microbiology Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, prot ...

, streaking is a technique used to isolate a pure

strain Strain may refer to: Science and technology * Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes * Strain (chemistry), a chemical stress of a molecule * Strain (injury), an injury to a mu ...

from a single species of microorganism, often

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Samples can then be taken from the resulting colonies and a

microbiological culture A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagn ...

can be grown on a new plate so that the organism can be identified, studied, or tested. The modern streak plate method has progressed from the efforts of

Robert Koch Heinrich Hermann Robert Koch ( , ; 11 December 1843 – 27 May 1910) was a German physician and microbiologist. As the discoverer of the specific causative agents of deadly infectious diseases including tuberculosis, cholera (though the Vibrio ...

and other microbiologists to obtain microbiological cultures of bacteria in order to study them. The dilution or isolation by streaking method was first developed by Loeffler and Gaffky in Koch's laboratory, which involves the dilution of bacteria by systematically streaking them over the exterior of the

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar is ...

in a

Petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...

to obtain isolated colonies which will then grow into quantity of cells, or isolated colonies. If the agar surface grows microorganisms which are all genetically same, the culture is then considered as a

Technique

Streaking is rapid and ideally a simple process of isolation dilution. The technique is done by diluting a comparatively large concentration of bacteria to a smaller concentration. The decrease of bacteria should show that

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

are sufficiently spread apart to affect the separation of the different types of

microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

. Streaking is done using a

sterile Sterile or sterility may refer to: *Asepsis, a state of being free from biological contaminants * Sterile (archaeology), a sediment deposit which contains no evidence of human activity *Sterilization (microbiology), any process that eliminates or ...

tool, such as a

cotton swab Cotton is a soft, fluffy Staple (textiles), staple fiber that grows in a wikt:boll, boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose ...

or commonly an

inoculation loop An inoculation loop (also called a smear loop, inoculation wand or microstreaker) is a simple tool used mainly by microbiologists to pick up and transfer a small sample of microorganisms called inoculum from a microbial culture, e.g. for streakin ...

. Aseptic techniques are used to maintain microbiological cultures and to prevent contamination of the

growth medium A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differen ...

. There are many different types of methods used to streak a plate. Picking a technique is a matter of individual preference and can also depend on how large the number of

the sample contains. FINAL mmg 301 honors option

The three-phase streaking pattern, known as the T-Streak, is recommended for beginners. The streaking is done using a

tool, such as a

or commonly an

. The inoculation loop is first sterilized by passing it through a flame. When the loop is cool, it is dipped into an

inoculum In biology, inoculum refers to the source material used for inoculation. ''Inoculum'' may refer to: * In medicine, material that is the source of the inoculation in a vaccine * In microbiology, propagules: cells, tissue, or viruses that are used t ...

such as a broth or patient specimen containing many species of bacteria. The inoculation loop is then dragged across the surface of the

back and forth in a zigzag motion until approximately 30% of the plate has been covered. The loop then is re-sterilized and the plate is turned 90 degrees. Starting in the previously streaked section, the loop is dragged through it two to three times continuing the zigzag pattern. The procedure is then repeated once more being cautious to not touch the previously streaked sectors. Each time the loop gathers fewer and fewer bacteria until it gathers just single bacterial cells that can grow into a colony. The plate should show the heaviest growth in the first section. The second section will have less growth and a few isolated colonies, while the final section will have the least amount of growth and many isolated colonies.

Growth medium

The sample is spread across one quadrant of a

containing a

. Bacteria need different nutrients to grow. This includes water, a source of energy, sources of carbon, sulfur, nitrogen, phosphorus, certain minerals, and other vitamins and growth factors. A very common type of media used in microbiology labs is known as

, a gelatinous substance derived from seaweed. The

nutrient agar Nutrient agar is a general purpose liquid medium supporting growth of a wide range of non-fastidious organisms. It typically contains ( mass/volume): * 0.5% peptone - this provides organic nitrogen * 0.3% beef extract/yeast extract - the wate ...

has a lot of ingredients with unknown amounts of nutrients in them. On one hand, this can be a very selective media to use because as mentioned bacteria are particular. If there is a certain nutrient in the media the bacteria could most certainly not grow and could

die Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semicondu ...

. On the other hand, this media is very complex. Complex media is important because it allows for a wide range of microbial growth. The bacteria growth can be supported by this media greatly due in part to the high amounts of nutrients. Choice of which growth medium is used depends on which microorganism is being cultured, or selected for. Agarplate redbloodcells edit

Incubation

Dependent on the strain, the plate may then be incubated, usually for 24 to 36 hours, to allow the bacteria to reproduce. At the end of incubation there should be enough bacteria to form visible colonies in the areas touched by the inoculation loop. From these mixed colonies, single bacterial or fungal species can be identified based on their morphological (size/shape/colour) differences, and then sub-cultured to a new media plate to yield a pure culture for further analysis. Automated equipment is used at industrial level for streak plating the solid media in order to achieve better sterilization and consistency of streaking and for reliably faster work. While streaking manually it is important to avoid scratching the solid medium as subsequent streak lines will be damaged and non-uniform deposition of inoculum at damaged sites on the medium yield clustered growth of microbes which may extend into nearby streak lines.

Importance

Bacteria exist in water, soil and food, on skin, and intestinal tract

normal flora The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, including the skin, mammary glands, seminal fluid, uterus, ovarian ...

. The assortment of

that exist in the environment and on human bodies is enormous. The human body has billions of bacteria which creates the normal flora fighting against the invading pathogens. Bacteria frequently occur in mixed populations. It is very rare to find a single occurring species of bacteria. To be able to study the cultural, morphological, and physiological characteristics of an individual species, it is vital that the bacteria be divided from the other species that generally originate in the environment. This is important in determining a

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

in a clinical sample. When the bacteria is streaked and isolated, the causative agent of a bacterial disease can be identified.

References

* Black, Jacquelyn G. ''Microbiology: Principles and Explorations'' Marymount University, 1999 * Biotechnology and Biomedical Engineering : Amrita Vishwa Vidyapeetham Virtual Lab. * http://www.personal.psu.edu/faculty/k/h/khb4/enve301/301labs/lab4pureculture.html * Bauman, R. (2004) Microbiology. Pearson Benjamin Cummings. *Austerjost J, Marquard D, Raddatz L, Geier D, Becker T, Scheper T, Lindner, P, Beutel S. 2017. A smart device application for the automated determination of E. coli colonies on agar plates. Engineering in Life Sciences. 17(8): 959-966. *Bhattacharjee K, Joshi S. 2016. A selective medium for recovery and enumeration of endolithic bacteria. Journal of Microbiological Methods. 129(1): 44-54. *Brugger S, Baumberger C, Jost M,Jenni W, Brugger U, Mühlemann K. 2012. Automated counting of bacterial colony forming units on agar plates. PLoS ONE. 7(3):1-6. *Chang G, Grinshpun S, Willeke K, Mancher, J,Donnelly C. 1995. Factors affecting microbiological colony count accuracy for bioaerosol sampling and analysis. American Industrial Hygiene Association Journal. 56(10): 979-986. *Choi Q, Kim HJ, Kim JW, Kwon GC, Koo SH. 2018. Manual versus automated streaking system in clinical microbiology laboratory: Performance evaluation of Previ Isola for blood culture and body fluid samples. Journal of Clinical Laboratory Analysis. 32(5):1-7. *Geun C, Myoungjoo R, Choong-Min R. 2019. Beyond the two compartments Petri-dish: Optimising growth promotion and induced resistance in cucumber exposed to gaseous bacterial volatiles in a miniature greenhouse system. Plant Methods. 15(1): 1-11. *Ghivari S, Kubasad G, Deshpande P. 2012. Comparative evaluation of apical extrusion of bacteria using hand and rotary systems : An in vitro study. Journal of Conservative Dentistry. 15(1): 32-35. *Jones D, Smith H, Thieme H, Röst G. 2012. On Spread of Phage Infection of Bacteria in a Petri Dish. SIAM Journal on Applied Mathematics, 72(2): 670-688. *Kabanova N, Stulova I, Vilu R. 2013. Microcalorimetric study of growth of Lactococcus lactis IL1403 at low glucose concentration in liquids and solid agar gels. Thermochimica Acta, 559: 69-75. *Nottingham P, Rushbrook A, Jury K. 1975. The effect of plating technique and incubation temperature on bacterial counts. IFST. 10(3):273-279. *Safwat, N. 2013. Automation and beyond: Improving efficiency in the pathway from collection to care. Medical Laboratory Observer. 45(1). *Tomasino S, Pines R, Cottrill M, Hamilton M. 2008. Determining the efficacy of liquid sporicides against spores of Bacillus subtilis on a hard nonporous surface using the quantitative Three Step Method: Collaborative study. Journal of AOAC International, 91(4): 833-852. *Wang Z, Liu Y, Feng C, Wang C. 2016. Isolation and Identification of Saccharomycetes in Wine Grape Region of Chateau Changyu Moser XV. Agricultural Science & Technology. 17(12): 2689-2691,2700.

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