Antimicrobial Susceptibility Testing

Clinical Background

Resistance to antibiotics has increased over the last 25 years. Appropriate therapy is crucial for disease eradication. Susceptibility testing for specific antibiotics allows therapy based on sensitivities.

Organism group	Organisms	Drugs tested	Test/s to order
Enterococcus spp	Enterococcus	Ampicillin Chloramphenicol Daptomycin High-level Gentamicin High-level Streptomycin Levofloxacin Linezolid Nitrofurantoin Quinupristin & dalfopristin Tetracycline Vancomycin	0060708 Antimicrobial Susceptibility - Enterococcus Daptomycin upon request
Enteric gram-negative organisms	Citrobacter , Enterobacter, Serratia, Morganella and Providencia spp Proteus vulgaris, P. mirabilis, P. penneri Pantoea agglomerans, Klebsiella spp E. coli spp	Amikacin Amoxicillin/Clavulanic Acid Ampicillin Aztreonam Cefepime Ceftazidime Ceftriaxone Cefuroxime Cephalothin Ciprofloxacin Gentamicin Imipenem Levofloxacin Meropenem Nitrofurantoin Piperacillin/Tazobactam Ticarcillin/Clavulanic Acid Tobramycin Trimethoprim/Sulfamethoxazole	0060200 Antimicrobial Susceptibility -Not Otherwise Specified Tigecycline upon request OR 0060790 Automated Susceptibility Testing Possible additional testing: 0063999 Antimicrobial Susceptibility - Extended Spectrum Beta Lactamase for E. coli, Klebsiella and Proteus mirabilis (Currently no CLSI guidelines exist for testing other organisms for ESBL activity)
Diarrhea-causing Enteric gram-negative rods	Salmonella and/or Shigella	Fecal source: Amoxicillin/Clavulanic Acid Ampicillin Ceftriaxone Ciprofloxacin Extraintestinal source: Ampicillin Ceftriaxone Chloramphenicol Ciprofloxacin Nalidixic Acid Trimethoprim/Sulfamethoxazole	0060200 Antimicrobial Susceptibility - Not Otherwise Specified OR 0060790 Automated Susceptibility Testing
Streptococcus spp.	Streptococcus spp Groups A, B, C or G Large colony pyogenic strains	Ceftriaxone Clindamycin Doxycycline Erythromycin Levofloxacin Meropenem Penicillin Trimethoprim/Sulfamethoxazole Vancomycin	0060485 MIC Panel Viridans Strep
Viridans streptococcus spp	Viridans Streptococcus spp & small colony Beta-hemolytic strains of Group A, C, F or G	Ceftriaxone Clindamycin Daptomycin Doxycycline Erythromycin Gentamicin Levofloxacin Linezolid Meropenem Penicillin Rifampin Trimethoprim-sulfamethoxazole Quinupristin/Dalfopristin Vancomycin	0060222 Antimicrobial Susceptibility -Viridans Streptococcus
Streptococcus pneumoniae	S. pneumoniae	Ceftriaxone Clindamycin Daptomycin Doxycycline Erythromycin Gentamicin Levofloxacin Linezolid Meropenem Penicillin Rifampin Quinupristin/Dalfopristin Trimethoprim/Sulfamethoxazole Vancomycin	0060221 Antimicrobial Susceptibility - Streptococcus pneumoniae
Staphylococcus spp	Staphylococcus	Cephalothin Clindamycin Daptomycin Erythromycin Gentamicin Levofloxacin Linezolid Nitrofurantoin Oxacillin Penicillin Quinupristin/Dalfopristin Rifampin Tetracycline Trimethoprim/Sulfamethoxazole Vancomycin	0060707: Antimicrobial Susceptibility - Staphylococcus Daptomycin upon request Possible additional testing: 0060211 Antimicrobial Susceptibility - mecA Gene by PCR
Gram-positive rods	Bacillus, Lactobacillus, Corynebacterium spp & others)	Ceftriaxone Clindamycin Doxycycline Erythromycin Gentamicin Levofloxacin Meropenem Rifampin Trimethoprim/Sulfamethoxazole Vancomycin	0060346 Antimicrobial Susceptibility - Gram Positive Rod OR 0060200 Antimicrobial Susceptibility - Not Otherwise Specified
Unusual organisms gram-positive	Erysipelothrix rhusiopathiae	Ceftriaxone Clindamycin Erythromycin Levofloxacin Linezolid Meropenem Penicillin	0060200 Antimicrobial Susceptibility - Not Otherwise Specified
	Leuconostoc spp	Ceftriaxone Chloramphenicol Clindamycin Doxycycline Erythromycin Gentamicin Levofloxacin Linezolid Meropenem Penicillin	0060200 Antimicrobial Susceptibility - Not Otherwise Specified
	Pediococcus spp	Chloramphenicol Clindamycin Doxycycline Erythromycin Gentamicin Levofloxacin Linezolid Meropenem	0060200 Antimicrobial Susceptibility - Not Otherwise Specified
Aeromonas, Plesiomonas & Vibrio spp	Aeromonas, Plesiomonas & Vibrio spp (Not V. cholera)	Amoxicillin/Clavulanic Acid Ampicillin Ceftazidime Ceftriaxone Chloramphenicol Ciprofloxacin Doxycycline Gentamicin Meropenem Tetracycline Trimethoprim/Sulfamethoxazole	0060201 Antimicrobial Susceptibility - MIC, individual OR 0060200 Antimicrobial Susceptibility - Not Otherwise Specified
Non-fastidious glucose non-fermenting gram-negative bacilli	Pseudomonas spp Acinetobacter B. cepacia S. maltophilia	Amikacin Ampicillin/Sulbactam Aztreonam Cefepime Ceftazidime Chloramphenicol Ciprofloxacin Gentamicin Imipenem Levofloxacin Meropenem Minocycline Piperacillin/Tazobactam Ticarcillin/Clavulanic Acid Tobramycin Trimethoprim/Sulfamethoxazole	0060216 Antimicrobial Susceptibility - Nonfermenter Colistin upon request
Fastidious organisms		Ampicillin Amoxicillin/Clavulanic Acid Ampicillin/Sulbactam Azithromycin Ceftriaxone Cefuroxime Gatifloxacin Levofloxacin Meropenem Moxifloxacin Penicillin Tetracycline Trimethoprim/Sulfamethoxazole	0060345 Antimicrobial Susceptibility - Fastidious Organism
Fastidious gram-negative bacilli (respiratory pathogens)	Haemophilus, Moraxella, Oligella, Pasteurella spp	Amoxicillin/Clavulanic Acid Ampicillin Azithromycin Beta-lactamase Ceftriaxone Cefuroxime Gatifloxacin Meropenem Penicillin Tetracycline Trimethoprim/Sulfamethoxazole	0060201 Antimicrobial Susceptibility - MIC, individual
	Legionella pneumophila	Ciprofloxacin Erythromycin	0060201 Antimicrobial Susceptibility - MIC, individual
	Bordetella pertussis	Erythromycin Trimethoprim/Sulfamethoxazole	0060201 Antimicrobial Susceptibility - MIC, individual
Unusual gram-negative bacilli	HACEK	Amoxicillin/Clavulanic Acid Ampicillin Azithromycin Beta-lactamase Ceftriaxone Gatifloxacin Meropenem Trimethoprim/Sulfamethoxazole	0060201 Antimicrobial Susceptibility - MIC, individual
	C. jejuni/coli	Ciprofloxacin Doxycycline Erythromycin	0060201 Antimicrobial Susceptibility - MIC, individual
	C. fetus	Ampicillin Beta-lactamase Gentamicin	0060201 Antimicrobial Susceptibility - MIC, individual
	Capnocytophaga	Amoxicillin/Clavulanic Acid Ceftriaxone Clindamycin Gatifloxacin Meropenem Penicillin	0060201 Antimicrobial Susceptibility - MIC, individual
	H. pylori	Clarithromycin	0060201 Antimicrobial Susceptibility - MIC, individual
Anaerobes	Actinomyces spp	Ceftriaxone Clindamycin Penicillin G or Ampicillin	0060202 Antimicrobial Susceptibility - Anaerobe
	B. fragilis group	Ampicillin/Sulbactam Cefoxitin Clindamycin Meropenem Metronidazole Penicillin G or Ampicillin	0060202 Antimicrobial Susceptibility - Anaerobe
	not B. fragilis group	Ampicillin/Sulbactam Beta-lactamase Cefoxitin Ceftriaxone Clindamycin Meropenem Metronidazole Penicillin G or Ampicillin	0060202 Antimicrobial Susceptibility - Anaerobe
Yeasts and Molds	Mold	5-Fluorocytosine Amphotericin B Fluconazole Itraconazole Voriconazole	Antimicrobial Susceptibility - Mould Susceptibility 0060227
Yeasts and Molds	Yeast	5-Fluorocytosine Amphotericin B Anidulafungin Caspofungin Fluconazole Itraconazole Micafungin Posaconazole Voriconazole	0060235 Antimicrobial Susceptibility - Yeast (Candida spp)
Rapidly growing Mycobacterium spp Aerobic Actinomycetes		Amikacin Amoxicillin/Clavulanic Acid Cefoxitin Ceftriaxone Ciprofloxacin Clarithromycin Gatifloxacin Imipenem Linezolid Minocycline Tobramycin Trimethoprim/Sulfamethoxazole	0060217 Antimicrobial Susceptibility - AFB/Mycobacteria 0060193 Antimicrobial Susceptibility - Nocardia Tigecycline upon request
Slowly growing Nontuberculous Mycobacterium spp Acterium	MAI M. marinum M. kansasii Atypical (NTM)	Amikacin Ciprofloxacin Clarithromycin Ethambutol Gatifloxacin INH (for M. kansasii only) Linezolid Minocycline Moxifloxacin Rifabutin Rifampin Streptomycin Trimethoprim/Sulfamethoxazole	0060217 Antimicrobial Susceptibility - AFB/Mycobacteria
Mycobacterium tuberculosis spp	Mycobacterium tuberculosis complex	First-line drugs Ethambutol Isoniazid Pyrazinamide Rifampin Second-line drugs Amikacin Capreomycin Cycloserine Ethionamide Kanamycin Ofloxacin Para-aminosalicylic Acid (PAS) Streptomycin	0060217 Antimicrobial Susceptibility - AFB/Mycobacteria

See Also

Health Care Associated Infections - Nosocomial Infections

Tests

Tests generally appear in the order most useful for common clinical situations

Test name: Antimicrobial Susceptibility - Staphylococcus

ARUP #: 0060707

Methodology: Automated Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

For serious infections with coagulase-negative staphylococci, testing for mecA will be performed to interpret the results for beta-lactam agents

Test name: Antimicrobial Susceptibility - mecA Gene by PCR

ARUP #: 0060211

Methodology: Polymerase Chain Reaction

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - D-Test (Macrolide, Lincosamide, Streptogramin Resistance)

ARUP #: 0060059

Methodology: Disk Diffusion

Use:

See Clinical Background for specific drug types

Limitations:

Positive test results usually indicate resistance to clindamycin; however clindamycin may still be effective in some patients with positive test results

Follow-up:

Test name: Antimicrobial Susceptibility - Enterococcus

ARUP #: 0060708

Methodology: Automated Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

If vancomycin resistant, order 0060363

Test name: Antimicrobial Susceptibility - Not Otherwise Specified

ARUP #: 0060200

Methodology: Broth Microdilution/Disk Diffusion/Gradient Diffusion

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Vancomycin-Resistant Enterococcus (VRE) Culture

ARUP #: 0060363

Methodology: Standard reference procedures for aerobic bacterial culture and identification

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Yeast Susceptibility

ARUP #: 0060235

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

CLSI-interpretive guidelines are available for testing Candida species against itraconazole, 5-fluorocytosine and fluconazole

- Fluconazole and itraconazole MIC guidelines are based on mucosal infections
- Clinical data for invasive infections are not available

Follow-up:

Test name: Antimicrobial Susceptibility - AFB/Mycobacteria

ARUP #: 0060217

Methodology: Varies with organism identification

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Extended Spectrum Beta Lactamase

ARUP #: 0063999

Methodology: Disk Diffusion

Use:

See Clinical Background for specific drug types

Limitations:

There are no CLSI guidelines for testing organisms other than E. coli, Klebsiella spp and Proteus mirabilis, for the presence of ESBL activity

The CLSI-approved method does not rule out resistance by other mechanisms

Test name: Antimicrobial Susceptibility - Streptococcus pneumoniae

ARUP #: 0060221

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Viridans Streptococcus

ARUP #: 0060222

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Nocardia

ARUP #: 0060193

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Anaerobe

ARUP #: 0060202

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Anaerobic susceptibility testing appropriate for serious infections involving blood, bone, joint, tissue or brain abscess

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - MIC, Individual

ARUP #: 0060201

Methodology: Gradient Diffusion (E-Test) or Broth Microdilution

Use:

See Clinical Background for specific drug types

Use to determine dosages and routes of administration other than those usually prescribed

Relate susceptibility to achievable antibiotic concentration in urine, bile, CSF and other body fluids which may vary widely from achievable concentration in serum

Provide physician with information to select most appropriate antibiotic for patient based on:
- Infectious organism's degree of susceptibility
- Site and severity of the infection
- Pharmacology of antibiotics

Limitations:

Follow-up:

For serious infections with coagulase-negative staphylococci, testing for presence of mecA will be performed to interpret results for beta-lactam agents

Test name: Antimicrobial Susceptibility - Nonfermenter

ARUP #: 0060216

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Limitations:

Follow-up:

Test name: Antimicrobial Susceptibility - Fastidious Organism

ARUP #: 0060345

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Test name: Antimicrobial Susceptibility - Gram Positive Rod

ARUP #: 0060346

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Test name: Antimicrobial Susceptibility - Mould Susceptibility

ARUP #: 0060227

Methodology: Broth Microdilution

Use:

See Clinical Background for specific drug types

Additional Tests Available

Test name: Limulus Amebocyte Lysate (LAL)

ARUP #: 0097328

Methodology: Chromogenic Assay

Comments: