Bacteria Of Lower GI Flashcards
Enterobacteriaceae (gram , 5 major features)
Gram negative bacilli
- All ferment glucose –
- All reduce nitrates to nitrites(energy r) –
- All are oxidase negative –
- All Facultative anaerobes.
- All are motile except Klebsiella,.Shigella and some Yersinia
Virulence and Antigenic Factors of Enterics(3)
Ability to colonize, adhere, produce various toxins and enzymes to invade tissues
• Some possess plasmids that may mediate resistance to antibiotics
• Many enterics possess antigens that can be used to identify groups
Antigenic Factors of Enterics
O antigen – somatic, heat-stable antigen in the
cell wall
H antigend – flagellar antigen
K antigen – capsular antigen
Antigenic Factors of Enterics
O antigen – somatic, heat-stable antigen in the
cell wall
H antigend – flagellar antigen
K antigen – capsular antigen
enterics are divided into two categories:
Opportunistic pathogens : normally part of the usual intestinal flora that may produce infection outside the intestine
Primary intestinal pathogens : Salmonella, Shigella, and Yersinia sp.
Escherichia coli ( Common isolate from colon flora) cause(3)
- meningitis (neonatal)
- urinary tract infections, wound infection, bacteremia
- Gastrointestinal Infections(DIARRHOEA)
Pathogenesis of E-coli (5)
- Pili
- Capsule
- Endotoxin (fever, hypotension,DIC)
- Two exotoxins (enterotoxins)
- Motility
Laboratory diagnosis of E-coli (6)
1.Culture on MacConkey’s agar. They produce pink colonies due to lactose fermentation.
2.Biochemical tests: eg, Indole positive and methyl red tests
- Ferments glucose, lactose, xylose
- Does NOT produce H2S or phenylalanine deaminase
- Citrate negative
- Usually motile
Klebsiella species (3)
• K. pneumoniae makes the colonies moist and mucoid – Has a distinctive “yeasty” odor – Frequent cause of nosocomial lober pneumonia.
K. ozaenae: atrophic rhinitis.
K.rhinoscleromatis :destructive granuloma of the nose and the pharynx
Significant biochemical reactions ofKlebsiella (4)
- Lactose positive
- Citrate positive
- Most are urease positive
- Non-motile
Proteus, Morganella & Providencia species
- All are normal intestinal flora
- Opportunistic pathogens
- Deaminate phenylalanine positive
- All are lactose negative
Proteus (mirabilis , vulgaris)
UTI (promoting stone formation by precipitating Mg and Ca (stag horn ) )
Wounds
Ear
Bacteremia
Pneumonia
Why the urine of UT infection with proteus is alkaline ?
Proteus produce urease
Lab test for proteus
Swarming colonies (motile)
Urease +
Phenylalanine deaminase +
When cultured aerobically at 37 smells fishy
Salmonella disease
Enteritis
Bacteremia
Enteric fever
Salmonella diagnosis
Stool is cultured in selenite F
Widal test
Salmonellae are facultative intracellular pathogen
No answer here
Treatment of Enteric fever and bacteremia(2)
- require antibiotic treatment: chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole.
- Surgical drainage of metastatic abscesses may be required.
Treatment of Salmonella enterocolitis
needs only supportive therapy
Treatment of Chronic carriers of S. typhi
may be cured by antibiotics alone or combined with cholecystectomy.
Prevention and control of salmonella (4)
- Sanitary measures.
- Carriers must not be allowed to work as food handlers.
- Strict hygienic precautions for food handling
- Vaccines against S.typhi
Vaccines against S.typhi:
Purified Vi antigen, parentral
Oral, live attenuated vaccine.
Shigella species All species cause bacillary dysentery
No answer here
Characteristics Of Shigella (5)
Non lactose ferment – Non-motile – Do not produce gas from glucose – Do not hydrolyze urea – Do not produce H2S on TSI
