Facultative Anaerobic Bacteria

• Produce acid & gas anaerobically
• Medically very important
• 3 families:
  • Enterobacteriaceae (peritrichous)
  • Vibrionaceae (polar)
  • Pasteurellaceae (none)

Enterobacteriaceae

General comments

• Most important heterogenous collection of medically significant bacteria (27genera & 110 sp)
• Ubiquitous- soil, water, vegetation (saprophytes) & some normal flora of humans & animals but opportunistic (E.coli, Klebsiella pneumoniae, Proteus mirabilis) and some always pathogenic (Salmonella, Shigella & Yersinia pestis).
• Infections can originate from an animal reservoir (Salmonella), from a human carrier (S. typhi, Shigella) or by endogenous spread of the organism in a suspetible patient (E. coli)
• Readily culturable on non-selective media from sterile specimens (spinal fluid, tissues), selective media eosin methylene blue (EMB), MacConkey agar for contaminated specimens (sputum, feces), highly selective media (eg stool samples-- normal flora mask) & cold enrichment technique (stool sample + saline --> 4 C / 2 weeks; most enerobacters killed but not Yersinia enterocolitica (slow grower)
• Identification based on fermentation products (types & ratio) eg Butanediol (Enterobacter); mixed acids (E. coli; Salmonella & Shigella-- ratios of products important) (LINK to metabolic pathways), serological properties but cross-reactions limit usefulness [flagella (H), lipopolysaccaharide (O) & capsular (K); eg E.coli (170H, 56H & numerous K), biochemical propeties identification within 4 to 24 hrs; Capsules-- Klebsiella
• Treatment with antibiotics (E. coli, Proteus miabilis) but some highly ressistant & in some cases not recommended (S. enteriditis, prolongs carrier state). Antibiotic ressistant bacterial infections commonly hospital acquired (not community aquired)
• Pathogenecity
• Endotoxins (lipid A of LPS) released from cell lysis (LINK), flagella, pilli & fimbrae (LINK) in adherence & attachment; capsules --weakly antigenic & protect against antibody mediated phagocytosis

• Salmonella
  • 2000 serotypes based on H (flagella protein), O (outer membrane protein) & K (Capsular protein)
  • Antibodies obtained commercially for serotyping using Kauffmann-White scheme.
  • Some Salmonella serotypes are host specific (humans= S. typhi S. paratyphi; animals (S. cholerae-suis but cause severe disease if transmitted to humans) & some others not host specific (affect humans & animals)
  • Food borne disease mainly thro' poultry, eggs & dairy products
  • Exposure to Salmonella is frequent but requires a high dose of 1 to 100 million (eg improperly refrigerated foods; low dose for immunocompromised, very young and the elderly or with decreased gastric acidity
  • Disease is due to microbial growth in body tisssue & not by ingestion of foods contaminated with toxins as a result of microbial growth
  • Salmonella infections occurs in one of four forms:
    • Gastoeneteritis (S. enteritis) most common form; eating contaminated foods; elevated temperatures, cramps & head ache. Symptoms disappear spontaneously in 2 to 7 days
    • Septicimia--All Salmonella can cause bacterimia (S. cholera-suis, S. typhi & S. paratyphi)
    • Enetric fever (S. typhi- typhoid fever & S. paratyphi- paratyphoid fever)-- Similar symptoms but paratyphoid fever milder; Transmission by consumption of contaminated foods --> multiplication in intestine (endothelial cells)--> invades lymphatic tissues to blood stream & kidneys (excreted in urine)
    • Asymptomatic carriage-- Establishes in gall bladder (ressists bile & bile salts); continuous feedback into intestine; known as carrier state (2-5% typhoid patients become carriers & excrete 1 to 1000 million S. typhi /gm feces & also in urine); Carrier state is important in transmission of the disease. Mary Mallon (1901), aka Typhoid Mary, was the first carrier case to be detected; In 15 years infected 200 & jailed to prevent spred of typhoid fever. Disease has declined due to curative & preventative measures (heat killed injectable vaccines or the new live oral vacciine; same efficacy but later has less side effects

• Shigella
  • Simple taxonomy (4 species & 32 serotypes) unlike Salmonella
  • Found in humans, apes & monkey only unlike Salmonella
  • Cause bacillary dysentry (shigellosis); S. sonnei (industrialized nations) & S. flexneri (developing nations); S. sonnei mild but S. dysenteriae (aka Shiga bacillus produces Shiga toxin) severe.
  • Shigella enter endothelial cells (intestine) & multiply causing tissue damage; exotoxins stop host cell protein synthesis. Rarely (with the exception of S. dysenteriae) cause septicimia. 20 bowel motions a day.
  • Transmission by fecal-oral route thro' contaminated hands & usually not by food-water
  • Low dose required-- 200 Shigella cells can establish disease

• Escherichia
  • Most common inhabitants of intestinal tracts.
  • Food & water presence indicates fecal contamination; indicator bacterium
  • Endogenous spread (septacemia, urinary tract infections, meningitis) or food-water borne transmission (gastroenteritis, travellers diarrhea)
  • Antigenic composition complex: 170, 57 H and several K antigens (epidemiological & specific serotypes associated with increased virulence (H157:O7)
  • Septicimia: Focus of infection is urinary tract or intestine and spreads to bloodstream (higher incidence of death in immunocmpromised patients)
  • Urinary tract infection: 80% = community aquired or hospital aquired. 10 specific serotypes usually involved (eg 01, 02, 016, 075) & origin is from gastrointestinal tract.
  • Pathogenecity --serotypes more adhesive to uroepithelial cells than other serotypes
  • Meningitis: E.coli & B streptococci cause 75%. Serotype K1
  • Gastroenteritis: 4 groups; enterotoxigenic (ETEC) causes travellers & infant diarrhea, pathogenecity similar to V. cholera toxin ie stimulates hypersecretion of fluids & electrolytes in gastrointestinal tract (LINK), not serotype specific, produce heat labile & heat stable plasmid mediated enterotoxins, not serotype specific (NA probing, tissue culture or animal models & not serotyping for identification. Enteroinvasiveness (EIEC)

• Klebsiella
  • Capsulated
  • K. pneumoniae-- pneumonia (old or immunocompromised eg alcoholics); also causes septecimia in hospital pediatric wards

• Serratia
  • S. marcesens- red pigmented colonies
  • Causes hospital aquired infections (nosocomial) like Enerobacter
  • Urinary & respiratory tract infection
  • Isolated from sterile saline solution, catheters

• Proteus
  • Extremely motile
  • P. mirabilis-- urinary tract infection; produces urease & splits urea to CO2 and NH3 to increase pH & therefore facilitate renal stone formation & uroepithelium toxicity.
  • Pili decreases phagocytosis & therefore decreases virulence unlike E. coli

• Erwinia
  • Plant pathogens (phytopathogens)
  • Produce pectinase which hydrolyse pectin between plant cells & cause plants to rot

Vibrionaceae

• Curved to comma shaped
• Polarly flagellated
• Facultative anaerobes
  • Aerobic & therefore catalase & oxidase +ve (similar to aerobic Pseudomonads)
  • Fermenters ie anaerobic
• Widespread distribution (fresh water, sea water) & human & animal intestinal tracts); not indicators of fecal pollution.
• 3 genera (Vibrio, Aeromonas, Photobacterium)
  • Vibrio Cholera (aka Asiatic cholera)
    • Two biotypes of serogroup O:1 known (classic cholera & Eltor [Mecca camp]); Eltor endemic in coastal regions eg India, Bangladesh & South America; USA non-O1 serogroup due to consumption of contaminated seafood.
    • Transmitted thro' sewage contaminated water & food; rice water stools
    • Multiplies in intestinal epithelial cells (but not invasive to other tissues) & produces an enterotoxin (binds irreversibly to epithelial cells stimulating the production of cyclic which changes cell permeability leading to the secretion of water & electrolytes into the lumen. 12 to 20 litres of water lost-- dehydration; replacement of electrolytes & water necessary is the best treatment; Tetracycline decreases disease period; vaccines provide short immunity but natural infections provide a longer duration (against enterotoxin & cells)
    • Culture in alkaline medium (high pH decreases the growth of other bacteria)
    • Vibrio parahemolyticus
    • Habitat is salt water and requires > 2% NaCl for growth in laboratory media (halophilic) Gastroenteritis from contaminated shell fish, crabs; USA, Japan, Hawaii Large nos. within 24 hr & recovery follows in a few days.
  • Aeromonas
    • Mainly pathogens of fresh water fish, turtles & frogs.
    • May be encountered as causative agents of human diseases.
  • Photobacterium
    • Interesting due to the property of bioluminescence (aka luminescent bacteria); ATP + electron transport chain + enzyme luciferase = luminescence
    • Normal flora of some fish (flash light fish); behavioral activities (mating, protection)

Pasteurellaceae

• Pasteurella
  • Pathogen of domestic animals (septacemia = cattle; fowl cholera = chickens)
  • P. multocida transmitted to humans by dog / cat bites.
  • Nutritionally fastidious; requires complex media for growth in the laboratory
• Haemophilus:
  • Common inhabitants of upper respiratory tract mucous membrane, mouth, vagina, GI.
  • Requires X factor (unknown component of hemoglobin) for synthesising parts of the cytochrome system; eg choclate agar (blood heated & gives brown color) supllemented with NAD or NADP (V factor).
  • H. influenzae - flu like
  • H. ducreyi -- veneral disease aka soft chancre
  • H. suis-- hog influenza