TABLE 2.
Fosfomycin disk diffusion testing of 199 isolates of Enterobacterales other than E. coli and 90 isolates of nonfermenting Gram-negative bacilli
| Pathogen (no. of isolates) | EUCAST ZD, mm |
ZD interpretationa (%) |
Test method agreement and error rates (%) |
CLSI ZD, mm |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| ZD50b | ZD90c | Ranged | Susceptible | Resistant | CAe (n) | MEf (n) | VMEg (n) | ZD50 | ZD90 | Range | |
| Enterobacterales (199) | 23 | 15 | 6–37 | 80.4 | 19.6 | 87.9 (175/199) | 3.4 (5/146) | 35.8 (19/53) | 20 | 7 | 6–37 |
| Enterobacter cloacae (32) | 25 | 20 | 19–35 | 84.4 | 15.6 | 75.0 (24/32) | 4.8 (1/21) | 63.6 (7/11) | 19 | 9 | 6–30 |
| Klebsiella aerogenes (21) | 23 | 20 | 6–30 | 85.7 | 14.3 | 85.7 (18/21) | 5.9 (1/17) | 50.0 (2/4) | 20 | 16 | 6–29 |
| Klebsiella oxytoca/Raoultella spp. (30) | 24 | 22 | 22–32 | 100 | 0 | 93.3 (28/30) | 0 (0/28) | 100 (2/2) | 22 | 17 | 12–28 |
| Klebsiella pneumoniae (51) | 22 | 18 | 12–29 | 80.4 | 19.6 | 82.4 (42/51) | 5.7 (2/35) | 56.3 (9/16) | 18 | 14 | 9–28 |
| Morganella morganii (15) | 6 | 6 | 6–13 | 0 | 100 | 100 (15/15) | NAh | 0 (0/15) | 6 | 6 | 6–11 |
| Proteus mirabilis (20) | 34 | 15 | 6–37 | 75.0 | 25.0 | 100 (20/20) | 0 (0/15) | 0 (0/5) | 28 | 8 | 6–37 |
| Serratia marcescens (30) | 27 | 25 | 20–33 | 96.7 | 3.3 | 96.7 (29/30) | 3.3 (1/30) | NA | 24 | 18 | 12–32 |
| Acinetobacter baumannii (15) | 15 | 13 | 13–20 | 8 | 6 | 6–15 | |||||
| Pseudomonas aeruginosa (50) | 18 | 6 | 6–38 | 16 | 6 | 6–35 | |||||
| Stenotrophomonas maltophilia (25) | 15 | 12 | 6–22 | 11 | 6 | 6–20 | |||||
EUCAST zone diameter breakpoints (susceptible, ≥21 mm; resistant, <21 mm [4]) apply to isolates of Enterobacterales and intravenous use of fosfomycin.
ZD50, zone diameter at which 50% of isolates were inhibited.
ZD90, zone diameter at which 90% of isolates were inhibited.
Additional information regarding EUCAST zone diameter measurements; 97.8% (180/184) of all isolates of Enterobacterales tested that produced a zone of inhibition had ≥1 colony within the zone of inhibition, and 83.2% (153/184) of all isolates tested that produced a zone of inhibition had ≥10 colonies within the zone of inhibition; 100% (15/15) of all isolates of Acinetobacter baumannii tested had ≥1 colony within the zone of inhibition; 93.3% (14/15) of all isolates tested had ≥10 colonies within the zone of inhibition; 54.5% (24/44) of all isolates of Pseudomonas aeruginosa tested that produced a zone of inhibition had ≥1 colony within the zone of inhibition; 29.5% (13/44) of all isolates tested that produced a zone of inhibition had ≥10 colonies within the zone of inhibition; 95.8% (23/24) of all isolates of Stenotrophomonas maltophilia tested that produced a zone of inhibition had ≥1 colony within the zone of inhibition; 87.5% (21/24) of all isolates tested that produced a zone of inhibition had ≥10 colonies within the zone of inhibition.
CA, categorical agreement. The number of isolates included in calculation appears in brackets after the percentage. CA was calculated using agar dilution as the reference method.
ME, major errors. The number of isolates included in calculation appears in brackets after the percentage. The ME rate was calculated using agar dilution as the reference method.
VME, very major errors. The number of isolates included in calculation appears in brackets after the percentage. The VME rate was calculated using agar dilution as the reference method.
NA, not applicable.