Gram staining involves three steps: 1. crystal violet (purple) staining, 2. decolorization, 3. counterstaining (red). If you look under a microscope after the first step, you will see that:Group of answer choicesonly gram negative bacteria are purpleonly gram positive bacteria are purpleboth gram positive and negative bacteria are purpleneither gram positive and negative bacteria are purple

Gram staining is based on:a) the ability of the bacterial cell wall to retain crystal violet dyeb) the lysis of bacterial cellsc) differences in bacterial shape and sized) growth of bacterial cells

You are performing a Gram stain on gram-positive bacteria and you stop after the addition of the first dye. What is the appearance of the bacteria at this point?Question 13Answera.purpleb.colorlessc.redd.brown

You are performing a Gram stain on gram-negative bacteria and you stop after the decolorizer step. What is the appearance of the bacteria at this point?Question 11Answera.redb.colorlessc.purpled.brownClear my choice

Bacteria can be broadly classified into two groups, Gram-negative and Gram-positive, based on the results of the Gram-staining procedure, in which bacteria are exposed to crystal violet dye and iodide.  Both crystal violet dye and iodide molecules are small enough to cross cell walls and bacterial lipid membranes (such as those found on the exterior of Gram-negative bacteria), but not bacterial phospholipid membranes (such as the plasma membrane).  Crystal violet and iodide form complexes with each other in both Gram-negative and Gram-positive bacteria, but only Gram-positive bacteria retain the complexes after a subsequent alcohol wash in the Gram staining procedure.  As a result, Gram staining imparts a purple color to Gram-positive but not Gram-negative cells.Researchers studying antibiotic sensitivity in Gram-negative bacteria measured the transfer of a naturally occurring plasmid (R plasmid) to recipient bacteria lacking the plasmid.  The wild-type (WT) R plasmid contains several types of genes: 1) an antibiotic resistance gene, 2) the gene for a protein called pixR, and 3) other genes (eg, pilX11, taxB) that promote the spread of the R plasmid to recipient cells.  In an experiment, the researchers measured R plasmid transfer from donor groups that differed with respect to pixR expression: (1) wild-type (WT) bacteria, (2) bacteria lacking pixR in the R plasmid (ΔpixR), and (3) ΔpixR bacteria experimentally induced to overexpress pixR (ΔpixR+pixR).  The number of recipient bacteria taking up the plasmid per donor bacterium was measured for the three groups in both solid and liquid environments and is presented in Figure 1.Figure 1  Bacteria receiving R plasmid from donor bacteriaIn a second experiment, plasmid-free and plasmid-containing bacteria were coincubated over several days.  Researchers monitored uptake of the plasmids from WT and ΔpixR bacteria into plasmid-free recipient bacteria.  The results are shown in Figure 2.Figure 2  Prevalence of plasmid-free and plasmid-containing bacteria during coincubation Question 39In Gram-negative bacteria, what is the maximum number of peptidoglycan layers through which crystal violet may pass during Gram staining?A.0B.1C.2D.3

similarities and differences between gram-positive and gram-negative bacteria.