Appendix A Intrinsic, implied and default resistance
Magiorakos et al. [1] and CLSI [2] are our primary sources of information on intrinsic resistance.
Sanford et al. [3] and Gilbert et al. [4] have been used to fill in missing susceptibilities,
but do not distinguish between acquired and instrinsic resistance. In cases where Sanford
et al. [3] and Gilbert et al. [4] indicate resistance we therefore rely on other sources to
distinguish between intrinsic and acquired resistance. These sources are explicitly acknowledged
in the following notes, as are instances of disagreement among our primary sources:
•Amoxicillin and penicillin: Amoxicillin is similar to ampicillin [5], and penicillin does
not cover Gram-negative bacilli [6].
•Enterobacteriacea: We assume that all Enterobacteriaceae resistant to ceftriaxone,
cefazolin or cefotaxime produce ESBLs, AmpC beta-lactamases, or KPCs, and are
therefore resistant to flouroquinolones, trimethaprim-sulfamethoxazole, penicillins,
cephalosporins, cephamycins, and β-lactam/lactamase inhibitor combinations [4, 7,
8]. We assume that all Enterobacteriaceae resistant to carbapenems produce KPCs,
and are therefore also resistant to chloramphenicol [4, 8]. CLSI [2] provides breakpoints
for Polymyxin B, and FDA drug labels indicate susceptibility among E. coli, Enterobacter
aerogenes, and Klebsiella pneumoniae strains. We assume that resistance to cephalexin
among Enterobacter spp. and Serratia marcescens strains [3, 4] is intrinsic, and that
all strains are intrinsically resistant to oxacillin and cloxacillin [5].
•Pseudomonas aeruginosa: CLSI [2] suggests that P. aeruginosa is intrinsically resistant
to fosfomycin, but Magiorakos et al. [1] does not. We follow Magiorakos et al. [1].
FDA labels and Sanford et al. [3] suggest that some strains were once susceptible to
ceftriaxone, but we follow CLSI [2] and assume intrinsic resistance. We also assume
that resistance to the following drugs [3, 4] is intrinsic: nitrofurantoin, tigecycline,
ampicillin, cefotaxime, cephalexin, oxacillin, cloxacillin and ceftaroline.
