12 - Facultative anaerobes part 2 ( ENTEROBACTERIACEAE )

• Salmonella :

o 2000 serotypes based on H (flagella protein), O (outer membrane protein) & K (Capsular protein)

o Antibodies obtained commercially for serotyping using Kauffmann-White scheme.

o 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)

o Food borne disease mainly thro' poultry, eggs & dairy products

o 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

o Disease is due to microbial growth in body tisssue & not by ingestion of foods contaminated with toxins as a result of microbial growth

o 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 : 

o Simple taxonomy (4 species & 32 serotypes) unlike Salmonella

o Found in humans, apes & monkey only unlike Salmonella

o 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.

o 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.

o Transmission by fecal-oral route thro' contaminated hands & usually not by food-water

o Low dose required-- 200 Shigella cells can establish disease

11 - Facultative anaerobes part 1 ( ENTEROBACTERIACEAE )

• Produce acid & gas anaerobically
• Medically very important
• 3 families:
o ENTEROBACTERIACEAE (peritrichous)
o VIBRIONACEAE (polar)
o PASTEURELLACEAE (none)
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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) , 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 , flagella, pilli & fimbrae in adherence & attachment; capsules --weakly antigenic & protect against antibody mediated phagocytosis