Integrons in Escherichia coli from food-producing animals in The Netherlands

The presence and character of class 1 integrons in multidrug-resistant Escherichia coli from slaughter animals and meat was determined by integrase-specific PCR and conserved segment PCR-restriction fragment length polymorphism (RFLP). At least five different class 1 integron types were found and three types were shared between hospitalized patients, humans in the community, meat, and slaughter animals. Common integron types indicate that antibiotic resistance genes are exchanged via the food chain between different reservoirs of both human and animal origin.

Presence of tetracycline resistance determinants and susceptibility to tigecycline and minocycline

No relation between the presence of tetracycline resistance determinants tet(A) to tet(E) and the MICs of tigecycline was observed for Enterobacteriaceae, although tetracycline-susceptible isolates were more susceptible overall to tigecycline, whereas the presence of tet(M) in Staphylococcus aureus was associated with higher MICs of minocycline.

Human-to-dog transmission of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) was cultured from the nose of a healthy dog whose owner was colonized with MRSA while she worked in a Dutch nursing home. Pulsed-field gel electrophoresis and typing of the staphylococcal chromosome cassette mec (SCCmec) region showed that both MRSA strains were identical.

Towards more virulent and antibiotic-resistantSalmonella?

Salmonella are well-known pathogens. Virulence determinants can be present on the chromosome, usually encoded on pathogenicity islands, or on plasmids and bacteriophages. Antibiotic resistance determinants usually are encoded on plasmids, but can also be present on the multidrug resistance region of Salmonella Genomic Island 1 (SGI1). Virulence plasmids show a remarkable diversity in the combination of virulence factors they encode, which appears to adapt them to specific hosts and the ability to cause gastroenteritidis or systemic disease. The appearance of plasmids with two replicons may help to extend the host range of these plasmids and thereby increase the virulence of previously non- or low pathogenic serovars. Antibiotic resistance among Salmonella is also increasing. This increase is not only in the percentage isolates resistant to a particular antibiotic, but also the development of resistance against newer antibiotics. The increased occurrence of integrons is particularly worrying. Integrons can harbour a varying set of antibiotic resistance encoding gene cassettes. Gene cassettes can be exchanged between integrons. Although the gene cassettes currently present in Salmonella integrons encode for older antibiotics (however, some still frequently used) gene cassettes encoding resistance against the newest antibiotics has been documented in Enterobacteriaceae. Furthermore, beta-lactamases with activity against broad-spectrum cephalosporins, which are often used in empiric therapy, have been found associated with integrons. So, empiric treatment of Salmonella infections becomes increasingly more difficult. The most worrisome finding is that virulence and resistance plasmids form cointegrates. These newly formed plasmids can be selected by antibiotic pressure and thereby for virulence factors. Taken together these trends may lead to more virulent and antibiotic-resistant Salmonella.

Beta-lactam susceptibilities and prevalence of ESBL-producing isolates among more than 5000 European Enterobacteriaceae isolates

In vitro susceptibility to 15 beta-lactam antibiotics was evaluated using Enterobacteriaceae isolated during the SENTRY Antimicrobial Surveillance Program. Piperacillin/tazobactam was the most active penicillin against Escherichia coli, Proteus mirabilis, Klebsiella oxytoca and Klebsiella pneumoniae (94.9%, 98.3%, 87.4% and 82.9% of isolates susceptible). Of the cephalosporins, cefepime was most effective against Escherichia coli, Proteus mirabilis and Enterobacter cloacae (99.2%, 96.3% and 95.2% of isolates susceptible, respectively) and cefoxitin against Klebsiella oxytoca and Klebsiella pneumoniae (98.6% and 95.6% of isolates susceptible). Carbapenems had excellent activity (> or =99.5% of all isolates). ESBL-production was confirmed with the ESBL-Etest and disk diffusion test in 1.3% of Escherichia coli isolates, 18.4% of Klebsiella pneumoniae, 12.6% of Klebsiella oxytoca and 5.3% of Proteus mirabilis isolates.

Antibiotic rotation and development of gram-negative antibiotic resistance

To attain a better understanding of antibiotic cycling and its effects on the epidemiology of antibiotic resistance in gram-negative microorganisms, two different antibiotic classes (quinolone and beta-lactam) were cycled during four 4-month periods in a surgical intensive care unit. Respiratory aspirates and rectal swabs were obtained and DNA fingerprinting was performed. Primary endpoint of the study was the acquisition rate with gram-negative bacteria resistant to the antibiotic of choice during each cycle. Secondary endpoints were changes in endemic prevalence of resistant bacteria and the relative importance of cross-transmission. In all, 388 patients were included and 2,520 cultures analyzed. Adherence to antibiotic protocol was 96%. Overall antibiotic use increased with 24%. Acquisition rates with resistant bacteria were highest during levofloxacin exposure (relative risk [RR] 3.2; 95% confidence interval [CI]: 1.4-7.1) and piperacillin/tazobactam exposure (RR 2.4; 95% CI 1.2-4.8). The relative importance of cross-transmission decreased during the study. For individual patients, treatment with levofloxacin was the only independent risk factor for acquisition of levofloxacin-resistant bacteria (hazard ratio 12.6; 95% CI 3.8-41.6). Potential for selection of antibiotic-resistant gram-negative bacteria during periods of homogeneous exposure increased from cefpirome to piperacillin/tazobactam to levofloxacin. Cycling of homogeneous antibiotic exposure is unlikely to control the emergence of gram-negative antimicrobial resistance in intensive care units.

The evolution of Pseudomonas aeruginosa during antibiotic rotation in a medical intensive care unit: the RADAR-trial

Bacterial spread between patients may contribute to the high prevalence of antibiotic-resistant pathogens within ICUs. The aim of this study was to evaluate the fate of Pseudomonas aeruginosa during the different antibiotic regimens. Susceptibility patterns and genotyping were performed to determine whether there was a predominant clone and to track the spread of resistant strains within the unit. Twenty-eight different ribotypes were found among 82 Pseudomonas isolates. Four ribotypes accounted for 42 (51%) isolates and were designated the "major clones" occurring throughout multiple cycles. The ribotypes with multiple occurrences were more resistant to antibiotics than ribotypes that appeared only once. The correlation of antibiotic use with antibiotic resistance and the finding of a large number of ribotypes suggested that de novo development of antibiotic resistance is a likely event in P. aeruginosa. In addition, ribotypes associated with antibiotic resistance appeared to have a survival advantage and can become frequent colonizers in the ICU.

Methicillin-resistant staphylococci isolated from animals

Staphylococci isolated from animals (n=311) were screened for methicillin resistance by oxacillin agar screening. Oxacillin-resistant strains were tested for the presence of the mecA gene by PCR. Isolates were identified by standard techniques and 16S rDNA analysis, and their antimicrobial susceptibilities were tested using an agar diffusion method. MecA-positive strains were further analyzed using pulsed-field gel electrophoresis (PFGE). From 11 multidrug-resistant staphylococci, 6 were mecA-positive: 2 methicillin-resistant Staphylococcus aureus (MRSA) and 4 Staphylococcus haemolyticus. Screening of 300 staphylococci (100 S. aureus, 100 S. intermedius and 100 coagulase-negative staphylococci (CNS)) randomly chosen from the strain collection of the Veterinary Microbiological Diagnostic Center yielded five oxacillin-resistant coagulase-negative staphylococci, four of which were mecA-positive. PFGE showed that all mecA-positive staphylococci isolated from animals had distinct patterns. However, one MRSA isolated from a flank fistula of a dog showed homology to a human epidemic MRSA cluster, suggesting that transfer of MRSA between humans and dogs might occur.

Daptomycin in vitro susceptibility in European Gram-positive clinical isolates

The objective of this study was to determine the activity of daptomycin, a novel lipopeptide, against European Gram-positive isolates (n = 1539). The MIC(90)-values of daptomycin against Staphylococcus aureus isolates was 0.25 mg/L, against Enterococcus faecalis 4 mg/L, against Enterococcus faecium 8 mg/L, 0.25 mg/L against Staphylococcus epidermidis, and 0.25mg/L against Streptococcus pneumoniae. Daptomycin was equally potent against antibiotic-susceptible and resistant strains within a particular species. Based on a breakpoint of 1 mg/L for S. aureus and group A streptococci, all isolates tested were susceptible to daptomycin. Based on a breakpoint of 4 mg/L for vancomcyin-susceptible E. faecalis 99.7% of these isolates were susceptible to daptomycin.

Evaluation of genetic determinants involved in β-lactam- and multiresistance in a surgical ICU

Antibiotic resistance is a major and well-known problem in intensive care units (ICUs) world-wide and previously susceptible isolates become resistant through the acquisition of resistance determinants from other bacteria or the development of mutations, as is the case in beta-lactam resistance. We evaluated the presence of resistance determinants involved in beta-lactam resistance and multi-resistance in order to establish the contribution of horizontal gene transfer to the spread of resistance in a surgical ICU during an antibiotic rotation study. Pseudomonas aeruginosa and Enterobacteriaceae isolates were selected and iso-electric focusing (IEF), DNA-typing methods such as specific beta-lactamase and specific integron PCRs were performed to determine the presence of beta-lactamases. The PCRs specific for IMP-1, OXA-1, and VIM-type beta-lactamases performed on the selected P. aeruginosa and Enterobacteriaceae isolates with MICs for cephalosporins >1 mg/l did not demonstrate any of these beta-lactamases. IEF for 14 pseudomonads, representing 7 genotypes from 9 patients, showed a beta-lactamase with a pI larger than 8.5 in 13 of the isolates. The integrase PCR was positive for only five isolates from three patients and conserved segment PCR showed integrons of variable sizes (700, 900, 1,400 and 1,500 bp). Each patient had its own integron types. It can be concluded that integrons and associated resistance determinants played only a minor role in the surgical ICU and beta-lactam resistance among P. aeruginosa isolates was most likely due to the derepression of its AmpC gene.

Resistance integrons and super-integrons

Integrons are genetic elements composed of a gene encoding an integrase, gene cassettes and an integration site for the gene cassettes (att). The integrase excises and integrates the gene cassettes from and into the integron, but integrons themselves are not mobile. Two groups of integrons are known: resistance integrons and super-integrons. Nearly all known gene cassettes from resistance integrons encode resistance to antibiotics or disinfectants. These integrons are found on transposons, plasmids and the bacterial chromosome. Gene cassettes in super-integrons encode a variety of different functions. Super-integrons are located on the bacterial chromosome. More than 100 gene cassettes may be present, in contrast to resistance integrons where less than ten cassettes are present. Many species harbour super-integrons, which are species-specific, whereas particular resistance integrons can be found in a variety of species. The gene cassettes in resistance integrons probably originated from super-integrons. In the last few years, a variety of new gene cassettes have been described. Many of these encode resistance against newer antibiotics such as cephalosporins and carbapenems. Resistance integrons have been found in isolates from a wide variety of sources, including food.

In vitro activity of daptomycin against gram-positive European clinical isolates with defined resistance determinants

The in vitro activity of daptomycin against 337 gram-positive European clinical isolates with known resistance genes was determined. The MIC ranges for Staphylococcus aureus, enterococci, pneunococci, and streptococci were 0.03 to 1, 0.25 to 8, 0.12 to 1, and 0.06 to 8 micro g/ml, respectively. For only one streptococcus isolate and seven enterococcus isolates was the MIC 8 micro g/ml.

False-positive results and contamination in nucleic acid amplification assays: suggestions for a prevent and destroy strategy

Contamination of samples with DNA is still a major problem in microbiology laboratories, despite the wide acceptance of PCR and other amplification techniques for the detection of frequently low amounts of target DNA. This review focuses on the implications of contamination in the diagnosis and research of infectious diseases, possible sources of contaminants, strategies for prevention and destruction, and quality control. Contamination of samples in diagnostic PCR can have far-reaching consequences for patients, as illustrated by several examples in this review. Furthermore, it appears that the (sometimes very unexpected) sources of contaminants are diverse (including water, reagents, disposables, sample carry over, and amplicon), and contaminants can also be introduced by unrelated activities in neighboring laboratories. Therefore, lack of communication between researchers using the same laboratory space can be considered a risk factor. Only a very limited number of multicenter quality control studies have been published so far, but these showed false-positive rates of 9-57%. The overall conclusion is that although nucleic acid amplification assays are basically useful both in research and in the clinic, their accuracy depends on awareness of risk factors and the proper use of procedures for the prevention of nucleic acid contamination. The discussion of prevention and destruction strategies included in this review may serve as a guide to help improve laboratory practices and reduce the number of false-positive amplification results.

High levels of hydrolytic enzymes secreted by Candida albicans isolates involved in respiratory infections

Differences in production of two putative virulence factors of Candida albicans, phospholipase and proteinase, were determined for a large panel of clinical C. albicans isolates (n = 186) obtained from the European SENTRY programme. Seventy-two per cent of isolates produced detectable amounts of phospholipase and 95 % of isolates produced detectable amounts of proteinase. There was no clear correlation between the results of the phospholipase and proteinase assays and the geographical distribution of the isolates. However, isolates that originated from respiratory infections produced significantly higher amounts of phospholipase than isolates obtained from blood, the urinary tract or wounds/skin/soft tissue and also appeared to produce more proteinase. These virulent isolates involved in respiratory infections may originate from the oral cavity. Whether these results are caused by selection for these highly virulent isolates remains to be resolved.

Site-specific manifestations of invasive group a streptococcal disease: type distribution and corresponding patterns of virulence determinants

As part of a national surveillance program on invasive group A streptococci (GAS), isolates that caused specific manifestations of invasive GAS disease in The Netherlands were collected between 1992 and 1996. These site-specific GAS infections involved meningitis, arthritis, necrotizing fasciitis, and puerperal sepsis. An evaluation was performed to determine whether GAS virulence factors correlate with these different disease manifestations. PCRs were developed to detect 9 genes encoding exotoxins and 12 genes encoding fibronectin binding proteins. The genetic backgrounds of all isolates were determined by M genotyping and pulsed-field gel electrophoresis (PFGE) analysis. The predominant M types included M1, M2, M3, M4, M6, M9, M12, and M28. Most M types were associated with all manifestations of GAS disease. However, M2 was found exclusively in patients with puerperal sepsis, M6 predominated in patients with meningitis, and M12 predominated in patients with GAS arthritis. While characteristic gene profiles were detected in most M types, the resolution of detection of different gene profiles within M genotypes was enhanced by PFGE analysis, which clearly demonstrated the existence of some clonal lineages among invasive GAS isolates in The Netherlands. M1 isolates comprised a single clone carrying highly mitogenic toxin genes (speA, smeZ) and were associated with toxic shock-like syndrome. Toxin profiles were highly conserved among the most virulent strains, such as M1 and M3.

Toxin‐Gene Profile Heterogeneity among Endemic Invasive European Group A Streptococcal Isolates

We determined the toxin-gene profiles of 239 endemic, invasive group A streptococcal (GAS) isolates that circulated, within a 5-year period, in European university hospitals. Profiling was performed by use of multiplex polymerase chain reaction that screened for 9 streptococcal pyrogenic exotoxins (speA, speB, speC, speF, speG, speH, speJ, ssa, and smeZ). Analysis revealed that invasive GAS isolates do not share a common toxin-gene profile. Although all emm types were characterized by several different toxin-gene profiles, a predominance of 1 or 2 toxin-gene profiles could be observed, reflecting that a few invasive clones have spread successfully throughout the world. Remarkably, statistical pair-wise analysis of individual toxin genes revealed that strains that did not share the predominant profile still showed a nonrandom distribution of key toxin genes characteristic of the specific emm type. This could indicate that M proteins function, directly or indirectly, as barriers for horizontal gene exchange.

Epidemic and nonepidemic multidrug-resistant Enterococcus faecium

The epidemiology of vancomycin-resistant Entero- coccus faecium (VREF) in Europe is characterized by a large community reservoir. In contrast, nosocomial outbreaks and infections (without a community reservoir) characterize VREF in the United States. Previous studies demonstrated host-specific genogroups and a distinct genetic lineage of VREF associated with hospital outbreaks, characterized by the variant esp-gene and a specific allele-type of the purK housekeeping gene (purK1). We investigated the genetic relatedness of vanA VREF (n=108) and vancomycin-susceptible E. faecium (VSEF) (n=92) from different epidemiologic sources by genotyping, susceptibility testing for ampicillin, sequencing of purK1, and testing for presence of esp. Clusters of VSEF fit well into previously described VREF genogroups, and strong associations were found between VSEF and VREF isolates with resistance to ampicillin, presence of esp, and purK1. Genotypes characterized by presence of esp, purK1, and ampicillin resistance were most frequent among outbreak-associated isolates and almost absent among community surveillance isolates. Vancomycin-resistance was not specifically linked to genogroups. VREF and VSEF from different epidemiologic sources are genetically related; evidence exists for nosocomial selection of a subtype of E. faecium, which has acquired vancomycin-resistance through horizontal transfer.

Clinical evaluation of a NASBA-based assay for detection of Candida spp. in blood and blood cultures

The number of life-threatening opportunistic fungal infections has shown a dramatic increase. However, the diagnosis of candidemia remains difficult. Nucleic acid amplification assays may improve the detection rate and decrease the time needed for detection and identification of Candida spp. Whole blood samples of patients suspected of having candidemia were analyzed using Nucleic Acid Sequence-Based Amplification (NASBA). Furthermore, aliquots of blood cultures of the patients after 2 days of culturing were tested. Eleven data sets from ten patients in two hospitals were generated. None of the whole blood samples was positive in the NASBA assay. Eight samples were positive in the NASBA assay after two days of culturing, whereas only two additional positive samples were found after longer incubation periods. Thus, a two-day culture step is sufficient to greatly improve the sensitivity of the NASBA assay. The NASBA assay detected Candida RNA in three patients. In one patient, the yeast was not detected by automated blood culturing, in another patient the NASBA assay detected the infection two days earlier than the blood culture system.

[Fatal pneumonia in an adolescent due to community-acquired methicillin-resistant Staphylococcus aureus positive for Panton-Valentine-leukocidin]

A 15-year-old girl developed a severe Staphylococcus aureus pneumonia following an influenza virus infection. The patient was admitted to a paediatric intensive-care facility because of respiratory and circulatory failure. Despite aggressive therapy, she died on the third day following admission to the intensive care unit due to secondary hypoxic-ischaemic encephalopathy. Blood and respiratory aspirate cultures showed community-acquired methicillin-resistant S. aureus (CA-MRSA) with a normal antibiotic sensitivity except for betalactam antibiotics. PCR-based methods demonstrated that the isolate possessed the Panton-Valentine-leukocidin (PVL) gene, encoding an S. aureus exotoxin that is associated with fulminant necrotising pneumonia. This case shows that clinicians in the Netherlands should also be aware of the possibility of CA-MRSA in patients without risk factors for MRSA carriage. Especially in children and adolescents with an influenza virus infection, pneumonia due to PVL-positive S. aureus strains may be life-threatening.

[Methicillin resistant Staphylococcus aureus (MRSA) infection in a dog in the Netherlands]

In the Netherlands, methicillin resistant Staphylococcus aureus (MRSA) are regularly isolated from humans. We present the first isolation of MRSA from animal origin in the Netherlands. A coagulase positive staphylococcus was cultured from an infected wound in a Dutch dog that recently underwent surgery abroad. The staphylococcus was resistant to methicillin, ampicillin, amoxycillin + clavulanic acid, cephalexin, erythromycin, lincomycin, tetracycline, gentamicin and enrofloxacin. It was identified as S. aureus by fermentation of mannitol and Martineau-PCR. The presence of mecA was confirmed by PCR.

Mutations in GyrA, ParC, MexR and NfxB in clinical isolates of Pseudomonas aeruginosa

The target enzymes GyrA and ParC and two efflux pump regulatory genes mexR and nfxB were analysed to determine changes associated with fluoroquinolone resistance in Pseudomonas aeruginosa. Both low- and high-level ciprofloxacin resistance was associated with a Thr-83Ile substitution in GyrA. A ParC Ser-80Leu substitution was found in highly resistant isolates in tandem with the Thr-83Ile substitution in GyrA. Mutations in the efflux regulatory genes were associated with resistance only when in tandem with a mutation in GyrA or ParC. These data show that the main mechanism of fluoroquinolone resistance in P. aeruginosa is mediated primarily through mutations in GyrA, and that mutations in ParC and the efflux regulatory genes are secondary.

Use of amplified fragment length polymorphism analysis to identify medically important Candida spp., including C. dubliniensis

Non-Candida albicans Candida species are increasingly being isolated. These species show differences in levels of resistance to antimycotic agents and mortality. Therefore, it is important to be able to correctly identify the causative organism to the species level. Identification of C. dubliniensis in particular remains problematic due to the high degree of phenotypic similarity between this species and C. albicans. The use of amplified fragment length polymorphism (AFLP) analysis as an identification method for medically important Candida species was investigated. Our results show very clear differences among medically important Candida species. Furthermore, when screening a large collection of clinical isolates previously identified on CHROMagar as C. albicans, we found a misidentification rate of 6%. AFLP analysis is universally applicable, and the patterns can easily be stored in a general, accessible database. Therefore, AFLP might prove to be a reliable method for the identification of medically important Candida species.

Fluoroquinolones: structure and target sites

The quinolones are a potent group of drugs that target the essential bacterial enzymes DNA gyrase and topoisomerase IV. DNA gyrase is the primary target of Gram negative organisms however, it is topoisomerase IV that is the primary target of Gram positive organisms. Within these enzymes is a highly conserved region centered round the active site where resistance mutations occur. These mutations are almost always identical, irrespective of organism. In spite of the homology of this region, amino acid sequence analysis shows that there are defined differences between the Gram groups, particularly in topoisomerase IV, and it is speculated that herein lies the origin of target preference. Since the first quinolone nalidixic acid was developed, the quinolones have undergone structural modifications, in particular the addition of a fluorine at position 6, to produce the fluoroquinolones. This has seen their potency and pharmakokinetic profile greatly increase. In vitro selection of resistance mutations has allowed the observation of how resistance is acquired and some of the modifications in newer fluoroquinolones have resulted in the shift of primary target from topoisomerase IV to gyrase with Gram positives. Curiously, purified topoisomerase IV is still more sensitive even if gyrase is the primary target. Gyrase remains the primary target for Gram negatives.

Resistance to beta-lactams among blood isolates of Salmonella spp. in European hospitals: results from the SENTRY Antimicrobial Surveillance Program 1997-98

The susceptibility to beta-lactams and the beta-lactamase content of 110 Salmonella spp. blood isolates collected during 1997-98 in 19 European centers participating in the SENTRY Surveillance Program were studied. Thirty-one isolates (28%) were resistant to penicillins, due to production of TEM-1 (27 isolates), OXA-1 (three isolates) or TEM-1 + OXA-1 (one isolate). All OXA-1 producers and 10 TEM-1-producing isolates were also resistant to penicillin-clavulanic acid combinations. In the latter isolates, this phenotype was associated with increased production of TEM-1. Sixteen TEM-1-producing Salmonella Enteritidis isolates and one OXA-1-producing S. Typhimurium isolate were able to transfer beta-lactam resistance by conjugation.

Multidrug resistance among Enterobacteriaceae is strongly associated with the presence of integrons and is independent of species or isolate origin

This study investigated the extent to which multidrug resistance (MDR) among Enterobacteriaceae is related to DNA elements called "integrons," whether the relationship is species dependent or origin dependent, and which resistance patterns are associated with integrons. Analysis of 867 nonrepeat isolates comprising 8 species and originating from the community and 23 European hospitals showed a significant relation between MDR and integrons, independent of species or origin. Although resistance to each tested antimicrobial agent was significantly associated with integrons, only resistance to sulfamethoxazole, cotrimoxazole, gentamicin, tobramycin, ampicillin, piperacillin, and cefuroxime predicted the presence of integrons. Combined resistance to both ampicillin and sulfamethoxazole-trimethoprim was the starting point for the development of resistance to additional beta-lactams, aminoglycosides, cephalosporins, and ciprofloxacin, a development paralleled by an increasing prevalence of integrons. The acquisition of resistance genes is not random, and the transfer of integron-carrying elements plays a dominant role in the development of MDR by Enterobacteriaceae.

Activities of the glycylcycline tigecycline (GAR-936) against 1,924 recent European clinical bacterial isolates

The in vitro activities of tigecycline against 1,924 clinical isolates were examined. The new glycylcycline exhibited excellent activity against all gram-positive cocci (MICs at which 90% of the isolates tested were inhibited [MIC(90)s], <or=1 microg/ml). In addition, it was also very potent against most members of the Enterobacteriaceae, with most MIC(90)s being <or=2 microg/ml. Among the nonfermenters, Acinetobacter spp. and Stenotrophomonas maltophilia are included in the in vitro spectrum of tigecycline activity.

mecA gene is widely disseminated in Staphylococcus aureus population

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of hospital infections worldwide. High-level resistance to methicillin is caused by the mecA gene, which encodes an alternative penicillin-binding protein, PBP 2a. To determine the clonal relationships between methicillin-susceptible S. aureus (MSSA) and MRSA, we typed 1,069 S. aureus isolates (493 MSSA isolates and 576 MRSA isolates), collected mainly in North American and European hospitals between the 1960s and the year 2000, using pulsed-field gel electrophoresis and ribotyping. Of 10 widespread S. aureus lineages recognized, 8 had corresponding mecA-positive strains. Multiresistant MRSA strains are found in hospitals worldwide, while unrelated and more susceptible strains represent less than 1% of the MRSA population. This supports the hypothesis that horizontal transfer plays an important role in the dissemination of the mecA gene in the S. aureus population.

Evaluation of the Etest ESBL and the BD Phoenix, VITEK 1, and VITEK 2 automated instruments for detection of extended-spectrum beta-lactamases in multiresistant Escherichia coli and Klebsiella spp

Seventy-four isolates of multiresistant Escherichia coli and Klebsiella spp. recovered during a 3-year period and 17 control strains with genotypically identified beta-lactamases were tested for the production of extended-spectrum beta-lactamases (ESBLs) by using the Etest and the VITEK 1, VITEK 2, and Phoenix automated instruments. The use of the Etest was evaluated by investigating its accuracy in detecting the ESBLs of the control strains and by comparing interpretation results of laboratory technicians and experts. The accuracy of the Etest was 94%. With the Etest as the reference for the clinical strains and the genotype as the reference for the control strains, the automated instruments detected the ESBLs with accuracies of 78% (VITEK 2), 83% (VITEK 1), and 89% (Phoenix). No significant difference between the systems with regard to the control strains was detected. The VITEK 2 did, however, perform less well than the Phoenix (P = 0.03) on the collection of clinical isolates, mainly because of its high percentage of indeterminate test results (11%). No significant difference between the performances of the VITEK 1 and either the VITEK 2 or the Phoenix was found. However, because of its associated BDXpert system the Phoenix showed the best performance. The Etest was found to be an accurate test but was limited by its indeterminate results (4%), its inability to differentiate between K1 hyperproduction and ESBLs, questionable guidelines concerning mutants inside the inhibition zones, and the inability of the technicians to recognize subtle zone deformations.

Activity of quinolones against gram-positive cocci: mechanisms of drug action and bacterial resistance

The quinolones are a potent class of antimicrobial agents that target two essential enzymes of bacterial cells: DNA gyrase and topoisomerase IV. Resistance is mediated chiefly through stepwise mutations in the genes that encode these enzymes, leading to alterations of the target site. These mutations occur in an area called the "quinolone resistance determining region". In gram-positive organisms, mutations occur more often in topoisomerase IV than in DNA gyrase. This target preference appears to depend upon two factors: the species of organism and the selecting drug. Resistance can be enhanced by a decrease in intracellular drug concentration, which is mediated through efflux pumps. The newer generation of fluoroquinolones and non-fluorinated quinolones exhibits enhanced activity against gram-positive organisms compared to the older members of this drug class, although development of resistance to these drugs has been demonstrated in vitro. This review gives a chronological perspective of the literature on the action of DNA gyrase and topoisomerase IV and the mechanisms of resistance to quinolones in staphylococci, streptococci and enterococci.

Presence of integron-associated resistance in the community is widespread and contributes to multidrug resistance in the hospital

Integrons are strongly associated with the multidrug resistance seen in gram-negative bacilli in the hospital environment. No data, however, are available on their prevalence in the community. This study is the first to show that integrons are widespread in Enterobacteriaceae in the community and that integron-associated resistance genes in the community constitute a substantial reservoir for multidrug resistance in the hospital.

In vitro activity of AZD2563, a novel oxazolidinone, against European Gram-positive cocci

AZD2563 is a new oxazolidinone that has targeted activity against Gram-positive bacteria. The in vitro activity of AZD2563 and nine comparators against 1543 European enterococcal, staphylococcal and streptococcal isolates was determined. The compound is a potent oxazolidinone, with no isolate tested displaying an MIC > 4 mg/L and 94.4% having an MIC < or =2 mg/L. Compared with linezolid, the distribution of MICs for all species of bacteria tested, with the exception of Enterococcus faecium, was shifted by one or two dilution steps to lower values for AZD2563. Thus, this oxazolidinone is a promising new antibiotic for the treatment of infections with Gram-positive cocci.

Evidence of extensive interspecies transfer of integron-mediated antimicrobial resistance genes among multidrug-resistant Enterobacteriaceae in a clinical setting

Multidrug resistance in gram-negative bacteria appears to be primarily the result of the acquisition of resistance genes by horizontal transfer. To what extent horizontal transfer may be responsible for the emergence of multidrug resistance in a clinical setting, however, has rarely been investigated. Therefore, the integron contents of isolates collected during a nosocomial outbreak of genotypically unrelated multidrug-resistant Enterobacteriaceae were characterized. The integron was chosen as a marker of transfer because of its association with multiresistance. Some genotypically identical isolates harbored different integrons. Grouping patients carrying the same integron yielded 6 epidemiologically linked clusters, with each cluster representing a different integron. Several patients carried multiple species harboring the same integron. Conjugation experiments with these strains resulted in the transfer of complete resistance patterns at high frequencies (10(-2) to 10(-4)). These findings provide strong evidence that the horizontal transfer of resistance genes contributed largely to the emergence of multidrug-resistant Enterobacteriaceae in this clinical setting.

Outbreak of a susceptible strain of Acinetobacter species 13 (sensu Tjernberg and Ursing) in an adult neurosurgical intensive care unit

Between December 1999 and June 2000, an outbreak caused by Acinetobacter emerged on the neurosurgical intensive care unit of our hospital. It was shown using automated ribotyping using Eco RI and pulsed-field gel electrophoresis that the outbreak was caused by spread of a single strain, which was identified by ribotyping and amplified ribosomal DNA restriction analysis as Acinetobacter DNA group 13TU (sensu Tjernberg and Ursing). The outbreak strain, which showed no antibiotic resistance, was identified in 23 patients, five of whom developed an infection. The organism was also isolated from various environmental sites. Cross-transmission among patients continued despite contact isolation of colonized patients and reinforcement of basic disinfection procedures. Eventually, after implementation of additional stringent measures such as cohorting of positive patients and daily disinfection of the floor, the outbreak was brought under control. This study demonstrates that apart from Acinetobacter baumanii, Acinetobacter 13TU strains, even when they are fully susceptible, may cause outbreaks that are difficult to control. Correct identification to the species level of Acinetobacter by genotypic methods is necessary to get insight in the importance of the different Acinetobacter genomic species in hospital epidemiology.

Production of BRO beta-lactamases and resistance to complement in European Moraxella catarrhalis isolates

Of the 419 Moraxella catarrhalis isolates collected during the 1997-1999 European SENTRY surveillance study, 385 (92%) were beta-lactamase positive. Twenty-two (5.7%) produced BRO-2 beta-lactamase. Twenty-one new mutations were found in the putative promoter region of the bro genes. Nineteen percent of all isolates tested were complement sensitive. Resistance to beta-lactams is not linked to the phylogenetic lineages associated with susceptibility to complement.

Increased in vitro activity of the novel des-fluoro(6) quinolone BMS-284756 against genetically defined clinical isolates of Staphylococcus aureus

The in vitro activities of the novel des-fluoro(6) quinolone BMS-284756, ciprofloxacin, gatifloxacin and moxifloxacin were tested against 248 genetically defined Staphylococcus aureus isolates, comprised of 116 unrelated S. aureus, seven heterogeneous vancomycin-intermediate S. aureus (hetero-VISA) strains and 125 clonally related MRSA. All strains were susceptible to BMS-284756 at an investigational breakpoint of 1 mg/L. Reserpine did not decrease the MIC of BMS-284756 in any of the strains tested. The novel des-fluoro(6) quinolone BMS-284756 showed a significantly increased anti-staphylococcal activity.

Genotyping of clinical methicillin-susceptible Staphylococcus aureus isolates in a Dutch teaching hospital

Methicillin-susceptible Staphylococcus aureus isolates, recovered from 204 patients in our hospital in a 22-month period, were characterized by pulsed-field gel electrophoresis. Among the multiple S. aureus types six clonal lineages dominated, comprising isolates from 158 patients. Despite the limited genetic variation, cross-transmission was made plausible only sporadically.