Serratia infection laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Diagnosis of Serratia infection is made by growth of Serratia in culture media. Other laboratory findings are non-specific.

Laboratory Findings

Laboratory findings may be non-specific and depend on the site of infection.

Culture Growth

Procedure

According to the Centers for Disease Control and Prevention (CDC), the following procedure should be followed to properly culture Serratia:

• Biosafety Level: 2
• Medium: Trypticase Soy Agar with 5% Sheep Blood (BAP)
• Growth Conditions:

• Temperature: 35 °C (95 °F)
• Atmosphere: Aerobic

• Procedure

• Remove the sample vial to a container with dry ice or a freezer block. Keep vial on ice or block. (Do not let vial content thaw)
• Open vial aseptically to avoid contamination
• Using a sterile loop, remove a small amount of frozen isolate from the top of the vial
• Aseptically transfer the loop to BAP
• Use streak plate method to isolate single colonies
• Incubate inverted phase at 35 °C (95 °F) for 18-24 hours

MIC Results and Interpretation

The following table demonstrates the minimum inhibitory concentration (MIC) results following Serratia culture/antibiogram and interpretation:

MIC (µg/ml) Results and Interpretation
Drug	MIC	Interpretation
Amikacin	2	S
Amoxicillin/Clavulanic Acid *	> 32	R
Ampicillin	> 32	R
Ampicillin/Sulbactam	> 32	R
Aztreonam	16	R
Cefazolin	> 32	R
Cefepime	≤ 0.5	S
Cefotaxime	≤ 1	S
Cefoxitin	2	S
Ceftazidime	1	S
Ceftriaxone	≤ 1	S
Ciprofloxacin	≤ 0.12	S
Colistin	> 4	_
Doripenem	_	_
Ertapenem	> 16	R
Gentamicin	0.5	S
Imipenem	> 32	R
Imipenem + chelators **	_	_
Levofloxacin	≤ 0.25	S
Meropenem	> 16	R
Piperacillin/Tazobactam *	2	S
Polymyxin B	> 4	_
Tetracycline	8	I
Tigecycline ***	1	S
Tobramycin	1	S
Trimethoprim/Sulfamethoxazole (TMP - SMX)	2	S

^{* Reflects MIC of first component
** Screen for metallo-beta-lactamase production
*** Based on FDA break points
Abbreviations: MIC=Minimum inhibitory concentration; I=Intermediate; R=Resistant; S=Susceptible
Table adapted from Antimicrobial Resistance Bank - Serratia marcescens. Centers for Disease Control and Prevention.}