TABLE 1

Site-specific ranked cefazolin MICs at SI and HI with associated blaZ gene types and CInEa

SiteNo. (%) of isolates:Cefazolin MIC24 value for:No. (%) of isolates:
SI (105 CFU/ml); HI (107 CFU/ml)bla positive [n = 196 (73)]With blaZ gene type:Presenting InEb :
TotalUsing either definition [n = 45 (23)]Using each definitionc:
≥4-fold increase in MIC [n = 44 (22)]Pronounced InE [n = 5 (3)]
Collected (n = 308)Excluded (n = 39)Included (n = 269)MedianModeMIC90RangeABCDNegABCDNegABCDNegABCDNeg
181 (26)1269 (26)0.5; 1.00.5; 0.52.0; 4.00.25–8; 0.25–1652 (75)17 (25)3 (4)30 (43)2 (3)17 (25)14 (20)8 (12)0 (0)5 (7)1 (1)0 (0)7512d1e
268 (22)563 (23)0.5; 1.00.5; 21.0; 2.00.125–2; 0.125–448 (76)14 (22)8 (13)26 (41)0 (0)15 (24)11 (17)4 (6)1 (2)6 (10)0 (0)0 (0)416
381 (26)378 (29)0.5; 1.00.5; 11.0; 2.00.0625–4; 0.25–3255 (71)14 (18)11 (14)30 (39)0 (0)23 (29)14 (18)3 (4)0 (0)11 (14)0 (0)4 (5)31141e1e1e
478 (26)1959 (22)0.5; 1.00.5; 0.51.0; 2.00.625–2; 0.25–241 (69)16 (27)3 (5)22 (37)0 (0)18 (31)6 (10)2 (3)1 (2)3 (5)0 (0)1 (2)2131
P value0.660.380.0001; 0.012f0.520.25
  • a CInE, cefazolin inoculum effect; MIC24, MIC read at 24 h; SI, standard inoculum; HI, high inoculum; bla, β-lactamase gene.

  • b Instances of InE associated with bla-positive isolates.

  • c Definitions of InE used are as follows: isolates presenting (i) a ≥4-fold increase in cefazolin MIC between SI and HI and/or (ii) a pronounced InE represented by a nonsusceptible cefazolin MIC of ≥16 μg/ml at HI.

  • d Isolated from an abscess.

  • e Isolated from a wound.

  • f For SI, the ranked MIC was significantly higher at site 1 than at sites 2, 3, and 4 (adjusted P values of 0.02, 0.0035, and 0.0001, respectively); for HI, the ranked MIC was significantly higher at site 1 than at site 4 (adjusted P value of 0.006).