TABLE 1.

Stratification of isolates included in this study into phenotypic groups

Group	No. of isolates	% per phenotype
All resistant isolates (with at least the pncA coding region sequenced)	2,760	100
Resistant isolates with PZase and its promoter sequenced	2,565	93
Resistant isolates only with mutations in PZase	2,187	79
Resistant isolates only with mutations in the promoter region of pncA	78	3
Resistant isolates with mutations in both the promoter and the open reading frame	12	0.4
Resistant isolates without a mutation in PZase	483	18a
All susceptible isolates (with at least the pncA coding region sequenced)	3,329	100
Susceptible isolates with pncA and its promoter sequenced	3,207	96
Susceptible isolates only with mutations in PZase	307	6
Susceptible isolates only with mutations in the promoter region of pncA	14	0.4
Susceptible isolates with mutations in both the promoter and the open reading frame	0	0
Susceptible isolates without a mutation in PZase or the promoter region	3,022	91

^aIt is important to recognize that not all the isolates in this group are considered “unexplained resistance” cases. These percent values have been calculated with respect to all isolates with a pncA sequence of the same phenotype. Because not all isolates included an analysis of the promoter region, some of these isolates may harbor a mutation in the promoter region and therefore are not in the unexplained resistance group.