Micrococcus Luteus

Micrococcus is a genus of bacteria that is present in the Micrococcaceae family. Micrococcus species occur in a wide range of environments, including dust, water, and soil. Micrococci have Gram-positive types of spherical cells that are ranging from about 0.5 to three micrometres in diameter and typically they appear in tetrads. They are indole negative, oxidase-positive, catalase-positive, and citrate negative. Micrococcus has a substantial cell wall in which it may comprise as much as 50% of the cell mass. The genome of the Micrococcus is rich in guanine and cytosine, they typically exhibit about 65 to 75% GC-content. Micrococci can often carry plasmids that provide the organism with useful traits.

Some of the species of Micrococcus, such as M. luteus which is yellow in colour, and M. roseus which is red. They also produce yellow or pink colonies when they are grown on the mannitol salt agar, micrococcus flavus, M. terreus, and M. yunnanensis. Isolates of the M. luteus have been found to overproduce the riboflavin virus when they are grown on toxic organic pollutants like pyridine. Hybridization studies indicate that species within the genus Micrococcus are not closely related, showing as little as 50% sequence similarity. This suggests that some of the Micrococcus species on the basis of ribosomal RNA analysis eventually can be re-classified into other microbial genera.

  • Kingdom: Bacteria

  • Phylum: Actinobacteria

  • Class: Actinobacteria

  • Subclass: Actinobacteridae

  • Order: Actinomycetales

  • Suborder: Micrococcineae

  • Family: Micrococcaceae

  • Genus: Micrococcus

Micrococcus Luteus Gram Stain Characteristics

The genus Micrococcus consists of Gram-positive spheres occurring in tetrads and in irregular clusters that are usually non-motile and non-spore-forming. They are catalase-positive and usually aerobic with strictly respiratory metabolism. Most of the species produce carotenoid pigments. The GC content of the DNA ranges from about 65 to 75 mol%. There are around nine species that are recognized in the genus. The data on the GC content of the DNA, chemical cell wall analysis, and a comparative analysis of the 16S rRNA sequences. These can indicate that the genus of the Micrococcus is more closely related to the genus Arthrobacter than it is to other coccoid genera such as Staphylococcus and Planococcus.

Micrococcus spp. are gram-positive, oxidase-positive, and strictly they are aerobic cocci that are belonging to the family Micrococcaceae. They usually can occur in the irregular clusters, tetrads, and in pairs, where the individual cells are about one to 1.8 mm in diameter and these are usually non-motile and non-spore-forming in nature.

Micrococci have been isolated from the human skin, animal and dairy products, and in beer. They are found in many other places in the environment, including dust, water, and soil. M. luteus present on the human skin can transform compounds present in sweat into compounds with an unpleasant odour. Micrococci can grow well in environments with little water or high salt concentrations, including sportswear that is made with synthetic fabrics. Most of these are mesophiles; some, like Micrococcus antarcticus which is found in Antarctica, are psychrophiles. Though not a spore former, the Micrococcus cells can survive for an extended period of time, both at refrigeration temperatures and in nutrient-poor conditions such as sealed in amber.

M. luteus has one of the smallest genomes of all the bacteria. Hybridization studies show that there is no close genetic relationship between the species of Micrococcus bacteria. For example, M. luteus and M. lylae are 40-50% genetically different. M. luteus has a G-C content of about 65-75 mol%. Whereas the M. variant has a G-C content of about 66-72mol%. About half of the Micrococcus luteus gram stain was found to carry plasmids of about one to 100MDa in size. So far there are two genome sequences that have been done. The M. luteus genome encodes about four sigma factors and fourteen response regulators, a finding indicative of the adaptation to a rather strict ecological niche. The mammalian skin that has M. luteus strain is also highly sensitive to the beta-lactam antibiotics. This can occur due to the presence of a reduced number of proteins that can bind to penicillin.

Micrococcus Luteus Morphology

Micrococcus is the Gram-positive cocci that are about 0.5 to 3.5 micrometres in diameter and usually, these are arranged in tetrads or in irregular clusters. They are generally strict aerobes and these can generally reduce nitrate concentration. M. luteus oxidize carbohydrates to form carbon dioxide and water, and it does not produce acid from the glucose as well as it does not make arginine dihydrolase or b-galactosidase. Some of the Micrococcus are pigmented bacteria, for example, M. roseus produces reddish colonies and M. luteus produces yellow colonies. Micrococcus species are oxidase-positive, where these can be used to distinguish them from some other bacteria like most of the Staphylococcus species, which are generally oxidase-negative. 

Micrococcus species by the Taxo A Bacitracin disk test can also be differentiated from staphylococcus species. Micrococcus species are more sensitive to the Bacitracin while the staphylococci are resistant. While defining the characteristics of the Micrococcus are the ability to produce acid aerobically from the aesculin hydrolysis, glucose glycerol, arginine dihydrolase, motility, major pigment production, and conversion of nitrate to nitrite. Micrococcus luteus can synthesize the iso-branched and anteiso-branched alkenes by the head-to-head condensation of fatty-acid thioesters.

Micrococcus Luteus Infection

M. luteus is considered an opportunistic pathogen that can be responsible for some of the nosocomial infections. Where the M. luteus can cause severe skin infections and is sometimes clinically mistaken for Staphylococcus aureus. This bacterium can also be transmitted to others due to poor hand-washing practices. M. luteus can also cause septic shocks in immuno-compromised people.

Although the Micrococcus rarely causes infections or problems in the body, with the compromised immune systems, it has been known to get certain skin infections that are caused by Micrococcus luteus. The skin infections or chronic cutaneous infections that are caused can result in pruritic eruptions of the skin in some of the areas as well as scattered papule lesions with or without central ulcerations. Micrococcus as the cause of infections is easy to overlook because the infections that are caused by this bacterium are rare as well as the bacterium is a natural part of the skin's bacterial flora. Thus, when dealing with Micrococcus infections, it usually takes several cultures that are being grown and examined before one realizes that Micrococcus is indeed the culprit. 

Most of the Micrococcus infections are discovered through the process of elimination along with the presence of the abundant Micrococcus tetrads in the lesions or cysts. Though today the immuno-compromised patients take the risk of the infection that has grown. There have been several deaths in immuno-compromised children that are caused by leukemia from the pulmonary hemorrhages because of Micrococcus. Recently, as an opportunistic pathogen, this organism was recognized and it has been implicated in recurrent bacteremia,  septic arthritis, septic shock, endocarditis, intracranial suppuration, meningitis, and cavitating pneumonia in immunosuppressed patients.

Micrococcus Luteus Gram Stain Tests

1. Micrococcus Luteus Oxidase Test: The microdase test, also known as modified oxidase test is a rapid test to differentiate Staphylococcus from Micrococcus which are Gram-positive cocci possessing catalase enzymes. The differentiation is based on the detection of the oxidase enzymes. For the detection of oxidase enzyme, filter paper circular disks impregnated with tetramethyl-p-phenylenediamine dihydrochloride in dimethyl sulfoxide are used. The modified oxidase reagent is prepared as tetramethyl-p-phenylenediamine in certified grade dimethyl sulfoxide. In the presence of atmospheric oxygen, the oxidase enzyme reacts with the oxidase reagent and cytochrome C to form the coloured compound, indophenol indicated as blue or purplish-blue colouration on the disc after the introduction of the bacterial colony on the disc. A positive test leads to the development of blue or purple-blue on the disc within two minutes. In the case of a negative test, no colour change is observed.

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2. Micrococcus Catalase Test: The catalase test facilitates the detection of the enzyme catalase in bacteria. It is essential for differentiating catalase-positive Micrococcaceae from catalase-negative Streptococcaceae. These include the slide or drop catalase test, the tube method, the semiquantitative catalase for the identification of Mycobacterium tuberculosis.

Micrococcus Luteus Gram Stain Facts

  • M. luteus is found in the soil, dust, water, and human skin flora. It has also been isolated from foods such as milk and goat’s cheese.

  • This bacterium is often arranged in the form of circular tetrads and it forms bright yellow colonies on nutrient agar.

  • This bacterium can withstand massive doses of UV radiation and it also has the capability to degrade certain pollutants such as petrol.

  • M. luteus played an important part in Fleming’s discovery of Lysozyme which is the body’s natural antibiotic.

  • M. luteus has the capability to show dormancy without the formation of spores. Unlike other actinobacteria, M. luteus expresses only one resuscitation-promoting factor that is required for the emergence from dormancy and has few other dormancy-related proteins.

  • M. luteus causes odours in humans when breaking down the components of sweat.

Micrococcus Luteus Treatment

A rare case of prosthetic valve endocarditis is caused by Micrococcus luteus, it is described and compared with the few cases that are reported in the literature, as well as the clinical features, microbiological profile, therapy, and prognosis of common prosthetic valve endocarditis. Micrococcus luteus is a constituent of the normal human buccal bacterial flora which forms yellowish colonies and appears as a gram-positive coccus typically arranged in tetrads. Although of low virulence, the germs may become more pathogenic in patients with impaired resistance, colonizing the surface of heart valves. In contrast to staphylococci, usually, penicillin is sensitive. However, the most promising antibiotic regimen that is proposed for the treatment of the Micrococcus luteus seems to be a combination of amikacin, vancomycin, and rifampicin. If the infection leads to severe hemodynamic alterations, thus the valve replacement may become necessary. Similar to the situation in the prosthetic valve endocarditis that is caused by more aggressive and highly resistant bacteria.


Micrococcus luteus characteristics possess unusual abilities to tolerate and to use very toxic organic molecules as carbon sources and it combines these activities with tolerance to metals. The sequencing of Micrococcus luteus was supported because of its major potential role in the case of bioremediation and its importance in the field of biotechnology.

FAQs (Frequently Asked Questions)

1. What are the Uses of Micrococcus Gram Stain?

Ans: Micrococci, like many other representatives of the Actinobacteria, can be catabolically versatile, with the ability to utilize a wide range of unusual substrates, such as herbicides, pyridine, chlorinated biphenyls, and oil. They are likely involved in the biodegradation of many other environmental pollutants or detoxification. Other Micrococcus isolates produce various useful products, such as long-chain aliphatic hydrocarbons for lubricating oils.

2. What are the Diseases that are Caused By Micrococcus?

Ans: Although it is a harmless saprophyte, Micrococcus luteus can act as an opportunistic pathogen. It has been associated with causing a variety of illnesses including septic arthritis, meningitis, endocarditis, chronic cutaneous infections in HIV-positive patients, and catheter infections.