Selection of relevant antimicrobial agents is based on the criteria outlined in Box 1. These criteria should be carefully considered when antimicrobial agents are selected to avoid cluttering reports with superfluous information, to minimize the risk of confusing physicians, and to substantially decrease the waste of time and resources in the clinical microbiology laboratory.
Box1. Criteria for Antimicrobial Battery Content and Use
Antimicrobial agents that may be considered for inclusion in batteries to be tested against certain bacterial groups are provided in Table 1. The list is not exhaustive but is useful for illustrating some points about the development of relevant testing batteries. For example, with all the penicillins, cephalosporins, and other beta lactam antibiotics available for testing, only penicillin and oxacillin need to be tested against staphylococci. The information acquired with these two agents reflects the general effectiveness of any other beta-lactam. In essence, these drugs are predictor agents, as discussed earlier in this chapter. Similarly, ampicillin can be used independently as an indicator of enterococcal susceptibility to various penicillins, and because of intrinsic resistance, cephalosporins should never be tested against these organisms.
Table1. Selection of Antimicrobial Agents for Testing Against Common Bacterial Groups*
In contrast to the relatively few agents that may be included in testing batteries for gram-positive cocci, several potential choices exist for use against gram negative bacilli. This is mostly due to the commercial availability of several β-lactams with similar activities against Enterobacteriaceae and the general inability of one β-lactam to serve as a reliable predictor drug for other β-lactams. For example, an organism resistant to cefazolin may or may not be resistant to cefotetan, and an organism resistant to cefotetan may or may not be resistant to ceftazidime. With the lack of potential for selecting a predictor drug in these instances, more agents must be tested. However, in some instances overlap in activities does exist, so some duplication of effort can be avoided. For example, the spectra of activity of ceftriaxone and cefotaxime are sufficiently similar to allow the use of one in the testing battery.
Many scenarios exist in which the spectrum of activity and other criteria listed in Box 1 are considered for the sake of designing the most relevant and useful testing batteries. These criteria should be considered in consultation with patients’ physicians and the pharmacy staff.
