Based on the growth of these amdinocillin resistant clinical isolates grown in M

Question

Based on the growth of these amdinocillin resistant clinical isolates grown in Minimal Media (MM) with and without supplementation, what phenotype is being examined in Table 5? What general term is this phenotype referred to as?

Table 5. Amdinocillin susceptible and resistant clinical isolates, relevant phenotype, growth in various media, and MIC on Mueller-Hinton (MH) plates TABLE 5 Effects of cysteine addition on Amd resistance of clinical isolates Growth on MM Amd MIC (mg/liter) 0.3 mM Cys No Cys Strain Relevant phenotype M9 M9 Cys 0.75 mM Cys 0.125 DA5438 Yes Yes 0.125 0.125 DA28439 No Yes 24 0.25 DA14704 No Yes 32 0.125 0.125 DA14709 No Yes 0.38 No 0.125 DAI 4710 Yes DA14712 No Yes 32 16 0.5 DA14713 0.125 No No DA14715 No Yes 0.19 16 0.38 DA14718 No Yes 32 DA14719 No Yes 0.094 16 0.5 0.38 DA24678 No Yes 16 DA24686 No Yes 32 16 0.19 No Yes 24 DA24690 32 0.125 DA24692 No Yes 0.19 "Shown are growth on M9 glucose minimal medium (MM) with or without cysteine added and Amd Etest MICs on MH plates with different concentrations of cysteine. DAS438 is E. coli MG1655, DA28439 is a constructed cysB knockout strain, and all of the other strains are Amd clinical E. coli isolates with cysi mutations. cysB out.

Explanation / Answer

The phenotype being examined here is the ability of the organism to grow in the presence or absence of cysteine supplementation. This phenotype is generally refered to as auxotrophy i.e the mutants which require the presence of a nutrient for their growth. In this case some of the strains require cysteine (an aminoacid) to grow, so this is an example of screening for Cysteine Auxotrophy

Explanation : Auxotrophy is a type of mutant phenotype where the organism lacks the ability to grow in the absence of some nutrient. E.g. if an organism is an auxotrophic mutant for amino acid cysteine, then it will grow only in minimal media supplemented with cysteine but NOT in minimal media without cysteine. This is how clinical isolates are screened in the table shown. All organisms are plated on two plates one containing minimal media alone (M9) and another containing minimal media supplemented with Cysteine (M9+cys). If the clinical isolate is

A) cysteine auxotroph : It will not show growth in M9 but it will show growth in M9+cys. In the table, except the isolates DA5438 and DA14713, all other are Cysteine auxotrophs since they can't grow in M9 alone but can grow in M9+cys media

B) Not a cysteine auxotroph : It will show growth in both M9 and M9 +cys media

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