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I have developed a habit of keeping culture plates always inverted, especially those of non-selective media. This precaution is followed after the poured plate is placed inverted in the incubator for 24hr to dry and test for contaminants. The reason is that I'm afraid when the plate is opened for streaking or subculturing, some contaminants might fall on the lid which is not given as much care as the dish itself when used for inoculation or subculturing: as the lid is kept on the bench underneath the bunsen flame. I fear that such possible contaminants might fall from the lid when the plate is kept upright on a surface, as I need when taking pictures of the cultures.

My fear might be right in theory, but i hope I'm missing something that would make such a scenario practically impossible.

Question

Can placing a culture plate upright, as for taking pictures, introduce contaminants from the lid?

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Are you careful not to have your arms/hands over the lid when you inoculate your plate ? If yes, then I would not worry. But the best way to know if you worked clean enough is to have a control handled in the same conditions (and non inoculated of course). You said "the lid is kept on the bench under the Bunsen flame" right ?

The habit of keeping media plates upside-down is mainly to prevent condensation from flooding your inoculum.

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    $\begingroup$ If condensation can fall, so do spores/cells. I meant to say the lid is placed on the bench with the side that normally faces the base being upward. $\endgroup$
    – Freezing Soul
    Commented Jan 20 at 7:17
  • $\begingroup$ I would say that if your lid is not clean, whether the plate is upside-down or not will not matter. $\endgroup$
    – CaroZ
    Commented Jan 20 at 18:14
  • $\begingroup$ -Upside-down: contaminants would have to go against gravity to reach the culture -Upright: ......... with gravity $\endgroup$
    – Freezing Soul
    Commented Jan 20 at 19:15
  • $\begingroup$ Why don't you just try ? $\endgroup$
    – CaroZ
    Commented Jan 21 at 23:45
  • $\begingroup$ What if its a borderline theoretical concern: has 10% of practical occurrence? $\endgroup$
    – Freezing Soul
    Commented Jan 22 at 14:02

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