Table 1 Effect of 12 β-lactam antibiotics or β-lactam–β-lactamase inhibitor combinations on antibiotic-induced filamentation (AIF) of three E. coli strains. The antibiotic concentrations of which filamentation is induced are given, if not detected for all concentrations (All) or if no filamentation is detected (N.D.; not detected). In addition, MIC values and the time required to detect them are included (time-to-result in minutes; TTR, (mean ± SE))

β-lactam antibiotics or β-lactam–β-lactamase inhibitor combinations

AIF

MIC

TTR

AIF

MIC

TTR

AIF

MIC

TTR

conc.

(min)

conc.

(min)

conc.

(min)

ampicillin/sulbactam 2:1 ratio

2/1–8/4

4/2

97 ± 3.33

16/8

16/8

100 ± 0

2/1–8/4

≤2/1

113 ± 6.67

aztreonam

All

≤ 2

115 ± 5

N.D.

>16

65 ± 5

All

≤ 2

103 ± 1.67

carbenicillin

32–128

≤ 32

102 ± 1.67

N.D.

256

55 ± 5

All

≤ 32

60 ± 0

cefepime

2–4

≤ 2

103 ± 1.67

All

4

117 ± 3.33

2–4

≤ 2

132 ± 6.01

cefoperazone

All

≤ 4

117 ± 3.33

All

8

133 ± 6.67

All

≤ 4

155 ± 5

cefotaxime

4–8

≤ 4

102 ± 1.67

All

≤ 4

103 ± 1.67

4–8

≤ 4

93 ± 3.33

ceftazidime

All

≤ 1

133 ± 6.67

N.D.

>16

62 ± 1.67

All

≤ 1

117 ± 3.33

ceftriaxone

4–8

≤ 4

93 ± 3.33

All

≤4

115 ± 5

4–8

≤ 4

97 ± 3.33

piperacillin

All

≤ 8

103 ± 1.67

N.D.

>64

55 ± 5

All

≤ 8

163 ± 1.67

piperacillin/tazobactam constant four

All

≤ 8/4

113 ± 6.67

F

≤8/4

162 ± 1.67

All

≤ 8/4

115 ± 5

ticarcillin

All

≤ 8

123 ± 3.33

N.D.

>64

65 ± 5

All

≤ 8

100 ± 0

ticarcillin/clavulanic acid constant two

16/2–32/2

8/2

138 ± 1.67

N.D.

128/2

163 ± 1.67

16/2–64/2

≤ 16/2

102 ± 1.67