Ideally, doctors would have two bits of information available to guide antibiotic therapy: bacterial identification and antibiotic susceptibility. Not all antibiotics work on all types of bacteria. In particular, Gram-negative bacteria (those with an outer membrane covering their cell wall) are treatable with fewer and different antibiotics than Gram-positive bacteria (those with a naked cell wall). Within those two categories, optimal antibiotics vary by species.
In the era before widespread antibiotic resistance, bacterial identification was sufficient to insure appropriate antibiotic treatment in the vast majority of cases. This is no longer the case, although doctors and hospitals have been slow to recognize the new reality. Resistance rates for first-line antibiotics are now commonly 30-60%. Doctors have responded to these high levels of resistance by treating ALL infections with broad-spectrum antibiotics. One of these, vancomycin, is now the most commonly prescribed drug in US hospitals. The inevitable consequence of this behavior is to hasten the day when these antibiotics are no longer effective.
In the best-case scenario, doctors would have (and use) timely antibiotic susceptibility results in addition to identification results, so that they would prescribe broad-spectrum antibiotics only to patients whose infections are resistant to narrow-spectrum antibiotics. This would not only preserve the usefulness of broad-spectrum antibiotics, but result in better patient outcomes.
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