MUTANT GONORRHEA:A STATISTICAL ANALYSISLauren Myers Theory of Statistics

The Organism

Neisseria gonorrhoeae Etiological agent of gonorrhea Type IV Pili (Tfp) are an important virulence factor

Filamentous appendages Through cycles of adhesion, retraction, and release, they

mediate: Twitching motility DNA uptake Host cell adhesion Host cell invasion

The pilus is assembled from many constituent proteins PilC, PilE, PilT, Gcp, etc…

The Experiment

Generated null Gcp mutant Mutant retracted Tfp with much greater force Mutant had increased invasion index

Generated inducible Gcp mutant (IF_1β_4) Uninduced strain should have mutant phenotype Induced strain should have wild type phenotype

Unable to demonstrate consistent invasion phenotype Fe2+ regulation of Gcp

Are we inducing Gcp correctly? Statistical analysis may justify time and expense to

investigate this question

The Data

X and Y are normally distributed random variables, representing the invasion indices of the induced and uninduced mutant, respectively

Table I: Invasion Indices of Induced & Uninduced IF_1β_4

nX = nY = 10 X = 0.0693% Y = 0.0831%

i 1 2 3 4 5 6 7 8 9 10Xi 0.2673% 0.0210% 0.0387% 0.2796% 0.0075% 0.0049% 0.0146% 0.0170% 0.0322% 0.0103%

Yi 0.2097% 0.0102% 0.0054% 0.2767% 0.0016% 0.0180% 0.0701% 0.1297% 0.0063% 0.1033%

The Statistical Analysis

X and Y have unknown population means μX and μY, respectively

H0: μX = μY against H1: μX ≠ μY

T-statistic:

Critical region: equal tails of Student t-distribution |t| > t0

Degrees of freedom = μX + μY -2

The Statistical Analysis

Evaluate t-statistic to obtain: t = -0.3004 Obtain t0 from table:

Degrees of freedom = 18 According to convention, α = 0.05 t0 = 2.1009

Clearly, |t| < t0

Accept the null hypothesis: H0: μX = μY There is no significant difference between the

invasion indices of the induced and uninduced mutant

Conclusions and Future Directions Confirmed that my experiments did not

show a difference in invasion phenotype New experiments showed Gcp levels do

change over the course of infection We have conducted our first experiments

under fundamentally unnatural conditions Future experiments: time induction to

coincide with natural increase in Gcp expression Repeat invasion assays; compare

population means using the same analysis