Association of high-level mupirocin resistance and multidrug-resistant methicillin-resistant Staphylococcus aureus at an academic center in the midwestern United States

Dissemination of Methicillin-Resistant Staphylococcus aureus Sequence Type 764 Isolates with Mupirocin Resistance in China

Mupirocin, a topical antimicrobial agent, is an important component in the eradication of methicillin-resistant Staphylococcus aureus (MRSA) colonization. The molecular characteristics of 46 mupirocin-resistant MRSA (MR-MRSA) clinical isolates were analyzed by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec element (SCCmec) typing, spa typing, and analysis of virulence genes. All 26 MRSA isolates with low-level mupirocin resistance possessed a V588F mutation in ileS. Among 20 MRSA isolates with high-level resistance to mupirocin, all carried mupA; 2 isolates also possessed the V588F mutation in ileS, and 1 possessed the V631F mutation in ileS (isoleucyl-tRNA synthetase). The majority of MR-MRSA isolates were resistant to erythromycin, clindamycin, tetracycline, ciprofloxacin, and gentamicin, but the rates of resistance to rifampin and fusidic acid were 8.7% and 6.5%, respectively. Eight sequence types (STs) were found among the 46 MR-MRSA isolates, of which ST764 was the most prevalent (76.1%). The most frequent spa type identified was t1084 (52.2%). The SCCmec type most frequently found was type II (80.4%). The most common clone among low-level MR-MRSA isolates was ST764-MRSA-SCCmec type II-t1084 (23 isolates), while ST764-MRSA-SCCmec type II-t002 (9 isolates) was the most common clone among high-level MR-MRSA isolates. Additionally, all toxin genes except the seb gene were not identified among ST764 isolates. Among clonal complex 5 (CC5) isolates, immune evasion cluster (IEC)-associated genes (chp, sak, and scn) and seb were present in ST764 but absent in ST5, while sec, sel1, tsst-1, and hlb genes were identified in ST5 but absent in ST764. In conclusion, the spread of CC5 clones, especially a novel ST764-MRSA-SCCmec type II-t1084 clone with high-level resistance to mupirocin, was responsible for the increase in mupirocin resistance. These findings indicated that the emergence of the ST764 MR-MRSA clone involves a therapeutic challenge for treating serious MRSA infections. IMPORTANCE Mupirocin, a topical antibiotic that is commonly used for the nasal decolonization of MRSA and methicillin-sensitive Staphylococcus aureus in hospital settings and nursing homes, was introduced as a highly effective antibiotic against MRSA. Mupirocin acts by competitively binding isoleucyl-tRNA synthetase, thereby disrupting protein synthesis. This drug shows bacteriostatic and bactericidal activity at low and high concentrations, respectively. However, with the increase in mupirocin use, low-level and high-level resistance during nasal mupirocin treatment has been reported. In a previous study, the proportion of MRSA strains with high-level mupirocin resistance in a Canadian hospital increased from 1.6% in the first 5 years of surveillance (1995 to 1999) to 7.0% (2000 to 2004).

Molecular Mechanisms of Drug Resistance in Staphylococcus aureus

This paper discusses the mechanisms of S. aureus drug resistance including: (1) introduction. (2) resistance to beta-lactam antibiotics, with particular emphasis on the mec genes found in the Staphylococcaceae family, the structure and occurrence of SCCmec cassettes, as well as differences in the presence of some virulence genes and its expression in major epidemiological types and clones of HA-MRSA, CA-MRSA, and LA-MRSA strains. Other mechanisms of resistance to beta-lactam antibiotics will also be discussed, such as mutations in the gdpP gene, BORSA or MODSA phenotypes, as well as resistance to ceftobiprole and ceftaroline. (3) Resistance to glycopeptides (VRSA, VISA, hVISA strains, vancomycin tolerance). (4) Resistance to oxazolidinones (mutational and enzymatic resistance to linezolid). (5) Resistance to MLS-B (macrolides, lincosamides, ketolides, and streptogramin B). (6) Aminoglycosides and spectinomicin, including resistance genes, their regulation and localization (plasmids, transposons, class I integrons, SCCmec), and types and spectrum of enzymes that inactivate aminoglycosides. (7). Fluoroquinolones (8) Tetracyclines, including the mechanisms of active protection of the drug target site and active efflux of the drug from the bacterial cell. (9) Mupirocin. (10) Fusidic acid. (11) Daptomycin. (12) Resistance to other antibiotics and chemioterapeutics (e.g., streptogramins A, quinupristin/dalfopristin, chloramphenicol, rifampicin, fosfomycin, trimethoprim) (13) Molecular epidemiology of MRSA.

A Novel Biofilm-Disrupting Wound Care Technology for the Prevention of Surgical Site Infections Following Total Joint Arthroplasty: A Conceptual Review

Surgical site infections (SSIs) are a major driver for increased costs following lower extremity joint arthroplasty procedures. It has been estimated that these account for over $2 billion in annual costs in the United States. While many of the current strategies for the prevention and treatment of SSIs target planktonic bacteria, 80 to 90% of bacterial pathogens exist in a sessile state. These sessile bacteria can produce extracellular polymeric substance (EPS) as protective barriers from host immune defenses and antimicrobial agents and thus, can be exceedingly difficult to eradicate. A novel wound care gel that disrupts the EPS and destroys the inciting pathogens has been developed for the treatment and prevention of biofilm-related infections. This is achieved by the simultaneous action of four key ingredients: (1) citric acid; (2) sodium citrate; (3) benzalkonium chloride; and (4) polyethylene glycol. Together, these constituents create a high osmolarity, pH-controlled environment that deconstructs and prevents biofilm formation, while destroying pathogens and promoting a moist environment for optimal wound healing. The available clinical evidence demonstrating the efficacy of this technology has been summarized, as well as the economic implications of its implementation and the authors' preferred method of its use. Due to the multifaceted burden associated with biofilm-producing bacteria in arthroplasty patients, this technology may prove to be beneficial for patients who have higher risks for infection, or perhaps, as a prophylactic measure to prevent infections for all patients.

Clinical relevance of topical antibiotic use in co-selecting for multidrug-resistant Staphylococcus aureus: Insights from in vitro and ex vivo models

Topical antibiotic preparations, such as fusidic acid (FA) or mupirocin, are used in the prevention and treatment of superficial skin infections caused by staphylococci. Previous genomic epidemiology work has suggested an association between the widespread use of topical antibiotics and the emergence of methicillin resistant Staphylococcus aureus in some settings. In this study, we provide experimental proof of co-selection for multidrug resistance in S. aureus following exposure to FA or mupirocin. Through targeted mutagenesis and phenotypic analyses, we confirmed that fusC carriage confers resistance to FA, and mupA carriage confers high-level resistance to mupirocin in multiple S. aureus genetic backgrounds. In vitro experiments demonstrated that carriage of fusC and mupA confer a competitive advantage in the presence of sub-inhibitory concentrations of FA and mupirocin, respectively. Further, we used a porcine skin colonisation model to show that clinically relevant concentrations of topical antibiotics can co-select for presence of unrelated antimicrobial resistance determinants, such as mecA, blaZ, and qacA, in fusC or mupA harbouring S. aureus These findings provide valuable insights on the role of acquired FA or mupirocin resistance in co-selecting for broader antibiotic resistance in S. aureus, prompting greater need for judicious use of topical antibiotics.

Low prevalence of mupirocin resistance among Staphylococcus aureus clinical isolates from a Chinese tertiary hospital

Between September 2013 and March 2016, 26 (1.95 %) of 1333 Staphylococcus aureus clinical isolates from a Chinese hospital were found to be resistant to mupirocin, including 18 (1.35 %) with high-level mupirocin resistance and 8 (0.6 %) with low-level mupirocin resistance. Among the 18 isolates with high-level mupirocin resistance, 17 were associated with plasmid-mediated mupA. Meanwhile, the 8 isolates with low-level mupirocin resistance were shown to have a V588F mutation in ileS. A total of 14 sequence types (STs) and 18 spa types were identified. All four isolates with t062 belonged to ST965. Three ST5-MRSA-SCCmec II were linked to t311, which was not previously reported. Furthermore, ST764-MRSA-SCCmec II-t002, exclusively found in Japan before, was identified in this study. In conclusion, we observed relatively low prevalence of mupirocin resistance among S. aureus with considerable heterogeneity in East China. Newly emerging MRSA clones with high-level mupirocin resistance should be of concern.

Genetic Diversity Analysis of Mupirocin-Resistant Staphylococcus aureus Clinical Isolates in Tehran Hospitals, Iran

Few studies describe the molecular characterization of mupirocin resistance in Staphylococcus aureus strains. In this study, we evaluated the characteristics of mupirocin resistance in S. aureus isolates for 1-year period in Tehran, Iran. In a cross-sectional study, we collected 51 unique mupirocin-resistant strains obtained from 648 S. aureus isolates. High- and low-level resistance were determined by minimum inhibitory concentration with broth microdilution method. Presence of the genes for resistance to antibiotics and toxins was detected by polymerase chain reaction assays. Genotyping was performed by S. aureus protein A (spa) and staphylococcal cassette chromosome mec (SCCmec) typing, whereas clones were determined by multilocus sequence typing. Among mupirocin-resistant isolates, methicillin-resistant S. aureus (MRSA) 23 (45.1%) and 28 (54.9%) isolates were classified as high- and low-level mupirocin resistance, respectively. Among the 51 tested strains 25 (49%) isolates were positive for mupA genes. Seven different clones were detected in this study. High-level mupirocin-resistant (HLMUPR) strains belonged to ST8-SCCmec IV/t064 (n = 10, 19.6%), ST5-SCCmec IV/t002 (n = 5, 9.8%), ST8-SCCmec IV/t008 (n = 4, 7.8%), and ST239-SCCmec III/t631 (n = 4, 7.8%) clones, while low-level mupirocin-resistant (LLMUPR) strains belonged to ST22-SCCmec IV/t790 (n = 11, 21.6%), ST239-SCCmec III/t860 (n = 9, 17.7%), and ST15-SCCmec IV/t084 (n = 8, 15.7%) clones. Two strains belonged to ST22-SCCmec IV/t790 clone, despite carrying mupA gene, and demonstrated LLMUPR phenotype. One ST8-SCCmecIV/t008 strain with HLMUPR was confirmed as Vancomycin-intermediate S. aureus strain. Our data demonstrated the need for thorough epidemiological monitoring and a routine mupirocin testing program to prevent and detect mupirocin resistance in MRSA.

A review on mechanism of action, resistance, synergism, and clinical implications of mupirocin against Staphylococcus aureus

Mupirocin (MUP), bactroban, or pseudomonic acid is a natural crotonic acid derivative drug extracted from Pseudomonas fluorescens which is produced by modular polyketide synthases. This antibiotic has a unique chemical structure and mechanism of action. It is a mixture of A-D pseudomonic acids and inhibits protein synthesis through binding to bacterial isoleucyl-tRNA synthetase. MUP is often prescribed to prevent skin and soft tissue infections caused by S. aureus isolates and where the MRSA isolates are epidemic, MUP may be used as a choice drug for nasal decolonization. It is also used for prevention of recurring infections and control the outbreaks. The emergence of MUP resistance has been increasing particularly among methicillin-resistant Staphylococcus aureus (MRSA) isolates in many parts of the world and such resistance is often related with MUP widespread uses. Although both low-level and high-level MUP resistance were reported among MRSA isolates, the rate of resistance is different in various geographic areas. In this review, we will report the global prevalence of MUP resistance, discuss synergism and mechanism of action of MUP, and provide new insights into the clinical use of this antibiotic.

Molecular Characterization of Nasal Methicillin-Resistant Staphylococcus aureus Isolates Showing Increasing Prevalence of Mupirocin Resistance and Associated Multidrug Resistance following Attempted Decolonization

Sequential methicillin-resistant Staphylococcus aureus (MRSA) isolates from patients following attempted mupirocin nasal decolonization showed an increase in mupirocin resistance (MR) from 6.6% to 20%. MR isolates from patients who failed decolonization yielded indistinguishable spa types and carried multiple antimicrobial and antiseptic resistance genes, which may guide infection control and prevention.

Antimicrobial Resistance to Agents Used for Staphylococcus aureus Decolonization: Is There a Reason for Concern?

PURPOSE OF REVIEW

Chlorhexidine gluconate (CHG) and mupirocin are increasingly used for Staphylococcus aureus decolonization to prevent healthcare-associated infections; however, increased use of these agents has led to concerns for growing resistance and reduced efficacy. In this review, we describe current understanding of reduced susceptibility to CHG and mupirocin in S. aureus and their potential clinical implications.

RECENT FINDINGS

While emergence of S. aureus tolerant or resistant to topical antimicrobial agents used for decolonization is well described, the clinical impact of reduced susceptibility is not clear. Important challenges are that standardized methods of resistance testing and interpretation are not established, and the risk for selection for co- or cross-resistance using universal, as opposed to targeted decolonization, is unclear. Evidence continues to support S. aureus decolonization in certain patient groups, although further studies are needed to determine the long-term impact of CHG and mupirocin resistance on efficacy. Strategies to mitigate further development of reduced susceptibility and the consequences of selection pressures through universal decolonization on resistance will benefit from further investigation.

Identification of a protective B-cell epitope of the Staphylococcus aureus GapC protein by screening a phage-displayed random peptide library

The impact of epidemic Staphylococcus aureus (S. aureus) on public health is increasing. Because of the abuse of antibiotics, the antibiotic resistance of S. aureus is increasing. Thus, there is an urgent need to develop new immunotherapies and immunoprophylaxes. Previous studies showed that the GapC protein of S. aureus, which is a surface protein with high glyceraldehyde 3-phosphate dehydrogenase activity, transferrin binding activity, and other biological activities, is highly conserved. GapC induces an effective humoral immune response in vivo. However, the B-cell epitopes of S. aureus GapC have not been well identified. Here we used the bioinformatics tools to analyze the sequence of GapC, and we generated protective anti-GapC monoclonal antibodies (mAbs). A protective mAb (1F4) showed strong specificity to GapC and the ability to induce macrophages to phagocytose S. aureus. We screened the motif ²⁷²GYTEDEIVSSD²⁸², which was recognized by mAb 1F4, using a phage display system. Then, we used site-directed mutagenesis to identify key amino acids in the motif. Residues G272 D276 E277 I278 and V279 formed the core of the ²⁷²GYTEDEIVSSD²⁸² motif. In addition, we showed that this epitope peptide induced a protective humoral immune response against S. aureus infection in immunized mice. Our results will be useful for the further study of epitope-based vaccines against S. aureus infection.

Six-Year Retrospective Review of Hospital Data on Antimicrobial Resistance Profile of Staphylococcus aureus Isolated from Skin Infections from a Single Institution in Greece

Objective: To determine the prevalence of resistant strains of Staphylococcus aureus (S. aureus) isolated from Skin and soft tissue infections (SSTI) to various antibiotics. Material and Methods: All culture-positive results for S. aureus from swabs taken from patients presenting at one Greek hospital with a skin infection between the years 2010–2015 were examined retrospectively. Bacterial cultures, identification of S. aureus and antimicrobial susceptibility testing were performed using the disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines and European Committee on Antimicrobial testing (EUCAST) breakpoints. EUCAST breakpoints were applied if no CLSI were available. Results: Of 2069 S. aureus isolates identified, 1845 (88%) were resistant to one or more antibiotics. The highest resistance was observed for benzylpenicillin (71.9%), followed by erythromycin (34.3%). Resistant strains to cefoxitin defined as MRSA (methicillin-resistant S. aureus) represented 21% of total isolates. Interestingly, resistance to fusidic acid was 22.9% and to mupirocin as high as 12.7%. Low rates were observed for minocycline, rifampicin and trimethoprim/sulfamethoxazole (SXT). Resistance to antibiotics remained relatively stable throughout the six-year period, with the exception of cefoxitin, fusidic acid and SXT. A high percentage of MRSA strains were resistant to erythromycin (60%), fusidic acid (46%), clindamycin (38%) and tetracycline (35.5%). Conclusions: Special attention is required in prescribing appropriate antibiotic therapeutic regimens, particularly for MRSA. These data on the susceptibility of S. aureus may be useful for guiding antibiotic treatment.

Multiresistant ST59-SCCmec IV-t437 clone with strong biofilm-forming capacity was identified predominantly in MRSA isolated from Chinese children

Background

This study aimed to investigate the clinical and molecular epidemiology and biofilm formation of Staphylococcus aureus (SA) isolated from pediatricians in China.

Methods

SA strains were isolated from Beijing Children’s hospital from February 2016 to January 2017. Isolates were typed by multilocus sequence typing (MLST), spa and SCCmec typing (for Methicillin-resistant SA [MRSA] only). Antimicrobial susceptibility testing was performed by agar dilution method except sulphamethoxazole/trimethoprim (E-test method). Biofilm formation and biofilm associated genes were detected.

Results

Totally 104 children (41 females and 63 males; median age, 5.2 months) were enrolled in this study, in which 60 patients suffered from MRSA infection. Among the 104 cases, 54.8% were categorized as community associated SA (CA-SA) infections. The children under 3 years were more likely to occur CA-SA infections compared with older ones (P = 0.0131). ST59-SCCmec IV-t437 (61.7%) was the most prevalent genotype of MRSA, and ST22-t309 (18.2%), ST5-t002 (9.1%), ST6-t701 (9.1%), ST188-t189 (9.1%) were the top four genotypes of methicillin-sensitive SA (MSSA). All the present isolates were susceptible to linezolid, vancomycin, trimethoprim-sulfamethoxazole, mupirocin, tigecyclin, fusidic acid. No erythromycin-susceptible isolate was determined, and only a few isolates (3.8%) were identified as susceptible to penicillin. Multi-drug resistant isolates were reponsible for 83.8% of the ST59-SCCmec IV-t437 isolates. The isolates with strong biofilm formation were found in 85% of MRSA and 53.2% of MSSA, and in 88.7% of ST59-SCCmec IV-t437 isolates. Biofilm formation ability varied not only between MRSA and MSSA (P = 0.0053), but also greatly among different genotypes (P < 0.0001). The prevalence of the biofilm associated genes among ST59-SCCmec IV-t437 clone was: icaA (100.0%), icaD (97.3%), fnbpA (100.0%), fnbpB (0), clfA (100%), clfB (100%), cna (2.7%), bbp (0), ebpS (88.5%), sdrC (78.4%), sdrD (5.4%), and sdrE (94.5%).

Conclusions

These results indicated strong homology of the MRSA stains isolated from Chinese children, which was caused by spread of multiresistant ST59-SCCmec IV-t437 clone with strong biofilm formation ability. The MSSA strains, in contrast, were very heterogeneity, half of which could produce biofilm strongly.

Electronic supplementary material

The online version of this article (10.1186/s12879-017-2833-7) contains supplementary material, which is available to authorized users.

A single dose of epidermicin NI01 is sufficient to eradicate MRSA from the nares of cotton rats

Objectives: To investigate the efficacy of a potent novel antimicrobial protein of mass 6 kDa, epidermicin NI01, for eradicating the nasal burden of MRSA in a cotton rat (Sigmodon hispidus) model.

Methods: MRSA strain ATCC 43300 was used to establish a robust colonization of cotton rat nares. This model was used to evaluate the efficacy of topical 0.04% and 0.2% epidermicin NI01, administered twice daily for 3 days consecutively, and topical 0.8% epidermicin NI01 administered once, for reducing nasal MRSA burden. Control groups remained untreated or were administered vehicle only (0.5% hydroxypropylmethylcellulose) or 2% mupirocin twice daily for 3 days. The experiment was terminated at day 5 and MRSA quantitative counts were determined. Tissues recovered from animals treated with 0.2% epidermicin twice daily for 3 days were examined for histological changes.

Results: Mupirocin treatment resulted in a reduction in burden of log₁₀ (log R) of 2.59 cfu/nares compared with vehicle (P < 0.0001). Epidermicin NI01 administered once at 0.8% showed excellent efficacy, resulting in a log R of 2.10 cfu/nares (P = 0.0004), which was equivalent to mupirocin. Epidermicin NI01 administered at 0.2% or 0.04% twice daily for 3 days did not have a significant impact on the tissue burden recovered from the nares. Mild to marked histological abnormalities were noted, but these were determined to be reversible.

Conclusion: A single dose of topical epidermicin NI01 was as effective as mupirocin administered twice daily for 3 days in eradication of MRSA from the nares of cotton rats. This justifies further development of epidermicin for this indication.

Emergence of a Staphylococcus aureus Clone Resistant to Mupirocin and Fusidic Acid Carrying Exotoxin Genes and Causing Mainly Skin Infections

Skin and soft tissue infections (SSTIs) caused by mupirocin-resistant Staphylococcus aureus strains have recently increased in number in our settings. We sought to evaluate the characteristics of these cases over a 43-month period. Data for all community-acquired staphylococcal infections caused by mupirocin-resistant strains were retrospectively reviewed. Genes encoding products producing high-level resistance (HLR) to mupirocin (mupA), fusidic acid resistance (fusB), resistance to macrolides and lincosamides (ermC and ermA), Panton-Valentine leukocidin (PVL) (lukS/lukF-PV), exfoliative toxins (eta and etb), and fibronectin binding protein A (fnbA) were investigated by PCRs in 102 selected preserved strains. Genotyping was performed by SCCmec and agr typing, whereas clonality was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). A total of 437 cases among 2,137 staphylococcal infections were recorded in 2013 to 2016; they were all SSTIs with the exception of 1 case of primary bacteremia. Impetigo was the predominant clinical entity (371 cases [84.9%]), followed by staphylococcal scalded skin syndrome (21 cases [4.8%]), and there were no abscesses. The number of infections detected annually increased during the study years. All except 3 isolates were methicillin susceptible. The rates of HLR to mupirocin and constitutive resistance to clindamycin were 99% and 20.1%, respectively. Among the 102 tested strains, 100 (98%) were mupA positive and 97 (95%) were fusB positive, 26/27 clindamycin-resistant strains (96.3%) were ermA positive, 83 strains (81.4%) were lukS/lukF positive, 95 (93%) carried both eta and etb genes, and 99 (97%) were fnbA positive. Genotyping of methicillin-sensitive S. aureus (MSSA) strains revealed that 96/99 (96.7%) belonged to one main pulsotype, pulsotype 1, classified as sequence type 121 (ST121). The emergence of a single MSSA clone (ST121) causing impetigo was documented. Resistance to topical antimicrobials and a rich toxinogenic profile confer to this clone adaptability for spread in the community.

Prevention of Recurrent Staphylococcal Skin Infections

Staphylococcus aureus infections pose a significant health burden. The emergence of community-associated methicillin-resistant S aureus has resulted in an epidemic of skin and soft tissue infections (SSTI), and many patients experience recurrent SSTI. As S aureus colonization is associated with subsequent infection, decolonization is recommended for patients with recurrent SSTI or in settings of ongoing transmission. S aureus infections often cluster within households, and asymptomatic carriers serve as reservoirs for transmission; therefore, a household approach to decolonization is more effective than measures performed by individuals alone. Novel strategies for the prevention of recurrent SSTI are needed.

Staphylococcus aureus: the current state of disease, pathophysiology and strategies for prevention

Staphylococcus aureus is both a commensal organism and also an important opportunistic human pathogen, causing a variety of community and hospital-associated pathologies, such as bacteremia-sepsis, endocarditis, pneumonia, osteomyelitis, arthritis and skin diseases. The resurgence of S. aureus during the last decade in many settings has been facilitated not only by bacterial antibiotic resistance mechanisms but also by the emergence of new S. aureus clonal types with increased expression of virulence factors and the capacity to neutralize the host immune response. Prevention of the spread of S. aureus infection relies on the use of contact precautions and adequate procedures for infection control that so far have not been fully effective. Prevention using a prophylactic vaccine would complement these processes, having the potential to bring additional, significant progress toward decreasing invasive disease due to S. aureus.

Antimicrobial resistance of Staphylococcus aureus isolated from skin infections and its implications in various clinical conditions in Korea

BACKGROUND

Periodic investigations into patterns of antimicrobial resistance can help to optimize the efficacy of treatment and limit the development of resistance.

OBJECTIVES

The aim of this study was to update information on patterns of antimicrobial resistance in Staphylococcus aureus isolated from skin infections in South Korea.

METHODS

We retrospectively analyzed clinical information and in vitro antimicrobial resistance data for 965 clinical S. aureus isolates obtained from skin infections during 2010-2013 in a university hospital in South Korea.

RESULTS

The rate of resistance to oxacillin (methicillin-resistant S. aureus [MRSA]) was 47.4%. Similar rates of resistance to erythromycin (45.6%), fusidic acid (44.0%), and clindamycin (42.3%) were noted. The rate of resistance to mupirocin was 8.4%. Overall, 4.9% of isolates were resistant to both fusidic acid and mupirocin. None of the isolates showed resistance to habekacin, synercid, teicoplanin, or vancomycin. Generally, antimicrobial resistance rates did not increase from 2010 to 2013 except with reference to a few agents such as mupirocin and rifampin. Isolates from surgical patients, inpatients, non-dermatology outpatients, and adult patients showed relatively high rates of resistance to multiple antimicrobials. Resistance to mupirocin was not only lower than that to fusidic acid but was consistent across clinical contexts.

CONCLUSIONS

The prevalence of MRSA in skin infections in South Korea did not increase during 2010-2013. Isolates from dermatology outpatients showed relatively lower rates of resistance to multiple antimicrobials than isolates from non-dermatology outpatients. Among topical antimicrobials, resistance to mupirocin was relatively low regardless of clinical condition.

Prevalence of Mupirocin Resistance Among Staphylococci, its Clinical Significance and Relationship to Clinical Use

Introduction:

Mupirocin competitively inhibits bacterial isoleucyl transfer-RNA synthetase and inhibit bacterial protein synthesis. Widespread usage and over the counter availability of the drug has resulted in resistance among Staphylococcus species.

Objectives:

This study aimed to determine the overall prevalence of mupirocin resistance among staphylococci. Correlate clinical significance of mupirocin resistance and its relationship to clinical use.

Methods:

Consecutive, nonrepetitive, clinical isolates of Staphylococcus aureus (n = 98), and coagulase-negative staphylococci (CoNS) (n = 45) from skin and soft-tissue infections between January 2014 and June 2014 were studied. Antibiotic susceptibility testing was done according to Clinical and Laboratory Standards Institute guidelines. Low- and high-level mupirocin resistance was screened by using 5 µg and 200 µg discs respectively and confirmed by agar dilution. Annual consumption of mupirocin was studied and correlated with resistance.

Results:

High-level mupirocin resistance was found in 8.2% S. aureus and 15.6% of CoNS, while low-level mupirocin resistance was found in 17% S. aureus and 8.9% CoNS. High-level mupirocin resistance was more common in methicillin-sensitive S. aureus isolates when compared with methicillin-resistant S. aureus isolates (P < 0.05). Mupirocin resistant S. epidermidis were associated with methicillin resistance and constitutive clindamycin resistance.

Conclusion:

High prevalence of mupirocin resistance was found in the present study. Increased prevalence of mupirocin resistance among community-acquired staphylococci demands the judicious use of the drug in the community.

Characterization of Staphylococcus aureus infections in children with Down syndrome

Staphylococcus aureus infections in the Down syndrome (DS) population have not been well characterized. This study determined clinical and molecular characteristics of S. aureus infections in children with DS followed at Texas Children's Hospital (TCH), from 2001 to 2011. Patients were retrospectively identified from an ongoing S. aureus surveillance study. Medical records were reviewed. Isolates were characterized by antimicrobial susceptibility, pulsed-field gel electrophoresis patterns, and detection of PVL genes (pvl), mupA (high-level mupirocin resistance gene), smr (chlorhexidine resistance conferring gene), and Staphylococcal Chromosomal Cassette mec (SCCmec) type. Twenty-six patients with DS had a total of 34 S. aureus infections (8 recurrent); 61% were MRSA. DS patients represented 16.8 per 10,000 community onset S. aureus infections seen at TCH. Among 26 initial infections 17 were skin and soft tissue (SSTI), 7 were outer or middle ear and 2 were invasive infections. Seventeen patients were hospitalized. Thirteen (65%) of 20 available isolates were USA300, 14 were pvl+, 5 were mupA+, and 8 were smr+. Five of 8 (63%) recurrent infections were ear infections. All 4 recurrent ear isolates available for study were smr+, ciprofloxacin non-susceptible and treated with ciprofloxacin otic drops. S. aureus infections among patients with DS were similar in presentation to other patient groups, except for a greater proportion being associated with ear infections. Seventy percent of ear fluid isolates carried antiseptic and fluoroquinolone resistance genes. A study of a greater number of DS patients is warranted to further explore these findings.

Clonal variation in high- and low-level phenotypic and genotypic mupirocin resistance of MRSA isolates in south-east London

OBJECTIVES

Both low-level mupirocin resistance (LMR) and high-level mupirocin resistance (HMR) have been identified. The aim of this study was to determine the epidemiology of LMR and HMR in MRSA isolates at five hospitals that have used mupirocin for targeted decolonization as part of successful institutional control programmes.

METHODS

All MRSA identified in three microbiology laboratories serving five central and south-east London hospitals and surrounding communities between November 2011 and February 2012 were included. HMR and LMR were determined by disc diffusion testing. WGS was used to derive multilocus sequence types (MLSTs) and the presence of HMR and LMR resistance determinants.

RESULTS

Prevalence of either HMR or LMR amongst first healthcare episode isolates from 795 identified patients was 9.69% (95% CI 7.72-11.96); LMR was 6.29% (95% CI 4.70-8.21) and HMR was 3.40% (95% CI 2.25-4.90). Mupirocin resistance was not significantly different in isolates identified from inpatients at each microbiology laboratory, but was more common in genotypically defined 'hospital' rather than 'community' isolates (OR 3.17, 95% CI 1.36-9.30, P = 0.002). LMR was associated with inpatient stay, previous history of MRSA and age ≥65 years; HMR was associated with age ≥65 years and residential postcode outside London. LMR and HMR varied by clone, with both being low in the dominant UK MRSA clone ST22 compared with ST8, ST36 and ST239/241 for LMR and with ST8 and ST36 for HMR. V588F mutation and mupA carriage had high specificity (>97%) and area under the curve (>83%) to discriminate phenotypic mupirocin resistance, but uncertainty around the sensitivity point estimate was large (95% CI 52.50%-94.44%). Mutations in or near the mupA gene were found in eight isolates that carried mupA but were not HMR.

CONCLUSIONS

Mupirocin resistance was identified in <10% of patients and varied significantly by clone, implying that changes in clonal epidemiology may have an important role in determining the prevalence of resistance in conjunction with selection due to mupirocin use.

High prevalence of mupirocin resistance in Staphylococcus aureus isolates from a pediatric population

Topical mupirocin is used widely to treat skin and soft tissue infections and to eradicate nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA). Few studies to date have characterized the rates of S. aureus mupirocin resistance in pediatric populations. We retrospectively studied 358 unique S. aureus isolates obtained from 249 children seen in a predominantly outpatient setting by the Division of Pediatric Dermatology at a major academic center in New York City between 1 May 2012 and 17 September 2013. Mupirocin resistance rates and the associated risk factors were determined using a logistic regression analysis. In our patient population, 19.3% of patients had mupirocin-resistant S. aureus isolates at the time of their first culture, and 22.1% of patients with S. aureus infection had a mupirocin-resistant isolate at some time during the study period. Overall, 31.3% of all S. aureus isolates collected during the study period were resistant to mupirocin. Prior mupirocin use was strongly correlated (odds ratio [OR] = 26.5; P = <0.001) with mupirocin resistance. Additional risk factors for mupirocin resistance included methicillin resistance, atopic dermatitis (AD), epidermolysis bullosa (EB), immunosuppression, and residence in northern Manhattan and the Bronx. Resistance to mupirocin is widespread in children with dermatologic complaints in the New York City area, and given the strong association with mupirocin exposure, it is likely that mupirocin use contributes to the increased resistance. Routine mupirocin testing may be important for MRSA decolonization strategies or the treatment of minor skin infections in children.

Epidemic MRSA clone ST22-IV is more resistant to multiple host- and environment-related stresses compared with ST228-I

BACKGROUND

ST22-IV is a successful hospital-associated MRSA clone. Due to its known ability to replace other MRSA clones in hospitals, it became a dominant clone in Europe and beyond. So far, there are no studies investigating the relationship between the epidemiological success of MRSA clones and their capacity to withstand commonly encountered stresses.

METHODS

We investigated the fitness of ST22-IV in comparison with the replaced clone ST228-I, evaluating its resistance to oxidative stress, autolytic activity, growth at high osmolarity and in acid and alkaline environments and survival under desiccation and heat shock. We also compared their phenotypic characteristics and examined the impact of antibiotic consumption on epidemiological success.

RESULTS

Here we demonstrate that the dominance of ST22-IV is linked neither to changes in antibiotic consumption nor to acquisition of additional resistances over time. Strong α-haemolysin activity, the production of β-haemolysin and the presence of an active agr could partly explain the virulence of ST22-IV previously observed in a murine model of pneumonia. Most importantly, we show that ST22-IV compared with ST228-I, besides retaining susceptibility to most antibiotics over time, has a superior capacity to survive under all stress conditions tested, which bacteria commonly face during their life cycle.

CONCLUSIONS

Our results support our hypothesis that ST22-IV has a fitness advantage over ST228-I. This fitness advantage could have allowed ST22-IV to displace ST228-I without acquiring additional resistances and could help explain its epidemic success in hospital settings and its spread in Europe and beyond.

Susceptibility of Staphylococcus aureus to topical agents in the United States: a sentinel study

BACKGROUND

Mupirocin has been used topically for treating skin and skin structure infections and for nasal decolonization before surgical interventions. Pleuromutilin compounds, including retapamulin, provide similar treatment/interventional options. Rates of resistance of Staphylococcus aureus to mupirocin and other agents used to treat skin and skin structure infections vary between countries and medical centers, including those in the United States. These resistance rates may be associated with higher usage and/or improper epidemiologic practices.

OBJECTIVE

This study aimed to determine rates of resistance to topical and other class agents against S aureus isolates collected from SSSIs.

METHODS

Isolates were obtained from outpatients at 6 US dermatology centers in 5 states. Demographic data were collected from medical records, and each patient completed a study questionnaire on recent history of skin infections, antibiotic use, and hospitalization. Each isolate was tested against cephalothin, clindamycin, erythromycin, gentamicin, mupirocin, tetracycline, retapamulin, and trimethoprim/sulfamethoxazole.

RESULTS

Although methicillin-resistance rates varied between centers (range, 15.8%-35.5%), macrolide resistance was ~50% at all of the sites in this study. Mupirocin-resistant isolates were observed much more frequently from 1 center (33.9%), and nearly all demonstrated high-level resistance. Only 1 retapamulin-resistant isolate (0.5%) was observed, with a minimum inhibitory concentration of 16 µg/mL. The other agents had relatively low resistance rates, which varied between centers and were dependent on susceptibility to methicillin.

CONCLUSIONS

Although the rate of mupirocin-resistant S aureus isolates collected in this investigation was >10%, retapamulin resistance was infrequent. Surveillance of topical agents to determine resistance rates against targeted bacteria is necessary.

Decreased susceptibilities to Retapamulin, Mupirocin, and Chlorhexidine among Staphylococcus aureus isolates causing skin and soft tissue infections in otherwise healthy children

Topical antimicrobial and antiseptic agents are commonly used in the management of minor skin and soft tissue infections (SSTIs). Resistance to mupirocin has been documented in Staphylococcus aureus isolates causing SSTIs. Data are limited, however, on the prevalence of retapamulin resistance or tolerance to antiseptics. We sought to determine the prevalence of decreased susceptibility to retapamulin and mupirocin as well as the potential for decreased chlorhexidine susceptibility of S. aureus isolates from SSTIs in children. Two hundred isolates from patients with a single SSTI and 200 isolates from patients with ≥3 previous episodes from the years 2010 to 2012 were selected from an S. aureus surveillance study. Screening for retapamulin resistance was performed by the broth macrodilution method; mupirocin MICs were determined by Etest. PCR was performed for the presence of the smr gene associated with elevated MICs/minimum bactericidal concentrations (MBCs) to chlorhexidine. Among the isolates screened, 38 isolates (9.5%) exhibited retapamulin resistance, of which 22 (57.9%) were methicillin-resistant S. aureus (MRSA). Two isolates (0.5%) displayed cross-resistance to retapamulin and linezolid. Thirty-nine isolates (9.8%) were found to have mupirocin resistance. smr-positive S. aureus accounted for 14% of isolates. The proportion of smr-positive organisms increased during the study (P = 0.005). The prevalence of in vitro resistance to topical antimicrobials among S. aureus isolates causing SSTI in healthy children in our community is almost 10%. Retapamulin resistance was associated with cross-resistance to linezolid in 0.5% of isolates. In addition, there was an increase in the proportion of smr-positive isolates. Further research including clinical correlations with these findings is warranted.

Improved understanding of factors driving methicillin-resistant Staphylococcus aureus epidemic waves

Methicillin-resistant Staphylococcus aureus (MRSA) remains one of the most important causes of nosocomial infections worldwide. Since the global spread of MRSA in the 1960s, MRSA strains have evolved with increased pathogenic potential. Notably, some strains are now capable of causing persistent infections not only in hospitalized patients but also in healthy individuals in the community. Furthermore, MRSA is increasingly associated with infections among livestock-associated workers, primarily because of transmission from animals to humans. Moreover, many MRSA strains have gained resistance to most available antibiotics. In this review, we will present current knowledge on MRSA epidemiology and discuss new endeavors being undertaken to understand better the molecular and epidemiological underpinnings of MRSA outbreaks.

MRSA decolonization of cotton rat nares by a combination treatment comprising lysostaphin and the antimicrobial peptide ranalexin

OBJECTIVES

To evaluate the in vivo effectiveness of a combination treatment containing ranalexin (a natural antimicrobial peptide) and lysostaphin (an antistaphylococcal endopeptidase) for reducing nasal burden of methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

The community-acquired MRSA strain S. aureus NRS384 (USA300-0114) was used in the present study because it is commonly isolated from human nares and it established consistent and reproducible colonization of cotton rat nares. This model was used to evaluate the efficacy of ranalexin/lysostaphin gels (0.1%-1% w/v; administered intranasally once or once per day for 3 consecutive days) for reducing nasal MRSA burden. Control animals were administered vehicle gel only (0.5% hydroxypropyl methylcellulose) or 2% mupirocin, which is used clinically for nasal decolonization of MRSA. Nasal MRSA burden was assessed at 192 h post-inoculation, which was at least 72 h after the final treatment had been administered. An additional study assessed the efficacy of 0.1% ranalexin/lysostaphin against a mupirocin-resistant MRSA strain (MUP20), which had been selected by serial passage of S. aureus NRS384 through subinhibitory concentrations of mupirocin.

RESULTS

Gels containing 0.1% ranalexin/lysostaphin consistently reduced median nasal burden of MRSA to an extent similar to or greater than 2% mupirocin. Treatment with 0.1% ranalexin/lysostaphin was also effective against the MUP20 strain. There was evidence for only minimal irritancy in cotton rat nares administered three doses of 0.1% ranalexin/lysostaphin, suggesting that this agent is suitable for short-course therapy such as is employed currently for nasal decolonization with mupirocin.

CONCLUSIONS

Ranalexin/lysostaphin could serve as an alternative to mupirocin for nasal decolonization of MRSA.

Prevention of peritoneal dialysis catheter infections in Saudi peritoneal dialysis patients: the emergence of high-level mupirocin resistance

PURPOSE

Exit-site infection (ESI) and peritonitis remain the major causes of morbidity and mortality in peritoneal dialysis (PD) patients. This study compared the effectiveness of local mupirocin ointment and gentamicin cream in preventing both gram-positive and gram-negative bacterial infections in PD patients.

METHODS

Patients from two centers (n = 203) were assigned to daily mupirocin ointment or gentamicin cream application. Infections were tracked prospectively by organisms and expressed as episodes per patient-year for both ESI and peritonitis.

RESULTS

The rate of gram-positive ESI was 0.31/episode/patient-year and 0.22 episodes/patient-year (p<0.05), whereas the rate of gram-negative ESI was 0.28 episode/patient-year and 0.11 episode/patient-year (p<0.01) in the mupirocin group and gentamicin group, respectively. Gram-positive ESI occurred in 17.1% vs 10.2% of patients (p<0.05), whereas 20% of and 5.1% of patients (p<0.001) had gram-negative ESI in the 2 groups respectively. S.aureus was cultured at exit-site in the mupirocin group in 27.8% patients, 60% (16.7% of the total Gram-positive isolates) of them being with high-level mupirocin-resistance. Pseudomonas aeruginosa was cultured in 21.8% of ESI in the mupirocin group, and in only 6.7% in the gentamicin group (p<0.01). Peritonitis rates were lower using gentamicin cream, 0.17 episode/patient-year compared with mupirocin, 0.39 episode/patient-year (p<0.01). With multivariate analysis, only gentamicin exit-site use was a significant predictor for lower catheter infection rate.

CONCLUSION

Prolonged use of mupirocin for ESI-prophylaxis is associated with the emergence of mupirocin-resistant S. aureus. Gentamicin cream is superior to mupirocin ointment in the prevention of PD catheter infections.

Chlorhexidine and mupirocin susceptibilities of methicillin-resistant staphylococcus aureus from colonized nursing home residents

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 μg/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.

Mupirocin and chlorhexidine resistance in Staphylococcus aureus in patients with community-onset skin and soft tissue infections

Decolonization measures, including mupirocin and chlorhexidine, are often prescribed to prevent Staphylococcus aureus skin and soft tissue infections (SSTI). The objective of this study was to determine the prevalence of high-level mupirocin and chlorhexidine resistance in S. aureus strains recovered from patients with SSTI before and after mupirocin and chlorhexidine administration and to determine whether carriage of a mupirocin- or chlorhexidine-resistant strain at baseline precluded S. aureus eradication. We recruited 1,089 patients with community-onset SSTI with or without S. aureus colonization. In addition to routine care, 483 patients were enrolled in a decolonization trial: 408 received intranasal mupirocin (with or without antimicrobial baths), and 258 performed chlorhexidine body washes. Patients were followed for up to 12 months with repeat colonization cultures. All S. aureus isolates were tested for high-level mupirocin and chlorhexidine resistance. At baseline, 23/1,089 (2.1%) patients carried a mupirocin-resistant S. aureus strain and 10/1,089 (0.9%) patients carried chlorhexidine-resistant S. aureus. Of 4 patients prescribed mupirocin, who carried a mupirocin-resistant S. aureus strain at baseline, 100% remained colonized at 1 month compared to 44% of the 324 patients without mupirocin resistance at baseline (P = 0.041). Of 2 patients prescribed chlorhexidine, who carried a chlorhexidine-resistant S. aureus strain at baseline, 50% remained colonized at 1 month compared to 48% of the 209 patients without chlorhexidine resistance at baseline (P = 1.0). The overall prevalence of mupirocin and chlorhexidine resistance is low in S. aureus isolates recovered from outpatients, but eradication efforts were less successful in patients carrying a mupirocin-resistant S. aureus strain at baseline.

Phenotypic and molecular characterization of Staphylococcus aureus recovered from different clinical specimens of inpatients at a teaching hospital in Shanghai between 2005 and 2010

Staphylococcus aureus, including meticillin-sensitive and -resistant S. aureus (MSSA and MRSA, respectively), is associated with severe nosocomial human infections. This study aimed to investigate the molecular profile, including the dynamic changes and genotype/phenotype correlation, of S. aureus isolates recovered from different clinical specimens of inpatients with S. aureus infection over a 6-year span at a teaching hospital in Shanghai, China. Between 2005 and 2010, a random sample of 610 unique S. aureus isolates was collected from different clinical samples of inpatients with S. aureus infection for molecular and antibiotic susceptibility analysis. The results showed that, among the 610 S. aureus isolates, 20 sequence types (STs) determined by multi-locus sequence typing (primarily ST239, ST5, ST7, ST188 and ST398) and 52 spa types (primarily t002, t037, t030 and t601) were found. In total, 444 isolates (72.8 %) were MRSA and 166 (27.2 %) were MSSA. ST239-MRSA-III-spa t037 and ST5-MRSA-II-spa t002 were the predominant MRSA clones. From 2005 to 2010, spa t002, spa t037 and their corresponding STs (ST5 and ST239) were the most frequent clones among all of the S. aureus isolates and showed the most resistant phenotypes to various antibiotics. Generally, the different genotypes showed different drug resistance rates, but no isolates were resistant to vancomycin, teicoplanin or linezolid. The profiles of virulence and resistance genes differed by genetic background, with the ST239 and ST5 strains showing higher resistance rates to gentamicin, cefoxitin, ampicillin, cefazolin, erythromycin, clindamycin and levofloxacin than strains of other types. Moreover, the antiseptic resistance genes qacA/B were generally associated with these two types. The prevalence of STs was different among different clinical specimens and also changed by year. Recently (2009-2010), the distribution of predominant MRSA clones decreased, whilst the prevalence of non-predominant MSSA clones increased, especially for the isolates causing bacteraemia. Continual monitoring of clinical isolates is necessary to develop and maintain an effective strategy against S. aureus infection in the hospital setting.

Rare occurrence of mupirocin resistance among clinical Staphylococcus isolates in Jordan

Staphylococcal infections have high occurrence in Jordanian patients. This study was carried out to determine the rates of high- and low-level mupirocin resistance (MupH and MupL) among staphylococci with the molecular characterization. Two hundred and thirty-two non-duplicate Staphylococcus spp. isolated from different clinical specimens were tested for mupirocin susceptibility using disk diffusion method and minimum inhibitory concentration (MIC). Resistance genes and clone relatedness was studied using polymerase chain reaction (PCR) and enterobacterial repetitive intergenic consensus primers (Eric-PCR) for the latter. Plasmid curing was performed to determine the genetic location of MupA gene. Among the 232 strains, 144 (62%) were methicillin-resistant Staphylococcus aureus (MRSA), 33 (14.2%) methicillin-susceptible Staphylococcus aureus (MSSA) and 55 (23.7%) were of other coagulase-negative Staphylococcus spp. (CoNS). Of all strains tested, only 6 (2.6%) were mupirocin resistant. MecA gene was detected in both MupL and MupH strains but MupA gene was only detected in MupH. Plasmid curing improved the plasmidic location of MupA gene. Molecular typing by Eric-PCR method revealed heterogenicity of the genetic make up of our MupL and MupH strains. Staphylococci with MupA-carrying genes are present in Jordanian hospitals, but thank to the limited use of mupirocin, they remain rare.

Progress toward a Staphylococcus aureus vaccine

High attack rates and the ability of Staphylococcus aureus to develop resistance to all antibiotics in medical practice heightens the urgency for vaccine development. S. aureus causes many disease syndromes, including invasive disease, pneumonia, and skin and soft tissue infections. It remains unclear whether a single vaccine could protect against all of these. Vaccine composition is also challenging. Active immunization with conjugated types 5 and 8 capsular polysaccharides, an iron scavenging protein, isdB, and passive immunization against clumping factor A and lipoteichoic acid have all proven unsuccessful in clinical trials. Many experts advocate an approach using multiple antigens and have suggested that the right combination of antigens has not yet been identified. Others advocate that a successful vaccine will require antigens that work by multiple immunologic mechanisms. Targeting staphylococcal protein A and stimulating the T-helper 17 lymphocyte pathway have each received recent attention as alternative approaches to vaccination in addition to the more traditional identification of opsonophagocytic antibodies. Many questions remain as to how to successfully formulate a successful vaccine and to whom it should be deployed.

Association of high-level mupirocin resistance and multidrug-resistant methicillin-resistant Staphylococcus aureus at an academic center in the midwestern United States

Mupirocin is a topical antimicrobial used to eradicate methicillin-resistant Staphylococcus aureus (MRSA) colonization, usually in the absence of susceptibility testing. We hypothesized that high-level (HL) mupirocin resistance was associated with multidrug resistance (MDR). To this end, unique patient isolates identified at our institution during 2008 were stratified into those resistant to ≥ 3 non-β-lactam antimicrobial classes (MDR) and non-MDR MRSA. HL mupirocin resistance was screened by mupA PCR on all MDR isolates (n = 191) and a 20% random sample (n = 130) of non-MDR isolates; E-testing confirmed HL resistance. We found that among MDR isolates, 13 (6.8%) carried mupA, whereas none of the non-MDR isolates did (P = 0.001). Thus, although the overall prevalence of HL mupirocin resistance is low among MRSA isolates at our institution, an association exists between mupA carriage and MDR. Using genotyping and antimicrobial susceptibility profiling, we identified nine HL mupirocin-resistant clones. Whereas the majority of mupA-negative MDR isolates had a health care-associated MRSA (HA-MRSA) genotype (multilocus sequence type 5 [ST5] or SCCmec type II), the majority of mupA-positive MDR isolates had a community-associated MRSA (CA-MRSA) genotype (ST8 or SCCmec type IV). However, CA- and HA-MRSA genotypes were more evenly distributed among mupA-positive isolates compared to mupA-negative MDR isolates. Thus, in Chicago, mupA is circulating among both CA- and HA-MRSA backgrounds.