Bacteria; we’re good and bad enough for you

The estimated number of bacterial cells in our body are about 10 times the number of human cells. Bacteria are present everywhere including our entire body.

Bacteria; we’re good and bad enough for youSome species of bacteria are harmful, but some are also beneficial, necessary for maintaining our health. The bacteria present on our skin, in airways and the digestive system comprise the first line of defense. They protect us from foreign “invaders” (pathogens) that can cause infections and other disease conditions.

Even though, bacterial species can also harm you if they grow unchecked. Pathogenic bacteria can cause cholera, typhoid, pneumonia, dysentery and spoil our food, causing food borne diseases. In this article, we have summarized some good and bad effects of bacteria with special reference to humans health.


Everybody has a personalized collection of bacteria, called microbiome. We acquire our first bacteria at birth and also from daily environmental exposure. Some of these bacteria can become a permanent part of our body and play an important role in our immune system. Bacteria are of different types.

Probiotics are the live bacteria, good for us and our digestive system. Good bacteria are important for our gut health and some of our food and supplements contain probiotics such as yogurt [1].

Some bacteria make colonies in our body such as respiratory and digestive tract. They help us to keep balance in our immune system. Bacteria are necessary for the proper functioning of our body cells. We cannot proceed with some important functions without the help of bacteria.

For example, bacteria have the ability to breakdown the carbohydrates (sugars and starch) present in our food into simple compounds which are easily digestible. Bacteria are helpful in fatty acid absorption which is important for the growth of cells. 

Bacteria protect the cells in our intestines from foreign invaders and repair the damaged tissue. If beneficial bacteria are present in our body, harmful bacteria cannot get a chance to grow and cause disease [1].


Beneficial bacteria in our gut like gastrointestinal Lactobacillus and Escherichia coli (E. coli) help to digest our food and fight against invading microbes. Humans lack an important enzyme cellulase, so bacteria promote food breakdown in the absence of cellulase thus help us in digestion. We also get important vitamins like biotin and vitamin K from our gut inhabiting bacteria [2].

Bacteria are some of the best decomposers, involved in the breakdown of dead and decaying organic matter within or at the upper side of the soil. Bacteria are major players in the decomposition of organic matter and cycling of chemical elements such as carbon and nitrogen into the soil and in the ocean which are necessary for human life [3].

Bacteria are also being used to clean up oil spills in oceans to keep our environment clean. Plants don’t excrete enough nitrogen required by primary producers in the food chain. Bacteria and cyanobacteria (blue-green algae) also play an indispensable role in turning atmospheric nitrogen into ammonium or nitrates making atmospheric N available to plants.

With this nitrogen, plants produce biomass and biomolecules. We eat the plant parts as fruits, nuts, leaves (leafy vegetables) and roots (tuber vegetables) to get nutrition. Water is a limiting factor at planet Earth and important substance for human life.

Bacteria also play an important role in the cycling of water. Even though, it was found that bacteria could produce clouds to precipitate in the atmosphere and cause snow falling and rains [4].


There are several distinct classes of probiotics (Figure 1), the most common are: Bifidobacterium, Lactobacillus. The manufacturers of probiotics may also call them as “live culture” or “active culture”. Many fermented products include probiotics, which means that they contain beneficial bacteria.

Most often, in the process of food production, live bacteria are destroyed. Examples of milk product containing probiotics include: aged cheeses such as cheddar, gouda, or mozzarella, kefir, a probiotic milk drink, traditional buttermilk and yogurt [4].


Although, bacteria are helpful to us, some species are harmful too, causing many serious problems. Diabetes, cardiovascular diseases, and obesity are caused by different species of bacteria in our body. The disease is caused when the normal microbiome of our body gets disturbed by some factors.

When that happens, the bad bacteria that normally are kept in check have room to grow, creating optimum conditions for disease. Antibiotics kill harmful bacteria and even good bacteria which we need for our health.

Bad bacteria (Figure # 2) can exist in our body at low levels without causing harm, but, when growing in excess, they cause serious problems. Staphylococcus aureus can cause something as simple as a pimple or as serious as pneumonia or toxic shock syndrome.

Similarly, Porphyromonas gingivalis can cause an inflammatory disease which destroys the supporting tissues of the tooth. Another strain of bacteria, Klebsiella pneumonia (a common gut bacteria) can cause colitis which subsequently leads to colorectal cancer [5]. 

In addition to allowing harmful bacteria to flourish, the elimination of good bacteria also weakens our immune system, resulted in simple allergies or very debilitating autoimmune diseases. Without the appropriate balance of bacteria, our body may suffer from constant inflammation.

Inflammation is the body’s alarm system, which calls white blood cells to heal a wound or to get rid of the infection. Chronic inflammation can make the body more susceptible to autoimmune disorders and cancer such as inflammatory bowel disease, if remained untreated, can cause colon cancer  [5]. 


The ultimate effect of bad bacteria on our health is death. The Center for Disease Control and Prevention (CDC) demonstrated that 3,000 people die each year due to foodborne illnesses including deaths caused by bad bacteria. E. coli is a bacterial species, can be good as  well bad, live in our intestines and the food we eat.

Some pathogenic strains of E. coli cause diarrhea, respiratory illness, urinary tract infection, and other illnesses. Similarly, Salmonella sp, Clostridium perfringens, Listeria monocytogenes, and Staphylococcus aureus are associated with the leading cause of illness, hospitalization, and deaths in America.


Historically, pathogenic bacteria have been the root cause of some of the deadliest diseases and widespread epidemics of human civilization. Pathogenic bacteria are disease causing bacteria in animals and humans and impose a serious threat to living organisms. Cholera, typhoid, pneumonia, dysentery, tuberculosis, tetanus, etc., are the most common human diseases.

There are specialized groups of bacteria in humans which can cause devastating diseases [6]. One of the major groups is Staphylococcus, colonizes on our skin and mucous membranes without causing any disease until specific conditions are provided, cause superficial or systemic infections.

Boils, impetigo and folliculitis are some of the superficial infections caused by a specie of this group named as Staphylococcus aureus. Most common and serious infections caused by Staphylococcus are pneumonia, bone and wound infections and food poisoning etc. Another group which can cause serious problems to humans is Streptococcus.

Streptococcus pyogenes, a strain of Streptococcus, can cause strep throat (bacterial pharyngitis) in human. Other infections caused by this strain include impetigo and necrotizing fasciitis. Necrotizing fasciitis is a fatal disease, characterized by rapid destruction of soft tissues and muscles [7].


Food spoilage is the change in appearance, consistency, taste, and smell of food caused by bacteria. Acids and other toxic chemicals are produced during bacterial break down of food. Although the bacteria themselves may or may not be dangerous, they may produce odor, unpleasant taste or even affect one’s health.

There are two kinds of pathogenic bacteria targeting distinct food categories. The first type is known as Clostridium perfingen, targeting foods like meat and poultry while second one is Bacillus cereus, targeting milk and cream.

Some saprophytic bacteria may spoil food items by causing decay of unprotected foods such as fruits, pickles, jams, jellies, bread, etc. In preserving pickles and jams, the use of salt, sugar, and oil controls the development of such bacteria. Clostridium botulinum in canned food generates a very virulent poison which may cause death [8].


Bacteria are present everywhere and help us in digestion and decomposition of food. Although, bacteria are beneficial but, there are certain strains which are damaging for humans if left untreated. So, appropriate cleaning or removal of harmful bacteria is necessary for human’s health.


The study was conducted in absence of any financial grant and there is no conflict of interest declared authors.

Authors: Muhammad Zubair Ghouri1, Samia Hassan1, Ovais Aftab2, Muhammad Amjad2, Aftab Ahmad1

1Center for Advanced Studies in Agriculture and Food Security (CAS-AFS), University of Agriculture, Faisalabad, Pakistan.

2Center for Agricultural Biochemistry and Biotechnology (CABB), University of Agriculture, Faisalabad.