AST Pattern of Bacteria: Introduction, Group of AST Pattern, List of

AST Pattern of Bacteria

Table of Contents

AST Pattern of Bacteria covers common bacterial pathogens groups like Enterobacteriaceae, Staphylococcus, Enterococcus, Pseudomonas aeruginosa, Streptococcus pneumoniae, beta-haemolytic streptococci (Streptococcus pyogenes, Streptococcus agalactiae), Haemophilus species, Acinetobacter, Viridans group of streptococci, Shigella, and Neisseria species.

Antibiotic Susceptibility Testing (AST)-Kirby-Bauer Disk Diffusion Method — Fig. Antibiotic Susceptibility Testing (AST) of Bacteria-Kirby-Bauer Disk Diffusion Method

Enterobacteriaceae

Antimicrobial Agents- Zone Diameter (Intermediate)

Ampicillin (10 μg) : 14-16 mm
Ceftriaxone (30 μg): 20-22
Ciprofloxacin(5 μg): 16-20
0floxacin (Salmonella,5 μg):21-30
Co-trimoxazole(1.25/23.75 μg): 11-15
Chloramphenicol (except urine, 30 μg): 13-17
Nitrofurantoin (only urine,300 μg ): 15-16
Gentamicin (10 μg): 13-14
Amikacin (30 μg ): 15-16
Cefotaxime (30 μg): 23-25
Cefuroxime (oral, 30): 15-22
Cefixime (oral, 5 μg):16-18
Doxycycline (30 μg): 11-13
Nalidixic acid (30 μg): 14-18 (don’t report I)
Meropenem (10 μg): 20-22 (Ignore for Salmonella
and Shigella spp.)
Azithromycin (Only for S. Typhi, 15 μg): ≥13

Extra

Amoxycillin clavulanate (20/10 μg): 14-17
Ampicillin-sulbactam (10/10 μg): 12-14
Piperacillin-tazobactam (100/10 μg): 18-20
Cefepime (30 μg): 19-24
Ceftazidime (30 μg): 18-20
Cefoperazone (75 μg): 16-20
Aztreonam (30 μg): 18-20
Imipenem (10 μg): 20-22
Levofloxacin(5 μg): 14-16
Tobramycin (10 μg): 13-14

AST Pattern of Enterobacteriaceae -E. coli — Fig. AST Pattern of Enterobacteriaceae –*E. coli* (uropathogen)

Staphylococcus species

Fig. Staphylococcus antimicrobial sensitivity testing

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Penicillin (10 U) : ≥29

Cefoxitin (30 µg): ≥ 22 (S. aureus)

Cefoxitin (30 µg): ≥ 25 (CoNS)

Ciprofloxacin (5 µg): 16-20

Ofloxacin (5 µg):15-17

Levofloxacin (5 µg): 16-18

Co-trimoxazole (1.25/23.75 µg): 11-15

Chloramphenicol (except urine, 30 µg): 13-17

Nitrofurantoin (only urine,300 µg): 15-16

Gentamicin (10 µg): 13-14

Azithromycin (15 µg): 14-17

Erythromycin (15 µg): 14-17

Doxycycline (30 µg): 13-15

Clindamycin (2 µg): 15-20

Vancomycin (MIC≤2):4-8 (S. aureus)

Vancomycin (MIC≤4):8-16 (CoNS)

Teicoplanin (MIC≤8):16

Linezolid (30 µg): ≥29

Ceftaroline (30 µg): 21-23 (for MRSA)

Keynotes on AST Pattern of Bacteria

Novobiocin (): S. saprophyticus is intrinsically resistant to novobiocin.

Inducible clindamycin resistance can be detected by disk diffusion using the D-zone test.
MRSA/MRS: They are considered resistant to other ß-lactam agents, i.e., penicillin, ß-lactam/ ß-lactamase inhibitor combination, cephems (with the exception of cephalosporins with anti-MRSA activity), and carbapenems.

Cefoxitin is a screening drug and therefore do not report.

Determining vancomycin Etest MIC in patient with MRSA — Fig. Determining vancomycin Etest MIC in patients with MRSA

Enterococcus species

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Penicillin (10 U): ≥15

Ampicillin (10 µg): ≥17

Ciprofloxacin (5 µg): 16-20

Norfloxacin (10 µg):13-16

Levofloxacin (5 µg): 14-16

Chloramphenicol (except urine, 30 µg): 13-17

Nitrofurantoin (only urine,300 µg): 15-16

Erythromycin (15 µg): 14-22

Doxycycline (30 µg): 13-15

Vancomycin (30 µg): 15-16

Teicoplanin (30 µg): 11-13

Linezolid (30 µg): ≥21-22

Gentamicin (HLG,120 µg): 7-9

Fig. Enterococcus Antimicrobial Susceptibility Testing (AST) Pattern

Pseudomonas aeruginosa

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Ciprofloxacin (5 µg): 16-20

Ofloxacin (5 µg):13-15

Levofloxacin (5 µg): 14-16

Gentamicin (10 µg): 13-14

Tobramycin (10 µg): 13-14

Amikacin (30 µg): 15-16

Aztreonam (30 µg): 16-21

Meropenem (10 µg): 16-18

Imipenem (10 µg): 16-18

Piperacillin (100 µg): 15-20

Piperacillin tazobactam (100/10 µg): 15-20

Ceftazidime (30 µg): 15-17

Cefepime (30 µg): 15-17

Colistin (10 µg): MIC≤2

Polymyxin B (300U): MIC≤2

Fig. Pseudomonas aeruginosa Antimicrobial Sensitivity Testing (AST) Pattern

Extrinsic Resistance

Amoxicillin-clavulanate

Ampicillin

Amoxicillin

Ampicillin-sulbactam

Azithromycin

Cefotaxime

Ceftriaxone

Trimethoprim

Cephalosporin I (Cephalothin, cefazolin)

Cephamycins (cefoxitin, cefotetan)

Chloramphenicol

Clarithromycin

Ertapenem

Erythromycin

Tetracycline

Trimethoprim-sulfamethoxazole

Cephalosporin II (Cefuroxime)

Streptococcus pneumoniae

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Oxacillin (1 µg): ≥20 (screening drug, do not report)

0floxacin (5 µg):13-15

Levofloxacin (5 µg): 14-16

Chloramphenicol (30 µg): ≥ 21

Erythromycin (15 µg): 16-20

Azithromycin (15 µg): 14-17

Doxycycline (30 µg): 25-27

Vancomycin (30 µg): ≥ 17

Clindamycin (2 µg): 16-18

Co-trimoxazole (1.25/23.75 µg): 16-18

Linezolid (30 µg): ≥21

Streptococcus pneumoniae AST Pattern — Fig. *Streptococcus pneumoniae* AST Pattern

Keynotes on AST pattern of bacteria-

For non-meningitis isolates, oxacillin zone ≥20 mm can predict susceptibility to the following lactams- ampicillin, ampicillin-sulbactam, Amoxycillin, amoxicillin-clavulanate, cefaclor, cefdinir, cefditoren, cefepime, cefotaxime, cefpodoxime, cefprozil, ceftaroline, ceftizoxime, ceftriaxone, cefuroxime, doripenem, ertapenem, imipenem, loracarbef, meropenem, and penicillin.
For isolates with oxacillin zones less than 19 mm, do not report penicillin as resistant without performing a penicillin MIC test.

Streptococcus species (ß-Haemolytic Group)

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Penicillin (10 U): ≥24 or

Ampicillin (10 µg): ≥24

Cefotaxime (30 µg): ≥24 or

Ceftriaxone (30 µg): ≥24

Vancomycin (30 µg): ≥ 17

Azithromycin (15 µg): 14-17

Erythromycin (15 µg): 16-20

Tetracycline (30 µg):19-22

Levofloxacin (5 µg): 14-16

0floxacin (5 µg):13-15

Chloramphenicol (30 µg): 18-20

Clindamycin (2 µg): 16-18

Linezolid (30 µg): ≥21

Keynotes on AST Pattern of Bacteria-

Penicillin and ampicillin are drugs of choice for the treatment of beta-hemolytic streptococcal infection.

Non-susceptible isolates (i.e., penicillin MICs>0.12 µg/mL and ampicillin MICs >0.25 µg/mL) are extremely rare in any ß-haemolytic streptococcus and have not been reported for Streptococcus pyogenes.

This type of isolate should be re-identified and retested in such a scenario. For confirmation, it should be submitted to the national public health laboratory.

Streptococcus agalactiae Antibiogram Pattern — Fig. *Streptococcus agalactiae* Antibiogram Pattern

Haemophilus influenzae/ parainfluenzae

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Ampicillin (10 µg): 19-21

Ampicillin-sulbactam (10/10 µg): ≥ 20

Amoxycillin clavulanate (20/10 µg): 14-17

Piperacillin tazobactam (100/10 µg): ≥21

Ceftazidime (30 µg): ≥26

Cefotaxime (30 µg): ≥26

Ceftriaxone (30 µg): ≥26

Cefuroxime (oral, 30): 17-19

Cefepime (30 µg): ≥26

Aztreonam (30 µg): ≥26

Imipenem (10 µg): ≥16

Meropenem (10 µg): ≥20

Levofloxacin (5 µg): ≥17

Ciprofloxacin (5 µg): ≥21

Ofloxacin (5 µg): ≥16

Co-trimoxazole (1.25/23.75 µg): 11-15

Chloramphenicol (except urine, 30 µg): 26-28

AST Pattern of Bacteria-Haemophilus influenzae — Fig. AST Pattern of Bacteria-*Haemophilus influenzae*

Acinetobacter spp.

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Ciprofloxacin (5 µg): 16-20

Levofloxacin (5 µg): 14-16

Co-trimoxazole (1.25/23.75 µg): 11-15

Doxycycline (30 µg): 10-12

Gentamicin (10 µg): 13-14

Tobramycin (10 µg): 13-14

Amikacin (30 µg): 15-16 Colistin (10 µg): MIC≤2

Polymyxin B (300U): MIC≤2

Meropenem (10 µg): 15-17

Imipenem (10 µg): 19-21

Piperacillin (100 µg): 18-20

Piperacillin tazobactam (100/10 µg): 18-20

Ceftazidime (30 µg): 15-17

Cefepime (30 µg): 15-17

Cefotaxime (30 µg): 15-22

Ceftriaxone (30 µg): 14-20

Ampicillin-sulbactam (10/10 µg): 12-14

Acinetobacter Antimicrobial Susceptibility Testing (AST) — Fig. *Acinetobacter* Antimicrobial Susceptibility Testing (AST)

Extrinsic Resistance

Amoxicillin-clavulanate

Ampicillin

Amoxicillin Azithromycin Aztreonam Fosfomycin

Cephalosporin I (Cephalothin, cefazolin)

Cephalosporin II (Cefuroxime)

Chloramphenicol

Clarithromycin

Ertapenem

Erythromycin

Trimethoprim

Cephamycins (cefoxitin, cefotetan)

Streptococcus spp. Viridans Group

Antimicrobial Agents Zone Diameter (Intermediate, mm)

Penicillin (MIC) :≤0.12 or
Ampicillin (MIC): ≤ 0.25
Cefotaxime (30 μg): 26-27 or
Ceftriaxone (30 μg): 25-26
Vancomycin (30 μg): ≥ 17
Azithromycin (15 μg): 14-17
Erythromycin (15 μg): 16-20
Tetracycline (30 μg):19-22
Levofloxacin (5 μg): 14-16
0floxacin (5 μg):13-15
Chloramphenicol (30 μg): 18-20
Clindamycin(2 μg): 16-18
Linezolid (30 μg): ≥21
Meropenem (MIC): ≤0.5

AST Pattern of Bacteria: Introduction, Group of AST Pattern, List of Antimicrobial Agents, and Keynotes