279. The Effects of Daily Chlorhexidine Bathing on Cutaneous Bacterial Isolates
Session: Poster Abstract Session: Antimicrobial Therapy: Clinical Studies
Friday, October 21, 2011
Room: Poster Hall B1
Background: Chlorhexidine gluconate (CHG) is a frequently used bactericidal antiseptic. Limited data suggest that CHG exposure selects for bacteria with elevated CHG minimal inhibitory concentrations (MICs), but the clinical significance of these findings is unclear. Our objectives were to study 1) the effect of CHG bathing on cultivable cutaneous bacteria, 2) the effect of CHG bathing on the CHG MICs of cutaneous coagulase-negative staphylococci (CoNS) isolates, and 3) the relationship between CHG MIC and antimicrobial susceptibility.

Methods: Axillary skin swabs collected from patients receiving daily CHG baths and from control patients receiving standard baths were categorized by CHG exposure. The cutaneous bacteria present on swabs were identified by culture-based methods. The bacterial load of each swab was defined as its total colony count. The number of phenotypically different bacteria on each swab was also obtained. CHG MIC and antimicrobial susceptibility testing was conducted for all CoNS isolates, and PCR was performed for the qacA/B antiseptic-resistance determinants.

Results: With increasing CHG exposure, median bacterial load decreased: 4030 cfu/ml, 10 cfu/ml, and 0 cfu/ml for the “none,” “moderate,” and “heavy” exposure groups (p < 0.0001). The median number of different bacterial phenotypes also decreased with greater CHG exposure: 2, 1, and 0, respectively (p < 0.001). The median CHG MIC of CoNS isolates did not increase significantly with heavier CHG exposure: 1 ug/ml, 1 ug/ml, and 2 ug/ml, respectively.  Isolates with MICs ≥ 2 had significantly lower frequencies of susceptibility to cefoxitin, ceftriaxone, clindamycin, erythromycin, gentamicin, and trimethoprim-sulfamethoxazole than isolates with MICs ≤1 (p = 0.004 – 0.03). qacA/B was detected in 75% of CoNS isolates with CHG MICs ≥ 2  compared with 44% of isolates with MICs ≤ 1 (p = 0.1).

Conclusion: We found that an elevated CHG MIC was associated with decreased antimicrobial-susceptibility in CoNS. While qacA/B may mediate elevated CHG MICs among CoNS, other undescribed mechanism(s) may also cause elevated CHG MICs and be associated with antibiotic-resistance determinants. 

Subject Category: A. Antimicrobial agents and Resistance

Viju Soma, MD1,2, Xuan Qin, PhD2,3, Amanda Adler, BA2, Jessica Berry, BS3 and Danielle Zerr, MD, MPH4,5, (1)Pediatrics, University of Washington, Seattle, WA, (2)Seattle Children's Research Institute, Seattle, WA, (3)Department of Laboratory Medicine, University of Washington, Seattle, WA, (4)Department of Pediatrics, University of Washington, Seattle, WA, (5)Seattle Children's Hospital Research Institute, Seattle, WA


V. Soma, None

X. Qin, None

A. Adler, None

J. Berry, None

D. Zerr, Sage products, Inc.: Investigator, Research grant
Vioguard, Ltd.: Investigator, Research grant

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