How to style Disabled Options in a form

I'm using a form with a drop-down menu that contains some options disabled, so the users cannot select them. I'm trying to customize via css these elements but I have some problems with Chrome and IE7/8/9/10.

HTML:

<div class="formBody">
    <select  name="form[categoria][]"  id="categoria"  class="rsform-select-box">
      <option selected="selected" value="">Scegli una categoria</option>
      <option disabled="disabled" value="">Impresa </option>
    </select>
    <span class="formValidation">
        <span id="component50" class="formNoError">Scegli una categoria</span>
    </span>
</div>

CSS:

select option[disabled] { color: #000; font-weight: bold }

This code works only with Firefox and doesn't work with Chrome and IE (all version).

Any idea to solve this problem?

Below the html code for select-box

<div class="formBody"><select  name="form[categoria][]"  id="categoria"  class="rsform-select-box" ><option selected="selected" value="">Scegli una categoria</option><option disabled="disabled" value="">Impresa </option><option  value="Servizi">Servizi</option><option  value="Informatica">Informatica</option><option  value="Commercio">Commercio</option><option  value="Telecomunicazioni">Telecomunicazioni</option><option  value="Editoria/Stampa">Editoria/Stampa</option><option  value="Meccanica/Elettrica">Meccanica/Elettrica</option><option  value="Alimentare">Alimentare</option><option  value="Chimica/Farmaceutica">Chimica/Farmaceutica</option><option disabled="disabled" value="">Edilizia </option><option  value="Tessile/Moda">Tessile/Moda</option><option  value="Mobili/Arredamenti">Mobili/Arredamenti</option><op