This article is more than 5 years old. Information may no longer be current.

Emerging S. aureus resistance found with topical antibiotics

SAN FRANCISCO — Additional research is needed into the emerging staphylococcal resistance to topical antimicrobials used to treat skin and soft tissue infections in healthy children.

Chase McNeil, MD, department of pediatrics, Baylor College of Medicine, Houston, and colleagues studied the prevalence of decreased susceptibility to retapamulin, mupirocin and chlorhexidine of Staphylococcus aureus isolates from community-acquired SSTIs in children and discovered cross resistance to two commonly used drugs.

“It seems clear that in vitro resistance to retapamulin and mupirocin is higher than expected in our population compared with other studies,” McNeil said. “Retapamulin resistance was associated with cross resistance to mupirocin or linezolid in 2.2% and 0.5% of isolates, respectively. In addition, there was a dramatic increase in the proportion of isolates with genotypic tolerance to antiseptics. Further research involving clinical correlations with these findings is warranted.”

McNeil and colleagues selected isolates from a prospective S. aureus surveillance study. A total of 200 isolates from patients with their first SSTI and 200 isolates from patients with three or more previous episodes from the years 2010 through 2012 were selected for inclusion. Children with immunodeficiencies were excluded, according to McNeil.

Retapamulin resistance screening was performed by the macrobroth dilution method; mupirocin and linezolid minimum inhibitory concentrations were determined by E-test. PCR was performed for the presence of the chlorhexidine tolerance gene qacA/B.
Among the 400 isolates from both patient groups, 269 were methicillin-resistant S. aureus (67.3%) and 14.3% were clindamycin resistant. Among those screened, 45 isolates exhibited retapamulin resistance, and 28 of 45 retapamulin-resistant isolates were MRSA; all were SCC mec type IV.

“Something notable is that five patients in the study who had a mupirocin-resistant isolate who were prescribed mupirocin by their health care provider without systemic antibiotics being added,” McNeil said during his presentation. “None of these patients experienced a treatment failure.”

Two isolates displayed cross-resistance to retapamulin and linezolid, and 39 isolates (9.8%) were found to have mupirocin resistance; nine of those isolates displayed cross-resistance to retapamulin. The proportion of retapamulin- and mupirocin-resistant isolates increased significantly with the number of SSTIs.
qacA/B-positive S. aureus accounted for 14% of isolates.

The proportion of retapamulin and mupirocin resistance was stable during the study period while the proportion of qacA/B-positive organisms increased (P=.005).

“What seems important about this resistance to topical antimicrobials is that associated with resistance to systemic antimicrobials, which seems to be of clinical importance,” McNeil said. “The full clinical significance of these findings are unclear.”

For more information:
McNeil J. Abstract 130. Presented at ID Week 2013; Oct. 2-6, 2013; San Francisco.

Disclosure: This study was supported by Stiefel Inc. McNeil receives research support from Stiefel Inc.