Pseudomonas aeruginosa (Contact lens): Dose Response Models

Pseudomonas aeruginosa (Ocular Infection)

Author: Sushil Tamrakar

General overview of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative, aerobic rod belonging to the bacterial family Pseudomonadaceae. Like other members of the genus, Pseudomonas aeruginosa is a free-living bacterium, commonly found in soil, water and biofilms. However, it occurs regularly on the surfaces of plants and occasionally on the surfaces of animals. Pseudomonas aeruginosa is an opportunistic pathogen, meaning that it exploits some break in the host defenses to initiate an infection. (CDC 1990, Todar 2012).

Pseudomonas aeruginosa generally invades the body or organs lacking natural defenses, and usually the infection are chronic rather than acute, evoking little systemic response. When introduced into the cornea, however, as in penetration by a foreign body or in contaminated medicines, it acts with extreme virulence, in many cases causing blindness and even necessitating enucleation (Spencer, 1953). It is the organism most frequently implicated in contact lens related keratitis (Lawin-Brüssel et al., 1993).

http://www.cdc.gov/mmwr/preview/mmwrhtml/00001546.htm

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Summary Data

Lawin-Brussel et al. (1993) studied the effect of Pseudomonas aeruginosa in experimental contact lens related microbial keratitis. Forty white New Zealand rabbits were used in the experiment. New and worn soft contact lenses were soaked in 5 ml bacterial suspension of different concentrations for an hour, then fitted into the eyes of the rabbit (one lense per rabbit). The clinical findings after seven days of contact lens wear and additional 48 hours of P. aeruginosa contaminated lens wear were recorded. The experimental dose unit was CFU/ml. However, Lawin-Brussel et al. (1993) had observed quantification of bacterial attachment on soft contact lens after an hour of soaking in different concentration of P. aeruginosa. Based on the figure, the bacterial attachment on a lens was calculated as the dose.

Dose Conversion Table

CFU/ml	CFU (per lens)
100	63.22
10000	2220.49
100000	13159.77
1000000	77991.7
10000000	86799.77
100000000	462219,6

Relationship between P. aeruginosa suspension and the amount of bacterial adherent on lens.

Similarly, Hazlett et al (1978) studied the susceptibility of newborn and infant mice to eye infection by P. aeruginosa. 15-16-day old mice were infected by topical application of P. aeruginosa of various dilutions onto wounded and unwounded corneas. None of the infected mice died of bacteremia and only those mice receiving corneal wounding before infection showed keratitis and eye shrinkage. Moreover, no cataract formation was detected in the mice (Hazlett, Rosen et al. 1978).

Experiment serial number Reference Host type Agent strain Route # of doses Dose units Response Best fit model Optimized parameter(s) LD50/ID50 297 and 298* white rabbit contact lens 10 CFU corneal ulceration beta-Poisson α = 1.9E-01 , N50 = 1.85E+04 1.85E+04 297 white rabbit contact lens 5 CFU corneal ulceration beta-Poisson α = 3.55E-01 , N50 = 6.57E+03 6.57E+03 298 white rabbit contact lens 5 CFU Severe stromal ulceration beta-Poisson α = 1.09E-01 , N50 = 1.52E+05 1.52E+05 286 Swiss webster mice ATCC 19660 injected ro cornea 5 CFU infection (Keratitis) exponential k = 8.8E-08 7.88E+06 *This model is preferred in most circumstances. However, consider all available models to decide which one is most appropriate for your analysis.

^*Recommended Model

The pooled model (experiment number 279 and 280) was recommended as both the data could statistically pooled and more data in the model means improvement in fits. The recommended model is as the marker of severe eye infection , it could be either corneal ulceration or stromal ulceration.

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Optimization Output for experiment 297 (Pseudomonas aeruginosa)

white rabbit/Pseudomonas aeruginosa Dose CORNEAL ULCERATION NOT CORNEAL ULCERATION Total 63.2 0 5 5 2220 2 3 5 13200 3 2 5 78000 3 2 5 462000 5 0 5

Goodness of fit and model selection Model Deviance Δ Degrees of freedom χ20.95,1 p-value χ20.95,m-k p-value Exponential 9.41 7.02 4 3.84 0.00807 9.49 0.0516 Beta Poisson 2.39 3 7.81 0.495 Beta-Poisson fits better than exponential; cannot reject good fit for beta-Poisson.

Optimized parameters for the beta-Poisson model, from 10000 bootstrap iterations Parameter MLE estimate Percentiles 0.5% 2.5% 5% 95% 97.5% 99.5% α 3.55E-01 1.53E-01 1.76E-01 1.91E-01 4.52E+00 1.73E+07 1.35E+11 N50 6.57E+03 7.71E+02 1.44E+03 1.70E+03 2.55E+04 4.30E+04 8.32E+04

Parameter scatter plot for beta Poisson model ellipses signify the 0.9, 0.95 and 0.99 confidence of the parameters

Beta-Poisson model plot, with confidence bounds around optimized model

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Optimization Output for experiment 298 (Pseudomonas aeruginosa)

white rabbit/Pseudomonas aeruginosa Dose SEVERE STROMAL ULCERATION NOT SEVERE STROMAL ULCERATION Total 63.2 0 5 5 2220 2 3 5 13200 1 4 5 78000 1 4 5 462000 4 1 5

Goodness of fit and model selection Model Deviance Δ Degrees of freedom χ20.95,1 p-value χ20.95,m-k p-value Exponential 13.2 8.73 4 3.84 0.00313 9.49 0.0105 Beta Poisson 4.43 3 7.81 0.219 Beta-Poisson fits better than exponential; cannot reject good fit for beta-Poisson.

Optimized parameters for the beta-Poisson model, from 10000 bootstrap iterations Parameter MLE estimate Percentiles 0.5% 2.5% 5% 95% 97.5% 99.5% α 1.09E-01 4.05E-02 5.23E-02 5.72E-02 9.05E+06 4.82E+07 2.53E+12 N50 1.52E+05 4.66E+03 1.13E+04 1.55E+04 1.55E+07 6.25E+07 1.96E+09

Parameter scatter plot for beta Poisson model ellipses signify the 0.9, 0.95 and 0.99 confidence of the parameters

Beta-Poisson model plot, with confidence bounds around optimized model

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Optimization Output for pooled data (experiment 297 and 298)(Pseudomonas aeruginosa)

Pooled data of White rabbit/Pseudomonas aeruginosa Dose CORNEAL ULCERATION NOT CORNEAL ULCERATION Total 63.2 0 5 5 63.2 0 5 5 2220 2 3 5 2220 2 3 5 13200 3 2 5 13200 1 4 5 78000 3 2 5 78000 1 4 5 462000 5 0 5 462000 4 1 5

Goodness of fit and model selection Model Deviance Δ Degrees of freedom χ20.95,1 p-value χ20.95,m-k p-value Exponential 30.9 20.8 9 3.84 5.11e-06 16.9 0.000312 Beta Poisson 10.1 8 15.5 0.26 Beta-Poisson fits better than exponential; cannot reject good fit for beta-Poisson.

Optimized parameters for the beta-Poisson model, from 10000 bootstrap iterations Parameter MLE estimate Percentiles 0.5% 2.5% 5% 95% 97.5% 99.5% α 1.9E-01 9.63E-02 1.15E-01 1.24E-01 3.86E-01 5.51E-01 2.50E+00 N50 1.85E+04 3.18E+03 4.73E+03 6.01E+03 7.05E+04 8.98E+04 1.97E+05

Parameter scatter plot for beta Poisson model ellipses signify the 0.9, 0.95 and 0.99 confidence of the parameters

Beta-Poisson model plot, with confidence bounds around optimized model

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Optimization Output for experiment 286 (Pseudomonas aeruginosa)

Swiss webster mice/Pseudomonas aeruginosa Dose INFECTION (KERATITIS) NOT INFECTION (KERATITIS) Total 1E+04 0 8 8 1E+05 1 9 10 1E+06 1 7 8 1E+07 5 5 10 1E+08 10 0 10

Goodness of fit and model selection Model Deviance Δ Degrees of freedom χ20.95,1 p-value χ20.95,m-k p-value Exponential 3.6 0.134 4 3.84 0.715 9.49 0.464 Beta Poisson 3.46 3 7.81 0.326 Exponential is preferred to beta-Poisson; cannot reject good fit for exponential.

Optimized k parameter for the exponential model, from 10000 bootstrap iterations Parameter MLE estimate Percentiles 0.5% 2.5% 5% 95% 97.5% 99.5% k 8.8E-08 3.31E-08 3.89E-08 4.53E-08 1.58E-07 1.94E-07 2.47E-07 ID50/LD50/ETC* 7.88E+06 2.81E+06 3.57E+06 4.38E+06 1.53E+07 1.78E+07 2.09E+07 *Not a parameter of the exponential model; however, it facilitates comparison with other models.

Parameter histogram for exponential model (uncertainty of the parameter)

Exponential model plot, with confidence bounds around optimized model

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References

CDC (1990) Pseudomonas aeruginosa Corneal Infection Related to Mascara Applicator Trauma - Georgia. Morbidity and Mortality Weekly Report. CDC. 39 (3), 47–48.

Hazlett LD, Rosen DD and Berk RS (1978) Age-Related Susceptibility to Pseudomonas aeruginosa Ocular Infections in Mice. Infection and Immunity 20(1), 25-29.

Kreger AS (1983) Pathogenesis of Pseudomonas aeruginosa Ocular Diseases. Reviews of Infectious Diseases. 5, S931–S935.

Lawin-Brüssel CA, Refojo MF, Leong FL, Hanninen L and Kenyon KR (1993) Effect of Pseudomonas aeruginosa concentration in experimental contact lens-related microbial keratitis. Cornea. 12 (1), 10–18.

Ledbetter EC, Mun JJ, Kowbel D and Fleiszig SMJ (2009) Pathogenic Phenotype and Genotype of Pseudomonas aeruginosa Isolates from Spontaneous Canine Ocular Infections. Investigative Ophthalmology & Visual Science 50(2), 729-736.

Spencer WH (1953) Pseudomonas aeruginosa infections  of the eye. California Medicine. 79 (6), 438–443.

Todar K (1012) Pseudomonas aeruginosa. Todar's Online Textbook of Bacteriology. Madison, Wisconsin