Principal beta-lactamases responsible for resistance to beta-lactam antibiotics in urinary tract infections

Emerging Strategies to Combat β-Lactamase Producing ESKAPE Pathogens

Since the discovery of penicillin by Alexander Fleming in 1929 as a therapeutic agent against staphylococci, β-lactam antibiotics (BLAs) remained the most successful antibiotic classes against the majority of bacterial strains, reaching a percentage of 65% of all medical prescriptions. Unfortunately, the emergence and diversification of β-lactamases pose indefinite health issues, limiting the clinical effectiveness of all current BLAs. One solution is to develop β-lactamase inhibitors (BLIs) capable of restoring the activity of β-lactam drugs. In this review, we will briefly present the older and new BLAs classes, their mechanisms of action, and an update of the BLIs capable of restoring the activity of β-lactam drugs against ESKAPE (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens. Subsequently, we will discuss several promising alternative approaches such as bacteriophages, antimicrobial peptides, nanoparticles, CRISPR (clustered regularly interspaced short palindromic repeats) cas technology, or vaccination developed to limit antimicrobial resistance in this endless fight against Gram-negative pathogens.

Review of phenotypic assays for detection of extended-spectrum β-lactamases and carbapenemases: a microbiology laboratory bench guide

Background

Infections caused by gram-negative antibiotic-resistant bacteria continue to increase. Despite recommendations by the Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) with regards to detection of antibiotic degrading enzymes secreted by these bacteria, the true prevalence of extended-spectrum β-lactamase (ESBL) and carbapenemase producers remains a difficult task to resolve. Describing of previously designed phenotypic detection assays for ESBLs and carbapenemases in a single document avails a summary that allows for multiple testing which increases the sensitivity and specificity of detection.

Methods and aims

This review, therefore, defined and classified ESBLs and carbapenemases, and also briefly described how the several previously designed phenotypic detection assays for the same should be performed.

Conclusion

Extended-spectrum β-lactamase and carbapenemase detection assays, once performed correctly, can precisely discriminate between bacteria producing these enzymes and those with other mechanisms of resistance to β-lactam antibiotics.

SHV Hyperproduction as a Mechanism for Piperacillin-Tazobactam Resistance in Extended-Spectrum Cephalosporin-Susceptible Klebsiella pneumoniae

This study aimed to determine the mechanism of resistance to piperacillin-tazobactam (TZP) in Klebsiella pneumoniae bloodstream isolates that are susceptible to extended-spectrum cephalosporins (ESCs). Antibiotic susceptibility was determined for K. pneumoniae isolated from children with bacteremia. The β-lactamase genes were detected using a large-scale bla detection method (_LARGE-SCALEblaFinder) and confirmed by sequencing analysis. The isolates were further characterized by β-lactamase activity assays and multilocus sequence typing. Among the 300 bloodstream isolates of K. pneumoniae, 11 (3.7%) were TZP resistant but ESC susceptible. The TZP minimum inhibitory concentrations (MICs) of the isolates ranged from 128/4 to >2,048/4 mg/L. Avibactam markedly inhibited piperacillin resistance, reducing the MICs to the range of ≤1 to 8 mg/L. Among the 11 isolates, four hyperproduced SHV-1 and two hyperproduced SHV-11, exhibiting 77- to 496-fold higher β-lactamase activity compared with the SHV-1- and SHV-11-producing reference strains that are susceptible to TZP. OXA-1 was coproduced in three isolates, and the remaining two isolates produced TEM-30. Transformants with recombinant plasmids carrying the β-lactamase genes demonstrated an increase in MICs of TZP. The TZP-resistant and ESC-susceptible isolates were not epidemiologically related. Hyperproduction of SHV-1 and SHV-11 represents a novel mechanism for reducing TZP activity in K. pneumoniae isolates resistant to ESCs. Continuous monitoring and investigation of TZP-resistant isolates are needed in the current era of high TZP consumption.

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.

Production of β-Lactamase Inhibitors by Streptomyces Species

β-Lactamase inhibitors have emerged as an effective alternative to reduce the effects of resistance against β-lactam antibiotics. The Streptomyces genus is known for being an exceptional natural source of antimicrobials and β-lactamase inhibitors such as clavulanic acid, which is largely applied in clinical practice. To protect against the increasing prevalence of multidrug-resistant bacterial strains, new antibiotics and β-lactamase inhibitors need to be discovered and developed. This review will cover an update about the main β-lactamase inhibitors producers belonging to the Streptomyces genus; advanced methods, such as genetic and metabolic engineering, to enhance inhibitor production compared with wild-type strains; and fermentation and purification processes. Moreover, clinical practice and commercial issues are discussed. The commitment of companies and governments to develop innovative strategies and methods to improve the access to new, efficient, and potentially cost-effective microbial products to combat the antimicrobial resistance is also highlighted.

β-Lactams and β-Lactamase Inhibitors: An Overview

β-Lactams are the most widely used class of antibiotics. Since the discovery of benzylpenicillin in the 1920s, thousands of new penicillin derivatives and related β-lactam classes of cephalosporins, cephamycins, monobactams, and carbapenems have been discovered. Each new class of β-lactam has been developed either to increase the spectrum of activity to include additional bacterial species or to address specific resistance mechanisms that have arisen in the targeted bacterial population. Resistance to β-lactams is primarily because of bacterially produced β-lactamase enzymes that hydrolyze the β-lactam ring, thereby inactivating the drug. The newest effort to circumvent resistance is the development of novel broad-spectrum β-lactamase inhibitors that work against many problematic β-lactamases, including cephalosporinases and serine-based carbapenemases, which severely limit therapeutic options. This work provides a comprehensive overview of β-lactam antibiotics that are currently in use, as well as a look ahead to several new compounds that are in the development pipeline.

Bottlenecks in the transferability of antibiotic resistance from natural ecosystems to human bacterial pathogens

It is generally accepted that resistance genes acquired by human pathogens through horizontal gene transfer originated in environmental, non-pathogenic bacteria. As a consequence, there is increasing concern on the roles that natural, non-clinical ecosystems, may play in the evolution of resistance. Recent studies have shown that the variability of determinants that can provide antibiotic resistance on their expression in a heterologous host is much larger than what is actually found in human pathogens, which implies the existence of bottlenecks modulating the transfer, spread, and stability of antibiotic resistance genes. In this review, the role that different factors such as founder effects, ecological connectivity, fitness costs, or second-order selection may have on the establishment of a specific resistance determinant in a population of bacterial pathogens is analyzed.

Identification and characterization of beta-lactamase inhibitor protein-II (BLIP-II) interactions with beta-lactamases using phage display

Protein-protein interactions are critical to cellular processes yet the ability to predict and rationally design interactions is limited because of incomplete knowledge of the principles governing these interactions. The beta-lactamase inhibitory protein (BLIP)/beta-lactamase interaction has become a model system to investigate protein-protein interactions and has been the focus of several structural, thermodynamic and binding specificity studies. BLIP-II also inhibits beta-lactamase but has no sequence homology with BLIP. The structure of BLIP-II in complex with TEM-1 beta-lactamase revealed that BLIP-II has a completely different structure than BLIP but it interacts with the same protruding loop-helix region of TEM-1 as does BLIP. The significance of the individual interacting residues in molecular recognition by BLIP-II is currently unknown. Therefore, a phage display vector was developed with the purpose of expressing BLIP-II onto the surface of the M13 filamentous bacteriophage. The BLIP-II displayed phage bound to TEM-1 with picomolar affinity indicating that BLIP-II is properly folded while on the surface of the phage. The phage system, as well as enzyme inhibition assays with purified proteins, revealed that BLIP-II is a more potent inhibitor than BLIP for several class A beta-lactamases with K(i) values in the low picomolar range.

Pyrosequencing using the single-nucleotide polymorphism protocol for rapid determination of TEM- and SHV-type extended-spectrum beta-lactamases in clinical isolates and identification of the novel beta-lactamase genes blaSHV-48, blaSHV-105, and blaTEM-155

TEM- and SHV-type extended-spectrum beta-lactamases (ESBLs) are the most common ESBLs found in the United States and are prevalent throughout the world. Amino acid substitutions at a number of positions in TEM-1 lead to the ESBL phenotype, although substitutions at residues 104 (E to K), 164 (R to S or H), 238 (G to S), and 240 (E to K) appear to be particularly important in modifying the spectrum of activity of the enzyme. The SHV-1-derived ESBLs are a less diverse collection of enzymes; however, the majority of amino acid substitutions resulting in an ESBL mirror those seen in the TEM-1-derived enzymes. Pyrosequencing by use of the single-nucleotide polymorphism (SNP) protocol was applied to provide sequence data at positions critical for the ESBL phenotype spanning the bla(TEM) and bla(SHV) genes. Three novel beta-lactamases are described: the ESBLs TEM-155 (Q39K, R164S, E240K) and SHV-105 (I8F, R43S, G156D, G238S, E240K) and a non-ESBL, SHV-48 (V119I). The ceftazidime, ceftriaxone, and aztreonam MICs for an Escherichia coli isolate expressing bla(SHV-105) were >128, 128, and >128 microg/ml, respectively. Likewise, the ceftazidime, ceftriaxone, and aztreonam MICs for an E. coli isolate expressing bla(TEM-155) were >128, 64, and > 128 microg/ml, respectively. Pyrosequence analysis determined the true identity of the beta-lactamase on plasmid R1010 to be SHV-11 rather than SHV-1, as previously reported. Pyrosequencing is a real-time sequencing-by-synthesis approach that was applied to SNP detection for TEM- and SHV-type ESBL identification and represents a robust tool for rapid sequence determination that may have a place in the clinical setting.

Extended-Spectrum β-Lactamases (ESBLs): Characterization, Epidemiology and Detection

Beta-lactamases of Enterobacteriaceae are the most important mechanism of resistance against beta-lactam drugs. Two types of beta-lactamases can confer resistance against 3rd generation cephalosporins. Chromosomally mediated beta-lactamases are inducible and are not inhibited by clavulanic acid. Resistance due to these enzymes is non-transferable. The 2nd type of enzyme is plasmid-mediated beta-lactamases, which are inhibited by clavulanic acid. These enzymes are more important clinically as these can be transferred between various species of Enterobacteriaceae. These enzymes are called extended-spectrum beta-lactamases (ESBLs). ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Antibacterial choice is often complicated by multi-resistance. ESBLs can confer resistance against all beta-lactam drugs except carbapenems and cephamycins. Nursing home patients may be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms. Use of broad-spectrum oral antibiotics and probably poor infection control practices may facilitate spread of this plasmid-mediated resistance. In addition to known populations at risk, ambulatory patients with chronic conditions represent another patient population that may harbor ESBL-producing organisms. Various methods can be used for detection of ESBLs in the laboratory. These tests include double disc diffusion test, Vitek ESBL test, E Tests, MIC Determination, genetic method, and isoelectric focusing (IEF).

Carbapenemases: the versatile beta-lactamases

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.

Hospital outbreak of Klebsiella pneumoniae resistant to broad-spectrum cephalosporins and beta-lactam-beta-lactamase inhibitor combinations by hyperproduction of SHV-5 beta-lactamase

An aminoglycoside- and ceftazidime-resistant strain of Klebsiella pneumoniae K2 producing the extended-spectrum beta-lactamase SHV-5 infected or colonized 14 pediatric patients at Guy's Hospital. The patients were mostly neonates recovering from cardiac surgery for congenital defects. The organism was also isolated from a nurse and from the father of one of the children. Four patients had septicemia, and two septicemic neonates with postoperative renal failure died. Aminoglycoside and cephalosporin resistance transferred to Escherichia coli in vitro on a 160-kb plasmid, and a similar resistant E. coli strain was isolated from the stools of one of the affected children. The epidemic organism colonized the bowel and skin and was probably transmitted via staff hands. Five wards were involved because of extensive patient movements. The outbreak was controlled by patient isolation and attention to handwashing. All of the isolates of the outbreak strain were identical by phage typing, ribotyping, plasmid profiling, and biochemical and serological testing, but they varied in their production of SHV-5. Some isolates produced normal amounts of SHV-5 and were susceptible to beta-lactam-beta-lactamase inhibitor combinations. Others, including the single isolate of multiresistant E. coli, produced up to five times as much enzyme as "normal" isolates. This hyperproduction resulted in increased resistance to several penicillins and cephalosporins and to the beta-lactam-beta-lactamase inhibitor combinations amoxicillin-clavulanic acid, ampicillin-sulbactam, piperacillin-tazobactam, and ceftazidime-clavulanic acid. The hyperproduction of SHV-5 by K. pneumoniae and E. coli seen in this outbreak suggests that beta-lactam-beta-lactamase inhibitor combinations may be unreliable for the treatment of organisms producing extended-spectrum beta-lactamases.

Bacteriuria, incidence, causative microorganism, and susceptibility pattern at Qatif Central Hospital

From August 1988 to January 1990, a total of 13,193 urine specimens were collected from inpatients and outpatients of Qatif Central Hospital, located in the Eastern Province of Saudi Arabia, to determine the incidence of significant bacteriuria, causative microorganisms, and antimicrobial susceptibility. Among these, 1004 specimens (7.6%) showed significant bacteriuria. In community-acquired cases of bacteriuria, the prevalence was greater in female than in male patients. The most common organisms isolated were Escherichia coli and Klebsiella-Enterobacter species. Antimicrobial susceptibility showed high resistance to ampicillin, and therefore we suggest that norfloxacin be considered in empherical therapy, particularly in suspected cases of Pseudomonas urinary tract infections. For patients with an indwelling catheter, it is important to differentiate between colonization and infection before initiating antimicrobial therapy. The difficulties in treating urinary tract infections in patients with an indwelling catheter emphasize the importance of preventive measures.

SAR-2: identification of a novel plasmid-encoded beta-lactamase from India

A novel beta-lactamase has been identified in an Escherichia coli strain isolated in South India. The beta-lactamase gene was carried on a plasmid (pUK734) along with resistance determinants to sulphonamides and tetracycline. The novel enzyme has a pI of 8.3 and an Mr of 36,000. The enzyme has a broad-spectrum of activity against both penicillins and cephalosporins. It is also active against oxacillin and methicillin.

Antibiotic resistance in the tropics. 1. The genetics of bacterial ampicillin resistance in tropical areas

Ampicillin and its derivatives are the most widely used beta-lactam antibiotics throughout the world. Ampicillin resistance in Gram-negative bacteria is usually manifested by plasmid-encoded beta-lactamases, which hydrolyse the beta-lactam ring of the antibiotic. There are at least 30 different plasmid-encoded beta-lactamases but almost all of them are found very infrequently. The one exception is the TEM-1 beta-lactamase which is found wherever transferable ampicillin resistance emerges and accounts for over 50% of all plasmid encoded ampicillin resistance. In India, the incidence of ampicillin resistance is high (82%) and, amongst Escherichia coli, a significant proportion of the plasmid-encoded beta-lactamases are different from those found in the United Kingdom. Although many Gram-negative species are able to accept the TEM-1 beta-lactamase, certain species have a pre-disposition to their own plasmid beta-lactamase types.

Evaluation of plasmid-encoded beta-lactamase resistance in Escherichia coli blood culture isolates

The frequency of beta-lactam resistance was determined among 313 strains of Escherichia coli, 119 of Enterobacter/Klebsiella/Proteus spp., and 48 of Pseudomonas spp. isolated from blood cultures (at Turku University Central Hospital and Turku City Hospital) in 1983-1987. During this period the MIC50 of ampicillin for Escherichia coli increased from 8 to 32 micrograms/ml, the MIC90 of piperacillin from 16 to greater than 32 micrograms/ml and the MIC90 of cefuroxime from 4-8 to 16 micrograms/ml. Among 172 ampicillin-resistant isolates beta-lactamase-mediated resistance was characterized by DNA hybridization with TEM-1, SHV-1, OXA-1, OXA-2, PSE-1, PSE-2 and PSE-4 beta-lactamase probes and by isoelectric focusing. Beta-lactamase types found were TEM-1, TEM-2, SHV-1 and OXA-1. Isoelectric focusing did not show any other plasmid-mediated beta-lactamase varieties. Piperacillin-resistant strains showed mostly TEM-1 activity, but also produced OXA-1 and chromosomal beta-lactamase. Interestingly, a decrease in cefuroxime susceptibility in Escherichia coli occurred in a few OXA-1 producing strains as well as in strains that produced only chromosomal beta-lactamase. Two Escherichia coli strains that overproduced chromosomal beta-lactamase had increased ceftazidime MIC values (8-16 micrograms/ml).

Cephaloridine resistance in gram-negative bacteria isolated in Scotland

The incidence of cephaloridine resistance (minimum inhibitory concentration, MIC greater than 8 mg L-1) in isolates from urinary tract infections was 45.1% in Glasgow, 22.6% in Dundee and 25.9% in Edinburgh. The incidence of ampicillin resistance (MIC greater than 8 mg L-1) was even higher:- being 45.2% in Dundee and 48.5% in Edinburgh. In Glasgow, the incidence was 71.9% which is the highest proportion of ampicillin resistance reported in the United Kingdom. The cephaloridine resistant strains were examined for beta-lactamase production. Amongst these strains 50.8% produced only a chromosomal beta-lactamase, whereas 47.9% produced beta-lactamases which were potentially plasmid-mediated on the basis of biochemical tests. Only 1% of the resistant strains produced no detectable beta-lactamase.

In vitro evaluations of aminopenicillin/beta-lactamase inhibitor combinations

Sulbactam/ampicillin (Unasyn) possesses the antimicrobial activity of each drug plus the synergistic action and qualities of sulbactam used as a beta-lactamase inhibitor. The combination has a spectrum of activity against many Enterobacteriaceae, Haemophilus species, Branhamella catarrhalis, pathogenic Neisseria species, Acinetobacter anitratus, some pseudomonads, nearly all anaerobes (including Bacteroides), Staphylococcus species, streptococci, and the enterococci. Sulbactam/ampicillin was found to be bactericidal, and its minimum inhibitory concentrations (MICs) affected only by high inoculum concentrations (greater than 10(6) CFU/ml). Fixed ratio in vitro susceptibility tests appear to be preferred, since they best approximate clinical formulations and drug pharmacokinetics. The ratio of 1:1 has been studied, but other ratios such as 1:2 (sulbactam/ampicillin) should be evaluated to promote greater test accuracy. Separate interpretive criteria for most Gram-negative bacteria, Haemophilus, and staphylococci appear unnecessary for some tests.

Monoclonal antibodies to TEM-1 plasmid-mediated beta-lactamase

At least 28 plasmid-mediated beta-lactamases have been described in gram-negative bacteria. To assess the relationship among these enzymes, we produced and characterized 28 murine monoclonal antibodies to the TEM-1 plasmid-mediated beta-lactamase. Radial immunodiffusion identified 3 monoclonal antibodies as immunoglobulin M (IgM), 18 as subclass IgG1, 2 as IgG2a, and 5 as IgG2b. Using a newly described enzyme immunoassay, cross-reactivity of 16 of these monoclonal antibodies was tested against 24 plasmid-determined beta-lactamases. The 16 monoclonal antibodies cross-reacted with TEM-2 and TLE-1 and, to a certain extent, SHV-1. Different levels of cross-reactivity were also observed with OXA-3 (11 of 16), OXA-7 (8 of 16), OXA-1 (2 of 16), OXA-6 (2 of 16), and AER-1 (2 of 16). Six monoclonal antibodies demonstrated partial neutralization of beta-lactamase activity. This study suggests that common epitopes are shared by nine biochemically distinct plasmid-mediated beta-lactamases. On the basis of cross-reactivities with these monoclonal antibodies, we identified four epitopes on TEM-1, TEM-2, TLE-1, and SHV-1 beta-lactamases.

In vitro antimicrobial spectrum, occurrence of synergy, and recommendations for dilution susceptibility testing concentrations of the cefoperazone-sulbactam combination

Broth microdilution tests and an antimicrobial interaction (synergy) studies using various combinations of cefoperazone and sulbactam were performed in an effort to determine the most appropriate in vitro dilution test system. The test results with cefoperazone and sulbactam were categorized as synergistic (complete or partial) for nearly 80% of the strains isolated from clinical trial patients. The results indicate that the cefoperazone-sulbactam fixed ratio (2:1) maximized the cefoperazone spectrum of activity and best approximated the parenteral formulation of the drug. The cefoperazone-sulbactam combination had a greater antimicrobial activity than did the other comparison beta-lactams, except for imipenem, tested against strains of the family Enterobacteriaceae. To be consistent with the National Committee for Clinical Laboratory Standards interpretive breakpoints for cefoperazone alone, the following MIC breakpoints should be applied to the combination (2:1 ratio): less than or equal to 16/8 micrograms/ml, susceptible; 32/16 micrograms/ml, moderately susceptible; and greater than or equal to 64/32 micrograms/ml, resistant.

Detection of TEM beta-lactamase genes by non-isotopic spot hybridisation

A 998 bp fragment of plasmid pBR322, comprising part of the TEM-1 beta-lactamase gene, was labelled with biotin-11-dUTP for use as a DNA probe in a rapid non-isotopic spot hybridisation test. Diluted broth cultures of bacteria producing different beta-lactamases were filtered onto nitrocellulose and lysed in situ. Following pre-hybridisation treatment with proteinase K, hybridisation with the labelled probe was demonstrated using a commercially available streptavidine/polyalkaline phosphatase-based detection system. The probe was highly specific, reacting only with strains producing either the TEM-1 or structurally similar TEM-2 enzyme. An inoculum of 3-4 X 10(6) cells gave optimum positive discrimination. When 90 recent ampicillin-resistant strains of Escherichia coli isolated from patients with urinary tract infections were screened using the system, 72% gave a positive hybridisation signal.

Cost-effective use of antibiotic prophylaxis for cesarean section

Clinical experience has indicated that the prophylactic use of antibiotics reduces infectious morbidity in patients undergoing cesarean section. Several factors must be considered (for instance, in vivo and in vitro efficacy, patient allergies, side effect profiles, status of host defenses, the total cost of therapy, and the risk of selecting resistant organisms that cause superinfections) before prescribing prophylactic antibiotic drugs for this indication. Moreover, medical-legal consequences associated with potential postpartum infections must be considered in assessing the costs and impact of a prophylactic regimen. Results of comparative antibiotic trials in indigent patients undergoing cesarean section demonstrated differing rates of successful antibiotic prophylaxis: piperacillin, 98%; cefoxitin, 91%; cephalothin and ceftazidime, 82%; cefotaxime, 80%; and ampicillin, 77%. Although the acquisition costs of antibiotics vary greatly, these costs are dwarfed by the substantial cost savings that can be realized by use of broad-spectrum antibiotics, which, in our hands, have resulted in reduced laboratory and pharmacy expenses and decreased hospital stays for both mother and neonate. Controlled studies designed to investigate microbiologic as well as clinical efficacy of antibiotics are indicated. Further refinements in individualizing antibiotic regimens according to patient population should be sought.

Spread of SHV-1 beta-lactamase in Escherichia coli isolated from fecal samples in Africa

Ninety-seven (42%) Escherichia coli strains isolated in Senegal from fecal samples produced beta-lactamases. Among them, 29 (30%) isolates produced SHV-1 beta-lactamase that was plasmid mediated. The plasmids belonged to four incompatibility groups. Various degrees of TEM-1 expression in the presence of SHV-1 were observed.

Molecular hybridization versus isoelectric focusing to determine TEM-type beta-lactamases in gram-negative bacteria

Isoelectric focusing and molecular hybridization with a TEM DNA probe were used to screen for TEM beta-lactamase in 328 bacterial isolates representing 11 gram-negative genera. The TEM enzyme was detected in 50% of isolates, and nine additional types of beta-lactamase could be identified in 36.9% of isolates. The TEM gene was detected in 53.6% of isolates. The results obtained by both methods were concordant in 92.7% of the entire sample. In situ colony hybridization with a specific probe therefore appears to be a convenient method to screen rapidly for the presence of homologous genetic sequences among a large number of isolates. Positive hybridization was observed for 16 isolates in which no TEM beta-lactamase was detected by isoelectric focusing. The significance of this hybridization remains to be determined.

Plasmid penicillin resistance in Vibrio cholerae: identification of new beta-lactamase SAR-1

Two strains of Vibrio cholerae biotype El Tor, isolated in Tanzania, possessed a single IncC resistance plasmid of 113 kilobases. Both plasmids encoded the production of a novel beta-lactamase, SAR-1, which was 33,700 daltons in size and was able to hydrolyze carbenicillin as well as penicillin G. The SAR-1 beta-lactamase was quite distinct from all other plasmid beta-lactamases by virtue of its unusually low isoelectric point and a combination of its size, substrate profile, and inhibition properties. This enzyme is only the second beta-lactamase identified in V. cholerae species and the first to be reported in V. cholerae strains isolated in Southern Africa.

Differential effect of impaired renal function on the kinetics of clavulanic acid and amoxicillin

Amoxicillin and clavulanic acid are prescribed as a fixed drug combination. The purpose of the present study was to assess the influence of various degrees of renal insufficiency (glomerular filtration rate [GFR], less than 5 to greater than 75 ml/min per 1.73 m2) on the pharmacokinetics of amoxicillin and clavulanic acid following oral (500 and 125 mg of amoxicillin and clavulanic acid, respectively) and intravenous (1,000 and 200 mg, respectively) dosing. The volume of distribution and the systemic availability were independent of the renal function, while the total body clearance and the renal and the nonrenal clearance of amoxicillin and clavulanic acid decreased with decreasing renal function. The decrease in the total body clearance was more pronounced for amoxicillin than for clavulanic acid. This explains the increase in the ratio of the area under the plasma concentration versus time curve of amoxicillin to that of clavulanic acid with decreasing glomerular filtration rate after oral dosing; for example for a GFR of 75 ml/min, the ratio of amoxicillin to clavulanic acid was 4.9 +/- 1.2; for a GFR of 35 to 75 ml/min, 5.3 +/- 2.4; for a GFR of 10 to 35 ml/min, 11.9 +/- 5.8; for a GFR of 5 to 10 ml/min, 13.4 +/- 9.1; and for patients on hemodialysis, 14.7 +/- 5.3. Dosage recommendations are suggested which prevent undue accumulations of amoxicillin while maintaining adequate concentrations of clavulanic acid.

Contribution of beta-lactamases to bacterial resistance and mechanisms to inhibit beta-lactamases

Resistance of bacteria to beta-lactam antibiotics has become a serious problem in the past several decades. Virtually all Staphylococcus aureus, and many Hemophilus influenzae, Branhamella catarrhalis, Neisseria gonorrhoeae, Enterobacteriaceae, and Bacteroides species possess beta-lactamases that hydrolyze penicillins and cephalosporins. The most common plasmid-mediated beta-lactamase is the TEM enzyme (Richmond-Sykes type IIIa), which is present in Hemophilus, Neisseria, and Enterobacteriaceae. One technique to overcome bacterial resistance has been the development of beta-lactamase inhibitors. Clavulanic acid is a beta-lactamase inhibitor that inhibits the beta-lactamases of S. aureus, Hemophilus, Neisseria, Branhamella, Eschericia coli, Klebsiella, and Bacteroides. Clavulanate acts as a "suicide" inhibitor, forming a stable enzyme complex that binds to serine at the active site of the enzyme. Clavulanate readily crosses the outer cell wall of most Enterobacteriaceae to interact with beta-lactamases in the periplasmic space. Clavulanate does not inhibit beta-lactamases such as the Richmond-Sykes type I enzymes found in Pseudomonas aeruginosa, Enterobacter, and Citrobacter species, which are inducible enzymes that function primarily as cephalosporinases.

Current mechanisms of resistance to antimicrobial agents in microorganisms causing infection in the patient at risk for infection

The mechanisms of resistance encountered in bacteria causing infection in the patient at risk for infection are diverse. Most resistance currently seen is the result of plasmid transfer rather than mutational events. However, extensive use of antimicrobial agents in the hospital has caused the selection of organisms resistant to many agents by virtue of chromosomally mediated mechanisms. Staphylococcus aureus resistant to beta-lactams due to altered penicillin-binding proteins has become a problem in certain patients such as narcotic addicts and chronic care facility patients exposed to many beta-lactam antibiotics. S. epidermidis has also proved to be a problem in patients with indwelling foreign devices, and altered penicillin-binding proteins also make these organisms resistant to available penicillins and cephalosporins. Streptococcus fecalis has become increasingly resistant to aminoglycosides, erythromycin, and tetracyclines due to plasmid-mediated enzymes. Hemophilus influenzae resistant to both penicillins and chloramphenicol by virtue of beta-lactamases and chloramphenicol transacetylase has been encountered. Beta-lactamase-mediated resistance of Enterobacteriaceae, Escherichia coli, and Klebsiella pneumoniae to beta-lactam antibiotics has increased, and resistance of Serratia marcescens and Pseudomonas aeruginosa to aminoglycosides and penicillins is a widespread phenomenon. Mechanisms to reduce resistance will include not only careful attention to hygienic practices but also more appropriate use of antibiotics selecting the proper agent depending on the type of patient and environment in which the infection develops.

Amoxicillin plus clavulanic acid in the treatment of recurrent urinary tract infections

Forty-four patients (43 female, 1 male), all with a history of recurrent urinary tract infections, were treated with 250 mg of amoxicillin plus 125 mg of clavulanic acid (one tablet of Augmentin) every 8 h for 7 days. The microbiological cure rates were 84% 1 week after the end of treatment and 67% 1 month later. Side effects, which were reported by 20% of the patients, were mild and in no case caused interruption of treatment. In view of the increasing trend in resistance to agents commonly used for the treatment of urinary tract infections in outpatients, the combination of amoxicillin and clavulanic acid may now be considered a first-line drug in patients with recurrent urinary tract infections.

In-vitro activity of augmentin against clinically important gram-positive and gram-negative bacteria in comparison with other antibiotics

The susceptibility to Augmentin of a total of 1,417 bacterial isolates was investigated. Augmentin is a new formulation of the broad-spectrum beta-lactam-antibiotic amoxicillin together with the beta-lactamase-inhibitor clavulanic acid. It was demonstrated that 88% of all isolates tested were sensitive to Augmentin, 9% were resistant. 88% of all Pseudomonas aeruginosa strains fell in the "resistant" category. Only 1/71 anaerobes and 15/286 staphylococci were classified as resistant to Augmentin.

Susceptibility of gram-negative bacteria and Staphylococcus aureus to combinations of ticarcillin and clavulanic acid

Four hundred and fifty-nine blood culture isolates were tested for susceptibility to ticarcillin alone and ticarcillin plus clavulanic acid, a potent beta-lactamase inhibitor. The susceptibilities of the Staphylococcus aureus strains to cloxacillin, methicillin, vancomycin, rifampicin, cefoperazone, ceftriaxone and moxalactam and of the gram-negative strains to Augmentin, azlocillin, mezlocillin, piperacillin, cefoperazone, ceftriaxone, cefotaxime, cefsulodin and tobramycin were also measured. Seventy-one percent of staphylococcal strains were beta-lactamase positive. In the presence of clavulanic acid the ticarcillin spectrum was extended to include beta-lactamase producing Staphylococcus aureus, Serratia marcescens and Klebsiella. All the ticarcillin-resistant Enterobacteriaceae were rendered ticarcillin-sensitive by clavulanic acid. The anti-Pseudomonas activity of ticarcillin plus clavulanic acid differed little from that of azlocillin and piperacillin and was comparable to that of the third generation cephalosporins. The combination of ticarcillin with clavulanic acid should be tested in the treatment of patients with infections caused by ticarcillin-sensitive and ticarcillin-resistant bacteria.

Characterization of ampicillin-resistant Haemophilus parainfluenzae

Carriage of ampicillin-resistant (Ampr) Haemophilus parainfluenzae has become frequent among children in our community, although carriage of Ampr Haemophilus influenzae remains uncommon. In this study we characterized the mechanism of ampicillin resistance in 27 representative isolates of H. parainfluenzae. As determined by isoelectric focusing, each isolate had a TEM-1 beta-lactamase; substrate profiles assessed for enzymes from 10 strains were also consistent with TEM-1 enzyme. Agarose gel electrophoresis revealed a plasmid of 23 to 34 megadaltons in each isolate and a small plasmid (less than or equal to 4 megadaltons) in 14 isolates. Transfer of ampicillin resistance to H. influenzae Rd was achieved during membrane mating with 14 of 15 donors. The transconjugants exhibited high-level ampicillin resistance (greater than or equal to 50 micrograms/ml), which was stable despite serial passage of isolates on antibiotic-free media. The transconjugants tested retained fertility. Cryptic plasmids were discovered in 7 of 25 antibiotic-susceptible H. parainfluenzae isolates. Our data suggest that H. parainfluenzae may play an important role in the exchange of Ampr genes among throat bacteria.

Spread of a "Pseudomonas-specific" beta-lactamase to plasmids of enterobacteria

Eleven isolates including Escherichia coli, Salmonella enteritidis, and Shigella sonnei, obtained in Brazil, Hong Kong, Indonesia, Thailand, and the United States, were found to produce beta-lactamase of the PSE-1 type, which was previously considered to be Pseudomonas specific. The enterobacterial strains produced a beta-lactamase with the same isoelectric point, immunological reactions, and substrate profile as those of the prototype PSE-1 enzyme determined by Pseudomonas plasmid RPL11. The producer strains were resistant to multiple antibiotics, and all contained plasmids, ranging in size from 37 x 10(6) to 130 x 10(6), that belonged to at last six incompatibility groups. Plasmids of IncH2 and IncFIme were shown to contain 8 x 10(6)-molecular-weight transposons Tn1401 and Tn1402 that encoded PSE-1 beta-lactamase production, resistance to streptomycin and spectinomycin via AAD(3"), and resistance to sulfonamide. PSE-1 beta-lactamase was not Pseudomonas specific and appeared to have spread among plasmids found in enterobacteria by transposition.

Classification of beta-lactamase-producing bacteria

The resistance of bacteria to beta-lactam antibiotics, penicillins or cephalosporins, is usually associated with the production of beta-lactamase enzymes which are capable of inactivating these compounds. A number of recent surveys have reported a significant increase in the frequency of isolation of beta-lactamase-producing strains of bacteria from infections in general practice in the United Kingdom. A wide variety of bacterial beta-lactamases with different properties have been described and it is now recognised that most bacteria produce a chromosomally-mediated beta-lactamase which is characteristic of each species. In addition, Gram-negative bacteria may acquire beta-lactamases which are mediated by plasmids which are readily transferable by cell to cell contact. Schemes for the classification of bacterial beta-lactamases are outlined.