A decline in mupirocin resistance in methicillin-resistant Staphylococcus aureus accompanied administrative control of prescriptions

Impact of formulary interventions on the minimum inhibitory concentration of methicillin-resistant Staphylococcus aureus to mupirocin, chlorhexidine, and octenidine in a Singapore tertiary institution

Methicillin-resistant Staphylococcus aureus (MRSA) decolonization is an effective measure to prevent clinical infection but resistance is a concern. We aim to evaluate the impact of mupirocin (MUP) ointment formulary removal, plateauing use of chlorhexidine gluconate (CHG), and hospital-wide introduction of octenidine (OCT)-based products on the minimum inhibitory concentration (MIC) of MRSA to MUP, CHG, and OCT in our hospital. A prevalence study was conducted at three time points (TP) on consecutive MRSA screening isolates to evaluate for their MICs to MUP, CHG, and OCT using broth microdilution sensititre plates and detection of the ileS-2 gene encoding high-level MUP resistance in 2013 (pre-intervention TP1; n = 160), 2016 (early post-intervention TP2; n = 99) and 2017 (late post-intervention TP3; n = 76). Statistical analyses were performed using Chi square test with reference from TP1. There was a significant improvement in MUP susceptibility (MIC < 4 mcg/ml) from 71.9% (TP1) to 86.9% (TP2; p = 0.006) to 88.2% (TP3; p = 0.007). The prevalence of MUP high-level resistance (MIC > 256 mcg/ml) reduced from 25.0% (TP1) to 12.1% (TP2; p = 0.014) to 5.3% (TP3; p = 0.001). Likewise, the prevalence of isolates harboring the ileS-2 gene decreased from 28.1% (TP1) to 18.2% (TP2; p = 0.072) to 9.2% (TP3; p = 0.002). OCT MIC range remains stable at 0.5 to 1 mcg/ml across all three TPs. The proportion of isolates with reduced CHG susceptibility (MIC ≥ 4 mcg/ml) increased over the three TPs from 23.1 to 27.2% (p = 0.45) to 42.1% (p = 0.003). Active formulary regulations have an impact on the resistance profile of MRSA and can be used as a strategy to preserve the MRSA decolonization armamentarium.

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.

Continued expansion of USA300-like methicillin-resistant Staphylococcus aureus (MRSA) among hospitalized patients in the United States

We characterized spa types, SCCmec types, and antimicrobial resistance patterns of 516 methicillin-resistant Staphylococcus aureus (MRSA) isolates, collected between 2011 and 2014 from nares and blood cultures of United States patients. Among nares isolates, 45 spa types were observed; 29.9% were t002/SCCmec II and 30.9% were t008/SCCmec IV. Among blood isolates, 40 spa types were identified; 24.4% were t002/SCCmec II and 39.9% were type t008/SCCmec IV. Compared to data from our 2009-2010 survey, the percentage of t008/SCCmec IV isolates from nares increased significantly (20.4%-30.9%; P=0.004) while the percentage from positive blood cultures remained similar (39.2% versus 39.9%; P=0.921). There were also significant changes in the overall antimicrobial resistance patterns observed, including the decrease of the clindamycin, erythromycin, levofloxacin and moxifloxacin multidrug resistance pattern, likely the result of t002/SCCmec II strains being displaced by t008/SCCmec IV strains. Rates of high-level mupirocin resistance did not change significantly from our past study (4.1% compared to 4.7%; P=0.758) but an increase in low-level resistance, particularly among t002/SCCmec II isolates, was observed.

Reduction of methicillin-resistant Staphylococcus aureus infection in long-term care is possible while maintaining patient socialization: A prospective randomized clinical trial

BACKGROUND

Antibiotic resistance is a challenge in long-term care facilities (LTCFs). The objective of this study was to demonstrate that a novel, minimally invasive program not interfering with activities of daily living or socialization could lower methicillin-resistant Staphylococcus aureus (MRSA) disease.

METHODS

This was a prospective, cluster-randomized, nonblinded trial initiated at 3 LTCFs. During year 1, units were stratified by type of care and randomized to intervention or control. In year 2, all units were converted to intervention consisting of universal decolonization using intranasal mupirocin and a chlorhexidine bath performed twice (2 decolonization-bathing cycles 1 month apart) at the start of the intervention period. Subsequently, after initial decolonization, all admissions were screened on site using real-time polymerase chain reaction, and those MRSA positive were decolonized, but not isolated. Units received annual instruction on hand hygiene. Enhanced bleach wipe cleaning of flat surfaces was done every 4 months.

RESULTS

There were 16,773 tests performed. The MRSA infection rate decreased 65% between baseline (44 infections during 365,809 patient days) and year 2 (12 infections during 287,847 patient days; P <.001); a significant reduction was observed at each of the LTCFs (P <.03).

CONCLUSIONS

On-site MRSA surveillance with targeted decolonization resulted in a significant decrease in clinical MRSA infection among LTCF residents.

Distribution of high-level mupirocin resistance among clinical MRSA

Mupirocin is a topical antibiotic for methicillin-resistant Staphylococcus aureus (MRSA) decolonization in hospital settings and nursing homes and is used as a highly effective antibiotic against MRSA. In this study, we aimed to evaluate the frequency of high-level mupirocin-resistant (HLMR) strains among the MRSA subtypes. A total of 188 clinical MRSA isolates were collected from 2011 to 2014, and their susceptibility to antimicrobial agents and vancomycin resistance was evaluated using disc diffusion method and micro-dilution method, respectively. Furthermore, the presence of mecA, SSCmec, mupA and mupB was assessed by PCR. All isolates were multi-drug resistant (MDR) but 2 strains (1.06%) were resistant to mupirocin. Minimum inhibitory concentration (MIC) of vancomycin for 8 strains (4.7%) was higher than 2 μg/ml. Of 188 isolates, 188 (100%), 64 (34.04%), 8 (4.3%), 150 (79.8%), 26 (13.8%), 2 (1.06) and 2 (1.06%) isolates possessed mecA, SCCmec types I, II, III, IV, mupA and mupB genes, respectively. Our data showed that despite infection control policy enforced by health care committee, the rate of mupirocin resistance among MRSA strains is continuously rising.

Mupirocin for Controlling Methicillin-ResistantStaphylococcus Aureus: Lessons From a Decade of Use at a University Hospital

Background:

From 1990 to 1995 at Hospital Universitario dementino Fraga Filho, patients colonized or infected with methicillin-resistantStaphylococcus aureus(MRSA) were treated with mupirocin to eliminate MRSA carriage. In 1995, 65% of MRSA patients at this hospital had mupirocin-resistant isolates. Starting in 1996, mupirocin use was restricted to patients colonized, but not infected, with MRSA.

Objectives:

To describe the use of mupirocin for controlling MRSA over a decade and to analyze the molecular epidemiology of mupirocin-resistant MRSA infections at this hospital.

Setting:

A 490-bed, tertiary-care university hospital.

Methods:

The incidence densities of patients with MRSA and acquisition of mupirocin by the hospital were calculated for the period 1992–2001.S. aureusisolates from 1999–2000 were analyzed by pulsed-field gel electrophoresis. Mupirocin-resistant MRSA isolates from 1994–1995 and 1999–2000 were analyzed forileS-2gene background polymorphisms.

Results:

The incidence density of MRSA patients increased slightly over time, whereas the purchase of mupirocin decreased dramatically. Mupirocin-resistant MRSA infections decreased from 65% in 1994–1995 to 15% in 1999–2000. The MRSA Brazilian clone, detected in 1992, was still highly prevalent. The sameileS-2 encoding plasmid found in 1994–1995 persisted in three identical MRSA isolates from 1999–2000 belonging to the Brazilian clone.

Conclusions:

After mupirocin use decreased, theileS-2 encoding plasmid persisted in only a few Brazilian clone isolates. Our data on mupirocin-resistant MRSA incidence and mupirocin use strongly suggested that restricted use was related to decreased rates of mupirocin resistance at our hospital. (Infect Control Hosp Epidemiol 2005;26:662-667)

Aminoacyl-tRNA Synthetases in the Bacterial World

Aminoacyl-tRNA synthetases (aaRSs) are modular enzymes globally conserved in the three kingdoms of life. All catalyze the same two-step reaction, i.e., the attachment of a proteinogenic amino acid on their cognate tRNAs, thereby mediating the correct expression of the genetic code. In addition, some aaRSs acquired other functions beyond this key role in translation. Genomics and X-ray crystallography have revealed great structural diversity in aaRSs (e.g., in oligomery and modularity, in ranking into two distinct groups each subdivided in 3 subgroups, by additional domains appended on the catalytic modules). AaRSs show huge structural plasticity related to function and limited idiosyncrasies that are kingdom or even species specific (e.g., the presence in many Bacteria of non discriminating aaRSs compensating for the absence of one or two specific aaRSs, notably AsnRS and/or GlnRS). Diversity, as well, occurs in the mechanisms of aaRS gene regulation that are not conserved in evolution, notably between distant groups such as Gram-positive and Gram-negative Bacteria. The review focuses on bacterial aaRSs (and their paralogs) and covers their structure, function, regulation, and evolution. Structure/function relationships are emphasized, notably the enzymology of tRNA aminoacylation and the editing mechanisms for correction of activation and charging errors. The huge amount of genomic and structural data that accumulated in last two decades is reviewed, showing how the field moved from essentially reductionist biology towards more global and integrated approaches. Likewise, the alternative functions of aaRSs and those of aaRS paralogs (e.g., during cell wall biogenesis and other metabolic processes in or outside protein synthesis) are reviewed. Since aaRS phylogenies present promiscuous bacterial, archaeal, and eukaryal features, similarities and differences in the properties of aaRSs from the three kingdoms of life are pinpointed throughout the review and distinctive characteristics of bacterium-like synthetases from organelles are outlined.

South-East Asia study alliance guidelines on the management of acne vulgaris in South-East Asian patients

The management of acne in South-East Asia is unique, as Asian skin and local variables require a clinical approach unlike that utilized in other parts of the world. There are different treatment guidelines per country in the region, and a group of leading dermatologists from these countries convened to review these guidelines, discuss current practices and recent advances, and formulate consensus guidelines to harmonize the management of acne vulgaris in the region. Emphasis has been placed on formulating recommendations to impede the development of antibiotic resistance in Propionibacterium acnes. The group adopted the Acne Consensus Conference system for grading acne severity. The group recommends that patients may be treated with topical medications including retinoids, benzoyl peroxide (BPO), salicylic acid, a combination of retinoid and BPO, or a combination of retinoids and BPO with or without antibiotics for mild acne; topical retinoid with topical BPO and a oral antibiotic for moderate acne; and oral isotretinoin if the patient fails first-line treatment (a 6- or 8-week trial of combined oral antibiotics and topical retinoids with BPO) for severe acne. Maintenance acne treatment using topical retinoids with or without BPO is recommended. To prevent the development of antibiotic resistance, topical antibiotics should not be used as monotherapy or used simultaneously with oral antibiotics. Skin care, comprised of cleansing, moisturizing and sun protection, is likewise recommended. Patient education and good communication is recommended to improve adherence, and advice should be given about the characteristics of the skin care products patients should use.

Drug utilization review of mupirocin ointment in a Korean university-affiliated hospital

BACKGROUND/AIMS

Intranasal mupirocin and chlorhexidine bathing are candidate strategies to prevent healthcare-associated infections caused by methicillin-resistant Staphylococcus aureus (MRSA). In Korea, intranasal mupirocin is not available, and mupirocin ointment, an over-the-counter drug, has been used indiscriminately. Furthermore, because it is covered by health insurance, mupirocin is easy to prescribe within hospitals.

METHODS

We performed a mupirocin drug utilization review (DUR) within Hallym University Sacred Heart Hospital. Annual use of mupirocin was investigated between 2003 and 2013, and monthly consumption of mupirocin was assessed during the final 2-year period. The DUR focused on August 2012, the period of highest use of mupirocin. Also, we investigated trends in mupirocin resistance in MRSA between 2011 and 2013.

RESULTS

Annual consumption of mupirocin increased from 3,529 tubes in 2003 to 6,475 tubes in 2013. During August 2012, 817 tubes were prescribed to 598 patients; of these, 84.9% were prescribed to outpatients, and 77.6% at the dermatology department. The most common indication was prevention of skin infections (84.9%), and the ointment was combined with systemic antibiotics in 62.9% of cases. The average duration of systemic antibiotic administration was about 7.8 days. The rate of low-level mupirocin resistance in MRSA increased from 8.0% to 22.0%, and that of high-level mupirocin resistance increased from about 4.0% to about 7.5%.

CONCLUSIONS

Inappropriate use of mupirocin is prevalent. Considering the increase in resistance and the future application of intranasal mupirocin, prophylactic use of mupirocin in dermatology departments should be reconsidered.

Effects of fluoroquinolone restriction (from 2007 to 2012) on resistance in Enterobacteriaceae: interrupted time-series analysis

BACKGROUND

Antibiotic stewardship is a key component in the effort to reduce healthcare-associated infections.

AIM

To describe the implementation and analyse the impact of fluoroquinolone restriction on resistance in Enterobacteriaceae, focusing on urinary isolates of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, which were historically almost universally resistant to fluoroquinolones.

METHODS

ESBL-producing E. coli hospital and community isolates, obtained between April 2009 and March 2012 from consecutive non-duplicate urine samples, were included in an interrupted time-series analysis based on a Poisson distribution model. Periods before and after fluoroquinolone restriction were compared. The trend in fluoroquinolone resistance in all urinary isolates of Enterobacteriaceae (N ≈ 20,000 per year) and blood culture isolates of E. coli (N ≈ 350) between 2009 and 2013 were also analysed.

FINDINGS

A large decline in the percentage of ciprofloxacin-resistant ESBL-producing urinary E. coli isolates was observed in both hospital (risk ratio: 0.473; 95% confidence interval: 0.315-0.712) and community settings (0.098; 0.062-0.157). The decline was also marked in all urinary isolates of Enterobacteriaceae and E. coli isolates from blood cultures.

CONCLUSION

We conclude that reducing fluoroquinolone usage to a level of ≤2 defined daily doses per 100 occupied bed-days in hospital sufficiently removed selection pressure to allow resistant Enterobacteriaceae – specifically, the UK endemic strains of ESBL-producing E. coli – to revert back to fluoroquinolone susceptibility within a short span of four months. This was accompanied with a concomitant reduction in overall ESBL burden.

Mupirocin-induced mutations in ileS in various genetic backgrounds of methicillin-resistant Staphylococcus aureus

Topical mupirocin is widely used for the decolonization of methicillin-resistant Staphylococcus aureus (MRSA) carriers. We evaluated the capacity of various MRSA clonotypes to develop mutations in the ileS gene associated with low-level mupirocin resistance. Twenty-four mupirocin-sensitive MRSA isolates from a variety of genotypes (determined by a multilocus variable-number tandem-repeat assay) were selected. Mupirocin MICs were determined by Etest. The isolates were then incubated in subinhibitory concentrations of mupirocin for 7 to 14 days. Repeat MIC determinations and sequencing of the ileS gene were then performed. Doubling times of isolates exposed to mupirocin and of unexposed isolates were compared. We found that exposure to mupirocin led to rapid induction of low-level resistance (MICs of 8 to 24 μg/ml) in 11 of 24 (46%) MRSA isolates. This phenomenon was observed in strains with diverse genetic backgrounds. Various mutations were detected in 18 of 24 (75%) MRSA isolates. Acquisition of mutations appeared to be a stepwise process during prolonged incubation with the drug. Among the five isolates exhibiting low-level resistance and the highest MICs, four tested sensitive after incubation in the absence of mupirocin but there was no reversion to the susceptible wild-type primary sequence. Resistance was not associated with significant fitness cost, suggesting that MRSA strains with low-level mupirocin resistance may have a selective advantage in facilities where mupirocin is commonly used. Our findings emphasize the importance of the judicious use of this topical agent and the need to closely monitor for the emergence of resistance.

Emergence of new CMRSA7/USA400 methicillin-resistant Staphylococcus aureus spa types in Alberta, Canada, from 2005 to 2012

Methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most significant pathogens affecting global public health and health care systems. In Canada and the United States, the spread of MRSA is primarily attributed to a single dominant epidemic clone: CMRSA10/USA300. Despite this, the CMRSA7/USA400 epidemic clone has been reported to be the predominate epidemic clone in several Canadian provinces and some parts of the United States. This study examined the epidemiology of CMRSA7/USA400 MRSA in Alberta, Canada, from June 2005 to December 2012. Molecular characterization of CMRSA7/USA400 isolates was done using spa, SCCmec, PVL, and PFGE typing and identified two predominant spa types in Alberta: t128 and t1787. Although closely related, these spa types have distinct geographic distributions. From 2010 to 2012, the number of t128 infections has remained stable while there has been a nearly 3-fold increase in the number of provincial t1787 infections, accompanied by 10-fold increases in t1787 infection rates in some communities. Most t128 and t1787 patients were First Nations or Inuit people, and isolates were usually from skin and soft tissue infections in outpatients. t128 patients were significantly older than t1787 patients. Antimicrobial susceptibility testing showed higher mupirocin resistance in t1787 than in t128 MRSA. Improved strategies to reduce or stabilize t1787 infections in Alberta are needed.

Changing molecular epidemiology and high rates of mupirocin resistance among meticillin-resistant Staphylococcus aureus in Singaporean hospitals

A prospective cross-sectional study was performed to determine the continuing shift in the molecular epidemiology of meticillin-resistant Staphylococcus aureus (MRSA) in Singapore. In total, 666 MRSA isolates from screening cultures performed between 7 and 20 January 2013 were obtained from all seven public sector hospitals in Singapore and were subjected to molecular typing using multilocus variable-number tandem-repeat fingerprinting with confirmatory multilocus sequencing typing for clustered isolates. Isolates were also tested for the presence of the orfX-ACME insert and the high-level mupirocin resistance gene ileS-2. The major circulating clones in Singaporean hospitals were ST22 (63.2%), ST45 (18.9%) and ST239 (10.7%). The orfX-ACME insert was only found in ST239 isolates (31/71, 43.7%), but ileS-2 was found in 207 (31.1%) of the MRSA isolates, varying between 10.0% and 47.8% among the hospitals. In conclusion, the molecular epidemiology of MRSA in Singaporean hospitals has continued to change, with ST45 now replacing ST239 in addition to the ongoing replacement of the latter by ST22. Although a greater proportion of ST239 isolates carry the orfX-ACME insert, the actual clinical impact may be marginal as ST239 MRSA continues to decline. Finally, high-level mupirocin resistance rates are remarkably high in local healthcare-associated MRSA, with implications for MRSA decolonisation and infection prevention. Further surveillance is required to monitor the changing epidemiological trends.

Aminoacyl-tRNA Synthetases in the Bacterial World

Aminoacyl-tRNAsynthetases (aaRSs) are modular enzymesglobally conserved in the three kingdoms of life. All catalyze the same two-step reaction, i.e., the attachment of a proteinogenic amino acid on their cognate tRNAs, thereby mediating the correct expression of the genetic code. In addition, some aaRSs acquired other functions beyond this key role in translation.Genomics and X-ray crystallography have revealed great structural diversity in aaRSs (e.g.,in oligomery and modularity, in ranking into two distinct groups each subdivided in 3 subgroups, by additional domains appended on the catalytic modules). AaRSs show hugestructural plasticity related to function andlimited idiosyncrasies that are kingdom or even speciesspecific (e.g.,the presence in many Bacteria of non discriminating aaRSs compensating for the absence of one or two specific aaRSs, notably AsnRS and/or GlnRS).Diversity, as well, occurs in the mechanisms of aaRS gene regulation that are not conserved in evolution, notably betweendistant groups such as Gram-positive and Gram-negative Bacteria.Thereview focuses on bacterial aaRSs (and their paralogs) and covers their structure, function, regulation,and evolution. Structure/function relationships are emphasized, notably the enzymology of tRNA aminoacylation and the editing mechanisms for correction of activation and charging errors. The huge amount of genomic and structural data that accumulatedin last two decades is reviewed,showing how thefield moved from essentially reductionist biologytowards more global and integrated approaches. Likewise, the alternative functions of aaRSs and those of aaRSparalogs (e.g., during cellwall biogenesis and other metabolic processes in or outside protein synthesis) are reviewed. Since aaRS phylogenies present promiscuous bacterial, archaeal, and eukaryal features, similarities and differences in the properties of aaRSs from the three kingdoms of life are pinpointedthroughout the reviewand distinctive characteristics of bacterium-like synthetases from organelles are outlined.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Alberta, Canada: population-based surveillance, 2005-2008

SUMMARYIncreasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) has been reported in Canada. We report the results of a prospective surveillance of MRSA infections in Alberta over a consecutive 3-year period. A total of 8910 unique clinical MRSA isolates was analysed from July 2005 to June 2008. The incidence of MRSA infection increased over the study period and was highest in males, age group ⩾85 years, and the Calgary Area. CMRSA10 (USA300) and CMRSA2 (USA100/800) were the most common PFGE strain types, representing 53·0% and 27·9% of all isolates, respectively. Significant differences were noted between MRSA strains in the source of infection and antimicrobial susceptibility. The incidence of MRSA infection in Alberta has nearly doubled in the last 3 years; this is attributed to the emergence of CMRSA10 as the predominant strain.

Risk factors associated with mupirocin resistance in meticillin-resistant Staphylococcus aureus

Implementation of meticillin-resistant Staphylococcus aureus (MRSA) decolonisation programmes has been increasing and the emergence of mupirocin resistance has been reported. However, the patient-level risk factors associated with mupirocin resistance are not clear. In this study, independent predictors of mupirocin resistance in MRSA among Providence Veterans Affairs Medical Center patients with MRSA-positive culture dates between 1 July 2004 and 30 June 2008 were identified using a frequency-matched case-control study. Forty cases (mupirocin-resistant) were matched on culture date quarter and year to 270 controls (mupirocin-susceptible). The adjusted conditional logistic regression model identified three significant independent predictors associated with mupirocin resistance in MRSA: (1) exposure to mupirocin in the year prior to the culture date [odds ratio (OR): 9.84; 95% confidence interval (CI): 2.93-33.09]; (2) Pseudomonas aeruginosa infection in the year before the culture-related admission (4.85; 1.20-19.61); and (3) cefepime use in the year prior to culture (2.80; 1.03-7.58). In sensitivity analyses, previous mupirocin exposure was associated with low-level [minimum inhibitory concentration (MIC) 8-128mg/L; 23 cases, 202 controls; OR: 6.32; 95% CI: 1.58-25.33] and high-level (MIC ≥256mg/L; 17 cases, 151 controls; OR: 11.18; 95% CI: 1.89-66.30) mupirocin resistance. To our knowledge, this is the first case-control study to reveal a strong association between previous mupirocin exposure and subsequent mupirocin resistance in MRSA, with demonstrated robustness in low- and high-level mupirocin resistance. Mupirocin susceptibility monitoring is critical for facilities instituting decolonisation with mupirocin as increased use may reduce effectiveness through resistance.

Mupirocin resistance related to increasing mupirocin use in clinical isolates of methicillin-resistant Staphylococcus aureus in a pediatric population

We investigated the proportion of methicillin-resistant Staphylococcus aureus (MRSA) isolates from pediatric patients demonstrating mupirocin resistance related to mupirocin use at our institution. No mupirocin resistance was found in 98% of isolates, whereas mupirocin prescriptions increased by 110%. Resistance rates remained low despite the increasing use of mupirocin.

Livestock-associated methicillin-resistant Staphylococcus aureus sequence type 398 in humans, Canada

Recent emergence of infections resulting from this strain is of public health concern.

Rates of colonization with livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) sequence type 398 have been high for pigs and pig farmers in Canada, but prevalence rates for the general human population are unknown. In this study, 5 LA-MRSA isolates, 4 of which were obtained from skin and soft tissue infections, were identified from 3,687 tested MRSA isolates from persons in Manitoba and Saskatchewan, Canada. Further molecular characterization determined that these isolates all contained staphylococcal cassette chromosome (SCC) mecV, were negative for Panton-Valentine leukocidin, and were closely related by macrorestriction analysis with the restriction enzyme Cfr91. The complete DNA sequence of the SCCmec region from the isolate showed a novel subtype of SCCmecV harboring clustered regularly interspaced short palindromic repeats and associated genes. Although prevalence of livestock-associated MRSA seems to be low for the general population in Canada, recent emergence of infections resulting from this strain is of public health concern.

A comparison of risk factors associated with community-associated methicillin-resistant and -susceptible Staphylococcus aureus infections in remote communities

In this case-control study, cases [community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), n=79] and controls [community-associated methicillin-susceptible S. aureus (CA-MSSA), n=36] were defined as a laboratory-confirmed infection in a patient with no previous hospital-associated factors. Skin and soft tissue were the predominant sites of infection, both for cases (67·1%) and controls (55·6%). Most of the cases (79·7%) and controls (77·8%) were aged <30 years. Investigations did not reveal any significant statistical differences in acquiring a CA-MRSA or CA-MSSA infection. The most common shared risk factors included overcrowding, previous antibiotic usage, existing skin conditions, household exposure to someone with a skin condition, scratches/insect bites, and exposure to healthcare workers. Similar risk factors, identified for both CA-MRSA and CA-MSSA infections, suggest standard hygienic measures and proper treatment guidelines would be beneficial in controlling both CA-MRSA and CA-MSSA in remote communities.

Mupirocin resistance in patients colonized with methicillin-resistant Staphylococcus aureus in a surgical intensive care unit

BACKGROUND

Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) can be a precursor to serious infection, and decolonization with topical mupirocin has been studied as a means of preventing clinical infection. Mupirocin resistance in patients with MRSA has been reported, usually in the context of widespread mupirocin use.

METHODS

Patients admitted to a surgical intensive care unit (SICU) had nasal swab cultures for MRSA performed at admission, weekly, and at discharge in an active surveillance program. Collected MRSA isolates were tested for mupirocin resistance, and molecular analysis was performed. Clinical data on the characteristics and outcomes of the patients who stayed in the SICU for >48 h were collected prospectively.

RESULTS

Of the 302 MRSA isolates available for testing, 13.2% were resistant to mupirocin, with 8.6% having high-level resistance (minimum inhibitory concentration, >or=512 microg/mL) and 4.6% having low-level resistance (minimum inhibitory concentration, 8-256 microg/mL). Patients admitted to the SICU for >48 h who were colonized with mupirocin-resistant MRSA were more likely to have been admitted to our hospital during the previous year (P=.016), were older (P=.009), and had higher in-hospital mortality (16% vs. 33%; P=.027), compared with patients colonized with mupirocin-susceptible MRSA. Molecular analysis of the mupirocin-resistant isolates revealed that 72.5% of isolates contained staphylococcal cassette chromosome mec II. Repetitive sequence polymerase chain reaction typing revealed that high-level mupirocin resistance was present in multiple clonal groups. The rate of mupirocin use hospital-wide during the study period was 6.08 treatment-days per 1000 patient-days.

CONCLUSIONS

We documented a high rate of mupirocin resistance in MRSA isolates from SICU patients, despite low levels of in-hospital mupirocin use.

Antibacterial resistance and their genetic location in MRSA isolated in Kuwait hospitals, 1994-2004

Background

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major cause of serious infections in hospitals and in the community worldwide. In this study, MRSA isolated from patients in Kuwait hospitals were analyzed for resistance trends and the genetic location of their resistance determinants.

Methods

Between April 1994 and December 2004, 5644 MRSA isolates obtained from different clinical samples were studied for resistance to antibacterial agents according to guidelines from the National Committee for Clinical Laboratory Standards and the British Society for Antimicrobial Chemotherapy. The genetic location of their resistance determinants was determined by curing and transfer experiments.

Results

They were resistant to aminoglycosides, erythromycin, tetracycline, trimethoprim, fusidic acid, ciprofloxacin, chloramphenicol, rifampicin, mupirocin, cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide but susceptible to vancomycin, teicoplanin and linezolid. The proportion of the isolates resistant to erythromycin, ciprofloxacin and fusidic acid increased during the study period. In contrast, the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined. High-level mupirocin resistance increased rapidly from 1996 to 1999 and then declined. They contained plasmids of 1.9, 2.8, 3.0, 4.4, 27 and 38 kilobases. Genetic studies revealed that they carried plasmid-borne resistance to high-level mupirocin resistance (38 kb), chloramphenicol (2.8 – 4.4 kb), erythromycin (2.8–3.0 kb) and cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide (27 kb) and chromosomal location for methicillin, the aminoglycosides, tetracycline, fusidic acid, ciprofloxacin and trimethoprim resistance. Thus, the 27 kb plasmids had resistance phenotypes similar to plasmids reported in MRSA isolates in South East Asia.

Conclusion

The prevalence of resistance to erythromycin, ciprofloxacin, high-level mupirocin and fusidic acid increased whereas the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined during the study period. They contained 27-kb plasmids encoding resistance to cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide similar to plasmids isolated in MRSA from South East Asia. Molecular typing of these isolates will clarify their relationship to MRSA from South East Asia.

Staphylococcus aureus throat colonization is more frequent than colonization in the anterior nares

The aim of this study was to determine the frequency and persistence of Staphylococcus aureus carriage in the throat in relation to anterior naris carriage. By use of a sensitive enrichment broth, S. aureus was cultured from the two sites from 259 patients upon admission to an orthopedic ward and from 87 staff members of the same ward. The throat was the most common carriage site in both groups. Forty percent of the patients and 54% of the staff were positive for S. aureus in the throat, compared to 31% and 36%, respectively, in the anterior nares. To determine the persistence of carriage, 67 individuals were repeatedly sampled from the anterior nares and the throat over 2 years (5 to 10 sampling occasions; mean, 7.8). The majority, 58% (39/67), were defined as persistent carriers of S. aureus, considering culture results from both sites. Of the 39 persistent carriers, 15 individuals were culture positive from only the throat on more than half of the sampling occasions (these are called preferential throat carriers) while only 5% (two individuals) were preferential anterior naris carriers by use of the same definition. Typing of the collected S. aureus isolates by pulsed-field gel electrophoresis revealed that the same strain of S. aureus was present, over time, in the throat of an individual at least to the same extent as in the anterior nares. Throat carriage was at least as persistent as carriage in the anterior nares.

Decrease in the incidence of mupirocin resistance among methicillin-resistant Staphylococcus aureus in carriers from an intensive care unit

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious nosocomial problem, globally distributed. Decolonization with mupirocin can be used to control its dissemination.

OBJECTIVE

To determine the incidence of mupirocin resistance among MRSA carriers from an intensive care unit.

METHODS

We obtained 2723 nasal swabs during 3 years. Resistance to methicillin and mupirocin were verified (agar diffusion and the E test) and confirmed by polymerase chain reaction (PCR) (mecA for methicillin; ileS-2 and mupA for mupirocin). Plasmid-curing procedure and pulsed-field gel electrophoresis (PFGE) were employed in isolates exhibiting high resistance to mupirocin (HR-Mup) and in other selected organisms.

RESULTS

The overall incidence of HR-Mup among MRSA carriers during the studied period was 4.84% (8/165); however, the incidence decreased from 13.04% (6/46) in the first year to 3.5% (2/57) in the second year and was 0% in the last year (P = .02). LR-Mup, in contrast, increased significantly (P = .01).

CONCLUSION

Plasmid-curing procedure showed the plasmid location of genes responsible for HR-Mup. PFGE demonstrated that most MRSA, including the isolates with HR-Mup, were genetically related. The decline in HR-Mup may be attributable to the plasmid location of genes (ileS-2/mupA) and to the fact that all patients colonized with HR-Mup MRSA died or were discharged in a relatively short period of time.

Contemporary antimicrobial activity of triple antibiotic ointment: a multiphased study of recent clinical isolates in the United States and Australia

Triple antibiotic ointment (TAO) containing neomycin, polymyxin B, and bacitracin was launched in the 1950s in the United States (USA) as a prescription product and then was used over the counter (OTC) since the 1970s (USA) to prevent superficial wound infections. In Australia, TAO has been restricted to prescription use. This study 1) determined cross-resistance patterns of neomycin compared with other aminoglycosides; 2) determined the level and trend of resistance to TAO and individual components especially versus mupirocin-resistant strains (USA); and 3) established the baseline TAO activity level against pathogens from Australia. A total of 200 strains (> or =50% gentamicin-resistant) from the United States were used for the cross-resistance study including Staphylococcus aureus (110), coagulase-negative staphylococci (CoNS; 50), Pseudomonas aeruginosa (10), Escherichia coli (20), and other Enterobacteriaceae (10) tested against TAO, bacitracin, polymyxin B, neomycin, amikacin, gentamicin, streptomycin, tobramycin, and mupirocin. Fifty gentamicin-resistant isolates from each year (1997-2002) were used to determine the activity of TAO over time. Baseline resistance rates of TAO among 300 Australian isolates (AGARS Program, 2002-2003) were also studied. Reference broth microdilution methods were used in all phases of this study. At a 1:100 dilution of the ointment concentration, TAO inhibited all CoNS, Pseudomonas aeruginosa, and Enterobacteriaceae isolates, and resistance to TAO among Staphylococcus aureus at this concentration was only 5% in the cross-resistance study. Patterns of susceptibility in the United States did not significantly vary from 1997 to 2002. Australian pathogens showed that TAO was 98% active against methicillin-resistant Staphylococcus aureus and 100% for Enterobacteriaceae, methicillin-susceptible S. aureus, CoNS, and P. aeruginosa, the rates equivalent to those observed in the United States. Mupirocin-resistant S. aureus (5%) and CoNS (47%) were all TAO-susceptible. All Gram-negative species were also mupirocin-resistant, but inhibited by neomycin and/or polymyxin B components of TAO. In conclusion, aminoglycoside resistance patterns differ significantly, and none of the commonly tested agents could accurately predict neomycin resistance. TAO resistance was rare in the United States after extensive OTC use and was not adversely influenced by decades of parenteral aminoglycoside use. Australian surveillance showed high levels of TAO susceptibility in sampled isolates as a baseline for possible OTC availability. TAO maintains a wider spectrum of activity compared with mupirocin and was usable against mupirocin-resistant Gram-positive strains.

Community-associated methicillin-resistant Staphylococcus aureus, Canada

A total of 184 methicillin-resistant Staphylococcus aureus (MRSA) strains were collected from patients who sought treatment primarily for skin and soft tissue infections from January 1, 1999, to March 31, 2002, in east-central Saskatchewan, Canada. Molecular subtyping analysis using pulsed-field gel electrophoresis showed 2 major clusters. Cluster A (n = 55) was composed of a multidrug-resistant MRSA strain associated with a long-term care facility and was similar to the previously reported nosocomial Canadian epidemic strain labeled CMRSA-2. Cluster B (n = 125) was associated with cases identified at community health centers and was indistinguishable from a community-associated (CA)-MRSA strain identified previously in the United States (USA400). Cluster B remained susceptible to a number of classes of antimicrobial agents and harbored the lukF-PV and lukS-PV toxin genes. Over 50% of both clonal groups displayed high-level resistance to mupirocin. This is the first report of the USA400 strain harboring the lukF-PV and lukS-PV toxin genes in Canada.

Staphylococcus aureus colonization and nosocomial infections: Implications for prevention

Colonization with Staphylococcus aureus is a risk factor for invasive S. aureus infections. Intranasal mupirocin has effectively eradicated S. aureus colonization and appears to prevent S. aureus nosocomial infections in some patient populations. In hospitals and communities where mupirocin use has been widespread, resistance to the drug has emerged. New strategies and agents are needed if we want to significantly decrease the risk of S. aureus infections.