Clonal relationships of fluoroquinolone-resistant E. coli recovered from nursing home residents

Background:  Nursing home residents are commonly colonized with fluoroquinolone-resistant E. coli (FQREC). Resistance in healthcare settings may occur through endogenous selection or exogenously through cross-transmission between individuals. The extent to which either of these mechanisms contributes to observed patterns of resistance in nursing homes (NHs) is incompletely understood.

Objective: To determine if clustering of FQREC occurs in NHs

Methods:  Residents of 6 NHs in Wisconsin were screened to determine if they were colonized with FQREC using swabs of stool, wounds and urine (if catheterized) which were then plated on selective media. Recovered isolates were identified to the species level using phenotypic and biochemical methods. Recovered FQREC isolates were typed by PFGE using a XbaI endonuclease.  Resulting macrorestriction patterns were analyzed using the unweighted pair group method using arithmetic averages (UPGMA) with a 1.25% position tolerance. Clonal relationships between isolates were defined at the 95% and 100% Dice similarity cut points.

Results:  79 FQREC isolates were identified in 76 of the 441 (17.2%) participating subjects. 42/79 (53%) and 25/79 (32%) of isolates were clustered using a 0.95 and 1.00 similarity cut point, respectively. There was considerable variation in clustering across study facilities (Table).

 

Cut point	Facilities						Total
	F1	F2	F3	F4	F5	F6
0.95	73%	58%	44%	100%	40%	0%	53%
1.00	60%	38%	28%	0%	20%	0%	32%

Conclusions:  A large proportion of FQREC isolates in this sample of NHs were genetically similar suggesting a prominent role for cross-transmission. Moreover, there was considerable variation in rates of clustering across facilities. These findings suggest that infection control precautions may have an important role in controlling the spread of fluoroquinolone-resistance in NHs.