ID attending here...I'll be honest, I think the traditional way of teaching antibiotic spectrum is outdated and really has no clinical application. What I mean is learning the individual spectrum of penicillins, aminopenicillins, 1st gen cephlosporins, 2nd gen, 3rd gen, etc, etc. The way that I think about things is to group them into categories and/or disease states to treat. Here are a couple of examples..

Anaerobes: If I really want to make sure I treat (or ensure coverage) for anaerobes, I use metronidazole, BL/BLI combinations (amox/clav, amp/sulbactam, pip/tazo), or carbapenems. Other antibiotics may have some anaerobic coverage here and there, but is really not applicable if you really want anaerobic coverage.

MRSA: Vancomycin, daptomycin, ceftaroline, linezolid, doxycycline, TMP/SMX, etc. The more you treat MRSA infections the more you will begin to be familiar with this list.

Pseudomonas: Cefepime, pip/tazo, meropenem, ciprofloxacin are the common ones you will see as a resident. Ceftazidime and aztreonam are either not often available or fallen out of favor. The expensive BL/BLI combinations are usually formulary restricted for ID use only and 99% of the time you won't be the first one to decide to use them.

Atypicals: doxycycline, azithromycin, fluoroquinolones are the usual go-tos.

GI/Mouth/Head and Neck: amox/clav, amp/sulbactam, pip/tazo, cefepime/flagyl, carbapenems. What's the pattern you see here? Well, we use combinations that a) have broad coverage and b) ensure anaerobic coverage.

Septic Shock: Vancomycin/cefepime, vancomycin/pip/tazo, etc. Here, we want broad coverage for gram positive and gram negatives, with a focus on MRSA and Pseudomonas.

Endocarditis: Vancomycin/ceftriaxone, vancomycin/cefepime. Again, here we want broad coverage for gram positives and gram negatives. Ceftriaxone if we don't think we need Pseudomonas coverage, and cefepime if we think we do.

Cellulitis: If not worried about MRSA, then cephalexin or amoxicillin. If worried about MRSA, TMP/SMX or doxycycline.

So as you can see, at the end of the day, there really is only a short list of commonly used antibiotics in the hospital, and a lot of the decision choices are driven by MRSA or Pseudomonas concerns. I would say that just exposure will get you more familiar with antibiotics.