Broad-spectrum, transmissible beta-lactamases

Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Antimicrobial resistance is a normal evolutionary process for microorganisms. Antibiotics exerted accelerated selective pressure that hasten bacterial resistance through mutation, and acquisition external genes. These genes often carry multiple antibiotic resistant determinants allowing the recipient microbe an instant "super-bug" status. The extent of Antimicrobial Resistance (AMR) has reached a level of global crisis, existing antimicrobials are no long effective in treating infections caused by AMR pathogens. The great majority of clinically available antimicrobial agents are administered through oral and intra-venous routes. Overcoming antibacterial resistance by novel drug delivery approach offered new hopes, particularly in the treatment of AMR pathogens in sites less assessible through systemic circulation such as the lung and skin. In the current review, we will revisit the mechanism and incidence of important AMR pathogens. Finally, we will discuss novel drug delivery approaches including novel local antibiotic delivery systems, hybrid antibiotics, and nanoparticle-based antibiotic delivery systems.

Differential Trends in Extended-Spectrum Beta-Lactamase-Producing Escherichia coli Infections in Four Health Care Facilities in a Single Metropolitan Area: A Retrospective Analysis

Background: Prevalence of extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-E. coli) is increasing worldwide, but greatly varies geographically. We compared the prevalence of ESBL-E. coli infections at four distinct health care facilities in San Francisco, California. Methods: Antimicrobial susceptibility reports were obtained for E. coli isolates from (1) a county hospital, (2) a public skilled nursing facility, (3) a university hospital, and (4) a Veterans Affairs (VA) Medical Center. We compared change in frequency of ESBL-E. coli and antimicrobial resistance to trimethoprim-sulfamethoxazole between 2012 and 2018. Results: From 2012 to 2018, frequency of ESBL-E. coli increased in urine and nonurine isolates from the county hospital (urine: 1.1% per year, 95% confidence interval [CI]: 0.5-1.6, p < 0.01; nonurine: 1.9% per year, 95% CI: 0.9-2.9, p < 0.01) and in urine isolates from the VA hospital (0.9% per year, 95% CI: 0.3-1.4, p < 0.01). The frequency of trimethoprim-sulfamethoxazole resistance fluctuated in all facilities. Conclusions: At the skilled nursing facility, the prevalence of ESBL-E. coli was highest, but remained stable over time, while the prevalence of ESBL-E. coli increased among urine and nonurine isolates at the county hospital and urine isolates at the VA hospital. The temporal trend of ESBL-E. coli infections, even within one city, varied by health care facility.

Early-Onset Neonatal Sepsis with Extended Spectrum Beta-Lactamase Producing Escherichia Coli in Infants Born to South and South East Asian Immigrants: A Case Series

Extended-spectrum β -lactamase (ESBL)-producing Enterobacteriaceae represent a major worldwide threat. We present three cases of early onset ESBL Escherichia coli sepsis in infants born to families from South and Southeast Asia to inform the practitioner community about this emerging threat. Infants with suspected sepsis, whose mother is from Asia or Southeast Asia, should be suspected of having an infection with an ESBL-producing organism, and practitioners should strongly consider adding a carbapenem to their usual initial antibiotic regimen.

Past and Present Perspectives on β-Lactamases

β-Lactamases, the major resistance determinant for β-lactam antibiotics in Gram-negative bacteria, are ancient enzymes whose origins can be traced back millions of years ago. These well-studied enzymes, currently numbering almost 2,800 unique proteins, initially emerged from environmental sources, most likely to protect a producing bacterium from attack by naturally occurring β-lactams. Their ancestors were presumably penicillin-binding proteins that share sequence homology with β-lactamases possessing an active-site serine. Metallo-β-lactamases also exist, with one or two catalytically functional zinc ions. Although penicillinases in Gram-positive bacteria were reported shortly after penicillin was introduced clinically, transmissible β-lactamases that could hydrolyze recently approved cephalosporins, monobactams, and carbapenems later became important in Gram-negative pathogens. Nomenclature is based on one of two major systems. Originally, functional classifications were used, based on substrate and inhibitor profiles. A later scheme classifies β-lactamases according to amino acid sequences, resulting in class A, B, C, and D enzymes. A more recent nomenclature combines the molecular and biochemical classifications into 17 functional groups that describe most β-lactamases. Some of the most problematic enzymes in the clinical community include extended-spectrum β-lactamases (ESBLs) and the serine and metallo-carbapenemases, all of which are at least partially addressed with new β-lactamase inhibitor combinations. New enzyme variants continue to be described, partly because of the ease of obtaining sequence data from whole-genome sequencing studies. Often, these new enzymes are devoid of any phenotypic descriptions, making it more difficult for clinicians and antibiotic researchers to address new challenges that may be posed by unusual β-lactamases.

Phage puppet masters of the marine microbial realm

Viruses numerically dominate our oceans; however, we have only just begun to document the diversity, host range and infection dynamics of marine viruses, as well as the subsequent effects of infection on both host cell metabolism and oceanic biogeochemistry. Bacteriophages (that is, phages: viruses that infect bacteria) are highly abundant and are known to play critical roles in bacterial mortality, biogeochemical cycling and horizontal gene transfer. This Review Article summarizes current knowledge of marine viral ecology and highlights the importance of phage particles to the dissolved organic matter pool, as well as the complex interactions between phages and their bacterial hosts. We emphasize the newly recognized roles of phages as puppet masters of their bacterial hosts, where phages are capable of altering the metabolism of infected bacteria through the expression of auxiliary metabolic genes and the redirection of host gene expression patterns. Finally, we propose the 'royal family model' as a hypothesis to describe successional patterns of bacteria and phages over time in marine systems, where despite high richness and significant seasonal differences, only a small number of phages appear to continually dominate a given marine ecosystem. Although further testing is required, this model provides a framework for assessing the specificity and ecological consequences of phage-host dynamics.

Vital Signs: Containment of Novel Multidrug-Resistant Organisms and Resistance Mechanisms - United States, 2006-2017

BACKGROUND

Approaches to controlling emerging antibiotic resistance in health care settings have evolved over time. When resistance to broad-spectrum antimicrobials mediated by extended-spectrum β-lactamases (ESBLs) arose in the 1980s, targeted interventions to slow spread were not widely promoted. However, when Enterobacteriaceae with carbapenemases that confer resistance to carbapenem antibiotics emerged, directed control efforts were recommended. These distinct approaches could have resulted in differences in spread of these two pathogens. CDC evaluated these possible changes along with initial findings of an enhanced antibiotic resistance detection and control strategy that builds on interventions developed to control carbapenem resistance.

METHODS

Infection data from the National Healthcare Safety Network from 2006-2015 were analyzed to calculate changes in the annual proportion of selected pathogens that were nonsusceptible to extended-spectrum cephalosporins (ESBL phenotype) or resistant to carbapenems (carbapenem-resistant Enterobacteriaceae [CRE]). Testing results for CRE and carbapenem-resistant Pseudomonas aeruginosa (CRPA) are also reported.

RESULTS

The percentage of ESBL phenotype Enterobacteriaceae decreased by 2% per year (risk ratio [RR] = 0.98, p<0.001); by comparison, the CRE percentage decreased by 15% per year (RR = 0.85, p<0.01). From January to September 2017, carbapenemase testing was performed for 4,442 CRE and 1,334 CRPA isolates; 32% and 1.9%, respectively, were carbapenemase producers. In response, 1,489 screening tests were performed to identify asymptomatic carriers; 171 (11%) were positive.

CONCLUSIONS

The proportion of Enterobacteriaceae infections that were CRE remained lower and decreased more over time than the proportion that were ESBL phenotype. This difference might be explained by the more directed control efforts implemented to slow transmission of CRE than those applied for ESBL-producing strains. Increased detection and aggressive early response to emerging antibiotic resistance threats have the potential to slow further spread.

Incidence of Extended-Spectrum β-Lactamase (ESBL)-Producing Escherichia coli and Klebsiella Infections in the United States: A Systematic Literature Review

BACKGROUND

Despite a reported worldwide increase, the incidence of extended-spectrum β-lactamase (ESBL) Escherichia coli and Klebsiella infections in the United States is unknown. Understanding the incidence and trends of ESBL infections will aid in directing research and prevention efforts.

OBJECTIVE

To perform a literature review to identify the incidence of ESBL-producing E. coli and Klebsiella infections in the United States.

DESIGN

Systematic literature review.

METHODS

MEDLINE via Ovid, CINAHL, Cochrane library, NHS Economic Evaluation Database, Web of Science, and Scopus were searched for multicenter (≥2 sites), US studies published between 2000 and 2015 that evaluated the incidence of ESBL-E. coli or ESBL-Klebsiella infections. We excluded studies that examined resistance rates alone or did not have a denominator that included uninfected patients such as patient days, device days, number of admissions, or number of discharges. Additionally, articles that were not written in English, contained duplicated data, or pertained to ESBL organisms from food, animals, or the environment were excluded.

RESULTS

Among 51,419 studies examined, 9 were included for review. Incidence rates differed by patient population, time, and ESBL definition and ranged from 0 infections per 100,000 patient days to 16.64 infections per 10,000 discharges and incidence rates increased over time from 1997 to 2011. Rates were slightly higher for ESBL-Klebsiella infections than for ESBL-E. coli infections.

CONCLUSION

The incidence of ESBL-E. coli and ESBL-Klebsiella infections in the United States has increased, with slightly higher rates of ESBL-Klebsiella infections. Appropriate estimates of ESBL infections when coupled with other mechanisms of resistance will allow for the appropriate targeting of resources toward research, drug discovery, antimicrobial stewardship, and infection prevention.

Infect Control Hosp Epidemiol 2017;38:1209–1215

Extended spectrum β-lactamase producing Escherichia coli and Klebsiella pneumoniae: critical tools for antibiotic resistance pattern

Drug resistance is a phenomenon where by an organism becomes fully or partially resistant to drugs or antibiotics being used against it. Antibiotic resistance poses an exacting intimidation for people with underlying medical immune conditions or weakened immune systems. Infections caused by the enzyme extended spectrum β-lactamase (ESBL) producing multi drug resistance (MDR) Enterobacteriaceae especially Escherichia coli and Klebsiella pneumoniae are resistant to a broad range of beta lactams, including third generation cephalosporins. Among all the pathogens, these two MDR E. coli and K. pneumoniae have emerged as one of the world's greatest health threats in past two decades. The nosocomial infections caused by these ESBL producing MDR E. coli and K. pneumoniae complicated the therapy and limit treatment options.

Escherichia coli β-Lactamases: What Really Matters

Escherichia coli strains belonging to diverse pathotypes have increasingly been recognized as a major public health concern. The β-lactam antibiotics have been used successfully to treat infections caused by pathogenic E. coli. However, currently, the utility of β-lactams is being challenged severely by a large number of hydrolytic enzymes – the β-lactamases expressed by bacteria. The menace is further compounded by the highly flexible genome of E. coli, and propensity of resistance dissemination through horizontal gene transfer and clonal spread. Successful management of infections caused by such resistant strains requires an understanding of the diversity of β-lactamases, their unambiguous detection, and molecular mechanisms underlying their expression and spread with regard to the most relevant information about individual bacterial species. Thus, this review comprises first such effort in this direction for E. coli, a bacterial species known to be associated with production of diverse classes of β-lactamases. The review also highlights the role of commensal E. coli as a potential but under-estimated reservoir of β-lactamases-encoding genes.

Liver abscesses in adult patients with and without diabetes mellitus: an analysis of the clinical characteristics, features of the causative pathogens, outcomes and predictors of fatality: a report based on a large population, retrospective study in China

In China, there are four types of liver abscesses (LAs) that meet the clinical criteria. Pyogenic liver abscesses (PLAs) and amoebic liver abscesses (ALAs) are two of the most common types of abscesses, followed by fungal liver abscesses (FLAs) and hydatid secondary liver abscesses (HsLAs). Diabetes mellitus (DM) is associated with the development of PLAs. However, there is a lack of population-based studies that have evaluated the underlying relationship between LAs (mainly PLAs and FLAs) and DM. We conducted a retrospective study based on a large population to identify the potential differences and factors that affect the mortality of PLA patients in DM and non-DM groups. Our results revealed that the prevalence of DM is 44.3% (158/357) in PLA patients and 35.3% (18/51) in FLA patients. Compared with the non-DM patients, statistically significant differences were found in DM patients according to symptomatology, clinical manifestations, laboratory findings, microbiological characteristics, antimicrobial resistance, clinical treatments and outcomes in relation to mortality. In addition, the status of antibiotic resistance to E. coli and K. pneumoniae, which were isolated from the patient samples, is severe in the area in which the study was conducted. Regarding the treatment of PLAs, our study indicated that broad-spectrum antimicrobial therapy and drug combinations should be recommended and initiated before the pathogens are cultured and identified. In the clinic, therapies that combine percutaneous drainage with antibiotics and surgery with antibiotics are the two most useful strategies for treating an LA. These two combined treatments resulted in satisfactory cure rates. In the DM and non-DM groups, the cure rates for percutaneous drainage with antibiotics were 90.3% and 92.0%, respectively, and the cure rates for surgery with antibiotics were 93.9% and 95.2%, respectively.

Bench-to-bedside review: The role of beta-lactamases in antibiotic-resistant Gram-negative infections

Multidrug resistance has been increasing among Gram-negative bacteria and is strongly associated with the production of both chromosomal- and plasmid-encoded β-lactamases, whose number now exceeds 890. Many of the newer enzymes exhibit broad-spectrum hydrolytic activity against most classes of β-lactams. The most important plasmid-encoded β-lactamases include (a) AmpC cephalosporinases produced in high quantities, (b) the expanding families of extended-spectrum β-lactamases such as the CTX-M enzymes that can hydrolyze the advanced-spectrum cephalosporins and monobactams, and (c) carbapenemases from multiple molecular classes that are responsible for resistance to almost all β-lactams, including the carbapenems. Important plasmid-encoded carbapenemases include (a) the KPC β-lactamases originating in Klebsiella pneumoniae isolates and now appearing worldwide in pan-resistant Gram-negative pathogens and (b) metallo-β-lactamases that are produced in organisms with other deleterious β-lactamases, causing resistance to all β-lactams except aztreonam. β-Lactamase genes encoding these enzymes are often carried on plasmids that bear additional resistance determinants for other antibiotic classes. As a result, some infections caused by Gram-negative pathogens can now be treated with only a limited number, if any, antibiotics. Because multidrug resistance in Gram-negative bacteria is observed in both nosocomial and community isolates, eradication of these resistant strains is becoming more difficult.

Healthcare-associated Infections: epidemiology, prevention, and therapy

Reducing nosocomial infection rates is a major component of healthcare improvement. This article reviews the epidemiology, prevention, and therapy for some of the most common healthcare-associated infections, including central line-associated bloodstream infections and catheter-associated urinary tract infections, and 3 common organisms: methicillin-resistant Staphylococcus aureus, multidrug- resistant gram-negative bacteria, and Clostridium difficile.

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.

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.

Rapid 4 to 6 hour detection of extended-spectrum beta-lactamases in a routine laboratory

With the growing frequency of extended-spectrum beta-lactamases (ESBL) among Enterobacteriaceae, treatment of Gram-negative nosocomial infections requires rapid and reliable detection of this enzyme. Quicolor agar (QC agar) (Salubris Inc., Massachusetts, USA) is a novel chromogenic agar medium changing colour within 4 to 6 h due to the metabolic activity of growing bacteria. This study investigated the use of QC agar compared to Mueller Hinton agar (MH) for the detection of ESBL using disk diffusion and E-test. 100 Enterobacteriaceae isolated at Hacettepe University Hospital, of which 50 were predetermined to be ESBL positive and 50 as negative using the CLSI disk diffusion ESBL (phenotypic confirmatory test) criteria. For disk diffusion and E-test, cefotaxime+/-clavulanate (CT/CTL) and ceftazidime+/-clavulanate (TZ/TZL) were used, and for E-test, cefepime+/-clavulanate (PM/PML) was also used. QC agar rapid ESBL results for all strains were in agreement with the standard overnight procedure. All 50 ESBL positives were detected by both methods. For the 50 ESBL negatives, QC agar rapid results from E-test and disk diffusion were in complete accordance with the overnight MH results. Moreover, E-test detected 8 additional ESBL positive strains that disk diffusion missed. For disk diffusion, CT/CTL alone detected all 50 ESBL positives while TZ/TZL alone missed 5 ESBL positives. E-test CT/CTL alone confirmed all 50 ESBL positives and identified 4 additional ESBL-positive strains. When used together, E-test CT/CTL, TZ/TZL and PM/PML identified a total of 58 ESBL positives among the 100 strains tested. QC agar can be used for rapid and reliable ESBL detection within 4 to 6 h, using disk diffusion and E-test ESBL reagents. This rapid method should be further validated using genotype characterized ESBL and other beta-lactamase positive strains.

Clinical and molecular epidemiology of community-onset, extended-spectrum beta-lactamase-producing Escherichia coli infections in Thailand: a case-case-control study

BACKGROUND

Extended-spectrum beta-lactamase (ESBL)-producing organisms, first identified in Germany in 1983, are now widely recognized as clinically relevant causes of infections in community.

METHODS

Our objective was to evaluate the clinical and molecular epidemiology of community-onset, extended-spectrum beta-lactamase (CO-ESBL)-producing Escherichia coli infections. We used a case-case-control study undertaken in a 450-bed, tertiary care hospital. Patients included case group (CG) I, which had confirmed CO-ESBL-producing E coli infections (n=46). Case group (CG) II (n=46) included patients with CO-non-ESBL-producing E coli infections. Controls (n=138) were patients without infections.

RESULTS

By multivariate analysis, diabetes (95% confidence interval [CI]: 1.9-13.2, P< .001), prior ESBL E coli colonization (<90 days) (95% CI: 1.2-67.8, P< .001), recent receipt of antibiotics (<90 days) (95% CI: 4.2-44.2, P= .004), and previous exposure to third-generation cephalosporins (95% CI: 2.2-16.4, P= .001) and fluoroquinolones (95% CI: 1.4-18.3; P= .003) were associated risks among CG I. Diabetes (95% CI: 1.6-15.4, P= .005), stroke (95% CI: 1.5-17.1, P= .001), and diarrhea (95% CI: 3.8-65.8, P= .001) were risks among CG II. Patients with CO-ESBL in CG I versus controls were more likely to die (30% vs 0%, respectively; P< .001), had prolonged hospital length of stay (8 vs 5 days, respectively; P< .001), and had higher hospitalization costs (median, US $528 vs $108, respectively; P< .001). The plasmid carrying the CTX-M-15 gene was identified in 13 of 25 (52%) available CO-ESBL-producing E coli isolates.

CONCLUSION

CO-ESBL-producing E coli is an emerging multidrug-resistant microorganism in Thailand. Patients with prior ESBL colonization and recent antibiotic exposures, especially to third-generation cephalosporins and fluoroquinolones, were at risk for CO-ESBL-producing E coli infection.

Identification of extended-spectrum, AmpC, and carbapenem- hydrolyzing beta-lactamases in Escherichia coli and Klebsiella pneumoniae by disk tests

Antibiotic disks with and without clavulanic acid, 3-aminophenylboronic acid, or EDTA were tested with a set of 55 Klebsiella pneumoniae and Escherichia coli strains producing well-characterized extended-spectrum, AmpC, or carbapenem-hydrolyzing beta-lactamases. A relatively simple scheme was devised for distinguishing beta-lactamase types in clinical isolates with or without intact outer membrane porins.

Investigation of the mechanism of resistance to third-generation cephalosporins by class C beta-lactamases by using chemical complementation

The widespread use of antibiotics to treat bacterial infections has led to the continuing challenge of antibiotic resistance. For beta-lactam antibiotics, the most common form of resistance is the expression of beta-lactamase enzymes, which inactivate the antibiotics by cleavage of the beta-lactam core. In this study, chemical complementation, which is a general method to link the formation or cleavage of a chemical bond to the transcription of a reporter gene in vivo, was employed in combination with combinatorial mutagenesis to study the mechanism by which the class C beta-lactamase P99 might evolve resistance to the commonly administered third-generation cephalosporin cefotaxime. The chemical complementation system was first shown to be able to distinguish between the wild-type (wt) class C beta-lactamase P99 and the clinically isolated extended-spectrum class C beta-lactamase GC1 in the presence of cefotaxime. The system was then employed to evaluate the activity of mutants of wt P99 towards cefotaxime. A number of single-point mutations at position 221 (Tyr in wt P99) were identified that conferred resistance towards inhibition by cefotaxime, with as much as a 2000-fold increase in k(cat) and a 100-fold increase in k(cat)/K(M) (k(cat)=the rate of catalysis; K(M)=the Michaelis constant), as compared to those of the wt enzyme. Finally, the chemical complementation system was employed in a high-throughput screen to identify a number of mutants of P99 that have multiple mutations around the substrate-binding pocket that increase resistance towards cefotaxime inhibition. The catalytic turnover of cefotaxime by the most active mutant identified was 5500 times higher than that of the wt P99. The resistant mutants suggest a mechanism by which a number of mutations can confer resistance by increasing the flexibility of the Omega loop and altering the positioning of residue 221. Thus, as illustrated in this study, chemical complementation has the potential to be used as a high-throughput screen to study a wide range of enzyme-drug interactions.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Risk Factors for Increasing Multidrug Resistance among Extended-Spectrum -Lactamase-Producing Escherichia coli and Klebsiella Species

BACKGROUND

The importance of infections due to extended-spectrum beta -lactamase-producing Escherichia coli and Klebsiella species (ESBL-EK) has been increasingly recognized in recent years. ESBL-EK infections are of clinical concern, because few antimicrobials are available as therapeutic options. Increased reliance on carbapenems has led to increasing carbapenem resistance. Efforts to maintain current therapeutic options for ESBL-EK infections are essential.

METHODS

We conducted a case-control study to identify risk factors for multidrug resistance (MDR) among ESBL-EK. All patients at our institution who had an inpatient clinical culture result positive for an ESBL-EK during the period of 1 June 1997 through 31 December 2002 were eligible for inclusion. An MDR ESBL-EK was defined as ESBL-EK demonstrating resistance to trimethoprim-sulfamethoxazole, aminoglycosides, and quinolones. All available ESBL-EK isolates were characterized by pulsed-field gel electrophoresis (PFGE).

RESULTS

Of 361 total ESBL-EK isolates, 68 (18.8%) were MDR. During the study period, the prevalence of MDR among ESBL-EK isolates increased from 12.5% to 26.9%. The only independent risk factor for MDR ESBL-EK was the infecting organism (i.e., Klebsiella pneumoniae; adjusted odds ratio, 11.7; 95% confidence interval, 4.77-28.51; P < .001). Prior antibiotic use was not independently associated with MDR ESBL-EK. PFGE patterns from K. pneumoniae isolates indicated close genetic relatedness among a substantial proportion of isolates.

CONCLUSIONS

The emergence of MDR among ESBL-EK has important implications for the future ability to treat these infections. The strong association between the species of infecting organism and MDR suggests that the epidemiology in K. pneumoniae may be unique. PFGE results suggest that horizontal spread is important in the emergence of MDR ESBL-EK.

Risk factors for the development of extended-spectrum beta-lactamase-producing bacteria in nonhospitalized patients

Although the risk factors for acquiring infection by extended-spectrum beta-lactamase (ESBL)-producing bacteria have been investigated in hospitalized patients, such risk factors have not been defined in the community setting. In this study, clinical data from a total of 311 nonhospitalized patients with community-acquired urinary tract infection (128 with ESBL-positive strains and 183 with ESBL-negative strains) were obtained. According to a multivariate analysis, the following were identified as independent risk factors: previous hospitalization in the past 3 months (OR=8.95, 95%CI, 3.77-21.25), antibiotic treatment in the past 3 months (OR=3.23, 95%CI, 1.76-5.91), age over 60 years (OR=2.65, 95%CI, 1.45-4.83), diabetes (OR=2.57, 95%CI, 1.20-5.51), male gender (OR=2.47, 95%CI, 1.22-5.01), Klebsiella pneumoniae infection (OR=2.31, 95%CI, 1.17-4.54), previous use of third-generation cephalosporins (P=0.014, OR=15.8, 95%CI, 1.7-143), previous use of second-generation cephalosporins (P<0.0001, OR=10.1, 95%CI, 4.2-24), previous use of quinolones (P=0.001, OR=4.1, 95%CI, 1.8-9.0), and previous use of penicillin (P=0.003, OR=4.0, 95%CI, 1.6-9.0).

Dio-Sensimedia: a novel culture medium for rapid detection of extended spectrum beta-lactamases

Background

Resistance to contemporary broad-spectrum β-lactams, mediated by extended-spectrum β-lactamases (ESBL), is an increasing problem worldwide. Many of the emerging antimicrobial resistance problems of this decade have been characterized by difficulty in the recognition of resistance in the laboratory, particularly by rapid susceptibility test methods. The plasmid-encoded ESBL represent such a resistance phenomenon that is difficult to recognize.

We compared Dio-Sensimedia-ES (DSM-ES; Diomed, Istanbul, Turkey) and Mueller-Hinton (MH) agar in the double-disk synergy test (DDST) as a novel rapid system for detecting ESBL directly from bacterial culture.

Methods

Sixty ESBL-producing Klebsiella pneumoniae isolates cultured from blood (30), endotracheal aspirates (20), urine (5) and pus (5), as well as 40 Escherichia coli isolates cultured from endotracheal aspirates (15), urine (10), blood (8) and pus (7) were studied. Isolates positive for ESBL by the combined disk tests were tested with the DDST using MH and DSM-ES agar to detect ESBL-mediated resistance in K. pneumoniae and E. coli. DSM-ES agar was also used to determine the susceptibility of Enterobacteriaceae and staphylococci.

Results

Among 60 ESBL-producing K. pneumoniae isolates, 59 (98.3%) were identified as ESBL-positive by the DDST using MH, and 58 (96.6%), using DSM-ES agar. Of 40 ESBL-producing E. coli isolates, 38 (95%) were ESBL-positive by the DDST on MH agar, and 37 (92.5%), on DSM-ES agar. The average incubation period required for ESBL detection by the DDST on DSM-ES agar was 4 hours.

Conclusions

Since the DDST results were available within 4 hours when DSM-ES agar was used, the use of this media may significantly lower the length of hospital stay, the total cost for patient care and even the mortality rate by fascilitating early treatment against ESBL-producing organisms.

Extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae: considerations for diagnosis, prevention and drug treatment

Extended spectrum beta-lactamase (ESBL)-producing organisms pose unique challenges to clinical microbiologists, clinicians, infection control professionals and antibacterial-discovery scientists. ESBLs are enzymes capable of hydrolysing penicillins, broad-spectrum cephalosporins and monobactams, and are generally derived from TEM and SHV-type enzymes. ESBLs are often located on plasmids that are transferable from strain to strain and between bacterial species. Although the prevalence of ESBLs is not known, it is clearly increasing, and in many parts of the world 10-40% of strains of Escherichia coli and Klebsiella pneumoniae express ESBLs. ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Clinical outcomes data indicate that ESBLs are clinically significant and, when detected, indicate the need for the use of appropriate antibacterial agents. Unfortunately, the laboratory detection of ESBLs can be complex and, at times, misleading. Antibacterial choice is often complicated by multi-resistance. Many ESBL-producing organisms also express AmpC beta-lactamases and may be co-transferred with plasmids mediating aminoglycoside resistance. In addition, there is an increasing association between ESBL production and fluoroquinolone resistance. Although in in vitro tests ESBLs are inhibited by beta-lactamase inhibitors such as clavulanic acid, the activity of beta-lactam/beta-lactamase inhibitor combination agents is influenced by the bacterial inoculum, dose administration regimen and specific type of ESBL present. Currently, carbapenems are regarded as the drugs of choice for treatment of infections caused by ESBL-producing organisms. Unfortunately, use of carbapenems has been associated with the emergence of carbapenem-resistant bacterial species such as Stenotrophomonas sp. or Pseudomonas sp.

Extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae: risk factors for infection and impact of resistance on outcomes

The prevalence of antibiotic resistance among extended-spectrum beta-lactamase (ESBL)--producing Escherichia coli and Klebsiella pneumoniae has increased markedly in recent years. Thirty-three patients with infection due to ESBL-producing E. coli or K. pneumoniae (case patients) were compared with 66 matched controls. Total prior antibiotic use was the only independent risk factor for ESBL-producing E. coli or K. pneumoniae infection (odds ratio, 1.10; 95% confidence interval, 1.03--1.18; P=.006). Case patients were treated with an effective antibiotic a median of 72 hours after infection was suspected, compared with a median of 11.5 hours after infection was suspected for controls (P<.001). ESBL-producing E. coli or K. pneumoniae infection was associated with a significantly longer duration of hospital stay and greater hospital charges (P=.01 and P<.001, respectively). Finally, many ESBL-producing E. coli and K. pneumoniae isolates were closely related. ESBL-producing E. coli and K. pneumoniae infections have a significant impact on several important clinical outcomes, and efforts to control outbreaks of infection with ESBL-producing E. coli and K. pneumoniae should emphasize judicious use of all antibiotics as well as barrier precautions to reduce spread.

Detection of genes coding for extended-spectrum SHV beta-lactamases in clinical isolates by a molecular genetic method, and comparison with the E test

A highly sensitive and specific method, termed PCR/NheI, for the detection of genes coding for SHV extended-spectrum beta-lactamases (ESBL) in clinical isolates is presented. It is based on polymerase chain reaction (PCR) amplification of the blaSHV genes, followed by restriction with NheI. Due to the glycine (positive 238) (SHV-non-ESBL)-->serine (position 238) (SHV-ESBL) mutation, only PCR fragments from the genes coding for SHV-ESBLs were cleaved. A commercially available test for ESBLs, the E test ESBL, identified 52% of our 29 clinical isolates carrying blaSHV-ESBL genes as ESBL producers.

Extended-spectrum beta-lactamases in clinical isolates of Enterobacter gergoviae and Escherichia coli in China

Resistance to ceftazidime, detected in isolates of Escherichia coli 5518 and Enterobacter gergoviae 3773 from our hospital, was transferred, together with resistance to aminoglycosides, trimethoprim, sulfonamide, and other beta-lactam antibiotics, by conjugation to E. coli JP559. Both E. coli transconjugants were resistant to ampicillin, all cephalosporins, and aztreonam but remained susceptible to cefoxitin and imipenem. The enzymes of the two transconjugant strains readily hydrolyzed cephalosporins in a spectrophotometric assay. Hybridization results suggested that the extended-spectrum beta-lactamase produced by E. coli 5518 was a non-TEM, non-SHV enzyme, the origin of which is currently unknown. The beta-lactamase produced by E. gergoviae 3773 was of the SHV type and was further proved to be SHV-2 by DNA sequencing. Thus, extended-spectrum beta-lactamases are occurring in China as well as in other parts of the world.

Prevalence of important pathogens and the antimicrobial activity of parenteral drugs at numerous medical centers in the United States. II. Study of the intra- and interlaboratory dissemination of extended-spectrum beta-lactamase-producing Enterobacteriaceae

The incidence of extended-spectrum beta-lactamases (ESBL)-producing Klebsiella pneumoniae and Escherichia coli has been increasing rapidly, and they are probably even more prevalent than is currently recognized because of difficulties in their detection by the clinical microbiology laboratory. In addition, several outbreaks associated with these multiresistant strains have been reported. In the present study we evaluated 30 clinical isolates (27 K. pneumoniae from 11 hospitals and three E. coli from three hospitals) that were resistant or intermediately susceptible to ceftazidime and/or cefuroxime. The main objective of the study was to evaluate the intra- and interhospital dissemination of ESBL-producing strains. The isolates were tested for susceptibility to ceftazidime, cefuroxime, gentamicin, and ofloxacin, and the ability of various susceptibility testing methods to detect resistance to these beta-lactams was evaluated. The production of ESBL was assessed by the disk approximation synergy test, and typing was performed by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA. ESBL production was demonstrated in 15 K. pneumoniae (from seven hospitals) and in one E. coli strain. Most ESBL-producing isolates demonstrated cross resistance with gentamicin and ofloxacin. Chromosomal DNA analysis by PFGE exhibited a great genomic variability among ESBL-producing isolates. Our results also indicated the occurrence of both intra- and interhospital dissemination of these multiresistant strains.

Multiply resistant Klebsiella pneumoniae strains from two Chicago hospitals: identification of the extended-spectrum TEM-12 and TEM-10 ceftazidime-hydrolyzing beta-lactamases in a single isolate

Ceftazidime-resistant Klebsiella pneumoniae strains began to appear when ceftazidime usage was increased in two unrelated Chicago hospitals. These strains produced a beta-lactamase with an isoelectric point of 5.6 (RP-5.6) and strong hydrolyzing activity against ceftazidime. Two different restriction digest profiles were associated with the ceftazidime resistance plasmids. A second beta-lactamase with a pI of 5.2 (RP-5.2) was coproduced in two representative strains. The second beta-lactamase hydrolyzed ceftazidime, cefotaxime, and aztreonam with relative hydrolysis rates of < 8% of that observed for benzylpenicillin. Both enzymes were inhibited by clavulanic acid and tazobactam. Nucleotide sequencing of the genes coding for RP-5.2 and RP-5.6 revealed sequences identical to those of the TEM-12 and TEM-10 beta-lactamase genes, respectively. Both genes were derived from a TEM-1 sequence related to that of the gene encoded on the Tn2 transposon. Single point mutations are required to progress from TEM-1 to TEM-12 and from TEM-12 to TEM-10. Extracts from broths grown from single cell isolates of the strain producing TEM-12 and TEM-10 were shown to contain both enzymes. Transconjugants producing either the TEM-12 or the TEM-10 beta-lactamase were obtained. A significant finding was that both enzymes were encoded by plasmids with identical restriction digest patterns. These studies show that mutations leading to extended-spectrum beta-lactamases can occur sequentially in the same organism, with the genes encoding both enzymes maintained stably.

Sequences of MGH-1, YOU-1, and YOU-2 extended-spectrum beta-lactamase genes

Genes for MGH-1, YOU-1, and YOU-2 extended-spectrum beta-lactamases have been cloned and sequenced. The gene for MGH-1 has the sequence of blaTEM-10, YOU-2 has that of blaTEM-12, and YOU-1 has that of blaTEM-26. All have evolved from blaTEM-1b but have the strong dual promoter sequence of blaTEM-2.

Novel and emerging mechanisms of antimicrobial resistance in nosocomial pathogens

Nosocomial pathogens frequently are resistant to antimicrobial agents. Although methicillin-resistant strains of Staphylococcus aureus continue to be a major problem in many hospitals, several new types of resistance determinants have been noted among organisms causing hospital-acquired infections. The mechanisms include extended spectrum beta-lactamases in gram-negative bacilli; resistance to beta-lactams, glycopeptides, and high levels of aminoglycosides among enterococci; quinolone resistance in isolates of methicillin-resistant S. aureus; and the spread of multiple resistance genes simultaneously in gram-negative organisms via Tn21-related genetic elements. These novel mechanisms of resistance complicate the treatment of nosocomial infections by limiting the number of effective antimicrobial agents available to the clinician. It is important for infection control practitioners and microbiologists to work together to detect and control the spread of resistant pathogens in the hospital setting.

High-level resistance to cefotaxime and ceftazidime in Klebsiella pneumoniae isolates from Cleveland, Ohio

Two isolates of Klebsiella pneumoniae possessing both TEM-1 and SHV-2 beta-lactamases were isolated from patients at the Cleveland Clinic in 1988. The beta-lactamases were discriminated and identified by using substrate hydrolysis data and an isoelectric focusing procedure in which the gel was overlaid with beta-lactamase inhibitors.

Properties of plasmids responsible for production of extended-spectrum beta-lactamases

The extended-spectrum beta-lactamases are believed to arise by mutations which alter the configuration around the active site of TEM- and SHV-type enzymes so as to increase their efficiency with otherwise nonhydrolyzable cephalosporins and monobactams. This hypothesis predicts that the genes for these new enzymes should be found on the same wide variety of plasmids that encode TEM-1, TEM-2, and SHV-1 beta-lactamases and that at least some of them should be mediated by transposons. Fifteen plasmids, each encoding an extended-spectrum beta-lactamase, were examined. Unlike the average TEM plasmid, all were large, ranging in size from 80 to 300 kb. All determined resistance to multiple antimicrobial agents, ranging from 5 to 11, and some conferred resistance to heavy metals and UV radiation as well. The plasmids belonged to a limited number of incompatibility (Inc) groups, including IncC, IncFI, IncHI2, and IncM. Because most of the mutations giving rise to extended-spectrum activity are G.C----A.T transitions and some of the mutant genes have as many as four base substitutions, a plasmid-determined mutator gene was searched for, but no such property was found. Several techniques were used to detect transposition of the extended-spectrum beta-lactamase genes, but a mobile genetic element could not be demonstrated even though eight of the plasmids hybridized with a DNA probe derived from the tnpR gene of Tn3. The genesis of extended-spectrum beta-lactamases may not be as simple as has been supposed.

Outbreak of ceftazidime resistance caused by extended-spectrum beta-lactamases at a Massachusetts chronic-care facility

During a 4-month period in late 1988, we isolated ceftazidime-resistant strains of Klebsiella pneumoniae and other members of the family Enterobacteriaceae from 29 patients at a chronic-care facility in Massachusetts. Ceftazidime resistance resulted from two distinct extended-spectrum beta-lactamases of the TEM type which efficiently hydrolyzed the cephalosporin: YOU-1 with a pI of 5.57 and YOU-2 with a pI of 5.2. Genes encoding these enzymes were present on different but closely related high-molecular-weight, multiple antibiotic resistance plasmids of the H12 incompatibility group and were transferable by conjugation in vitro. Agarose gel electrophoresis of extracts from clinical isolates indicated that this outbreak arose from plasmid transmission among different strains of the family Enterobacteriaceae rather than from dissemination of a single resistant isolate. Isolation rates of ceftazidime-resistant organisms transiently decreased after use of this drug was restricted, but resistant isolates continued to be recovered 7 months after empiric use of ceftazidime ceased.

Direct involvement of IS26 in an antibiotic resistance operon

The plasmid pBWH77, originally found in an isolate of Klebsiella pneumoniae, harbors a new antibiotic resistance operon containing two resistance genes transcribed from an IS26-hybrid promoter, as shown by nucleotide sequencing, mRNA mapping, and the effect of inserting a transcription terminator within the promoter-proximal gene. The nucleotide sequence of this region revealed that the operon (IAB) is made up of three sections that are closely related to previously described genetic elements. The -35 region of the promoter, together with the adjacent sequence, is identical to sequences of the IS26 element. One of the resistance genes, aphA7, which is located next to the hybrid promoter, confers assistance to neomycin and structurally related aminoglycosides. This aphA7 gene is highly homologous to aphA1 of Tn903, with five nucleotide differences. The second gene, blaS2A, encodes an evolved SHV-type beta-lactamase with a pI of 7.6 that confers resistance to the broad-spectrum cephalosporins cefotaxime and ceftizoxime. The deduced amino acid sequence of SHV-2A shows that amino acid 238 is a serine, a residue reported to confer resistance to cefotaxime. We discuss how the operon may have evolved by a combination of insertion sequence-mediated genetic rearrangements and acquisitive evolution. Using phylogenetic parsimony, we show that aphA7 in the IAB operon evolved from an ancestral form similar to aphA1 in Tn903 and that blaS2A evolved from an ancestral form similar to blaS1.

Failure of ceftazidime-amikacin therapy for bacteremia and meningitis due to Klebsiella pneumoniae producing an extended-spectrum beta-lactamase

A multiple trauma patient failed treatment with ceftazidime and amikacin for bacteremia and meningitis due to a Klebsiella pneumoniae strain that produced a novel, plasmid-mediated beta-lactamase. Both pre- and posttreatment isolates were resistant to ceftazidime (MIC, greater than or equal to 64 micrograms/ml) and various penicillins but not to other expanded-spectrum cephalosporins. The beta-lactamase had a pI of 5.25 and was encoded on a conjugal plasmid of approximately 150 kilobases. DNA hybridization studies indicated that the enzyme was a TEM derivative.

Pathophysiologic basis for the use of third-generation cephalosporins

After 10 years of use, the third-generation cephalosporins remain excellent antibiotics. They have superior activity against selected streptococcal species compared with other cephalosporins, and superior activity against Haemophilus, Neisseria, Branhamella, and other less common oral gram-negative aerobic species. Despite a very broad spectrum of activity, the third-generation cephalosporins, like all other cephalosporins, have only poor activity against enterococci, Listeria, Corynebacterium jekeium, and methicillin-resistant staphylococci. Over the past 10 years, the activity of the third-generation cephalosporins against Escherichia coli, Klebsiella, Proteus, Providencia, Serratia, Haemophilus, and Neisseria has remained excellent. Equally as important, though perhaps less well recognized, is the activity of some of these agents against mouth anaerobic species and the anaerobic Bacteroides and Clostridium spp. of the pelvic area. At present, there are two main threats to the continued use of the third-generation cephalosporins. These are the increasing number of infections due to Enterobacter spp., which constitutively produce large amounts of a beta-lactamase that hydrolyzes cephalosporins, and the recent appearance of Klebsiella spp. in many parts of the world that possess new plasmid-mediated beta-lactamases that destroy cefotaxime, ceftazidime, and related third-generation parenteral cephalosporins. Correlation of pharmacologic properties with in vitro activity provides information as to reasonable dosage regimens for the third-generation cephalosporins. For most serious infections cefotaxime, ceftizoxime, and ceftazidime should be given three times a day provided that the patient has relatively normal renal function. Ceftriaxone can be administered once daily in less severe infections. The use of lower doses or less frequent dosing with cefotaxime, ceftizoxime, or ceftazidime is recommended in aged patients whose renal function is impaired. The unique interaction of cefotaxime with its active metabolite, desacetylcefotaxime, allows cefotaxime to be administered less frequently than three times a day in selected anaerobic infections. Correlation of the antibacterial activity and pharmacology of cephalosporins will help us to tailor their use more appropriately, so that the third-generation cephalosporins will remain useful antimicrobial agents for a further decade.

Discovery and development of new antimicrobial agents

The unprecedented growth in the number of new antibiotics over the past two decades has been the result of extensive research efforts that have exploited the growing body of knowledge describing the interactions of antibiotics with their targets in bacterial cells. Information gained from one class of antimicrobial agents has often been used to advance the development of other classes. In the case of beta-lactams, information on structure-activity relationships gleaned from penicillins and cephalosporins was rapidly applied to the cephamycins, monobactams, penems, and carbapenems in order to discover broad-spectrum agents with markedly improved potency. These efforts have led to the introduction of many new antibiotics that demonstrate outstanding clinical efficacy and improved pharmacokinetics in humans. The current review discusses those factors that have influenced the rapid proliferation of new antimicrobial agents, including the discovery of new lead structures from natural products and the impact of bacterial resistance development in the clinical setting. The development process for a new antibiotic is discussed in detail, from the stage of early safety testing in animals through phase I, II, and III clinical trials.

Epidemiology of extended spectrum beta-lactamases

Beta-lactamases play a major part in resistance, as recently redemonstrated by the emergence of extended spectrum beta-lactamases. Since its discovery in FR Germany, SHV-2 has been reported from four continents and CTX-1 (TEM-3) was established in at least 26 French hospitals. More than 12 other enzymes have been individualized. The newest aspect of resistance was probably underestimated because most strains of enterobacteria (mainly Klebsiella pneumoniae) appeared susceptible to oxyimino-beta-lactams as suggested by MICs or diameters of inhibition zone sizes. The double-disk synergy test between amoxicillin/clavulanic acid and oxyimino-beta-lactams was useful to easily detect two susceptibility patterns (CTX, CAZ). Extended spectrum beta-lactamases isolated among nosocomial isolates of enterobacteria (urines, blood, wound, sputum cultures) mostly from intensive care units have spread through hospitals. If outbreaks were described, numerous serotypes were identified in Klebsiella pneumoniae. In France the distribution of extended spectrum beta-lactamases showed that CTX-1 (TEM-3) was well distributed among ten species unlike SHV-type enzymes (SHV-2, SHV-3, SHV-4) preferentially detected in Klebsiella pneumoniae. A majority of strains produced CAZ-type enzymes in Escherichia coli. Some isolates produced two extended spectrum beta-lactamases. In Tunisia extended spectrum beta-lactamase producing strains were mainly identified among pediatric isolates of Klebsiella pneumoniae, Salmonella and Escherichia coli; SHV-2 was predominant but recently CTX-1 and two other types with an isoelectric point of 6.35 and 5.4 (phenotype CTX) were individualized. Because plasmid-encoded, this mechanism was spreading in France among enterobacteria with other resistance markers (e.g. netilmicin, amikacin) for CTX-1 unlike SHV-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Overview of mechanisms of bacterial resistance

Many antimicrobial agents have been either found in nature or synthesized in the past 45 years. Antibacterial agents inhibit cell-wall formation, disrupt cytoplasmic membrane function, prevent DNA synthesis, interfere with protein synthesis, and halt folate synthesis. Resistance to antibiotics is a result of three major mechanisms: prevention of the antibacterial agent from reaching its receptor site, production of altered targets, and destruction or modification of the agents. Bacterial resistance has occurred due to chromosomal changes or the presence of plasmids and transposons. Resistance to beta-lactams is the result of beta-lactamases and the production of altered penicillin-binding proteins as well as altered cell-wall permeability. Important examples of these resistance forms occur in staphylococci and pneumococci which have altered penicillin-binding proteins. A new form of target change has been the production of proteins in enterococci that inhibit the activity of glycopeptides. Beta-lactamases are present in both Gram-positive and Gram-negative species; recently, new plasmid beta-lactamases have been isolated that destroy iminomethoxy and iminocarboxy cephalosporins. Resistance to aminoglycosides is due to enzymes that acetylate, adenylate, or phosphorylate aminoglycosides that inhibit binding to ribosomes and thus cause the poor uptake of drug. Tetracycline resistance is due to plasmids which cause efflux of the agent from the cytoplasm. Macrolide and lincinoid resistance is the result of an altered 23S ribosomal component of the 50S ribosomes. Sulfonamide and trimethoprim resistance is due to production of altered synthetase and reductase enzymes essential in the synthesis of folate.(ABSTRACT TRUNCATED AT 250 WORDS)