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. 2018 Nov 28;32(1):e00037-18. doi: 10.1128/CMR.00037-18

TABLE 2.

Structural determination of β-lactam antibiotics (ampicillin, piperacillin, cefotaxime, ceftazidime, ceftriaxone, cefpodoxime, cefepime, ertapenem, meropenem, and imipenem) and their corresponding hydrolyzed forms, defining the susceptibility and resistance patternsa by MALDI-TOF MSb

Antibiotic MW
(g/mol)c 		Susceptibility pattern (Da)
 Resistance pattern (Da)
[M +
H]+ 		[M +
Na]+ 		[M +
2Na]+ 		[M +
3Na]+ 		[M +
K]+ 		[M + Na
+ K]+ 		[M + Cd
+ H]+ 		[M − X
+ H]+ 		[M – Xe −
CO + H]+ 		[M – X – CO
− CO2 + H]+ 		[Mhydrol
+ H]+ 		[Mhydrol
+ Na]+ 		[Mhydrol
+ 2Na]+ 		[Mhydrol
+ Na +
K]+ 		[Mhydrol
− CO2 +
H]+ 		[Mhydrol
− CO2 +
Na]+ 		[Mhydrol
− CO2 +
K]+ 		[Mhydrol
− X + H]+ 		[Mhydrol
− X − CO2
+ H]+
Ampicillin 349.4 350.4 372.4 394.4 368.4 390.4 412.4 324.4
Piperacillin 517.5 518.5 540.5 562.5 536.5 558.5 580.5
Cefotaxime 455.5 456.5 478.5 396.5 414.5 370.5
Ceftazidime 546.6 547.6 468.6 486.6 442.6
Ceftriaxone 554.6 555.6 577.6 616.6 396.6 368.6 324.6 414.6 370.6
Cefpodoxime 427.5 428.5 450.5 473.5 466.5 414.5 370.5
Cefepime 480.6 481.6 296.6 414.6 370.6
Ertapenem 475.5 476.5 498.5 520.5 542.5 514.5 536.5 494.5 516.5 538.5 554.5 450.5 472.5 488.5
Meropenem 383.4 384.5 406.5 428.5
Imipenem 299.4 300.4 489.4
a

The terms susceptibility and resistance by MALDI-TOF MS refer to the characteristic mass peak pattern of the antibiotic without modifications and to its corresponding hydrolyzed form. Mhydrol, hydrolysis.

b

See references 47 and 55.

c

MW, molecular weight.

d

Imipenem is complexed with the matrix (α-cyano-4-hydroxy-cinnamic acid), resulting in a peak that is the summation of their molecular masses.

e

X, acetyl for cefotaxime, pyridine for ceftazidime, triazin-ythiol for ceftriaxone, methoxy for cefpodoxime, and pyrrolidine for cefepime.