What are pathogenic microorganisms?

What are pathogenic microorganisms?

Every one of us have heard about microorganisms, even if we can’t see them. Did you know that not all microorganisms are related to diseases and that an average adult carries about 2 kilograms of harmless useful necessary bacteria that participate in digestion¹?


Most fungi, bacteria, viruses and protozoa are harmless to human health and also brings benefits through its activity. Microorganisms can be divided in two big groups depending of gender, species, subspecies and serotype: the pathogenic and the non-pathogenic.

Amongst non-pathogenic, there are the harmless and beneficial/useful ones.

Harmless microorganisms are those ones that live around us and participate in many natural processes, but don’t cause us any harm in general, unless it reaches a body/individual with immunodeficiency (by air or oral ingestion, mainly) or else they exist in high concentrations in air or food. Amongst harmless microorganisms, a big part is represented by the spoilage ones.

Spoilage microorganisms form the natural microflora of innocuous (inoffensive) food like meat and dairy products. Microorganisms can grow excessively in this kind of food because of the water and nutrients available. In recently processed and fresh in natura food, they exist in a very low concentration, therefore in these conditions they are nontoxic to healthy humans. Shelf life of food is usually determined by the growth rate of these microorganisms. Inappropriate transport and storage conditions threatens the predicted shelf life of food, developing spoilage bacteria and fungi faster which causes texture and odour modifications such as oversoftening and non-characteristic smells. As an example of microorganisms of this kind, there is Lactobacillus and Pseudomonas in meat².

Beneficial/useful microorganisms are those who live in our intestine and other digestion organs, breaking and modifying molecules and performing our absorption of nutrients. Also, this kind of microorganisms is found in food industry usually playing specific roles in food production and providing special properties to foodstuffs. In this context, there should be a highlight on yeasts, that are basically fungi that transform sugar in alcohol through fermentation processes. These microorganisms, for example Saccharomyces cerevisiae, are used in bread, wine and beer. Amongst the benefits obtained from some microorganisms, there is also penicillin, substance produced by fungus Penicillum that radically changed pharmacology and human health with its antibacterial activity: diseases like syphilis and pneumonia could not be properly and easily treated before this discovery.  

Pathogenic microorganisms are the ones who causes us real trouble.

Pathogenic microorganisms are very different from those that inhabit our daily lives: they are able to make animals sick if there are conditions for its surviving and developing. They produce toxic substances and can be transmitted by air of ingestion of contaminated food, that must be correctly processed and handled in general (avoiding cross contamination, which spreads pathogens from a contaminated place to an innocuous place). The seriousness of infections and intoxications transmitted by contaminated food (called foodborn diseases) depends on the incubation time and the microorganism type, but the most important is the nutritional state of the individual, his/her immunological system strength and the amount of contaminated food ingested³. Not only humans can be affected; we know that all living things are exposed to microorganisms infections caused by exposure to pathogenic agents.

Microorganism-caused diseases in cattle and chicken, for example, minimize their hunger and well-being, causing premature death and making its meat unavailable for consumption. Amongst species and subspecies of a famous agent called Salmonella spp., there are some that can lead to mortal diseases in chicken, for example Salmonella enterica – serotypes Gallinarum and Pullorum – and in humans (more than 2500 other serotypes, most of them pathogenic), causing different symptoms and detected by completely different microbiological techniques in farms and labs. There is also Escherichia coli, that exists in a lot of natural places on Earth: most part of its serotypes are naturally present in mammals’ intestines. However, some strains of E. coli are strongly pathogenic and can cause hemorrhage and even death.

Plants are also likely to be attacked by specific pathogens. About 70% of main infections in plants are caused by fungi, such as Botrytis cinerea that strikes strawberries, grapes and flowers in general, leading to contamination of whole fields and economic losses as well. Most pathogens in plants develop themselves inside the plants where they are, or even in soil or decomposition of plants4.

Since antiquity, people study to characterize and differentiate pathogenic and non-pathogenic bacteria, mainly in aspects as resistance and interaction between them. In the food industry, research is made in order to enhance efficiency of heat treatments like pasteurization and also to develop new processes that kill pathogenic and spoilage microorganisms. There is also research on probiotics (beneficial microorganisms) to improve digestion, providing better health and life quality. There is a constant need of upgrading diagnoses of diseases caused by pathogens, especially during food production to make it safe and also in hospitals and laboratories in identify harmful agents.

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[1] Henrique Lins de Barros, Biodiversidade em questão, Rio de Janeiro: Claro Enigma/Fiocruz, 2011.

[2] ALCANTARA, Marcela de; MORAIS, Isabela Cristina Lobo de; SOUZA, Cyllene de M. O. da C. C. de. Principal Microorganisms involved in the decay of sensory characteristics of meat products. Revista Brasileira de Higiene e Sanidade Animal, [s.l.], v. 6, n. 1, p.1-20, 2012. GN1 Genesis Network. http://dx.doi.org/10.5935/1981-2965.20120001.

[3] Portal Educação. Microrganismos Patogênicos e Não-Patogênicos. Disponível em <https://www.portaleducacao.com.br/conteudo/artigos/educacao/micro-organismos-patogenicos-e-nao-patogenicos/29171> 2013.

[4] Tomaz, I. L. Doenças das Plantas – Diagnóstico das Micoses e Taxonomia dos seus Agentes. Colecção Euroagro, Publicações Europa-América, Portugal. 2002.

This article was written by Geórgia Aimée Bruel Müller