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

Physical and chemical compatibility of daptomycin with nine medications

BACKGROUND

Hospitalized patients with serious gram-positive infections tend to require concomitant therapy. Unfortunately, a number of antimicrobial agents have demonstrated incompatibility with other agents commonly administered intravenously.

OBJECTIVE

To evaluate the physical compatibility and chemical stability of the novel lipopeptide antibiotic daptomycin, at 20 mg/mL, with 9 commonly administered intravenous medications: aztreonam, ceftazidime, ceftriaxone, dopamine, gentamicin, fluconazole, heparin, levofloxacin, and lidocaine to support simultaneous Y-site administration.

METHODS

Daptomycin was admixed with each medication separately in NaCl 0.9%, incubated at room temperature, and assayed at 30, 60, and 120 minutes. Physical stability was assessed by visual inspection and by turbidity measurements. Chemical stability was assessed by HPLC analysis using standard methods.

RESULTS

All 9 daptomycin admixtures remained clear solutions, free of visible particulates. There were also few changes in turbidity (range 0 to -0.7 nephelometric turbidity units) during the study. In general, pH changes were within +/- 0.06 of baseline readings for all admixtures. HPLC analysis indicated no significant reduction (<4%) in daptomycin potency after 120 minutes at room temperature compared with baseline values in all 9 admixtures tested. In addition, there was no significant reduction (<5%) in potency compared with baseline values of the 9 medications tested in the daptomycin admixtures.

CONCLUSIONS

The results of this study indicate that solutions of 9 commonly administered intravenous medications simultaneously Y-site administered with daptomycin are stable and compatible, based on both physical and chemical potency analyses.

Widespread dissemination in The Netherlands of the epidemic berlin methicillin-resistant Staphylococcus aureus clone with low-level resistance to oxacillin

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen and represents a growing public health burden due to the emergence and spread of epidemic strains, particularly within the hospital environment. An epidemic MRSA clone, with characteristic low-level resistance to oxacillin, emerged in the year 2000 and became endemic in the Netherlands. Multilocus sequence typing characterized the strain as sequence type 45, which was previously designated the Berlin epidemic MRSA clone. In 2 years, this strain has become the predominant MRSA clone in the Netherlands.

Nosocomial bloodstream infections in US hospitals: analysis of 24,179 cases from a prospective nationwide surveillance study

BACKGROUND

Nosocomial bloodstream infections (BSIs) are important causes of morbidity and mortality in the United States.

METHODS

Data from a nationwide, concurrent surveillance study (Surveillance and Control of Pathogens of Epidemiological Importance [SCOPE]) were used to examine the secular trends in the epidemiology and microbiology of nosocomial BSIs.

RESULTS

Our study detected 24,179 cases of nosocomial BSI in 49 US hospitals over a 7-year period from March 1995 through September 2002 (60 cases per 10,000 hospital admissions). Eighty-seven percent of BSIs were monomicrobial. Gram-positive organisms caused 65% of these BSIs, gram-negative organisms caused 25%, and fungi caused 9.5%. The crude mortality rate was 27%. The most-common organisms causing BSIs were coagulase-negative staphylococci (CoNS) (31% of isolates), Staphylococcus aureus (20%), enterococci (9%), and Candida species (9%). The mean interval between admission and infection was 13 days for infection with Escherichia coli, 16 days for S. aureus, 22 days for Candida species and Klebsiella species, 23 days for enterococci, and 26 days for Acinetobacter species. CoNS, Pseudomonas species, Enterobacter species, Serratia species, and Acinetobacter species were more likely to cause infections in patients in intensive care units (P<.001). In neutropenic patients, infections with Candida species, enterococci, and viridans group streptococci were significantly more common. The proportion of S. aureus isolates with methicillin resistance increased from 22% in 1995 to 57% in 2001 (P<.001, trend analysis). Vancomycin resistance was seen in 2% of Enterococcus faecalis isolates and in 60% of Enterococcus faecium isolates.

CONCLUSION

In this study, one of the largest multicenter studies performed to date, we found that the proportion of nosocomial BSIs due to antibiotic-resistant organisms is increasing in US hospitals.

Single-dose pharmacokinetics and safety of a novel broad-spectrum cephalosporin (BAL5788) in healthy volunteers

BAL5788 is the water-soluble prodrug of BAL9141, a novel broad-spectrum cephalosporin with potent bactericidal activities against methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae. We investigated the safety and pharmacokinetics of BAL5788 in a double-blind, single-ascending-dose study with 40 healthy male subjects. The subjects were randomized to receive placebo (n = 2 subjects per dose) or BAL5788 (n = 6 subjects per dose) as a 200-ml intravenous infusion over 30 min. The BAL5788 doses used were 125, 250, 500, 750, and 1,000 mg (BAL9141 equivalents). All doses were well tolerated, with no severe or serious adverse events (AEs). The most frequent AE was taste disturbance. No electrocardiographic abnormalities and no trends or clinically significant changes in laboratory parameters or vital signs were observed. The maximum concentration of drug in serum and the area under the concentration-time curve for BAL9141 were dose proportional over the dosing range. The elimination half-life of BAL9141 was about 3 h. The volume of distribution at steady state was equal to the volume of the adult extracellular water compartment, and the rate of renal clearance of free drug corresponded to the normal glomerular filtration rate for adults. More than 70% of the administered dose was excreted as BAL9141 in the urine, and almost no prodrug was detected. After the infusion of 750 mg, the mean plasma BAL9141 concentrations exceeded the MIC at which 100% of MRSA isolates are inhibited (4 microg/ml) for approximately 7 h, or 58% of a 12-h dosing interval. These results indicate that infusions of 750 mg twice a day should be adequate for the treatment of infections caused by MRSA.

Use of Monte Carlo simulations to select therapeutic doses and provisional breakpoints of BAL9141

BAL9141, a new antimicrobial agent belonging to the class of parenteral pyrrolidinone-3-ylidenemethyl cephalosporins, is active against most gram-positive microorganisms, including methicillin-resistant variants (methicillin-resistant Staphylococcus aureus [MRSA] and methicillin-resistant Staphylococcus epidermidis [MRSE]), as well as against penicillin-resistant pneumococci (PRP) and many gram-negative microorganisms. BAL9141 is administered as the prodrug BAL5788, which is rapidly converted to BAL9141 by plasma esterases. Pharmacokinetic (PK) data obtained in a previous multiple ascending dose study were used to fit a population PK model to using the NPEM2 program, yielding PK parameter estimates and its covariance matrix for BAL9141. These estimates and matrix were used to perform Monte Carlo simulations (MCSs) and obtain unbiased target attainment rates (TARs) for various time periods during which the concentration remains above the MIC (T(>MIC)). Assuming a T(>MIC) of 40%, TARs of 100% were reached with a dose of 500 mg/liter every 12 h for pathogens with MICs of 2 mg/liter and with a dose of 750 mg/liter every 12 h for pathogens with MICs of 4 mg/liter. Because MICs are </=2 mg/liter for most strains of MRSA, MRSE, and PRP (with some strains showing an MIC of 4 mg/liter), a dosing regimen of 750 mg every 12 h is proposed for clinical studies. The corresponding provisional breakpoint is S (susceptible) </= 4 mg/liter.

Cleavage of complement C3b to iC3b on the surface of Staphylococcus aureus is mediated by serum complement factor I

Complement-mediated opsonization of Staphylococcus aureus bearing the dominant capsule serotypes, serotypes 5 and 8, remains incompletely understood. We have previously shown that complement plays a vital role in the efficient phagocytosis of a serotype 5 S. aureus strain and that the opsonic fragments of the central complement protein C3, C3b and iC3b, were present on the bacterial surface after incubation in human serum. In the present studies, C3b and iC3b were found on several serotype 5 and 8 S. aureus strains after incubation in human serum. Using purified classical activation pathway complement proteins and the Western blot assay, we showed that when C3b was generated on the S. aureus surface no iC3b fragments were found, suggesting that other serum proteins may be required for cleaving C3b to iC3b. When C3b-coated S. aureus was incubated with serum factor I, a complement regulatory protein, iC3b was generated. Purified factor H, a serum protein cofactor for factor I, did not enhance factor I-mediated cleavage of C3b. These findings suggest that C3b cleavage to iC3b on S. aureus is mediated by serum factor I and does not require factor H.

In vitro activities of 28 antimicrobial agents against Staphylococcus aureus isolates from tertiary-care hospitals in Korea: a nationwide survey

Staphylococcus aureus, one of the most frequently isolated pathogens in both hospitals and the community, has been particularly efficient at developing resistance to antimicrobial agents. As methicillin-resistant S. aureus (MRSA) has prevailed and, furthermore, as S. aureus with reduced susceptibility to vancomycin has emerged, the therapeutic options for the treatment of S. aureus infections have become limited. To update the current status of antibiotic resistance, clinical S. aureus isolates were collected from eight university-affiliated hospitals from June 1999 to January 2001. Susceptibility tests with 28 antibiotics were performed by the disk diffusion method. Among a total of 682 isolates, the methicillin resistance rate was 64% (439 of 682), and most of the MRSA isolates were resistant to multiple classes of antibiotics. Although a constitutive macrolide-lincosamide-streptogramin B resistance phenotype was common, no isolates were resistant to quinupristin-dalfopristin or linezolid. Rifampin, fusidic acid, trimethoprim-sulfamethoxazole, and arbekacin showed superior in vitro activity compared with the other antibiotics against the MRSA isolates. No isolates showed reduced susceptibility to vancomycin.

Accessory gene regulator group II polymorphism in methicillin-resistant Staphylococcus aureus is predictive of failure of vancomycin therapy

We studied methicillin-resistant Staphylococcus aureus (MRSA) isolates to determine if the group II polymorphism at the accessory gene regulator (agr) locus demonstrated any relationship with the clinical efficacy of vancomycin. One hundred twenty-two MRSA isolates from 87 patients treated with vancomycin were evaluated. Forty-five of 87 patients had no clinical or bacteriological response to vancomycin. Among the 36 clinically evaluable patients with the agr group II polymorphism, 31 had an infection that failed to respond to vancomycin, whereas only 5 had an infection that responded successfully to vancomycin. This finding is of interest in light of our previous findings that glycopeptide-intermediately resistant S. aureus (GISA) and hetero-GISA clinical isolates in the United States and Japan are enriched for the agr group II polymorphism, and it suggests a possible intrinsic survival advantage of some S. aureus clones with this genetic marker under vancomycin selective pressure.

Prevalence and antimicrobial susceptibilities of bacteria isolated from blood cultures of hospitalized patients in the United States in 2002

BACKGROUND

Bloodstream infections are associated with significant patient morbidity and mortality. Antimicrobial susceptibility patterns should guide the choice of empiric antimicrobial regimens for patients with bacteremia.

METHODS

From January to December of 2002, 82,569 bacterial blood culture isolates were reported to The Surveillance Network (TSN) Database-USA by 268 laboratories. Susceptibility to relevant antibiotic compounds was analyzed using National Committee for Clinical Laboratory Standards guidelines.

RESULTS

Coagulase-negative staphylococci (42.0%), Staphylococcus aureus (16.5%), Enterococcus faecalis (8.3%), Escherichia coli (7.2%), Klebsiella pneumoniae (3.6%), and Enterococcus faecium (3.5%) were the most frequently isolated bacteria from blood cultures, collectively accounting for >80% of isolates. In vitro susceptibility to expanded-spectrum beta-lactams such as ceftriaxone were high for oxacillin-susceptible coagulase-negative staphylococci (98.7%), oxacillin-susceptible S. aureus (99.8%), E. coli (97.3%), K. pneumoniae (93.3%), and Streptococcus pneumoniae (97.2%). Susceptibilities to fluoroquinolones were variable for K. pneumoniae (90.3-91.4%), E. coli (86.0-86.7%), oxacillin-susceptible S. aureus (84.0-89.4%), oxacillin-susceptible coagulase-negative staphylococci (72.7-82.7%), E. faecalis (52.1%), and E. faecium (11.3%). Combinations of antimicrobials are often prescribed as empiric therapy for bacteremia. Susceptibilities of all blood culture isolates to one or both agents in combinations of ceftriaxone, ceftazdime, cefepime, piperacillin-tazobactam or ciprofloxacin plus gentamicin were consistent (range, 74.8-76.3%) but lower than similar beta-lactam or ciprofloxacin combinations with vancomycin (range, 93.5-96.6%).

CONCLUSION

Ongoing surveillance for antimicrobial susceptibility remains essential, and will enhance efforts to identify resistance and attempt to limit its spread.

Bactericidal activity of antimicrobial coated polyurethane sleeves for external fixation pins

This study was conducted to assess the potential of gentamicin coated polyurethane sleeves to inhibit bacterial colonization on external fixation pins and wires. These antimicrobial sleeves have been designed to be fitted over the pins and wires, at the time of surgery, as a prophylactic approach to combat the major complication of external fixation treatment, pin tract infection. Elution testing was conducted to estimate the amount of gentamicin released into the pin tract. These gentamicin concentrations were compared to the gentamicin minimal inhibitory concentration (MIC) level for common pin tract pathogens. Elution testing revealed that the gentamicin coated polyurethane sleeves released significant quantities of the antibiotic for up to 26 weeks. The initial bolus release was characterized by predicted pin tract gentamicin concentrations of >80 microg/ml at the 2 h and 1 day elution time points. These amounts of gentamicin, delivered directly to the pin tract, are far beyond those that could be achieved via oral or intravenous administration. Furthermore, the expected concentration of gentamicin in the pin tract remained above the National Committee for Clinical Laboratory Standards (NCCLS) MIC breakpoint of 4 microg/ml, [Performance standards for antimicrobial susceptibility testing: twelfth informational supplement M100-S12, NCCLS, Wayne, PA, 2002], for at least 20 weeks. Data from the SENTRY antimicrobial surveillance program (1997-2002) established a high level of bactericidal activity for gentamicin, with 83.1% of the common pin tract pathogen isolates found to be susceptible to the antibiotic. The initial burst and subsequent long-term sustained local delivery of effective amounts of gentamicin from the antimicrobial sleeves would be expected to inhibit bacterial colonization on external fixation pins and wires. This inhibition of bacterial colonization should substantially reduce the incidence of pin tract infection, and improve the overall outcome and cost effectiveness of external fixation fracture management.

Report from the European Conference on the Role of Research in Combating Antibiotic Resistance, 2003

Europe has been at the forefront of efforts to control antibiotic resistance, and this globally important health care problem has prompted numerous recommendations for action at both the national and international levels. Starting in 2002, research on antimicrobial resistance has been considered to be one of the specific objectives of the Sixth Framework Programme (FP6) within the European Union. This report summarises the plenary presentations, as well as the findings of six Working Groups covering specific areas of antibiotic resistance, given at a conference in November 2003 entitled 'The Role of Research in Combating Antibiotic Resistance', co-organised by the European Union and the European Society for Clinical Microbiology and Infectious Diseases, and held in Rome under the patronage of the Italian government.

New real-time PCR assay for rapid detection of methicillin-resistant Staphylococcus aureus directly from specimens containing a mixture of staphylococci

Molecular methods for the rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) are generally based on the detection of an S. aureus-specific gene target and the mecA gene. However, such methods cannot be applied for the direct detection of MRSA from nonsterile specimens such as nasal samples without the previous isolation, capture, or enrichment of MRSA because these samples often contain both coagulase-negative staphylococci (CoNS) and S. aureus, either of which can carry mecA. In this study, we describe a real-time multiplex PCR assay which allows the detection of MRSA directly from clinical specimens containing a mixture of staphylococci in <1 h. Five primers specific to the different staphylococcal cassette chromosome mec (SCCmec) right extremity sequences, including three new sequences, were used in combination with a primer and three molecular beacon probes specific to the S. aureus chromosomal orfX gene sequences located to the right of the SCCmec integration site. Of the 1,657 MRSA isolates tested, 1,636 (98.7%) were detected with the PCR assay, whereas 26 of 569 (4.6%) methicillin-susceptible S. aureus (MSSA) strains were misidentified as MRSA. None of the 62 nonstaphylococcal bacterial species or the 212 methicillin-resistant or 74 methicillin-susceptible CoNS strains (MRCoNS and MSCoNS, respectively) were detected by the assay. The amplification of MRSA was not inhibited in the presence of high copy numbers of MSSA, MRCoNS, or MSCoNS. The analytical sensitivity of the PCR assay, as evaluated with MRSA-negative nasal specimens containing a mixture of MSSA, MRCoNS, and MSCoNS spiked with MRSA, was approximately 25 CFU per nasal sample. This real-time PCR assay represents a rapid and powerful method which can be used for the detection of MRSA directly from specimens containing a mixture of staphylococci.

Clinical, Epidemiologic, and Molecular Evaluation of a Clonal Outbreak of Methicillin‐ResistantStaphylococcus aureusInfection

San Francisco General Hospital (San Francisco, CA) experienced an overall increase in the recovery of methicillin-resistant Staphylococcus aureus (MRSA) isolates that were shown by pulsed-field gel electrophoresis to have a genotype (genotype A1) that was new to this institution. We performed a case-control study to identify risk factors for acquiring genotype A1 MRSA infection from 1 October 2001 to 19 July 2002. Patients with genotype A1 MRSA infection were compared with 2 control groups: MRSA-infected control patients (i.e., patients with infection due to non-genotype A1 MRSA) and non-MRSA infected control patients (i.e., hospitalized patients without MRSA infection). There were 41 case patients infected with genotype A1 MRSA, 99 control patients infected with MRSA, and 41 control patients without MRSA infection. Pneumonia, surgical wound infections, and line infections occurred more frequently among case patients. Intensive care unit exposure and invasive procedures conferred the greatest risk for genotype A1 MRSA infection in multivariate models. Case patients were not associated with increased mortality, after adjusting for age, comorbidities, and intensive care unit exposure. Genotype A1 MRSA caused a large nosocomial outbreak of infection that was associated with distinct risk factors and clinical manifestations.

An economic evaluation of a European cohort from a multinational trial of linezolid versus teicoplanin in serious Gram-positive bacterial infections: the importance of treatment setting in evaluating treatment effects

In a recent multinational trial, hospital resource use and total cost of treatment were compared between linezolid and teicoplanin for severe Gram-positive bacterial infections among 227 European hospitalised patients. The results show that the linezolid group had a 3.2-day (6.3 for linezolid versus 9.5 for teicoplanin groups) shorter mean intravenous antibiotic treatment duration. Certain baseline variables, particularly the inpatient location at enrolment and the presence of outpatient/home parenteral antibiotic therapy (OHPAT), had substantial effects on length of stay (LOS) and cost of treatment. After adjusting for the between-treatment difference in these two variables and other baseline variables, the results showed non-significant shorter LOS and lower mean total cost of treatment for the linezolid group among patients with no access to OHPAT.

The status of antimicrobial resistance in Taiwan among Gram-positive pathogens: the Taiwan Surveillance of Antimicrobial Resistance (TSAR) programme, 2000

In the Taiwan Surveillance of Antimicrobial Resistance programme, isolates were collected from 21 hospitals over a 3-month period in 2000 (TSAR II) and rates of resistance in Gram-positive pathogens were determined. Resistance rates were high including oxacillin resistance in Staphylococcus aureus (60%) and coagulase-negative staphylococci (80%), high-level gentamicin resistance (HLGR) in Enterococcus faecalis (60%) and penicillin non-susceptibility in Streptococcus pneumoniae (69%). Oxacillin resistance had increased from 1998 (TSAR I) and may be spreading into outpatient settings. In contrast, less than 2% enterococci were vancomycin-resistant. No linezolid resistance was found in either staphylococci or enterococci.

Identification of methicillin-resistant isolates of Staphylococcus aureus and coagulase-negative staphylococci responsible for bloodstream infections with the Phoenix™ system

We evaluated the reliability of the new Phoenix system (Becton Dickinson Microbiology Systems, Sparks, Md.) in species-level identification and detection of oxacillin (methicillin) resistance among 493 staphylococcal isolates (Staphylococcus aureus, n = 223; coagulase-negative staphylococci, CoNS, n = 270) recovered from patients with bacteremia. Identification results were concordant with those of the ID 32 STAPH system (bioMérieux, Marcy l'Etoile, France) for 100% of S. aureus (223/223) and 97.4% (263/270) of CoNS isolates. For S. aureus isolates, Phoenix oxacillin-susceptibility results fully concurred with those of mecA polymerase chain reaction (PCR) (reference method): 96 mecA-positive isolates identified as resistant, 127 mecA-negative strains as susceptible. Two of the 210 mecA-positive CoNS isolates were misclassified as susceptible by the Phoenix (sensitivity 99%, positive predictive value 97.6%). Five of 60 mecA-negative CoNS isolates were classified as resistant by the Phoenix (specificity 91.7%; negative predictive value 96.5%). The Phoenix system can provide accurate and reliable identification of methicillin-resistant staphylococci responsible for bloodstream infections.

Current and new antimicrobial agents

BACKGROUND

Infections may complicate cardiovascular surgery or may require surgery as an adjunct to successful treatment. Staphylococci, which are among the major pathogenic bacteria causing such infections, can be resistant to many of the older antibiotics.

METHODS

The properties of several newer antimicrobial agents, recently approved or still investigational, were reviewed, with an emphasis on in vitro activities against staphylococci.

RESULTS

The 2 approved agents, linezolid and quinupristin-dalfopristin, and several investigational agents being developed demonstrate in vitro antimicrobial activity against staphylococci. Three of these agents, daptomycin, which was approved by the US Food and Drug Administration in September 2003, and oritavancin and dalbavancin, which are in advanced stages of clinical development, are discussed.

CONCLUSIONS

Although clinical studies are required, the in vitro anti-staphylococcal activities of several agents suggest that these antimicrobial agents might be useful options for some infections in patients who are intolerant of older antibiotics or who are infected with organisms that are resistant to older agents.

In vitro combined bactericidal activity of cefpirome and glycopeptides against glycopeptides and oxacillin-resistant staphylococci

Infections caused by coagulase-negative staphylococci are becoming increasingly important, particularly those of nosocomial origin, as the organisms are frequently multi-resistant. New antimicrobial strategies are needed. The bactericidal activity of a combination of cefpirome with either vancomycin or teicoplanin against 12 strains of methicillin-resistant staphylococci with a decreased susceptibility to teicoplanin was determined in vitro by a time killing method. Strains Mu3 and Mu50 of Staphylococcus aureus were also studied. Cefpirome (0.125-0.5 x MIC) combined with vancomycin (0.25-1 x MIC) or teicoplanin (0.125-1 x MIC) acted synergically against 12 isolates over 18 h in most cases. A synergistic killing effect was also observed with the Mu3 and Mu50 strains of glycopeptide-intermediate S. aureus but over a longer period.

Bridges from hospitals to the laboratory: genetic portraits of methicillin-resistantStaphylococcus aureusclones

Methicillin-resistant Staphylococcus aureus (MRSA) emerged in the early 1960's after the acquisition of the methicillin resistance gene mecA, which is carried by the staphylococcal cassette chromosome mec (SCCmec). MRSA seemed to have arisen by multiple introductions of SCCmec into successful methicillin-susceptible S. aureus (MSSA) lineages. MRSA is one of the most common agents of nosocomial infections worldwide increasing the cost and mortality compared to MSSA infections. Little by little, MRSA has acquired resistance to all antibiotics available in clinical practice, which complicates treatment. This situation was further aggravated by the recent reports of vanA-mediated vancomycin-resistant S. aureus. As a reaction to the emergence and spread of multidrug-resistant MRSA worldwide, international surveillance systems such as the CEM/NET initiative have been created. The characterization of over 3000 MRSA isolates from different regions of the world evidenced the existence of only a few epidemic clones spread worldwide, namely the Iberian, Brazilian, Hungarian, New York/Japan, Pediatric and EMRSA-16 clones. It was found that in surveillance or evolutionary studies strains should be characterized by a combination of different typing methods, namely pulsed-field gel electrophoresis, multi-locus sequence typing and SCCmec typing. In recent years, community-acquired MRSA (CA-MRSA) has become a growing public health concern. However, although many authors reported the emergence of CA-MRSA isolates, a standard definition has not been created and the prevalence of MRSA among persons without risk factors seems to remain very low. CA-MRSA has distinct properties compared to epidemic nosocomial clones and its origin is still unclear. Certain authors suggest there is MRSA transmission from the hospital setting to the community, namely transfer of nosocomial MRSA minor clones or sporadic isolates showing a high degree of similarity with CA-MRSA; others believe CA-MRSA strains represent new acquisitions of SCCmec DNA in susceptible backgrounds. Many questions concerning this extraordinarily versatile and threatening pathogen remain unanswered, needing future investigation

In vitro activities of the novel cephalosporin LB 11058 against multidrug-resistant Staphylococci and Streptococci

LB 11058 is a novel parenteral cephalosporin with a C-3 pyrimidinyl-substituted vinyl sulfide group and a C-7 2-amino-5-chloro-1,3-thiazole group. This study evaluated the in vitro activity and spectrum of LB 11058 against 1,245 recent clinical isolates, including a subset of gram-positive strains with specific resistant phenotypes. LB 11058 was very active against Streptococcus pneumoniae. The novel cephalosporin was 8- to 16-fold more potent than ceftriaxone, cefepime, or amoxicillin-clavulanate against both penicillin-intermediate and -resistant S. pneumoniae. LB 11058 was also very active against both beta-hemolytic streptococci (MIC at which 90% of isolates were inhibited [MIC(90)], </=0.008 micro g/ml) and viridans group streptococci (MIC(90), 0.03 to 0.5 micro g/ml), including penicillin-resistant strains. Among oxacillin-susceptible Staphylococcus aureus, LB 11058 MIC results varied from 0.06 to 0.25 micro g/ml (MIC(50), 0.12 micro g/ml), while among oxacillin-resistant strains LB 11058 MICs varied from 0.25 to 1 micro g/ml (MIC(50), 1 micro g/ml). Coagulase-negative staphylococci showed an LB 11058 susceptibility pattern similar to that of S. aureus, with all isolates being inhibited at </=1 micro g/ml. LB 11058 also showed reasonable in vitro activity against Enterococcus faecalis, including vancomycin-resistant strains (MIC(50), 1 micro g/ml), and Bacillus spp. (MIC(50), 0.25 micro g/ml); however, it was less active against Enterococcus faecium (MIC(50), >64 micro g/ml) and Corynebacterium spp. (MIC(50), 32 micro g/ml). Against gram-negative pathogens, LB 11058 showed activity against Haemophilus influenzae (MIC(90), 0.25 to 0.5 micro g/ml) and Moraxella catarrhalis (MIC(90), 0.25 micro g/ml), with MICs not influenced by beta-lactamase production. In conclusion, LB 11058 demonstrated a broad antibacterial spectrum and was highly active against gram-positive bacteria, particularly against multidrug-resistant staphylococci and streptococci.

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.

Development of StaphVAX™, a polysaccharide conjugate vaccine against S. aureus infection: from the lab bench to phase III clinical trials

Staphylococcus aureus is the most common nosocomial pathogen and is responsible for approximately one-third of hospital-acquired bacteremias. The emergence of strains with multidrug resistance, including resistance to vancomycin, the antibiotic of last resort, presents the medical community with a major public health problem. Alternative therapies, including immunotherapy, have been in development for several decades. The discovery of S. aureus capsular polysaccharides from clinical isolates, and their importance to pathogenicity via antiphagocytic activity, opened a new window of opportunity for development of vaccines and immunotherapy against this pathogen. A conjugate vaccine, StaphVAX that includes the two most prevalent capsular polysaccharides, types 5 and 8, coupled to a carrier protein efficient in promoting a Th2 response, was developed. In a recent phase III clinical study in hemodialysis patients, StaphVAX was shown to prevent S. aureus bacteremia for up to 10 months following a single immunization. The history, epidemiology, serology, and development of StaphVAX, including preclinical and clinical studies demonstrating efficacy are described in this review.

Methicillin resistant Staphylococcus aureus in the critically ill

Methicillin resistant Staphylococcus aureus (MRSA) is endemic within many hospitals worldwide. Critically ill patients on intensive care units have increased risk factors making them especially prone to nosocomially acquired infections. This review addresses the current situation regarding the evolution of MRSA and the techniques for identifying and epidemiologically typing it. It discusses specific risk factors, the morbidity and mortality associated with critically ill patients, and possibilities for future antibiotic treatments.

Antimicrobial resistance among gram-positive organisms in the intensive care unit

PURPOSE OF REVIEW

The epidemiology of gram-positive pathogens in the intensive care unit are reviewed, recent trends in antimicrobial resistance among these organisms are discussed, and the significance of these data with respect to treatment are considered.

RECENT FINDINGS

Results of surveillance studies published in 2001 and 2002 have demonstrated that gram-positive organisms such as Staphylococcus aureus, coagulase-negative staphylococci, and enterococci are among the most common bacteria infecting patients in intensive care units. Furthermore, these organisms are becoming increasingly resistant to available antimicrobial agents, and 2002 has ushered in worrisome developments such as the appearance of vancomycin-resistant S. aureus. Community-acquired methicillin-resistant S. aureus and the rise in incidence of vancomycin-resistant enterococci are other problems of great concern. Novel antibiotics such as quinupristin/dalfopristin and linezolid have activity against these agents, but resistance may develop to these agents as well. Studies have shown that infections caused by antibiotic-resistant organisms may be associated with increased morbidity, mortality, and costs. Exposure to antibiotics is a major risk factor for producing antibiotic resistance in patients, and methods to limit the spread of these organisms include restriction of antibiotic use, infection control, surveillance programs, and isolation procedures.

SUMMARY

An awareness of the prevalence and patterns of resistance among gram-positive nosocomial pathogens is vital for the appropriate treatment of hospitalized patients. In addition, efforts must be made to minimize the selection and spread of these organisms.

Local variants of Staphylococcal cassette chromosome mec in sporadic methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative Staphylococci: evidence of horizontal gene transfer?

The mecA gene in Staphylococcus aureus is located on the genetic element staphylococcal cassette chromosome (SCC). Different SCCmecs have been classified according to their putative recombinase genes (ccrA and ccrB) and overall genetic composition. Clinical isolates of coagulase-negative staphylococci (CoNS; n = 39) and S. aureus (n = 20) from Norway, India, Italy, Finland, the United States, and the United Kingdom were analyzed by pulsed-field gel electrophoresis, which showed that most isolates were genetically unrelated. Cluster analyses of 16S rRNA gene and pta sequences confirmed the traditional biochemical species identification. The mecI, mecR1, mecA, and ccrAB genes were detected by PCRs, identifying 19 out of 20 S. aureus and 17 out of 39 CoNS isolates as carriers of one of the three published ccrAB pairs. New variants of SCCmec were identified, as well as CoNS isolates containing ccrAB genes without the mec locus. ccrAB and mec PCRs were verified by hybridization. Sequence alignments of ccrAB genes showed a high level of diversity between the ccrAB alleles from different isolates, i.e., 94 to 100% and 95 to 100% homology for ccrAB1 and ccrAB2, respectively. All of the ccrAB3 genes identified were identical. Genetically unique and sporadic methicillin-resistant S. aureus (MRSA) contained local variants of ccrAB gene pairs identical to those found in MR-CoNS but different from those in MRSA from other regions. Allelic variants of ccrAB in isolates from the same geographic region showed sequence conservation independent of species. The species-independent sequence conservation found suggests that there is a closer genetic relationship between ccrAB2 in Norwegian staphylococci than between ccrAB2 sequences in international MRSA and Norwegian MRSA. This might indicate that different staphylococcal species acquire these genes locally by horizontal gene transfer.

Antimicrobial Resistance Trends and Outbreak Frequency in United States Hospitals

We assessed resistance rates and trends for important antimicrobial-resistant pathogens (oxacillin-resistant Staphylococcus aureus [ORSA], vancomycin-resistant Enterococcus species [VRE], ceftazidime-resistant Klebsiella species [K-ESBL], and ciprofloxacin-resistant Escherichia coli [QREC]), the frequency of outbreaks of infection with these resistant pathogens, and the measures taken to control resistance in a stratified national sample of 670 hospitals. Four hundred ninety-four (74%) of 670 surveys were returned. Resistance rates were highest for ORSA (36%), followed by VRE (10%), QREC (6%), and K-ESBL (5%). Two-thirds of hospitals reported increasing ORSA rates, whereas only 4% reported decreasing rates, and 24% reported ORSA outbreaks within the previous year. Most hospitals (87%) reported having implemented measures to rapidly detect resistance, but only approximately 50% reported having provided appropriate resources for antimicrobial resistance prevention (53%) or having implemented antimicrobial use guidelines (60%). The most common resistant pathogen in US hospitals is ORSA, which accounts for many recognized outbreaks and is increasing in frequency in most facilities. Current practices to prevent and control antimicrobial resistance are inadequate.

Daptomycin

Daptomycin, the first in a class of agents known as lipopeptides, is a novel antimicrobial agent used for the treatment of gram-positive infections. The compound has a distinctive mechanism of action that exerts its bactericidal activity by disrupting plasma membrane function without penetrating into the cytoplasm. The agent has received much interest because of its activity against multidrug-resistant, gram-positive bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and glycopeptide-intermediate and -resistant S. aureus. Daptomycin demonstrates concentration-dependent killing and is eliminated primarily by glomerular filtration. It was approved in September 2003 for the treatment of complicated skin and soft tissue infections. It has a safety profile similar to other agents commonly administered to treat gram-positive infections. Daptomycin is a welcome addition to the antimicrobial armamentarium for the treatment of bacterial infections. Further clinical experience with this compound will help define its role in the treatment of resistant gram-positive organisms.

Multiresistant coagulase-negative staphylococci disseminate frequently between intubated patients in a multidisciplinary intensive care unit

Introduction

The intensive care unit is burdened with a high frequency of nosocomial infections often caused by multiresistant nosocomial pathogens. Coagulase-negative staphylococci (CoNS) are reported to be the third causative agent of nosocomial infections and the most frequent cause of nosocomial bloodstream infections. CoNS are a part of the normal microflora of skin but can also colonize the nasal mucosa, the lower airways and invasive devices. The main aim of the present study was to investigate colonization and the rate of cross-transmissions of CoNS between intubated patients in a multidisciplinary intensive care unit.

Materials and methods

Twenty consecutive patients, ventilated for at least 3 days, were included. Samples were collected from the upper and lower airways. All samples were cultured quantitatively and CoNS were identified by morphology and biochemical tests. A total of 199 CoNS isolates from 17 patients were genetically fingerprinted by pulsed-field gel electrophoresis in order to identify clones and to monitor dissemination within and between patients.

Results

An unexpected high number of transmission events were detected. Five genotypes were each isolated from two or more patients, and 14/20 patients were involved in at least one and up to eight probable transmission events.

Conclusions

A frequent transmission of CoNS was found between patients in the intensive care unit. Although transmission of bacteria does not necessarily lead to infection, it is nevertheless an indication that infection control measures can be improved.

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 decolonization.

Discussion

Screening identifies over 90% of patients colonised 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.

Epidemiology of methicillin-resistant staphylococci in Europe

Methicillin-resistant staphylococci are mostly resistant not only to all beta-lactams but also to a wide range of other antibiotics, and have emerged as major nosocomial pathogens during the past two decades. Considerable variations in the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) exist between institutions and between geographic areas. In Europe, in general, a north-south gradient is observed, MRSA strains being rare in Scandinavian hospitals (<2%) and far more prevalent in Mediterranean hospitals (>40%). Whether low or high, the rates of MRSA prevalence in European countries have remained approximately the same during the last decade. Recent findings suggest that MRSA might also be emerging as a community-acquired pathogen. The first stage in the emergence of MRSA is its acquisition by methicillin-susceptible S. aureus, and the integration into its chromosome, of the mecA gene, which, together with the other mec genes, is carried on a mobile genetic element, the staphylococcal chromosomal cassette mec (SCCmec). The origin of SCCmec elements as well as the mechanisms of their acquisition remain unknown. Molecular epidemiology studies using different techniques clearly indicate that the massive geographic spread of MRSA results from the dissemination of relatively few highly epidemic clones. Five major lineages (the so-called Iberian, Brazilian, Hungarian, New York/Japan and pediatric pandemic MRSA clones) have been defined. In Europe, the Iberian clone has been reported in several countries; the Brazilian, pediatric and Hungarian clones have also been detected, but less frequently. A unique Italian clone is predominant in Italy. As with S. aureus, coagulase-negative staphylococci (CNS) represent a serious concern in hospital-acquired infections. Despite marked geographic variations, in some areas of Europe high proportions (60-70%) of CNS are methicillin resistant. The formation of biofilm is a key virulence factor of S. epidermidis, the prominent CNS pathogen, which is the most common cause of bacteremia in device-related infections. Another emerging nosocomial pathogen, S. hemolyticus, is characterized by a tendency to develop multiple antibiotic resistances, with a unique predisposition to glycopeptide resistance.

Co-trimoxazole-sensitive, methicillin-resistant Staphylococcus aureus, Israel, 1988-1997

Among bloodstream methicillin-resistant Staphylococcus aureus (MRSA) isolates from adult patients in a single hospital, susceptibility to co-trimoxazole increased progressively from 31% in 1988 to 92% in 1997 (p<0.0001). If also observed in other institutions, these findings should encourage the performance of a clinical trial of sufficient size to compare co-trimoxazole to vancomycin in treating MRSA infections.

AAPS/RAPS/CAPRA collaborative program: exploring the challenges of drug regulation in a global environment: clinical concerns

Globalization of the pharmaceutical industry has led to a need to harmonize the regulatory requirements governing the marketing of medicinal products. To minimize the barriers impeding global drug product registration, the International Conference on the Harmonization of Technical Requirements of Pharmaceuticals for Human Use (ICH) was established in 1990. The ICH has developed a series of guidelines that reflect agreements reached by participating nations on aspects of the chemistry and clinical technical sections that will fulfill the regulatory requirements of these various jurisdications. Nevertheless, there continue to be points of divergent perspectives and barriers that can impede the use of foreign clinical data. Given the importance of these issues, the Regulatory Science (RS) section of the American Association of Pharmaceutical Scientists (AAPS), in conjunction with the Regulatory Affairs Professional Society (RAPS) and the Canadian Association of Professional Regulatory Affairs (CAPRA) cosponsored a public forum on this topic. This manuscript provides a summary of the speaker presentations and audience discussions regarding the design of clinical trials and the extrapolation of results from these trials to support international drug registration.

Use of the VITEK 2 system for rapid identification of clinical isolates of Staphylococci from bloodstream infections

Staphylococci are an increasing cause of bloodstream infections. Rapid reliable identification of these organisms is essential for accurate diagnosis and prompt effective treatment. We evaluated the ability of the VITEK 2 system (bioMérieux, Inc, Hazelwood, Mo.) to identify these organisms rapidly and accurately. A total of 405 clinically relevant nonduplicate staphylococcal isolates (Staphylococcus aureus, n = 130; coagulase-negative staphylococci, n = 275) collected from blood cultures were tested. VITEK 2 results were considered correct when they were identical to those furnished by the comparison method based on the ID 32 STAPH system (bioMérieux, Marcy l'Etoile, France) plus supplementary manual testing. When discrepancies occurred, isolate identity was verified by molecular typing. The VITEK 2 correctly identified 387 (95.6%) isolates at the species level: 379 (including all but one [99.2%] of 130 S. aureus isolates and 249 of 275 [90.5%] coagulase-negative isolates) were identified by the automated reading; for the other eight, supplemental tests suggested by the manufacturer had to be used. Only one strain (0.2%) was misidentified (Staphylococcus hominis as Staphylococcus epidermidis), and four (1%), all S. epidermidis, were not identified. For the remaining 13 strains (including 10 S. hominis), the VITEK 2 system was unable to discriminate among two species, and no supplemental tests were suggested for conclusive identification. Over 90% of results were obtained within 4 h. These results suggest that the VITEK 2 system can provide rapid, accurate, and reliable species-level identification of staphylococci responsible for bloodstream infections, although there is room for improvement in the identification of certain coagulase-negative species, especially S. hominis.

Detection of methicillin-resistant Staphylococcus aureus (MRSA) in blood with the EVIGENE MRSA detection kit

A total of 200 blood cultures containing putative staphylococci were analyzed by a commercial gene probe hybridization assay (EVIGENE; Statens Serum Institut, Copenhagen, Denmark), and 18 were identified as methicillin-resistant Staphylococcus aureus (MRSA) positive. Of these, 17 were positive by PCR and 16 were positive by culture. Detailed analysis of the discrepant results showed that the EVIGENE kit allowed specific identification of MRSA in blood cultures without any of the drawbacks associated with PCR.

Clinical impact of a PCR assay for identification of Staphylococcus aureus and determination of methicillin resistance directly from blood cultures

We evaluated the clinical usefulness of a PCR assay that discriminates Staphylococcus aureus from coagulase-negative staphylococci and detects methicillin resistance on blood cultures by measuring the adaptation of antimicrobial therapy based on the PCR results. Only 7 of 28 patients (25%) benefited from a modification of antibiotic therapy based on the PCR results, since empirical therapy was appropriate in a majority of cases.

Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: worldwide emergence

Infections caused by community-acquired (CA)-methicillin--resistant Staphylococcus aureus (MRSA) have been reported worldwide. We assessed whether any common genetic markers existed among 117 CA-MRSA isolates from the United States, France, Switzerland, Australia, New Zealand, and Western Samoa by performing polymerase chain reaction for 24 virulence factors and the methicillin-resistance determinant. The genetic background of the strain was analyzed by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The CA-MRSA strains shared a type IV SCCmec cassette and the Panton-Valentine leukocidin locus, whereas the distribution of the other toxin genes was quite specific to the strains from each continent. PFGE and MLST analysis indicated distinct genetic backgrounds associated with each geographic origin, although predominantly restricted to the agr3 background. Within each continent, the genetic background of CA-MRSA strains did not correspond to that of the hospital-acquired MRSA.

In vitro and in vivo activities of novel 2-(thiazol-2-ylthio)-1beta-methylcarbapenems with potent activities against multiresistant gram-positive bacteria

SM-197436, SM-232721, and SM-232724 are new 1beta-methylcarbapenems with a unique 4-substituted thiazol-2-ylthio moiety at the C-2 side chain. In agar dilution susceptibility testing these novel carbapenems were active against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE) with a MIC(90) of </=4 micro g/ml. Furthermore, SM-232724 showed strong bactericidal activity against MRSA, in contrast to linezolid, which was bacteriostatic up to four times the MIC. SM-232724 showed good therapeutic efficacy comparable to those of vancomycin and linezolid against systemic infections of MRSA in cyclophosphamide-treated mice. The MICs of SM-197436, SM-232721, and SM-232724 for streptococci, including penicillin-intermediate and penicillin-resistant Streptococcus pneumoniae strains, ranged from </=0.063 to 0.5 micro g/ml. These drugs were the most active beta-lactams tested against Enterococcus faecium, and the MIC(90) s for ampicillin-resistant E. faecium ranged between 8 and 16 micro g/ml, which were slightly higher than the value for linezolid. However, time-kill assays revealed the superior bactericidal activity of SM-232724 compared to those of quinupristin-dalfopristin and linezolid against an E. faecium strain with a 4-log reduction in CFU at four times the MIC after 24 h of exposure to antibiotics. In addition, SM-232724 significantly reduced the numbers of bacteria in a murine abscess model with the E. faecium strain: its efficacy was superior to that of linezolid, although the MICs (2 micro g/ml) of these two agents are the same. Among gram-negative bacteria, these three carbapenems were highly active against Haemophilus influenzae (including ampicillin-resistant strains), Moraxella catarrhalis, and Bacteroides fragilis, and showed antibacterial activity equivalent to that of imipenem for Escherichia coli, Klebsiella pneumoniae, and Proteus spp. Thus, these new carbapenems are promising candidates for agents to treat nosocomial bacterial infections by gram-positive and gram-negative bacteria, especially multiresistant gram-positive cocci, including MRSA and vancomycin-resistant enterococci.

Coagulase-negative staphylococci: comparison of phenotypic and genotypic oxacillin susceptibility tests and evaluation of the agar screening test by using different concentrations of oxacillin

This study evaluated the oxacillin susceptibilities of 152 coagulase-negative staphylococcal (CoNS) strains of 12 species by disk diffusion; agar dilution; E-test; the slide latex agglutination test (Slidex MRSA Detection test; bioMérieux S/A, Paris, France); the agar screening test with 1, 2, 4, or 6 microg of oxacillin per ml and incubation for 24 or 48 h; and detection of the mecA gene by PCR. The results revealed that the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h was superior to any single phenotype-based susceptibility assay, presenting a sensitivity and a specificity of 100% each. For the different methods evaluated, the sensitivities and specificities were as follows: for disk diffusion, 94.2 and 91.8%, respectively; for the agar dilution test 100 and 73.5%, respectively; for E-test, 100 and 71.4%, respectively; and for the slide latex agglutination test, 97.1 and 98%, respectively. A good correlation was observed between oxacillin susceptibility testing results and PCR results for Staphylococcus epidermidis, S. haemolyticus, S. hominis subsp. hominis, and all mecA-positive strains. However, at least 60% of the mecA-negative isolates of the species S. saprophyticus, S. cohnii subsp. urealyticum, S. lugdunensis, and S. sciuri were erroneously classified as oxacillin resistant by the agar dilution test. Conversely, the slide latex agglutination test presented a high sensitivity (97.1%) and a high specificity (98%) for all CoNS species. Our results demonstrated the accuracy of the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h and the slide latex agglutination test for the appropriate detection of the oxacillin susceptibilities of CoNS isolates. Both assays are technically simple and can be easier to perform in routine laboratories than PCR.

Evaluation of an isothermal signal amplification method for rapid detection of methicillin-resistant Staphylococcus aureus from patient-screening swabs

A new molecular assay (CytAMP) utilizing isothermal signal-mediated amplification of RNA was evaluated for rapid detection of methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA). The assay targeted the coa (coagulase) and mecA genes, thereby simultaneously identifying S. aureus and methicillin (oxacillin) resistance. Results were obtained in approximately 3.5 h as a color signal in 96-well microtiter plates. The detection limit was between 2 x 10(5) and 10(6) CFU/assay, equivalent to 4 x 10(6) to 2 x 10(7) CFU/ml in an overnight broth. This level of growth was obtained with an initial inoculum of 10 to 50 CFU. The CytAMP assay and a mecA-femB PCR assay both detected 113 MRSA strains among 396 clinical isolates of bacteria (CytAMP sensitivity and specificity were both 100% relative to those of PCR). Conventional culture detected 109 MRSA strains, but with 19 false-positive and 23 false-negative results relative to both molecular methods. Discrepancies were also observed for 100 enrichment broths containing MRSA screening swabs, with 11 broths culture negative but PCR positive. CytAMP and PCR were more in agreement, but six broths were CytAMP negative and PCR positive. Five of these contained 10(2) to 10(5) CFU/assay (below the CytAMP detection limit of 2 x 10(5) CFU/assay), and the sixth contained 10(6) CFU/assay. Overall, culture and CytAMP had similar sensitivities and specificities relative to those of PCR, but the CytAMP assay enabled swabs to be analyzed as a batch following overnight incubation in enrichment broth, with results reported before 12 noon the next day.

Real-time PCR assay for detection of fluoroquinolone resistance associated with grlA mutations in Staphylococcus aureus

Resistance to fluoroquinolones among clinical isolates of Staphylococcus aureus has become a clinical problem. Therefore, a rapid method to identify S. aureus and its susceptibility to fluoroquinolones could provide clinicians with a useful tool for the appropriate use of these antimicrobial agents in the health care settings. In this study, we developed a rapid real-time PCR assay for the detection of S. aureus and mutations at codons Ser-80 and Glu-84 of the grlA gene encoding the DNA topoisomerase IV, which are associated with decreased susceptibility to fluoroquinolones. The detection limit of the assay was 10 genome copies per reaction. The PCR assay was negative with DNA from all 26 non-S. aureus bacterial species tested. A total of 85 S. aureus isolates with various levels of fluoroquinolone resistance was tested with the PCR assay. The PCR assay correctly identified 100% of the S. aureus isolates tested compared to conventional culture methods. The correlation between the MICs of ciprofloxacin, levofloxacin, and gatifloxacin and the PCR results was 98.8%. The total time required for the identification of S. aureus and determination of its susceptibility to fluoroquinolones was about 45 min, including DNA extraction. This new rapid PCR assay represents a powerful method for the detection of S. aureus and its susceptibility to fluoroquinolones.

Effect of linezolid versus vancomycin on length of hospital stay in patients with complicated skin and soft tissue infections caused by known or suspected methicillin-resistant staphylococci: results from a randomized clinical trial

BACKGROUND

Complicated skin and soft tissue infections are common surgical indications usually requiring patients to be hospitalized, and are often caused by gram-positive bacteria, including methicillin-resistant staphylococci such as MRSA. Vancomycin has been the standard treatment for methicillin-resistant staphylococcal infections in many countries, but its intravenous-only formulation for systemic infections often confines patients to the hospital for the treatment. Linezolid, a novel oxazolidinone antibiotic available in intravenous and 100% bioavailable oral forms, was shown in a randomized trial to be as efficacious as vancomycin for suspected or proven methicillin-resistant staphylococcal infections. To determine if oral linezolid can reduce length of hospital stay (LOS) when compared to vancomycin, we compared the LOS for the 230 complicated skin and soft tissue infection patients enrolled in this trial.

MATERIALS AND METHODS

Patients received up to four weeks of linezolid (intravenous followed by optional oral) or vancomycin (intravenous only), followed by up to four weeks of observation. Unadjusted LOS was estimated using Kaplan-Meier survival functions, whereas the log-logistic survival analysis model was used to estimate the multivariate-adjusted LOS controlling for patient demographics and selected baseline clinical variables. Analysis was done on the intent-to-treat (n = 230) sample as well as on two subsamples of the clinically evaluable (n = 144) and surgical site infection (n = 114) patients.

RESULTS

The unadjusted Kaplan-Meier median LOS was five days shorter for the linezolid group than the vancomycin group in the intent-to-treat sample (9 vs. 14 days, p = 0.052). It was eight days shorter (8 vs. 16 days, p = 0.0025) in the clinically evaluable sample, but the difference in the surgical site infection sample was not significant (10 vs. 14 days; p = 0.29). The linezolid group's unadjusted mean LOS was 1.7, 5.3 and 0.8 days shorter in the intentto-treat, clinically evaluable, and surgical site infection samples, respectively. After adjusting for age, gender, race, geographic region, bacteremia, type of inpatient location, and number of concurrent medical conditions using the log-logistic model, between-treatment differences in the multivariate-adjusted median LOS decreased to 3, 6, and 3 days, whereas the differences in mean LOS increased to 3.1, 6.5 and 2.5 days for the intent-to-treat, clinically evaluable, and surgical site infection samples (p < 0.01, < 0.01, and < 0.10), respectively. When the between-treatment differences in LOS were expressed as odds ratio of hospital discharges, multivariate-adjustment increased the odds ratios in favor of linezolid for all the three samples.

CONCLUSION

Results from this randomized trial show that linezolid can significantly reduce LOS for patients with complicated skin and soft tissue infections from suspected or confirmed methicillin-resistant staphylococci.

Influence of reduced susceptibility to glycopeptides on activities of vancomycin and teicoplanin against Staphylococcus aureus in experimental endocarditis

The influence of reduced susceptibilities to glycopeptides on the activities of vancomycin and teicoplanin against an isogenic pair of clinical Staphylococcus aureus strains in experimental endocarditis was investigated. While vancomycin was similarly active against both strains, teicoplanin was approximately 100-fold less active against the resistant strain and selected for the emergence of more resistant subpopulations.