الفهرس 
biochemical tests for identification of Salmonella isolates.Only 14 pages are availabe for public view
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Abstract
1. Bacterial definition, structure, environments and shapes:
In the 1600s, Leeuwenhoek discovered that bacteria are single-celled, tiny organisms that can survive in a range of environments, as these organisms can be found in the air, in foods, and on the surfaces of objects that you touch. They can be found underground and in the depths of the ocean (Rogers et al., 2020). Bacteria can be found on your skin as well as inside your body. Bacteria can survive in both extremely hot and extremely cold settings. Only a few other organisms are capable of surviving in these conditions.
Bacteria, which are microscopic in size (Gupta and Gupta, 2021), (less than 1 pm to many pm in length) (Murray, 1984) and lack a definite nucleus, can be found even in the human intestine. They belong to the Prokaryote kingdom and DNA floats freely in a twisted, thread-like mass called the nucleoid or in separate, circular segments called plasmids in prokaryotes, which are single-celled creatures without a nucleus. Ribosomes are spherical components in bacterial cells that use information encoded in ribosomal RNA to build proteins from individual amino acids (Figure 1).
Bacteria come in three forms: spheres, rods, and spirals(Gupta and Gupta, 2021). Cocci are bacteria that have a sphere-like form. Bacilli are bacteria that have a rod-like form. Spirilla are bacteria with a spiral shape. Bacteria are single-celled creatures that live in groups or chains.
2. Basics of the bacterial classification :
Based on cell wall natures, there are four divisions within the prokaryotic kingdom (Murray, 1984):
Division I Gracilicutes have Gram-negative type cell wall (contains Gram-negative bacteria), Division II Firmicutes have Gram-positive type cell wall (contains Gram-positive bacteria), Division III Tenericutes have no cell wall (contains Mollicutes class), and Division IV Mendosicutes Prokaryotes have unusual walls, membrane lipids, ribosomes, and RNA sequences (contains class Archaeobacteria). In addition to the shape of their cell walls, bacteria can also be categorised according to differences in their genetic structure and organism morphology.
The Gram stain (Kohlerschmidt et al., 2021) is a test for identifying bacteria based on the structure of their cell walls. It was invented in 1884 by Hans christian Gram. The test stains gram-positive bacteria, or germs that lack an outer membrane. Gram-negative bacteria are resistant to the dye (Beveridge, 2002). For example, pneumonia is caused by gram-positive bacteria like Streptococcus pneumoniae (S. pneumoniae), while cholera is caused by gram-negative bacteria like Escherichia coli (E. coli) and Vibrio cholerae.
3. Microbial Interactions in the Food Ecosystem:
Most bacteria are free-living and do not create specialised relationships with one another. Microorganisms are, however, part of a complex ecosystem in which they maintain a constant relationship with their surroundings. With the exception of highly processed foods, most foods include a diverse range of microorganisms, including a wide range of bacteria, yeasts, and filamentous fungi, as well as several strains within each species (Fleet, 1999).
Viruses, bacteriophages, and yeast killers are also found in the microflora. Interactions between those strains and species occur naturally in a persistent bid for survival, growth, and eventual dominance—the outcome of which defines the population numbers of any particular microorganism at any given point during the manufacturing and retailing periods (Fleet, 1999).
Stress reactions triggered in response to changing physical and chemical conditions of the surrounding medium, the ability to colonise the food matrix (and grow into spatial heterogeneity), and in situ cell-to-cell ecological interactions are all factors that influence microorganism survival, growth, and biochemical activity in food (which often take place within a solid phase).
Ecological approaches to the evolution of microbial flora (Fleet, 1999) would be useful in the food industry to better understand the microbiological events involved in food processing, to improve microbiological safety by monitoring past and present viability of pathogenic bacteria, and to assess the effective composition of the microbial populations in question (Figure 2). These ecological principles are at the core of modern quality assurance, predictive modelling, and risk analysis methodologies aimed at preventing foodborne disease outbreaks.They also serve as the basis for using microorganisms in the manufacturing of fermented foods and drinks, as well as their usage as probiotics, starters, and biocontrol agents (Giraffa, 2004).