Review of Microbiology Concepts

Ensuring microbiological safety of the food products is one of the state healthcare system’s priority tasks, the solution of which is directly aimed at protecting public health. Abebe et al. (2020) claim that “Salmonella species, L. monocytogenes, and E. coli are the major zoonotic bacterial pathogens which are the causative agents of food-borne illness and death in the world” (p. 1). All over the world, this problem is gaining special relevance due to an increase in the number of foodborne diseases. Podolak and Black (20170 state that “bacterial contamination of low-moisture foods, such as peanut butter, present a vexing challenge to food safety” (p. 1). The need for a comprehensive study of this problem is obvious and includes a multifaceted assessment of factors affecting human health, such as age, present diseases, comorbidity, pregnancy, specific medical conditions and many others.

Escherichia Coli

Escherichia coli is a common inhabitant of the intestines of many mammals, in particular primates, including humans, thus, it is often called colibacillus. In the human body, Escherichia coli plays a beneficial role by inhibiting the growth of harmful bacteria and synthesizing certain vitamins. However, there are varieties of Escherichia coli that can cause acute intestinal diseases in humans. Currently, more than 150 types of pathogenic E. coli bacilli are isolated as a health hazard.

Salmonella Enteriditis and Salmonella Typhi

Salmonella enterica belongs to the class of gamma-proteobacteria within the Salmonella genus. This Enterobacteriaceae family is considered one of the most hazardous to human health due to the fact that every type of bacterium of this species is pathogenic. Abebe et al. (2020) supply that “non-typhoidal Salmonella are most important zoonotic bacterial food-borne pathogens of humans, and they account around 93.8 million food-borne illnesses and 155,000 deaths per year worldwide” (p. 5). Many serotypes of Salmonella enterica are causative agents of human diseases such as typhoid fever, paratyphoid fever, and salmonellosis. In epidemiological terms, however, only a few subspecies of Salmonella enterica are significant for humans, with the most hazardous being Salmonella enteriditis and Salmonella typhi.

Listeria Monocytogenes

Another hazardous bacteria species that can infiltrate food products is Listeria monocytogenes. Listeria are small gram-positive bacilli with a characteristically low motility. They are distributed throughout the world in both the environment and the intestines of humans, mammals, birds, arachnids and crustaceans. There are several species of Listeria, but only Listeria monocytogenes is the main pathogen in humans. Once in the human body, Listeria parasitizes inside body cells, where it can cause irreparable harm to the central nervous system or the brain specifically.

Methods: a Comparative Table of Pathogenic Bacteria

Types of BacteriumEscherichia coliSalmonella enteriditisSalmonella typhiListeria monocytogenes
ClassificationThe genus of Escherichia is part of the Enterobacteria family, the order of Enterobacteria, the class of Gamma-proteobacteria, the type of Proteobacteria, the kingdom of Bacteria.The subspecies Salmonella enteriditis and Salmonella typhi both belong to the species Salmonella enterica in the genus Salmonella, the family of Enterobacteria, the order of Enterobacteria, the class of Gamma-proteobacteria, the type of Proteobacteria, the kingdom of Bacteria.According to the modern classification, Listeria belong to the Firmicutes type, the Bacilli class, and the genus Listeria, which includes several species. However, Listeria monocytogenes holds the greatest importance in human pathology among other Listeria subspecies.  
SizeThe cells of Escherichia coli bacteria are rod-shaped, about 2 μm long and 0.25–1.0 μm in diameter. Its cell volume is about 0.6–0.7 μm3.All Salmonella bacteria are quick-moving, gram-negative rods. They are from 1 to 7 μm in length, and 0,3-0,7 μm in width.  Listeria monocytogenes are small gram-positive rods of regular shape. They are 0.5-2×0.4-0.5 microns in size, and are pleomorphic.  
HabitatEscherichia coli is a common inhabitant of mammals’ intestines, specifically, humans. Additionally, the bacterium can be found in soil and water bodies.Salmonella enteriditis is a ubiquitous and resistant bacterium that can survive for several weeks in dry environments, and for several months in water. Podolak and Black (2017) add that “Salmonella, due to its enhanced thermal resistance in dry environments, can survive the drying process and may persist for prolonged periods in low-moisture foods” (p. 1).Salmonella typhi is a short, motile, bacterial, facultative intracellular parasite that grows well in the presence of oxygen, although it can also exist in its absence. Abebe et al. (2020) add that “primary habitat of Salmonella species is the intestinal tract of the animals such as farm animals, humans, birds, reptiles, and insects” (p. 5).Listeria are widespread in the surrounding nature – soil, water, plants, as well as in sewage and excrement of humans and animals. Listeria live in a fairly wide temperature range and are capable of active reproduction at low temperatures.
Diseases CausedIntestinal diseases caused by pathogenic E. coli are collectively called Escherichiosis. According to Koutsoumanis et al. (2020), “the detection of any of Shiga toxin-producing E. coli serogroups in food has been considered to provide an early indication of the potential for serious illness, if there are no further treatment of E. coli” (p. 20). The terms coli-infection, coli-enteritis, travelers’ diarrhea, colibacillosis can be also used. Escherichiosis refers to acute intestinal diseases with a fecal-oral transmission mechanism. Each of the above classes of pathogenic E. coli is characterized by certain differences in the course of the disease, which in its symptoms may resemble cholera or dysentery.Salmonellosis is an acute infectious disease, caused by the non-typhoid Salmonella bacteria such as Salmonella enteriditis. According to Abebe et al. (2020), “the disease is of self-limiting nature and does not require specific treatments but can result in serious complication in young children, old, and immunocompromised individuals” (p. 6). More often the disease occurs in the form of acute gastritis, gastroenteritis or gastroenterocolitis, less often in the form of septicopyemia; however, a long-term illness is also possible.  One of the most dangerous diseases caused by Salmonella bacteria is the typhoid fever, which occurs through a contamination of the organism with Salmonella typhi. Typhoid fever affects only humans. The disease manifests through fever, symptoms of general intoxication, bacteremia, ulcerative lesions of the small intestine’s lymphatic apparatus, and the hepatolienal syndrome.  Listeriosis, which is caused specifically by Listeria monocytogenes, is a highly contagious infectious disease. It damages the protective cells of the immune system, leading to the development of numerous symptoms such as a septic angina, as well as the pathology of the nervous system. Mostly, listeriosis found in wild and farm animals.
Hazard Level to Human HealthThe infectious dose is highly dependent on the type of pathogenic E. coli. Koutsoumanis et al. (2020) state that “Most cases are self-limiting although severe life-threatening complications may occur, especially in developing countries where the host may be malnourished, immune-compromised and without access to adequate treatment” (p. 60). Young children, the elderly and people with immunodeficiency are most susceptible to the disease.The number of cases of salmonellosis, including in developed countries, has been increasing in recent years. Nosocomial salmonellosis is one of the major problems of modern healthcare.Patients with immunodeficiency or those with low acidity of gastric juice have a higher risk of Salmonella-associated typhoid infection, and the disease is more likely to be severe. Moreover, Salmonella typhi is highly resistant to various antibiotics.The greatest danger the listeriosis poses is the possibility of fetus pathology in pregnant women. Moreover, the elderly people also fall into the high-risk category, since they often have the most severe forms of the disease such as septic and meningoencephalitic ones. In addition, people of all ages with impaired immunity get infected with Listeria monocytogenes easily. Abebe et al. (2020) state that “Listeria is one of the most virulent pathogens, which is associated with the highest case fatality rate of 30%” (p. 9).


This exercise was quite helpful in terms of learning about the various hazards the bacterial food contamination poses. It is important to know the aspects and hazards pathogenic bacteria present to different parts of society, and recognize the potential risks of food contamination. Another point of interest is the possibility to do a thorough research of the topic to determine current trends in microbiology and food hygiene. Overall, it was an interesting and an insightful task to complete.


The phenomenon of foodborne infections and toxic infections should be considered from the general point of view of the epidemiological ecology of bacteria. The researchers need to study primarily the aspects of the existence of bacterial populations in the environment which determine the possibility of the occurrence of infectious diseases in humans. At the same time, food production processes must adapt in stride with the these studies to ensure the safety of the human health regarding the possibilities of bacterial contamination. The best way to prevent bacterial food diseases on the national level is to study closely the agents that cause them. Moreover, it is of highest importance to learn how exactly pathogenic bacteria affect the human organism – not only the healthy one, but impaired as well. Overall, this kind of study is highly recommended for any healthcare worker or student.


Abebe, E., Gugsa, G., & Ahmed, M. (2020). Review on major food-borne zoonotic bacterial pathogens. Journal of Tropical Medicine, 2020, 1–19.

EFSA BIOHAZ Panel, Koutsoumanis, K., Allende, A., Alvarez‐Ordóñez, A., Bover‐Cid, S., Chemaly, M., Davies, R., De Cesare, A., Herman, L., Hilbert, F., Lindqvist, R., Nauta, M., Peixe, L., Ru, G., Simmons, M., Skandamis, P., Suffredini, E., Jenkins, C., Monteiro Pires, S., … Bolton, D. (2020). Pathogenicity assessment of Shiga toxin‐producing Escherichia coli (STEC) and the public health risk posed by contamination of food with STEC. EFSA Journal, 18(1), e05967.

Podolak, R., & Black, D. G. (2017). Control of salmonella and other bacterial pathogens in low-moisture foods. John Wiley & Sons Ltd.