No legible magnification. If you just want a guess it looks like the patch left behind by a bacteria that was once stuck to the grid film. Once stained extracellular secretions are then hit by an electron beam the residue doesn't look like much. Maybe you washed most of the bacteria away during preparation and staining procedures?

It is difficult to determine whether the TEM image is of a damaged bacteria or just contamination due to staining without more information. However, negative staining for transmission electron microscopy (TEM) has been the “gold standard” for imaging microbial samples. Samples to be analyzed using a TEM must have very thin sections. But cells are too soft to cut thinly, even with diamond knives. To cut cells without damage, the cells must be embedded in plastic resin and then dehydrated through a series of soaks in ethanol solutions (50%, 60%, 70%, and so on).

https://www.researchgate.net/profile/Chuck-Arize is right about thin sectioning. It's the best. Negative stain is a good and quick way for very small microbes such as viruses. Mycoplasma and small bacteria also work reasonably well. Dirt from larger negative stained particles can start to contaminate some TEMs if used very regularly. For larger bacteria, such as those in fish gut thin sections are essential.

For bacteria culture + antibiotic SEM works better (and much easier to use).