Chlorhexidine and Mupirocin Susceptibilities of Methicillin-Resistant Staphylococcus aureus from Colonized Nursing Home Residents

Abstract

f Chlorhexidine and mupirocin are used in health care facilities to eradicate methicillin-resistant Staphylococcus aureus (MRSA) carriage. The objective of this study was to assess the frequency of chlorhexidine and mupirocin resistance in isolates from nares carriers in multiple nursing homes and to examine characteristics associated with resistance. Nasal swab samples were collected from approximately 100 new admissions and 100 current residents in 26 nursing homes in Orange County, CA, from October 2008 to May 2011. MRSA isolates were tested for susceptibility by using broth microdilution, disk diffusion, and Etest; for genetic relatedness using pulsed-field gel electrophoresis; and for qac gene carriage by PCR. Characteristics of the nursing homes and their residents were collected from the Medicare Minimum Data Set and Long-Term Care Focus. A total of 829 MRSA isolates were obtained from swabbing 3,806 residents in 26 nursing homes. All isolates had a chlorhexidine MIC of <4 g/ml. Five (0.6%) isolates harbored the qacA and/or qacB gene loci. Mupirocin resistance was identified in 101 (12%) isolates, with 78 (9%) isolates exhibiting high-level mupirocin resistance (HLMR). HLMR rates per facility ranged from 0 to 31%. None of the isolates with HLMR displayed qacA or qacB, while two isolates carried qacA and exhibited low-level mupirocin resistance. Detection of HLMR was associated with having a multidrug-resistant MRSA isolate (odds ratio [OR], 2.69; P ‫؍‬ 0.004), a history of MRSA (OR, 2.34; P < 0.001), and dependency in activities of daily living (OR, 1.25; P ‫؍‬ 0.004). In some facilities, HLMR was found in nearly one-third of MRSA isolates. These findings may have implications for the increasingly widespread practice of MRSA decolonization using intranasal mupirocin.

Recurrent Methicillin-Resistant Staphylococcus aureus Cutaneous Abscesses and Selection of Reduced Chlorhexidine Susceptibility during Chlorhexidine Use

“…While there are no established breakpoints for chlorhexidine resistance, the presence of these genes has been associated both with increased MICs and with untoward clinical outcomes (35)(36)(37)(38). Interestingly, multiple reports have identified chlorhexidine-resistant S. aureus isolates with MICs of Ն4 g/ml (30,31,38). The isolate described in this report, however, showed a reduced MIC (Յ0.8 g/ml).…”

“…Despite its widespread use, the prevalence of chlorhexidine resistance in the United States is low (approximately 1%) (25,30,31); this is in contrast to observations in other countries (11,32). When used in large trials in both community and hospital settings, chlorhexidine resistance has been only rarely reported (21,24,27,31).…”

Chlorhexidine and Mupirocin Susceptibility of Methicillin-Resistant Staphylococcus aureus Isolates in the REDUCE-MRSA Trial

“…Our results are consistent with several other published surveys that infrequently identified phenotypic or genotypic evidence of reduced susceptibility to CHG in MRSA isolates from U.S. health care facilities (22,23,35). More recently, reports have emerged of (49).…”

“…CHG has been used widely in health care for more than 50 years, and reduced susceptibility as measured by in vitro methods has been reported across the globe (18,(20)(21)(22)(23)(24)46), yet decolonization failure related to nonsusceptibility has been described only rarely (16,25,26). Of note, topical concentrations of CHG used for decolonization remain Ͼ200-fold higher than the highest CHG MICs and minimum bactericidal concentrations (MBCs) recorded for staphylococci (15,25).…”

LTX-109 Is a Novel Agent for Nasal Decolonization of Methicillin-Resistant and -Sensitive Staphylococcus aureus

“…Mupirocin is bacteriostatic and has a proven effect on nasal S. aureus carriage, with a transient eradication rate of up to 80 to 90% in controlled studies (37); however, S. aureus has been evolving resistance to mupirocin (8,14,(38)(39)(40)(41). The mechanism of action of LTX-109 represents a new and innovative bactericidal approach via a direct membrane disruption (17,18).…”