Bactericidal efficacy of molybdenum oxide nanoparticles against antimicrobial-resistant pathogens

Multidrug-resistant bacteria pose a major threat to effective antibiotics and alternatives to fight multidrug-resistant pathogens are needed. We synthetized molybdenum oxide (MoO3) nanoparticles (NP) and determined their antibacterial activity against 39 isolates: (i) eight Staphylococcus aureus, including representatives of methicillin-resistant S. aureus epidemic clones; (ii) six enterococci, including vancomycin-resistant isolates; and (iii) 25 Gram-negative isolates (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae), including extended spectrum beta-lactamases and carbapenemases producers. All isolates showed a MoO3 NP MIC of 700-800 mg l^-1. MoO3 NP produced a clear inhibition zone for S. aureus and all Gram-negative isolates at concentrations ≥25 mg ml^-1 and ≥50 mg ml^-1 for enterococci. When the NP solutions were adjusted to pH ~7, the biocidal activity was completely abolished. MoO3 NP create an acidic pH and show a universal antimicrobial activity against susceptible and resistant isolates belonging to the most relevant bacterial species responsible for hospital-acquired infections.

Frequent MRSA nasal colonization among hospitalized children and their parents in Angola and São Tomé and Príncipe

BACKGROUND

The prevalence of nosocomial meticillin-resistant Staphylococcus aureus (MRSA) was previously estimated as 23% in a paediatric hospital in Luanda, Angola and 18% in a general hospital in São Tomé and Príncipe.

AIM

To evaluate the prevalence of S. aureus/MRSA colonization among hospitalized children and their parents at two hospitals in Angola and São Tomé and Príncipe.

METHODS

In 2017, 127 hospitalized children and 129 of their parents had nasal swabs for S. aureus/MRSA carriage in the two countries. The isolates were tested for the presence of the mecA and Panton-Valentine leukocidin (PVL) genes, and characterized by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing and SCCmec typing.

FINDINGS

Twenty of 127 children (15.7%) and 13 of 129 parents (10.1%) were MRSA nasal carriers. Three lineages comprised 88% of the MRSA isolates: (i) PFGE A-ST5-SCCmec IVa (N=15; 45%), associated with spa type t105, recovered in Angola alone; (ii) PFGE N-ST8-IV/V (N=7; 21%), associated with spa types t008/t121, recovered in São Tomé and Príncipe alone; and (iii) PFGE B-ST88-IVa (N=7; 21%), associated with spa types t325/t786, present in both countries. Fifteen child/guardian pairs were colonized with identical MRSA (N=8) or meticillin-susceptible S. aureus (N=7) strains. PVL was detected in 25% of isolates, including two MRSA (ST30-V and ST8-IVa).

CONCLUSION

Hospitalized children and their parents are important reservoirs of MRSA. Infection control measures should focus on parents in order to minimize the spread of MRSA to the community.

Frequent occurrence of trimethoprim-sulfamethoxazole hetero-resistant Staphylococcus aureus isolates in different African countries

High rates of trimethoprim/sulfamethoxazole (SXT) resistance, a combination of two antifolate antibiotics trimethoprim (TMP) and sulfamethoxazole (SMZ), have been reported among Staphylococcus aureus isolates in Portuguese-speaking African countries. Our study aimed to evaluate the occurrence of TMP resistance markers in major SXT^R methicillin-resistant S. aureus (MRSA) clones from these countries. We accessed also different fitness traits that could explain the success of these isolates over the Brazilian MRSA (the most successful SXT^R MRSA clone worldwide but never identified in these countries). Minimum inhibitory concentrations for SXT, TMP and SMZ were determined, and genes encoding TMP resistance (dfrG, dfrA, dfrK and dfrB) were searched. Representatives of the Brazilian clone and of the major MRSA African clones were evaluated for their fitness by individual growth curves, competition assays, survival under desiccation, autolytic activity, resistance to oxidative stress, and also growth at high osmolarity and in acid and alkaline environments. Although all African isolates showed high-level resistance to TMP, the majority presented hetero-resistance to SXT. TMP resistance was linked to the presence of dfrG (78%), dfrA (19%) or both (3%) genes. Compared to the Brazilian clone, the African isolates showed higher growth rates and autolytic activity, and better survival to desiccation and alkaline conditions. Since isolates exhibiting SXT hetero-resistance are frequent in Africa, the implementation of standardized guidelines to detect this phenomenon is of major interest. The predominant MRSA clones in Portuguese-speaking African countries likely possess significant advantages over other clones, such as the Brazilian MRSA, that may explain their epidemiological success.

Staphylococcus aureus in former Portuguese colonies from Africa and the Far East: missing data to help fill the world map

The aim of the present study was to determine the prevalence and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage among patients and healthcare workers in Angola (ANG), São Tomé and Príncipe (STP), Cape Verde (CV) and East Timor (ET), and to characterize the antimicrobial susceptibility, virulence content and population structure of all S. aureus. Despite the importance of MRSA as a major human pathogen, data from these former Portuguese colonies in Africa and Asia are scarce. A total of 2065 nasal swabs recovered between 2010-14 were included in the study. Antimicrobial susceptibility testing and molecular characterization of S. aureus showed: (i) a very high MRSA prevalence in ANG (61.6%), moderate in STP (25.5%), low in CV (5.6%) and null in ET; (ii) a high prevalence of Panton-Valentine leukocidin in STP (36.8%), ET (29.2%) and CV (28.3%) contrasting with ANG (7.9%); (iii) ST5-SCCmecIVa, ST8-IV/V and ST5-VI were the major MRSA clones in ANG (65.2%), STP (44.8%) and CV (50%), respectively; (iv) a high resistance to trimethoprim-sulfamethoxazole in ANG (66.5%) and STP (50.9%), to rifampin in ANG (77.3%), and to tetracycline in STP (26.3%) and ET (20.8%); (v) three major methicillin-susceptible S. aureus clones (ST15, ST508, ST152) were present in all four countries. Age <18 years (OR 2.03, 95% CI 1.24-3.31), previous surgery (OR 2.45, 95% CI 1.24-4.83), no smoking (OR 4.04, 95% CI 1.05-15.50), and longer hospitalization (OR 2.53, 95% CI 1.49-4.28) were risk factors for MRSA carriage. This study provided the first comprehensive overview on MRSA in former Portuguese colonies in Africa and Asia, missing data in the world map.

Prevalence, risk factors, and epidemiology of methicillin-resistant Staphylococcus aureus carried by adults over 60 years of age

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in the community in Portugal is not completely understood. To evaluate S. aureus and MRSA carriage among the elderly, we conducted a large cross-sectional study between April 2010 and December 2012. A total of 3,361 adults over 60 years of age were screened for S. aureus nasopharyngeal and oropharyngeal carriage. MRSA were characterized by staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, multilocus sequence typing (MLST), and tested for the presence of Panton-Valentine leukocidin (PVL). Risk factors for MRSA carriage were identified by multiple logistic regression analysis. The prevalence of S. aureus and MRSA carriage among the elderly was 20.1 % and 1.8 %, respectively. The risk of being an MRSA carrier was higher among the elderly living in retirement homes [odds ratio (OR) = 2.90, 95 % confidence interval (CI): 1.48-5.48] and those that had been hospitalized in the previous year (OR = 2.64, 95 % CI: 1.47-4.58). Among the 62 MRSA isolates, 64.5 % were multidrug-resistant and none carried PVL. Most MRSA (82.3 %) were related to three hospital-associated (HA-MRSA) clones disseminated in Portugal: ST105-II (New York/Japan clone; 43.5 %), ST5-IVc (Pediatric clone; 19.4 %), and ST22-IVh (EMRSA-15 clone; 19.4 %). The New York/Japan and Pediatric clones were significantly associated with carriers living in retirement homes, while the EMRSA-15 clone was associated with carriers that had been hospitalized. We conclude that the elderly population in Portugal is essentially free of MRSA. Given the current European societal challenges for a healthy active aging, these results are of importance to healthcare professionals and public authorities to decide on strategies to promote health in this age group.

High prevalence of ST121 in community-associated methicillin-susceptible Staphylococcus aureus lineages responsible for skin and soft tissue infections in Portuguese children

In order to evaluate the incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Portugal, we analyzed a collection of 38 S. aureus isolates recovered from 30 children attending the pediatric emergency department of a central hospital in Lisbon due to skin and soft tissue infections. Molecular characterization identified seven clonal lineages among the 35 methicillin-susceptible S. aureus (MSSA) isolates, of which the major lineage PFGE A/t159/ST121 included 63% of the isolates. The three MRSA isolates belonged to the Pediatric clone PFGE D/t535/ST5-IV (n = 2) and to the European CA-MRSA clone PFGE G/t044/ST80-IVc (n = 1). All isolates harbored several virulence factors, namely, leukocidins. Panton-Valentine leukocidin (PVL) was produced by isolates from five MSSA lineages and by the ST80 MRSA. Of interest, this is the first reported isolation of CA-MRSA ST80 in Portugal.

Prevalence and clonality of methicillin-resistant Staphylococcus aureus (MRSA) in the Atlantic Azores islands: predominance of SCCmec types IV, V and VI

In order to obtain insights into the methicillin-resistant Staphylococcus aureus (MRSA) population structure in the Azores archipelago, 106 MRSA isolates were collected from patients attending an Azorean central hospital between January 2007 and February 2008. Antimicrobial resistance was determined for all isolates. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing (MLST), staphylococcal chromosome cassette mec (SCCmec) typing and the presence of Panton–Valentine leukocidin (PVL). The majority of the isolates (87%, n = 92) belonged to the EMRSA-15 clone (ST22, SCCmec-IVh), followed by the Pediatric clone (ST5-VI/IVc) (11%, n = 12). The Berlin clone (ST45-IVa) and a new clone (spa type t1839, ST1339 and SCCmec V variant) were represented by single isolates. All of the isolates carried SCCmec types IV, V or VI and a non-multiresistant antibiotic profile, resembling the currently emerging community MRSA. Moreover, PVL was described for the first time to be associated with the Pediatric clone carrying SCCmec type VI. We provided the first description of the population structure of MRSA in the Azores islands, which seems to be shaped by genetic events occurring locally, as well as by the regular population exchange between the islands, continental Portugal, the United Kingdom and the United States.

Changes in pneumococcal serotypes and antibiotypes carried by vaccinated and unvaccinated day-care centre attendees in Portugal, a country with widespread use of the seven-valent pneumococcal conjugate vaccine

The seven-valent pneumococcal conjugate vaccine (PCV7) has been available in Portugal since June 2001, but is not included in the National Vaccination Plan. Its impact on colonization is unknown. A point-prevalence study to evaluate PCV7 usage was carried out in 2006 among day-care centre attendees from the Lisbon area. Pneumococcal carriage rates, serotypes, and antibiotypes were determined and compared with results from a similar study conducted in 2001 before vaccine approval. In 2001 and 2006, 717 and 571 children, respectively, were enrolled. In 2006, 45.9% of the participants were appropriately vaccinated and 11.5% were incompletely vaccinated. Carriage of pneumococci remained stable (64.9% in 2001; 68.7% in 2006). Vaccine types (VT) decreased from 53.1% of all pneumococci to 11.2% (p <0.001). Serotype replacement was observed among vaccinated and unvaccinated children. Non-vaccine types (NVT) 1, 6C, 7F, 15A, 16F, 21, 23A, 29, and non-typeable (NT) strains increased significantly; serotype 19A increased, but not significantly. Rates of resistance to penicillin, erythromycin, clindamycin and tetracycline remained stable (p >0.05) due to significant increases in intermediate resistance to penicillin (from 5.5% to 17.8%), erythromycin (from 9.2% to 21.8%), clindamycin (from 6.4% to 19.3%) and tetracycline (from 8.3% to 15.8%) among NVT. Whereas in 2001 resistance among NVT was mostly associated with serotype 19A and NT strains, in 2006 resistance was also found among serotypes 6C, 15A, 24F and 33F. In conclusion, dramatic shifts in serotypes of colonizing pneumococci were observed among vaccinated and unvaccinated children. Rates of antibiotic resistance remained unchanged due to a balance between reduction in VT and an increase in antimicrobial-resistant NVT.

Identification of the first vancomycin intermediate-resistant Staphylococcus aureus (VISA) isolate from a hospital in Portugal

A clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA) with intermediate resistance to vancomycin (minimal inhibitory concentration [MIC] of 4 mug/ml) was isolated in 2006 from a surgical wound of a patient hospitalized at the orthopedics ward of Hospital de São Marcos--Braga, in the town of Braga. A combination of molecular typing methods, including pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing, and staphylococcal chromosomal cassette mec typing, identified the vancomycin intermediate-resistant S. aureus VISA-BRAGA as a derivative of the epidemic MRSA (EMRSA)-15 clone, which has been isolated with increasing frequency from several Portuguese hospitals recently. Compared to another EMRSA-15 isolate with the same genetic background (including PFGE subtype) the VISA-BRAGA isolate exhibited relatively high oxacillin MIC, slow growth, loss of hemolytic activity, and increased resistance to vancomycin and to daptomycin although neither of these two antibiotics was used in therapy. The VISA-BRAGA isolate described here appears to represent the first S. aureus with decreased susceptibility to vancomycin identified in a Portuguese hospital.

A European laboratory network for sequence-based typing of methicillin-resistant Staphylococcus aureus (MRSA) as a communication platform between human and veterinary medicine – an update on SeqNet.org

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Replacement of methicillin-resistant Staphylococcus aureus clones in Hungary over time: a 10-year surveillance study

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in Hungary has been increasing and is now close to 20% among invasive isolates of S. aureus. In order to understand the evolution of MRSA in Hungary, two collections of isolates were studied: 22 representatives of a collection of 238 MRSA isolates recovered between 1994 and 1998, and a collection of 299 MRSA isolates recovered between 2001 and 2004. The isolates were first characterised by pulsed-field gel electrophoresis (PFGE) and were distributed into 19 different PFGE patterns. Representatives of each pattern were further characterised by spa typing, multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. The Hungarian clone that was predominant in 1994-1998 (PFGE E, ST239-III) had almost disappeared in 2003-2004, being replaced by the Southern German clone (PFGE B, ST228-I) and the New York/Japan epidemic clone (PFGE A, ST5-II), which represented c. 85% of the 2001-2004 isolates. Thus, this study describes, for the first time, the co-dominance and extensive spread of the New York/Japan clone in a European country.

Changes in the clonal nature and antibiotic resistance profiles of methicillin-resistant Staphylococcus aureus isolates associated with spread of the EMRSA-15 clone in a tertiary care Portuguese hospital

Two hundred eighty methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates recovered from a tertiary care hospital in Oporto, Portugal, between 2003 and 2005 were studied by a combination of molecular typing techniques in order to investigate the genetic backgrounds associated with the changes in the resistance phenotypes observed since 2001 and compare them to those previously found in the hospital. All MRSA isolates were grouped into resistance profiles for a panel of seven antibiotics and characterized by pulsed-field gel electrophoresis (PFGE) and SCCmec (staphylococcal cassette chromosome mec) typing. Representative isolates of PFGE types were further studied by spa typing and multilocus sequence typing. Our findings clearly document that the increasing isolation of nonmultiresistant MRSA strains was associated with the decline (from 69% in 1996 to 2000 to 12% in 2003 to 2005) and massive replacement of the multiresistant Brazilian clone (ST239-IIIA) by the epidemic EMRSA-15 clone (ST22-IV), in which resistance to antibiotics other than beta-lactams is very rare, as the major clone (80% of isolates). The Iberian clone (ST247-IA), a major clone in 1992 to 1993, was represented in the present study by just one isolate. Two other pandemic MRSA clones were detected, as sporadic isolates, for the first time in our hospital: the New York/Japan (ST5-II) and the EMRSA-16 (ST36-II) clones. Furthermore, the pattern of susceptibility of MRSA isolates both to gentamicin and to trimethoprim-sulfamethoxazole was shown to be an excellent phenotypic marker for the discrimination of the EMRSA-15 clone from other nonmultiresistant MRSA clones present in our hospital.

Role of PBP1 in cell division of Staphylococcus aureus

We constructed a conditional mutant of pbpA in which transcription of the gene was placed under the control of an IPTG (isopropyl-beta-D-thiogalactopyranoside)-inducible promoter in order to explore the role of PBP1 in growth, cell wall structure, and cell division. A methicillin-resistant strain and an isogenic methicillin-susceptible strain, each carrying the pbpA mutation, were unable to grow in the absence of the inducer. Conditional mutants of pbpA transferred into IPTG-free medium underwent a four- to fivefold increase in cell mass, which was not accompanied by a proportional increase in viable titer. Examination of thin sections of such cells by transmission electron microscopy or fluorescence microscopy of intact cells with Nile red-stained membranes showed a morphologically heterogeneous population of bacteria with abnormally increased sizes, distorted axial ratios, and a deficit in the number of cells with completed septa. Immunofluorescence with an antibody specific for PBP1 localized the protein to sites of cell division. No alteration in the composition of peptidoglycan was detectable in pbpA conditional mutants grown in the presence of a suboptimal concentration of IPTG, which severely restricted the rate of growth, and the essential function of PBP1 could not be replaced by PBP2A present in methicillin-resistant cells. These observations suggest that PBP1 is not a major contributor to the cross-linking of peptidoglycan and that its essential function must be intimately integrated into the mechanism of cell division.

Inferring a population structure for Staphylococcus epidermidis from multilocus sequence typing data

Despite its importance as a human pathogen, information on population structure and global epidemiology of Staphylococcus epidermidis is scarce and the relative importance of the mechanisms contributing to clonal diversification is unknown. In this study, we addressed these issues by analyzing a representative collection of S. epidermidis isolates from diverse geographic and clinical origins using multilocus sequence typing (MLST). Additionally, we characterized the mobile element (SCCmec) carrying the genetic determinant of methicillin resistance. The 217 S. epidermidis isolates from our collection were split by MLST into 74 types, suggesting a high level of genetic diversity. Analysis of MLST data using the eBURST algorithm revealed the existence of nine epidemic clonal lineages that were disseminated worldwide. One single clonal lineage (clonal complex 2) comprised 74% of the isolates, whereas the remaining isolates were clustered into 8 minor clonal lineages and 13 singletons. According to our evolutionary model, SCCmec was acquired at least 56 times by S. epidermidis. Although geographic dissemination of S. epidermidis strains and the value of the index of association between the alleles, 0.2898 (P < 0.05), support the clonality of S. epidermidis species, examination of the sequence changes at MLST loci during clonal diversification showed that recombination gives rise to new alleles approximately twice as frequently as point mutations. We suggest that S. epidermidis has a population with an epidemic structure, in which nine clones have emerged upon a recombining background and evolved quickly through frequent transfer of genetic mobile elements, including SCCmec.

Origins and evolution of methicillin-resistant Staphylococcus aureus clonal lineages

Most methicillin-resistant Staphylococcus aureus (MRSA) isolates identified among blood isolates collected in Denmark between 1957 and 1970 belonged to either phage group III or the closely related 83A complex and had a PSTM antibiotype (resistance to penicillin [P], streptomycin [S], tetracycline [T], and methicillin [M]). Recently, some of these isolates were shown to have the same genetic backgrounds as contemporary epidemic MRSA isolates, and Danish methicillin-susceptible S. aureus (MSSA) isolates from the 1960s with a PST antibiotype were proposed to have been the recipients of the mecA gene in those lineages. In this study, we investigated the genetic backgrounds of isolates from the 83A complex that were fully susceptible or resistant to penicillin only in order to try to trace the evolutionary trajectory of contemporary MRSA lineages. We also studied MSSA and MRSA isolates from other phage groups in order to investigate if they had the potential to develop into contemporary MRSA clones. Most susceptible or penicillin-resistant isolates from phage group III or the 83A complex belonged to sequence type 8 (ST8) or ST5, while four isolates were ST254. STs 30, 45 and 25 were represented by MSSA isolates from other phage groups, which also included several singletons. Representatives of most of the current major epidemic MRSA lineages were identified among fully susceptible isolates collected in the 1960s, suggesting that these were MSSA lineages which carried genetic traits important for superior epidemicity before the acquisition of methicillin resistance.

Unusually high prevalence of nosocomial Panton-Valentine leukocidin-positive Staphylococcus aureus isolates in Cape Verde Islands

Characterization of nosocomial methicillin-susceptible Staphylococcus aureus isolates from Cape Verde showed that (i) Panton-Valentine leukocidin genes were present in 35% of the isolates and (ii) half of the collection had the same genetic background as methicillin-resistant pandemic clones. Introduction of the staphylococcal chromosome cassette mec (SCCmec) into virulent and epidemic isolates could pose serious threats to public health.

Illustration of a common framework for relating multiple typing methods by application to macrolide-resistant Streptococcus pyogenes

The studies that correlate the results obtained by different typing methodologies rely solely on qualitative comparisons of the groups defined by each methodology. We propose a framework of measures for the quantitative assessment of correspondences between different typing methods as a first step to the global mapping of type equivalences. A collection of 325 macrolide-resistant Streptococcus pyogenes isolates associated with pharyngitis cases in Portugal was used to benchmark the proposed measures. All isolates were characterized by macrolide resistance phenotyping, T serotyping, emm sequence typing, and pulsed-field gel electrophoresis (PFGE), using SmaI or Cfr9I and SfiI. A subset of 41 isolates, representing each PFGE cluster, was also characterized by multilocus sequence typing (MLST). The application of Adjusted Rand and Wallace indices allowed the evaluation of the strength and the directionality of the correspondences between the various typing methods and showed that if PFGE or MLST data are available one can confidently predict the emm type (Wallace coefficients of 0.952 for both methods). In contrast, emm typing was a poor predictor of PFGE cluster or MLST sequence type (Wallace coefficients of 0.803 and 0.655, respectively). This was confirmed by the analysis of the larger data set available from http://spyogenes.mlst.net and underscores the necessity of performing PFGE or MLST to unambiguously define clones in S. pyogenes.

Role of murF in cell wall biosynthesis: isolation and characterization of a murF conditional mutant of Staphylococcus aureus

The Staphylococcus aureus murF gene was placed under the control of a promoter inducible by IPTG (isopropyl-beta-d-thiogalactopyranoside). It was demonstrated that murF is an essential gene; it is cotranscribed with ddlA and growth rate, level of beta-lactam antibiotic resistance, and rates of transcription of the mecA and pbpB genes paralleled the rates of transcription of murF. At suboptimal concentrations of the inducer, a UDP-linked muramyl tripeptide accumulated in the cytoplasm in parallel with the decline in the amounts of the normal pentapeptide cell wall precursor. The abnormal tripeptide component incorporated into the cell wall as a monomeric muropeptide, accompanied by a decrease in the oligomerization degree of the peptidoglycan. However, incorporation of the tripeptide into the cell wall was limited to a relatively low threshold value. Further reduction of the amounts of pentapeptide cell wall precursor caused a gradual decrease in the cellular amounts of peptidoglycan, the production of a thinner peripheral cell wall, aberrant septae, and an overall increase in the diameter of the cells. The observations suggest that the role of murF exceeds its primary function in peptidoglycan biosynthesis and may also be involved in the control of cell division.

High interlaboratory reproducibility of DNA sequence-based typing of bacteria in a multicenter study

Current DNA amplification-based typing methods for bacterial pathogens often lack interlaboratory reproducibility. In this international study, DNA sequence-based typing of the Staphylococcus aureus protein A gene (spa, 110 to 422 bp) showed 100% intra- and interlaboratory reproducibility without extensive harmonization of protocols for 30 blind-coded S. aureus DNA samples sent to 10 laboratories. Specialized software for automated sequence analysis ensured a common typing nomenclature.

Natural history of drug-resistant clones of Streptococcus pneumoniae colonizing healthy children in Portugal

A total of 3,539 Streptococcus pneumoniae (Pn) were recovered from 4,969 nasopharyngeal samples of children attending 13 day-care centers (DCCs) located in Lisbon, Portugal, during a surveillance study from January, 2001, through March, 2003, integrated in the European intervention project (EURIS, European Resistance Intervention Study). All Pn isolates were tested for anti-biotyping and drug-resistant pneumococci (DRPn) were further tested by serotyping and pulsed-field gel electrophoresis (PFGE). Overall carriage of Pn was very high (71.2%) and 39.9% of the isolates were resistant to antimicrobials (22.5% with decreased susceptibility to penicillin and 17.4% susceptible to penicillin and resistant to other antimicrobials). Serotypes 6B, 14, 23 F, 19F, and 19 A were prevalent among the 1,287 DRPn and 5.8% of the isolates were non-typeable. Eighty PFGE patterns were identified among 1,285 DRPn, and 93.1% of the DRPn belonged to 26 major clonal types that comprised: Pneumococcal Molecular Epidemiology Network (PMEN) clones (76.3%), Portuguese (PT)-DCC clones, previously detected in 1996-1999 (14.3%), and EURIS PT-DCC new clones, identified for the first time in the EURIS study, during 2001-2003 (9.4%). Comparing with previous Portuguese surveillance studies carried out since 1996, we observed that carriage increased from 47% to 71%, but no major changes were detected on the prevalence of pneumococcal serotypes. Moreover, although PMEN clones were predominant in all DCCs, in the present study the majority of them were gradually decreasing in time whereas several PT-DCC and new clones seemed to be increasing.

Molecular characterisation of a dominant methicillin-resistant Staphylococcus aureus (MRSA) clone in a Mexican hospital (1999–2003)

Methicillin-resistant Staphylococcus aureus (MRSA) isolates (n = 216), collected between January 1999 and May 2003 in a tertiary-care university hospital in Guadalajara, Mexico, were characterised by antibiotype, pulsed-field gel electrophoresis (PFGE) of SmaI macrorestriction fragments, and hybridisation of ClaI digests with mecA- and Tn554-specific DNA probes. Representatives of the single clonal type found were analysed by spa typing, multilocus sequence typing and staphylococcal chromosomal cassette mec (SCCmec) typing, and were tested for the presence of 22 virulence determinants and agr type. A single PFGE pattern was identified, with minor variations over time, with spa type 2, sequence type 5, SCCmec type II, agr type 2 and the presence of the enterotoxin genes seg and sei, the gamma-haemolysin variant gene hlg-v and the leukocidin lukE-lukD genes. In addition, the isolates showed antimicrobial resistance to beta-lactams, macrolides, chloramphenicol and imipenem, and susceptibility to gentamicin, rifampicin, trimethoprim-sulphamethoxazole and vancomycin. Following its appearance in 1997, this clone spread within the hospital, and is now present in most of the hospital units and wards.

Assessment of band-based similarity coefficients for automatic type and subtype classification of microbial isolates analyzed by pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) has been the typing method of choice for strain identification in epidemiological studies of several bacterial species of medical importance. The usual procedure for the comparison of strains and assignment of strain type and subtype relies on visual assessment of band difference number, followed by an incremental assignment to the group hosting the most similar type previously seen. Band-based similarity coefficients, such as the Dice or the Jaccard coefficient, are then used for dendrogram construction, which provides a quantitative assessment of strain similarity. PFGE type assignment is based on the definition of a threshold linkage value, below which strains are assigned to the same group. This is typically performed empirically by inspecting the hierarchical cluster analysis dendrogram containing the strains of interest. This approach has the problem that the threshold value selected is dependent on the linkage method used for dendrogram construction. Furthermore, the use of a linkage method skews the original similarity values between strains. In this paper we assess the goodness of classification of several band-based similarity coefficients by comparing it with the band difference number for PFGE type and subtype classification using receiver operating characteristic curves. The procedure described was applied to a collection of PFGE results for 1,798 isolates of Streptococcus pneumoniae, which documented 96 types and 396 subtypes. The band-based similarity coefficients were found to perform equally well for type classification, but with different proportions of false-positive and false-negative classifications in their minimal false discovery rate when they were used for subtype classification.

Comparison of genetic backgrounds of methicillin-resistant and -susceptible Staphylococcus aureus isolates from Portuguese hospitals and the community

In order to understand the origins of the dominant methicillin-resistant Staphylococcus aureus (MRSA) clones in Portuguese hospitals, we compared the genetic backgrounds of nosocomial MRSA with methicillin-susceptible S. aureus (MSSA) isolates from the same hospitals (n=155) and from the community (n=157) where they were located. Pulsed-field gel electrophoresis, spa typing, multilocus sequence typing, and agr type analysis revealed that the genetic backgrounds correspondent to the dominant MRSA clones in Portuguese hospitals during the last 15 years (Iberian ST 247, Brazilian ST 239, and EMRSA-15 ST 22) were scarcely or not found among the present MSSA collection. The four major MSSA clones encountered (A-ST 30, B-ST 34, C-ST 5, and H-ST 45) correspond, or are very similar, to the background of other international MRSA pandemic clones, i.e., EMRSA-16, New York/Japan, Pediatric, and Berlin clones. However, with the exception of the Pediatric clone, none of these MRSA clones has been detected in Portugal. Our findings suggest the three major MRSA clones identified in Portuguese hospitals have not originated from the introduction of SCCmec into dominant MSSA backgrounds present in the Portuguese nosocomial or community environment but were probably imported from abroad. In contrast, the MRSA Pediatric clone might have originated in our country by the acquisition of SCCmec type IV into MSSA clone C. Furthermore, we provide evidence that the introduction of SCCmec into sensitive clones is most likely a relatively infrequent event that seems to depend not exclusively on the presence of a successful MSSA lineage.

Genetic Diversity among Methicillin-ResistantStaphylococcus epidermidis(MRSE)

We selected 106 methicillin-resistant Staphylococcus epidermidis (MRSE) and 22 methicillin-susceptible S. epidermidis (MSSE) hospital isolates--each with a different PFGE pattern--for more detailed documentation of genetic diversity. The 106 MRSE isolates showed extensive variation in the SmaI DNA fragments hybridizing with the DNA probe for mecA, the molecular size of which varied from as low as 20 kb up to over 500 kb. Parallel variation was also observed in the size of DNA fragments hybridizing with the chromosomal genes orfX and gyrA, and this was also observed in MSSE isolates. In contrast, SmaI fragments associated with the housekeeping genes murE and aroE, both located distantly from orfX, showed little size variation. Typing for the mec complex and ccr identified 10 different SCCmec structures and a large number of strains (21 isolates) that were non-typeable. The majority of strains studied (36%) carried a SCCmec type IV-like structure, including strains with non-related PFGE profiles. On the other hand, closely related strains often carried different types of SCCmec. The findings indicate that the acquisition and/or loss of mobile genetic elements, including various structural types of SCCmec, may occur frequently in the vicinity of the orfX gene on the S. epidermidis chromosome.

Trends in drug resistance, serotypes, and molecular types of Streptococcus pneumoniae colonizing preschool-age children attending day care centers in Lisbon, Portugal: a summary of 4 years of annual surveillance

Of the nasopharyngeal cultures recovered from 942 day care center (DCC) attendees in Lisbon, Portugal, 591 (62%) yielded Streptococcus pneumoniae during a surveillance performed in February and March of 1999. Forty percent of the isolates were resistant to one or more antimicrobial agents. In particular, 2% were penicillin resistant and 20% had intermediate penicillin resistance. Multidrug resistance to macrolides, lincosamides, and tetracycline was the most frequent antibiotype (17% of all isolates). Serotyping and molecular typing by pulsed-field gel electrophoresis were performed for 202 out of 237 drug-resistant pneumococci (DRPn). The most frequent serotypes were 6B (26%), 14 (22%), 19F (16%), 23F (10%), and nontypeable (12%). The majority (67%) of the DRPn strains were representatives of nine international clones included in the Pneumococcal Molecular Epidemiology Network; eight of them had been detected in previous studies. Fourteen novel clones were identified, corresponding to 26% of the DRPn strains. The remaining 7% of the strains were local clones detected in our previous studies. Comparison with studies conducted since 1996 in Portuguese DCCs identified several trends: (i) the rate of DRPn frequency has fluctuated between 40 and 50%; (ii) the serotypes most frequently recovered have remained the same; (iii) nontypeable strains appear to be increasing in frequency; and (iv) a clone of serotype 33F emerged in 1999. Together, our observations highlight that the nasopharynxes of children in DCCs are a melting pot of successful DRPn clones that are important to study and monitor if we aim to gain a better understanding on the epidemiology of this pathogen.

Analysis of the genetic variability of virulence-related loci in epidemic clones of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) isolates have previously been classified into major epidemic clonal types by pulsed-field gel electrophoresis in combination with multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec typing. We aimed to investigate whether genetic variability in potentially polymorphic domains of virulence-related factors could provide another level of differentiation in a diverse collection of epidemic MRSA clones. The target regions of strains representative of epidemic clones and genetically related methicillin-susceptible S. aureus isolates from the 1960s that were sequenced included the R domains of clfA and clfB; the D, W, and M regions of fnbA and fnbB; and three regions in the agr operon. Sequence variation ranged from very conserved regions, such as those for RNAIII and the agr interpromoter region, to the highly polymorphic R regions of the clf genes. The sequences of the clf R domains could be grouped into six major sequence types on the basis of the sequences in their 3' regions. Six sequence types were also observed for the fnb sequences at the amino acid level. From an evolutionary point of view, it was interesting that a small DNA stretch at the 3' clf R-domain sequence and the fnb sequences agreed with the results of MLST for this set of strains. In particular, clfB R-domain sequences, which had a high discriminatory capacity and with which the types distinguished were congruent with those obtained by other molecular typing methods, have potential for use for the typing of S. aureus. Clone- and strain-specific sequence motifs in the clf and fnb genes may represent useful additions to a typing methodology with a DNA array.

Clonal types and multidrug resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) recovered in Italy during the 1990s

A large number (272) of methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from Italian hospitals during the early and late 1990s were characterized for multidrug resistance pattern and clonal type using a combination of genotyping methods, including pulsed-field gel electrophoresis (PFGE), spaA typing, multilocus sequence typing (MLST), determination of SCC mec type, and hybridization pattern with Tn 554. The majority of MRSA belonged to four genetic lineages: the pandemic Iberian and Brazilian clones, and two unique clonal types-the "Italian" and "Rome" clones of MRSA. The Italian clone carried the SCC mec type I in the genetic background of ST228, which is a double-locus variant of the sequence type of the multidrug-resistant New York/Japanese clone (ST5). The properties of the Rome clone showed several striking similarities to those of the Archaic clone of MRSA that was dominant among MRSA isolates in the mid-1960s to 1970s, but has not been detected since then in recent global surveillance studies.

Delineation of the Endemic and Sporadic Methicillin-Resistant Staphylococcus aureus Clones in a Czech Hospital

The aim of this study was to define the endemic clones of methicillin-resistant Staphylococcus aureus (MRSA) among strains collected between September, 2001, and February, 2003, at the regional hospital of Nový Jicín, Czech Republic. The isolates were characterized by susceptibility tests, HindIII ribotyping, and pulsed-field gel electrophoresis. Representatives of each clonal type were analyzed by multilocus sequence typing and staphylococcal cassette chromosome mec (SCCmec) typing. The prevalence of the most important macrolide (ermA, ermB, ermC, and msrA) and aminoglycoside (aac6'-aph2", aph3', and ant4') resistance genes was evaluated as well. Our results document the existence of two international MRSA clones: (1) the Iberian clone (ST247:SCCmec IA:PFGE A:ribotype H2), endemic in the hospital and associated to a single multiresistant phenotype; and (2) clone EMRSA-15 (ST22:SCCmec IV:PFGE H-ribotype H7), appearing in the beginning of 2002 and associated with three phenotypes. These two clones could be distinguished by antibiogram, distribution of macrolide and aminoglycoside resistance genes (ermA, aac6'-aph2", ant4' versus ermC and msrA in a few isolates), production of beta-lactamase, and presence of enterotoxin A (in the Iberian clone).

Surveillance of methicillin-resistant Staphylococcus aureus in a pediatric hospital in Mexico City during a 7-year period (1997 to 2003): clonal evolution and impact of infection control

Between 1997 and 2000 a single multidrug-susceptible methicillin-resistant Staphylococcus aureus clone, M (sequence type 30 [ST30]-staphylococcal cassette chromosome mec [SCCmec] type IV), was present in a pediatric hospital in Mexico City, Mexico. In 2001 the international multidrug-resistant New York-Japan clone (ST5-SCCmec type II) was introduced into the hospital, completely replacing clone M by 2002.

Role of murE in the Expression of beta-lactam antibiotic resistance in Staphylococcus aureus

It was shown earlier that Tn551 inserted into the C-terminal region of murE of parental methicillin-resistant Staphylococcus aureus strain COL causes a drastic reduction in methicillin resistance, accompanied by accumulation of UDP-MurNAc dipeptide in the cell wall precursor pool and incorporation of these abnormal muropeptides into the peptidoglycan of the mutant. Methicillin resistance was recovered in a suppressor mutant. The murE gene of the same strain was then put under the control of the isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible promoter P(spac). Bacteria grown in the presence of suboptimal concentrations of IPTG accumulated UDP-MurNAc dipeptide in the cell wall precursor pool. Both growth rates and methicillin resistance levels (but not resistance to other antibiotics) were a function of the IPTG concentration. Northern analysis showed a gradual increase in the transcription of murE and also in the transcription of pbpB and mecA, parallel with the increasing concentrations of IPTG in the medium. A similar increase in the transcription of pbpB and mecA, the structural genes of penicillin-binding protein 2 (PBP2) and PBP2A, was also detected in the suppressor mutant. The expression of these two proteins, which are known to play critical roles in the mechanism of staphylococcal methicillin resistance, appears to be-directly or indirectly-under the control of the murE gene. Our data suggest that the drastic reduction of the methicillin MIC seen in the murE mutant may be caused by the insufficient cellular amounts of these two PBPs.

Update on the major clonal types of methicillin-resistant Staphylococcus aureus in the Czech Republic

The purpose of our study was the molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in 21 hospitals in the Czech Republic in the period 2000-2002 and comparison with previous results from 1996-1997. Strains were analyzed by pulsed-field gel electrophoresis (PFGE) of SmaI digests and ribotyping of HindIII digests hybridized with a 16S-23S DNA probe. The prevalence of the most clinically important macrolide (ermA, ermB, ermC, and msrA) and aminoglycoside (aph3', ant4', and aac6'-aph2") resistance genes was evaluated as well. Selected isolates representative of each clonal type were analyzed by multilocus sequence typing and by a multiplex PCR method capable of identifying the structural type of the staphylococcal cassette chromosome mec (SCCmec) carried by the bacteria. Our results document the displacement of the Brazilian clone (ST239, SCCmec type IIIA, PFGE type B, ribotype H1) by a new clone that we named "Czech clone" (ST239, SCCmec type IIIA, PFGE type F, ribotype H6) and the maintenance of the Iberian clone (ST247, SCCmec type IA, PFGE type A, ribotype H2) exclusively in one hospital in the Czech Republic. In addition, we found a correlation between the distribution of aminoglycoside resistance genes and MRSA clonal types.

Application of molecular typing methods to characterize nosocomial coagulase-negative staphylococci collected in a Greek hospital during a three-year period (1998-2000)

A total of 143 methicillin-resistant coagulase-negative staphylococci (MR-CNS) collected between 1998 and 2000 at the University Hospital of Patras, Greece, were characterized by antibiogram and genomic typing to define the clonal types endemic in this hospital and their evolution during the 3-year period. These isolates corresponded to 93 methicillin-resistant Staphylococcus epidermidis (MRSE) and 50 other MR-CNS, which were isolated from patients in different wards, exclusively from blood and catheter tips cultures. Pulsed-field gel electrophoresis (PFGE) of SmaI macrofragments and hybridization of ClaI digests with mecA and murE DNA probes were performed. The application of these methodologies demonstrated the existence, persistence and spread of MRSE, MR-Staphylococcus haemolyticus, and MR-Staphylococcus hominis clones in this hospital, whereas the SmaI/murE hybridization pattern was shown to be a valuable tool for the MRSE identification.

Evolution of sporadic isolates of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals and their similarities to isolates of community-acquired MRSA

Forty-one methicillin-resistant Staphylococcus aureus (MRSA) hospital isolates that clearly differed from the six major pandemic clones of MRSA in pulsed-field gel electrophoresis type, mecA and Tn554 polymorphism, and epidemic behavior were selected from an international strain collection for more detailed characterization. SpaA typing, multilocus sequence typing, and SCCmec (staphylococcal cassette chromosome mec) typing demonstrated extensive diversity among these sporadic isolates both in genetic background and also in the structure of the associated SCCmec elements. Nevertheless, the isolates could be grouped into restricted clonal complexes by using the BURST (i.e., based upon related sequence types) program algorithm, which predicted that most sporadic MRSA isolates evolved from pandemic MRSA clones. Several of the sporadic MRSA resembled community-acquired MRSA isolates in properties that included a relatively limited multiresistance pattern, faster growth rates, diversity of genetic backgrounds, and a frequent association with SCCmec type IV.

Clonal and antibiotic resistance profiles of methicillin-resistant Staphylococcus aureus (MRSA) from a Portuguese hospital over time

Methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from a general hospital in Oporto, Portugal, during two periods (1992-1993 and 1996-2000) were characterized by pulsed-field gel electrophoresis (PFGE) of SmaI fragments, and by hybridization of ClaI digests with mecA and Tn554 probes, discriminating the isolates in mecA::Tn554::PFGE genotypes. In addition, a representative sample of the defined genotypes was characterized by multilocus sequence typing (MLST) and SCCmec (staphylococcal cassette chromosome mec) typing, generating the corresponding ST-SCCmec types. In 1992-1993, 77% of MRSA belonged to the Iberian clone (genotype I::E::A or ST247-IA). In 1996-2000, the frequency of this clone decreased to 19% and the majority (69%) of the isolates belonged to another international clone, the Brazilian MRSA (genotype XI::B::B or ST239-IIIA). Trimethoprim/sulfamethoxazole (SXT) was confirmed to be an important phenotypic marker to distinguish the Iberian (SXT-susceptible) and the Brazilian (SXT-resistant) clones in MRSA isolates from Portugal. Our observations document major shifts in the dominant MRSA clonal types that occurred in this hospital since 1992, suggesting a selective advantage of the Brazilian relatively to the Iberian clone. In addition to these two MRSA clones that are the most frequent in Portuguese hospitals since the early 1990s, sporadic MRSA clones (representing 14% of the total) were identified and characterized.

Serotyping Streptococcus pneumoniae by multiplex PCR

The capsule is a major virulence factor of pneumococci, and it was shown that some capsular variants are associated with antimicrobial resistance and certain types of disease. Moreover, pneumococcal capsular typing has received renewed interest since the availability of conjugate vaccines, which include serotypes frequently associated with pediatric disease. Our aim was to develop a simple, reliable, and economical method for detecting epidemiologically important serotypes present in the proposed 11-valent conjugate vaccine. We designed primers based on the sequences available for the capsular types 1, 3, 4, 6B, 14, 18C, 19F, 19A, and 23F and combined them into seven multiplex PCRs. The method involves streamlined DNA template preparation and agarose gel electrophoresis to analyze the amplification products. A total of 446 pneumococci selected from among isolates colonizing the nasopharynx of children attending day care centers in Lisbon, Portugal, were typed both by conventional immunological techniques and by multiplex PCR. Capsular types identified by the PCR method invariably produced results concordant with the conventional serotyping technique. Even when the method presented does not fully type an isolate, the PCR data can guide the experimenter when using immunological serotyping. Multiplex PCR for the analysis of pneumococci provides an accurate, expeditious, and cost-effective way of reducing the number of strains that have to be serotyped by conventional immunological techniques.

Two international methicillin-resistant Staphylococcus aureus clones endemic in a university hospital in Patras, Greece

Pulsed-field gel electrophoresis (PFGE) of SmaI macrofragments and hybridization of ClaI digests with the mecA- and Tn554-specific DNA probes were used to define the endemic clones of methicillin-resistant Staphylococcus aureus (MRSA) among strains collected in 1993 and 1998 to 2000 at the University Hospital of Patras, Patras, Greece. Representatives of each clonal type were analyzed by spaA typing, multilocus sequence typing (MLST), and staphylococcal chromosomal cassette mec (SCCmec) typing. The results indicated the existence of two successive international MRSA clones: (i) a clonal type with PFGE type A, sequence type (ST) 30 (ST30), and SCCmec type IV, which was very similar to a clone widely spread in the United Kingdom, Mexico, and Finland, and (ii) a clonal type with PFGE type B, ST239, and SCCmec III, which was related to the Brazilian clone. Both clones seem to be widespread in Greece as well. A novel MRSA clone is also described and is characterized by a new MLST type (ST80) associated with SCCmec type IV and with the presence of Panton-Valentine leukocidin genes.

Frequent recovery of a single clonal type of multidrug-resistant Staphylococcus aureus from patients in two hospitals in Taiwan and China

One hundred thirty-two methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from patients with S. aureus infections between January 1998 and February 1999 in two hospitals, one located in Taipei, Taiwan, and another in Nanjing, People's Republic of China, were examined for antibiotic susceptibility and for clonal type by a combination of three methods: hybridization of ClaI restriction digests with mecA- and Tn554-specific DNA probes and pulsed-field gel electrophoresis of chromosomal SmaI digests. Selected isolates representing each clonal type were also analyzed by spaA typing, multilocus sequence typing, and a multiplex PCR method capable of identifying the structural type of the staphylococcal cassette chromosome mec (SCCmec) carried by the bacteria. The overwhelming majority of isolates (126 of 132 or 95%) belonged to minor variants of a single clonal type resembling the Brazilian and Hungarian epidemic MRSA clones, which showed a common spaA type and which were either sequence type 239 (ST239) or ST241 (a single-locus variant of ST239) in association with SCCmec type III or IIIA.

The evolution of pandemic clones of methicillin-resistant Staphylococcus aureus: identification of two ancestral genetic backgrounds and the associated mec elements

Previous surveillance studies carried out by our laboratories, primarily in Southern and Eastern Europe, Latin America, and the United States, have characterized 3,067 methicillin-resistant Staphylococcus aureus (MRSA) hospital isolates by a combination of molecular typing methods. Nearly 70% of these isolates could be classified into five clonal types showing extensive geographic spread. Representative isolates of these clonal types were now reexamined for their genetic relatedness by multilocus sequence typing (MLST) and by sequencing the polymorphic region of protein A (spaA typing), and also for the type of the Staphylococcal Chromosomal Cassette (SCCmec) resident in the bacteria. Three of the previously classified clonal types (Iberian, Brazilian, and Hungarian clones) shared a common or closely related genetic background A, which was the same as the background of the earliest European isolates of MRSA from England and Denmark. The Pediatric and New York/Japan clones belonged to a completely different genetic background B. The three recently described SCCmec types were specifically associated with different pandemic clones: types I and III with isolates of genetic background A and type II with isolates of genetic background B. A novel SCCmec related to type I, called SCCmec type IV, was identified in some MRSA strains belonging to genetic background A as well as B. Structural variations in SCCmec types I and III were also observed. The data allow tentative identification of an evolutionary pathway for the emergence of pandemic MRSA clones and also provide evidence for the multiple, yet restricted, numbers of acquisition of the mec element by S. aureus.

Low prevalence of methicillin-resistant strains among Staphylococcus aureus colonizing young and healthy members of the community in Portugal

Recent reports suggest that methicillin-resistant Staphylococcus aureus (MRSA) may be emerging as a community pathogen. In Portuguese hospitals, the incidence of MRSA among disease causing isolates is extremely high (48-50%). To determine the prevalence of MRSA in the Portuguese community, nasal samples were obtained from 823 draftees, 484 nonmedical university students, and 107 high-school students. In addition, throat samples were obtained from the 823 draftees and S. aureus isolates were also recovered from 283 (13%) nasopharyngeal samples obtained from 2,111 children attending day-care centers. The rate of nasal colonization of S. aureus was 34%, 25%, and 46% for draftees, nonmedical university students, and high-school students, respectively. The rate of pharyngeal colonization of the draftees was 33%. Of the 1,001 S. aureus isolates obtained, seven were MRSA and eight were borderline oxacillin-resistant S. aureus (BORSA). By molecular typing techniques, five of the seven MRSA were identified as belonging to one of three highly epidemic clones, the Brazilian, Iberian, and Pediatric clones of MRSA, which were identified as endemic in Portuguese hospitals. The eight BORSA were all members of clones previously identified in international samples. In spite of the extremely high prevalence of MRSA in Portuguese hospitals, the carriage rate of MRSA in healthy and young individuals remains low.

Complementation of the essential peptidoglycan transpeptidase function of penicillin-binding protein 2 (PBP2) by the drug resistance protein PBP2A in Staphylococcus aureus

The essential function of penicillin-binding protein 2 (PBP2) in methicillin-susceptible Staphylococcus aureus RN4220 was clearly established by placing the pbp2 gene under control of the inducible P(spac) promoter; the resulting bacteria were unable to grow in the absence of inducer. In contrast, the deficit in PBP2 caused by inhibition of transcription of the pbp2 gene did not block growth of a methicillin-resistant S. aureus strain expressing the extra penicillin-binding protein PBP2A, a protein of extraspecies origin that is central to the mechanism of methicillin resistance. Several lines of evidence indicate that the essential function of PBP2 that can be compensated for by PBP2A is the transpeptidase activity. This provides direct genetic evidence that PBP2A has transpeptidase activity.

Multilocus sequence typing of Streptococcus pneumoniae clones with unusual drug resistance patterns: genetic backgrounds and relatedness to other epidemic clones

Six drug-resistant Streptococcus pneumoniae clones were previously identified from day care centers in Portugal, primarily on the basis of common pulsed-field gel electrophoresis (PFGE) patterns. These clones were susceptible to penicillin or had only very low-level resistance to it (most MICs, < or =0.25 microg/mL) and accounted for a large proportion (35%) of all drug-resistant pneumococci colonizing the nasopharynx of healthy children attending day care. Five of the 6 clones were identified among pneumococcal clinical isolates collected in other countries. In this study, we applied multilocus sequence typing (MLST) to describe the genetic background of these clones. MLST confirmed previous findings obtained by PFGE and allowed for the extension of the international clonal relationships by showing that each of the 6 clones was internationally disseminated and was able to cause pneumococcal disease.

Streptococcus pneumoniae isolates with reduced susceptibility to ciprofloxacin in Spain: clonal diversity and appearance of ciprofloxacin-resistant epidemic clones

Analysis of the pulsed-field gel electrophoretic profiles of 82 pneumococcal isolates with reduced susceptibility to ciprofloxacin (RSC) and of 90 co-occurring susceptible isolates indicates a considerable genetic diversity among isolates with RCS and points to a close relation between the two groups. This finding suggests that pneumococci with RCS emerge through independent mutational events.

An acquired and a native penicillin-binding protein cooperate in building the cell wall of drug-resistant staphylococci

The blanket resistance of methicillin-resistant Staphylococcus aureus to all beta-lactam antibiotics--which had such a devastating impact on chemotherapy of staphylococcal infections--is related to the properties of the key component of this resistance mechanism: the "acquired" penicillin-binding protein (PBP)-2A, which has unusual low affinity for all beta-lactam antibiotics. Until now, the accepted model of resistance implied that in the presence of beta-lactam antibiotics in the surrounding medium, PBP2A must take over the biosynthesis of staphylococcal cell wall from the four native staphylococcal PBPs because the latter become rapidly acylated and inactivated at even low concentrations of the antibiotic. However, recent observations indicate that this model requires revision. Inactivation of the transglycosylase domain, but not the transpeptidase domain, of PBP2 of S. aureus prevents expression of beta-lactam resistance, despite the presence of the low-affinity PBP2A. The observations suggest that cell-wall synthesis in the presence of beta-lactam antibiotics requires the cooperative functioning of the transglycosylase domain of the native staphylococcal PBP2 and the transpeptidase domain of the PBP2A, a protein imported by S. aureus from an extra species source.

Identification of clinical staphylococcal isolates from humans by internal transcribed spacer PCR

The emergence of coagulase-negative staphylococci not only as human pathogens but also as reservoirs of antibiotic resistance determinants requires the deployment and development of methods for their rapid and reliable identification. Internal transcribed spacer-PCR (ITS-PCR) was used to identify a collection of 617 clinical staphylococcal isolates. The amplicons were resolved in high-resolution agarose gels and visually compared with the patterns obtained for the control strains of 29 staphylococcal species. Of the 617 isolates studied, 592 (95.95%) were identified by ITS-PCR and included 11 species: 302 isolates of Staphylococcus epidermidis, 157 of S. haemolyticus, 79 of S. aureus, 21 of S. hominis, 14 of S. saprophyticus, 8 of S. warneri, 6 of S. simulans, 2 of S. lugdunensis, and 1 each of S. caprae, S. carnosus, and S. cohnii. All species analyzed had unique ITS-PCR patterns, although some were very similar, namely, the group S. saprophyticus, S. cohnii, S. gallinarum, S. xylosus, S. lentus, S. equorum, and S. chromogenes, the pair S. schleiferi and S. vitulus, and the pair S. piscifermentans and S. carnosus. Four species, S. aureus, S. caprae, S. haemolyticus, and S. lugdunensis, showed polymorphisms on their ITS-PCR patterns. ITS-PCR proved to be a valuable alternative for the identification of staphylococci, offering, within the same response time and at lower cost, higher reliability than the currently available commercial systems.