Pathogenic bacteria

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Bacterial infection
Classification and external resources
Clostridium tetani 01.png
Clostridium tetani is a pathogenic bacterium that causes tetanus
MeSH D001424

Pathogenic bacteria are bacteria that cause bacterial 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.

Koch's postulates are criteria designed to establish a causal relationship between a causative microbe and a disease.

Diseases[edit]

Each pathogenic species has a characteristic spectrum of interactions with its human hosts.

Conditionally pathogenic[edit]

Conditionally pathogenic bacteria are only pathogenic under certain conditions, such as a wound that allows for entry into the blood, or a decrease in immune function.

For example, Staphylococcus or Streptococcus are also part of the normal human flora and usually exist on the skin or in the nose without causing disease, but can potentially cause skin infections, pneumonia, meningitis, and even overwhelming sepsis, a systemic inflammatory response producing shock, massive vasodilation and death.[1]

Some species of bacteria, such as Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium, are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis.[2][3]

Intracellular[edit]

Other organisms invariably cause disease in humans, such as obligate intracellular parasites (e.g. Chlamydophila, Ehrlichia, Rickettsia) that are able to grow and reproduce only within the cells of other organisms. Still, infections with intracellular bacteria may be asymptomatic, such as during the incubation period. An example of intracellular bacteria is Rickettsia. One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever.

Chlamydia, another phylum of obligate intracellular parasites, contains species that can cause pneumonia or urinary tract infection and may be involved in coronary heart disease.[4]

Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, and Yersinia pestis can exist intracellularly, though they are facultative (not obligate) intracellular parasites.

By location[edit]

Following is a list of bacterial infections classified by location in the body:

How Bacterial Pathogens Damage Host Cells[edit]

Using the Host’s 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.[13]

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.[13]

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 1mg of the botulinum exotoxin is enough to kill one million guinea pigs. Diseased caused this way are often caused by minute amounts of exotoxins, not by the bacteria themselves.[13]

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.[14] 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.[15] Phage therapy can also be used to treat certain bacterial infections.[16] 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 pathogenic bacteria by basic laboratory characteristics[edit]

Following are the genera that contain the most important human pathogenic bacteria species:[17]

Genus Important species Gram staining Shape Capsulation Bonding tendency Motility Respiration Growth medium Intra/Extracellular
Bordetella Gram-negative Small coccobacilli Encapsulated Singly or in pairs Non-motile Aerobic Regan-Lowe agar Extracellular
Borrelia Gram-negative, but stains poorly Spirochete Unencapsulated Long, slender, flexible, spiral- or corkscrew-shaped rods Highly motile Anaerobic (Difficult to culture) Extracellular
Brucella Gram-negative Small coccobacilli Unencapsulated Singly or in pairs Non-motile Aerobic Ruiz Castaneda medium Intracellular
Campylobacter Gram-negative Curved, spiral, or S-shaped
bacilli
with single, polar flagellum
Unencapsulated Singly characteristic darting motion microaerophilic Blood agar inhibiting other fecal flora extracellular
Chlamydia and Chlamydophila (not Gram-stained) Small, round, ovoid Unencapsulated motile Facultative or strictly aerobic Obligate intracellular
Clostridium Gram-positive Large, blunt-ended rods Normally encapsulated mostly motile Obligate anaerobic Anaerobic blood agar extracellular
Corynebacterium Gram-positive (unevenly) Small, slender, pleomorphic rods Unencapsulated clumps looking like Chinese characters or a picket fence nonmotile Mostly facultative anaerobic Aerobically on Tinsdale agar extracellular
Enterococcus Gram-positive Round to ovoid (cocci) pairs or chains Non-motile Facultative Anaerobic 6.5% NaCl, bile-esculin agar extracellular
Escherichia Gram-negative Short rods (bacilli) Encapsulated and Unencapsulated Normally motile Facultative anaerobic MacConkey agar extracellular or intracellular
Francisella Gram-negative Small, pleomorphic coccobacillus Encapsulated Non-motile strictly aerobic (rarely cultured) Facultative intracellular
Haemophilus Gram-negative Ranging from small coccobacillus to long, slender filaments Encapsulated or Unencapsulated Non-motile Chocolate agar with hemin and NAD+ extracellular
Helicobacter Gram-negative Curved or spiral rods
with multiple polar flagella
rapid, corkscrew motility Microaerophile Medium containing antibiotics against other fecal flora extracellular
Legionella Gram-negative, but stains poorly Slender rod in nature, cocobacillary in laboratory.
monotrichious flagella
unencapsulated motile aerobic Specialized medium facultative intracellular
Leptospira Gram-negative, but stains poorly Long, very slender, flexible, spiral- or corkscrew-shaped rods Highly motile Strictly aerobic Specialized medium extracellular
Listeria Gram-positive, darkly Slender, short rods diplobacilli or short chains Distinct tumbling motility in liquid medium Facultative Anaerobic enriched medium intracellular
Mycobacterium (none) Long, slender rods Unencapsulated nonmotile aerobic M. tuberculosis: Lowenstein-Jensen agar
M. leprae: (none)
extracellular
Mycoplasma (none) Plastic, pleomorphic Encapsulated singly or in pairs Mostly facultative anaerobic; M.pneumoniae strictly aerobic (rarely cultured) extracellular
Neisseria Gram-negative Kidney bean-shaped Encapsulated or Unencapsulated diplococci Non-motile aerobic Thayer-Martin agar Gonococcus: facultative intracellular
N. meningitidis
: extracellular
Pseudomonas Gram-negative rods encapsulated motile Obligate aerobic MacConkey agar extracellular
Rickettsia Gram-negative, but stains poorly Small, rod-like coccobacillary Slime/microcapsule Non-motile Aerobic (rarely cultured) Obligate intracellular
Salmonella Gram-negative Bacilli Encapsulated Normally motile Facultative anaerobic MacConkey agar Facultative intracellular
Shigella Gram-negative rods Unencapsulated Non-motile Facultative anaerobic Hektoen agar extracellular
Staphylococcus Gram-positive, darkly Round cocci Encapsulated or Unencapsulated in bunches like grapes Non-motile Facultative anaerobic enriched medium (broth and/or blood) extracellular, facultative intracellular
Streptococcus Gram-positive ovoid to spherical Encapsulated or Unencapsulated pairs or chains nonmotile Facultative anaerobic blood agar extracellular
Treponema Gram-negative, but stains poorly Long, slender, flexible, spiral- or corkscrew-shaped rods highly motile Aerobic none extracellular
Vibrio Gram-negative Short, curved, rod-shaped with single polar flagellum Unencapsulated rapidly motile Facultative anaerobic blood- or MacConkey agar. Stimulated by NaCl extracellular
Yersinia Gram-negative, stains bipolarly Small rods encapsulated nonmotile Facultative Anaerobe MacConkey or CIN agar Intracellular

List of pathogenic bacteria by clinical characteristics[edit]

This is a rather clinical description of the species presented in the previous section, containing the main examples of transmission, diseases, treatment, prevention and laboratory diagnosis, which all can differ substantially among the species of the same genus.

Species of human pathogenic bacteria[17]
Species Transmission Diseases Treatment Prevention laboratory diagnosis
Bacillus anthracis
  • Contact with sheep, goats and horses
  • Inhalation or skin penetration through abrasions of spore-contaminated dust
In early infection:
  • Large, grayish, nonhemolytic colonies with irregular borders on blood agar
  • Direct immunofluorescence
Bordetella pertussis
  • Contact with respiratory droplets expelled by infected human hosts.

Complications:

Macrolide antibiotics
Borrelia burgdorferi Ixodes ticks
reservoir in deer, mice and other rodents
  • Direct contact with infected animal
  • Oral, by ingestion of unpasteurized milk or milk products
Combination therapy of: -
Campylobacter jejuni
  • Fecal/oral from animals (mammals and fowl)
  • Contaminated meat (especially poultry)
  • Contaminated water
  • Symptomatically by fluid and electrolyte replacement
  • Ciprofloxacin in severe cases
No available vaccine
  • Good hygiene
  • Avoiding contaminated water
  • Pasteurizing milk and milk products
  • Cooking meat (especially poultry)
  • Finding campylobacter in feces
Chlamydia pneumoniae
  • Respiratory droplets
Community-acquired respiratory infection None None for routine use
Chlamydia trachomatis
  • Sexual (NGU, LGV)
  • Direct or contaminated surfaces and flies (trachoma)
  • Passage through birth canal (ICN)
No vaccine
  • Erythromycin or silver nitrate in newborn's eyes
  • Safe sex
Chlamydophila psittaci Inhalation of dust with secretions or feces from birds (e.g. parrots) Psittacosis -
  • Rise in antibody titre
    • Complement fixation
    • indirect immunofluorescence
Clostridium botulinum Spores from soil and aquatic sediments contaminating vegetables, meat and fish
  • Proper food preservation techniques
  • Mouse inoculation detects toxin from food, intestinal contents or serum
  • Culture in standard aerobic culture
Clostridium difficile
  • Spores both indoors and outdoors
  • Human flora, overgrowing when other flora is depleted
None
Clostridium perfringens Gas gangrene:

Food poisoning:

  • Self-limiting; Supportive care is sufficient
Appropriate food handling
  • Microscopically
  • Blood agar culture, forming double-zone β-hemolysis
  • Sugar fermentation
  • Organic acid production
Clostridium tetani
  • Spores in soil infecting puncture wounds, severe burns or surgery
(difficult)
Corynebacterium diphtheriae
  • Respiratory droplets
  • Part of human flora
(no rapid)
Enterococcus faecalis and Enterococcus faecium
  • Part of human flora, opportunistic or entering through GI tract or urinary system wounds
  • Nosocomial infections
No vaccine
  • Culture in 6.5% NaCl
  • Can hydrolyze esculin in presence of bile
Escherichia coli (generally)
  • Part of gut flora, spreading extraintestinally or proliferating in the GI tract
UTI:

(resistance-tests are required first)

Meningitis:

Diarrhea:

  • Antibiotics above shorten duration
  • Electrolyte and fluid replacement
(no vaccine or preventive drug)
  • Food and water preparation
    • Cooking ground beef and pasteurizing milk against O157:H7
  • Hand washing and disinfection
  • Culture on MacConkey agar and study carbohydrate fermentation patterns:
    • Lactose fermentation (most E. coli strains)
    • Gas production in glucose fermentation
    • Mannitol fermentation
Enterotoxigenic Escherichia coli (ETEC)
  • Fecal-oral through food and water
  • Direct physical contact
Enteropathogenic E. coli
  • Diarrhea in infants
E. coli O157:H7
  • Reservoir in cattle
Francisella tularensis
  • vector-borne by arthropods
  • Infected wild or domestic animals, birds or house pets
  • Avoiding insect vectors
  • Precautions when handling wild animals or animal products
(rarely cultured)
  • Serology
Haemophilus influenzae
  • Droplet contact
  • Human flora of e.g. upper respiratory tract
Meningitis:

(resistance-tests are required first)

Helicobacter pylori
  • Colonizing stomach
  • Unclear person-to-person transmission
(No vaccine or preventive drug)
  • Microscopically
    • Corkscrew movement
  • Urease-positivity by radioactively labeled urea
  • Serology by ELISA
Legionella pneumophila (no vaccine or preventive drug)

Heating water

  • Culture from respiratory secretions on buffered charcoal yeast extract enriched with L-cysteine, iron and α-ketoglutarate
  • Serology, including direct immunofluorescence and radioimmunoassay for antigen in urine
  • Hybridization to ribosomal RNA using DNA probe
Leptospira interrogans
  • Food and water contaminated by e.g. urine from wild or domestic animals. Leptospira survives for weeks in stagnant water.
(no vaccine)

Prevention of exposure

Listeria monocytogenes
  • Dairy products, ground meats, poultry
  • Vertical to newborn or fetus
(no vaccine)
  • Proper food preparation and handling
Isolation from e.g. blood and CSF
  • Beta-hemolysis and catalase production on blood agar
  • Microscopy for morphology and motility
Mycobacterium leprae
  • Prolonged human-human contact, e.g. through exudates from skin lesions to abrasion of other person
Tuberculoid form:

Lepromatous form:

Tuberculoid form:
Hard to isolate (diagnosis on clinical findings and histology of biopsies)

Lepromatous form:

  • Acid-fast staining from e.g. skin scrapings
Mycobacterium tuberculosis
  • Droplet contact

(difficult, see Tuberculosis treatment for more details)

Standard "short" course:

Mycoplasma pneumoniae
  • Human flora
  • Droplet contact
(difficult to culture)
Neisseria gonorrhoeae Uncomplicated gonorrhea:

Ophthalmia neonatorum:

(No vaccine)
Neisseria meningitidis
  • Respiratory droplets
  • Microscopy showing gram-negative diplococci, often with PMNs
  • Culture on chocolate agar, giving positive oxidase test and fermentation of glucose and maltose in 5% CO2 in air
Pseudomonas aeruginosa Infects damaged tissues or people with reduced immunity.

Localized to eye, ear, skin, urinary, respiratory or gastrointestinal tract or CNS, or systemic with bacteremia, secondary pneumonia bone and joint infections, endocarditis, skin, soft tissue or CNS infections.

(no vaccine)
Rickettsia rickettsii (no preventive drug or approved vaccine)
  • Vector control, such as clothing
  • Prompt removal of attached ticks
Salmonella typhi Human-human
  • Fecal-oral through food or water
  • Ty21a and ViCPS vaccines
  • Hygiene and food preparation
  • Isolation from blood, feces, bone marrow, urine or rose spots on skin
  • Colorless, non-lactose fermenting colonies on MacConkey agar
  • Serology for antibodies against O antigen
Salmonella typhimurium
  • Fecal-oral
  • Food contaminated by fowl (e.g. eggs), pets and other animals
  • Fluid and electrolyte replacement for severe diarrhea
  • Antibiotics (in immunocompromised to prevent systemic spread)
(No vaccine or preventive drug)
  • Proper sewage disposal
  • Food preparation
  • Good personal hygiene
Shigella sonnei
  • Fecal-oral
  • Flies
  • Contaminated food or water
  • Protection of water and food supplies
  • Vaccines are in trial stage[18]
  • Culture on Hektoen agar or other media for intestinal pathogens
Staphylococcus aureus
  • Human flora on mucosae in e.g. anterior nares and vagina, entering through wound
Coagulase-positive staphylococcal infections: (no vaccine or preventive drug)
  • Barrier precautions, washing hands and fomite disinfection in hospitals
Staphylococcus epidermidis Human flora in skin and anterior nares
  • Infections of implanted prostheses, e.g. heart valves and catheters
None
Staphylococcus saprophyticus Part of normal vaginal flora None
Streptococcus agalactiae Human flora in vagina or urethral mucous membranes, rectum None
Streptococcus pneumoniae
  • Respiratory droplets
  • Often human flora in nasopharynx (spreading in immunocompromised)
  • 23-serotype vaccine for adults (PPV)
  • Heptavalent conjugated vaccine for children (PCV)
Streptococcus pyogenes
  • Respiratory droplets
  • Direct physical contact with impetigo lesions
No vaccine
  • Rapid antibiotic treatment helps prevent rheumatic fever
Treponema pallidum
  • Sexual
No preventive drug or vaccine
  • Safe sex
  • Antibiotics to pregnant women at risk of transmitting congenital syphilis
Cannot be cultured or viewed in gram-stained smear
Vibrio cholerae
  • Contaminated water and food, especially raw seafood
  • Fluid and electrolyte replacement
  • e.g. doxycycline to shorten duration
  • Preventing fecal contamination of water supplies and food
  • Adequate food preparation
Yersinia pestis
  • Fleas from animals
  • Ingestion of animal tissues
  • Respiratory droplets
Plague:
  • Formalin-killed plague vaccine
  • Minimize exposure to rodents and fleas

See also[edit]

References[edit]

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  2. ^ Heise E (1982). "Diseases associated with immunosuppression". Environ Health Perspect 43: 9–19. doi:10.2307/3429162. JSTOR 3429162. PMC 1568899. PMID 7037390. 
  3. ^ Saiman L (2004). "Microbiology of early CF lung disease". Paediatr Respir Rev 5 (Suppl A): S367–9. doi:10.1016/S1526-0542(04)90065-6. PMID 14980298. 
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  7. ^ "Urinary Tract Infections". Retrieved 2010-02-04. 
  8. ^ "Adult Health Advisor 2005.4: Bacteria in Urine, No Symptoms (Asymptomatic Bacteriuria)". Archived from the original on 2007-07-12. Retrieved 2007-08-25. 
  9. ^ NHS Impetigo
  10. ^ Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson; & Mitchell, Richard N. (2007). Robbins Basic Pathology (8th ed.). Saunders Elsevier. pp. 843 ISBN 978-1-4160-2973-1
  11. ^ "erysipelas" at Dorland's Medical Dictionary
  12. ^ "cellulitis" at Dorland's Medical Dictionary
  13. ^ a b c Tortota, Gerard (2013). Microbiology an Introduction. ISBN 978-0-321-73360-3. 
  14. ^ Yonath A, Bashan A (2004). "Ribosomal crystallography: initiation, peptide bond formation, and amino acid polymerization are hampered by antibiotics". Annu Rev Microbiol 58: 233–51. doi:10.1146/annurev.micro.58.030603.123822. PMID 15487937. 
  15. ^ Khachatourians GG (November 1998). "Agricultural use of antibiotics and the evolution and transfer of antibiotic-resistant bacteria". CMAJ 159 (9): 1129–36. PMC 1229782. PMID 9835883. 
  16. ^ Keen, E. C. (2012). "Phage Therapy: Concept to Cure". Frontiers in Microbiology 3. doi:10.3389/fmicb.2012.00238. PMC 3400130. PMID 22833738.  edit
  17. ^ a b Unless else specified then ref is: Fisher, Bruce; Harvey, Richard P.; Champe, Pamela C. (2007). Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series). Hagerstown, MD: Lippincott Williams & Wilkins. pp. 332–353. ISBN 0-7817-8215-5. 
  18. ^ Institut Pasteur Press Office - Vaccine against shigellosis (bacillary dysentery):a promising clinical trial 15 January 2009. Retrieved on 27 February 2009

External links[edit]