Use Of Beta-lactam Antibiotics Research Articles

Breast abscess caused by penicillin resistant Pneumococci

Breast abscess is mostly caused by Staphylococcus aureus. A 26-year-old immunocompetent lady was admitted with breast abscess. Incision and drainage (I/D) was done and Pneumococci were isolated from the drained pus. The patient was earlier treated with Augmentin which was later changed to linezolid after testing for antibiotic susceptibility. This strain showed a high level of resistance to penicillin. It had been noticed that there was a slow increase in the number of penicillin resistant Pneumococci isolated in our hospitals. The increase in penicillin-resistant Pneumococci correlates with the intensive use of beta-lactam antibiotics. Hence, antibiotics should be used judiciously, avoiding their use particularly in mild self-limiting upper respiratory infections. Attention therefore, should focus on monitoring resistance in Pneumococci to prevent mortality and morbidity associated with this organism, which continues to take a heavy toll on children and the elderly.

Meta‐Analysis of a Possible Signal of Increased Mortality Associated with Cefepime Use

On the basis of meta-analyses, concern has been raised regarding a possible signal of increased mortality associated with the use of cefepime versus other beta-lactam antibiotics. To further investigate this possible signal, we accessed findings and data from published and unpublished cefepime clinical trials. We performed meta-analyses using trial- and patient-level data from comparative trials. Trial-level analyses were performed using summary data from all patients in the trials, and patient-level analyses were performed on trials for which patient-level data were available. Thirty-day, all-cause mortality was analyzed using the Mantel-Haenszel adjusted risk difference (ARD) method. The trial-level meta-analysis was based on 88 trials (9467 cefepime patients and 8288 comparator patients). The 30-day, all-cause mortality rates were 6.21% (588/9467) for the cefepime patients and 6.00% (497/8288) for comparator patients (ARD per 1000 population, 5.38; 95% confidence interval [CI], -1.53 to 12.28). In the patient-level analysis (35 trials, 5058 cefepime patients, and 3976 comparator patients), 30-day, all-cause mortality rates were 5.63% (285/5058) for cefepime patients and 5.68% (226/3976) for comparator patients (ARD per 1000 population, 4.83; 95% CI, -4.72 to 14.38). A sensitivity analysis based solely on the 24 febrile neutropenia trials did not show a statistically significant increase in mortality with cefepime use (ARD per 1000 population, 9.67; 95% CI, -2.87 to 22.21). In both trial-level and patient-level meta-analyses, we did not identify a statistically significant increase in mortality among cefepime-treated patients, compared with those treated with other antibacterials.

Effects of reducing beta-lactam antibiotic pressure on intestinal colonization of antibiotic-resistant gram-negative bacteria

BackgroundWe determined the effects of two antibiotic policies (predominance of either β-lactam antibiotics or fluroquinolones) on acquisition with third-generation cephalosporin-resistant Enterobacteriaceae (CRE) and fluoroquinolone-resistant CRE (FCRE) in two ICUs, with monitoring of other variables that may influence acquisition.MethodsAfter an 8-month baseline period, units were randomized to a predominant β-lactam antibiotic regimen (weekly cycling of ceftriaxone, amoxicillin–clavulanic acid and fluroquinolones) or a fluoroquinolone regimen for 3 months, with cross-over for another 3 months. Acquisition of CRE and FCRE was determined by microbiological surveillance.ResultsDuring baseline, acquisition rates for CRE and FCRE were 14/1,000 and 2/1,000 patient days at risk, respectively. Cross-transmission of CRE accounted for ≤25% of acquisitions, and CRE acquisition was associated with the use of β-lactam antibiotics (amoxicillin–clavulanic acid in particular). As compared to baseline, β-lactam antibiotic use [in defined daily dose (DDD)/1,000 patient days] was reduced from 854 to 526 (−39%) and 555 (−35%) during both intervention periods. Fluoroquinolone use was increased from 150 and 129 DDD/1,000 patient days in baseline and the β-lactam period to 514 DDD/1,000 patient days (+243%) in the fluoroquinolone period. Reductions in β-lactam use were not associated with reduced CRE acquisition [adjusted HRs were 1.0 (95% CR: 0.5–2.2) and 1.1 (95% CI: 0.5–2.5) during both periods, respectively]. Increased use of fluoroquinolones was associated with increased acquisition of FCRE [adjusted HR 4.1 (95% CI: 1.4–11.9; p < 0.01]. Infection control variables remained comparable during all periods.ConclusionA 35–39% reduction of β-lactam exposure was not associated with reduced acquisition of CRE, whereas a 243% increase of fluoroquinolone use increased acquisition of FCRE.

Identification of AmpC Beta-Lactamases Using Phenotypic Tests and PCR in Clinical Isolates of Klebsiella spp. and Escherichia coli

Background: Indiscriminate use of beta-lactam antibiotics has resulted in emergence of AmpC Beta-lactamases. Considering the lack of comprehensive studies from India the present study was undertaken to detect and characterize AmpC Beta-lactamases in clinical isolates of Escherichia coli and Klebsiellaspp. Methods: One hundred non-repeat clinical isolates each of Escherichia coli and Klebsiella spp recovered from pus, urine, blood and sputum, were collected from various hospitals of Delhi. These were screened for susceptibility to cefoxitin (30 μg) by disc diffusion method. The screen positive isolates were subjected to Modified 3 Dimensional test (M3D), AmpC disk tests 1 and 2 and Inhibitor (Boronic acid) based detection method. AmpC positive isolates were subjected to Polymerase chain reaction (PCR) using family specific primers and also tested for production of ESBLs and inducible AmpC Beta-lactamases. Results: 34/100 (34%) of Escherichia coli and 21/100 (21%) of Klebsiella spp. were resistant to cefoxitin. Of the screen positive isolates 12 (35%) of Escherichia coli, and 5 (24%) of Klebsiella spp. were positive for AmpC by various phenotypic tests. Out of the AmpC positive isolates as many as 8/12 of Escherichia coli and 3/5 of Klebsiella isolates were positive for ESBLs. In 3/12 (25%) of Escherichia coli and 3/5 (60%) of Klebsiella isolates AmpC were inducible. PCR identified the AmpC of Escherichia coli as MIR/ACT- I and CIT types. Amongst Klebsiella isolates, the AmpC were found to be of MIR/ACTI, CIT, FOX and DHA families. Conclusion: The incidence of AmpC production was higher (12%) in Escherichia coli than in Klebsiella (5%) isolates. However, co-production of ESBLs was much higher in Klebsiella (60%) than in Escherichia coli (25%) isolates. The AmpC Beta-lactamases in Indian isolates were of common families reported from different parts of the world.

Toxic epidermal necrolysis managed with immunoglobulin

We thank the reader for critical appraisal of our report and kind remarks. The reply to queries raised by him is as follows; Our patient had presented with fever and was receiving antibiotics at the time of presentation which was the reason of negative cultures. Sepsis is the most debilitating complication in TEN and is one of the leading causes of mortality [1]. Patient had onset of TEN following therapy for fever, cough and sore throat and was continuing antibiotics till consultation in the emergency at our centre. In presence of >80% body surface area involvement with purulent mucositis of the oral and urethra and urinalysis full of pus cells, infection was very much evident which prompted us to continue with changed antibiotics despite culture reports being negative. Lastly, offering antibiotic therapy after obtaining culture positive reports and or signs of septic shock seems purely academic and sometimes dangerous in day to day practice. IgE mediated hypersensitivities are well known to be cross reactive between cephalosporins and penicillins, however, non IgE mediated hypersensitivities usually are not cross reactive. Patients with a prior immediate hypersensitivity reaction to penicillin should generally not be treated with cephalosporin unless: Penicillin or cephalosporin skin testing, if available, is negative or a graded challenge with the cephalosporin can be given under careful observation by an allergist. A history of a rash or unclear reaction to penicillin does not necessarily preclude administration of cephalosporins [2]. Moreover, there is not a single report of TEN attributable to piperacillin till date on medline search. Only single case report putatively linking cephalosporin hypersensitivity to Meropenem induced TEN has been reported [3]. This does not preclude the use of other beta lactam antibiotics, it just merits caution. Compared to sulfonamides antibiotics, other sulfonamides like sulfonylurea, thiazides etc do not show cross sensitivity just because of the structural similarities. It may be other metabolites of the drugs that can induce TEN or individuals with metabolic defects or polymorphisms in cytochrome metabolizing enzymes are predisposed to TEN. It will be too hasty to generalize and blame beta lactam structure as the cause of TEN. Our patient did not have immediate hypersensitivity reaction to cephalosporins hence Tazobactum Piperacillin was continued under supervision. Regarding IgE mediated allergic reaction to piperacillin in a case of ceftriaxone induced TEN, the reason is evident in the case report itself, if the reader would have cared to read the paper carefully. This patient had received piperacillin before ceftriaxone administration that could have sensitized him and led to IgE mediated Type I hypersensitivity reaction, subsequently. Moreover TEN is mediated by T cells and macrophages/monocytes, and is unrelated to B cell mediated effects. Lastly, the SCORTEN score of 3 was arrived at based on following criteria, age >40 years, tachycardia (>120) and BSA >80% involvement. Regarding the biopsy confirmation of the diagnosis, the clinical presentation was so characteristic and therefore it was needless to subject already critical patient to an invasive procedure which would have been purely academic without any additional advantage. On the basis of experience in one case, we are not advocating IVIg as panacea for all the cases of TEN, rather since there are not many reports of similar experience from our country we thought it prudent to share our experience with medical fraternity to increase the awareness. Moreover, after the index case, we have treated three more cases of TEN with IVIg and one patient died. This patient had presented with severe neutropenia (absolute neutrophil count <200/µl) and respiratory tract infection. We encourage other centers from our country to share their experience with therapy of TEN. As far as the rationale of IVIg is concerned, there is ample evidence both in vitro [4] and clinical to recommend its use in such a life threatening condition [1, 5]. The numbers of studies that question the efficacy of IVIg are small with small patient population as compared to numbers of studies that report benefit with large number of patients. Since randomized placebo controlled trial is virtually impossible for such a rare and sporadic adverse event, it's up to readers to decide which school of thought to follow. Regarding the discontinuation of the offending agent and intensive supportive therapy, it cannot be over emphasized and we agree with the reader but since the aim of our case report was to highlight the beneficial effect of IVIg in addition to these measures, we discussed more about IVIg. However, we never intend to sideline the significance of these measures.

Randomized, Double-Blind, Placebo-Controlled Trial of Cephalexin for Treatment of Uncomplicated Skin Abscesses in a Population at Risk for Community-Acquired Methicillin-Resistant Staphylococcus aureus Infection

Empirical use of beta-lactam antibiotics, the preferred agents for treating uncomplicated skin and soft tissue infections, may no longer be appropriate for these infections because of the increasing prevalence of community strains of methicillin-resistant Staphylococcus aureus (MRSA). Retrospective studies, however, suggest that outcomes are good even when beta-lactams are used. We conducted a randomized, double-blind trial of 166 outpatient subjects comparing placebo to cephalexin at 500 mg orally four times for 7 days after incision and drainage of skin and soft tissue abscesses. The primary outcome was clinical cure or failure 7 days after incision and drainage. S. aureus was isolated from 70.4% of abscess cultures. Of the isolates tested 87.8% were MRSA, 93% of which were positive for Panton-Valentine leucocidin genes. Clinical cure rates were 90.5% (95% confidence interval, 0.82 to 0.96) in the 84 placebo recipients and 84.1% (95% confidence interval, 0.74 to 0.91) in the 82 cephalexin recipients (difference in the two proportions, 0.0006; 95% confidence interval, -0.0461 to 0.0472; P = 0.25). The 90.5% cure rate observed in the placebo arm and 84.1% cure rate observed in the cephalexin arm provide strong evidence that antibiotics may be unnecessary after surgical drainage of uncomplicated skin and soft tissue abscesses caused by community strains of MRSA.

Role of Zinc Content on the Catalytic Efficiency of B1 Metallo β-Lactamases

Metallo beta-lactamases (MbetaL) are enzymes naturally evolved by bacterial strains under the evolutionary pressure of beta-lactam antibiotic clinical use. They have a broad substrate spectrum and are resistant to all the clinically useful inhibitors, representing a potential risk of infection if massively disseminated. The MbetaL scaffold is designed to accommodate one or two zinc ions able to activate a nucleophilic hydroxide for the hydrolysis of the beta-lactam ring. The role of zinc content on the binding and reactive mechanism of action has been the subject of debate and still remains an open issue despite the large amount of data acquired. We report herein a study of the reaction pathway for binuclear CcrA from Bacteroides fragilis using density functional theory based quantum mechanics-molecular mechanics dynamical modeling. CcrA is the prototypical binuclear enzyme belonging to the B1 MbetaL family, which includes several harmful chromosomally encoded and transferable enzymes. The involvement of a second zinc ion in the catalytic mechanism lowers the energetic barrier for beta-lactam hydrolysis, preserving the essential binding features found in mononuclear B1 enzymes (BcII from Bacillus cereus) while providing a more efficient single-step mechanism. Overall, this study suggests that uptake of a second equivalent zinc ion is evolutionary favored.

Impact of Antibiotics on Expression of Virulence‐Associated Exotoxin Genes in Methicillin‐Sensitive and Methicillin‐ResistantStaphylococcus aureus

Extracellular protein toxins contribute to the pathogenesis of a wide variety of Staphylococcus aureus infections. The present study investigated the effects that cell-wall active antibiotics and protein-synthesis inhibitors have on transcription and translation of genes for Panton-Valentine leukocidin, alpha-hemolysin, and toxic-shock syndrome toxin 1, in both methicillin-sensitive and methicillin-resistant S. aureus. Subinhibitory concentrations of nafcillin induced and prolonged mRNA for Panton-Valentine leukocidin, alpha-toxin, and toxic-shock syndrome toxin 1 and increased toxin production. In contrast, clindamycin and linezolid markedly suppressed translation, but not transcription, of toxin genes. These results suggest (1) that protein-synthesis inhibition is an important consideration in the selection of antimicrobial agents to treat serious infections caused by toxin-producing gram-positive pathogens and (2) that, by inducing and enhancing toxin production, inadvertent use of beta-lactam antibiotics to treat methicillin-resistant S. aureus infections may contribute to worse outcomes.

Risk of emergence of Pseudomonas aeruginosa resistance to β-lactam antibiotics in intensive care units

The emergence of Pseudomonas aeruginosa resistance to antimicrobial drugs is frequent in intensive care units and may be correlated with the use of some specific drugs. The purpose of our study was to identify a relationship between the use of various beta-lactam antibiotics and the emergence of resistance and to characterize the mechanism of resistance involved. We conducted an open prospective study over a 3-yr period by including all patients in whom P. aeruginosa had been isolated from one or more specimens: bronchial aspiration, blood cultures, catheters, and urinary cultures. General intensive care unit. One hundred and thirty-two intensive care unit patients. The antibiotics studied were amoxiclav, piperacillin-tazobactam, cefotaxime, ceftazidime, cefepim, and imipenem. The mechanisms of resistance studied were production of penicillinase or cephalosporinase, nonenzymatic mechanisms, and loss of porin OprD2. Analysis was performed using Cox proportional-hazard regression with time-dependant variables. Forty-two strains became resistant, 30 to one antibiotic, nine to two, and three to three, leading to the study of 57 resistant strains. Imipenem (hazard ratio 7.8; 95% confidence interval, 3.4-18.1), piperacillin-tazobactam (hazard ratio 3.9; 95% confidence interval, 1.3-11.9), and cefotaxim (hazard ratio 9.3; 95% confidence interval, 2.9-30.2) were strongly linked to the emergence of resistance. The use of imipenem (p<.0001) was associated with the loss of porin OprD2. Thirty-six strains from nine patients, assayed by pulsed-field gel electrophoresis, showed that for any one patient, all the strains were genetically related. Our results show that there is a high risk of the emergence of drug resistance during treatment with cefotaxime, imipenem, and piperacillin-tazobactam. This has to be taken into account in the therapeutic choice and in the patient's surveillance.

Hospital-Based Strategies for Combating Resistance

Selective pressures generated by the indiscriminate use of beta-lactam antibiotics have resulted in increased bacterial resistance across all beta-lactams classes. In particular, the use of third-generation cephalosporins has been associated with the emergence of extended-spectrum beta-lactamase-producing and AmpC beta-lactamase-producing Enterobacteriaceae and vancomycin-resistant enterococci. Conversely, beta-lactams (e.g., cefepime, piperacillin-tazobactam, and ampicillin-sulbactam) have not demonstrated such strong selective pressures. Chief among institutional strategies to control outbreaks of multidrug-resistant bacteria are infection-control measures and interventional programs designed to minimize the use of antimicrobial agents that are associated with strong relationships between use and resistance. Successful programs include antimicrobial stewardship programs (prospective audit and feedback), formulary interventions (therapeutic substitutions), formulary restrictions, and vigilant infection control. Fourth-generation cephalosporins, such as cefepime, have proven to be useful substitutes for third-generation cephalosporins, as a part of an overall strategy to minimize the selection and impact of antimicrobial-resistant organisms in hospital settings.

The outpatient use of beta lactam antibiotics in Montenegro before the introduction of new reform strategy on drug market

The study represents the first investigation of outpatient use of beta lactam antibiotics in Montenegro carried out in accordance with internationally approved methodology (DDD/ATC). The objective of our study was to establish both the scope and overall use of beta lactam antibiotics, and to assess their compatibility with current pharmacotherapeutic guidelines and their use in developed countries. The retrospective pharmaco-epidemiological study comprised a 100%-sample of beta lactams that were used in the period prior to introduction of new reform strategy on drug market. Beta lactam antibiotics (J01C, J01D) were the most frequently applied anti-infectives for systemic use (ATC group J) in 2000 (11.3 DDD/1000 inh./day, 61%). Penicillins (J01C) were the most utilized (8.0 DDD/1000 inh./day, 71%). Cephalosporin derivatives (cephalexin and cefaclor) accounted for the remaining 29% (3.3 DDD/1000 inh./day). Aminopenicillins were prevailing among penicillins (85%). Beta lactamase sensitive penicillins were in the second place and approximately accounted for 14%. The results of our study showed that the use of beta lactam antibacterials could be estimated as partially satisfactory. There is a need to make additional efforts with a view of further rationalization.

β-lactam antibiotic-induced vancomycin resistant MRSA (BIVR) によるマウス感染モデルに対するvancomycinあるいはteicoplaninとβ-lactam薬との併用効果

The concomitant use of low concentration beta-lactam antibiotics antagonizes the activity of vancomycin against some strains of MRSA. These strains, called beta-lactam antibiotic-induced vancomycin resistant MRSA (BIVR), have been increasing for a number of years. We previously reported that the combination of VCM and ceftizoxime displayed this antagonism not only in vitro, but also in vivo, in a systemic infection caused by BIVR in mice. In the present study, we validated the antagonism in combinations of VCM with other beta-lactams, i.e., flomoxef (FMOX), ampicillin (AMPC), azthreonam (AZT) and imipenem/cilastatin (IPM/CS), in systemic infections and pneumoniain in mice. The survival rate of the mice with systemic infections caused by BIVR treated with combinations of FMOX, AMPC, AZT, and IPM/CS with VCM were significantly lower than with VCM monotherapy, and the number of residual viable cells in the kidneys of mice treated with combinations of FMOX and IPM/CS with VCM were significantly higher than with VCM monotherapy The number of residual viable cells in the lungs of mice with pneumonia caused by BIVR treated with the combination of IPM/CS and VCM was significantly higher than with VCM monotherapy. On the other hand, the survival rate with combination therapy consistings IPM/CS plus teicoplanin (T EIC) was significantly higher, and the number of residual viable cells in the kidney was significantly lower, than with TEIC monotherapy alone. In the mice with pneumonia, the number of residual viable cells in the lung after combination therapy with IPM/CS and TEIC was significantly lower than with TEIC monotherapy. Combination therapy with beta-lactams plus VCM showed antagonistic in models of systemic infection and pulmonary infection caused by BIVR, whereas combination therapy consisting of a beta-lactam plus TEIC had a synergistic effect in the same models, even though VCM and TEIC are member of the same glycopeptide antibiotic class.

Penicillin sensitivity among children without a positive history for penicillin allergy.

To establish the prevalence of positive penicillin skin tests among outpatients without any drug reaction history. Skin testing was performed in 147 children (aged 6-13 years) who had had received a penicillin preparation at least three times in the last 12 months without any allergic reaction. Before testing, detailed pediatric and allergy history were learned and then all children were tested with benzyl penicilloyl polylysin (PPL) and mixture of minor antigenic determinants. The test procedures were made epidermally and intradermally subsequently in every subject. The overall frequency of positive skin reactions to penicillin antigens was 10.2%. A mild systemic reaction was observed in one of the children during testing with PPL. We concluded that frequent use of penicillin and other beta-lactam antibiotics leads to sensitization of children in our study population despite these children seem to be asymptomatic during testing time.

Evolution of the serine β-lactamases: past, present and future

We present a protein structure-based phylogeny of Classes A, C and D of the serine beta-lactamases, and a new, detailed, sequence-based phylogeny of the Class A beta-lactamases. In addition, we discuss the historical evolution of Classes C and D. The evolutionary histories of all three classes indicate that the serine beta-lactamases are ancient enzymes, originating over two billion years ago, and that some have been on plasmids for millions of years. We also discuss the recent, antibiotic-era, evolution of the serine beta-lactamases in response to the clinical use of beta-lactam antibiotics. We also discuss a method that is being used to predict the future evolution of beta-lactamases in response to selection with new drugs.

Bacterial resistance to penicillin G by decreased affinity of penicillin-binding proteins: a mathematical model.

Streptococcus pneumoniae and Neisseria meningitidis have very similar mechanisms of resistance to penicillin G. Although penicillin resistance is now common in S. pneumoniae, it is still rare in N. meningitidis. Using a mathematical model, we studied determinants of this difference and attempted to anticipate trends in meningococcal resistance to penicillin G. The model predicted that pneumococcal resistance in a population similar to that of France might emerge after 20 years of widespread use of β-lactam antibiotics; this period may vary from 10 to 30 years. The distribution of resistance levels became bimodal with time, a pattern that has been observed worldwide. The model suggests that simple differences in the natural history of colonization, interhuman contact, and exposure to β-lactam antibiotics explain major differences in the epidemiology of resistance of S. pneumoniae and N. meningitidis.

A European study on the relationship between antimicrobial use and antimicrobial resistance.

In Europe, antimicrobial resistance has been monitored since 1998 by the European Antimicrobial Resistance Surveillance System (EARSS). We examined the relationship between penicillin nonsusceptibility of invasive isolates of Streptococcus pneumoniae (an indicator organism) and antibiotic sales. Information was collected on 1998-99 resistance data for invasive isolates of S. pneumoniae to penicillin, based on surveillance data from EARSS and on outpatient sales during 1997 for beta-lactam antibiotics and macrolides. Our results show that in Europe antimicrobial resistance is correlated with use of beta-lactam antibiotics and macrolides.

Molecular analysis of beta-lactamase structure and function

AbstractThe extensive and sometimes irresponsible use of beta-lactam antibiotics in clinical and agricultural settings has contributed to the emergence and widespread dissemination of antibiotic-resistant bacteria. Bacteria have evolved three strategies to escape the activity of beta-lactam antibiotics: 1) alteration of the target site (e.g. penicillin-binding protein (PBPs), 2) reduction of drug permeation across the bacterial membrane (e.g. efflux pumps) and 3) production of beta-lactamase enzymes. The beta-lactamase enzymes inactivate beta-lactam antibiotics by hydrolyzing the peptide bond of the characteristic four-membered beta-lactam ring rendering the antibiotic ineffective. The inactivation of the antibiotic provides resistance to the bacterium. Currently, there are over 300 beta-lactamase enzymes described for which numerous kinetic, structural, computational and mutagenesis studies have been performed. In this review, we discuss the recent work performed on the four different classes (A, B, C, and D) of beta-lactamases. These investigative advances further expand our knowledge about these complex enzymes, and hopefully, will provide us with additional tools to develop new inhibitors and antibiotics based on structural and rational designs.

An Observational Study on the Epidemiology of Respiratory Tract Bacterial Pathogens and Their Susceptibility to Four Injectable Beta-Lactam Antibiotics: Piperacillin, Piperacillin/Tazobactam, Ceftazidime and Ceftriaxone

Bacterial infections of the respiratory tract account for a large proportion of total medical consultations in general practice. In recent years, antibiotic resistance has increased alarmingly in a number of bacterial species that are common causes of these infections. The aim of this observational study was to determine the antibiotic resistance of microbial agents isolated from patients with acute or acutely exacerbated respiratory infections. Subjects recruited as potential sources of bacteria were either outpatients seen in a number of specialized clinics and hospital practices, or hospitalized patients. Overall, 64-a8 consecutive patients (67% male, mean age 48.1 ± 27.0 years) with infection of the upper or lower respiratory tract were observed during a 13-month period. A total of 551 pathogenic microbial strains were isolated and tested for their in vitro susceptibility to piperacillin, piperacillin/tazobactam, ceftazidime, and ceftriaxone. Among all isolates, the four most frequent pathogens were Pseudomonas aeruginosa (132 isolates, 24%), Streptococcus pyogenes (99 isolates, 18%), Staphylococcus aureus (93 isolates, 17%), and Klebsiella pneumoniae (46 isolates, 8%). The susceptibility of Gram-positive isolates ranged from 97.5% to 95.1%, and no remarkable difference was found in the antibacterial activity of tested b-lactam antibiotics. The susceptibility of Gram-negative isolates to piperacillin and piperacillin/tazobactam was also similar: 96.5% and 97.1%, respectively. In contrast, differences were found between piperacillin (or piperacillin/tazobactam) and either ceftazidime (p=0.003) or ceftriaxone (p<0.0003) in Gram-negative isolates.We conclude that, despite the extensive use of beta-lactam antibiotics (piperacillin, ceftazidime, and ceftriaxone) in medical practice during the past three decades, the susceptibility of the most common pathogens involved in the etiology of upper and lower respiratory tract infections to these antibiotics is still high. In particular, bacterial resistance developed by Gram-positive organisms against piperacillin is negligible and not alarming.

A secondary drug resistance mutation of TEM-1 beta -lactamase that suppresses misfolding and aggregation

In Gram-negative bacteria, TEM-1 beta-lactamase provides the major mechanism of plasmid-mediated beta-lactam resistance. Natural variants of TEM-1 with increased antibiotic resistance have appeared in response to the use of extended-spectrum beta-lactam antibiotics (e.g., ceftazidime) and beta-lactamase inhibitors (e.g., clavulanic acid). Some of the variant enzymes are more efficient at catalyzing beta-lactam hydrolysis, whereas others are more resistant to inhibitors. M182T is a substitution observed in both types of variant TEM-1 beta-lactamases. This mutation is found only in combination with other amino acid substitutions, suggesting that it may correct defects introduced by other mutations that alter the specificity. An engineered core mutation, L76N, which diminishes the periplasmic beta-lactamase activity by 100-fold, was used as a model to understand the mechanism of suppression of the M182T mutation. Biochemical studies of the L76N enzyme alone and in combination with the M182T mutation indicate that the M182T substitution acts at the level of folding but does not affect the thermodynamic stability of TEM-1 beta-lactamase. Thus, the M182T substitution is an example of a naturally occurring mutation that has evolved to alter the folding pathway of a protein and confer a selective advantage during the evolution of drug resistance.

Search for Staphylococcus aureus heterogeneously resistant to vancomycin (hetero-VRSA) in MRSA strains isolated from clinical samples during 1990s

Hetero-VRSA was studied in 978 MRSA strains isolated from clinical samples during 1991 to 1998. Although no VRSA was detected, 23 strains (2.4%) were identified as hetero-VRSA by the vancomycin-resistance using MU3 agar plate. The frequency of hetero-VRSA was not increased in the course of time. MIC of the hetero-VRSA to vancomycin and teicoplanin was 1-2 micrograms/ml and 0.5-12 micrograms/ml, respectively. All of the hetero-VRSA strains were confirmed as a heterogeneous strain by a population analysis. Although 43% of the hetero-VRSA strains were coagulase type II, positive for TSST-1, and enterotoxin type C, others were various in the characteristics. In the gene analysis by pulse field gelelectrophoresis (PFGE), 4 sets of 2 strains were found to be identical among the 23 strains but the other 15 strains were genetically different. We speculate that hetero-VRSA strains were generated in 1991 secondary possibly by use of beta-lactam antibiotics.