project nazir naidkhai new
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Salmonella has been long recognsized as an important pathogen of
human, animals and poultry. The organism has its global distribution and
usually causes enteric disease in human and animals through ingestion of
contaminated food/feed mostly of origin (Sharma and Singh, 1997). Non-
typhoidal salmonellosis is an important food borne infection with an estimated
incidence of 1.3 billion cases and 3 million deaths all over the world (Thong et
Enteric Salmonella infection is a global problem both in human beings
and animals. Newborn and young animals commonly suffer from enteric
infection within 15 days of their birth (Kaura et al., 2001). Enteric disorders
that occur at organized animal farms in this country account for 10 to 30% of
annual mortaility and thus are responsible for great economic losses. In human,
diarrhoeal syndrome caused by non-typhoidal salmonella is common in tropical
and developing countries. Available data on food poisoning indicate that
poultry meat is frequently involved in cases of human salmonellosis (Galbraith,
Although, many of routine epidemiological features viz. host specificity,
sources of infection, the forms of disease manifestation and carrier status of the
organisms have been documented (Wray and Sojka, 1997; Thapliyal, 1979).
Some new epidemiological parameters are being studied in recent years to
elucidate the disease process of salmonellosis. Among these, antimicrogram
studies and plasmid profile are of major importance. On study of
epidemiological feature of salmoellosis, plasmids have been reported to play an
important role in virulence and antibiotic resistance of Salmonella (Aarestrup
et al., 1997).
Bacteria are among the chief causal agents of acute diarrhoea and the
majority of the bacterial enteropothogens appear to cause fluid lose by
stimulation enterocytes to actively secrete electrolytes (Rao and Field, 1985).
Elaboration of one or more enterotoxins is recognized as an important
pathological attribute of some non-invasive diarrhoea including bacteria in
elucidating of their enteropoathogenic activity (Rao and Field, 1985; Harne et
al., 1994). Various Salmonella serotypes have been shown to produce
enterotoxins (Baloda et al., 1983; Rahman et al 1991a). The enterotoxic moiety
from salmonella serotypes has been purified and characterized by several
workers (Finkalstein et al., 1987; Rahman et al., 1994). Salmonella
pathogenesis is a complex and multifactorial phenomenon. Salmonella species
interact with ileal mucosa and disrupt normal intestinal functions, which result
in acute inflammatory cell influx, fluid secretion and enteritis (Wood et al.,
1998). Many genes are required for full virulence but only a few of these have
been shown to be necessary for the induction of enteritis (Wallis and Galyov,
2000). Like many other gram-negative pathogenic bacteria, Salmonella
possesses a dedicated protein secretion system denoted as Type III Secretion
System (TTSS), which plays a central role in virulence (Huech, 1998).
Salmonella serovars have been reported to produce several Type III secretions
including SIP (Salmonella Invasion Protein) and Sop (Salmonella outer
protein). Of the different Sop proteins, Sop B is associated with enteritis and
diarrhoea. The gene encoding production of Salmonella outer protein (Sop B)
is located on Salmonella specific DNA fragment representing a pathogenicity
island, SPI 5 (Wood et al., 1998) and is found to be widely distributed among
Salmonella (Rahman et al., 2001).
Another important type III secretion is Sop E, which is associated with
invasion by stimulating membrane ruffling (Hard et al., 1998). Unlike Sop B
gene, the Sop E is not widely distributed among Salmonellae and diarrhoea and
as the cases of this kind is frequently observed in livestock and poultry as well
as in human.
Apart from these outer proteins an important pathogenicity is exhibited
by Salmonella species i.e. Salmonella enterotoxin. Although most of the
Salmonella serovars were shown to produce enterotoxins, enterotoxigenicity of
Salmonella has been found difficult to detect by different assays since
Salmonella produce very level of enterotoxin when cultured by conventional
methods (Baloda et al., 1983). Moreover, a major portion of Stn is retained as
cell-bound content, which is not released in the extrcellular milieu (Kaura and
Sharma, 1988). These are some Salmonella strains, which produce enterotoxin
but do not release extracellularly and thus may escape different tests and
detected to be non-enterotoxigenic if only entracellular occurrence of Stn is
tested (Rahman et al., 1991a).
Production of the enterotoxin (Stn) has been found to be mediated by the
presence of Stn gene and it has been cloned and sequenced (Chary et al., 1993;
Chopra et al., 1994). More recently, the Polymerase Chain Reaction (PCR) has
been used for the detection of Stn gene (Prager et al., 1995; Rahman, 1999). Its
detection by the PCR in field isolates of various Salmonella can indicate the
protential of Stn production. Use of the standard PCR technique to study the
presence of Stn gene among the field isolates can an important tool in the
molecular characterization of field Salmonella isolates.
The epidemiology and pathogenic process in salmonellosis is dictated
by an array of factors that act in tandem and ultimately manifest into the typical
symptoms of salmonellosis. In recent years, a number of virulence-associated
fimbriae including Salmonella Enteritidis Fimbriae designated as SEF and
Plasmid Encoded fimbriae designated as PEF have been identified and cloned
(Clouthier et al., 1994). However, information on the occurrence of these
fimbriae among the field isolates is still meagre (Rahman et al., 2000a). Both
the above types of fimbriae are genetically encoded and its characterization can
help in understanding the role of these genes in expression of these virulence
AIM AND OBJECTIVES
The aim of the project was undertaken with the following objectives
with given 50 samples:
I. To study the Antimicrogram patterning of the given isolates.
II. To study some of the molecular characteristics of the given
isolates such as
III. Detection of Sop B gene.
IV. Detection of fimbrial genes (Sef and Pef).
V. Detection of salmonella enterotoxin gene (Stn)
VI. Detection of Sop E protein by Dot-ELISA.
VII. Study on plasmid profiles.
REVIEW OF LITERATURE
The importance of bacteria of the genus Salmonella as potential
pathogens of human and animals needs no emphasis. Salmonella are widely
distributed in nature. Currently, there are more than 2400 Salmonella serotypes
prevalent in the world. A few of them are highly host specific, while majority
of them are unadapted and can cause infection in a wide variety of animals
species (Gupta and Verma, 1993). They are the chief cause of diarrhoeal
disease all over the world (Gianella, 1980). Newborn and young animals
commonly suffer from enteric infections within 15 days of their birth (Kaura et
al., 2001). Enteric disorders that occur at organized animal farms account for
10 to 30% of annual mortality in our country and are thus responsible for great
economic loss Kaura et al., (2001).
The genus name Salmonella has been adopted in the honor of Salmon,
who isolated the hog cholera bacillus considered to be the causal agent of
swine plague (Salmon and smith, 1885) but subsequently the organism was
found to be only a secondary invader and named as Salmonella Choleraesuis.
The typhoid bacillus was first seen by Eberth (1880) in the spleen and
mesenteric gland of patient that died of typhoid and the organism was isolated
by Gaffkey (1884) and Schotmuller (1901) differentiated Salmonella
Paratyphi A and Salmonella Paratyphi B.
The genus Salmonella of the Enterobacteriaceae family consists of
Gram-negative bacilli, fermentative, aerobic or facultative anaerobic bacteria
that are generally motile with peritichous flagella except Salmonella pullorum
and Salmonella gallinarum. The organisms of the genus are non-lactose
fermenters, oxidase negative, urease negative acetyl carbinol negative,
potassium cyanide negative but citrate positive (Sleigh and Duguid, 1989).
Nomenclature of Salmonella species
Nomenclature and classification of Salmonella are ever changing. In
recent years, the Kauffman- white Antigenic scheme as proposed by Ewing
(1986) has been modified and updated and this updated version is being
accepted by majority of the laboratories worldwide.The members of of the
genus Salmonella have been grouped in two species, viz. Salmonella bongori
containing 18 serovars and Salmonella enterica consisting of more than 2400