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Wild Type Strains Introduction

Wild type strains are specific reference micro-organisms in microbial genetics e.g. Staphylococcus aureus ATCC 25923,   Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Enterococcus faecalis ATCC 29212, Candida albicans ATCC 90028 ( fungus)  S. cerevisiae ATCC 9763( fungus), etc, and descendants that have mutations in their genomes are called mutants. Therefore, mutants are characterized by the inherited differences between them and their ancestral wild-type strains.

Features of Wild Type Strains versus Mutants

• Alleles: Variant forms of a specific genetic determinant
• Genotypic symbols: They are lower case, italicized abbreviations that specify individual genes, with a (+) superscript indicating the wild type allele.
• Phenotypic symbols: They are capitalized and not italicized, to distinguish them from genotypic symbols. e.g. the genotypic symbol for the ability to produce β-galactosidase, required to ferment lactose, is lacZ+, and mutants that cannot produce β-galactosidase are lacZ.
• The lactose-fermenting phenotype: It is designated Lac+, and the inability to ferment lactose is Lac–.
• Differential media permit wild-type and mutant bacteria to grow and form colonies that differ in appearance.
• Selective and differential media are helpful for isolating bacterial mutants. Some selective media permit particular mutants to grow, but do not allow the wild-type strains to grow.
• Consider a wild-type strain of E. coli that is susceptible to the antibiotic streptomycin (phenotype Strs) and can utilize lactose as the sole source of carbon (phenotype Lac+)
• The above image is showing an organism ( bacterium) that is susceptible to following antimicrobial agents like erythromycin, clindamycin, ciprofloxacin, ofloxacin, gentamycin, chloramphenicol, doxycycline, sulfamethoxazole-trimethoprim, and cefoxitin that reflects the probability of bacterium being wild type strain.

 Some Related Terminologies-

• Clone: A strain developed from  a single parent cell
• Strain: The descendants of single isolation in pure culture
• Isolation: Separation of particular microorganisms from a mixed population that exists in nature.
• Pure culture: A culture that contains only one type of microorganisms.

References

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1951032/
2. https://www.ncbi.nlm.nih.gov/books/NBK7908/
3. Textbook of practical Microbiology by Subhash Chandra Parija
4. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
5. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
6.  Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.