Spread of a methicillin-resistant and multiresistant epidemic clone of Staphylococcus aureus in Argentina

Community-acquired methicillin-resistant Staphylococcus aureus invasive infections: a case series from Central-South Chile

The emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections at the end of the 20th century represents a significant shift in the epidemiology of staphylococcal infections and, consequently, their clinical management. There are diverse CA-MRSA clones that are widely spread worldwide, showing differences in their regional dissemination, which has been dynamically changing over time. Although the first CA-MRSA description occurred about 30 years ago, its epidemiology in certain regions, such as South America, has been poorly explored, resulting in a gap in the understanding of the epidemiology of CA-MRSA in under-represented countries/regions. This report describes the first four clinical cases of invasive infections caused by CA-MRSA in a tertiary hospital in the central-southern region of Chile. It also associates the clinical characteristics of the infections with the microbiological and molecular features of the isolates. The four S. aureus isolates belong to sequence type 8, which has been widely described as a cause of community-acquired infections. All of them presented a wide resistome and virulome. Additionally, in two of them, it was possible to reconstruct the COMER genetic element, present in the USA300-Latin American variant clone. Considering these findings, it is crucial to prepare for a potential increase in invasive CA-MRSA infections in Chile. This would involve enhancing current surveillance systems and maintaining a low threshold of suspicion for these infections among clinicians.

First Isolation of Methicillin-Resistant Livestock-Associated Staphylococcus aureus CC398 and CC1 in Intensive Pig Production Farms in Argentina

Since the mid-2000s, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has been identified among pigs worldwide, CC398 being the most relevant LA-MRSA clone. In the present work, nasal swabs were taken from healthy pigs of different age categories (25 to 154 days) from 2019 to 2021 in four intensive farms located in three provinces of Argentina. The aim of the present study was to characterize the first LA-MRSA isolates that colonized healthy fattening pigs in Argentina in terms of their resistance phenotype and genotype and to know the circulating clones in the country. Antimicrobial susceptibility, presence of the mecA gene and PCR screening of CC398 were evaluated in all the isolates. They were resistant to cefoxitin, penicillin, tetracycline, chloramphenicol and ciprofloxacin but susceptible to nitrofurantoin, rifampicin, vancomycin and linezolid. Furthermore, 79% were resistant to clindamycin and lincomycin, 68% to erythromycin, 58% to gentamicin and 37% to trimethoprim/sulfamethoxazole. All the isolates were multidrug resistant. The clonal relation was assessed by SmaI-PFGE (pulsed-field gel electrophoresis) and a representative isolate of each PFGE type was whole genome sequenced by Illumina. MLST (multilocus sequence typing), resistance and virulence genes and SCCmec typing were performed on sequenced isolates. The isolates were differentiated in three clonal types by PFGE, and they belonged to sequence-type ST398 (58%) and ST9, CC1 (42%) by MLST. SCCmec typeV and several resistance genes detected showed complete correlation with resistance phenotypes. The present study revealed that LA-MRSA colonizing healthy pigs in Argentina belongs to CC398 and CC1, two MRSA lineages frequently associated to pigs in other countries.

The History of Methicillin-Resistant Staphylococcus aureus in Brazil

Since the emergence of MRSA in the 1960s, a gradual increase in infections by resistant bacteria has been observed. Clinical manifestations may vary from brand to critical condition due to host risk factors, as well as pathogen virulence and resistance. The high adaptability and pathogenic profile of MRSA clones contributed to its spread in hospital and community settings. In Brazil, the first MRSA isolates were reported in the late 1980s, and since then different genetic profiles, such as the Brazilian epidemic clone (BEC) and other clones considered a pandemic, became endemic in the Brazilian population. Additionally, Brazil's MRSA clones were shown to be able to transfer genes involved in multidrug resistance and enhanced pathogenic properties. These events contributed to the rise of highly resistant and pathogenic MRSA. In this review, we present the main events which compose the history of MRSA in Brazil, including numbers and locations of isolation, as well as types of staphylococcal cassette chromosome mec (SCCmec) found in the Brazilian territory.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

The world's microbiology laboratories can be a global microbial sensor network

The microbes that infect us spread in global and local epidemics, and the resistance genes that block their treatment spread within and between them. All we can know about where they are to track and contain them comes from the only places that can see them, the world's microbiology laboratories, but most report each patient's microbe only to that patient's caregiver. Sensors, ranging from instruments to birdwatchers, are now being linked in electronic networks to monitor and interpret algorithmically in real-time ocean currents, atmospheric carbon, supply-chain inventory, bird migration, etc. To so link the world's microbiology laboratories as exquisite sensors in a truly lifesaving real-time network their data must be accessed and fully subtyped. Microbiology laboratories put individual reports into inaccessible paper or mutually incompatible electronic reporting systems, but those from more than 2,200 laboratories in more than 108 countries worldwide are now accessed and translated into compatible WHONET files. These increasingly web-based files could initiate a global microbial sensor network. Unused microbiology laboratory byproduct data, now from drug susceptibility and biochemical testing but increasingly from new technologies (genotyping, MALDI-TOF, etc.), can be reused to subtype microbes of each genus/species into sub-groupings that are discriminated and traced with greater sensitivity. Ongoing statistical delineation of subtypes from global sensor network data will improve detection of movement into any patient of a microbe or resistance gene from another patient, medical center or country. Growing data on clinical manifestations and global distributions of subtypes can automate comments for patient's reports, select microbes to genotype and alert responders.

MRSA Pediatric clone expressing ermC plus lnuA genes causing nosocomial transmission and healthcare workers colonization in a neonatal intensive care unit

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of both nosocomial and community-acquired infections. We describe an outbreak caused by the MRSA Pediatric clone expressing an unusual lincosamide resistant phenotype. Between January and May 2006, an MRSA outbreak was detected at the Neonatal Unit of Hospital Interzonal General de Agudos "Evita", Buenos Aires Province, Argentina that affected ten patients. Seven isolates from seven patients plus five MRSA recovered from health care workers (nasal carriage) were studied. Two phenotypes were observed: (i) ELCi (10), resistance to erythromycin and lincomycin and inducible resistance to clindamycin; (ii) ELiCi (2), resistance to erythromycin and inducible resistance to lincomycin and clindamycin. All 12 MRSA were resistant to oxacillin, erythromycin and gentamicin. Isolates expressing the ELCi-phenotype showed lincomycin MIC values between 16 and 32mg/L, while the remaining 2 isolates with ELiCi-phenotype presented a MIC value of 0.5mg/L. No differences were observed between the clindamycin MIC values in both phenotypes, ranging 0.25-0.5mg/L. Isolates showing ELCi-phenotype harbored ermC plus lnuA genes, and the other two only ermC gene. All 12 isolates were genetically related and belonged to the Pediatric clone (ST100) harboring a new variant of SCCmecIV. This is the first MRSA outbreak expressing an unusual ELCi phenotype due to a combination of ermC plus lnuA genes.

Molecular epidemiology of hospital-onset methicillin-resistant Staphylococcus aureus infections in Southern Chile

Methicillin-resistant Staphylococcus aureus (MRSA) is a pathogen of public health importance. In Chile, the Cordobes/Chilean clone was the predominant healthcare-associated MRSA (HA-MRSA) clone in 1998. Since then, the molecular epidemiological surveillance of MRSA has not been performed in Southern Chile. We aimed to investigate the molecular epidemiology of HA-MRSA infections in Southern Chile to identify the MRSA clones involved, and their evolutionary relationships with epidemic international MRSA lineages. A total of 303 single inpatient isolates of S. aureus were collected in the Valdivia County Hospital (2007-2008), revealing 33% (100 MRSA/303) prevalence for HA-MRSA infections. The SCCmec types I and IV were identified in 97% and 3% of HA-MRSA, respectively. All isolates lacked the pvl genes. A random sample (n = 29) of all MRSA was studied by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), SCCmec subtyping, agr and spa typing, and virulence genes profiling. PFGE analysis revealed the predominance (89%, 26/29) of pulsotype A and three additional pulsotypes, designated H1, I33, and G1. Pulsotype A (ST5-SCCmecI-spa-t149) is clonally related to the Cordobes/Chilean clone. Pulsotype H1 (ST5-SCCmecIVNT-spa-t002) is genetically related to the Pediatric clone (ST5-SCCmecIV). Pulsotype I33 (ST5-SCCmecIVc-spa-t002) is clonally related by PFGE to the community-associated MRSA (CA-MRSA) clone spread in Argentina, I-ST5-IVa-PVL(+). The G1 pulsotype (ST8-SCCmecIVc-spa-t024) is clonally related to the epidemic USA300 CA-MRSA. Here, we demonstrate the stability of the Cordobes/Chilean clone over time as the major HA-MRSA clone in Southern Chile. The identification of two CA-MRSA clones might suggest that these clones have entered into the healthcare setting from the community. These results emphasize the importance of the local surveillance of MRSA infections in the community and hospital settings.

Spread of epidemic MRSA-ST5-IV clone encoding PVL as a major cause of community onset staphylococcal infections in Argentinean children

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus-(CA-MRSA) strains have emerged in Argentina. We investigated the clinical and molecular evolution of community-onset MRSA infections (CO-MRSA) in children of Córdoba, Argentina, 2005-2008. Additionally, data from 2007 were compared with the epidemiology of these infections in other regions of the country.

METHODOLOGY/PRINCIPAL FINDINGS

Two datasets were used: i) lab-based prospective surveillance of CA-MRSA isolates from 3 Córdoba pediatric hospitals-(CBAH1-H3) in 2007-2008 (compared to previously published data of 2005) and ii) a sampling of CO-MRSA from a study involving both, healthcare-associated community-onset-(HACO) infections in children with risk-factors for healthcare-associated infections-(HRFs), and CA-MRSA infections in patients without HRFs detected in multiple centers of Argentina in 2007. Molecular typing was performed on the CA-MRSA-(n: 99) isolates from the CBAH1-H3-dataset and on the HACO-MRSA-(n: 51) and CA-MRSA-(n: 213) isolates from other regions. Between 2005-2008, the annual proportion of CA-MRSA/CA-S. aureus in Córdoba hospitals increased from 25% to 49%, P<0.01. Total CA-MRSA infections increased 3.6 fold-(5.1 to 18.6 cases/100,000 annual-visits, P<0.0001), associated with an important increase of invasive CA-MRSA infections-(8.5 fold). In all regions analyzed, a single genotype prevailed in both CA-MRSA (82%) and HACO-MRSA(57%), which showed pulsed-field-gel electrophoresis-(PFGE)-type-"I", sequence-type-5-(ST5), SCCmec-type-IVa, spa-t311, and was positive for PVL. The second clone, pulsotype-N/ST30/CC30/SCCmecIVc/t019/PVL(+), accounted for 11.5% of total CA-MRSA infections. Importantly, the first 4 isolates of Argentina belonging to South American-USA300 clone-(USA300/ST8/CC8/SCCmecIVc/t008/PVL(+)/ACME(-)) were detected. We also demonstrated that a HA-MRSA clone-(pulsotype-C/ST100/CC5) caused 2% and 10% of CA-MRSA and HACO-MRSA infections respectively and was associated with a SCCmec type closely related to SCCmecIV(2B&5).

CONCLUSIONS/SIGNIFICANCE

The dissemination of epidemic MRSA clone, ST5-IV-PVL(+) was the main cause of increasing staphylococcal community-onset infections in Argentinean children (2003-2008), conversely to other countries. The predominance of this clone, which has capacity to express the h-VISA phenotype, in healthcare-associated community-onset cases suggests that it has infiltrated into hospital-settings.

Rapid change of methicillin-resistant Staphylococcus aureus clones in a Chinese tertiary care hospital over a 15-year period

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) has been increasing yearly at Peking Union Medical College Hospital (PUMCH). In order to understand the molecular evolution of MRSA at PUMCH, a total of 466 nonduplicate S. aureus isolates, including 302 MRSA and 164 methicillin-susceptible (MSSA) isolates recovered from 1994 to 2008 were characterized by staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST). The 302 MRSA isolates were classified into 12 spa types and 9 sequence types (STs). During the years from 1994 to 2000, the most predominant MRSA clone was ST239-MRSA-III-spa t037. Since 2000, ST239-MRSA-III-spa t030 has rapidly replaced t037 and become the major clone. Another clone, ST5-MRSA-II-spa t002 emerged in 2002 and constantly existed at a low prevalence rate. The 164 MSSA isolates were classified into 62 spa types and 40 STs. ST398 was the most common MLST type for MSSA, followed by ST59, ST7, ST15, and ST1. Several MSSA genotypes, including ST398, ST1, ST121, and ST59, were identical to well-known epidemic community-acquired MRSA (CA-MRSA) isolates. MLST eBURST analysis revealed that the ST5, ST59, and ST965 clones coexisted in both MRSA and MSSA, which suggested that these MRSA clones might have evolved from MSSA by the acquisition of SCCmec. Two pvl-positive ST59-MRSA-IV isolates were identified as CA-MRSA according to the clinical data. Overall, our data showed that the ST239-MRSA-III-spa t037 clone was replaced by the emerging ST239-MRSA-III-spa t030 clone, indicating a rapid change of MRSA at a tertiary care hospital in China over a 15-year period.

Evolution of methicillin-resistant Staphylococcus aureus clones in Latin America

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a prominent nosocomial bacterial pathogen, associated with significant morbidity and mortality. The global incidence is increasing, and Latin America is no exception. This article reviews MRSA clonal distribution in Latin America and implications for clinical practice.

DESIGN

A PubMed literature search (1966-2008) identified 32 articles that characterized MRSA clones in Latin America.

RESULTS

Data from these articles show that since 1990, several epidemic MRSA clones have spread in Latin America. The multidrug-resistant Brazilian clone is widespread, especially in Brazil and Argentina, but more recently clones with susceptibility to a range of antibiotics have been detected in Brazil, whereas in Argentina, as in Chile, Colombia and Paraguay, the multidrug-resistant Cordobes/Chilean clone prevails. In Mexico, the New York/Japan clone is most frequent. Data were not available from every country and, despite the increasing prevalence of community MRSA infections, most were collected from tertiary care centers.

CONCLUSIONS

A variety of epidemic MRSA clones are circulating in Latin America, some of which harbor genes that encode multidrug resistance or enhanced pathogenicity. Continued collection and reporting of epidemiological data is crucial for effective prevention and treatment.

Characterization of meticillin-resistant Staphylococcus aureus isolates from hospitals in KwaZulu-Natal province, Republic of South Africa

Epidemiological data based on phenotypic and molecular characterization of meticillin-resistant Staphylococcus aureus (MRSA) in sub-Saharan Africa are limited. This investigation studied 61 MRSA isolates obtained from 13 health-care institutions in KwaZulu-Natal (KZN) province, South Africa, from March 2001 to August 2003. More than 80 % of the isolates were resistant to at least four classes of antibiotics and six isolates were resistant to the aminoglycoside, macrolide-lincosamide and tetracycline groups of antibiotics, heavy metals and nucleic acid-binding compounds. PFGE of SmaI-digested genomic DNA revealed seven types, designated A-G. Type A was the main pulsotype (62.3 %) and was identified in 11 of the 13 health-care institutions, suggesting that it represented a major clone in health-care institutions in KZN province. Analysis of representative members of the three major pulsotypes by spa, multilocus sequence typing and SCCmec typing revealed the types t064-ST1173-SCCmec IV and t064-ST1338-SCCmec IV (PFGE type A, single-locus and double-locus variants of ST8), t037-ST239-SCCmec III (PFGE type F) and t045-ST5-SCCmec III (PFGE type G). The combination of various typing methods provided useful information on the geographical dissemination of MRSA clones in health-care institutions in KZN province. The observation of major clones circulating in health-care facilities in KZN province indicates that adequate infection control measures are urgently needed.

Staphylococcal interspersed repeat unit typing of Staphylococcus aureus: evaluation of a new multilocus variable-number tandem-repeat analysis typing method

The present study evaluates the performance of the staphylococcal interspersed repeat unit (SIRU) method applied to a diverse collection of 104 Staphylococcus aureus isolates previously characterized by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec typing for methicillin-resistant S. aureus. The SIRU method distributed the 104 strains into 81 SIRU profiles that could be clustered into 12 groups and 29 singletons. The discriminatory power of the method at the profile level, translated by Simpson's index of diversity (SID), was similar to that of PFGE subtyping (SID = 99.23% versus 99.85%) and slightly higher than that of spa typing (SID = 97.61%). At the group level, the SIRU SID (93.24%) was lower than that of PFGE typing (95.41%) but higher than that of MLST (SID = 91.77%). The adjusted Rand (AR) coefficient showed that SIRU typing at the group level had the highest congruence with MLST (AR = 0.5736) and with clonal complex (CC) (AR = 0.4963) but the lowest congruence with PFGE subtype (AR = 0.0242). The Wallace coefficient indicated that in the present collection, two strains with the same SIRU profile have a 100% probability of belonging to the same CC, a 90% probability of sharing the same spa type, and an 83% probability of being classified in the same sequence type. The high discriminatory power of the SIRU method, along with its apparent concordance with MLST results, makes it potentially valuable for S. aureus short-term epidemiological investigations and population dynamics as well.

Changing patterns in frequency of recovery of five methicillin-resistant Staphylococcus aureus clones in Portuguese hospitals: surveillance over a 16-year period

A total of 629 nonduplicate methicillin-resistant Staphylococcus aureus MRSA isolates were recovered between June and November 2006 from 11 hospitals located in different areas of Portugal. Selected isolates (n = 271, 43%) were typed by pulsed-field gel electrophoresis (PFGE), representatives of which were additionally characterized by spa typing, multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec) typing, and the presence of Panton-Valentine leukocidin (PVL). The 271 isolates were classified into 13 different clonal types. Three pandemic clones included the majority (n = 241, 88%) of the isolates and were observed in several hospitals: (i) EMRSA-15 (54%)-PFGE type A, ST22, spa type t022, SCCmec IV-was found in the 11 hospitals studied and was identified as the major clone in seven of them; (ii) the New York/Japan clone (17%)-PFGE B, ST5, spa type t067, SCCmec II-was identified in nine hospitals and represented the major clone in four; and (iii) the Brazilian MRSA (17%)-PFGE C, ST239, spa type t037, SCCmec IIIA-was also detected in nine hospitals but never as the main clone. All isolates tested were PVL negative. Clone EMRSA-15 is currently the predominant MRSA clonal type circulating in Portuguese hospitals, but a new wave of MRSA has emerged in the country with the recent introduction and spread of the New York/Japan clone. The Brazilian MRSA that was the leading clone in Portugal in the late 1990s is declining and being progressively replaced by the two former clones. We report the first isolate SCCmec type V (ST45) in Portugal.

A 7-year national survey on bacterial resistance in bronchoalveolar lavage from patients hospitalized in Argentina

The purpose of this study is to undertake a nationwide survey on bacterial resistance in bronchoalveolar lavage (BAL) from patients hospitalized in Argentina. A 2-month point prevalence study was conducted twice yearly (April-May and October-November) from 1997 to 2003 by 36 Argentinean centers. Antimicrobial susceptibility data of the potential pathogens recovered from the BAL (samples containing <1% of squamous epithelial cells and bacterial counts >or=10(4) CFU/mL) of inpatients (i.e., >or=48-h hospital length of stay) with suspected hospital-acquired pneumonia (HAP) were collected on a computerized system (SIR) described previously. The survey was split into 2 periods for comparison purposes, 1997 to 2000 and 2001 to 2003. A total of 752 organisms were included. Staphylococcus aureus was the most frequent species, followed by Acinetobacter spp. and Pseudomonas aeruginosa. In both periods, more than a half of the Klebsiella pneumoniae strains displayed a phenotype of extended-spectrum beta-lactamase producer. A doubling of imipenem-resistant Acinetobacter frequency was shown from the 1st period to the 2nd one (25-48%). More than two-thirds of the S. aureus strains proved to be methicillin resistant in both periods, and a pronounced decrease of resistance rates to trimethoprim/sulfamethoxazole and rifampin was shown in the 2nd period. The present study shows the worrisome increasing bacterial resistance in BAL samples to most available antimicrobial options for treating patients with suspected HAP. Variations over time support the need for systematic tailored surveillance and compel us to establish a rational usage of antimicrobial agents in our country.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

Synergistic effect of polyoxometalates in combination with oxacillin against methicillin-resistant and vancomycin-resistant Staphylococcus aureus: a high initial inoculum of 1 x 108 cfu/ml for in vivo test

Synergistic effect of polyoxometalates, K(6)[P(2)W(18)O(62)].14H(2)O (P(2)W(18)), K(4)[SiMo(12)O(40)].3H(2)O (SiMo(12)), K(7)[PTi(2)W(10)O(40)].6H(2)O (PTi(2)W(10)), and K(9)H(5)[alpha-Ge(2)Ti(6)W(18)O(77)].16H(2)O (Ge(2)Ti(6)W(18)), in combination with a beta-lactam oxacillin against methicillin-resistant and vancomycin-resistant Staphylococcus aureus (characterized by possessing the penicillin-binding protein 2' (PBP2') as a cell-wall synthesis enzyme) with a high initial inoculum of 1 x 10(8) cfu/ml (for in vivo test) was investigated with a help of the growth curve and the reverse transcription polymerase chain reaction (RT-PCR) analyses. The growth curves showing the suppression of cell proliferation of the strains based on the synergistic effect of the polyoxometalates in combination with oxacillin indicated a recovery of the cell proliferation during continuous cultivation. The duration of the suppression of the cell proliferation increased with increasing the concentration of the polyoxometalates, depending on the amounts of the initial inoculum of the strain. The RT-PCR results for P(2)W(18), SiMo(12), and PTi(2)W(10) indicated the suppression of expression of the PBP2'-encoding mecA gene in contrast to the ones for Ge(2)Ti(6)W(18). The difference in the RT-PCR results among the polyoxometalates suggests that there remain other factors for the inhibition of PBP2' production such as post-transcription process.

Application of molecular techniques in the study of Staphylococcus aureus clonal evolution - A Review

Staphylococcus aureus is an important agent of healthcare-associated and community-acquired infections. A major characteristic of this microorganism is the ability to develop resistance to antimicrobial agents. Several molecular techniques have been applied for the characterization of S. aureus in epidemiological studies. In the present review, we discuss the application of molecular techniques for typing S. aureus strains and describe the nomenclature and evolution of epidemic clones of this important pathogen.

Clonal Structure of the Methicillin-ResistantStaphylococcus aureus(MRSA) Population in Poland: Revision and Update

The clonal structure of the methicilin-resistant Staphylococcus aureus (MRSA) population in Poland has been analyzed in several reports since the mid-1990s. The present study was performed on 253 MRSA isolates (146 archival and 107 new isolates) recovered in 26 hospitals between 1990 and 2001. Whereas all isolates were typed by pulsed-field gel electrophoresis (PFGE) and the analysis of the ClaI::mecA and ClaI::Tn554 RFLP polymorphism, selected isolates were also subjected to multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) comparisons. Based on the PFGE data, 15 MRSA clones were discerned, seven of which were observed in multiple hospitals. Five of these were related to the pandemic Hungarian (MLST clonal complex, CC8), Iberian (CC8), Pediatric (CC5), Mexican (CC30), and Brazilian clones (CC8). MLST confirmed the earlier reports on the similarity of the Hungarian and Brazilian clones, and it revealed that one of the two remaining epidemic clones was related to the Hungarian/Brazilian, and the other--to the Berlin clones. A local strain from the Northeastern part of the country was found to be similar to a minor Greek clone. The MRSA clonal structure and the increasing complexity of the relationships between the genetic and phenotypic traits of this micro-organism in Poland has now been firmly established.

Trimethoprim-sulfamethoxazole as a viable treatment option for infections caused by methicillin-resistant Staphylococcus aureus

OBJECTIVE

To review available data regarding the efficacy of trimethoprim-sulfamethoxazole (TMP-SMX) for the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA).

DATA SOURCES

A MEDLINE search was performed (January 1966-December 2003) using the search terms Staphylococcus aureus , sulfamethoxazole, trimethoprim, co-trimoxazole, and methicillin resistance. Abstracts from infectious diseases meetings also were reviewed.

DATA SYNTHESIS

The reported rate of TMP-SMX resistance in S. aureus is highly variable. From a mechanistic standpoint, TMP-SMX resistance among MRSA appears to be distinct from multidrug resistance, although some anecdotal reports suggest otherwise. Clonal outbreaks of MRSA resistant to TMP-SMX have been described; of these, the Brazilian clone has more often been resistant to TMP-SMX than the Iberian clone. Rates of TMP-SMX resistance are particularly high in institutions serving large numbers of patients infected by the human immunodeficiency virus, due to increased exposure for Pneumocystis prophylaxis. Limited studies and case reports have found TMP-SMX useful against infections caused by MRSA.

CONCLUSIONS

A large body of anecdotal data, but only one randomized clinical trial, indicates the effectiveness of TMP-SMX as a treatment for MRSA infections. Double-blind, randomized controlled trials are needed to compare the two available oral agents-TMP-SMX and linezolid-against MRSA.

Molecular genotyping of methicillin-resistant Staphylococcus aureus strains in a teaching hospital in Turkey

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of nosocomial infections in our hospital. Therefore, we aimed to characterize MRSA isolates phenotypically from patients with nosocomial infections at Cumhuriyet University Hospital between December, 1999, and June, 2001, in Sivas by analysis of antibiotic patterns and genotypically using pulsed-field gel electrophoresis (PFGE) and repetitive element sequence-based polymerase chain reaction (rep-PCR). Forty-three nosocomial isolates were collected from various wards. All isolates were resistant to penicillin, tetracycline, oxacillin, and gentamicin. By rep-PCR and by separation of SmaI fragments of genomic DNA using PFGE, one major type (eight subtypes with PFGE) was identified among the strains. This clone was found to be different than some clones such as Iberian, Brazilian, and a major clone that was found in another Turkish University Hospital in Ankara. According to our results, there is a major MRSA clone with a potential to spread in our hospital. Infection control measures should be directed toward restricting the further spread of this clone. Therefore, in accordance with these findings, a surveillance culturing program should be established.

mecA Locus diversity in methicillin-resistant Staphylococcus aureus isolates in Brisbane, Australia, and the development of a novel diagnostic procedure for the Western Samoan phage pattern clone

An emerging public health phenomenon is the increasing incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections that are acquired outside of health care facilities. One lineage of community-acquired MRSA (CA-MRSA) is known as the Western Samoan phage pattern (WSPP) clone. The central aim of this study was to develop an efficient genotyping procedure for the identification of WSPP isolates. The approach taken was to make use of the highly variable region downstream of mecA in combination with a single nucleotide polymorphism (SNP) defined by the S. aureus multilocus sequence typing (MLST) database. The premise was that a combinatorial genotyping method that interrogated both a highly variable region and the genomic backbone would deliver a high degree of informative power relative to the number of genetic polymorphisms interrogated. Thirty-five MRSA isolates were used for this study, and their gene contents and order downstream of mecA were determined. The CA-MRSA isolates were found to contain a truncated mecA downstream region consisting of mecA-HVR-IS431 mec-dcs-Ins117, and a PCR-based method for identifying this structure was developed. The hospital-acquired isolates were found to contain eight different mecA downstream regions, three of which were novel. The Minimum SNPs computer software program was used to mine the S. aureus MLST database, and the arcC 272G polymorph was identified as 82% discriminatory for ST-30. A real-time PCR assay was developed to interrogate this SNP. We found that the assay for the truncated mecA downstream region in combination with the interrogation of arcC position 272 provided an unambiguous identification of WSPP isolates.

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.

Heterogeneity of methicillin-resistant Staphylococcus aureus isolated in Norway

Our objective was to look for differences in susceptibility patterns between Norwegian and imported methicillin-resistant Staphylococcus aureus (MRSA) strains. All MRSA isolates from the participating hospitals (87 isolates from 81 patients) throughout the period 1994-98 were examined, to study the clonal distribution of MRSA isolated in Norway and to identify any epidemic clones among the isolates. We found that imported isolates were resistant to an average of 5.6 antibiotics, while Norwegian isolates were resistant to an average of 2.6 antibiotics. MRSA isolates imported to Norway are more often multiresistant than domestic isolates. MRSA isolates in Norway show a striking diversity. Epidemic clones are present, but no single clone is predominant.

STAR gene restriction profile analysis in epidemiological typing of methicillin-resistant Staphylococcus aureus: description of the new method and comparison with other polymerase chain reaction (PCR)-based methods

A method based on restriction profile analysis of the STAR repetitive element PCR (STAR-RP PCR) product obtained by digestion with AluI and Tru9I was developed for typing methicillin resistant Staphylococcus aureus (MRSA). We evaluated a well defined collection of MRSA from Argentina, previously characterized by PFGE (pulsed field gel electrophoresis) of chromosomal SmaI digests and hybridization with DNA probes for probes ClaI-mecA and ClaI-Tn554. We comparatively evaluated STAR-RP analysis with other PCR based methods such as Inter IS256-PCR, Rep-MP3 PCR and Coa-RP. The discriminatory power (D) of STAR-RP (0.86) was similar to that of PFGE (0.84) at the type level. Comparable results were obtained with Inter IS256 PCR (0.85) and Rep-MP3 PCR (0.80). A lower value (0.74) was obtained for Coa-RP. An excellent reproducibility (100%) of STAR-RP was observed. Good concordance between STAR-RP and other molecular typing methods was found for MRSA isolates (n = 39). STAR-RP typing showed 87% concordance with mecA::Tn554::PFGE, 87% with Inter IS256 PCR and 71% with Rep-MP3 typing. STAR-RP is suggested as an adequate molecular typing assay for MRSA epidemiologic assessment.

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.

Genotyping of methicillin-resistant Staphylococcus aureus by assaying for the presence of variable elements associated with mecA

The region surrounding mecA in methicillin-resistant Staphylococcus aureus (MRSA) is highly variable. We describe an approach for the rapid genotyping of MRSA by assaying for the presence or absence of variable or mobile elements previously shown to be associated with the mecA region.

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.

Identification of a novel methicillin-resistant Staphylococcus aureus epidemic clone in Córdoba, Argentina, involved in nosocomial infections

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are increasingly a main health concern worldwide for hospitalized patients. In addition, the prevalence of community-acquired infection has risen continuously during the last few years. Some MRSA clones spread easier than others within the hospital environment and therefore are frequently implicated in outbreaks. Thus, the spread of a unique epidemic multiresistant clone, the so-called South American clone, is the main cause of nosocomial infections produced by this bacterium in Brazil and in some regions of Argentina, Chile, and Uruguay. In the present work we describe the identification of a novel clone of MRSA that is involved in nosocomial infections and that shows a prevalence as high as that for the South American clone. A total of 53 consecutive single-patient MRSA isolates were recovered during a 3-month period (May to July 1999) from six different hospitals (955 beds) in Córdoba. The isolates were initially typed according the antibiotic resistance and phage susceptibility patterns, followed by genotyping using pulsed-field gel electrophoresis (PFGE). PFGE analysis of the 53 MRSA isolates revealed six major types (A to F) and 25 subtypes. The B-type DNA pattern was indistinguishable from that of the South American epidemic clone observed in 34% of the isolates. A novel highly prevalent clone, showing the A-type DNA pattern and representing 38% of the isolates, was also identified. Moreover, the most frequent subtype of the A clonal family triggered an outbreak in a hospital 2 months later, further confirming its epidemic feature.

Development of a Canadian standardized protocol for subtyping methicillin-resistant Staphylococcus aureus using pulsed-field gel electrophoresis

A panel of 24 methicillin-resistant Staphylococcus aureus strains was distributed to 15 laboratories in Canada to evaluate their in-house pulsed-field gel electrophoresis (PFGE) protocols and interpretation criteria. Attempts to compare fingerprint images using computer-aided analysis were not successful due to variability in individual laboratory PFGE protocols. In addition, individual site interpretation of the fingerprint patterns was inadequate, as 7 of 13 sites (54%) made at least one error in interpreting the fingerprints from the panel. A 2-day standardized PFGE protocol (culture to gel image) was developed and distributed to all of the sites. Each site was requested to use the standardized protocol on five strains from the original panel. Thirteen sites submitted gel images for comparisons. The protocol demonstrated excellent reproducibility and allowed interlaboratory comparisons with Molecular Analyst DST software (Bio-Rad) and 1.5% band tolerance.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Colombian hospitals: dominance of a single unique multidrug-resistant clone

The first study on the molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) isolates from Colombia was performed as part of a global surveillance established by the CEM/NET Initiative, under Project RESIST. Seventy-six MRSA isolates recovered from five hospitals during 1996-1998 were analyzed by the hybridization of ClaI restriction digests with mecA- and Tn554-specific probes, and by pulsed-field gel electrophoresis (PFGE) of chromosomal SmaI digests. All MRSA isolates, with one exception, belonged to a single clonal type II::NH::D. This clone, which was previously described among MRSA isolates recovered in the early 1990s in European and New York and South American hospitals, showed resistance to beta-lactam antibiotics only and appeared to be associated almost exclusively with pediatric infections ("Pediatric clone" of MRSA). While sharing identical molecular typing properties with the Pediatric clone, the Colombian isolates differed by extensive multidrug resistance and were recovered from patients of all ages. It is also noteworthy that the Brazilian clone of MRSA (XI::B::B), another multidrug-resistant international clone currently widely spread in Brazil, Argentina, Uruguay, Chile, and also in several European countries, was completely absent from this set of isolates from Colombia.

Three-year assessment of methicillin-resistant Staphylococcus aureus clones in Latin America from 1996 to 1998

Four hundred ninety-nine methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from 1996 to 1998 from 22 hospitals in five countries of Latin America-Argentina, Brazil, Chile, Uruguay and Mexico-were examined for antimicrobial susceptibility and clonal type in order to define the endemic clones in those hospitals. The hybridization of ClaI restriction digests with the mecA- and Tn554-specific DNA probes combined with pulsed-field gel electrophoresis of chromosomal SmaI digests (ClaI-mecA::ClaI-Tn554::PFGE clonal types) documented not only the predominance and persistence of the Brazilian clone (XI::B::B) in Brazil (97%) and Argentina (86%) but also its massive dissemination to Uruguay (100%). Moreover, a close relative of the Brazilian clone (XI::kappa::B) was highly represented in Chile (53%) together with a novel clone (47%) (II::E'::F) resistant to pencillin, oxacillin, ciprofloxacin, chloramphenicol, clindamycin, erythromycin, and gentamicin. A unique clonal type (I::NH::M) was detected in Mexico among pediatric isolates and was resistant to penicillin, oxacillin, and gentamicin only. This study clearly documented the very large capacity for geographic expansion and the persistence of the Brazilian clone, contributing not only to the increasing uniformity of the MRSA in South America but worldwide as well.

Genetic relatedness of multidrug-resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates from SENTRY Antimicrobial Resistance Surveillance Centers worldwide, 1998

We reviewed Staphylococcus aureus bloodstream infection isolates from SENTRY centers worldwide during 1998 to evaluate the molecular epidemiology of multiply drug-resistant methicillin (oxacillin)-resistant S. aureus (MDR-MRSA). MDR-MRSA was defined as a S. aureus isolate with a MIC for oxacillin at >2 microg/ml and with four or more additional resistances. A total of 325 unique patient isolates of MDR-MRSA from five continents were analyzed using ribotyping and pulsed-field gel electrophoresis (PFGE). The frequency of MDR-MRSA among all S. aureus BSI isolates ranged from only 2.2% in Canada to 35.6% in the Asia-Pacific region. Forty-eight ribotypes (RT) were distinguished, but over 80% of the isolates were contained within the 10 most prevalent RTs. The most common RT, RT 184.5, which included 30% of all MDR-MRSA, was found on four of five continents. PFGE provided superior discrimination and identified numerous clusters of possible clonal dissemination of MDR-MRSA within individual medical centers and between institutions that are in geographic proximity. In four instances, strains with indistinguishable PFGE patterns were found on more than one continent. The predominant PFGE subtype in South America (RT 893.5/Ia) was isolated from patients at centers in Brazil, Argentina, and Portugal, and closely related subtypes were isolated in Chile and Italy. There is great geographic variation in rates of methicillin- and multidrug-resistance among S. aureus bloodstream isolates worldwide. Although many MDR-MRSA strains group geographically, a few closely related epidemic strains have wide regional and even global range.

Patterns of multidrug resistance among methicillin-resistant hospital isolates of coagulase-positive and coagulase-negative staphylococci collected in the international multicenter study RESIST in 1997 and 1998

The primary purpose of the multicenter international study "RESIST" was to obtain an update on the degree of multidrug resistance among methicillin-resistant staphylococci collected from a geographically diverse sample. A total of 3,307 staphylococcal isolates were recovered from single patients and primarily from clinical specimens that were collected at 20 collaborating regional health centers located in several countries in Europe, Asia, and Latin America during a 3- to 4-month period each in 1997 and 1998. All strains were deposited at the Laboratory of Molecular Genetics at ITQB/UNL in Oeiras, Portugal, for quality control and for testing by microbiological and molecular typing techniques; the Laboratory of Microbiology at The Rockefeller University serving as organizational center. The majority of strains, 3,100, were methicillin-resistant, of which 1,749 were coagulase positive (methicillin-resistant Staphylococcus aureus, MRSA), and 1,351 were coagulase negative (methicillin-resistant coagulase negative staphylococci, MRCNS). The overall frequency of drug resistance traits among the 1,749 MRSA strains was high (over 70% and up to and over 90% of the strains) to ciprofloxacin, erythromycin, clindamycin, gentamicin, and tetracycline, and was somewhat less frequent to sulfamethoxazole-trimethoprim (45%), chloramphenicol (30%), and rifampin (38%). None of the 3,307 staphylococcal isolates showed reduced susceptibility to vancomycin except for a single methicillin-resistant coagulase-negative isolate. The great majority of staphylococci were also susceptible to the new antimicrobial Synercid. In contrast, resistance to teicoplanin was significant among methicillin-resistant strains of coagulase-negative staphylococci, particularly among Staphylococcus haemolyticus. MRSA isolates showed marked geographic variation in their patterns of multiresistance, most likely reflecting the properties of unique multiresistant MRSA clones dominant in the hospitals that provided the MRSA isolates from the various geographic areas. The multiresistance patterns of MRSA strains and strains of methicillin-resistant coagulase-negative staphylococci originating at the same country source also showed striking differences, suggesting that resistance to antimicrobial agents emerged under different antibiotic pressures in these bacterial species.

Genetic organization of the downstream region of the mecA element in methicillin-resistant Staphylococcus aureus isolates carrying different polymorphisms of this region

We describe here the genetic organization of the mec element downstream of the mecA gene in 34 different methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates carrying 13 of the most frequent polymorphisms of mecA and representing the major epidemic clones of MRSA. All polymorphisms carried three common genetic elements: the hypervariable region, a copy of IS431, and a unique 2-kb sequence (downstream constant segment, or dcs) for which no homologous sequences are found in data banks. Polymorphisms of the downstream region were shown to be caused by the presence of linearized plasmids flanked by insertion sequences (pUB110, pT181, and pI258) and the autonomous insertion sequence IS256.

Three-year surveillance study of nosocomial bacterial resistance in Argentina. The Antimicrobial Committee; and the National Surveillance Program (SIR) Participants Group

INTRODUCTION

A national surveillance program (SIR) was introduced in 1996 in Argentina by the Antimicrobial Committee of the Argentinean Society for Microbiology to assess bacterial resistance. The present study reports the rates of nosocomial bacterial resistance found by this program.

METHODS

A 2-month point-prevalence study was conducted twice yearly (i.e., April-May and October-November) from 1996 to 1998, by 27 Argentinean centers. Susceptibility testing was carried out by the disk diffusion method following the National Committee for Clinical Laboratory Standards guidelines.

RESULTS

In all, 6343 isolates recovered from 5603 inpatients (> or =48-hr hospitalization) were included. Methicillin resistance was 58% and 56% in Staphylococcus aureus and coagulase-negative staphylococci (CNS), respectively. Although no vancomycin resistance was found in staphylococci, 2% and 8% of the S. aureus and CNS strains, respectively, proved resistant to teicoplanin. No ampicillin resistance was displayed by Enterococcus faecalis. High-level gentamicin and streptomycin resistance in enterococci were 33% and 37%, respectively. Acquired glycopeptide resistance in enterococci emerged in 1997 (2%). Imipenem resistance in Acinetobacter spp and Pseudomonas aeruginosa was 9% and 21%, respectively. Among Enterobacteriaceae, 1% and 5% of the Klebsiella pneumoniae and Enterobacter cloacae isolates, respectively, proved resistant to imipenem. Ceftazidime and cefepime resistance was found in 63% and 33% of the E. cloacae strains. Resistance to extended-spectrum cephalosporins was shown by 48%, 26%, and 8% of the K. pneumoniae, Proteus mirabilis, and Escherichia coli isolates, respectively.

CONCLUSIONS

The alarming rates of resistance found in this study provide compelling evidence of the need for more rational use of antimicrobial agents in Argentina.

Methicillin-resistant Staphylococcus aureus (MRSA) isolated at Fukuoka University Hospital and hospitals and clinics in the Fukuoka city area

Bacteriological and epidemiological studies were carried out on 106 isolates of methicillin-resistant Staphylococcus aureus (MRSA) isolated at our hospital (56 isolates) and from 15 other hospitals and clinics (50 isolates) in the Fukuoka city area. Strains were studied regarding coagulase-type, beta-lactamase production, and antimicrobial susceptibility; genotype studies used pulsed-field gel electrophoresis (PFGE) with cluster analysis. The majority of isolates produced coagulase type II (75.5%) and beta-lactamase (72. 6%); there was high susceptibility to arbekacin (84.9%) but no resistance to vancomycin. Dendrogram analysis of PFGE patterns identified five major clusters that generally correlated with coagulase-type and beta-lactamase production. Though isolates of two clusters were both coagulase type II and beta-lactamase producing, which was the most common circulating strain both in our hospital and other hospitals and clinics, dendrogram analysis of PFGE patterns showed that they were heterogeneous. Four genetically identical isolates from the same hospital suggested the existence of hospital-specific strains. Nine genetically identical isolates from intensive care units (ICU) in our hospital suggested that a unique strain of MRSA was found there. It had not been transmitted from another area. PFGE with cluster analysis seemed to be an essential tool to detect area-specific or hospital-specific strains undifferentiated by phenotyping. These findings confirmed that a combination of PFGE, including cluster analysis along with coagulase-type and beta-lactamase production may provide more detailed information for the epidemiological study of MRSA.

Methicillin-resistant Staphylococcus aureus clonal types in the Czech Republic

Molecular surveillance studies have documented the extensive spread of methicillin-resistant Staphylococcus aureus (MRSA) clones. Studies carried out by Centro de Epidemiologia Molecular-Network for Tracking Gram-Positive Pathogenic Bacteria (CEM/NET) led to the identification of two international multidrug-resistant strains, which were designated as the Iberian and Brazilian MRSA clones and which were defined by multiple genomic typing methods; these included ClaI restriction digests hybridized with mecA- and Tn554-specific DNA probes and pulsed-field gel electrophoresis (PFGE). The genotypic characteristics of these clones are distinct: the Iberian clone is defined as mecA type I, Tn554 type E (or its variants), and PFGE pattern A (I:E:A), whereas the Brazilian clone is defined as mecA type XI (or its variants), Tn554 type B, and PFGE pattern B (XI:B:B). In this study, we characterized 59 single-patient isolates of MRSA collected during 1996 and 1997 at seven hospitals located in Prague and five other cities in the Czech Republic by using the methodologies mentioned above and by using ribotyping of EcoRI and HindIII digests hybridized with a 16S-23S DNA probe. The Brazilian MRSA clone (XI:B:B) was the major clone (80%) spread in two hospitals located in Prague and one located in Brno; the Iberian MRSA clone (I:E:A or its variant I:DD:A), although less representative (12%), was detected in two hospitals, one in Prague and the other in Plzen. Almost all the strains belonging to clone XI:B:B (45 of 47) corresponded to a unique ribotype, E1H1, whereas most strains of the I:E:A and I:DD:A clonal types (6 of 7) corresponded to ribotype E2H2.

Detection of an archaic clone of Staphylococcus aureus with low-level resistance to methicillin in a pediatric hospital in Portugal and in international samples: relics of a formerly widely disseminated strain?

Close to half of the 878 methicillin-resistant Staphylococcus aureus (MRSA) strains recovered between 1992 and 1997 from the pediatric hospital in Lisbon were bacteria in which antibiotic resistance was limited to beta-lactam antibiotics. The other half were multidrug resistant. The coexistence of MRSA with such unequal antibiotic resistance profiles prompted us to use molecular typing techniques for the characterization of the MRSA strains. Fifty-three strains chosen randomly were typed by a combination of genotypic methods. Over 90% of the MRSA strains belonged to two clones: the most frequent one, designated the "pediatric clone," was reminiscent of historically "early" MRSA: most isolates of this clone were only resistant to beta-lactam antimicrobials and remained susceptible to macrolides, quinolones, clindamycin, spectinomycin, and tetracycline. They showed heterogeneous and low-level resistance to methicillin (MIC, 1.5 to 6 microg/ml), carried the ClaI-mecA polymorph II, were free of the transposon Tn554, and showed macrorestriction pattern D (clonal type II::NH::D). The second major clone was the internationally spread and multiresistant "Iberian" MRSA with homogeneous and high-level resistance to methicillin (MIC, >200 microg/ml) and clonal type I::E::A. Surprisingly, the multidrug-resistant and highly epidemic Iberian MRSA did not replace the much less resistant pediatric clone during the 6 years of surveillance. The pediatric clone was also identified among contemporary MRSA isolates from Poland, Argentina, The United States, and Colombia, and the overwhelming majority of these were also associated with pediatric settings. We propose that the pediatric MRSA strain represents a formerly widely spread archaic clone which survived in some epidemiological settings with relatively limited antimicrobial pressure.