19 + Facultative Bacteria Examples: Detailed Explanations and Images


In this article, we will explore different facultative bacteria and their images.

An array of facultative bacteria has been extensively used in various industrial processes and also plays a prominent role in sustaining ecology. Apart from that their versatility allows them to survive in injured tissues having inadequate blood supply.  

Facultative bacteria examples:

Facultative aerobic bacteria examples:

Escherichia coli

E. coli is a gram-negative, facultative, rod-shaped (1.1–1.5 μm wide by 2–6 μm long), aerobic bacterium. It has a reputation for causing food contamination in warm-blooded organisms as it commonly resides in the small intestine of endotherms contributing substantially to the gut microbiome. Due to the availability of genome sequences of numerous E. coli strains, it is largely used for molecular cloning and is interestingly familiar as a ‘molecular biologist toolbox’ amongst researchers.

facultative bacteria examples
Scanning electron micrograph of Escherichia coli from Wikimedia

Its rapid growth and easy scale-up process make it a good choice for an expression host in the biotechnology industry, where it is used for the large-scale production of recombinant proteins for therapeutics.

Klebsiella pneumoniae

K. pneumoniae is an encapsulated, gram-negative, rod-shaped (0.5 μm wide by 2 μm long), facultative aerobic bacterium.

Klebsiella pneumoniae Bacterium from Wikimedia

This non-motile bacterium is strongly associated with pneumonia due to its inhabitancy in the human mucosal surfaces. In an oxygen-deprived environment, this naturally occurring bacterium has the ability to fix nitrogen.

Proteus mirabilis

P. mirabilis is a rod-shaped (2 μm long), facultative aerobic, gram-negative bacterium. It is well known for its swarming ability across solid or semi-solid surfaces with the help of flagella.

Colonies of Proteus mirabilis from Picryl

Also, the bacterium is known to produce high levels of urease leading to the alkalinity of urine which is a common cause of kidney failure. Interestingly, P. mirabilis is not reported to have detrimental effects on poultry animals.

Listeria monocytogenes

L. monocytogenes is popularly known as listeriosis causing pathogenic, facultative anaerobic bacterium. It successfully passes through three major barriers in the host viz; the intestines, the blood-brain barrier, and the feto-placenta barrier thereby causing infections in high-risk individuals. Ongoing studies have used this bacterium as a vector in gene delivery therapies.

Staphylococcus epidermidis

S. epidermidis is a spherical-shaped (0.5 – 1.5 µm in diameter), facultative anaerobic, gram-positive bacterium. It is a part of human skin flora and is thought to provide benefits to the human host by out-competing more virulent pathogens.

Staphylococcus epidermidis Bacteria from Wikimedia

However, its opportunistic nature in patients receiving medical devices causes orthopedic device-related infections which lead to the tag ‘accidental pathogen’.

  Streptococcus agalactiae

S. agalactiae is a gram-positive, ovoid (0.5-1.0 X 1.0-2.0 µm), facultative anaerobic bacterium. It is a virulent organism that causes serious health issues such as; pneumonia and meningitis in new-born.

Streptococcus agalactiae from Wikimedia

Streptococcus pneumonia

S. pneumoniae is a gram-positive, spherical (0.5 to 1.25 µm in diameter), facultative anaerobic bacterium.

Streptococcus pneumonia from Wikimedia

Apart from causing pneumococcal infection in the upper respiratory tract, it has been harnessed for a range of applications in biotechnology.

Streptococcus mutans

S. mutans is a round-shaped (0.5 to 0.75 µm), facultative anaerobic, gram-positive bacterium. It is commonly found in the human oral cavity and has evolved to increase its virulence by enhancing its ability to survive in a low pH environment.

Yersinia pestis

Y. pestis is a gram-negative, rod-ovoid (0.5-0.8 µm width 1-3 µm length), facultative anaerobic bacterium.

Yersinia pestis from Flickr

It is widely known to cause plague. Also, in response to the production of antibodies and phagocytosis, it suppresses the host immune system.

Staphylococcus saprophyticus

S. saprophyticus is a spherical-shaped (1 µm in diameter), facultative anaerobic, gram-positive, bacterium. It is commonly found in the female genital tract and is a causative agent of urinary tract infections in 17-27 years old.

Streptococcus salivarius

S. salivarius is a grampositive, spherical (2 µm in diameter), facultative anaerobic bacterium. It has a therapeutic effect against oral infections as it produces antimicrobial peptides that prevent the growth of more virulent strains of Streptococcus in the oral environment.

Streptococcus sanguinis

S. sanguinis is a coccus-shaped, gram-positive, facultative anaerobic bacterium. It is commonly found in dental plaque and has a tendency to enter the bloodstream leading to colonization of the heart valves.

Cutibacterium acnes

C. acnes is a rod-shaped (0.4-0.7 µm width; 3-5 µm length), slow-growing, gram-positive, facultative anaerobic bacterium. Its habitat includes healthy adult skin and endophytes of plants. In the North American and European populations, it is reported to show resistance against a range of antibiotics such as; erythromycin, azithromycin, and doxycycline.

Shewanella oneidensis

S. oneidensis isolated from Lake Oneida is a facultative bacterium capable of reducing metal ions. It is well known for the synthesis of several nanoparticles such as silver. Also, it is a potent candidate for use in wastewater treatment.

Streptococcus bovis

S. bovis is a facultative anaerobic, gram-positive bacterium. Its habitat includes the alimentary tract and gastrointestinal tract of ruminants and humans, respectively.

Streptococcus mitis

S. mitis is a spherical-shaped, gram-positive, facultative anaerobic bacterium. Its habitat includes the oral cavity and gastrointestinal tract along with the female genital tract. Interestingly, S. mitis survived for over two years on the Surveyor 3 of the American uncrewed Surveyor program indicating its ability to sustain radiation exposure without a nutrient source.

Streptococcus thermophilus

S. thermophilus is a gram-positive, round-shaped (0.7-0.9 µm) fermentative facultative anaerobic bacterium. It is also known as a lactic acid bacterium due to its use in the production of yogurt. Yogurt and cheese containing live cultures of S. thermophilus are easily digested by lactose-intolerant people.

Staphylococcus hominis

S. hominis is a gram-positive, spherical (1-2 mm), facultative anaerobic bacterium. It contributes to body odor by producing thioalcohol compounds.

Staphylococcus haemolyticus

S. haemolyticus is a gram-positive, coccus shaped (0.8-1.3 µm), facultative anaerobic bacterium. It is an opportunistic pathogen and forms a part of the human skin flora.

Staphylococcus lugdunensis

S. lugdunensis is a gram-positive, spherical (2-4 mm in diameter), facultative anaerobic bacterium. It is a causative agent of arthritis.

Streptococcus anginosus

S. anginosus is a gram-positive, facultative anaerobic bacterium. It is a part of the human bacteria flora. Colonies of this bacterium often smell like butterscotch or caramel.

Streptococcus dysgalactiae

S. dysgalactiae is a gram-positive, facultative anaerobic bacterium. It is popularly found in the alimentary tract and genital tract of both humans and animals.

Staphylococcus capitis

S. capitis is a gram-positive, spherical (0.5-1.5 µm in diameter), facultative anaerobic bacterium. Although it forms a major part of the human biome, it can be pathogenic in immunocompromised people.

Streptococcus constellatus

S. constellatus is a spherical-shaped (0.5-1 µm in diameter), facultative anaerobic, gram-positive bacterium. It is normally found in the oral cavities and upper respiratory tracts.

Staphylococcus warneri

S. warneri is a non-motile, spherical (2-4 mm) facultative bacterium.

Frequently Asked Questions

What are facultative bacteria?

Facultative bacteria are popularly known as both facultative aerobic or anaerobic bacteria. These are the most flexible type of bacteria with an ability to adapt to extreme environmental conditions. These organisms have the potential to survive in both oxygen-rich and oxygen-deficient environment.

In the presence of oxygen, they make ATP by aerobic respiration, while they use fermentation or anaerobic respiration in an oxygen-deficient environment.

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