This is the 13180th most frequent Russian word.
микроорганизмами
"Microorganisms" – microscopic organisms, such as bacteria, viruses, fungi, or protozoa.
Here, 'микроорганизмы' (microorganisms) is the subject of the sentence, indicating what was discovered.
На поверхности воды были обнаружены микроорганизмы.
Microorganisms were found on the water's surface.
In this sentence, 'микроорганизмами' (microorganisms) is in the instrumental case, used to describe the means (tools or entities) involved in combating.
Борьба с вредоносными микроорганизмами - важная задача медицины.
Combating harmful microorganisms is an important medical task.
Here, 'микроорганизмов' (microorganisms) is in the genitive case, specifying the target of the medicine's effectiveness.