[Comparison of five usual techniques for detection of methicillin-resistant Staphylococcus aureus]

The detection of methicillin-resistant Staphylococcus aureus in an usual and daily test in a microbiology laboratory. But its interpretation isn't easy because the resistance expression in vitro is so variable. The authors compare five methods about 100 clinical isolated strains. The results are: disk diffusion method using oxacillin 5 microg, on a NaCl 5% Mueller Hinton agar, 100 ml presentation (biorad): specificity 91%; disk diffusion method using oxacillin 5 microg, on a NaCl 5% Mueller Hinton agar, ready to use plate (AES): specificity 95%; the Oxascreen agar (BD): specificity 96%; the oxacillin cupule of ATB STAPH strip (ATB expression bioMerieux system) NaCl 2% semi solid Mueller Hinton agar medium: specificity 100% and disk diffusion method using cefoxitin 30 microg, on a Mueller Hinton agar plate (bioMerieux): specificity 100%. Therefore the cefoxitin disk diffusion method is very interesting to make better the difference between methicillin-resistant and methicillin-sensible S. aureus, in association with the ATB STAPH strip.

Prevalence of methicillin-resistant Staphylococcus aureus (MRSA) among patients visiting the emergency room at a tertiary hospital in Brazil

We surveyed patients seen at the emergency room at a tertiary hospital in Brazil from August to November 1997. All patients' (n = 600) anterior nares were cultured for MRSA; the results were confirmed by oxacillin disk diffusion methods and by detection of the mecA gene with PCR. Bacteria were found in 93.3% (560) of the patients and MRSA in 0.7% (n = 4). One patient had community-acquired MRSA. We concluded that MRSA is uncommon among patients visiting the emergency room. The presence of community-acquired MRSA can lead to serious medical and epidemiological issues, although initial clinical presentation may not differ from that of infections with other staphylococci. The empirical use of vancomycin for suspected community-acquired infections is seldom warranted.

Evaluation of cefoxitin 5 and 10 μg discs for the detection of methicillin resistance in staphylococci

OBJECTIVE

To evaluate cefoxitin 5 and 10 microg discs for detection of methicillin resistance in staphylococci.

METHODS

Six hundred and forty-one Staphylococcus aureus (261 mecA-negative and 380 mecA-positive) and 344 coagulase-negative staphylococci (CoNS) (132 mecA-negative and 212 mecA-positive) were investigated. The CoNS represented nine species, Staphylococcus epidermidis being the most frequent (n = 231). All isolates were tested using semi-confluent growth on Iso-Sensitest agar (ISA), and Mueller-Hinton agar (MH) using a 5 and a 10 microg cefoxitin disc and overnight incubation in ambient air at 35-37 degrees C.

RESULTS

For S. aureus, both cefoxitin discs performed with high accuracy on both media. The sensitivity and specificity for the following proposed interpretive zone diameters were: ISA 5 microg, R < 14 mm (99.5% and 98.1%); ISA 10 microg, R < 22 mm (99.5% and 98.1%); MH 5 microg, R < 12 mm (99.7% and 98.1%); and MH 10 microg, R < 18 mm (99.5% and 98.9%), respectively. All four variants were superior to oxacillin using the former SRGA methodology. In CoNS, a substantial overlap was seen for all variants. However, by avoiding primary interpretation in the overlapping interval, highly accurate results could be obtained for 81%, 80%, 91% and 97% of the isolates, respectively.

CONCLUSION

For S. aureus, cefoxitin 5 and 10 microg discs performed with high accuracy on both ISA and MH using semi-confluent growth and standard incubation conditions. With the introduction of a defined interval in which primary interpretation should be avoided, the method could also be used for CoNS.

Efficacy of Quinupristin-Dalfopristin against Methicillin-Resistant Staphylococcus aureus and Vancomycin-Insensitive S. aureus in a Model of Hematogenous Pulmonary Infection

BACKGROUND

Quinupristin-dalfopristin (Q-D) is a mixture of quinupristin and dalfopristin, which are semisynthetic antibiotics of streptogramin groups B and A, respectively.

METHODS

We compared the effect of Q-D to that of vancomycin (VCM) in murine models of hematogenous pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and VCM-insensitive S. aureus (VISA).

RESULTS

Treatment with Q-D resulted in a significant decrease in the number of viable bacteria in the lungs of mice in an MRSA infection model [Q-D 100 mg/kg, Q-D 10 mg/kg, VCM and control (mean +/- SEM): 2.99 +/- 0.44, 6.38 +/- 0.32, 5.75 +/- 0.43 and 8.40 +/- 0.14 log10 CFU/lung, respectively]. Compared with VCM, high-dose Q-D significantly reduced the number of bacteria detected in the VISA hematogenous infection model [Q-D 100 mg/kg, Q-D 10 mg/kg, VCM and control (mean +/- SEM): 5.17 +/- 0.52, 7.03 +/- 0.11, 7.10 +/- 0.49 and 7.18 +/- 0.36 log10 CFU/lung, respectively]. Histopathological examination confirmed the effect of Q-D.

CONCLUSION

Our results suggest that Q-D is potent and effective in the treatment of MRSA and VISA hematogenous pulmonary infections.

A Randomized Clinical Trial to Compare Fleroxacin-Rifampicin with Flucloxacillin or Vancomycin for the Treatment of Staphylococcal Infection

BACKGROUND

Oral combination therapy with fluoroquinolones plus rifampicin is a promising alternative to standard parenteral therapy for staphylococcal infections.

METHODS

In a multicenter, randomized trial, we compared the efficacy, safety, and length of hospital stay for patients with staphylococcal infections treated either with an oral combination of a fluoroquinolone (fleroxacin) plus rifampicin or with standard parenteral treatment (flucloxacillin or vancomycin). Patients were included if cultures showed the presence of bacteremia or deep-seated infections with Staphylococcus aureus (104 patients) or catheter-related bacteremia due to drug-susceptible, coagulase-negative staphylococci (23 patients).

RESULTS

The cure rate in the intention-to-treat analysis was 78% for the fleroxacin-rifampicin group (68 patients) and 75% for the standard therapy group (59 patients; 47 received flucloxacillin, and 12 received vancomycin); in the population of clinically evaluable patients (n=119), the cure rate was 82% and 80%, respectively; and in the population of microbiologically evaluable patients (n=103), the cure rate was 86% and 84%, respectively. Clinical and bacteriological failures after S. aureus infections were documented in similar proportions of patients. The median length of hospital stay after study entry was 12 days in the fleroxacin-rifampicin group, compared with 23 days in the standard treatment group (P=.006). More adverse events probably related to the study drug were reported in the fleroxacin-rifampicin group than in the standard therapy group (15 of 68 vs. 5 of 59 patients; P=.05).

CONCLUSIONS

This study suggests that an oral regimen containing a fluoroquinolone plus rifampicin may be effective for treating staphylococcal infections, allowing earlier discharge from the hospital.

Clinical concentrations of thioridazine enhance the killing of intracellular methicillin-resistant Staphylococcus aureus: an in vivo, ex vivo and electron microscopy study

Chlorpromazine (CPZ) is concentrated by human macrophages where it kills intracellular mycobacteria when the concentration outside the macrophage is sub-clinical. We have previously demonstrated that thioridazine (TZ), a much milder phenothiazine, has similar activity and kills intracellular methicillin-susceptible S. aureus at sub-clinical concentrations. We have extended this latter study to include methicillin-resistant S. aureus (MRSA) and show that TZ kills intracellular MRSA at clinically relevant concentrations. The ultrastructure of MRSA exposed to in vitro concentrations of TZ just below its MIC and that of MRSA phagocytosed by macrophages previously exposed to a clinically relevant concentration of TZ was also studied. TZ inhibits the replication of phagocytosed MRSA, affecting the structure of the cell envelope, resulting in lysis of the bacterium 6 hours post-phagocytosis. These ultrastructural changes are identical to those produced in vitro by a TZ concentration that is just below the MIC. Because macrophage intracellular MRSA is not killed by the macrophage and its intracellular location protects it from antibiotics that are unable to reach that site, recurrent infections which result may be successfully managed with the use of TZ.

Syntheses and anti-MRSA activities of the C3 analogs of mansonone F, a potent anti-bacterial sesquiterpenoid: insights into its structural requirements for anti-MRSA activity

Syntheses and excellent anti-MRSA activities of the mansonone F analogs are reported. In addition, the minimal structural requirements for its anti-MRSA activities as well as its structure-activity relationship including the C3 substituents effects on anti-MRSA activity are also described. In particular, this study revealed that both ortho-quinone and tricyclic systems of mansonone F are essential for anti-MRSA activities.

Antiseptic impregnated endotracheal tubes for the prevention of bacterial colonization

The effect of endotracheal tubes (ETTs) impregnated with chlorhexidine (CHX) and silver carbonate (antiseptic ETTs) against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacter aerogenes [organisms associated with ventilator-associated pneumonia (VAP)], was evaluated in a laboratory airway model. Antiseptic ETTs and control ETTs (unimpregnated) were inserted in culture tubes half-filled with agar media (airway model) previously contaminated at the surface with 10(8) cfu/mL of the selected test organism. After five days of incubation, bacterial colony counts on all ETT segments were determined. Swabs of proximal and distal ends of the agar tract in antiseptic and control models were subcultured. The initial and residual CHX levels, (five days post-implantation in the model) were determined. Cultures of antiseptic ETTs revealed colonization by the tested pathogens ranging from 1-100 cfu/tube, compared with approximately 10(6) cfu/tube for the control ETTs (P < 0.001). Subcultures from proximal and distal ends of the agar tract showed minimal or no growth in the antiseptic ETTs compared with the control ETTs (P < 0.001). The amount of CHX retained in the antiseptic ETTs after five days of implantation was an average of 45% of the initial level. Antiseptic ETTs prevented bacterial colonization in the airway model and also retained significant amounts of the antiseptic. These results indicate that the effectiveness of antiseptic-impregnated ETTs in preventing the growth of bacterial pathogens associated with VAP may vary with different organisms.

An In Vitro Model to Compare the Antimicrobial Activity of Silver-Coated Versus Rifampicin-Soaked Vascular Grafts

In situ replacement of infected vascular grafts is an accepted alternative to total graft excision and extraanatomic replacement. Its success relies upon the ability of the newly inserted graft to resist recurrent infection. This study compares the efficacy of two methods used to reduce the risk of graft reinfection: rifampicin soaking versus silver bonding of grafts. The grafts' resistance to infection was tested in vitro in two protocols, each using a panel of seven common bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The length of time the grafts remained free of organisms was compared between the groups. Both the silver graft and the rifampicin-soaked graft were significantly better than control graft at preventing bacterial growth on the graft surface. The rifampicin inhibited the growth of the gram-positive organisms, including MRSA, significantly better than the silver graft on days 2 and 3 (p < 0.001). Conversely, the silver graft was significantly more effective against the gram-negative organisms until day 4 (p < 0.0001). Both types of graft inhibit the in vitro growth of bacteria more effectively than controls, with rifampicin being most effective against gram-positive organisms and silver being best against the gram-negative organisms.

Regional delivery of vancomycin using pluronic F-127 to inhibit methicillin resistant Staphylococcus aureus (MRSA) growth in chronic otitis media in vitro and in vivo

For the effective treatment of chronic otitis media caused by methicillin resistant Staphylococcus aureus (MRSA), the local delivery of vancomycin was attempted based on a formulation with pluronic F-127. The phase transition property of pluronic F-127, which is liquid at room temperature and becomes solid at body temperature, enabled convenient injection and reduced the side effects of the potent antibiotic. The temperature responsive polymer-vancomycin matrix system was also shown to effectively deliver vancomycin locally to the infected inner ear, plus the MRSA growth was inhibited by the formulation. The otitis media was completely cured by the sustained local delivery of vancomycin from the matrix in vivo. Accordingly, this system has potential clinical application for treating chronic otitis media with improved patient compliance and better therapeutic efficacy.

Vancomycin ointment for MRSA infection at a cranioplasty site

OBJECTIVE

To report a case illustrating therapeutic success with long-term topical application of aseptic vancomycin ointment to treat methicillin-resistant Staphylococcus aureus (MRSA) infection at a cranioplasty site.

CASE SUMMARY

A 63-year-old Japanese woman underwent evacuation of a subdural hematoma complicated by subarachnoid hemorrhage. Subsequent craniotomy for clipping and external decompression of an aneurysm of the neck was followed by cranioplasty using an autologous bone graft. The graft became infected with MRSA, which responded to intravenously infused vancomycin. The graft was then replaced with a ceramic implant. The implant site became reinfected with MRSA. Vancomycin infusion failed on this occasion, despite a favorable in vitro sensitivity test. After obtaining patient consent, investigative treatment was begun using long-term aseptic application of vancomycin 2.5% ointment, resulting in control of the infection and negative cultures.

DISCUSSION

The care of an infection at the site of cranioplasty with a ceramic artificial bone implant is difficult. Our patient's infection resolved with the use of vancomycin ointment. In this case, blood concentrations of vancomycin remained below detectable levels, and no adverse effects resulted from application of vancomycin ointment.

CONCLUSIONS

Topical administration of vancomycin was more effective than systemic administration in the treatment of our patient's MRSA skull implant infection. No adverse effects from topical treatment were encountered over 3 years.

Inhibitory effects of Caesalpinia sappan on growth and invasion of methicillin-resistant Staphylococcus aureus

In the present study, we investigated antimicrobial activity of Caesalpinia sappan against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and effect of Caesalpinia sappan extract on the invasion of MRSA to human mucosal fibroblasts (HMFs). Chloroform, n-butanol, methanol, and aqueous extracts of the Caesalpinia sappan showed antimicrobial activity against standard methicillin-sensitive Staphylococcus aureus (MSSA) as well as MRSA. Methanol extract of Caesalpinia sappan demonstrated a higher inhibitory activity than n-butanol, chloroform, and aqueous extracts. In the checkerboard dilution method, methanol extract of Caesalpinia sappan markedly lowered the minimal inhibitory concentrations (MICs) of ampicillin and oxacillin against MRSA. To determine whether methanol extract of Caesalpinia sappan inhibits the MRSA invasion to HMFs, the cells were treated with various sub-MIC concentrations of methanol extract and bacterial invasion was assayed. MRSA invasion was notably decreased in the presence of 20-80 microg/ml of Caesalpinia sappan extract compared to the control group. The effect of Caesalpinia sappan extract on MRSA invasion appeared dose-dependent. These results suggest that methanol extract of Caesalpinia sappan may have antimicrobial activity and the potential to restore the effectiveness of beta-lactam antibiotics against MRSA, and inhibit the MRSA invasion to HMFs.

Fluoroquinolones and the risk for methicillin-resistant Staphylococcus aureus in hospitalized patients

To determine whether fluoroquinolone exposure is a risk factor for the isolation of Staphylococcusaureus and whether the effect is different for methicillin-resistant S.aureus (MRSA) versus methicillin-susceptible S.aureus (MSSA), we studied two case groups. The first case group included 222 patients with nosocomially acquired MRSA. The second case group included 163 patients with nosocomially acquired MSSA. A total of 343 patients admitted concurrently served as controls. Outcome measures were the adjusted odds ratio (OR) for isolation of MRSA and MSSA after fluoroquinolone exposure. Exposure to both levofloxacin (OR 5.4; p < 0.0001) and ciprofloxacin (OR 2.2; p < 0.003) was associated with isolation of MRSA but not MSSA. After adjustment for multiple variables, both drugs remained risk factors for MRSA (levofloxacin OR 3.4; p < 0.0001; ciprofloxacin OR 2.5; p = 0.005) but not MSSA. Exposure to levofloxacin or ciprofloxacin is a significant risk factor for the isolation of MRSA, but not MSSA.

Characteristics of French methicillin-resistant Staphylococcus aureus isolates with decreased susceptibility or resistance to glycopeptides

According to the French Society of Microbiology, Staphylococcus aureus isolates are suspected to have decreased susceptibility to glycopeptide(s) when at least one colony is able to grow from an inoculum of 10 microL of 2 McFarland bacterial suspension plated on Mueller-Hinton agar containing 5 mg/L teicoplanin and incubated for 48 h at 35-37 degrees C. We analysed 89 methicillin-resistant S. aureus isolates (MRSA), collected in 2000-2001 from 24 hospitals located in 18 French cities, which were able to grow on this selective medium. These isolates were distributed into six groups on the basis of their glycopeptide resistance phenotypes: (A) glycopeptide susceptible (GSSA, 21 isolates); (B) heterogeneous teicoplanin intermediately resistant (hetero-TISA, 24 isolates); (C) heterogeneous and intermediately resistant to both glycopeptides, teicoplanin and vancomycin (hetero-GISA, six isolates); (D) heterogeneous vancomycin intermediately resistant/teicoplanin intermediately resistant (hetero-VISA/TISA, 30 isolates); (E) GISA (four isolates); (F) TISA (four isolates). Despite the persistent decrease in gentamicin-resistant MRSA isolates in French hospitals since 1993, their prevalence is very high in groups D, E and F. Moreover, most of the group C, D and E isolates exhibiting decreased susceptibility to both glycopeptides belong to the same major SmaI genotype, which has been detected in Europe since at least 1989.

Triclosan resistance in methicillin-resistant Staphylococcus aureus (MRSA)

Two triclosan selected mutants showed four-fold and 16-fold increases in their minimum inhibitory concentrations (MICs) of triclosan (1 mg/L and 4 mg/L) compared with their parent strains. Four clinical isolates of MRSA were detected with the same triclosan susceptibility as the mutants. One mutant had a predicted change in the gene product on FabI (Thr 147-->His), whilst only one clinical isolate had predicted FabI amino-acid changes (Ala 198-->Gly, and Leu 208-->Phe). The lack of fabI mutations in one mutant and three of the clinical isolates showing reduced triclosan susceptibility suggest that genetic loci other than fabI may be involved in triclosan resistance.

Flavone Markedly Affects Phenotypic Expression of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus Strains Isolated Clinically

Flavone and its derivatives had very weak antibacterial effects on methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus, but dramatically intensified MRSA's susceptibility to beta-lactams. We named these compounds "ILSMR (intensifier of beta-lactam-susceptibility in MRSA)." We also found discrepancies among MRSA strains in their responses to flavone; some strains showed phenotypic susceptibility to methicillin while others showed phenotypic resistance to it. To understand the mechanism underlying this discrepancy, we characterized 20 MRSA strains in detail, analyzed their conventional and molecular typings, and examined each strain's resistance to beta-lactams, with COL serving as a reference. Neither SCCmec typing nor coagulase typing explained the diverse effects of flavone on the beta-lactam MICs of these strains. Likewise, changes in pulsed-field gel electrophoresis (PFGE) type were not associated with the profiles of ILSMR effects. However, the present observations suggest that the ILSMR effects on MRSA is strain-specific, and that this effect depends on an as-yet unknown mechanism that is essential for the expression of the phenotype conferring beta-lactam resistance to MRSA strains, independently of an interaction with the mecA-encoded penicillin-binding protein 2a or with the beta-lactamase.