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Table 5 Breakpoint values of antimicrobial agents according to CLSI, 2011 and phenotypic antimicrobial susceptibility profiles of E. coli isolates used in this study

From: Occurrence of Salmonella enterica and Escherichia coli in raw chicken and beef meat in northern Egypt and dissemination of their antibiotic resistance markers

Antibiotic class

Antimicrobial agent

Conc. (μg)

Zone diameter (9)

E. coli (21)

Resistance rate

Poultry (15)

Beef (6)

Total (21)

Poultry

Beef

Total

R

I

S

R

I

S

R

I

S

R

I

S

%

%

%

Penicillin

Amoxycillin–clavulanic acid

20

≤ 13

14–17

≥ 18

10

4

1

3

3

–

13

7

1

66.7

50.0

61.9

Ampicillin

10

≤ 13

14–16

≥ 17

12

2

1

3

3

–

15

5

1

80.0

50.0

71.4

Cephalosporin

Cefotaxime

30

≤ 22

23–25

≥ 26

6

7

2

1

3

2

7

10

4

40.0

16.7

33.3

Cefpodoxime

20

≤ 17

18–20

≥ 21

3

12

–

2

4

–

5

16

–

20.0

33.3

23.8

Ceftazidime

30

≤ 17

18–20

≥ 21

5

9

1

–

6

–

5

15

1

33.3

0

23.8

Ceftriaxone

30

≤ 19

20–22

≥ 23

3

5

7

1

3

2

4

8

9

20.0

16.7

19.0

Miscellaneous

Chloramphenicol

30

≤ 12

13–17

≥ 18

3

9

3

1

1

4

4

10

7

20.0

16.7

19.0

Colistin

10

≤ 11

12–13

≥ 14

–

1

14

–

–

6

–

1

20

–

–

–

Fluoroquinolone

Ciprofloxacin

5

≤ 15

16–20

≥ 21

4

3

8

2

2

2

6

5

10

26.7

33.3

28.6

Enrofloxacin

5

≤ 17

18–20

≥ 21

2

5

8

1

4

1

3

9

9

13.3

16.7

14.3

Nalidixic acid

30

≤ 13

14–18

≥ 19

5

12

3

1

2

3

6

14

6

33.3

16.7

28.6

Aminoglycoside

Streptomycin

10

≤ 11

12–14

≥ 15

9

5

1

4

2

–

13

7

1

60.0

66.7

61.9

Tetracycline

Tetracycline

30

≤ 11

12–14

≥ 15

12

3

–

5

1

–

17

4

–

80.0

83.3

81.0

Sulphonamide

Trimethoprim/sulphamethoxazole

25

≤ 4

3

≥ 2

10

2

3

3

–

3

17

2

6

66.7

50.0

81.0

  1. S sensitive, I intermediate, R resistant