Emergence of High-Level Mupirocin Resistance in Methicillin-Resistant Staphylococcus aureus Isolated From Brazilian University Hospitals

Evaluation of ebselen in resolving a methicillin-resistant Staphylococcus aureus infection of pressure ulcers in obese and diabetic mice

Pressure ulcers (PUs) are a source of morbidity in individuals with restricted mobility including individuals that are obese or diabetic. Infection of PUs with pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), impairs ulcers from healing. The present study evaluated ebselen as a topical antibacterial to treat MRSA-infected PUs. Against two different S. aureus strains, including MRSA USA300, resistance to ebselen did not emerge after 14 consecutive passages. Resistance to mupirocin emerged after only five passages. Additionally, ebselen was found to exert a modest postantibiotic effect of five hours against two MRSA strains. Ebselen was subsequently evaluated in MRSA-infected PUs in two models using obese and diabetic mice. In obese mice, topical ebselen (89.2% reduction) and oral linezolid (84.5% reduction) similarly reduced the burden of MRSA in infected PUs. However, in diabetic mice, topical ebselen (45.8% reduction in MRSA burden) was less effective. Histopathological evaluation of ulcers in diabetic mice determined that ebselen treatment resulted in fewer bacterial colonies deep within the dermis and that the treatment exhibited evidence of epithelial regeneration. Topical mupirocin was superior to ebselen in reducing MRSA burden in infected PUs both in obese (98.7% reduction) and diabetic (99.3% reduction) mice. Ebselen’s antibacterial activity was negatively impacted as the bacterial inoculum was increased from 10⁵ CFU/mL to 10⁷ CFU/mL. These results suggest that a higher dose of ebselen, or a longer course of treatment, may be needed to achieve a similar effect as mupirocin in topically treating MRSA-infected pressure ulcers.

High-level mupirocin resistance in methicillin-resistant staphylococci isolated from dogs and cats

BACKGROUND

Mupirocin is one of the few antimicrobials active against methicillin-resistant Staphylococcus aureus (MRSA), and is frequently used for the eradication of MRSA nasal colonisation in humans. Initially, mupirocin resistance was recognised in human S. aureus, including MRSA isolates, then also among coagulase-negative staphylococci (CoNS). Nowadays, mupirocin resistance is occasionally observed in canine staphylococci, along with Staphylococcus pseudintermedius (MRSP) strains, as well as CoNS, which usually show methicillin resistance. In the current study, high-level mupirocin resistance in methicillin-resistant staphylococci isolated from diseased dogs and cats was investigated.

RESULTS

Among 140 methicillin-resistant staphylococci isolates from dogs and cats, three showed high-level mupirocin resistance in a screening test using the agar disk diffusion method. One was recognised as methicillin-resistant S. aureus, one as methicillin-resistant S. pseudintermedius, and one as methicillin-resistant Staphylococcus haemolyticus. S. pseudintermedius and S. aureus were isolated from dogs, S. haemolyticus was obtained from a cat. All isolates showed high-level mupirocin resistance, confirmed by minimum inhibitory concentration (MIC) values of above 1024 μg/ml and the presence of the plasmid-located gene ileS2. This is the first report on the detection of high-level mupirocin resistance (HLMR) in S. haemolyticus of feline origin.

CONCLUSIONS

This study revealed the occurrence of HLMR in three Staphylococcus isolates obtained from companion animals in Poland. The results of this study indicate that the monitoring of mupirocin resistance in staphylococci of animal origin, especially in methicillin-resistant isolates, is strongly recommended.

Current and Emerging Topical Antibacterials and Antiseptics: Agents, Action, and Resistance Patterns

Bacterial skin infections represent some of the most common infectious diseases globally. Prevention and treatment of skin infections can involve application of a topical antimicrobial, which may be an antibiotic (such as mupirocin or fusidic acid) or an antiseptic (such as chlorhexidine or alcohol). However, there is limited evidence to support the widespread prophylactic or therapeutic use of topical agents. Challenges involved in the use of topical antimicrobials include increasing rates of bacterial resistance, local hypersensitivity reactions (particularly to older agents, such as bacitracin), and concerns about the indiscriminate use of antiseptics potentially coselecting for antibiotic resistance. We review the evidence for the major clinical uses of topical antibiotics and antiseptics. In addition, we review the mechanisms of action of common topical agents and define the clinical and molecular epidemiology of antimicrobial resistance in these agents. Moreover, we review the potential use of newer and emerging agents, such as retapamulin and ebselen, and discuss the role of antiseptic agents in preventing bacterial skin infections. A comprehensive understanding of the clinical efficacy and drivers of resistance to topical agents will inform the optimal use of these agents to preserve their activity in the future.

Mupirocin-resistant, methicillin-resistant Staphylococcus aureus strains in Canadian hospitals

Mupirocin resistance in Staphylococcus aureus is increasingly being reported in many parts of the world. This study describes the epidemiology and laboratory characterization of mupirocin-resistant methicillin-resistant S. aureus (MRSA) strains in Canadian hospitals. Broth microdilution susceptibility testing of 4,980 MRSA isolates obtained between 1995 and 2004 from 32 Canadian hospitals was done in accordance with CLSI guidelines. The clinical and epidemiologic characteristics of strains with high-level mupirocin resistance (HLMup(r)) were compared with those of mupirocin-susceptible (Mup(s)) strains. MRSA strains were characterized by pulsed-field gel electrophoresis (PFGE) and typing of the staphylococcal chromosomal cassette mec. PCR was done to detect the presence of the mupA gene. For strains with mupA, plasmid DNA was extracted and subjected to Southern blot hybridization. A total of 198 (4.0%) HLMup(r) MRSA isolates were identified. The proportion of MRSA strains with HLMup(r) increased from 1.6% in the first 5 years of surveillance (1995 to 1999) to 7.0% from 2000 to 2004 (P < 0.001). Patients with HLMup(r) MRSA strains were more likely to have been aboriginal (odds ratio [OR], 3.7; 95% confidence interval [CI], 1.5 to 9.4; P = 0.006), to have had community-associated MRSA (OR, 2.2; 95% CI, 1.0 to 5.0; P = 0.05), and to have been colonized with MRSA (OR, 1.7; 95% CI, 1.0 to 3.0; P = 0.04). HLMup(r) MRSA strains were also more likely to be resistant to fusidic acid (21% versus 4% for mupirocin-susceptible strains; P < 0.001). All HLMup(r) MRSA strains had a plasmid-associated mupA gene, most often associated with a 9-kb HindIII fragment. PFGE typing and analysis of the plasmid profiles indicate that both plasmid transmission and the clonal spread of HLMup(r) MRSA have occurred in Canadian hospitals. These results indicate that the incidence of HLMup(r) is increasing among Canadian strains of MRSA and that HLMup(r) MRSA is recovered from patients with distinct clinical and epidemiologic characteristics compared to the characteristics of patents with Mup(s) MRSA strains.

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

Susceptibility to mupirocin was assessed in methicillin-resistant Staphylococcus aureus isolates selected from eras corresponding to differences in usage rate and prescription policies at a Veterans Affairs medical center. The eras studied encompassed from the time of introduction of the drug to its widespread use, through recommended judicious use, and finally to subsequent stringent administrative control. Prescriptions declined from 3.0 to 0.1 per 1,000 patient days. Precipitous declines first in the numbers of isolates with high-level resistance (from 31% to 4%) and then in those with low-level resistance (from 26% to 10%) accompanied prescription control.

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.

Improvement of mupirocin E-test for susceptibility testing of Staphylococcus aureus

Interpretation of the mupirocin E-test for low-level mupirocin-resistant Staphylococcus aureus strains has been improved by adding the indicator dye tetrazolium. E-tests were compared with agar dilution methods for assessing mupirocin susceptibility. MICs obtained by the agar dilution method and E-tests showed 89.3% agreement within 2 log(2) dilution criteria. The agreement between MICs increased to 100% in the 1 log(2) dilution definition when the indicator dye tetrazolium was added to the E-test. The use of the E-test with tetrazolium reduction is more accurate for determining mupirocin MICs for S. aureus strains.