: In-vitro Study Documenting the Lack of Antibacterial Activity of Three Silver-impregnated/coated Mechanical Valve Needleless Connectors After Blood Exposure

Background: In efforts to reduce risks of bloodstream infections some manufacturers coated/impregnated components of needleless connectors with silver ions.  Although silver has antibacterial properties, the impact on this activity when the connector comes in contact with proteins, e.g., blood, in an IV needleless connector is not known.

Objective: We conducted an in-vitro study to assess the antibacterial activity of needleless connectors impregnated with silver nanoparticles. Unlike the only previous such assessment (Maki, 2010) we exposed the internal connector surface to blood, as would commonly be done in the clinical setting and then exposed the connector to bacterial challenge and evaluated their antibacterial activity.

Methods: Using a high-efficiency particulate air-filtered hood, bovine blood was drawn-up into needleless connectors from three manufacturers, V-Link™ (Baxter, Deerfield, IL), Ultrasite® Ag™ (B.Braun, Bethlehem, PA) and MaxGuard™ (Medegen/CareFusion, Ontario, CA), until seen in the syringe, flushed then left untouched four hours.  This was repeated times three.  Two mls of 10⁶ or 10⁸ cfu/ml inoculum of Staphylococcus aureus or S. epidermidis was flushed through connectors, syringe removed, connectors incubated 15 hours. Connector tops disinfected with 70% alcohol, flushed with 5 mls DYNE neutralizer broth,directly plated or membrane filtered and plated. All plates incubated for 2 days at 37^o + 2^oC.  Plates scored for growth.  Four controls, positive, negative, neutralization, and no flush were included. Six of each connector were tested with both organisms (N =36).

Results: All three silver coated/impregnated connectors grew S. aureus and S. epidermidis.  Log reduction was not clinically significant, range +0.19 to -1.82.  There was substantial and escalating bacterial growth (Table1).

Table 1. Staphylococcus aureus and epidermidis Colony Forming Units.

Device	MG -SA	US –SA	VL –SA	MG -SE	US -SE	VL-SE
+ control = 0 hour	1.6x108	7.9x107	2.1x108	1.2x106	9.1x106	3.0x108
+ control = 15 h	3.9x108	1.4x108	Not Done/ND	4.4x107	2.6x107	ND
Non-flush	5.7x108	1.9x108	ND	1.0x107	3.5x106	ND
Neutralization	94%	106%	100%	96%	96%	50%
#1 connector	2.8x108	1.8x108	2.4x108	8.0x107	2.5x107	2.2x108
#2	1.2x108	7.6x108	2.0x108	5.4x107	4.4x106	5.2x108
#3	3.5x108	1.0x108	1.5x108	3.0x107	3.6x107	4.0x108
#4	1.5x108	1.2x108	1.4x108	7.8x107	5.9x106	3.9x108
#5	1.3x108	4.1x108	1.4x108	3.0x107	2.9x107	3.6x108
#6	3.0x108	2.9x108	1.8x108	5.7x107	2.5x107	5.1x108

Conclusions: Once blood comes in contact with silver-coated/impregnated needleless connectors their antibacterial activity becomes significantly reduced.  Since intravenous connectors are in frequent contact with blood, these connectors may not offer benefits over connectors that are not silver-impregnated/coated and should be further evaluated in clinical settings.