Beta-lactams and beta-lactamase-inhibitors in current- or potential-clinical practice: a comprehensive update

The use of successive generations of beta-lactams has selected successive generations of beta-lactamases including CTX-M ESBLs, AmpC beta-lactamases, and KPC carbapenamases in Enterobacteriaceae. Moreover, this cephalosporin resistance, along with rising resistance to fluoroquinolones, is now driving the use of carbapenems and unfortunately the carbapenem resistance has emerged markedly, especially in Acinetobacter spp. due to OXA- and metallo-carbapenemases. The industry responded to the challenge of rising resistance and recently developed some novel beta-lactams such as ceftobiprole, ceftaroline etc. and many beta-lactam compounds, including beta-lactamase-inhibitors, such as BMS-247243, S-3578, RWJ-54428, CS-023, SMP-601, NXL 104, BAL 30376, LK 157, and so on are under trials. This review provides the comprehensive accounts of the developments in penicillins, cephalosporins, carbapenems, and beta-lactamase-inhibitors, and the insight about medicinal chemistry, mechanism(s) of action and resistance, potential strategies to overcome resistance due to beta-lactamases, and also the recent advancements in the development of newer beta-lactam compounds; some of which are still under trials and yet to be classified. This review will fill the gap since previously published reviews and will serve as a comprehensive update on the current topic.

Laboratory tools and strategies for methicillin-resistant Staphylococcus aureus screening, surveillance and typing: state of the art and unmet needs

The public health burden caused by methicillin-resistant Staphylococcus aureus (MRSA) infections is now widely recognized, and is a cause of public alarm. Effective MRSA risk management in the healthcare system as well as in the community should rely on accurate detection of reservoirs and sources of transmission, as well as on close monitoring of the impact of interventions on disease incidence and bacterial dissemination. MRSA carrier screening and disease surveillance, coupled with molecular typing, are key information tools for integrated MRSA control and individual risk assessment. These tools should be tailored to the distinct needs of local interventions and national prevention programmes. Surveillance schemes should primarily inform local staff and serve as quality assurance about MRSA risk management. New technologies, including the use of selective culture media and real-time PCR assays, allow faster detection of MRSA carriers upon admission or during stay in healthcare institutions. More research is needed to ascertain their cost-effectiveness for MRSA control. Likewise, tremendous progress has been made concerning molecular typing methods, with optimization and standardization of sequence-based technologies offering broad applicability and high throughput. However, no single S. aureus typing method is yet providing fully reliable information within the range of discrimination needed for public health action. Further refinement of genotyping methods and international harmonization of surveillance and typing schemes must be achieved to facilitate global MRSA control.

Novel CTX-M {beta}-lactamase genotype distribution and spread into multiple species of Enterobacteriaceae in Changsha, Southern China

OBJECTIVES

The aim of this study was to undertake a survey of the occurrence of CTX-M and SHV extended-spectrum beta-lactamase (ESBL) genotypes in Enterobacteriaceae from Hunan Province, China.

METHODS

Clinical isolates (425) from three major hospitals in Changsha, Hunan Province, were collected between October 2004 and July 2005, and their antimicrobial susceptibilities of the genotype of bla(CTX-M) and bla(SHV) were determined. Random amplified polymorphic DNA was used to characterize the clonality of all of the isolates.

RESULTS

The overall rate of ESBL-positive isolates was 33.4% (142/425). The dominant ESBLs were CTX-M types, and were found in 109/142 (76.8%) isolates comprising seven different genera/species, namely Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Proteus vulgaris and Providencia stuartii. The most common bla(CTX-M) genotypes were bla(CTX-M-14) (47.7%), bla(CTX-M-3) (29.4%) and bla(CTX-M-15) (17.4%). A novel gene derived from bla(CTX-M-15), bla(CTX-M-82) (Ala-40-->Pro), was identified.

CONCLUSIONS

The dominant ESBL genotype in Hunan Province was bla(CTX-M). The high prevalence (17.4%) of bla(CTX-M-15) has not previously been reported from China. Our results identify that an epidemic of bla(CTX-M) in Changsha, Hunan Province, has evolved with the appearance and spread of bla(CTX-M-15) against the dominant genotypes bla(CTX-M-14) and bla(CTX-M-3.) The worldwide dominance of bla(CTX-M-15) could be poised to spread to China, displacing the current prevailing genotypes.

Pre-clinical experience with daptomycin

Daptomycin is a broad-spectrum, bactericidal agent active against Gram-positive bacteria, acting largely and unusually through membrane depolarization. Activity is markedly affected in vitro by the availability of calcium ions, and its high molecular weight with associated poor diffusion means that conventional disc diffusion testing is not reliable (and as a consequence not available). In order to allow susceptibility categorization, it is recommended that the MIC be determined in the presence of a defined calcium concentration. The activity of daptomycin is concentration-dependent with a prolonged post-antibiotic effect. It has linear pharmacokinetics, with a half-life of 8-9 h, the primary route of excretion is renal, it exhibits serum protein binding of approximately 92% and there is no interaction with the P450 cytochrome. Daptomycin is inactivated by surfactant in the lung and, in consequence, is not recommended for the treatment of respiratory infections. Daptomycin is currently licensed for the treatment of complicated skin and soft tissue infections and for bacteraemia and right-sided endocarditis due to methicillin-susceptible and -resistant Staphylococcus aureus. To date, daptomycin-resistant bacteria have rarely been isolated from patients, although increases in vancomycin MIC may be linked to reduced susceptibility to daptomycin. Close monitoring of resistance is essential to maintain the clinical utility of the drug. Using once-daily dosing, daptomycin has been generally well tolerated; however, weekly monitoring of creatinine phosphokinase is recommended, as myopathy in skeletal muscles has been seen, albeit rarely. The rapid bactericidal action of daptomycin makes it a useful addition to the therapeutic armamentarium for the treatment of Gram-positive infections, providing a valuable alternative to vancomycin when it is inappropriate or resistance is a problem.

Prevalence and clonality of extended-spectrum beta-lactamases in Asia

Asia is almost certainly a part of the world in which extended-spectrum beta-lactamases (ESBLs) have emerged de novo, with some early antimicrobial resistance studies showing high levels of the ESBL phenotype, particularly among Klebsiella, and most notably in China, Korea, Japan and India. There is a lack of genotyping studies but work from the late 1990s suggests that SHV-5 and SHV-12 were most common then, with only very rare reports of TEM-related ESBL genes. As in other parts of the world, quite marked differences have since been seen in the pattern of ESBL genes, particularly in relation to the CTX-M family. The early emergence of TOHO CTX-M-2 in Japan contrasted with CTX-M-3 and -14 in China and many other parts of the Far East, suggesting the separate transfer of genes from the genome of Kluyvera spp. to mobile genetic elements in human-associated Enterobacteriaceae. ESBL production rates are now very high compared with Europe. In most countries, there are mixtures of CTX-M types, with VEB appearing significantly in Vietnam and Thailand, and ESBL isolates from India being completely dominated by the presence of bla(CTX-M-15) alone, with no other CTX-M types reported. With the total population of India and China being c. 2.4 billion and with faecal carriage rates of, probably, c. 10%, these countries represent major reservoirs of bla(CTX-M) genes. Increasing international travel and trade will lead to the movement of many of these ESBL genes. The high prevalence of ESBL genes in Asia means that the empirical treatment of serious infections with beta-lactam antibiotics, except carbapenems, is seriously compromised.

Molecular epidemiology of clinically significant antibiotic resistance genes

Antimicrobials were first introduced into medical practice a little over 60 years ago and since that time resistant strains of bacteria have arisen in response to the selective pressure of their use. This review uses the paradigm of the evolution and spread of beta-lactamases and in particular beta-lactamases active against antimicrobials used to treat Gram-negative infections. The emergence and evolution particularly of CTX-M extended-spectrum beta-lactamases (ESBLs) is described together with the molecular mechanisms responsible for both primary mutation and horizontal gene transfer. Reference is also made to other significant antibiotic resistance genes, resistance mechanisms in Gram-negative bacteria, such as carbepenamases, and plasmid-mediated fluoroquinolone resistance. The pathogen Staphylococcus aureus is reviewed in detail as an example of a highly successful Gram-positive bacterial pathogen that has acquired and developed resistance to a wide range of antimicrobials. The role of selective pressures in the environment as well as the medical use of antimicrobials together with the interplay of various genetic mechanisms for horizontal gene transfer are considered in the concluding part of this review.

A study of the efficacy and cost-effectiveness of MRSA screening and monitoring on surgical wards using a new, rapid molecular test (EMMS)

BACKGROUND

MRSA is a significant contributor to prolonged hospital stay, poor clinical outcome and increased healthcare costs amongst surgical patients. A PCR test has been developed for rapid detection of MRSA in nasal swabs. The aims of this study are (1) to estimate the effectiveness of screening using this rapid PCR tests vs culture in reducing MRSA cross-infection rates; (2) to compare the cost of each testing strategy, including subsequent health care costs; and (3) to model different policies for the early identification and control of MRSA infection in surgical patients.

METHODS/DESIGN

The study is a prospective two-period cross-over study set in 7 surgical wards covering different surgical specialities. A total of 10,000 patients > 18 years will be tested over 16 months. The only difference between the two study periods is the method used for the detection of MRSA in each ward (rapid v conventional culture), with all other infection control practices remaining consistent between the arms. The study has been designed to complement routine practice in the NHS. Outcomes are MRSA cross-infection rates (primary outcome) and need for antibiotic therapy and MRSA-related morbidity. Parallel economic and modelling studies are being conducted to aid in the interpretation of the results and to evaluate the cost-effectiveness of the rapid PCR screening strategy.

DISCUSSION

This paper highlights the design, methods and operational aspects of a study evaluating rapid MRSA screening in the surgical ward setting.

An IS6110-targeting fluorescent amplified fragment length polymorphism alternative to IS6110 restriction fragment length polymorphism analysis for Mycobacterium tuberculosis DNA fingerprinting

A rapid, simple and highly discriminatory DNA fingerprinting methodology which produces data that can be easily interpreted, compared and transported is the ultimate goal for studying the epidemiology of Mycobacterium tuberculosis. A novel TaqI fluorescent amplified fragment length polymorphism (fAFLP) approach to M. tuberculosis DNA fingerprinting that targeted the variable IS6110 marker was developed in this study. The new method was tested for specificity and reproducibility, and compared with the standard reference IS6110 restriction fragment length polymorphism (RFLP) method for a panel of 78 isolates. Clustering conflicts between the two methods were resolved using mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) data. Comparison with an in-silico digestion of strain H37Rv showed that fAFLP-detected fragments were highly specific in vitro. The reproducibility of repeated digestions of strain H37Rv was 100%. Clustering results obtained by fAFLP and RFLP were highly congruent, with fAFLP allocating 97% of RFLP-clustered isolates to the same eight clusters as RFLP. Two single-copy isolates that had been clustered by RFLP were not clustered by fAFLP, but the MIRU-VNTR patterns of these isolates were different, indicating that the RFLP data had falsely clustered these isolates. Analysis by fAFLP will allow rapid screening of isolates to confirm or refute epidemiological links, and thereby provide insights into the frequency, conservation and consequences of specific transposition events.

Genome analysis shows a common evolutionary origin for the dominant strains of Mycobacterium tuberculosis in a UK South Asian community

We have investigated the Mycobacterium tuberculosis strain types present in the South Asian population of the UK, in which tuberculosis is particularly prevalent. In contrast to the widespread Beijing strains which have the variable number tandem repeats (VNTR) profile 42435, isolates with the VNTR profile 42235, jointly with 02335 or 42234 profiles, appear more frequently in tuberculosis patients of South Asian ethnic origin (SA-strains) in the UK than in any other ethnic group. Using microarray-based comparative genomics to distinguish total or partially deleted genes, we found that three of the common deleted regions in the SA-strains were identical to some deleted genes in the strain CH, which caused an outbreak among South Asian patients in Leicester in 2001 but were different from genomic deletions found in Beijing/W strains. Analysis of some of the deleted regions revealed differences in comparison to the strain CH including the polymorphism in some of the PE/PPE and Esat-6 genes, which may be responsible for the diversity of antigenic variation or differences in the activation of the host immune response. Interrupted genes or the replacement by insertion elements was confirmed in some of the deleted genomic regions. Our results are consistent with the hypothesis that the SA-strains may present common features, implying a common origin for this group of strains.

Rapid recontamination with MRSA of the environment of an intensive care unit after decontamination with hydrogen peroxide vapour

Meticillin-resistant Staphylococcus aureus (MRSA) persists in the hospital environment and conventional cleaning procedures do not necessarily eliminate contamination. A prospective study was conducted on an intensive care unit to establish the level of environmental contamination with MRSA, assess the effectiveness of hydrogen peroxide vapour (HPV) decontamination and determine the rate of environmental recontamination. MRSA was isolated from 11.2% of environmental sites in the three months preceding the use of HPV and epidemiological typing revealed that the types circulating within the environment were similar to those colonising patients. After patient discharge and terminal cleaning using conventional methods, MRSA was isolated from five sites (17.2%). After HPV decontamination but before the readmission of patients, MRSA was not isolated from the environment. Twenty-four hours after readmitting patients, including two colonized with MRSA, the organism was isolated from five sites. The strains were indistinguishable from a strain with which a patient was colonized but were not all confined to the immediate vicinity of the colonized patient. In the eight weeks after the use of HPV, the environment was sampled on a weekly basis and MRSA was isolated from 16.3% sites. Hydrogen peroxide vapour is effective in eliminating bacteria from the environment but the rapid rate of recontamination suggests that it is not an effective means of maintaining low levels of environmental contamination in an open-plan intensive care unit.

Cluster of human tuberculosis caused by Mycobacterium bovis: evidence for person-to-person transmission in the UK

BACKGROUND

Despite a recent resurgence in the incidence of bovine tuberculosis in UK cattle herds, no associated rise in the number of cases in man has been noted. Disease due to human Mycobacterium bovis infection usually occurs in older patients, in whom drinking unpasteurised milk in the past is the probable source of infection. Person-to-person transmission is very rare.

METHODS

After identification of two epidemiologically-linked cases of human M bovis infection through routine laboratory and surveillance activities, all patients identified with M bovis infection in the Midlands from 2001-05 (n=20) were assessed by DNA fingerprinting (MIRU-VNTR and spoligotyping), with additional interviews for patients with a clustered strain.

FINDINGS

A cluster of six cases was identified. All clustered cases were young and UK-born; five patients had pulmonary disease, and one patient died due to M bovis meningitis, with four patients possessing factors predisposing to tuberculosis. All patients had common social links through visits to bars in two different areas. With the exception of the first case, there was an absence of zoonotic links or consumption of unpasteurised dairy products, suggesting that person-to-person transmission had occurred.

INTERPRETATION

This report of several instances of M bovis transmission between people in a modern urban setting emphasises the need to maintain control measures for human and bovine tuberculosis. Transmission and subsequent disease was probably due to a combination of host and environmental factors. Prospective surveillance and DNA fingerprinting identified the cluster, enabling health protection teams to set up control measures and prevent further transmission.

Subtyping of ST22-MRSA-IV (Barnim epidemic MRSA strain) at a university clinic in Germany from 2002 to 2005

Emergence of the meticillin-resistant Staphylococcus aureus (MRSA) Barnim epidemic strain (ST22-MRSA-IV) was demonstrated recently at University Hospital in Magdeburg, Germany. To aid the study of transmission events, it is important to have an epidemiological typing method with the ability to distinguish among MRSA isolates. The aim of this study was to determine the ability of phenotypic and genotypic methods to type ST22-MRSA-IV strains within a hospital for microevolution events. Forty-two ST22-MRSA-IV strains collected from 2002 to 2005 were analysed using antimicrobial testing, toxin gene analysis, PFGE, spa typing, fluorescent amplified fragment length polymorphism (fAFLP) and determination of staphylococcal interspersed repeat units (SIRUs). Four different antimicrobial patterns were observed. The majority of the isolates (n=31) were resistant towards erythromycin, ciprofloxacin and clindamycin, in addition to penicillin and oxacillin. All strains harboured the sec gene and showed a homogeneous profile of toxin genes. One isolate was typed as spa t022, two as spa t474 and the remainder belonged to spa type t032. PFGE yielded eight profiles and SIRU typing resulted in six different patterns. The fAFLP technique subdivided the individual PFGE profiles, but the grouping of isolates differed from that obtained by PFGE or SIRU typing. These results showed a diversity of ST22-MRSA-IV strains within a narrow clinical setting, indicating microevolution of the Barnim MRSA clone. The ability to distinguish among MRSA strains within an endemic setting will lead to a greater understanding of the transmission of MRSA and is necessary to be able to control the spread of various clones.

High-level gentamicin resistance mediated by a Tn4001-like transposon in seven nonclonal hospital isolates of Streptococcus pasteurianus

We report on the first occurrence of high-level gentamicin resistance (MICs > or = 512 microg/ml) in seven clinical isolates of Streptococcus pasteurianus from Hong Kong. These seven isolates were confirmed to be the species S. pasteurianus on the basis of nucleotide sequencing of the superoxide dismutase (sodA) gene. Epidemiological data as well as the results of pulse-field gel electrophoresis analysis suggested that the seven S. pasteurianus isolates did not belong to the same clone. Molecular characterization showed that they carried a chromosomal, transposon-borne resistance gene [aac(6')Ie-aph(2'')Ia] which was known to encode a bifunctional aminoglycoside-modifying enzyme. The genetic arrangement of this transposon was similar to that of Tn4001, a transposon previously recovered from Staphylococcus aureus and other gram-positive isolates. Genetic linkage with other resistance elements, such as the ermB gene for erythromycin resistance, was not evident. On the basis of these findings, we suggest that routine screening for high-level gentamicin resistance should be recommended for all clinically significant blood culture isolates. This is to avoid the inadvertent use of short-course combination therapy with penicillin and gentamicin, which may lead to the failure of treatment for endocarditis, the selection of drug-resistant Streptococcus pasteurianus and other gram-positive organisms, as well as the unnecessary usage of gentamicin, a drug with potential toxicity.

A novel reverse-line hybridization assay for identifying genotypes of CTX-M-type extended-spectrum β-lactamases

OBJECTIVES

To develop a reverse-line hybridization assay to identify CTX-M genotypes, potentially useful for large-scale investigation of surveillance collections.

METHODS

Isolates carrying previously characterized bla(CTX-M) genes were used to develop the method. In addition, 334 isolates from five separate surveys were used to validate the method. CTX-M group was known from an independent multiplex PCR for 122 isolates and genotype was confirmed for 80 isolates by DNA sequencing. A multiplex PCR was designed to amplify a genotype-specific region within the bla(CTX-M) open-reading frame. Oligonucleotides were designed to hybridize to regions within each amplicon, covering mutations that distinguish among bla(CTX-M) genotypes.

RESULTS

CTX-M phylogenetic groups were identified by the multiplex PCR with 100% concordance. The reverse-line hybridization assay specifically identified commonly-reported variants within these groups (98.7% concordance).

CONCLUSIONS

The hybridization method enabled precise identification of CTX-M genes, rather than just to group level, without the need for DNA sequencing. In its present format, the method enables 43 isolates to be processed per membrane, giving results within one working day. It is a useful tool for the epidemiological investigation of bla(CTX-M) genes among survey collections of Enterobacteriaceae.

Occurrence, prevalence and genetic environment of CTX-M beta-lactamases in Enterobacteriaceae from Indian hospitals

OBJECTIVES

To determine occurrence, prevalence and CTX-M genotypes produced by Enterobacteriaceae from clinical samples from three geographically distant Indian hospitals and to detect linkage of IS26 with bla(CTX-M) and map its precise insertion position.

METHODS

A total of 130, non-duplicate Escherichia coli and Klebsiella pneumoniae resistant to a third-generation cephalosporin (3GC) from three Indian centres were screened for extended-spectrum beta-lactamase (ESBL) production using phenotypic detection methods. All isolates were screened for bla(CTX-M) using multiplex PCR. Precise CTX-M genotype was identified using reverse-line hybridization. All CTX-M-producing isolates were screened for linkage of IS26 with bla(CTX-M). DNA sequencing was used to map the exact insertion position of this mobile element.

RESULTS

Ninety-five of 130 3GC-resistant (73%) (73% of total E. coli, 72% of total K. pneumoniae) isolates were found to carry bla(CTX-M-15). No other CTX-M genotype was detected. IS26 linkage with bla(CTX-M-15) was detected in 31% of isolates carrying bla(CTX-M-15). DNA sequencing revealed variable insertion of this mobile element within tnpA of ISEcp1. RAPD-PCR typing demonstrated great diversity in isolates carrying bla(CTX-M-15); no predominant clone was identified.

CONCLUSIONS

In contrast with other studies where greater diversity exists, CTX-M-15 was the only CTX-M ESBL produced in this Indian collection of unrelated E. coli and K. pneumoniae. This is the first systematic survey report from India detecting CTX-M-type beta-lactamases This is also the first report indicating such high mobility/diversity of insertion of IS26 in close association with bla(CTX-M) in a single bacterial collection.

bla(IMP-9) and its association with large plasmids carried by Pseudomonas aeruginosa isolates from the People's Republic of China

A novel plasmid-mediated metallo-beta-lactamase (IMP-9) is described in seven isolates of Pseudomonas aeruginosa from Guangzhou, China, isolated in 2000. The gene was carried on a large (approximately 450-kb) IncP-2 conjugative plasmid. This is the first report of carriage of bla(IMP) genes on such large plasmids.

Multicenter antimicrobial susceptibility survey of gram-negative bacteria isolated from patients with community-acquired infections in the People's Republic of China

A survey of 2,099 gram-negative bacilli from community infections at seven centers in the People's Republic of China is reported. The rates of resistance of 1,615 isolates of the family Enterobacteriaceae were as follows: 40.8% for ciprofloxacin, 32.2% for gentamicin, 0% for imipenem or ertapenem, and 14.7% for cefotaxime. The rates of extended-spectrum beta-lactamase production were 16% for Escherichia coli and 17% for Klebsiella.

Use of variations in staphylococcal interspersed repeat units for molecular typing of methicillin-resistant Staphylococcus aureus strains

Staphylococcal interspersed repeat unit typing has previously been shown to have the ability to discriminate between epidemic methicillin-resistant Staphylococcus aureus strains in the United Kingdom. The current study illustrates its ability to distinguish between strains within an endemic setting thereby providing a rapid transportable typing method for the identification of transmission events.

Mycobacterium tuberculosis complex genetic diversity: mining the fourth international spoligotyping database (SpolDB4) for classification, population genetics and epidemiology

Background

The Direct Repeat locus of the Mycobacterium tuberculosis complex (MTC) is a member of the CRISPR (Clustered regularly interspaced short palindromic repeats) sequences family. Spoligotyping is the widely used PCR-based reverse-hybridization blotting technique that assays the genetic diversity of this locus and is useful both for clinical laboratory, molecular epidemiology, evolutionary and population genetics. It is easy, robust, cheap, and produces highly diverse portable numerical results, as the result of the combination of (1) Unique Events Polymorphism (UEP) (2) Insertion-Sequence-mediated genetic recombination. Genetic convergence, although rare, was also previously demonstrated. Three previous international spoligotype databases had partly revealed the global and local geographical structures of MTC bacilli populations, however, there was a need for the release of a new, more representative and extended, international spoligotyping database.

Results

The fourth international spoligotyping database, SpolDB4, describes 1939 shared-types (STs) representative of a total of 39,295 strains from 122 countries, which are tentatively classified into 62 clades/lineages using a mixed expert-based and bioinformatical approach. The SpolDB4 update adds 26 new potentially phylogeographically-specific MTC genotype families. It provides a clearer picture of the current MTC genomes diversity as well as on the relationships between the genetic attributes investigated (spoligotypes) and the infra-species classification and evolutionary history of the species. Indeed, an independent Naïve-Bayes mixture-model analysis has validated main of the previous supervised SpolDB3 classification results, confirming the usefulness of both supervised and unsupervised models as an approach to understand MTC population structure. Updated results on the epidemiological status of spoligotypes, as well as genetic prevalence maps on six main lineages are also shown. Our results suggests the existence of fine geographical genetic clines within MTC populations, that could mirror the passed and present Homo sapiens sapiens demographical and mycobacterial co-evolutionary history whose structure could be further reconstructed and modelled, thereby providing a large-scale conceptual framework of the global TB Epidemiologic Network.

Conclusion

Our results broaden the knowledge of the global phylogeography of the MTC complex. SpolDB4 should be a very useful tool to better define the identity of a given MTC clinical isolate, and to better analyze the links between its current spreading and previous evolutionary history. The building and mining of extended MTC polymorphic genetic databases is in progress.

Examination of specimens for mycobacteria in clinical laboratories in 21 countries: a 10-year review of the UK National Quality Assessment Scheme for Mycobacteria Culture

Results from clinical diagnostic microbiology laboratories taking part in the UK National Quality Assessment Service (UK NEQAS) scheme for Mycobacteria Culture between 1993 and 2003 were evaluated and assessed to determine whether the perceived increase in the use of rapid methods is improving time-to-positive reporting of results. Four simulated sputum specimens containing mycobacteria in mixed cultures with normal commensal organisms were distributed three times a year. Participating laboratories were required to report on the presence of 'mycobacteria' and on the time required to obtain a positive result. The overall level of performance with the mycobacteria culture external quality assessment specimens remained consistently high, with an average success rate of 94% over 10 years. The mean time-to-positive decreased from 24 to 17 days during the previous 8 years. A survey questionnaire, circulated in 2002, addressed the use of continuous automated mycobacterial liquid culture (CAMLiC) and molecular methods. The increase in the use of rapid culture methods for the detection of Mycobacterium tuberculosis has resulted in an overall reduction in time-to-positive data reported by participants, and has provided an indication of participants' ability to meet the 21-day target recommended by the CDC for the detection and identification of M. tuberculosis.

Guidelines for the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA)

These evidence-based guidelines have been produced after a literature review of the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA). We have considered the detection of MRSA in screening samples and the detection of reduced susceptibility to glycopeptides in S. aureus. Recommendations are given for the identification of S. aureus and for suitable methods of susceptibility testing and screening for MRSA and for S. aureus with reduced susceptibility to glycopeptides. These guidelines indicate what tests should be used but not when the tests are applicable, as aspects of this are dealt with in guidelines on control of MRSA. There are currently several developments in screening media and molecular methods. It is likely that some of our recommendations will require modification as the new methods become available.

Characterization of toxigenic Corynebacterium ulcerans strains isolated from humans and domestic cats in the United Kingdom

In the United Kingdom there has been a marked increase in the number of human infections caused by toxigenic Corynebacterium ulcerans. During 2002 and 2003 the organism was also isolated from several domestic cats with bilateral nasal discharge. As C. ulcerans has never previously been isolated from cats, the 16S rRNA gene from three cat isolates was sequenced to confirm their species identities. Fifty clinical isolates from the United Kingdom isolated from 1986 to 2003 and seven cat isolates were characterized by ribotyping to determine whether the ribotypes of the cat isolates were genotypically related to those found for human clinical isolates. For comparison, the genotypes of 11 overseas isolates and 13 isolates from H. R. Carne's collection isolated between 1933 and 1979 were also determined. Strains isolated from domestic cats were found to exhibit the predominant ribotypes observed among human clinical isolates, suggesting that C. ulcerans isolated from cats could be a potential reservoir for human infection.

Incidence of class 1 integrons in a quaternary ammonium compound-polluted environment

Samples of effluent and soil were collected from a reed bed system used to remediate liquid waste from a wool finishing mill with a high use of quaternary ammonium compounds (QACs) and were compared with samples of agricultural soils. Resistance quotients of aerobic gram-negative and gram-positive bacteria to ditallowdimethylammomium chloride (DTDMAC) and cetyltrimethylammonium bromide (CTAB) were established by plating onto nutrient agar containing 5 microg/ml or 50 microg/ml DTDMAC or CTAB. Approximately 500 isolates were obtained and screened for the presence of the intI1 (class 1 integrase), qacE (multidrug efflux), and qacE Delta1 (attenuated qacE) genes. QAC resistance was higher in isolates from reed bed samples, and class 1 integron incidence was significantly higher for populations that were preexposed to QACs. This is the first study to demonstrate that QAC selection in the natural environment has the potential to coselect for antibiotic resistance, as class 1 integrons are well-established vectors for cassette genes encoding antibiotic resistance.

CTX-M: changing the face of ESBLs in the UK

The UK has experienced a sudden rise in extended-spectrum beta-lactamase (ESBL) rates, largely due to the appearance and spread of Escherichia coli producing CTX-M-15 type beta-lactamase. The British Society for Antimicrobial Chemotherapy organized two update meetings during 2004 to report and discuss the recognition, clinical diagnosis, treatment and control of bacteria producing these beta-lactamases. This paper reports the data and reviews made by contributors to the conferences. The historical distribution and emergence of ESBLs was reviewed along with the emergence of plasmid-mediated CTX-M ESBLs following their mobilization from the chromosome of Kluyvera spp. The first significant outbreak of CTX-M producers in the UK occurred in 2001 and involved Klebsiella pneumoniae with CTX-M-26 at one site, but by 2003, cloned and diverse E. coli with CTX-M-15 were widespread, with Shropshire one of the most affected regions. The specific experience in Shropshire was reported on and a comprehensive review made of the level of awareness of the need for ESBL detection in laboratories in England and Wales, together with a description of the variety of methods that may be applied, with recommendations for optimal methodology. The increased mortality associated with inappropriate treatment of infections caused by ESBL-producing strains was highlighted, together with discussion on potential control of cross-infection. The meeting concluded that the CTX-M genes have now become widespread in not only E. coli but other Enterobacteriaceae in the UK and this will represent a substantial threat to both the treatment of infections caused by these bacteria in the community and within hospitals.

Incidence of class 1 integrons in a quaternary ammonium compound-polluted environment

Samples of effluent and soil were collected from a reed bed system used to remediate liquid waste from a wool finishing mill with a high use of quaternary ammonium compounds (QACs) and were compared with samples of agricultural soils. Resistance quotients of aerobic gram-negative and gram-positive bacteria to ditallowdimethylammomium chloride (DTDMAC) and cetyltrimethylammonium bromide (CTAB) were established by plating onto nutrient agar containing 5 microg/ml or 50 microg/ml DTDMAC or CTAB. Approximately 500 isolates were obtained and screened for the presence of the intI1 (class 1 integrase), qacE (multidrug efflux), and qacE Delta1 (attenuated qacE) genes. QAC resistance was higher in isolates from reed bed samples, and class 1 integron incidence was significantly higher for populations that were preexposed to QACs. This is the first study to demonstrate that QAC selection in the natural environment has the potential to coselect for antibiotic resistance, as class 1 integrons are well-established vectors for cassette genes encoding antibiotic resistance.

Role of environmental cleaning in controlling an outbreak of Acinetobacter baumannii on a neurosurgical intensive care unit

An outbreak of Acinetobacter baumannii colonization and infection occurred in 19 patients over a 14-month period during 1998-1999 on a neurosurgical intensive care unit. During efforts to control the outbreak a significant correlation was observed between the number of environmental isolates of A. baumannii obtained during each monthly screening and the number of patients with A. baumannii colonization/infection in the same calendar month (P=0.004). Use of 1000 ppm hypochlorite solution and the introduction of new cleaning protocols reduced the number of environmental isolates. Failure to maintain low levels of environmental contamination with A. baumannii resulted in increases in patient colonization. This study showed that high standards of cleaning play an integral role in controlling outbreaks of A. baumannii in the intensive care unit setting.

Distribution and characterization of staphylococcal interspersed repeat units (SIRUs) and potential use for strain differentiation

Variable-number tandem repeats (VNTRs) have been shown to be a powerful tool in the determination of evolutionary relationships and population genetics of bacteria. The sequencing of a number of Staphylococcus aureus genomes has allowed the identification of novel VNTR sequences in S. aureus, which are similar to those used in the study of the evolution of Mycobacterium tuberculosis clades. Seven VNTRs, termed staphylococcal interspersed repeat units (SIRUs), distributed around the genome are described, occurring in both unique and multiple sites, and varying in length from 48 to 159 bp. Variations in copy numbers were observed in all loci, within both the sequenced genomes and the UK epidemic methicillin-resistant S. aureus (EMRSA) isolates. Clonally related UK EMRSA isolates were clustered using SIRUs, which provided a greater degree of discrimination than multi-locus sequence typing, indicating that VNTRs may be a more appropriate evolutionary marker for studying transmission events and the geographical spread of S. aureus clades.

Molecular characterization of diphtheria toxin repressor (dtxR) genes present in nontoxigenic Corynebacterium diphtheriae strains isolated in the United Kingdom

Nontoxigenic strains of Corynebacterium diphtheriae represent a potential reservoir for the emergence of toxigenic C. diphtheriae strains if they possessed functional diphtheria toxin repressor (dtxR) genes. We studied the predominant strain of nontoxigenic C. diphtheriae circulating in the United Kingdom to see if they possessed dtxR genes and ascertain whether they were functional. A total of 26 nontoxigenic C. diphtheriae strains isolated in the United Kingdom during 1995 and 4 nontoxigenic strains isolated in other countries were analyzed by PCR and direct sequencing to determine the presence and intactness of the dtxR genes. The functionality of the DtxR proteins was assayed by testing for the production of siderophore in medium containing high and low concentrations of iron. PCR amplification and sequence analysis of the dtxR genes revealed four variants of the predicted DtxR protein among the nontoxigenic strains isolated in the United Kingdom. Production of siderophore in medium containing a low concentration of iron and repression of siderophore production in medium containing a high concentration of iron demonstrated that in all the strains the dtxR genes were functional. These findings demonstrate that, if lysogenised by a bacteriophage, nontoxigenic strains circulating in the United Kingdom could produce toxin and therefore represent a potential reservoir for toxigenic C. diphtheriae.

Molecular and kinetic comparison of the novel extended-spectrum beta-lactamases CTX-M-25 and CTX-M-26

CTX-M-25 is a novel extended-spectrum beta-lactamase isolated from a single Canadian Escherichia coli isolate. Susceptibility testing demonstrated that this enzyme confers resistance to both cefotaxime and ceftazidime, but the level of resistance was reduced with the addition of beta-lactamase inhibitors. The bla(CTX-M-25) gene was detected on a 111-kb plasmid. It is a member of the CTX-M-8 group and has the closest amino acid identity (99%; three amino acid substitutions) with CTX-M-26. The bla(CTX-M-26) gene was detected on a 100-kb plasmid isolated from a Klebsiella pneumoniae strain from the United Kingdom, and plasmid profiling revealed that it showed some homology to the bla(CTX-M-25)-harboring plasmid. Both CTX-M genes were located downstream of ISEcp1, although the copy upstream of bla(CTX-M-25) was disrupted by IS50-A. Comparative kinetic studies of recombinant CTX-M-25 and CTX-M-26 enzymes showed that CTX-M-25 has a higher level of ceftazidime hydrolysis (kcat values, 33 and 0.005 s(-1) for CTX-M-25 and CTX-M-26, respectively).

Automated high-throughput mycobacterial interspersed repetitive unit typing of Mycobacterium tuberculosis strains by a combination of PCR and nondenaturing high-performance liquid chromatography

Mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) typing of Mycobacterium tuberculosis complex isolates is portable, 100% reproducible, and highly discriminatory. Nondenaturing high-performance liquid chromatography (non-dHPLC) with use of a WAVE microbial analysis system is a promising method of PCR amplicon analysis as it is low cost and requires no preanalysis processing. The aims of this study were to validate the application of WAVE microbial analysis system technology to MIRU-VNTR typing. A collection of 70 strains were cultivated in liquid culture and extracted using the QIAamp DNA minikit. Novel primers were designed to target the 12 MIRU-VNTR loci (P. Supply et al., J. Clin. Microbiol. 39:3563-3571, 2001). After amplification, each PCR product was analyzed on a WAVE microbial analysis system. The fragment size was calculated from the chromatogram, and the number of tandem repeats at each locus was determined. For the collection of 70 strains 100% concordance was achieved when comparing MIRU-VNTR profiles obtained from agarose gel electrophoresis and PCRs analyzed on a WAVE microbial analysis system. The calculated fragment sizes, obtained from the WAVE microbial analysis system, were sufficiently accurate to ensure 100% confidence when assigning the number of tandem repeats to a MIRU-VNTR locus. This study is the first to report the successful use of non-dHPLC for screening for variations in the number of MIRU-VNTRs in mycobacterial DNA. Non-dHPLC analysis was demonstrated to be a rapid, low-labor input method for the detection and analysis of MIRU-VNTR amplicons. The combination with non-dHPLC further enhances the utility of MIRU-VNTR typing.

Predominance and genetic diversity of community- and hospital-acquired CTX-M extended-spectrum β-lactamases in York, UK

OBJECTIVES

This study was conducted to detect the presence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae within the faecal flora of both community- and hospital-based patients in York and to characterize the bla(TEM), bla(SHV) and bla(CTX-M) genes present in these isolates.

METHODS

One thousand faeces samples were collected and screened at York Hospital during October-December 2003. Ninety-five non-duplicate Enterobacteriaceae isolates resistant to third-generation cephalosporins were recovered; 22 isolates were selected for further study on the basis of a positive double disc diffusion test for ESBL production. Antibiotic susceptibility testing was performed to a range of antibiotics. The TEM, SHV and CTX-M genes were detected by PCR and the DNA sequenced.

RESULTS

The distribution of ESBL-positive isolates from the hospital and community was 1.4:1. These included nine Escherichia coli, seven Enterobacter cloacae, four Citrobacter freundii and a single isolate each of Klebsiella spp. and Salmonella spp. A total of 17 isolates contained bla(CTX-M) (five bla(CTX-M-15), three bla(CTX-M-14) and nine bla(CTX-M-9)). ISEcp1 was present in isolates expressing CTX-M-14 and -15, but was absent upstream of In60-associated bla(CTX-M-9). E. coli isolates also contained either a bla(TEM-1) or bla(TEM-2), whereas six of the E. cloacae carried bla(SHV-12) and the Klebsiella spp. bla(SHV-36) in addition to bla(CTX-M-9). The single Salmonella spp. carried bla(SHV-12).

CONCLUSIONS

The overall prevalence of ESBL in isolates of Enterobacteriaceae from York was 1.9%. ESBL-producing isolates were found in both the community and hospital, with the CTX-M type most common. This is also the first report of an ESBL-producing Salmonella in the UK.

Role of environmental cleaning in controlling an outbreak of Acinetobacter baumannii on a neurosurgical intensive care unit

An outbreak of Acinetobacter baumannii colonization and infection occurred in 19 patients over a 14-month period during 1998-1999 on a neurosurgical intensive care unit. During efforts to control the outbreak a significant correlation was observed between the number of environmental isolates of A. baumannii obtained during each monthly screening and the number of patients with A. baumannii colonization/infection in the same calendar month (P < 0.004). Use of 1000 ppm hypochlorite solution and the introduction of new cleaning protocols reduced the number of environmental isolates. Failure to maintain low levels of environmental contamination with A. baumannii resulted in increases in patient colonization. This study showed that high standards of cleaning play an integral role in controlling outbreaks of A. baumannii in the intensive care unit setting.

Dissemination of CTX-M type β-lactamases in Enterobacteriaceae isolates in the People’s Republic of China

Previously there have been a number of reports of extended spectrum beta-lactamase (ESBL) producing isolates of the family Enterobacteriaceae in Asia. We first reported the occurrence of bla(CTX-M) in Guangzhou, China, subsequently there have been reports of bla(CTX-M) from a number of other south Asian countries. Initial surveillance study data suggested that bla(CTX-M) might be widely distributed in China. This study examines the type of bla(CTX-M) occurring in other major population centres in China. Initial disk diffusion method susceptibility testing (NCCLS) selected ESBL producing Escherichia coli and Klebsiella pneumoniae isolates from Beijing and near Wuhan, PRC. After screening in both China and the UK, 13 isolates producing CTX-M ESBLs were identified and studied, 11 also produced TEM-1, and 4 also produced SHV-1. Sequence analysis of the bla(CTX-M) containing isolates revealed these isolates contained two different bla(CTX-M), three with bla(CTX-M-3) and 10 with bla(CTX-M-14). After comparison with other previously published studies in the English language, we conclude that the most prevalent bla(CTX-M) so far reported in Asia are bla(CTX-M-14) and bla(CTX-M-3).

Methicillin resistant Staphylococcus aureus in the critically ill

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

Severe acute respiratory syndrome (SARS): breath-taking progress

Reports of a new severe respiratory disease, now defined as severe acute respiratory syndrome (SARS), began to emerge from Guangdong, in southern China, in late 2002. The condition came to international attention through an explosive outbreak in Hong Kong in March 2003. Cases appeared throughout South-East Asia and in Toronto, the spread of SARS being accelerated by international air travel. A global emergency was declared by the World Health Organization, bringing together an international team of epidemiologists, public health physicians and microbiologists to study and contain the disease. This response has enabled the nature of the infectious agent to be identified, its mode of transmission to be established and diagnostic tests to be created rapidly.

Description and clinical treatment of an early outbreak of severe acute respiratory syndrome (SARS) in Guangzhou, PR China

Severe acute respiratory syndrome (SARS), now known to be caused by a coronavirus, probably originated in Guangdong province in southern China in late 2002. The first major outbreak occurred in Guangzhou, the capital of Guangdong, between January and March 2003. This study reviews the clinical presentation, laboratory findings and response to four different treatment protocols. Case notes and laboratory findings were analysed and outcome measures were collected prospectively. The SARS outbreak in Guangdong province and the outbreak in Guangzhou associated with hospitals in the city are described, documenting clinical and laboratory features in a cohort of 190 patients randomly allocated to four treatment regimens. Patients were infected by close contact in either family or health-care settings, particularly following procedures likely to generate aerosols of respiratory secretions (e.g. administration of nebulized drugs and bronchoscopy). The earliest symptom was a high fever followed, in most patients, by dyspnoea, cough and myalgia, with 24 % of patients complaining of diarrhoea. The most frequent chest X-ray changes were patchy consolidation with progression to bilateral bronchopneumonia over 5-10 days. Thirty-six cases developed adult respiratory distress syndrome (ARDS), of whom 11 died. There was no response to antibiotics. The best response (no deaths) was seen in the group of 60 patients receiving early high-dose steroids and nasal CPAP (continuous airway positive pressure) ventilation; the other three treatment groups had significant mortality. Cross-infection to medical and nursing staff was completely prevented in one hospital by rigid adherence to barrier precautions during contact with infected patients. The use of rapid case identification and quarantine has controlled the outbreak in Guangzhou, in which more than 350 patients have been infected. Early administration of high-dose steroids and CPAP ventilation appears to offer the best supportive treatment with a reduced mortality compared with other treatment regimens.

Mycobacterial interspersed repetitive unit typing of Mycobacterium tuberculosis compared to IS6110-based restriction fragment length polymorphism analysis for investigation of apparently clustered cases of tuberculosis

An evaluation of the utility of IS6110-based restriction fragment length polymorphism (RFLP) typing compared to a combination of variable number tandem repeat (VNTR) typing and mycobacterial interspersed repetitive unit (MIRU) typing was undertaken. A total of 53 patient isolates of Mycobacterium tuberculosis from four presumed episodes of cross-infection were examined. Genomic DNA was extracted from the isolates by a cetyl trimethylammonium bromide method. The number of copies of tandem repeats of the five loci ETR(A) to ETR(E) and 12 MIRU loci was determined by PCR amplification and agarose gel electrophoresis of the amplicons. VNTR typing identified the major clusters of strains in the three investigations in which they occurred (each representing a different evolutionary clade: 32333, 42235, and 32433). The majority of unrelated isolates (by epidemiology and RFLP typing) were also identified by VNTR typing. The concordance between the RFLP and MIRU typing was complete, with the exception of two isolates with RFLP patterns that differed by one band each from the rest of the major epidemiologically linked groups of isolates in investigation A. All of these isolates had identical MIRU and VNTR types. A further pair of isolates differed in the number of tandem repeat copies at two MIRU alleles but had identical RFLP patterns. The speed of the combined VNTR and MIRU typing approach enabled results for some of the investigations to be supplied in "real time," influencing choices in contact tracing. The ease of comparison of results of MIRU and VNTR typing, which are recorded as single multidigit numbers, was also found to greatly facilitate investigation management and the communication of results to health care professionals.

Mechanisms of quinolone action and microbial response

Over the years, chromosomal mapping of the bacterial genome of Escherichia coli has demonstrated that many loci are associated with quinolone resistance, which is mainly a result of chromosomal mutation or alteration of the quantity or type of porins in the outer membrane of Gram-negative bacteria. There has been one report of a small and confined episode of plasmid-mediated resistance to fluoroquinolones, which did not appear to persist. With the increasingly widespread use of an expanding range of fluoroquinolone antibiotics, a range and mix in individual bacterial isolates of the different mechanisms of resistance to fluoroquinolones will undoubtedly be encountered amongst clinically significant bacteria. Currently, transferable resistance is extremely rare and most resistant bacteria arise from clonal expansion of mutated strains. However, it is conceivable that in the future, horizontal gene transfer may become a more important means of conferring resistance to fluoroquinolones.

A systematic review of the antifungal effectiveness and tolerability of amphotericin B formulations

OBJECTIVE

A systematic review was performed to compare the effectiveness and tolerability of lipid-based amphotericin B (AmB) formulations and conventional AmB in the treatment of systemic fungal infections.

METHODS

The literature and unpublished studies were searched using MEDLINE, EMBASE, Biological Abstracts, AIDSLINE, CANCERLIT, CRD database, Cochrane Controlled Trials Register, and other databases. Search terms included: amphotericin, liposom*, lipid*, colloid*, antifungal agents, and mycoses. Studies were selected according to predetermined criteria. The outcome measures reviewed were efficacy, mortality, renal toxicity, and infusion-related reactions. Meta-analyses and number-needed-to-treat (NNT) analyses were performed.

RESULTS

Seven studies (8 publications) met the entry criteria. Meta-analysis showed that lipid-based formulations significantly reduced all-cause mortality risk by an estimated 28% compared with conventional AmB (odds ratio [OR], 0.72; 95% CI, 0.54 to 0.97). There was no significant difference in efficacy between the lipid-based formulations and conventional AmB (OR, 1.21; 95% CI, 0.98 to 1.49). AmB lipid complex (ABLC) and liposomal AmB (L-AmB) significantly reduced the risk of doubling serum creatinine by an estimated 58% (OR, 0.42; 95% CI, 0.33 to 0.54). There was no significant reduction in risk of infusion-related reactions with lipid-based formulations, although this was difficult to interpret given the lack of consistent control of confounding factors. Comparing the lipid-based formulations with conventional AmB, the overall NNT to prevent 1 death was 31. The NNT to prevent a doubling of serum creatinine for both ABLC and L-AmB compared with conventional AmB was 6.

CONCLUSIONS

This study demonstrates advantages with lipid-based formulations over conventional AmB in terms of reduced risk of mortality and renal toxicity. Future trials in patients with proven fungal infection should control for factors such as premedication, infusion rates, fluid preloading, sodium/potassium supplementation, and concomitant medication.

Examination of single and multiple mutations involved in resistance to quinolones in Staphylococcus aureus by a combination of PCR and denaturing high-performance liquid chromatography (DHPLC)

Detection of DNA sequence variation is fundamental to the identification of the genomic basis of phenotypic variability. Denaturing high-performance liquid chromatography (DHPLC) is a novel technique that has been used to detect mutations in human DNA. We report on the first study to use this technique as a tool to detect mutations in genes encoding antibiotic resistance in bacteria. Three methicillin-sensitive and three methicillin-resistant clinical Staphylococcus aureus isolates, susceptible to ciprofloxacin (MIC <or= 0.4 mg/L), were used to derive mutants resistant to ciprofloxacin, levofloxacin, sparfloxacin, trovafloxacin and moxifloxacin. Genomic DNA from each strain was subjected to PCR amplification of 225-500 bp regions spanning the quinolone resistance determining regions of the gyrA, gyrB, grlA and grlB genes. Following DNA sequencing of these amplicons and identification of resistance mutations, DHPLC was undertaken to correlate the distinctive chromatogram with DNA sequence. The mutations detected by DHPLC resulted in the following amino acid substitutions: Ser-84-->Leu, Ser-112-->Pro, Glu-88-->Lys in GyrA, Glu-84-->Val, Ser-80-->Phe in GrlA, Pro-456-->Ser in GyrB and Glu-422-->Asp, Pro-451-->Ser, Asp-432-->Gly in GrlB. Mutations could be rapidly and reproducibly identified from the PCR products using DHPLC, producing specific peak patterns that correlate with genotypes. This system facilitates the detection of resistance alleles, providing a rapid (5 min per sample), economic (96 sample per run) and reliable technique for characterizing antibiotic resistance in bacteria.

Predominant VNTR family of strains of Mycobacterium tuberculosis isolated from South Asian patients

SETTING

Despite the low incidence of tuberculosis in the UK, some minority ethnic groups, particularly those originating from South Asia, experience very high incidence rates.

OBJECTIVE

Comparison of the variable number tandem repeat (VNTR) profiles of strains of Mycobacterium tuberculosis circulating in an immigrant community in the UK with those found in the country of ethnic origin.

DESIGN

Isolates of M. tuberculosis were collected from samples obtained from patients attending clinics in Leeds and Bradford, UK and Rawalpindi, Pakistan. Strains were compared using VNTR analysis and mixed-linker PCR.

RESULTS

Comparison of VNTR profiles found that one profile (42235) represented 37% of patient isolates from Rawalpindi and 23% of patient isolates in Leeds and Bradford, where it was associated exclusively with patients with South Asian names. A second profile (02235) represented 15% of patient isolates in Leeds and Bradford, and was also exclusively associated with the South Asian community. These profiles could be subdivided by mixed-linker PCR analysis.

CONCLUSION

The VNTR profile 42235 may represent a family of strains commonly found in communities associated with South Asia.

SHV-12, SHV-5, SHV-2a and VEB-1 extended-spectrum beta-lactamases in Gram-negative bacteria isolated in a university hospital in Thailand

Sixty-one extended-spectrum beta-lactamase (ESBL)-producing isolates were collected from Srinagarind Hospital, Thailand. These included 43 Enterobacteriaceae and 18 Pseudomonadaceae. The 43 Enterobacteriaceae were found to produce the following ESBLs: 26 (60.5%) SHV-12, 13 (30.2%) SHV-5, two (4.7%) SHV-2a, one (2.3%) VEB-1 and one (2.3%) unidentified. Twenty-four isolates (55.8%) also carried bla(TEM-1B), as well as bla(SHV) or bla(VEB-1). Plasmid DNA from transconjugants carrying the bla(SHV-12) gene showed various restriction patterns, indicating the distribution of the bla(SHV-12) gene among different antibiotic resistance plasmids. In contrast, bla(SHV-5) in 13 isolates was found on a single plasmid of c. 130 kb. Pulsed-field gel electrophoresis (PFGE) analysis of genomic DNA from these isolates revealed that nine of 11 Klebsiella pneumoniae gave the same pattern, indicating clonal spread of the strain within the hospital, together with the occasional spread of the plasmid to other strains. Among the pseudomonad isolates, 16 Pseudomonas aeruginosa and one Pseudomonas putida had bla(VEB-like) and one P. aeruginosa had bla(SHV-12). Nine of the 16 isolates carrying bla(VEB-like) (56.3%) had identical PFGE patterns, suggesting the dissemination of this gene, also by clonal spread. At least six different bla(VEB-like-)containing integrons were found among the 18 isolates. This is the first report of bacteria producing SHV-12 and SHV-2a in Thailand and the first report of SHV-12 in P. aeruginosa, of VEB-1 in Citrobacter freundii and a VEB-1-like beta-lactamase in P. putida. These findings indicate that ESBL genes in the Far East are part of a gene pool capable of broad horizontal gene transfer, in that these genes can transfer between different families of Gram-negative bacilli.