بسم الله الرحمن الرحيم
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بسم الله الرحمن الرحيم. Non Lactose-Gram Negative Bacilli. Dr. Manal El Said. Ass. Prof. of Medical Microbiology. Salmonella typhi. Diseases. Typhoid fever. Characteristics. Facultative gram-negative rods. Non–lactose-fermenting. Produces H2S. Habitat and Transmission.

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بسم الله الرحمن الرحيم

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6212539

بسم الله الرحمن الرحيم


6212539

Non Lactose-Gram Negative Bacilli

Dr. Manal El Said

Ass. Prof. of Medical Microbiology


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Salmonella typhi

Diseases

Typhoid fever.

Characteristics

  • Facultative gram-negative rods.

  • Non–lactose-fermenting.

  • Produces H2S.

Habitat and Transmission

  • Habitat is the human colon only.

  • Transmission is by fecal–oral route.


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Salmonella typhi

Pathogenesis

  • Infects the cells of the reticuloendothelial system, especially in the liver & spleen.

  • Endotoxinin cell wall causes fever.

  • Capsule (Vi antigen) is a virulence factor.

  • Predisposing factors:

  • Decreased stomach acid resulting from ingestion of antacids or gastrectomy.

  • Chronic carrierstate established in gallbladder.

  • Organism excreted in bilefecal–oral spread to others.


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Salmonella typhi

Pathogenesis


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Salmonella typhi

Laboratory Diagnosis

  • Gram-stained smear and culture.

  • Non–lactose-fermenting colonieson MacConkey's agar.

The used media selective for Salmonella are SS agar, bismuth sulfite agar, Hektoen enteric (HE) medium, brilliant green agar & xylose-lisine-deoxycholate (XLD) agar. They contain both selective and differential ingredients


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Salmonella typhi

Laboratory Diagnosis

  • TSI agar shows alkaline slant and acid butt, with no gas and a small amount of H2S.


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Salmonella typhi

Laboratory Diagnosis

  • Biochemical and serologic reactions used to identify species.

  • Identity by using known antisera against O, H, & Vi antigens .

  • Widal test detects agglutinating antibodies to O & H antigens in patient's serum, but its use is limited.


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Salmonella typhi

Treatment

  • Most effective drug is ceftriaxone.

  • Ampicillin & trimethoprim-sulfamethoxazole can be used in patients who are not severely ill.

  • Resistance to chloramphenicol & ampicillin is mediated by plasmid-encoded acetylating enzymes and β-lactamase, respectively.


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Salmonella typhi

Prevention

  • Public health measures:

  • - Sewage disposal

  • - Chlorination of the water supply

  • - Stool cultures for food handlers

  • - Handwashing prior to food handling.

  • Two vaccines are in common use:

  • - one vaccine contains purified Vi polysaccharide capsule

  • - other vaccine contains live attenuated S. typhi


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Salmonellaenteritidis

(Salmonella enterica)

Diseases

  • Enterocolitis.

  • Sepsis with metastatic abscesses.

Characteristics

  • Facultative gram-negative rods.

  • Non–lactose-fermenting.

  • Produces H2S.

  • Motile.


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Salmonellaenteritidis

(Salmonella enterica)

Habitat and Transmission

  • Habitat is the enteric tract of humans &animals, e.g., chickens & domestic livestock.

  • Transmission is by the fecal–oral route.

Pathogenesis

  • Invades the mucosa of small & large intestines.

  • Enter blood sepsis.

  • Infectious dose is at least 105 organisms because organism is inactivated by stomach acid.

  • Endotoxin in cell wall.

  • Predisposing factors: lowered stomach acidity from antacids or gastrectomy.


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Salmonella enterica ssp. enterica on Salmonella Shigella (SS) Agar . Lactose negative, H2S positive colonies.

Salmonellaenteritidis

(Salmonella enterica)

Laboratory Diagnosis

  • Gram-stained smear and culture.

  • Non–lactose-fermenting colonies on MacConkey's agar.

Lactose positive colonies of Klebsiella pneumoniae (larger) and lactose negative colonies of Salmonella enterica ssp.enterica on McConkey agar.


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Salmonellaenteritidis

(Salmonella enterica)

Laboratory Diagnosis

  • TSI agar shows alkaline slant & acid butt, with gas & H2S.


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Salmonellaenteritidis

(Salmonella enterica)

Laboratory Diagnosis

  • Biochemical & serologic reactions used to identify species.

  • Antisera is used to identify by using known in agglutination assay.

  • Widal test detects antibodies in patient's serum to the O and H antigens of the organism but is not widely used.


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Salmonellaenteritidis

(Salmonella enterica)

Treatment

  • Antibioticsnot recommended for uncomplicated enterocolitis.

  • Ceftriaxone are used for sepsis depending on sensitivity tests.

  • Resistance to ampicillin and chloramphenicol is mediated by plasmid-encoded β-lactamases & acetylating enzymes, respectively.


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Salmonellaenteritidis

(Salmonella enterica)

Prevention

  • Public health measures

  • Do not eat raw eggs or meat.

  • No vaccine is available.


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Shigella Species

(e.g., S. dysenteriae, S. sonnei)

Diseases

Enterocolitis (dysentery).

Characteristics

  • Facultative gram-negative rods.

  • Non–lactose-fermenting.

  • Nonmotile


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Shigella Species

(e.g., S. dysenteriae, S. sonnei)

Habitat and Transmission

  • Habitat is the human colon only

  • No animal carriers

  • Transmission is by the fecal–oral route.

Pathogenesis

  • Invades the mucosa of the ileum and colon sepsis (rare)

  • Endotoxin in cell wall.

  • The infectious dose ofShigellais low (1–10 organisms) because it is resistant to stomach acid.

  • Children in mental institutions & day care centers experience outbreaks.

  • No chronic carrier.


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Shigella Species

(e.g., S. dysenteriae, S. sonnei)

Laboratory Diagnosis

  • Gram-stained smear and culture.

  • Non–lactose-fermenting colonies on MacConkey's agar.

colonial morphology displayed by Shigella cultivated on a Hektoen enteric agar .

Fecal flora with Shigella on MacConkey Agar Plates


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Shigella Species

(e.g., S. dysenteriae, S. sonnei)

Laboratory Diagnosis

  • TSI agar shows an alkaline slant with an acid butt and no gas or H2S.

  • Identified by:

  • - biochemical reactions - serology with anti-O antibody.


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Shigella Species

(e.g., S. dysenteriae, S. sonnei)

Treatment

  • Fluid & electrolyte replacement.

  • In severe cases, ciprofloxacin.

  • Resistance is mediated by :

  • -Plasmid-encoded enzymes: ß-lactamase degrades ampicillin

  • -Mutant pteroate synthetase sensitivity to sulfonamides

.

Prevention

  • Public health measures.

  • No Prophylactic drugs.

  • No vaccine.


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Proteus Species

Dr. Manal El Said

Head of Medical Microbiology Department


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Diseases

  • UTI

  • Sepsis

Characteristics

  • Facultative gram-negative rods.

  • Non–lactose-fermenting.

  • Highly motile.

  • Produce urease.


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Habitat and Transmission

  • Habitat is the human colon & environment (soil & water).

  • Transmission to urinary tract is by ascending spread of fecal flora.


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Pathogenesis

  • Endotoxin causes fever and shock associated with sepsis.

  • Urease degrades urea to produce ammonia Ph.

  • This leads to stones

  • - Obstruct urine flow

  • - Damage urinary epithelium

  • - Serve as a nidus for recurrent infection (trapping

  • bacteria within the stone.

  • Organism is highly motile facilitate entry into bladder.

  • Predisposing factors are:

  • -Colonization of the vagina

  • -Urinary catheters

  • -Abnormalities of urinary tract (strictures, valves & stones)


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Laboratory Diagnosis

  • Gram-stained smear and culture.

  • Swarming (spreading) effect over blood agar plate as the organism's active motility.

  • Non–lactose-fermenting colonies on MacConkey's agar.

  • Produces urease

  • P. mirabilis is indole-negative


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Laboratory Diagnosis

  • TSI agar shows an alkaline slant and acid butt with H2S.


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Treatment

  • Trimethoprim-sulfamethoxazole or ampicillin is often used for uncomplicated UTIs

  • A third-generation cephalosporin should be used for serious infections.

  • The indole-negative species P. mirabilis is more likely to be sensitive to antibiotics such as ampicillin.

  • Resistance is mediated by plasmid-encoded enzymes.


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Proteus Species

(e.g., P. vulgaris, P. mirabilis)

Prevention

  • No vaccine or drug is available.

  • Prompt removal of urinary catheters helps prevent urinary tract infections.


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Morganellamorganii & Providenciarettgeri

  • Enteric gram-negative rod similar to Proteus species.

  • Causes UTIs & sepsis.

  • Highly motile & produces urease.

  • Indole-positive and more resistant to antibiotics than P. mirabilis.


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Yersiniapestis

Diseases

Bubonic & pneumonic plague.

Characteristics

  • Small gram-negative rods with bipolar ("safety pin") staining.

  • One of the most virulent organisms (very low ID50)

Habitat and Transmission

  • Reservoir is wild rodents, e.g. rats.

  • Transmission is by flea bite.


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Yersiniapestis

Pathogenesis

  • Virulence factors include:

  • Endotoxin

  • Exotoxin,

  • V & W proteins allow organism to grow within cells.

  • Envelope (capsular) antigen that protects against phagocytosis.

Bubo is a swollen inflamed lymph node, located in the region of the flea bite


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Yersiniapestis

Laboratory Diagnosis

  • Gram-stained smear.

  • Wayson's stain show typical "safety-pin" appearance.

  • Cultures are hazardous & done only in specially equipped laboratories.

  • Organism is identified by immunofluorescence.

  • Serologic tests that detect antibody in patient's serum.


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Yersiniapestis

Treatment

  • Streptomycin either alone or in combination with tetracycline.

  • Strict quarantine for 72 hours

Prevention

  • Control rodent & avoid contact with dead rodents.

  • Killed vaccine is available for high-risk occupations

  • Close contacts should be given tetracycline.


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Yersiniaenterocolitica

  • Gram-negative rods.

  • It Causes:

  • -Enterocolitis (similar to Shigella & Salmonella).

  • - Mesenteric adenitis (mimic appendicitis)

  • Found in domestic animals

  • Transmitted by fecal contamination of food.


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