Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997-1999

Rapid detection of methicillin-resistant Staphylococcus aureus from screening enrichment broths by real-time PCR

The aim of this study was to evaluate real-time PCR (LightCycler) kits for the detection of methicillin-resistant Staphylococcus aureus in enrichment broth using 200 sets of patient screening swab samples. One hundred sets were processed using a lysostaphin/lysozyme extraction method and a further 100 were tested using a column extraction kit. The PCR kits with lysostaphin/lysozyme lysis showed 95.7% sensitivity, 90.8% specificity, and negative and positive predictive values of 98.6% and 75.9%, respectively, compared with 88%, 95.9%, 84.6% and 95.9%, respectively, with the column extraction kit.

High prevalence of carriage of methicillin-resistant Staphylococcus aureus at hospital admission in elderly patients: implications for infection control strategies

BACKGROUND

Despite contact isolation precautions for patients with methicillin-resistant Staphylococcus aureus (MRSA), MRSA infections are increasing in many countries.

OBJECTIVE

To evaluate the role of a potential unrecognized reservoir of MRSA carried by patients in acute care wards, we determined the prevalence of MRSA at hospital admission, with special emphasis on screening-specimen yields.

SETTING

A 1100-bed teaching hospital in Paris, France.

METHODS

Nasal screening cultures were performed at admission to a tertiary-care teaching hospital for patients older than 75 years.

RESULTS

MRSA was isolated from 63 (7.9%) of 797 patients. On the multivariate analysis, variables significantly associated with MRSA carriage were presence of chronic skin lesions (adjusted odds ratio [AOR], 5.10; 95% confidence interval [CI95], 2.52-10.33); transfer from a nursing home, rehabilitation unit, or long-term-care unit (AOR, 4.52; CI95, 2.23-9.18); and poor chronic health status (AOR, 1.80; CI95, 1.02-3.18). Without admission screening, 84.1% of MRSA carriers would have been missed at hospital admission and 76.2% during their hospital stay. Furthermore, 81.1% of days at risk for MRSA dissemination would have been spent without contact isolation precautions had admission screening not been performed.

CONCLUSIONS

MRSA carriage at hospital admission is far more prevalent than MRSA-positive clinical specimens. This may contribute to failure of contact isolation programs. Screening cultures at admission help to identify the reservoir of unknown MRSA patients.

Community-acquired meticillin-resistant Staphylococcus aureus: an emerging threat

Community-acquired meticillin-resistant Staphylococcus aureus (MRSA) is becoming an important public-health problem. New strains of S aureus displaying unique combinations of virulence factors and resistance traits have been associated with high morbidity and mortality in the community. Outbreaks of epidemic furunculosis and cases of severe invasive pulmonary infections in young, otherwise healthy people have been particularly noteworthy. We review the characteristics of these new strains of community-acquired MRSA that have contributed to their pathogenicity and discuss new approaches to the diagnosis and management of suspected and confirmed community-acquired MRSA infections.

Nosocomial infection caused by methicillin-resistant Staphylococcus aureus in Palestine

This report presents the prevalence of Palestinian isolates of methicillin-resistant Staphylococcus aureus (MRSA) in nosocomial infections and their antibiotic resistant pattern. A total of 321 clinical isolates of S. aureus were identified from different patients. The prevalence of methicillin resistance among S. aureus isolates was 8.7% (28 isolates). Resistance rates of MRSA to other antibiotics were as follows: 82.1% resistant to erythromycin, 67.9% to clindamycin, 64.3% to gentamicin, and 32.1% to ciprofloxacin. No co-trimoxazole- and vancomycin-resistant isolates were identified in this study. The proportion of methicillin resistance was highest among S. aureus isolates associated with upper respiratory specimens (42.8%); the proportion of methicillin resistance was 39.3% among skin ulcer isolates, 10.7% among urinary tract infection isolates, and lowest among isolates associated with blood and prostate discharge (3.6% each).

Emergence of rifampicin resistance in methicillin-resistant Staphylococcus aureus isolated at a Turkish university hospital

Twenty-three rifampicin-resistant methicillin-resistant Staphylococcus aureus (MRSA) isolated in three wards at a university hospital in Turkey between June, 2000, and February, 2001, were studied for their genetic relatedness using a combination of antibiogram, coagulase serotyping, coagulase gene polymorphism (coa-RFLP), and pulsed-field gel electrophoresis (PFGE). They all expressed high-level rifampicin resistance (MIC, >256 mg/L) and were resistant to gentamicin, kanamycin, amikacin, ciprofloxacin, tetracycline, and cadmium acetate and were susceptible to fusidic acid, vancomycin, trimethoprim, and mupirocin. They belonged to the same coagulase serotype (serotype IV) and had identical coa-RFLP patterns. In contrast, PFGE generated nine banding patterns designated type A, types A1-A5, B, C, and D. The most common PFGE pattern (type A) and its subtypes (types A1-A5) were seen in 20 (87%) of the 23 isolates in the three wards. The results demonstrated the acquisition of rifampicin resistance by different MRSA clones and the spread of one clone among patients in the three wards.

Use of Long-Acting Tetracyclines for Methicillin-Resistant Staphylococcus aureus Infections: Case Series and Review of the Literature

BACKGROUND

Few data exist on the efficacy of the long-acting tetracyclines doxycycline and minocycline against methicillin-resistant Staphylococcus aureus (MRSA) infection.

METHODS

The medical records of 24 patients with serious tetracycline-susceptible MRSA infections who were treated with doxycycline or minocycline were reviewed. A review of the literature on the use of these antibiotics for treatment of both methicillin-susceptible and methicillin-resistant S. aureus infection was also performed.

RESULTS

Complicated skin and skin-structure infections were most common (67%). Clinical cure was achieved in 20 (83%) of 24 patients in our case series. Both drugs were well-tolerated. The review of the literature on a total of 85 patients with S. aureus infection revealed similar results.

CONCLUSIONS

Long-acting tetracyclines may be a reasonable treatment alternative for patients with certain types of MRSA infection.

Low-level vancomycin resistance in Staphylococcus aureus--an Australian perspective

Low-level vancomycin resistance in Staphylococcus aureus has emerged as a clinical problem over the past 8 years. The clinical relevance of this resistance has been questioned, and laboratory detection remains difficult and time consuming. There is, however, increasing evidence linking low-level vancomycin resistance with glycopeptide treatment failure in serious Staphylococcus aureus infections. Diagnostic laboratories and clinicians need to be aware of this resistance phenotype, to have procedures in place to detect the resistance, and to have strategies for managing patients with infections caused by resistant strains.

Fluoroquinolone- and Methicillin-Resistant Staphylococcus Aureus: Insights from the Antimicrobial Resistance Management Program

Background:

Staphylococcus aureus is a frequent cause of infections involving the bloodstream, skin and soft tissue, and lungs in hospitalized patients. These isolates are often multidrug resistant and represent a major therapeutic challenge.

Objective:

To explore the susceptibilities of S. aureus to nafcillin/oxacillin, a surrogate for methicillin resistance, and the fluoroquinolones and determine whether a relationship might exist between fluoroquinolone use and the prevalence of methicillin-resistant S. aureus (MRSA).

Methods:

To date, 353 institutions throughout the US and Puerto Rico have enrolled in the Antimicrobial Resistance Management (ARM) Program, and data have been submitted on nearly 5 million isolates of S. aureus. Isolates submitted from 1990 through 2002 were reviewed for sensitivity to nafcillin/oxacillin, clindamycin, erythromycin, and the fluoroquinolones ciprofloxacin and levofloxacin.

Results:

From 1990 through 2002 inclusive, susceptibility to nafcillin/oxacillin nationally was 64.9% (n = 360,460), ranging from 62.2% in the North Central and Northeast US to 72.8% in the Southwest. Nationally, S. aureus isolates were more resistant to levofloxacin (41.4%, n = 123,868) than ciprofloxacin (38.7%, n = 256,178). The greatest change in susceptibility of S. aureus to nafcillin/oxacillin and ciprofloxacin occurred concurrently from 1998 to 2002, which may implicate fluoroquinolone use with increasing rates of MRSA infection.

Conclusions:

Resistance to methicillin and the fluoroquinolones has increased in concert during the past 5 years. Collectively, data from the ARM Program, along with several other investigations, support a role of fluoroquinolone use in the emergence of MRSA. These observations, along with increasing resistance among gram-positive and gram-negative pathogens, underscore the need for judicious use of fluoroquinolones.

Methicillin-Resistant Staphylococcus aureus: An Emerging Pathogen in Small Animals

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen in humans and is increasingly implicated in community-associated infections in people. In household pets, MRSA infections are uncommon but are on the rise, possibly because of the increased prevalence of human MRSA in the community. Clinical MRSA infections in some animals can be life threatening and difficult to treat; however, other animals may develop mild disease or only become colonized. Veterinarians should be aware of the concerns regarding MRSA and should develop an understanding of appropriate disease surveillance, diagnostic testing, and infection control in order to lessen the impact of MRSA on small animals.

Low colonization prevalence of Staphylococcus aureus with reduced vancomycin susceptibility among patients undergoing hemodialysis in the San Francisco Bay area

BACKGROUND

Staphylococcus aureus exhibits varying degrees of reduced vancomycin susceptibility, and strains with intermediate levels of resistance are thought to emerge by antibiotic selection of subpopulations in heterogeneously resistant precursor strains exposed to this antibiotic. We sought to determine the prevalence of and risk factors for carriage of potential heterogeneous vancomycin-intermediate S. aureus (hVISA).

METHODS

We prospectively observed a cohort of 211 patients undergoing hemodialysis and performed quarterly surveillance cultures for up to 2 years. We screened for reduced vancomycin susceptibility using brain-heart infusion agar with 4 microg/mL vancomycin.

RESULTS

We identified 10 colonizing potential hVISA isolates recovered from 7 patients among both methicillin-susceptible and methicillin-resistant S. aureus strains. No confirmed hVISA isolates were identified; we can be 95% certain that the prevalence of confirmed hVISA carriage does not exceed 1.4%. When compared with noncolonized hemodialysis patients, neither vancomycin exposure, duration of hospitalization, nor any baseline clinical or demographic factor was found to predict colonization with potential hVISA on univariate analyses; increased number of months receiving hemodialysis was associated with potential hVISA colonization on multivariate analysis.

CONCLUSIONS

Despite numerous published reports of S. aureus with reduced vancomycin susceptibility, carriage of these isolates remains a rare phenomenon. Given the unclear clinical significance of potential hVISA, it is not clear whether clinical laboratories should identify such strains, or how they should do so.

[Methicillin-resistant Staphylococcus aureus (MRSA) in rehabilitation and chronic-care-facilities: what is the best strategy?]

BACKGROUND

The risk associated with methicillin-resistant Staphylococcus aureus (MRSA) has been decreasing for several years in intensive care departments, but is now increasing in rehabilitation and chronic-care-facilities (R-CCF). The aim of this study was to use published data and our own experience to discuss the roles of screening for MRSA carriers, the type of isolation to be implemented and the efficiency of chemical decontamination.

DISCUSSION

Screening identifies over 90% of patients colonized with MRSA upon admission to R-CCF versus only 50% for intensive care units. Only totally dependent patients acquire MRSA. Thus, strict geographical isolation, as opposed to "social reinsertion", is clearly of no value. However, this should not lead to the abandoning of isolation, which remains essential during the administration of care. The use of chemicals to decolonize the nose and healthy skin appeared to be of some value and the application of this procedure could make technical isolation unnecessary in a non-negligible proportion of cases.

SUMMARY

Given the increase in morbidity associated with MRSA observed in numerous hospitals, the emergence of a community-acquired disease associated with these strains and the evolution of glycopeptide-resistant strains, the voluntary application of a strategy combining screening, technical isolation and chemical decolonization in R-CCF appears to be an urgent matter of priority.

Methicillin-resistant Staphylococcus aureus disease in three communities

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infection has emerged in patients who do not have the established risk factors. The national burden and clinical effect of this novel presentation of MRSA disease are unclear.

METHODS

We evaluated MRSA infections in patients identified from population-based surveillance in Baltimore and Atlanta and from hospital-laboratory-based sentinel surveillance of 12 hospitals in Minnesota. Information was obtained by interviewing patients and by reviewing their medical records. Infections were classified as community-associated [correction] MRSA disease if no established risk factors were identified.

RESULTS

From 2001 through 2002, 1647 cases of community-associated [correction] MRSA infection were reported, representing between 8 and 20 percent of all MRSA isolates. The annual disease incidence varied according to site (25.7 cases per 100,000 population in Atlanta vs. 18.0 per 100,000 in Baltimore) and was significantly higher among persons less than two years old than among those who were two years of age or older (relative risk, 1.51; 95 percent confidence interval, 1.19 to 1.92) and among blacks than among whites in Atlanta (age-adjusted relative risk, 2.74; 95 percent confidence interval, 2.44 to 3.07). Six percent of cases were invasive, and 77 percent involved skin and soft tissue. The infecting strain of MRSA was often (73 percent) resistant to prescribed antimicrobial agents. Among patients with skin or soft-tissue infections, therapy to which the infecting strain was resistant did not appear to be associated with adverse patient-reported outcomes. Overall, 23 percent of patients were hospitalized for the MRSA infection.

CONCLUSIONS

Community-associated MRSA infections are now a common and serious problem. These infections usually involve the skin, especially among children, and hospitalization is common.

Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles

BACKGROUND

Necrotizing fasciitis is a life-threatening infection requiring urgent surgical and medical therapy. Staphylococcus aureus has been a very uncommon cause of necrotizing fasciitis, but we have recently noted an alarming number of these infections caused by community-associated methicillin-resistant S. aureus (MRSA).

METHODS

We reviewed the records of 843 patients whose wound cultures grew MRSA at our center from January 15, 2003, to April 15, 2004. Among this cohort, 14 were identified as patients presenting from the community with clinical and intraoperative findings of necrotizing fasciitis, necrotizing myositis, or both.

RESULTS

The median age of the patients was 46 years (range, 28 to 68), and 71 percent were men. Coexisting conditions or risk factors included current or past injection-drug use (43 percent); previous MRSA infection, diabetes, and chronic hepatitis C (21 percent each); and cancer and human immunodeficiency virus infection or the acquired immunodeficiency syndrome (7 percent each). Four patients (29 percent) had no serious coexisting conditions or risk factors. All patients received combined medical and surgical therapy, and none died, but they had serious complications, including the need for reconstructive surgery and prolonged stay in the intensive care unit. Wound cultures were monomicrobial for MRSA in 86 percent, and 40 percent of patients (4 of 10) for whom blood cultures were obtained had positive results. All MRSA isolates were susceptible in vitro to clindamycin, trimethoprim-sulfamethoxazole, and rifampin. All recovered isolates belonged to the same genotype (multilocus sequence type ST8, pulsed-field type USA300, and staphylococcal cassette chromosome mec type IV [SCCmecIV]) and carried the Panton-Valentine leukocidin (pvl), lukD, and lukE genes, but no other toxin genes were detected.

CONCLUSIONS

Necrotizing fasciitis caused by community-associated MRSA is an emerging clinical entity. In areas in which community-associated MRSA infection is endemic, empirical treatment of suspected necrotizing fasciitis should include antibiotics predictably active against this pathogen.

Antibiotic prescribing as a risk factor for MRSA

There is accumulating evidence to support the role of specific antibiotic classes as risk factors for selecting meticillin-resistant Staphylococcus aureus (MRSA). Crucially, however, controlled studies of antimicrobial prescribing interventions are lacking. The evidence for the association between antimicrobial prescribing and expansion of MRSA is reviewed here.

Resistance to antimicrobial agents: an update

Decades of overuse and misuse of antibiotics have turned the resistance problem into a crisis. Preventive and corrective measures are urgently needed. This article presents a broad overview of the status of antimicrobial resistance. Resistance in key bacterial pathogens such as enterococci, staphylococci, pneumococci, and gram-negative bacilli; resistance to fluoroquinolones, third-generation cephalosporins, and the carbapenems; and mechanisms of resistance are discussed. The article also reviews the adverse impact of resistance on outcomes for patients with nosocomial infections. Finally, a brief overview of how the medical community can face its moment of truth is presented.

Antimicrobial activity of dalbavancin tested against Gram-positive clinical isolates from Latin American medical centres

The activity of dalbavancin, a new semi-synthetic lipoglycopeptide antibiotic, was evaluated in comparison with other antibacterial agents against 1229 Gram-positive organisms collected from medical centres in Latin America. Dalbavancin was the most potent compound tested against isolates of Staphylococcus aureus (MIC(50), 0.06 mg/L) and coagulase-negative staphylococci (MIC(50), 0.03 mg/L), independently of methicillin susceptibility. Dalbavancin inhibited all Streptococcus pneumoniae isolates at </= 0.06 mg/L. Dalbavancin also demonstrated excellent activity against beta-haemolytic (MIC(50), </= 0.008 mg/L) and viridans group (MIC(50), 0.016 mg/L) streptococci. All vancomycin-susceptible Enterococcus spp. isolates were inhibited by dalbavancin at </= 0.25 mg/L, but some vancomycin-resistant Enterococcus spp. isolates were only inhibited by dalbavancin levels of >/= 8 mg/L. Dalbavancin exhibited excellent activity against isolates of Corynebacterium spp. and Listeria spp. Dalbavancin may provide an important therapeutic option for Gram-positive infections, excluding those caused by enterococci with VanA-type resistance.

Identification of methicillin-resistant Staphylococcus aureus carriage in less than 1 hour during a hospital surveillance program

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide and is responsible for significant morbidity, mortality, and health care costs. Control strategies to limit the emergence and spread of this organism rely on rapid and sensitive tests for detection of MRSA carriage. However, the standard surveillance culture method for detecting MRSA is labor intensive and time-consuming (2-3 days per procedure). There is thus a need for a rapid and accurate method to screen for MRSA carriage.

METHODS

We recently developed an easy-to-use real-time polymerase chain reaction (PCR) assay suitable for specific detection of MRSA in nasal specimens in <1 h. We studied the efficacy of our new PCR assay in routine screening for nasal MRSA carriage during a hospital surveillance program. A total of 331 nasal specimens obtained from 162 patients at risk for colonization were tested by both the standard mannitol agar culture method and our PCR assay.

RESULTS

The PCR assay detected MRSA in all 81 samples that were culture positive for MRSA. The PCR assay detected 4 additional MRSA-positive specimens, for a specificity of 98.4%, a positive predictive value of 95.3%, and a sensitivity and negative predictive value of 100%.

CONCLUSIONS

This novel PCR assay allows reliable identification of MRSA carriers in <1 h. This test should facilitate the efficacy of MRSA surveillance programs.

Cefoxitin resistance as a surrogate marker for the detection of methicillin-resistant Staphylococcus aureus

OBJECTIVES

To evaluate the usefulness of cefoxitin when used as a surrogate marker for the detection of methicillin resistance.

PATIENTS AND METHODS

Eight hundred and seventy-one strains of Staphylococcus aureus, collected from eight tertiary referral centres serving diverse socio-economic populations, were included in the study using NCCLS disc diffusion and the agar dilution methods.

RESULTS

Using cefoxitin and NCCLS criteria for disc diffusion, the sensitivity and specificity for recognizing methicillin resistance were both 100%. Similar results were obtained when the strains were tested by the agar dilution method. The cefoxitin MICs for methicillin-susceptible strains were < or = 4 mg/L.

CONCLUSIONS

Testing with cefoxitin as a surrogate marker for the detection of methicillin resistance was very accurate with both disc diffusion and agar dilution methods. Such testing clearly distinguished methicillin-resistant strains of S. aureus from methicillin-susceptible strains.

Comparison of antibody repertoires against Staphylococcus aureus in healthy individuals and in acutely infected patients

The management of staphylococcal diseases is increasingly difficult with present medical approaches. Preventive and therapeutic vaccination is considered to be a promising alternative; however, little is known about immune correlates of protection and disease susceptibility. To better understand the immune recognition of Staphylococcus aureus by the human host, we studied the antistaphylococcal humoral responses in healthy people in comparison to those of patients with invasive diseases. In a series of enzyme-linked immunosorbent assay analyses performed using 19 recombinant staphylococcal cell surface and secreted proteins, we measured a wide range of antibody levels, finding a pronounced heterogeneity among individuals in both donor groups. The analysis revealed marked differences in the antibody repertoires of healthy individuals with or without S. aureus carriage, as well as in those of patients in the acute phase of infection. Most importantly, we identified antigenic proteins for which specific antibodies were missing or underrepresented in infected patients. In contrast to the well-described transient nature of disease-induced antistaphylococcal immune response, it was demonstrated that high-titer antistaphylococcal antibodies are stable for years in healthy individuals. In addition, we provide evidence obtained on the basis of opsonophagocytic and neutralizing activity in vitro assays that circulating antistaphylococcal serum antibodies in healthy donors are functional. In light of these data we suggest that proper serological analysis comparing the preexisting antibody repertoires of hospitalized patients with different outcomes for nosocomial staphylococcal infections could be extremely useful for the evaluation of candidate vaccine antigens in addition to protection data generated with animal models.

Invertebrates as animal models forStaphylococcus aureuspathogenesis: a window into host–pathogen interaction

Recently, the use of invertebrate models of infection has given exciting insights into host-pathogen interaction for a number of bacteria. In particular, this has revealed important factors of the host response with remarkable parallels in higher organisms. Here, we review the advances attained in the elucidation of virulence determinants of a major human pathogen, Staphylococcus aureus, in relation to the invertebrate models thus far applied, the silkworm (Bombyx mori), the fruit fly (Drosophila melanogaster) and the roundworm (Caenorhabditis elegans). Also, the major pathways of host defence are covered in light of the response to S. aureus and the similarities and divergences in innate immunity of vertebrates and invertebrates. Consequently, we comparatively consider pathogen recognition receptors, signal transduction pathways (including Toll, Imd and others), and the humoral and cellular antimicrobial effectors. The technically convenient and ethically acceptable invertebrates appear as a valuable first tool to discriminate molecules participating from both sides of the host-S. aureus interaction as well as a high throughput method for antimicrobial screening.

Pharmacodynamics of cefepime alone and in combination with various antimicrobials against methicillin-resistant Staphylococcus aureus in an in vitro pharmacodynamic infection model

Treatment options for gram-positive resistant bacteria are limited; therefore, efforts to evaluate therapy options in the critical care population are warranted. Cefepime has broad-spectrum activity against gram-negative and gram-positive organisms. We have previously demonstrated that the combination of cefepime with vancomycin, linezolid, or quinupristin-dalfopristin had an improved or enhanced effect against methicillin-resistant Staphylococcus aureus (MRSA). We investigated various regimens of cefepime alone and in combination against two clinical MRSA isolates (R2481 and R2484) in an established in vitro pharmacodynamic model. Human pharmacokinetic regimen simulations were as follows: cefepime, 2 g every 8 h (q8h) (C8) and 12 h (C12), continuous-infusion 2-g loading dose followed by 4 g alone or in combination with gentamicin and tobramycin (1.0 or 2.0 [G1 and G2 or TB1 and TB2] mg/kg of body weight q12h and 5.0 [G5 or TB5] mg/kg q24h), arbekacin (ARB) (100 mg q12h), linezolid (LIN) (600 mg q12h), tigecycline (TIG) (100 mg q24h), or daptomycin (DAP) (6 mg/kg q24h) for 48 h. The MICs for cefepime, gentamicin, tobramycin, ARB, LIN, TIG, and DAP for the two clinical MRSA isolates (R2481 and R2484) were 4 and 4, 0.25 and 0.5, 128 and 0.5, 0.5 and 0.125, 2 and 4, 0.25 and 0.25, and 0.0625 and 0.125 microg/ml, respectively. At 48 h, combinations of C12 and C8 plus ARB, G1, or G5 (range, -2.05- to -4.32-log(10) decrease) demonstrated enhanced lethality against R2481 (resistant to tobramycin) (P < 0.05). A similar relationship was demonstrated against R2484 with cefepime plus ARB, gentamicin, or tobramycin (range, -2.05- to -3.63-log(10) decrease) (P < 0.05). A 99.9% kill was achieved with cefepime plus aminoglycoside combinations as early as 2 h and maintained throughout the 48-h period. TIG was antagonistic when combined with C12 against both isolates. DAP alone achieved 99.9% kill for up to 48 h for both isolates and was the most active agent against R2481 and R2484 (-2.89- and -3.61-log(10) decrease at 48 h); therefore, combination therapy did not enhance lethality. Overall, the most potent combinations noted were cefepime in combination with low- and high-dose aminoglycosides. Further investigations with combination therapies are warranted.

Methicillin-resistant Staphylococcus aureus and beyond: what's new in the world of the golden staph?

Methicillin-resistant Staphylococcus aureus (MRSA) continues to plague our hospitals. With the appearance of isolates that are resistant to vancomycin, now, more than ever, we must direct our efforts to controlling its development and spread. New antimicrobials have become available for treatment, but may only be a short-term answer. Our efforts towards control must be directed towards infection control measures such as improved hand hygiene with user-friendly products, such as alcohol-based hand disinfectants. Intranasal mupirocin may have a place in prevention of surgical site infection, although this role has not yet been clearly defined. Other areas where MRSA control may be effected include prudent controlled use of antibiotics, including surgical prophylaxis.

Pharmacokinetics of oritavancin in plasma and skin blister fluid following administration of a 200-milligram dose for 3 days or a single 800-milligram dose

Oritavancin is a novel glycopeptide currently being developed for the treatment of complicated skin and skin structure infections (cSSSI), including those caused by multidrug resistant gram-positive pathogens. The disposition of oritavancin in skin structures was investigated using a cantharide-induced blister fluid model. Seventeen healthy male subjects received oritavancin, but only 16 subjects were evaluated after one subject discontinued study drug. Each subject (eight per dose group) received 200 mg of oritavancin once a day for 3 days (group A) or 800 mg as one single dose (group B). Group A plasma samples and exudates from blister fluid were collected on days 3, 4, 7, 9, and 12 and on days 3, 4, 7, and 9, respectively. Group B samples and exudates were collected on days 1, 2, 5, 7, and 10 and on days 1, 2, 5, and 7, respectively. Drug concentrations were determined using a liquid chromatography-tandem mass spectrometry assay and, subsequently, pharmacokinetic analysis was performed. Differences between treatment groups in ratios for area under the concentration-time curve for blister fluid and plasma (AUC(blister fluid)/AUC(plasma) ratios) were evaluated using a t test (alpha = 0.05). Mean maximum concentration of drug in plasma or blister fluid was approximately 8-fold and 11-fold higher in plasma than in blister fluid following the 200- or 800-mg doses of oritavancin, respectively. Mean AUC(blister fluid)/AUC(plasma) ratios at 24 h were 0.190 (standard deviation [SD], 0.052) and 0.182 (SD, 0.062) for groups A and B, respectively (P = 0.791). To place these results in a clinical context, mean drug concentrations in blister fluid exceed the oritavancin MIC at which 90% of strains are inhibited of Staphylococcus aureus (2 microg/ml) by approximately 2- to 5.5-fold at 12 h and 1.5- to 3-fold at 24 h following administration of both dosing regimens. These results support the potential use of oritavancin for the treatment of cSSSI.

Oxacillin- and mupirocin-resistant Staphylococcus aureus: in vitro activity of silver sulphadiazine and cerium nitrate in hospital strains

Nasal carriage is an important reservoir of oxacillin-resistant Staphylococcus aureus (ORSA). Mupirocin is a topical drug used to remove S. aureus from nares. However, isolates resistant to mupirocin have been reported all over the world. Silver sulphadiazine (SSD) is a topical agent, which when associated with cerium nitrate (CN), has been shown to be useful in the treatment of burn infections and could be an alternative drug for patient decolonization. Susceptibility to oxacillin in 203 S. aureus isolates was evaluated by the agar diffusion test, while the agar diffusion and agar dilution methods were used for mupirocin. A PCR-multiplex method was performed to detect the mecA and ileS-2 genes. Minimum inhibitory concentration (MICs) to SSD and CN, used alone or in association, were determined by the agar dilution method. One hundred and sixty-three (80.3%) strains were oxacillin-resistant, and 37 (18.2%) were mupirocin resistant. The MIC of SSD alone or in association with CN was 64 microg/mL, while for CN alone was 2048 microg/mL for all isolates. SSD presented anti-staphylococcal activity at concentrations (64 microg/mL) much lower than those commonly used in commercial preparations (10 mg/g) and had good activity against mupirocin-resistant strains, showing that this drug could be used for nasal decolonization in ORSA carries.

Epidemiology and typing of Staphylococcus aureus strains isolated from bloodstream infections

We carried out an epidemiological study covering 2,365,067 patient days of hospitalization between 2000 and 2003. During this time, 413 Staphylococcus aureus bloodstream infections occurred. This corresponds to 15% of the 2,676 bloodstream infections observed during this period in the 31 hospitals in our region of France, which has 2.5 million inhabitants. The incidence of nosocomial S. aureus bloodstream infections was 0.11 per 1,000 days of hospitalization. The prevalence of methicillin-resistant S. aureus (MRSA) strains, of which 13% were nonmultiresistant MRSA (NORSA), was 33%, and this percentage was stable over the 4 years. In contrast, the prevalence of S. aureus strains susceptible to methicillin but resistant to quinolones or susceptible to methicillin but multiresistant to antibiotics (EMSSA strains) increased from 4% in 2000 to 23% in 2003. As previously reported, MRSA strains were mostly recovered from nosocomial bloodstream infections, whereas NORSA strains-generally considered to be responsible for community-acquired infections-were always isolated from nosocomial bloodstream infections. Pulsed-field gel electrophoresis (PFGE) analysis of 109 MRSA strains and 15 EMSSA strains demonstrated clonal diffusion of the three major French MRSA clones and revealed considerable genetic heterogeneity among EMSSA strains. Although no epidemiologically related NORSA strains clustered in particular PFGE groups, the distribution of MRSA strains isolated from bloodstream infections according to the portal of entry (vascular devices, pulmonary, and urinary) was not random for the major PFGE clones, suggesting that each MRSA lineage displays particular virulence features.

New quadriplex PCR assay for detection of methicillin and mupirocin resistance and simultaneous discrimination of Staphylococcus aureus from coagulase-negative staphylococci

Major challenges in diagnostic molecular microbiology are to develop a simple assay to distinguish Staphylococcus aureus from the less virulent but clinically important coagulase-negative staphylococci (CoNS) and to simultaneously determine their antibiotic resistance profiles. Multiplex PCR assays have been developed for the detection of methicillin- and mupirocin-resistant S. aureus and CoNS but not for the simultaneous discrimination of S. aureus from CoNS. We designed a new set of Staphylococcus genus-specific primers and developed a novel quadriplex PCR assay targeting the 16S rRNA (Staphylococcus genus specific), nuc (S. aureus species specific), mecA (a determinant of methicillin resistance), and mupA (a determinant of mupirocin resistance) genes to identify most staphylococci, to discriminate S. aureus from CoNS and other bacteria, and to simultaneously detect methicillin and mupirocin resistance. Validation of the assay with 96 ATCC control strains and 323 previously characterized clinical isolates, including methicillin- and mupirocin-sensitive and -resistant S. aureus and CoNS isolates and other bacteria, demonstrated 100% sensitivity, specificity, and accuracy. This assay represents a simple, rapid, accurate, and reliable approach for the detection of methicillin- and mupirocin-resistant staphylococci and offers the hope of preventing their widespread dissemination through early and reliable detection.

Evolution of ciprofloxacin-resistant Staphylococcus aureus in in vitro pharmacokinetic environments

The development of novel antibacterial agents is decreasing despite increasing resistance to presently available agents among common pathogens. Insights into relationships between pharmacodynamics and resistance may provide ways to optimize the use of existing agents. The evolution of resistance was examined in two ciprofloxacin-susceptible Staphylococcus aureus strains exposed to in vitro-simulated clinical and experimental ciprofloxacin pharmacokinetic profiles for 96 h. As the average steady-state concentration (C(avg ss)) increased, the rate of killing approached a maximum, and the rate of regrowth decreased. The enrichment of subpopulations with mutations in grlA and low-level ciprofloxacin resistance also varied depending on the pharmacokinetic environment. A regimen producing values for C(avg ss) slightly above the MIC selected resistant variants with grlA mutations that did not evolve to higher levels of resistance. Clinical regimens which provided values for C(avg ss) intermediate to the MIC and mutant prevention concentration (MPC) resulted in the emergence of subpopulations with gyrA mutations and higher levels of resistance. A regimen producing values for C(avg ss) close to the MPC selected grlA mutants, but the appearance of subpopulations with higher levels of resistance was diminished. A regimen designed to maintain ciprofloxacin concentrations entirely above the MPC appeared to eradicate low-level resistant variants in the inoculum and prevent the emergence of higher levels of resistance. There was no relationship between the time that ciprofloxacin concentrations remained between the MIC and the MPC and the degree of resistance or the presence or type of ciprofloxacin-resistance mutations that appeared in grlA or gyrA. Regimens designed to eradicate low-level resistant variants in S. aureus populations may prevent the emergence of higher levels of fluoroquinolone resistance.

Emergence in Asian countries of Staphylococcus aureus with reduced susceptibility to vancomycin

To investigate the prevalence of Staphylococcus aureus with reduced susceptibility to vancomycin among methicillin-resistant S. aureus (MRSA) strains in Asian countries, a total of 1,357 clinical isolates of MRSA collected from 12 Asian countries were screened by using brain heart infusion agar plates containing 4 mg of vancomycin per liter. The presence of strains that were heterointermediately resistant to vancomycin (hVISA) was confirmed by population analysis. Of 347 (25.6%) MRSA isolates that grew on the screening agar plates, 58 isolates (4.3%) were hVISA. hVISA strains were found in India, South Korea, Japan, the Philippines, Singapore, Thailand, and Vietnam. However, neither vancomycin-intermediate S. aureus nor vancomycin-resistant S. aureus isolates were found among MRSA isolates from Asian countries in this survey.

Genomic characterization of oxacillin-resistant Staphylococcus epidermidis and Staphylococcus haemolyticus isolated from Brazilian medical centres

Studies on the genetic diversity of oxacillin-resistant coagulase-negative staphylococcal (CNS) isolates are important for the control and prevention of infections. The present study evaluated the clonal diversity of oxacillin-resistant Staphylococcus epidermidis (ORSE) and Staphylococcus haemolyticus (ORSH) strains, isolated from patients in nine Brazilian medical centres by using pulsed-field gel electrophoresis (PFGE) after digestion of bacterial DNA using SmaI. PFGE analysis of ORSE (N=44) and ORSH (N=25) strains showed the presence of 29 restriction profiles clustered in 16 PFGE types, and 21 distinct profiles in 15 PFGE types, respectively, indicating a large genetic diversity among isolates of both of these species. Among the ORSE isolates, 23 (52%) strains belonged to two predominant PFGE types (named A and B), which were observed in most of the hospitals assessed, indicating the spread of these PFGE types in hospitals located in Rio de Janeiro. The spread of PFGE types of ORSH was also detected in some of the hospitals investigated. The results show that PFGE is a suitable tool for epidemiological studies of oxacillin-resistant CNS, and can be used as a basis for infection control procedures for these multiresistant organisms.

Current and emerging serious Gram-positive infections

Serious infections caused by Gram-positive pathogens are increasingly difficult to treat because of pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and penicillin-resistant Streptococcus pneumoniae. The more recent emergence of vancomycin-intermediate and -resistant MRSA (VISA and VRSA) has further compromised treatment options. Reports of resistance to, and clinical failures with newer antimicrobial agents such as linezolid and quinupristin/dalfopristin are also emerging. Consequently, there is a clinical need for new antimicrobial agents that have suitable pharmacokinetic properties and safety profiles, with activity against these Gram-positive pathogens.

Occurrence and antimicrobial resistance pattern comparisons among bloodstream infection isolates from the SENTRY Antimicrobial Surveillance Program (1997-2002)

The empiric treatment of patients with bloodstream infections (BSI) has become more complicated in an era of increasing antimicrobial resistance. The SENTRY Antimicrobial Surveillance Program has monitored BSI from patients in medical centers worldwide since 1997. During 1997-2002, a total of 81,213 BSI pathogens from North America, Latin America, and Europe were tested for antimicrobial susceptibility. S. aureus, E. coli, and coagulase-negative staphylococci were the three most common BSI pathogens in all three regions each year. Prevalence variability was noted in regions for some species, including higher rates of isolation of E. coli in Europe, Enterococcus spp. in North America, and Gram-negative enteric and nonenteric species in Latin America. Patient age analysis showed the most common BSI pathogen among neonates was coagulase-negative staphylococci and among elderly patients, E. coli. Resistance among BSI pathogens was much more prevalent in nosocomial infections and in patients in intensive care units (ICUs); age differences were also noted. Geographically, oxacillin-resistant S. aureus (39.1%, 2002) and vancomycin-resistant enterococci (17.7%, 2002) were highest in North America, and extended-spectrum beta-lactamase-producing Klebsiella spp. (35.8-46.7%) and multidrug-resistant P. aeruginosa (18.7%, 2002) were highest in Latin America. Activity of commonly used antimicrobial agents remained relatively stable in North America, except in the case of vancomycin-resistant enterococci (20% decline between 1997 and 2002). An epidemiologic investigation of oxacillin-resistant S. aureus in North America identified 10 significant clones (ribotypes) and the common resistance patterns associated with them. Surveillance of BSI pathogens is needed to determine trends of resistance and provide useful information regarding patient risk factors and geographic differences.

Pathogens resistant to antimicrobial agents: epidemiology, molecular mechanisms, and clinical management

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens and resistance traits in nursing homes, the community, as well as in hospitals. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Antibiotic Resistance Patterns ofmecA-PositiveStaphylococcus aureusIsolates from Clinical Specimens and Nasal Carriage

The present study demonstrates that the nasal carriage rate of Staphylococcus aureus was 40% in Jordanian healthy young adult population, and 19% of nasal S. aureus and 57% of clinical isolates over the same period were resistant to oxacillin (MRSA), respectively. The mecA gene was detected in all MRSA isolates in both groups. Most of MRSA isolates were multiresistant to three antibiotic classes (beta-lactams, aminoglycosides, macrolides-lincosamides). This result suggests a serious problem may be encountered in treatment of staphylococcal infections in Jordan.

Antimicrobial activity of tigecycline (GAR-936) tested against 3498 recent isolates of Staphylococcus aureus recovered from nosocomial and community-acquired infections

Tigecycline is a novel 9-t-butylglycylamido derivative of minocycline that has demonstrated activity against a variety of Gram-positive and -negative bacterial pathogens. In vitro activity of tigecycline and comparator agents was determined for 3498 recent (2000-2003) strains of Staphylococcus aureus recovered from patients with either nosocomial or community-acquired infections. Oxacillin-susceptible and -resistant S. aureus from both patient populations displayed identical results for tigecycline (MIC(50) and MIC(90) results at 0.25 and 0.5 mg/L, respectively) and all strains were inhibited by 1 mg/L or less. While co-resistances to other antimicrobial classes were present in oxacillin-resistant strains, susceptibility to tigecycline remained unaffected, making the compound an attractive candidate for treatment of serious hospital as well as community-acquired staphylococcal infections.

Linezolid eradicates MRSA better than vancomycin from surgical-site infections

BACKGROUND

The purpose of this analysis was to compare the efficacy of linezolid versus vancomycin in patients with suspected or proven gram-positive methicillin-resistant Staphylococcus aureus (MRSA) surgical-site infections.

METHODS

An open-label, randomized, comparator-controlled, multicenter, multinational study was conducted in hospitalized patients. Patients were randomized 1:1 to receive linezolid 600 mg (intravenous [IV] or oral) every 12 hours (n = 66) or vancomycin 1 g every 12 hours IV (n = 69) for 7 to 21 days. Patients were assessed at the test-of-cure (TOC) visit, 7 days after completing therapy.

RESULTS

Clinical success at TOC was documented in similar proportions of patients treated with linezolid or vancomycin. Of those with MRSA isolated, significantly more patients who received linezolid compared with those who received vancomycin were microbiologically cured (87% vs 48%, respectively; 95% confidence interval 16.51 to 60.27; P = 0.0022).

CONCLUSION

Intravenous or oral linezolid was well tolerated and superior to vancomycin in treating patients with MRSA-infected surgical-site infections.

Changing epidemiology of methicillin-resistant Staphylococcus aureus in Finland

Data on methicillin-resistant Staphylococcus aureus (MRSA) cases notified to the National Infectious Disease Register (NIDR) and antibiotic resistance profiles of MRSA isolates sent to the national reference laboratory between 1997 and 2002 were analysed. In addition, the diagnostic methods used for MRSA identification in Finnish microbiology laboratories, the number of MRSA screening specimens studied, and the MRSA situation in long-term care facilities in 2001 were reviewed. MRSA cases notified to the NIDR rose from 120 in 1997 to 597 in 2002 (from 2.3 to 11.5 cases per 100,000 population). The increase was greatest in elderly people and outside Helsinki metropolitan area, in the districts where the proportion of non-multiresistant strains was most prominent. The National Committee for Clinical Laboratory Standard's guidelines for the oxacillin disk diffusion test were followed, except for the incubation temperature and time, which may have hindered detection of some MRSA strains. There was a wide geographic variation in the rates of MRSA, but this was not related to screening activity. MRSA isolates from long-term facilities accounted for more than half of the notifications to the NIDR in 2001.

Tertiary structure of Staphylococcus aureus cell wall murein

The recently described scaffold model of murein architecture depicts the gram-negative bacterial cell wall as a gel-like matrix composed of cross-linked glycan strands oriented perpendicularly to the plasma membrane while peptide bridges adopt a parallel orientation (B. A. Dmitriev, F. V. Toukach, K. J. Schaper, O. Holst, E. T. Rietschel, and S. Ehlers, J. Bacteriol. 185:3458-3468, 2003). Based on the scaffold model, we now present computer simulation studies on the peptidoglycan arrangement of the gram-positive organism Staphylococcus aureus, which show that the orientation of peptide bridges is critical for the highly cross-linked murein architecture of this microorganism. According to the proposed refined model, staphylococcal murein is composed of glycan and oligopeptide chains, both running in a plane that is perpendicular to the plasma membrane, with oligopeptide chains adopting a zigzag conformation and zippering adjacent glycan strands along their lengths. In contrast to previous models of murein in gram-positive bacteria, this model reflects the high degree of cross-linking that is the hallmark of the staphylococcal cell wall and is compatible with distinguishing features of S. aureus cytokinesis such as the triple consecutive alteration of the division plane orientation and the strictly centripetal mode of septum closure.

Phenotypic and genotypic aminoglycoside resistance in blood culture isolates of coagulase-negative staphylococci from a single neonatal intensive care unit, 1989–2000

OBJECTIVES

To investigate the prevalence of aminoglycoside resistance and genes encoding aminoglycoside-modifying enzymes (AME) in blood culture isolates of coagulase-negative staphylococci (CoNS) from neonates.

MATERIALS AND METHODS

A total of 180 isolates from 148 patients collected in a single neonatal unit over a 12 year period were examined for susceptibility to gentamicin, tobramycin, netilmicin, amikacin and arbekacin by Etest and/or disc diffusion. AME genes were detected by PCR.

RESULTS

The overall non-susceptibility rates to gentamicin, tobramycin, netilmicin, amikacin and arbekacin were 66%, 68%, 52%, 38% and 1%, respectively. Gentamicin non-susceptibility rates were 4% and 91% in methicillin-susceptible and -resistant isolates, respectively. aac(6')-Ie-aph(2'')-Ia, aph(3')-IIIa and/or ant(4')-Ia were encountered in 125 (69%), 1 (0.5%) and 30 (16.6%) isolates, respectively. Forty-six (26%) isolates negative for AME genes were susceptible to all aminoglycosides. In contrast, 115 (92%), 91 (73%) and 66 (53%) of aac(6')-Ie-aph(2'')-Ia positive isolates were non-susceptible to gentamicin, netilmicin and amikacin, respectively. Only one isolate showed arbekacin resistance. However, aac(6')-Ie-aph(2'')-Ia positive isolates and isolates with gentamicin MIC > or =128 mg/L displayed a significant reduction in arbekacin inhibition zones.

CONCLUSIONS

A high prevalence of aminoglycoside resistance was detected and associated with methicillin resistance. Discrepancies between phenotypic and genetic detection of aminoglycoside resistance were discerned. Gentamicin was the preferred substrate for phenotypic detection of aac(6')-Ie-aph(2'')-Ia. Arbekacin showed favourable antibacterial activity even in aac(6')-Ie-aph(2'')-Ia-positive isolates. We suggest including arbekacin in future clinical trials of empirical treatment of late onset neonatal sepsis.

Evolution of the antimicrobial resistance of Staphylococcus spp. in Spain: five nationwide prevalence studies, 1986 to 2002

Data regarding the evolution of Staphylococcus resistance in a whole country have a definite influence on the design of empirical treatment regimens. Nevertheless, incidence studies over long periods of time are expensive and very difficult to carry out. In order to ascertain the present situation of the antimicrobial resistance of Staphylococcus in Spain and the change of this resistance over time, we performed five point prevalence studies (1986 to 2002) in a large group of Spanish hospitals (from 68 institutions in 1986 to 143 in 2002) collecting all Staphylococcus strains isolated on a single selected day. All microorganisms were identified in the five studies at the same laboratory, and antimicrobial susceptibility testing was performed against 17 antimicrobial agents by the agar dilution method and a microdilution method. During this period, there was an overall increase in resistance to most antimicrobials among Staphylococcus aureus/coagulase-negative staphylococci, mainly to oxacillin (1.5%/32.5% in 1986 versus 31.2%/61.3% in 2002) (P < 0.001), erythromycin (7%/41.1% in 1986 versus 31.7%/63% in 2002) (P < 0.001), gentamicin (5.2%/25.4% in 1986 versus 16.9%/27.8% in 2002) (P < 0.001; P = 0.5), and ciprofloxacin (0.6%/1.1% in 1986 versus 33.9%/44.9% in 2002) (P < 0.001). All of the isolates were uniformly susceptible to glycopeptides, linezolid, and quinupristin/dalfopristin. Resistance of S. aureus to trimethoprim/sulfamethoxazole was very low (from 0.5% to 2.1%) (P = 0.152). Periodic performance of prevalence studies is a useful, inexpensive, and easy tool to know the nationwide situation of a microorganism and its resistance to antimicrobials; it also helps us assess the emergence and spread of antimicrobial resistance.

Crystal Structures of the Apo and Penicillin-acylated Forms of the BlaR1 β-Lactam Sensor of Staphylococcus aureus

Staphylococcus aureus is among the most prevalent and antibiotic-resistant of pathogenic bacteria. The resistance of S. aureus to prototypal beta-lactam antibiotics is conferred by two mechanisms: (i) secretion of hydrolytic beta-lactamase enzymes and (ii) production of beta-lactam-insensitive penicillin-binding proteins (PBP2a). Despite their distinct modes of resistance, expression of these proteins is controlled by similar regulation systems, including a repressor (BlaI/MecI) and a multidomain transmembrane receptor (BlaR1/MecR1). Resistance is triggered in response to a covalent binding event between a beta-lactam antibiotic and the extracellular sensor domain of BlaR1/MecR1 by transduction of the binding signal to an intracellular protease domain capable of repressor inactivation. This study describes the first crystal structures of the sensor domain of BlaR1 (BlaRS) from S. aureus in both the apo and penicillin-acylated forms. The structures show that the sensor domain resembles the beta-lactam-hydrolyzing class D beta-lactamases, but is rendered a penicillin-binding protein due to the formation of a very stable acyl-enzyme. Surprisingly, conformational changes upon penicillin binding were not observed in our structures, supporting the hypothesis that transduction of the antibiotic-binding signal into the cytosol is mediated by additional intramolecular interactions of the sensor domain with an adjacent extracellular loop in BlaR1.

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.

Comparison of minimal inhibitory and mutant prevention drug concentrations of 4 fluoroquinolones against clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus

Staphylococcus aureus remains an important human pathogen affecting both outpatients and those hospitalized. Increasing antimicrobial resistance is global but prevalence rates are variable for different geographical areas. Fluoroquinolones have been used to treat S. aureus infections and the newer quinolones have enhanced in vitro activity against this organism. The mutant prevention concentration (MPC) defines the antimicrobial drug concentration threshold that would require an organism to simultaneously possess two mutations for growth in the presence of the drug. We tested clinical isolates of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) S. aureus by minimum inhibitory concentration (MIC) and MPC against gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin. For MSSA strains, the rank order of potency based on MIC(90) values were gemifloxacin (0.063 mg/l) = moxifloxacin (0.063 mg/l) > gatifloxacin (0.05 mg/l) = levofloxacin (0.25 mg/l) and by MPC values moxifloxacin (0.25 mg/l) > gemifloxacin (0.5 mg/l) > gatifloxacin (1 mg/l) = levofloxacin (1mg/l). For 87% of the isolates the MPC value was 0.5 mg/l for gatifloxacin. The rank order of potency based on the time the serum drug concentration exceeded the MPC(90), was as follows: moxifloxacin (>24 h) > levofloxacin (>18 h) > gatifloxacin (12 h) > gemifloxacin (9 h). Serum drug concentration remained in excess of the MPC(87) for 24 h for gatifloxacin. Both MIC(90) and MPC(90) values were higher against MRSA strains and the time above the MPC(90) was significantly shorter for all agents.

In vitro activity of the new quinolone WCK 771 against staphylococci

The activity of WCK 771, an experimental quinolone developed to overcome quinolone resistance in staphylococci and other bacteria, was determined against quinolone-susceptible and -resistant Staphylococcus aureus and S. epidermidis. WCK 771 MICs for 50 and 90% of the strains tested (MIC(50) and MIC(90), respectively) were 0.008 and 0.015 microg/ml for S. aureus (n = 43) and 0.015 and 0.03 microg/ml for S. epidermidis (n = 44) for quinolone-susceptible isolates, compared to ciprofloxacin values of 0.12 and 0.25 microg/ml and 0.25 and 0.5 microg/ml, respectively. Values for levofloxacin were 0.12 and 0.25 microg/ml and 0.12 and 0.25 microg/ml, those for clinafloxacin were 0.015 and 0.03 microg/ml and 0.015 and 0.03 microg/ml, those for moxifloxacin were 0.03 and 0.06 microg/ml and 0.06 and 0.12 microg/ml, and those for gatifloxacin were 0.06 and 0.12 microg/ml and 0.12 and 0.25 microg/ml, respectively. The WCK 771 MIC(50) and MIC(90), respectively, were 0.5 and 1 microg/ml for both species of staphylococci (n = 73 for S. aureus, n = 70 for S. epidermidis) for isolates highly resistant to ciprofloxacin (MIC(50) and MIC(90), >32 and >32 microg/ml, respectively). Values for levofloxacin were 8 and 32 microg/ml and 8 and 32 microg/ml, those for clinafloxacin were 1 and 2 microg/ml and 0.5 and 2 microg/ml, those for moxifloxacin 4 and >4 microg/ml and 4 and >4 microg/ml, and those for gatifloxacin were 4 and >4 microg/ml and 2 and >4 microg/ml, respectively. WCK 771 and clinafloxacin demonstrated MICs of 1 microg/ml against three vancomycin-intermediate strains. WCK 771 showed concentration-independent killing for up to 24 h at 2, 4, and 8 times the MICs against quinolone-resistant staphylococci and was also bactericidal after 8 h for high-density inocula (10(8) CFU/ml) of quinolone-resistant strains at 5 microg/ml, whereas moxifloxacin at 7.5 microg/ml was bacteriostatic. WCK 771 was not a substrate of the NorA efflux pump as evident from the similar MICs against both an efflux-positive and an efflux-negative strain. Overall, WCK 771 was the most potent quinolone tested against the staphylococci tested, regardless of quinolone susceptibility.

Effect of granulocyte colony-stimulating factor in experimental methicillin resistant Staphylococcus aureus sepsis

Background

Methicillin resistant Staphylococcus aureus (MRSA) is the leading pathogenic cause of nosocomial infections, especially in bacteraemia and sepsis. The essential therapy for MRSA infection is glycopeptides. Therapeutic failure can be seen with this therapy and the mortality is still high. The aim of this study was to evaluate the additional effect of G-CSF on the traditional antibiotic treatment in an experimental MRSA sepsis.

Methods

Experimental sepsis was performed in mice by intraperitoneal injection of MRSA isolate. Inoculum dose was estimated as 6 × 10⁹/ml. Mice were randomised for the study into four group; control group (not receive any therapy), G-CSF group (1000 ng/daily, subcutaneously for 3 d), antibiotic group (vancomycin 25 or 50 mg/kg intraperitoneally every 12 hours for 7 d), and vancomycin+G-CSF group (at the same concentrations and duration). Autopsy was done within one hour after mice died. If mice was still alive at the end of seventh day, they were sacrificed, and autopsy was done. In all groups, the effect of G-CSF therapy on the survival, the number of the MRSA colonies in the lung, liver, heart, spleen, and peritoneal cultures, the histopathology of the lung, liver, heart and spleen was investigated.

Results

One hundred and six mice were used. There were no significant differences in survival rates and bacterial eradication in G-CSF group compared with control group, and also in antibiotic +G-CSF group compared with antibiotic alone group. These parameters were all significantly different in antibiotic alone group compared with control group. Histopathologically, inflammation of the lung and liver were significantly reduced in vancomycin (25 mg/kg)+G-CSF and vancomycin (50 mg/kg)+G-CSF subgroups, respectively (p < 0.01). The histopathological inflammation of the other organs was not significantly different in antibiotic+G-CSF group compared with antibiotic group and, also G-CSF group compared with control group.

Conclusion

G-CSF treatment had no additional effect on survival and bacterial eradication in MRSA sepsis in nonneutropenic mice; and only a little effect on histopathology. G-CSF treatment is very expensive, likewise glycopeptides. The more interest in infection control measures, and prevent the spread of MRSA infections is more rational.

Generalized additive model demonstrates fluoroquinolone use/resistance relationships for Staphylococcus aureus

Mathematical models currently used to study the relationship between the prevalence of the resistance to an antibiotic and the amount of drug may not be adequate because they do not integrate temporal and area analyses simultaneously. Furthermore, the forms of such relationship are unknown. We applied the Generalized Additive Model (GAM) to study fluoroquinolone use and the incidence of fluoroquinolone-resistance in Staphylococcus aureus in our institution over a 3-year period. Overall institution and individual hospital unitrestricted analyses were performed. Relative risk (RR) observed for increasing fluoroquinolone use with a 4-month lag from the 25th percentile to the 75th percentile was 1.27 (95% CI: 1.13-1.42). In the surgery units, RR was 1.23 (95% CI: 1.01-1.50) for fluoroquinolone use with a 2-months lag. GAM enabled us to observe for the first time a significant temporal relationship between fluoroquinolone use and the incidence of fluoroquinolone-resistant nosocomial S. aureus isolates.

Antibiotic resistance in Staphylococcus aureus colonising the intestines of Swedish infants

Staphylococcus aureus has become a frequent coloniser of the intestinal tract of infants, but the health effects of such colonisation are not clear. In this study, the antibiotic resistance patterns of 116 S. aureus strains from the commensal intestinal microflora were determined. The strains were obtained from 81 Swedish infants who had been followed with regular stool samples and registration of antibiotic usage during their first year of life. The faecal population levels of the individual strains and the duration of their persistence in the microflora had been determined previously. The prevalence of antibiotic resistance among the 116 strains was modest: methicillin, 0%; penicillin G, 78%; erythromycin A, 3%; tetracycline, 2%; clindamycin, 0.9%; and fusidic acid, 0.9%. Colonisation by antibiotic-resistant strains was unrelated to antibiotic consumption by individual infants. Antibiotic-resistant strains were as capable of persisting in the intestinal microflora and reaching high faecal population levels as fully susceptible strains. No strain lost or acquired resistance during the colonisation period. Thus, antibiotic-resistant strains of S. aureus seem to be as fit for competition in the large bowel microflora as susceptible strains, even in the absence of selective pressure from antibiotics. This may aggravate the ecological consequences of antibiotic resistance development.

Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs

The etiology of nosocomial infections, the frequency of contaminated hands with the different nosocomial pathogens, and the role of health care workers' hands during outbreaks suggest that a hand hygiene preparation should at least have activity against bacteria, yeasts, and coated viruses. The importance of efficacy in choosing the right hand hygiene product is reflected in the new Centers for Disease Control and Prevention guideline on hand hygiene (J. M. Boyce and D. Pittet, Morb. Mortal. Wkly. Rep. 51:1-45, 2002). The best antimicrobial efficacy can be achieved with ethanol (60 to 85%), isopropanol (60 to 80%), and n-propanol (60 to 80%). The activity is broad and immediate. Ethanol at high concentrations (e.g., 95%) is the most effective treatment against naked viruses, whereas n-propanol seems to be more effective against the resident bacterial flora. The combination of alcohols may have a synergistic effect. The antimicrobial efficacy of chlorhexidine (2 to 4%) and triclosan (1 to 2%) is both lower and slower. Additionally, both agents have a risk of bacterial resistance, which is higher for chlorhexidine than triclosan. Their activity is often supported by the mechanical removal of pathogens during hand washing. Taking the antimicrobial efficacy and the mechanical removal together, they are still less effective than the alcohols. Plain soap and water has the lowest efficacy of all. In the new Centers for Disease Control and Prevention guideline, promotion of alcohol-based hand rubs containing various emollients instead of irritating soaps and detergents is one strategy to reduce skin damage, dryness, and irritation. Irritant contact dermatitis is highest with preparations containing 4% chlorhexidine gluconate, less frequent with nonantimicrobial soaps and preparations containing lower concentrations of chlorhexidine gluconate, and lowest with well-formulated alcohol-based hand rubs containing emollients and other skin conditioners. Too few published data from comparative trials are available to reliably rank triclosan. Personnel should be reminded that it is neither necessary nor recommended to routinely wash hands after each application of an alcohol-based hand rub. Long-lasting improvement of compliance with hand hygiene protocols can be successful if an effective and accessible alcohol-based hand rub with a proven dermal tolerance and an excellent user acceptability is supplied, accompanied by education of health care workers and promotion of the use of the product.

In vitro activities of ME1036 (CP5609), a novel parenteral carbapenem, against methicillin-resistant staphylococci

ME1036, formerly CP5609, is a novel parenteral carbapenem with a 7-acylated imidazo[5,1-b]thiazole-2-yl group directly attached to the carbapenem moiety of the C-2 position. The present study evaluated the in vitro activities of ME1036 against clinical isolates of gram-positive and gram-negative bacteria. ME1036 displayed broad activity against aerobic gram-positive and gram-negative bacteria. Unlike other marketed beta-lactam antibiotics, ME1036 maintained excellent activity against multiple-drug-resistant gram-positive bacteria, such as methicillin-resistant staphylococci and penicillin-resistant Streptococcus pneumoniae (PRSP). The MICs of this compound at which 90% of isolates were inhibited were 2 microg/ml for methicillin-resistant Staphylococcus aureus (MRSA), 2 microg/ml for methicillin-resistant coagulase-negative staphylococci, and 0.031 microg/ml for PRSP. In time-kill studies with six strains of MRSA, ME1036 at four times the MIC caused a time-dependent decrease in the numbers of viable MRSA cells. The activity of ME1036 against MRSA is related to its high affinity for penicillin-binding protein 2a, for which the 50% inhibitory concentration of ME1036 was approximately 300-fold lower than that of imipenem. In conclusion, ME1036 demonstrated a broad antibacterial spectrum and high levels of activity in vitro against staphylococci, including beta-lactam-resistant strains.

Bacterial pyomyositis

Bacterial pyomyositis has been defined as a subacute, deep bacterial infection of the soft tissues. The entity was originally described only in tropical climates, but it is increasing in incidence in temperate climates, such as in the United States. This is mainly attributed to the presence of immunocompromising states such as HIV/AIDS or liver disease. The etiology of pyomyositis remains a mystery, but its characteristics are well-described. If untreated, the disease process progresses through three distinct stages. The first stage is defined by vague complaints, muscle pain, and a low-grade fever. The second stage presents as worsening pain, swelling, fever, and actual abscess formation in the muscle. If the patient remains untreated, pyomyositis progresses to the third stage, which includes septicemia and possible septic shock. Large muscles around the pelvis are most commonly affected, and Staphylococcus aureus is the bacteria seen in most documented cases. To make a timely diagnosis and prevent serious sequelae, physical examination, laboratory results, imaging studies, and a high clinical suspicion must all be combined. Magnetic resonance imaging is the diagnostic study of choice, but it may be inconclusive early in the disease process. Definitive diagnosis must be made with aspiration or surgical drainage. Once diagnosed, treatment consists of appropriate intravenous antibiotics and possible surgical intervention. A full recovery is expected if appropriate treatment is initiated early in the process.