phage typing

Phage typing is based on the specific binding of phages to antigens and receptors on the surface of bacteria and the resulting bacterial lysis or lack thereof.{{Cite journal|last1=Felix|first1=A.|last2=Callow|first2=B. R.|date=1943-07-31|title=Typing of Paratyphoid B Bacilli by Vi Bacteriophage|journal=British Medical Journal|volume=2|issue=4308|pages=127–130|doi=10.1136/bmj.2.4308.127|issn=0007-1447|pmc=2284669|pmid=20784954}} The binding process is known as adsorption.{{Cite journal|last1=Bertozzi Silva|first1=Juliano|last2=Storms|first2=Zachary|last3=Sauvageau|first3=Dominic|date=2016-02-01|title=Host receptors for bacteriophage adsorption|journal=FEMS Microbiology Letters|volume=363|issue=4|pages=fnw002|doi=10.1093/femsle/fnw002|pmid=26755501|issn=0378-1097|doi-access=free}} Once a phage adsorbs to the surface of a bacteria, it may undergo either the lytic cycle or the lysogenic cycle.{{Cite journal|last=Kropinski|first=Andrew M|date=2006|title=Phage Therapy – Everything Old is New Again|journal=The Canadian Journal of Infectious Diseases & Medical Microbiology|volume=17|issue=5|pages=297–306|doi=10.1155/2006/329465|issn=1712-9532|pmc=2095089|pmid=18382643|doi-access=free}}

Virulent phages enter the lytic cycle where they replicate and lyse the bacterial cell.{{Cite web|date=2018-07-14|title=21.2B: The Lytic and Lysogenic Cycles of Bacteriophages|url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/21%3A_Viruses/21.2%3A_Virus_Infections_and_Hosts/21.2B%3A_The_Lytic_and_Lysogenic_Cycles_of_Bacteriophages|access-date=2021-10-31|website=Biology LibreTexts|language=en}} Virulent phages can differentiate between different species of bacteria based on their specific lytic action.{{Cite journal|last1=Koskella|first1=Britt|last2=Meaden|first2=Sean|date=2013-03-11|title=Understanding bacteriophage specificity in natural microbial communities|journal=Viruses|volume=5|issue=3|pages=806–823|doi=10.3390/v5030806|issn=1999-4915|pmc=3705297|pmid=23478639|doi-access=free}} Lysis will only occur if the virulent phage adsorbs to the bacterial surface, configuring species specificity to phages.

Temperate phages enter the lysogenic cycle and do not immediately lyse the cell. The phage is instead integrated into the bacterial genome as a prophage during lysogenization, which protects the cell from being lysed by phages which are serologically identical or related.{{Cite journal|last=Boyd|first=J. S. K.|date=1956-07-21|title=Immunity of Lysogenic Bacteria|journal=Nature|language=en|volume=178|issue=4525|pages=141|doi=10.1038/178141a0|pmid=13348647|bibcode=1956Natur.178..141B|s2cid=4162932|issn=1476-4687|doi-access=free}} Since it is incorporated into the genome, the prophage is also passed down to the bacteria's progenies. The bacterial strain carrying the prophage is known as a lysogenic strain. Lysogenization is strain-specific, so it allows for differentiation among different strains of bacteria within the same species.{{Cite web|title=Encyclopedia of Virology {{!}} ScienceDirect|url=https://www.sciencedirect.com/referencework/9780123744104/encyclopedia-of-virology|access-date=2021-11-15|website=www.sciencedirect.com}} The prophage may be chemically or physically induced to revert to the lytic pathway.

The bacterial strain to be characterized is cultured on an agar Petri dish and dried.{{Cite web|title=Encyclopedia of Virology {{!}} ScienceDirect|url=https://www.sciencedirect.com/referencework/9780123744104/encyclopedia-of-virology|access-date=2021-11-15|website=www.sciencedirect.com}} Once dry, a grid or another recognizable pattern is drawn on the base to mark out different regions. Each region is inoculated with a different phage at its routine test dilution and then incubated for 5-48 hours. The susceptible phage regions will display a clearing where the bacteria have been lysed, and this is used in differentiation.{{cite journal|vauthors=Turbadkar SD, Ghadge DP, Patil S, Chowdhary AS, Bharadwaj R|date=April 2007|title=Circulating phage type of Vibrio cholerae in Mumbai|url=http://www.ijmm.org/article.asp?issn=0255-0857;year=2007;volume=25;issue=2;spage=177;epage=178;aulast=Turbadkar|journal=Indian Journal of Medical Microbiology|volume=25|issue=2|pages=177–8|doi=10.4103/0255-0857.49436|pmid=17582202|doi-access=free|hdl=1807/53709|hdl-access=free}} The size, morphology, and pattern of the lysed region are important criteria for differentiating bacterial species and strains.{{Cite journal|last1=Schofield|first1=David A.|last2=Sharp|first2=Natasha J.|last3=Westwater|first3=Caroline|date=2012-04-01|title=Phage-based platforms for the clinical detection of human bacterial pathogens|journal=Bacteriophage|volume=2|issue=2|pages=105–283|doi=10.4161/bact.19274|issn=2159-7073|pmc=3442824|pmid=23050221}} They are compared against a standard scheme of lysis patterns to assign a type to the strain.{{cite journal|author=Baggesen DL, Sørensen G, Nielsen EM, Wegener HC|year=2010|title=Phage typing of Salmonella Typhimurium - is it still a useful tool for surveillance and outbreak investigation?|url=http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19471|journal=Eurosurveillance|volume=15|issue=4|pages=19471|doi=10.2807/ese.15.04.19471-en|pmid=20122382|doi-access=free}}

Routine test dilution (RTD) is typically defined as the lowest phage dilution that still yields lysis of its host. This technique prevents a phenomenon known as "lysis from without", which is bacterial lysis induced by high multiplicity phage adsorption rather than phage replication.{{Cite journal|last=Abedon|first=Stephen T|date=2011|title=Lysis from without|journal=Bacteriophage|volume=1|issue=1|pages=46–49|doi=10.4161/bact.1.1.13980|issn=2159-7073|pmc=3109453|pmid=21687534}}

The first reported use of bacteriophages to identify bacteria was in 1925 when Sonnenschein used typhoid and paratyphoid phages to diagnose typhoid.{{Citation|last=Brandis|first=Henning|title=Die Anwendung von Phagen in der bakteriologischen Diagnostik mit besonderer Berücksichtigung der Typisierung von Typhus- und Paratyphus B-Bakterien sowie Staphylokokken|date=1957|url=https://doi.org/10.1007/978-3-662-25832-3_3|work=Ergebnisse der Mikrobiologie, Immunitätsforschung und experimentellen Therapie: Fortsetzung der Ergebnisse der Hygiene, Bakteriologie, Immunitätsforschung und experimentellen Therapie|pages=96–159|editor-last=Kikuth|editor-first=W.|place=Berlin, Heidelberg|publisher=Springer|language=de|doi=10.1007/978-3-662-25832-3_3|isbn=978-3-662-25832-3|access-date=2021-11-15|editor2-last=Meyer|editor2-first=K. F.|editor3-last=Nauck|editor3-first=E. G.|editor4-last=Pappenheimer|editor4-first=A. M.|url-access=subscription}} In 1934, it was discovered that some strains of Salmonella typhi displayed Vi antigens on the surface.{{Cite journal|last1=Robertson|first1=R. C.|last2=Yu|first2=H.|date=1936|title=The Vi antigen of B. typhosus|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/path.1700430120|journal=The Journal of Pathology and Bacteriology|language=en|volume=43|issue=1|pages=191–196|doi=10.1002/path.1700430120|issn=1555-2039|url-access=subscription}} This led to the isolation of Vi phages capable of lysing typhoid bacteria strains but only if they displayed the Vi antigen{{Cite journal|last=Scholtens|first=R. Th.|date=1937|title=Adsorption of vi Bacteriophages by Typhoid Bacilli and Paratyphoid C Strains|journal=The Journal of Hygiene|volume=37|issue=2|pages=315–317|doi=10.1017/S0022172400035026|jstor=3859853|pmid=20475383|pmc=2199419|issn=0022-1724}} enabling the differentiation of typhoid species expressing the Vi antigen and those which do not.

In 1938, Craigie and Yen adapted Vi phages by selective propagation and used them at their critical test dilutions to differentiate 11 types of B. typhosus.{{Cite journal|last1=CRAIGIE|first1=JAMES|last2=YEN|first2=CHUN HUI|date=1938|title=The Demonstration of Types of B. Typhosus by Means of Preparations of Type II Vi Phage: I. Principles and Technique|url=https://www.jstor.org/stable/41977832|journal=Canadian Public Health Journal|volume=29|issue=9|pages=448–463|jstor=41977832|issn=0319-2652}} In 1943, Felix and Callow extended the method to Salmonella paratyphi B. in 1943 and differentiated 12 types with 11 phages.{{Cite journal|last1=Felix|first1=A.|last2=Callow|first2=B. R.|date=1943-07-31|title=Typing of Paratyphoid B Bacilli by Vi Bacteriophage|journal=British Medical Journal|volume=2|issue=4308|pages=127–130|doi=10.1136/bmj.2.4308.127|issn=0007-1447|pmc=2284669|pmid=20784954}} The International Committee for Enteric Phage Typing was established in 1947, and these phage typing methods were soon standardized.{{Cite web|title=International Federation for Enteric Phage Typing {{!}} UIA Yearbook Profile {{!}} Union of International Associations|url=https://uia.org/s/or/en/1100029572|access-date=2021-11-15|website=uia.org}}

Improvements to the specificity of phage typing schemes were made throughout the next few decades. In 1959, Callow improved her initial scheme to differentiate 34 types of Salmonella typhimurium with 29 phages.{{Cite journal|last1=Anderson|first1=E. S.|last2=Ward|first2=Linda R.|last3=de Saxe|first3=Maureen J.|last4=de Sa|first4=J. D. H.|date=1977|title=Bacteriophage-Typing Designations of Salmonella typhimurium|journal=The Journal of Hygiene|volume=78|issue=2|pages=297–300|doi=10.1017/S0022172400056187|jstor=3861882|pmid=321679|pmc=2129838|issn=0022-1724}} In 1977, this was extended to 207 types by Anderson at the Enteric Reference Laboratory in London. Since then, phage typing schemes have been developed for Salmonella typhi, Salmonella paratyphi B., Salmonella typhimurium, Shigella sonnei, Staphylococcus aureus, and Escherichia coli to name a few.{{Cite journal|last1=Anderson|first1=E. S.|last2=Williams|first2=R. E.|date=May 1, 1956|title=Bacteriophage typing of enteric pathogens and staphylococci and its use in epidemiology|journal=Journal of Clinical Pathology|volume=9|issue=2|pages=94–127|doi=10.1136/jcp.9.2.94|issn=0021-9746|pmc=1023924|pmid=13332068}}{{Cite journal|last1=Gershman|first1=M.|last2=Merrill|first2=Cynthia E.|last3=Hunter|first3=Jacqueline|date=1981-12-01|title=Phage Typing Set for Differentiating Escherichia coli|journal=Journal of Dairy Science|language=en|volume=64|issue=12|pages=2392–2400|doi=10.3168/jds.S0022-0302(81)82862-7|pmid=7042781|issn=0022-0302|doi-access=free}}

Phage typing requires the use of a comprehensive number of phages, so it is typically only used in reference laboratories.{{Cite web|date=2020-03-05|title=Phage Typing Method: Principle, Procedure, Results • Microbe Online|url=https://microbeonline.com/phage-typing-method/|access-date=2021-11-20|website=Microbe Online|language=en-us}} It also relies on the interpretation of the individual lysis pattern and comparison to a standard which has led to conflicting results from different laboratories in the past.{{cite journal|author=Baggesen DL, Sørensen G, Nielsen EM, Wegener HC|year=2010|title=Phage typing of Salmonella Typhimurium - is it still a useful tool for surveillance and outbreak investigation?|url=http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19471|journal=Eurosurveillance|volume=15|issue=4|pages=19471|doi=10.2807/ese.15.04.19471-en|pmid=20122382|doi-access=free}} Furthermore, bacteriophages mutate so reference phages must be maintained.

Phages used for phage typing are generally isolated from the native habitats of the host bacterial strain.{{Cite web|title=Encyclopedia of Virology {{!}} ScienceDirect|url=https://www.sciencedirect.com/referencework/9780123744104/encyclopedia-of-virology|access-date=2021-11-15|website=www.sciencedirect.com}} These may include sewage, feces, soil, and water. Temperate phages may be isolated from the bacterium itself since it is incorporated into the bacterial genome during lysogenization.

Category:Microbiology