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Bacterial classification

List of pathogenic bacteria by basic laboratory characteristics


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
aerobic Regan-Lowe agar extracellular
Borrelia Gram-negative, but stains poorly spirochete
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 Blood agar 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
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
pultiple 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 stricktly 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
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 Intracellula


List of pathogenic bacteria by clinical characteristics


Species of human pathogenic bacteria [15]
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:

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[16]
  • 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:

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