5 Salmonella

8/8/2019 5 Salmonella

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CVM6202: Microbiology K.V. Nagaraja

SALMONELLA




Learning Objectives

• To learn important characteristics of the agent

• To know species of importance

• To understand the pathogenesis and disease caused

by the agent• Diagnosis and control of the disease caused by the

agent




SALMONELLA

• From the epidemiological point of view, Salmonella can

be classified into 3 main groups

Group 1: Those infecting only humansEx. S. typhi, Paratyphi A and C

Group 2: Those adapted for particular species of vertebrates

Ex. S. gallinarum for poultry, S. dublin in cattle,

S. abortus equi in horses, S. abortus ovis in sheep,

S. choleraesuis in swine. Some of these are also

pathogenic for humans. (S. dublin and S. choleraesuis)

Group 3: Salmonella types with no particular host preferences.

Infect both humans and animals (PARATYPHOIDS)




Genus: Salmonella

• Approximately 2200 serotypes are known to exist

based on 67 “O” antigen groups and numerous “H”

antigens recognized so far.

O antigens H antigens

• Members of the genus are given names based on:

1. Disease syndrome or animal from which they were first

isolated. Ex. S. choleraesuis, S. hadar

2. Place where they were first reported. Ex. S. heidelberg,

S. St. Paul

3. Antigenic formula




Antigenic Variation

• In Salmonella variations in antigenic

structure takes place

• Kinds of antigenic variations:

1. Phase Variation

2. H - O Variation

3. S - R Variation

4. Form Variationa) O variation

b) V - W variation

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H - O Variation• Loss of H antigen or Flagella

• Usually proceeds in one direction onlyi.e. flagellated “HO” form to the non-flagellated

“O” form

• Mutant non-motile resulting from motile one

• Spontaneous change from HO forms to O forms is

rare and most often irreversible

• Genetic material responsible for development of

the enzyme system that synthesizes the flagella is

lost or altered

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“O” Antigen Variation

• O antigens of the genus Salmonella are designated by

Arabic numerals

• Ex. 1, 6, 12, 19, 24, 25, 27, 36, 37, 50

• Antigen 12 is made up of 3 components

Ex: 12(1), 12(2), and 12(3)

• The 12(2) component varies in that it is either strongly

or weakly developed. Some colonies contain large

amounts of 12(2)

So it is a quantitative difference in O antigen

• O form variation has been seen in some O antigens

Ex: 1, 6, and 12.

CVM6202: Microbiology K V Nagaraja




This variation affects Vi antigen

Certain species have an outermost polysaccharide layer

called a Vi antigen, that is usually too thin to be seenas a capsule

O and H antigens remain unchanged

Quantitative antigenic changes which take place in Vi

antigen are called the V - W variation

V - W Variation

Vi antigen

O antigen

H antigen





S - R VariationSmooth to Rough variation

• Change from smooth to rough forms• Known to occur in practically all bacteria

• Are not abrupt - is a gradual loss of O antigen thus

exposing the core polysaccharide

• Rough organisms give non-specific agglutination

• Low in virulence, can be used as vaccine strains• The flagellar antigens are unchanged in this

dissociation





Phase Variation

• Flagellar antigens are proteins in nature

• They are localized in the flagella of motile species• In contrast to somatic or “O” antigens, flagellar antigens

are destroyed by boiling

• They often exist in one of two different degrees of specificity called phases

• An individual bacterial cell will have flagella composed

of antigens either in phase 1 or in phase 2

• Cultures of a serotype may contain mixtures of

individual bacteria, some in phase 1 and some in phase 2





Phase Variation

• Bacteria which are originally in one phase may switch

to the other phase during multiplication. This switch is

called phase variation.

• Some Salmonella are monophasic and others are non-

motile. Non-motile strains do not demonstrate phasevariation

• Identification of both phases is necessary for the

identification of a serotype

• Flagellar antigens are denatured by heat, alcohol and

dilute acids






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Human Salmonellosis

• Salmonella typhi : typhoid fever

Typical symptoms may be preceded by acute

gastroenteritis coming on shortly after

consumption of infected water or food

• Diarrhea, vomiting, abdominal tenderness,

death in some cases




Human Salmonellosis

• Salmonella typhi (typhoid fever) 7 - 14 days incubation

• Ingestion- multiplies in the GI tract, enter intestinal

lymphatics, disseminated throughout the body by the blood

stream

• Typhoid bacillus localizes in the gall bladder, bile ducts. It

may persist here for many years after convalescence

• Relapses may occur during convalescence due to reinvasion

of blood stream from the tissues in which typhoid bacilli are

still proliferating

• Diagnosis: Culture of blood, feces, urine or bile

• Inactivated bacterins are used as vaccines




Salmonellosis in Humans

• 40,000 cases reported annually• 2,000,000 cases estimated annually

• Medical expenses and lost productivity estimated

to be $553 to $988 million annually

• Cost to industry- The milkborne 1985 outbreak

resulted in 20,000 litigations and the plant wasclosed from poor publicity




Salmonellosis in Poultry

• Poultry constitute an important animal reservoir forSalmonella

• A very wide variety of serotypes have been isolated

from chickens, turkeys, ducks, and other species of

domestic poultry




Salmonellosis in Poultry

• S. gallinarum and S. pullorum

S. pullorum:

World-wide in its distribution, National schemes (NPIP-

National Poultry Improvement Plan) have reduced the

incidence of this disease in the U.S.

Adult birds may be symptomless carriers of the disease

Ovaries are the organs where infection commonly persistsA proportion of eggs laid by adults with infected ovaries

contain S. pullorum in the yolks




S. pullorum Infection

• Hatching of chicks from infected eggs constitutes a serious

source of infections for all the remaining chicks in an

incubator and hatcher

• The feces of infected chicks contaminate the environment

thus spreading infection to other chicks

• Chicks which may survive infection may become

symptomless carriers of S. pullorum, excrete the organism in

feces. S. pullorum can survive in the litter for several months

• All turkey and chicken breeder flocks are tested for the

presence of infection. Use agglutination test. MN -free of

S. pullorum in domestic turkey breeders (1974)







Salmonella gallinarum

Fowl typhoid

• The cycle of infection from the hen to the chick, as

occurs in pullorum disease, can also take place withS. gallinarum

• It is more usual, however, for fowl typhoid to develop

as a disease of varying severity among growing birdsand adult stock

• Common route of infection is by ingestion• The severity of outbreaks can vary from acute with

high mortality rates to chronic infection




Fowl Typhoid

• When the disease occurs in young chicks the

symptoms are indistinguishable from pullorum

disease

• Mortality rate can go up to 50% or more

• Diarrhea with greenish colored feces, purplediscoloration of comb and wattles

• Diagnosis: Culture liver, spleen, and heart blood

Disease not present in MN in domestic turkey

breeding flocks










Non-host adapted Salmonella

• Other non-host adapted Salmonella types also infect

poultry• Contaminated animal by-products (Meat and Bone

meal) used in animal feeds

• Contaminated hatcheries, environment

• Egg transmission from infected breeder flocks

• Day-old antibiotic (Gentamycin and Spectinomycin)injection is practiced in many hatcheries




Salmonellosis in Cattle

• Salmonella dublin and Salmonella typhimurium are

the most common causes of bovine Salmonellosis

• Affect cattle of all ages, disease may be acute orchronic. Calves are more susceptible to infection than

adults

• Adult cattle infected with S. dublin may act as

symptomless carriers, excrete the organism

intermittently in the feces

• S. dublin can survive in feces for 2-4 months.

Pastures, food, and water may become contaminated

from feces of carrier animals or aborted fetuses and

fetal membranes.




Salmonella infection in cattle

• Salmonella typhimurium: A non-host adapted Salmonella

• Occurs in 2-6 week old calves• Infection of cattle may originate from disease in another

animal species or from cattle

• Pathogenesis is similar to infection with S. dublin except thatthe development of chronic carriers over a period of several

years does not occur frequently

• Fever, diarrhea with brown or greenish-brown feces withblood sometimes

• Sometimes arthritis, pneumonia, encephalitis may be evident





• Adult cattle: go off their milk, run high temperature.

Blood may appear in the feces and followed by astinking which may contain shreds of mucus

membrane. The cow becomes very weak and rapidly

goes down and may die in 1 to 5 days

• If death does not occur, diarrhea, emaciation may

continue for sometime before recovery finally ensues• If the cow is pregnant abortion may occur





• Non-host adapted Salmonella types have also

been reported in the cattle

• Human infection results through consumption of raw or improperly pasteurized milk, milk

products or contaminated beef




Salmonellosis in pigs

• S. choleraesuis, S. typhisuis, and non-host adapted types

• Salmonella choleraesuis var kunzendorf is the mostcommon type in the US and causes necrotic enteritis

• Incubation period is usually several days, mode of

infection is mainly by ingestion• S. typhisuis is antigenically related to S. choleraesuis,

not common, Causes intermittent diarrhea, emaciation,

lesions in the lymph nodes and intestine, generalizedsepsis

• S. typhimurium is also an important cause of disease in

pigs




Non-host adapted Salmonella in pigs

• Less frequently a wide variety of other non-host

adapted Salmonella types have been isolated from

both diseased animals and from mesentric lymph

glands, intestinal tracts and other sites in thecarcases of apparently healthly animals at

slaughter.

• Salmonella in swine - a source for humans




Salmonella infection in Horses

• In the US the most common types have been

S. typhimurium, S. enteritidis, S. newport, andS. heidelberg

• Young animals are particularly susceptible

• Stress apparently has a major role in the initiation of clinical disease and predisposing factors including

surgery, passing nasogastric tubes, concurrent illness

• High temperature, colicky pains are frequenty the first

symptoms followed by diarrhea




Salmonella infection in Dogs

• Salmonella can be found in the feces of manynormal dogs, intermittent diarrhea is all that

one might expect in infected adults

• Many different types can be seen in dogs• Puppies are more susceptible

• Adults rarely develop septicemia




Salmonella infection in Cats

• Many different types of Salmonella have been isolated

• Cats are affected by eating usually contaminated food,

wild rats and mice and contact with feces of other

animals

• Kittens are more susceptible than adults• Cats may be carriers without showing symptoms

• In kittens, acute or subacute outbreaks of enteritis with

or without septicemia may occur

• In adult cats, intermittent diarrhea, vomiting may occur

sometimes




Salmonella infection in Sheep

• Many Salmonella types have been isolated from sheep

• Most common in some countries: S. typhimurium

• Raised temperature in most cases scouring is usually

present, passing of blood in feces is occasionally noted

• In acute Salmonellosis, a severe watery putrid diarrheaoccurs and a high proportion of sheep die

• In some cases persistent scouring of greenish or yellowish

paint like material with a foul smell is the striking symptom

• Overcrowding, housed together

• Pregnant animals may die of septicemia before aborting.

Aborted fetus and placenta -highly contaminated




Salmonella in wild animals

• Turtles: Rearing turtles for sale in contaminated

stagnent water particularly where a heavy sewagecontamination exists has led to a high level of

Salmonella

• In some establishments in the USA, 25-50% of theseanimals were found to be actively excreting

Salmonella

• In 1975 the interstate shipment of turtles was banned

in US




Salmonella in wild animals and birds

• Infection of wild animals and birds reflect contamination of

their environment

• A source of infection to domestic animals• S. typhimurium is the commonest Salmonella found in

captive birds. Infection is particularly frequent in canaries.

Captive birds are at particular risk of being exposed toSalmonella because surplus feed tends to attract rodents and

wild birds

• Homing pigeons very frequently suffer from Salmonellosis.In large cities wild pigeons may theoretically pose a risk to

humans

• Pet turtles and iguanas -source of human infection




Salmonella in feed

• Use of improperly cooked animal by-products inanimal feed

5 Salmonella

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