Genus Salmonella - Biology - Lecture Slides, Slides for Biology. Agra University

Biology

Description: Genus Salmonella, Foodborne Disease, Faculatively Anaerobic, Oxidase Negative, Glucose Fermentative, Generally Motile, Biochemical Characteristics, Lactose Negative, Urease Negative, Heat Resistance describes lecture layout.
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1

Microorganisms Causing Foodborne Disease

Enterobacteriaceae Family Genus Salmonella

Family Enterobacteriaceae

• Gram-negative • Non-sporeforming rods • Faculatively anaerobic • Oxidase negative • Glucose fermentative • Generally motile

Peritrichous flagella

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Salmonella • Named after Dr. D. E. Salmon

– First described Salmonella cholerae-suis • Currently only 2 species are recognized

– S. bongori – S enterica.

• 6 subspecies »enterica »salamae »arizonae »diarizonae »houtenae »Indica

Principal biochemical characteristics

• Lactose negative • Lysine decarboxylase positive • H2S positive • Urease negative

• 0.8% of strains can ferment lactose • A few strains do not produce H2S

Salmonella • Salmonellae are separated in somatic

groups (O antigens) and flagellar types (H antigens)

• About 2,400 serovars (or serotypes) have been described

• Example of correct nomenclature: – Salmonella enterica subsp. enterica serovar

Typhimurium – Abbreviated: Salmonella Typhimurium

• After having defined by full name • Also there is a phage-based classification

– Phage types

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Growth characteristics • Temperature

– Minimum 7°C – Maximum 47°C – Optimum 37°C

• pH – Minimum

• Acetic acid 4.7 • HCl 4.05

– Optimum 7.0

• aw – Minimum 0.93

Heat resistance

• Non-thermoduric • S. Senftenberg 775W is heat resistant

– D71 in milk = 0.09 min D f S T hi i i ilk 0 003 i– 71 or . yp mur um n m = . m n

• Heating mestruum affects heat resistance – D70 for S. Typhimurium in chocolate sauce =

11.3 – 17.5 h.

Ecology

• Most salmonellae infect a wide range of animal species

• Some serovars are host adapted – S. Enteritidis PT4, S. Pullorum, S.

Gallinarum in poultry – S. Cholerae-suis in pigs – S. Tiphy in humans

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Clinical features

• Enteritis – Diarrhea, nausea and fever

• Incubation period – 6 – 48 h

• Infectious dose – 1 to 106 cells

Pathogenesis

• Pathogenesis – Adhesion to epithelial cells of the ileum via mannose-

resistant fimbriae – Bacterial uptake by host cells (endocytes) – Passage through epithelial cells within a vacuole,

where the bacterium multiplies – Influx of inflammatory cells leading to the release of

prostaglandins – Prostaglandins activate adenylate cyclase which

produces fluid secretion to the intestinal lumen

Activity in foods

• Low aw enhances the survival of Salmonella – The lower the aw the greater the survival rate

Survival of Salmonella in meringue powder as affected by aw

0 50

100 150 200 250

D ay

s of

s to

ra ge

0.3 0.2 0.1

a w

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Survival of Salmonella in different foods

Commodity Temperature Survival time

Butter -23 to 25°C >10 weeks

Room temp Milk

. 6 months

Ice box

Various vegetables 2 to 4°C >28 days

Chocolate Room temp. Months

Foods associated with Salmonella infection

• Eggs – Salmonella serovar

Enteritidis • Meat

• Cheese – S. Zanzibar

• Chocolate – S. Typhimurium

• Fruits and vegetables – S. Montevideo (tomatoes) – S. Poona (cantaloupes) – S. Newport (mangoes)

– S. Eastbourne • Milk

– S. Typhimurium – S. Newbrunswick

Transmission routes

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S. Enteritidis • Associated with eggs • Present in the yolk at oviposition • Food associated:

– Homemade mayonnaise w/raw eggs – Tartar sauce

Egg nogg– – Milk shakes – Mousse – Ice cream

• Control – Decreasing S. Enteritidis populations at the farm – Refrigerating eggs – Egg pasteurization or irradiation

S. Typhimurium DT 104 • First reported in the UK in 1984 • Increasing prevalence • Isolated from food animals

As well as other domestic and wild animals–

• R-factor as a natural DNA component – Typically resistant to ampicillin,

chloramphenicol, streptomycin, sulfonamides, and tetracycline

– R-type ACSSuT

DT 104

• Resistant to multiple antibiotics • UK reported case-fatality rate = 3%

– 0 1% for other non-typhoid salmonellae.

• R-type ACSSuT present in 30% of human isolates in the U. S. – Resistance to trimethoprim, fluroquinones and

ciprofloxacin is being reported

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Outbreak of salmonellosis caused by DT 104 in the U.S.

• Nebraska, 1996 • 19 cases

– Elementary school children

• 3 required hospitalization • Vehicle implicated: cold chocolate milk

– Relative Risk=8.2

• Isolates were R-type ACSSuT • Phage typing confirmed DT 104

Isolation methods • Methods include enrichment prior to plating

on selective media • Most methods for food analysis also include a

pre enrichment • Enrichment in a non-selective broth

– Lactose broth • After enrichment, a rapid method can be

used – Immunoassays (ELISA, 1-2-3) – DNA probes

• If rapid method indicates + test, Salmonella must be confirmed by plating method

• Examples of enrichment broths – Tetrathionate broth

Isolation methods (cont.)

– Selenite cystine broth – Rappaport-Vassiliadis

• Examples of plating media – Brilliant green agar – XLD agar (xylose lysine deoxycholate) – Bismuth sulfite agar

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Isolation methods (cont.) Typical colonies on plating media are

suibjected to identification tests • Biochemical tests

– TSI agar – LIA agar – Urea broth

• Serological tests – Polyvalent O antiserum – Serogrouping and serotyping

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