent
avoid areas where ticks are found

Brucella

abortus
canis
melitensis
suis

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

Brucellosis

doxycycline
streptomycin
or gentamicin

Campylobacter

jejuni

Fecal/oral from animals (mammals and fowl)
Contaminated meat (especially poultry)
Contaminated water

Acute enteritis

treat symptoms
Ciprofloxacin in severe cases

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

Chlamydia
pneumoniae

Respiratory droplets

Community-acquired respiratory infection

Doxycycline
Erythromycin

None
Chlamydia
trachomatis

sexual intercourse
oral sex
anal sex Vertical from mother to newborn(ICN)
Direct or contaminated surfaces and flies (trachoma)

Nongonococcal urethritis (NGU)
Lymphogranuloma venereum (LGV)
Trachoma
Inclusion conjunctivitis of the newborn
Pelvic inflammatory disease
Urethritis
Prostatitis
Epididymitis
Ectopic pregnancy
Neonatal pneumonia
Neonatal conjunctivitis

Erythromycin
Doxycycline

Erythromycin or silver nitrate in newborn's eyes
Safe sex
Abstinence

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

Tetracycline
Doxycycline
Erythromycin

-
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]
Penicillin[34]
Hyperbaric oxygen[34]
Mechanical ventilation[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]
Vancomycin or metronidazole if severe[20][34]

Fecal bacteriotherapy
Clostridium perfringens

Spores in soil[20][34]
Vaginal flora and gut flora[20]

Anaerobic cellulitis[20][34]
Gas gangrene[20][34] Acute food poisoning[20][34]

Gas gangrene:

Debridement or amputation[20][34]
Hyperbaric medicine[20][34]
High doses of doxycycline[20] or penicillin G[20][34] and clindamycin[34]
Food poisoning: Supportive care is sufficient[20]

Appropriate food handling[20]
Clostridium tetani

Spores in soil, skin penetration through wounds[20][34]

Tetanus[20]

Tetanus immune globulin[20][34] Sedatives[20]
Muscle relaxants[20]
Mechanical ventilation[20][34]
Penicillin or metronidazole[34]

Tetanus vaccine (such as in the DPT vaccine)[20]

Corynebacterium diptheriae

respiratory droplets
part of human flora

Diphtheria

Horse serum antitoxin
Erythromycin
Penicillin

DPT vaccine

Enterococcus

faecalis
faecium

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) UTI:[20]

(resistance-tests are required first)

Meningitis:[20]

Diarrhea:[20]

  • Antibiotics above shorten duration
  • Electrolyte and fluid replacement
(no vaccine or preventive drug)[20]
Enterotoxigenic E. coli (ETEC)
Enteropathogenic E. coli
  • Diarrhea in infants[20]
Enteroinvasive E.coli (EIEC)
Enterohemorrhagic (EHEC), including E. coli O157:H7
  • Reservoir in cattle[20]
Klebsiella pneumoniae
Listeria monocytogenes
(no vaccine)[20]
  • Proper food preparation and handling[20]
Salmonella typhi
Staphylococcus aureus Coagulase-positive staphylococcal infections: (no vaccine or preventive drug)
  • Barrier precautions, washing hands and fomite disinfection in hospitals
epidermidis Human flora in skin,[20][34] anterior nares[20] and mucous membranes[34] None
saprophyticus Part of normal vaginal flora None
Streptococcus agalactiae Human flora in vagina,[20][34] urethral mucous membranes,[20] rectum[20] None
pneumoniae
  • 23-serotype vaccine for adults (PPV)[20][34]
  • Heptavalent conjugated vaccine for children (PCV)[20]
pyogenes
  • Respiratory droplets
  • Direct physical contact with impetigo lesions
No vaccine
  • Rapid antibiotic treatment helps prevent rheumatic fever
viridans Oral flora,[34] penetration through abrasions Penicillin G[34]
Vibrio cholerae

See also[edit]

References[edit]

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External links[edit]