Isolation and characterisation of salmonella from frozen food sold in Uyo metropolis


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1.1 Background of the Study

Salmonella remains significantly high as food borne pathogens compared to others and has not being declined for over a decade. Salmonella poses as a leading cause of foodborne diseases in few countries, sometimes contributing to the highest morbidity and mortality rates among foodborne pathogens (CDC, 2009). Most of the Salmonella spp. associated to humans and other mammals’ diseases are from S.enterica subsp. enterica with S.Enteritidis and S. Typhimurium were responsible for most of the infections (Dunkley et al., 2009). Other Salmonella serovars are zoonotic or potentially zoonotic, while some usually found in the environment such as Salmonella bongori, Salmonella enterica subsp. salamae, Salmonellaenterica subsp. arizonae, Salmonella enterica subsp. diarizonae, Salmonella enterica subsp.houtenae and Salmonella entericasubsp. indicaare occasionally associated with human disease (WHO, 2003; Matheson et al., 2010; Das et al., 2012).

Various food products have been depicted as transporting agent against infection by Salmonella to humans, including beef, poultry, pork, eggs and seafood. Salmonella is also persistent pathogen that capable of surviving and proliferating in a variety of environmental conditions including food production and processing plant (Mezalet al., 2013). According to El-Aziz (2013), Salmonella contamination in beef and chicken can occur at several stages along food supply chain includes productions, processing, distribution, retailing and also preparing and handling by consumers. The persistence of Salmonella in premises may include resistance of the specific strains to the disinfection, desiccation and also biofilm production (Vestbyet al., 2009).

Foodborne illness worldwide is often related with the consumption of meat and poultry products contaminated with pathogenic microorganism mainly from retail level (Vindigniet al., 2007). The microbiology quality of chicken and beef sold may differ based on type of retail outlets depends on the hygiene management, management of the meat supplied from receiving until selling include temperature controls, storage, packing and handling at the point of sale which sometimes involve cutting and mincing. Uncontrolled conditions at the retail level might contribute to the multiplication of the microorganism includes pathogenies especially Salmonella spp. where could enhance the risk of contamination at consumer level.

Commonly chicken meat is popular poultry species in the world and considered as the main protein source in Nigerian diet. It is also served as major option of meat offered in most of food service outlets.  Due to its popularity, Jayaraman et al. (2013) had reported per capita consumption of chicken meat and chicken based products by Nigerian were increased 0.03 million tonnes from 1.4 million tonnes at year 2013 to year 2014. Approximately, 500 million chickens produced by 3,200 broiler grower farms in Peninsular Nigeria which 30% of it went to modern processing plant and sold in supermarket. Remaining sold as live chickens for wet markets (Jayaramanet al. 2013; Fadhilah, 2015). To ensure enough supplies, Nigeria also imported chicken most from China then followed by Thailand, Denmark, and the Netherlands (, 2014).

Beside chicken meat, production of beef and beefbased products in Uyo metropolis also increased annually 1.6 million tons reported in 2010 and projected to achieve 2.1 million tons in 2020. Beef products also had increased by around 78% from 29,000 million tons in year 2005 to year 2014. Demand for beef is increasing every year in line with the increase of population and consumption per capita (Fadhilah, 2015).

In Nigeria, both meats are most commonly served in food outlets especially in hotel, restaurants, school canteen and even small outlets which involved various types of preparations. It also being a favourite main dish served during festive and occasions.  Thus, these meats are very easily available and sold in all types of retail outlets in Nigeria. The most popular retail outlet visited by Nigerian to get this type of meat supplies are supermarket, butcher shop and wet market which are selected based on their nearest location, cheaper price offered, an adequate supplies and in certain circumstances freshness of the meat and hygiene being a priority criteria. With regards to consumer safety towards the risk of chicken and beef being contaminated with pathogens at the retail level, we conducted this study to determine the prevalence of Salmonella spp. in the main chicken and beef sales outlet.

Illnesses from food are one of the most important economic and health problems among industrial and non-industrial countries. In recent years, Salmonella has been one of the most common causes of food born disease Salmonellosis is an infectious disease which often occurs through contaminated food, especially food products with an animal origin such as meat, chicken, egg, animal foods and sometimes vegetables in the food chain. In developing countries, estimation of Salmonelosis is difficult because there has not been sufficient surveillance. Therefore, globally, many studies have been performed reporting that the prevalence and kind of salmonella serotypes are different based on geographical regions. Salmonella entericaserovarsEnteritidis and Typhimurium were reported to be the two most frequent serotypes of Salmonella isolated in Iran and other countries. During the two past decades, the emergence of antibiotic-resistant Salmonella has become a serious problem worldwide. Wide usage of antibiotics in the diet of domestic animals has made drug resistant bacteria which could be transfered to human beings. Also, in recent years, problem of resistant strains to multiple drugs (MDR) is increasing and most studies in Iran and other countries have shown high resistance of Salmonella strains to several antibiotics It belongs to the family Emtero-bacteriaceae and it is a facultative anaerobic gram-negative bacillus that parasitizes the intestine of a large number of vertebrate species. It also infects man leading to enteric fever, gastroenteritis and septicemia, collectively known as Salmonellosis infection.

Of all the enterobacteriaceae, the genus salmonella is the most complex with more than 2,000 closely related bacteria that causes illness by reproducing in the digestive tract. (Aora, 2004). Each salmonella subgroup or serotype share common antigen and has its own name and the antigenic complexity of the bacteria have been described by Kauffman-White scheme. According to this scheme, the terminology that identifies the particular protein coats, or serovars, is not well settled, and what previously were thought to be various species of the genus Salmonella are now thought to be serovars of only two species by many researchers, Salmonella enterica and Samonellabongori.

However, these designations are not always accepted in the scientific literature and so common serovars that have been named in the past are still used (for example, S. typhi, S. typhimurium, S. enteritidis, S. cholerasuis, S. saintpaul ). The Serovars are identified by the Kauffman-White classification that uses two major types of antigens (Somatic O and flagella H) to distinguish the over 2, 500 types of samonella bacteria. Initially each Salmonella species was named according to clinical consideration, e.g. Salmonella typhi-murium (mouse typhoid fever), S. cholerae-suis (hog cholera). After it was recognized that host specificity did not exist for many species, new strains (or serovar, short for serological variants) received species name according to the location at which the new strain was first isolated.

Serovar Typhimurium has considerable diversity and may be very old. The majority of the isolates belong to a single clonal complex. Isolates are divided into phage types, but some phage types do not have a single origin as determined using mutational changes. Phage type DT104 is heterogeneous and represented in multiple sequence types, with its multidrug-resistant variant being the most successful and causing epidemics in many parts of the world. Serovartyphi is relatively young compared to Typhimurium, and probably originated approximately 30,000-50,000 year ago. The common salmonella serotypes that are important in Animals and mammals include;

*     Salmonella enterica subspecies arizonae – is found in cold-blooded animals, poultry, mammals.

*     Serovars of Salmonella enterica subspecies enterica.

*     Salmonella choleraesuis (Bacillus paratyphoid B and C). This is an intestinal commensalists in pigs; it becomes pathogenic if resistance is weak; humans can be infected by ingesting sick animals; the bacteria cause septicemic salmonellosis in swine.

*     Salmonella enteritidis – It is found in the intestines of cattle, rodents, ducks and humans; it causes calf paratyphoid fever and acute gastroenteritis in humans.

*     Salmonella paratyphi B, in central Europe usually human pathogen, causes paratyphoid fever.

*     Salmonella typhi, occurs in temperate and subtropical zones. It is the human pathogen of typhoid fever; 3-5% of persons falling ill remain permanent carriers of the pathogen.

*     Salmonella typhimurium, causes a wide range of infections in birds to severe systemic paratyphoid diseases. It causes salmonella enteritis (food poisoning) in humans.

*     Salmonella dublin, one of the pathogens causing cattle salmonellosis.

*     Salmonella typhisuis, one of the pathogen causing hog Salmonellosis.

*     Salmonella brandenburg, causes abortion and enteritis in shepherd cattle.

*     Salmonella anatum and Salmonella montevideo.

Animals consume Salmonella from the soil or contaminated processed food e.g. feeds. The bacteria are then shed alive in the infected animals’ faeces.

Humans on the other hand consume Salmonella through contact with Unclean food, particularly in institutional kitchens and restaurants

Excretions from either sick or infected but apparently clinically healthy people and animals (especially endangered are caregivers and animals)

Polluted surface Food and standing Food (such as in shower hoses or unused Food dispensers)

Unhygienically thawed fowl (the melt Food contains many bacteria).

An association with reptiles (Pet tortoises and snakes) primarily aquatic turtles is well described.

Salmonella bacteria can survive several weeks in a dry environment and several months in Food; thus, they are frequently found in polluted Food, contamination from the excrement of carrier animals being particularly important. Aquatic vertebrates, notably birds and reptiles, are important vectors of salmonella. Poultry, cattle, and sheep are frequently agents of contamination. Salmonella can be found in food, particularly meats and raw eggs.

Salmonella infections other than typhoid fever are termed enteric fever, salmonella food poisoning and gastroenteritis. These diseases are usually less severe than typhoid fever and are scribed to one of the many serotypes of Salmonella enteritidis. Most outbreaks of epidemics and food poisoning in humans and animals are caused by salmonella enteritidis and Salmonella typhimurium, others are Salmonella Dublin, Salmonella Thompson. Non-typhodial salmonellosis are more prevalent than typhoid fever and currently holding steady at 40,000 to 50,000 case a year. All strains are zoonotic in origin though human may be some carriers under certain circumstances by contrast. The type of salmonella that affect humans usually cause disease which can be recognized by diarrhea, vomiting.

Diarrohoeal disease seems to be one of the major health hazards both for human and animals. Many salmonella grow in the gut of their host and once in the gut, salmonella wave-long filament called flagella moves about until they touch a suitable cell. The bacteria stick to the cell and are “swallowed” smaller “hairs” called fimbriae are important in stimulating immunity in the host.

1.2 Aims and Objective of This Study

The main aim and objective of this study is to investigate the Isolation and characterisation of salmonella from frozen food sold in Uyo metropolis. The specific objective are:

  1. To isolate salmonella species from Frozen Foods in Uyo metropolis.
  2. To identify the isolated species.
  3. To identify the market location from where salmonella were isolated.
  4. To determine the locations (or market) with the high isolation numbers.

1.3 Definition of Terms

Frozen Food: food that has been subjected to rapid freezing and is kept frozen until used. Freezing food preserves it from the time it is prepared to the time it is eaten. Since early times, farmers, fishermen, and trappers have preserved grains and produce in unheated buildings during the winter season.

Salmonella: Salmonella is a genus of rod-shaped Gram-negative bacteria of the family Enterobacteriaceae. The two species of Salmonella are Salmonella entericaand Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes.

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