High-level mupirocin resistance among Spanish methicillin-resistant Staphylococcus aureus

Increasing Mupirocin Resistance of Staphylococcus Aureus in CAPD — Should it Continue to be Used as Prophylaxis?

This editorial summarizes the mechanisms of mupirocin resistance and the conditions that promote its development. While there is increasing evidence that high-level mupirocin resistance is developing during systematic use of mupirocin as prophylaxis against Staphylococcus aureus, the appearance of resistance does not preclude the beneficial effect of regular prophylaxis. Vigilance has to be exercised to notice larger-scale resistance that may require limiting the use of mupirocin.

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)

Peritoneal catheter exit-site infections: predisposing factors, prevention and treatment

Catheter-related infections, exit-site-tunnel infections and peritonitis remain the Achilles heel of peritoneal dialysis. Although the overall incidence of peritoneal-dialysis-related infectious complications has been reduced since the introduction of the Y-set and double bag system, approximately one-fifth of peritonitis episodes are associated with catheter exit-site and tunnel infections. Since its development in 1968, the Tenckhoff catheter has become one of the most widely used peritoneal catheters, and many have proposed that a number of modifications have made it a better choice. Controversies concerning the effect on exit-site infections of catheter(s) with one or two cuffs, with straight, coiled, Swan-Neck, or other modifications led to the randomized controlled studies that are reviewed in this paper. Several studies have confirmed that mupirocin, applied at the exit-site as part of regular exit-site care, reduces the risk of S. aureus exit-site and tunnel infections. Recently, the emergence on a world-wide basis of mupirocin-resistant S. aureus (MuRSA) in peritoneal dialysis patients has brought this prophylactic strategy into question. However the low frequency of resistant organisms after four years of mupirocin prophylaxis suggests that we can continue its use with annual surveillance. Once established, exit-site infections may respond to appropriate treatment, but if not the only option may be catheter removal and replacement. Although peritonitis risk has decreased over the past decade, mainly due to improvements in connection technology, exit-site and tunnel infections have not. An exit-site infection that does not respond to treatment may lead to tunnel infection and to persistent peritonitis, which may require catheter removal and occasionally discontinuation of the peritoneal dialysis. Therefore it is important to be familiar with these factors that predispose to exit-site infection and to know how to prevent and to treat such infections. This review will discuss factors that predispose to catheter-related exit-site infections, techniques of exit-site care, and ways to prevent exit-site infection, with emphasis on S. aureus infections and their treatment.

Mupirocin resistance in methicillin-resistant Staphylococcus aureus clinical isolates in a Spanish hospital. Co-application of multiplex PCR assay and conventional microbiology methods

A total of 1785 Staphylococcus aureus clinical isolates were collected in our hospital during 1998 (526), 1999 (564) and 2000 (695). Among them, one hundred and thirty (39, 33 and 58, respectively) were phenotypically assigned as methicillin-resistant Staphylococcus aureus (MRSA); sixteen of these isolates (3, 2 and 11, respectively) were detected as highly mupirocin-methicillin resistant Staphylococcus aureus (MMRSA). In this work, our goal was to characterize MRSA and MMRSA clinical isolates by co-application of phenotypic and genotypic methods in order to determine the MMRSA incidence in our hospital during the period 1998-2000. With this purpose we compared and integrated the results obtained using conventional microbiology methods with those obtained using a multiplex polymerase chain reaction (PCR) assay. Our results showed a good complementation between these two approximations to determine the incidence of MMRSA clinical isolates and permitted to estimate that such incidence increased from 7.7% in 1998 to 19% in 2000.

Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, Etest and reference dilution methods

Staphylococci cause one-third of all serious invasive infections in the SENTRY Antimicrobial Surveillance Program including bacteremias and lower respiratory tract infections. Staphylococci are also commensals of the skin and nasal passages; therefore, topical agents active against these organisms are valuable in preventing infections or transfer of the organisms between patients and/or health care workers. Mupirocin is a potent topical anti-staphylococcal compound, but its effectiveness has been compromised by emerging resistance. In early 2000, the SENTRY Program detected 302 mupirocin-resistant isolates (131 Staphylococcus aureus, and 171 coagulase-negative staphylococci [CoNS]) from the United States (19/25 medical centers), Canada (4/5), Latin America (3/9) and Europe (7/18). One hundred sixty-eight mupirocin-resistant and 59 susceptible isolates were tested further by reference MIC, Etest (AB BIODISK, Solna, Sweden) and disk diffusion (5-microg) methods. Mupirocin resistance rates for blood stream infections varied by geographic area: for S. aureus from 1.9 to 5.6%, and for CoNS from 12.8 to 39.9%. Using elevated mupirocin MIC results, two resistant populations were noted: low-level resistance at 8-128 microg/mL and high-level resistance at > or = 1024 microg/mL. Acceptable correlation was observed between Etest and disk diffusion results (r = 0.84) without serious intermethod interpretive errors. High-level resistant isolates had heavy growth with no visible zone around the disk; low-level resistant isolates produced hazy zones of inhibition, and susceptible strains had clear zones of inhibition at > or = 17 mm. As mupirocin resistance can be plasmid-mediated, the prudent and appropriate use of this topical agent is important to minimize the ongoing development of resistance. Local surveillance for emerging mupirocin resistance appears warranted particularly in the United States and Canada, pragmatically using a disk diffusion test screening. Where more precise data are needed, the Etest is a very accurate method for distinguishing mupirocin low-level from high-level resistance patterns.

Multiplex PCR for simultaneous identification of Staphylococcus aureus and detection of methicillin and mupirocin resistance

In this work, we describe a multiplex PCR assay for the detection of clinically relevant antibiotic resistance genes harbored by some Staphylococcus aureus isolates and for the simultaneous identification of such isolates at the species level. Conditions were optimized for the simultaneous detection of the 310-, 456-, and 651-bp regions of the mecA (encoding high-level methicillin resistance), ileS-2 (encoding high-level mupirocin resistance), and femB (encoding a factor essential for methicillin resistance) genes, respectively, from a single colony in a single reaction tube. The femB PCR fragment allows the specific identification of S. aureus. Validation of the method was performed using 50 human isolates of methicillin-resistant S. aureus (MRSA) and the appropriate control strains. This assay offers a rapid, simple, feasible, specific, sensitive, and accurate identification of mupirocin-resistant MRSA clinical isolates and could be systematically applied as a diagnostic test in clinical microbiology laboratories, facilitating the design and use of antibiotic therapy.

In vitro and in vivo efficacy of catheters impregnated with antiseptics or antibiotics: evaluation of the risk of bacterial resistance to the antimicrobials in the catheters

OBJECTIVE

To compare the efficacy of a new antiseptic catheter containing silver sulfadiazine and chlorhexidine on the external surface and chlorhexidine in the lumens to an antibiotic catheter impregnated with minocycline and rifampin on its external and luminal surfaces.

DESIGN

Experimental trial.

METHODS

Antimicrobial spectrum of catheters was determined by zones of inhibition. Resistance to luminal colonization was tested in vitro by locking catheter lumens with Staphylococcus epidermidis or Staphylococcus aureus culture after 7 days of perfusion. In vitro development of resistance to the antiseptic or antibiotic combination used in catheters was investigated. In vivo efficacy was tested (rat subcutaneous model) by challenge with sensitive or antibiotic-resistant bacteria.

RESULTS

Antiseptic and antibiotic catheters exhibited broad-spectrum action. However, antibiotic catheters were not effective against Candida species and Pseudomonas aeruginosa. Both catheters prevented luminal colonization. Compared to controls, both test catheters resisted colonization when challenged with S aureus 7 and 14 days' postimplant (P<.05). Repeated in vitro exposure of S epidermidis culture to the antibiotic and antiseptic combinations led to small increases in the minimum inhibitory concentration (15 times and 2 times, respectively). Unlike the antibiotic catheter, the in vitro and in vivo activity of the antiseptic catheter was unaffected by the resistance profile of the test organism. Antiseptic catheters were more effective than antibiotic catheters in preventing colonization by rifampin-resistant S epidermidis in vivo (P<.05).

CONCLUSIONS

Antiseptic and antibiotic catheters exhibit similar efficacy; however, when challenged with a rifampin-resistant strain, the antibiotic catheter appeared to be more susceptible to colonization than the antiseptic device.

In vitro evaluation of the risk of developing bacterial resistance to antiseptics and antibiotics used in medical devices

The risk of development of resistance in Staphylococcus epidermidis to the antibiotics and antiseptics impregnated in central venous catheters was evaluated. The culture was passaged 10-20 times through subinhibitory concentrations of different antimicrobials, singly and in combination, and the MIC of each antimicrobial before and after passage was compared. There was a 10- to 16-fold increase in the MIC of the combination of minocycline and rifampicin, while no significant increase in the MIC of minocycline alone was seen. The MIC of rifampicin was 25,000-fold higher against strains passaged through rifampicin alone (as compared with that for the original strain), while the increase was only 80-fold when it was combined with minocycline for passage. There was no substantial change in susceptibility to the antiseptic chlorhexidine when used alone or in combination with either silver sulphadiazine or triclosan (the MIC of triclosan alone increased eight-fold). In time-kill studies, synergy was observed between chlorhexidine and both triclosan and silver sulphadiazine. Zone of inhibition tests of catheters impregnated with minocycline and rifampicin showed that their activity against rifampicin-resistant strains was lower than that against the susceptible strain. On the other hand, the activity of the antiseptic (chlorhexidine and silver sulphadiazine) catheters against the rifampicin-resistant and -susceptible strains was similar. Although this study indicates that antibiotic catheters may be at a higher risk of being colonized by antibiotic-resistant bacteria, the implications of these results in clinical settings need to be determined.