5 Salmonella

CVM6202: Microbiology

K.V. Nagaraja

SALMONELLA


K.V. Nagaraja

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


K.V. Nagaraja

SALMONELLA • From the epidemiological point of view, Salmonella can be classified into 3 main groups Group 1: Those infecting only humans Ex. 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)


K.V. Nagaraja

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


K.V. Nagaraja

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 Variation a) O variation b) V - W variation


K.V. Nagaraja

H - O Variation • Loss of H antigen or Flagella • Usually proceeds in one direction only i.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


K.V. Nagaraja

“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.


K.V. Nagaraja

V - W Variation This variation affects Vi antigen Certain species have an outermost polysaccharide layer called a Vi antigen, that is usually too thin to be seen as a capsule H antigen Vi antigen

O antigen

O and H antigens remain unchanged Quantitative antigenic changes which take place in Vi antigen are called the V - W variation


K.V. Nagaraja

S - R Variation Smooth 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


K.V. Nagaraja

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


K.V. Nagaraja

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 nonmotile. Non-motile strains do not demonstrate phase variation • Identification of both phases is necessary for the identification of a serotype • Flagellar antigens are denatured by heat, alcohol and dilute acids


K.V. Nagaraja

Salmonellosis in humans • Caused by certain Salmonella serotypes • Salmonella paratyphi A, S. paratyphi B, S. paratyphi C, S. typhi • Only in humans • Human infections are also caused by non-host adapted Salmonella


K.V. Nagaraja

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


K.V. Nagaraja

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


K.V. Nagaraja

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 was closed from poor publicity


K.V. Nagaraja

Salmonellosis in Poultry • Poultry constitute an important animal reservoir for Salmonella • A very wide variety of serotypes have been isolated from chickens, turkeys, ducks, and other species of domestic poultry


K.V. Nagaraja

Salmonellosis in Poultry • S. gallinarum and S. pullorum S. pullorum: World-wide in its distribution, National schemes (NPIPNational 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 persists A proportion of eggs laid by adults with infected ovaries contain S. pullorum in the yolks


K.V. Nagaraja

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)


K.V. Nagaraja


K.V. Nagaraja

Salmonella gallinarum Fowl typhoid

• The cycle of infection from the hen to the chick, as occurs in pullorum disease, can also take place with S. gallinarum • It is more usual, however, for fowl typhoid to develop as a disease of varying severity among growing birds and adult stock • Common route of infection is by ingestion • The severity of outbreaks can vary from acute with high mortality rates to chronic infection


K.V. Nagaraja

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, purple discoloration of comb and wattles • Diagnosis: Culture liver, spleen, and heart blood Disease not present in MN in domestic turkey breeding flocks


K.V. Nagaraja


K.V. Nagaraja


K.V. Nagaraja

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


K.V. Nagaraja

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 or chronic. 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.


K.V. Nagaraja

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 that the development of chronic carriers over a period of several years does not occur frequently • Fever, diarrhea with brown or greenish-brown feces with blood sometimes • Sometimes arthritis, pneumonia, encephalitis may be evident


K.V. Nagaraja

Salmonella infection in cattle • Adult cattle: go off their milk, run high temperature. Blood may appear in the feces and followed by a stinking 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


K.V. Nagaraja

Salmonella infection in cattle

• 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


K.V. Nagaraja

Salmonellosis in pigs • S. choleraesuis, S. typhisuis, and non-host adapted types • Salmonella choleraesuis var kunzendorf is the most common 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, generalized sepsis • S. typhimurium is also an important cause of disease in pigs


K.V. Nagaraja

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 the carcases of apparently healthly animals at slaughter. • Salmonella in swine - a source for humans


K.V. Nagaraja

Salmonella infection in Horses • In the US the most common types have been S. typhimurium, S. enteritidis, S. newport, and S. 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


K.V. Nagaraja

Salmonella infection in Dogs • Salmonella can be found in the feces of many normal 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


K.V. Nagaraja

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


K.V. Nagaraja

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 diarrhea occurs 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


K.V. Nagaraja

Salmonella in wild animals • Turtles: Rearing turtles for sale in contaminated stagnent water particularly where a heavy sewage contamination exists has led to a high level of Salmonella • In some establishments in the USA, 25-50% of these animals were found to be actively excreting Salmonella • In 1975 the interstate shipment of turtles was banned in US


K.V. Nagaraja

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 to Salmonella 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


K.V. Nagaraja

Salmonella in feed

• Use of improperly cooked animal by-products in animal feed

5 Salmonella

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