Performance of the ESwab (ES) Transport System for Recovery of Acinetobacter baumannii (AB)

Background: AB is an important nosocomial pathogen. Detection of AB carriage is important for infection control but has limitations that may possibly be related to recovery from swabs and swab transport and storage conditions. ES is a new system utilizing a flocked nylon swab and liquid Amies medium, that is possibly superior over standard swabs (SS). However, the use of ES for recovery of AB has not been studied.

Objective: To evaluate the performance of ES for recovery of AB and the impact of swab transport time (TT) and storage conditions on AB recovery rate (ReR).

Methods: AB strains ATCC 19606 and 2 clinical multi-resistant isolates (#4593, #4871) were each suspended in sterile saline to the turbidity of 0.5MF. Suspensions were further diluted 1:100 yielding the stock incula. ES or SS (Copan Diagnostics Inc., CA, USA) were inoculated by swab suspension in 100µl of inoculum. The effects of 1h, 24h and 48h TT at 25°c as well as of storage conditions (1 week, 2 weeks and 1 month at 4°c or -80°c) on AB viability were evaluated. Swabs were vortexed prior to elution. SS were directly eluted in 0.9ml saline. For ES, 100µL of liquid medium were obtained and added to 0.9ml saline. Suspensions were serially diluted in saline and plated onto BHI agar and colonies were counted. Viability was determined by bacterial live counts expressed as the % ReR as compared to baseline live counts

Results:

Swab type	AB Strain	Mean ReR (%) by TT				Mean ReR (%) by storage condition
		0h	1h	24h	48h	temp.	0h	1w	2w	4w
SS	19606	100	5.1	2846	5112	4°C	100	0.03	0.03	0
						-80°C		0.4	0.6	0.2
ES	19606		73.2	643	553	4°C		3.5	1.6	0.01
						-80°C		1.2	1.2	0
	4593		20.5	4464	8146	4°C		4.2	0.6	0
						-80°C		1.5	0.85	1
	4871		83.3	4541	64125	4°C		9.9	0.8	4
						-80°C		0.4	0.1	0.06

Conclusions: The ES had higher ReR after 1h of transport compared to SS, while at both 24h and 48h, bacterial overgrowth was evident. ES had better ReR than SS after 1 week of storage at either 4°C or -80°C, but this difference diminished at storage times of 2-4 weeks. Thus, ES may the preferred swab type for sampling AB, as long as swabs are processed within reasonable transport and storage times.