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Lactivicin, a naturally occurring non-beta-lactam antibiotic having beta-lactam-like action: biological activities and mode of action.

Lactivicin is moderately active against a wide range of Gram-negative bacteria and highly active against Gram-positive bacteria. It shows various biological activities commonly observed with beta-lactam antibiotics, such as higher activity against beta-lactam hypersensitive mutants than against their parents, sensitivity to beta-lactamases, inhibitory activity against beta-lactamases and ability to induce beta-lactamase activity. The primary lethal target of lactivicin in Escherichia coli is highly likely to be penicillin-binding protein (PBP) 1; lactivicin strongly lysed E. coli cells with induction of spheroplasts at its MIC, and showed high affinity for PBPs 1A and 1B. At concentrations above x 5 MIC, however, lactivicin dominantly exhibited secondary antibacterial action possibly owing to inhibition of crucial SH proteins engaged in the fundamental membrane functions. In contrast, against Bacillus subtilis, lactivicin showed the typical beta-lactam action under a wide range of concentrations. It showed high affinity for PBPs 1, 2 and 4, the possible lethal targets of beta-lactam antibiotics in this organism. In conclusion, lactivicin is the first non-beta-lactam antibiotic showing beta-lactam action through binding to PBPs.

Anti-Bacterial Agents↗

[Mechanisms of resistance to beta-lactam antibiotics].

Beta-lactam antibiotics share the structural feature of a beta-lactam ring. This feature is responsible for inhibition of bacterial cell wall synthesis. The target molecules are peptidoglycan cross-linking enzymes (e.g. transpeptidases and carboxypeptidases) which can bind beta-lactam antibiotics (penicillin binding proteins, PBP). Bacterial cell death is initiated by beta-lactam antibiotic-triggered release of autolytic enzymes. In contrast to gram-positive bacteria (absence of an outer membrane) the antibiotic has to penetrate through porins of the outer membrane of gram-negative bacteria before touching PBP's. Bacterial resistance to beta-lactam antibiotics includes modification of porins (permeability barrier) and of targets (low affinity of PBP's for the drug), production of inactivating enzymes (beta-lactamases) and inhibition of release of autolytic enzymes. Moreover, bacteria have developed sophisticated genetic mechanisms to adapt to treatments with novel beta-lactam antibiotics. To allow successful antibiotic treatment of bacterial infection in the future, knowledge about antibiotic resistance mechanisms is required.

Amino Acids↗

[Bacterial resistance against beta-lactam antibiotics].

Beta-lactam antibiotics include the penicillins, cephalosporins, oxacephems (moxalactam), carbapenems (imipenem) and monobactams (azthreonam)--all with a common beta-lactam ring. Beta-lactam antibiotics block the synthesis and growth of the bacterial cell wall by binding to penicillin-binding proteins on the cytoplasma membrane. The bacteria may escape the effect of beta-lactam antibiotics by reducing the permeability of the cell wall (gramnegative bacteria), by producing beta-lactamases, by reducing the affinity for beta-lactams in their penicillin-binding proteins, or by developing tolerance to beta-lactam antibiotics. A combination of these resistance mechanisms may be found in the most resistant bacteria, such as Pseudomonas, Serratia and Enterobacter; bacteria often involved in nosocomial infections. Increased antibiotic pressure may select for beta-lactam resistance among other bacteria as well, such as staphylococci, streptococci, Haemophilus influenzae, meningococci and gonococci. Prudent use of antibiotics is mandatory essential to ensure a bactericidal effect of this most important and valuable group of antibiotics in the future.

Anti-Bacterial Agents↗

Inhibition of granulopoiesis in vivo and in vitro by beta-lactam antibiotics.

beta-Lactam antibiotics can induce severe neutropenia by a hitherto unknown mechanism. Fifty cases of beta-lactam antibiotic-induced neutropenia (less than 1,000 neutrophils/mm3) from 17 hospitals were analyzed and compared with 140 literature cases. The incidence of neutropenia was 5%-greater than 15% in patients treated for greater than or equal to 10 days with large doses of any beta-lactam antibiotic but less than 0.1% with shorter duration of therapy. In greater than 95% of cases recovery occurred between one to seven days after withdrawal of beta-lactam antibiotics. Bone marrow aspirates were characterized by a lack of well-differentiated myeloid elements in the presence of numerous immature granulocyte precursors. Nine penicillins and eight cephalosporins inhibited in vitro granulopoiesis in a dose-dependent manner. There was a good correlation between the inhibitory capacity of beta-lactam antibiotics in vitro and the doses inducing neutropenia in vivo. These observations may be relevant for therapy in the granulocytopenic patient.

Agranulocytosis↗

Beta lactam antibiotic monotherapy versus beta lactam-aminoglycoside antibiotic combination therapy for sepsis.

BACKGROUND: Optimal antibiotic treatment for sepsis is imperative. Combining a beta-lactam antibiotic with an aminoglycoside antibiotic may have certain advantages over beta-lactam monotherapy. OBJECTIVES: We compared clinical outcomes for beta lactam-aminoglycoside combination therapy versus beta lactam monotherapy for sepsis. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library, Issue 3, 2004); MEDLINE (1966 to July 2004); EMBASE (1980 to March 2003); LILACS (1982 to July 2004); and conference proceedings of the Interscience Conference of Antimicrobial Agents and Chemotherapy (1995 to 2003). We scanned citations of all identified studies and contacted all corresponding authors. SELECTION CRITERIA: We included randomized and quasi-randomized trials comparing any beta-lactam monotherapy to any combination of one beta-lactam and one aminoglycoside for sepsis. DATA COLLECTION AND ANALYSIS: The primary outcome was all-cause fatality. Secondary outcomes included treatment failure, superinfections, colonization, and adverse events. Two authors independently collected data. We pooled relative risks (RR) with their 95% confidence intervals (CI) using the fixed effect model. We extracted outcomes by intention-to-treat analysis whenever possible. MAIN RESULTS: We included 64 trials, randomizing 7586 patients. Twenty trials compared the same beta-lactam in both study arms, while the remaining compared different beta-lactams using a broader spectrum beta-lactam in the monotherapy arm. In studies comparing the same beta-lactam, we observed no difference between study groups with regard to all-cause fatality, RR 1.01 (95% CI 0.75-1.35) and clinical failure, RR 1.11 (95% CI 0.95-1.29). In studies comparing different beta-lactams, we observed an advantage to monotherapy: all cause fatality RR 0.85 (95% CI 0.71-1.01), clinical failure RR 0.77 (95% CI 0.69-0.86). No significant disparities emerged from subgroup and sensitivity analyses, including the assessment of patients with Gram-negative and Pseudomonas aeruginosa infections. We detected no differences in the rate of resistance development. Adverse events rates did not differ significantly between the study groups overall, although nephrotoxicity was significantly more frequent with combination therapy, RR 0.30 (95% CI 0.23-0.39). We found no heterogeneity for all comparisons. We included a small subset of studies addressing patients with Gram-positive infections, mainly endocarditis. We identified no difference between monotherapy and combination therapy in these studies. AUTHORS' CONCLUSIONS: The addition of an aminoglycoside to beta-lactams for sepsis should be discouraged. All-cause fatality rates are unchanged. Combination treatment carries a significant risk of nephrotoxicity.

Aminoglycosides↗

Appropriate prescribing of oral beta-lactam antibiotics.

Beta-lactam antibiotics include penicillins, cephalosporins and related compounds. As a group, these drugs are active against many gram-positive, gram-negative and anaerobic organisms. Information based on "expert opinion" and antimicrobial susceptibility testing supports certain antibiotic choices for the treatment of common infections, but less evidence-based literature is available to guide treatment decisions. Evidence in the literature supports the selection of amoxicillin as first-line antibiotic therapy for acute otitis media. Alternative drugs, such as amoxicillin-clavulanate, trimethoprim-sulfamethoxazole and cefuroxime axetil, can be used to treat resistant infections. Penicillin V remains the drug of choice for the treatment of pharyngitis caused by group A streptococci. Inexpensive narrow-spectrum drugs such as amoxicillin or trimethoprim-sulfamethoxazole are first-line therapy for sinusitis. Animal and human bites can be treated most effectively with amoxicillin-clavulanate. For most outpatient procedures, amoxicillin is the preferred agent for bacterial endocarditis prophylaxis. Beta-lactam antibiotics are usually not the first choice for empiric outpatient treatment of community-acquired pneumonia. Based on the literature, the role of beta-lactam antibiotics in the treatment of bronchitis, skin infections and urinary tract infections remains unclear.

Administration, Oral↗

Absence of convulsive liability of doripenem, a new carbapenem antibiotic, in comparison with beta-lactam antibiotics.

beta-Lactam antibiotics have been suggested to have some degree of convulsive activity and neurotoxicity in experimental animals as well as in clinical situations. We examined the convulsive activities of a new carbapenem antibiotic, (+)-(4R,5S,6S)-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-3-[[(3S,5S)-5-[(sulfamoylamino)methyl]-3-pyrrolidinyl]thio]-1-azabicyclo[3.2.0]hept-2-ene-2-carboxic acid monohydrate (doripenem) using several animals and compared them with beta-lactam antibiotics. In intravenous (IV) injection studies, imipenem/cilastatin, at 400/400mg/kg produced seizure discharges on electroencephalogram (EEG) accompanied with clonic convulsions in rats. Meropenem showed only wet dog shaking behavior at 200 and 400mg/kg. Doripenem caused no changes in the EEG and behavior in rats at 400mg/kg. Imipenem/cilastatin IV potentiated the pentylenetetrazol (PTZ)-induced convulsions in mice at 250/250 mg/kg, while meropenem, panipenem/betamipron, cefazolin or doripenem did not cause any marked effects at up to 500 mg/kg. In mouse intracerebroventricular (ICV) injection studies, imipenem, panipenem and cefazolin induced clonic convulsions in a dose-dependent manner in mice. Doripenem and meropenem did not induce convulsions at up to 100 microg/mouse. In dog ICV injection studies, imipenem produced generalized seizure discharge with clonic convulsions at 100 microg/dog. Meropenem also produced spikes or seizure discharges at 100, 300 and 1,000 microg/dog. However, doripenem had no effects on the EEG and behavior in dogs at any doses. In in vitro binding studies, imipenem, panipenem, cefazolin and meropenem inhibited [(3)H]muscimol binding to the GABA(A) receptor in mouse brain homogenates while doripenem did not cause any inhibition at up to 10mM. In addition, doripenem had no influence on the anti-convulsant actions of valproic acid in the PTZ- or bicuculine-induced convulsive model. These results clearly indicate that doripenem has no convulsive activity, suggesting that its neurotoxicity may be negligible in clinical use.

Alanine↗

Crystal structure and activity studies of the Mycobacterium tuberculosis beta-lactamase reveal its critical role in resistance to beta-lactam antibiotics.

beta-Lactam antibiotics are extremely effective in disrupting the synthesis of the bacterial cell wall in both gram-positive and gram-negative bacteria. However, they are ineffective against Mycobacterium tuberculosis, due to the production of a beta-lactamase enzyme encoded on the chromosome of M. tuberculosis that degrades these antibiotics. Indeed, recent studies have demonstrated that deletion of the blaC gene, the only gene encoding a beta-lactamase in M. tuberculosis, or inhibition of the encoded enzyme resulted in significantly increased sensitivity to beta-lactam antibiotics. In this paper we present a biochemical and structural characterization of M. tuberculosis BlaC. Recombinant BlaC shows a broad range of specificity with almost equal penicillinase and cepholothinase activity. While clavulanate is a mechanism-based inhibitor to class A beta-lactamase with high potency (typically K(i) < 0.1 microM), it is a relatively poor inhibitor of the M. tuberculosis BlaC (K(i) = 2.4 microM). The crystal structure of the enzyme, determined at a resolution of 1.7 A, shows that the overall fold of the M. tuberculosis enzyme is similar to other class A beta-lactamases. There are, however, several distinct features of the active site, such as the amino acid substitutions N132G, R164A, R244A, and R276E, that explain the broad specificity of the enzyme, relatively low penicillinase activity, and resistance to clavulanate.

Amino Acid Sequence↗

Pharmacokinetics of beta-lactam antibiotics.

Beta-lactam antibiotics represent the oldest class of antibiotics used in the treatment of infections. Consequently, a large number of agents have been developed. Penicillins and cephalosporins are generally available for parenteral application. Some are absorbed from the gastrointestinal tract. The serum half-life (t1/2) of most beta-lactams is 1-2 hours. Ceftazidime and temocillin are more long-lasting with a t1/2 of 4-6 hours and ceftriaxone of 8-10 h. These values relate to patients with normal renal function. The elimination is only moderately prolonged for beta-lactams and of little consequences for the dosage regimens, partly because of the high tolerance of this group of antibiotics. Penicillins and cephalosporins are eliminated by glomerular filtration and varying degrees of active transport across the epithelial cells of the renal tubuli and hepatobiliary system. Active transport mechanisms also explain the low concentrations of beta-lactam antibiotics in cerebrospinal fluid. Otherwise, penetration of these agents to unspecialized tissues is good. Substances with a low serum protein binding, such as ampicillin and amoxicillin, reach concentrations in peripheral human lymph which as assessed by the ratios of areas under the concentration curves are 50-80% of the serum levels. The serum protein binding appears to act mainly by inhibiting the rate with which the antibiotic passes into extravascular foci. For instance, temocillin with a serum albumin binding around 85% establishes levels in peripheral lymph which are 50-60% of those in serum. This may be explained by the fact that a higher protein binding is accompanied by more lipid solubility, which are two factors acting in opposite directions as concerns passage by diffusion across body barriers.

Absorption↗

Intestinal absorption of several beta-lactam antibiotics. V. Effect of amino beta-lactam analogues and dipeptides on the absorption of amino beta-lactam antibiotics.

The absorption mechanism of amino beta-lactam antibiotics was investigated by using the whole small intestine of a rat. Mutual inhibition among amino beta-lactam analogues and the effects of dipeptides were studied. The influences of glycylglycine on the absorption of cephradine at the four different parts of intestine were also studied. Similarly to the case of cephalexin and cephradine, the absorption of amoxicillin was significantly inhibited by cyclacillin, cephradine, and cephalexin, but the absorption of ampicillin was not reduced by all tested antibiotics. In the experiments using dipeptides (6.0 mM), the absorption of cyclacillin was reduced significantly by glycylglycine, not by L-carnosine. And cephalexin absorption was influenced by L-carnosine (6.0, 10 mM), not by glycylglycine (6 mM). On the contrary, the absorption of cephradine was not reduced at all by these dipeptides. And from the experiment using the four different parts of intestine, it was shown that the transport interaction of glycylglycine with cephradine was observed in only one segment (the upper part of jejunum). These result suggest that the carrier-mediated transport system correlated to dipeptides participates only to a small degree in the common absorption mechanisms of these amino beta-lactam antibiotics.

Amoxicillin↗

Impaired hemostasis caused by beta-lactam antibiotics.

Beta-lactam antibiotics can directly impair hemostasis by two separate nonimmune mechanisms. First, the NMTT-substituted cephalosporin drugs may cause hypoprothrombinemia by interfering with the hepatic activation of clotting factors II, VII, IX, and X. Second, the antipseudomonal penicillins may cause the bleeding time to be prolonged by interfering with platelet aggregation to physiologic agonists. In surgical patients who are malnourished, have impaired gastrointestinal function, or have renal failure, the potential for these adverse effects is increased. Serious bleeding requires treatment with fresh frozen plasma when hypoprothrombinemia is caused by NMTT-containing cephalosporins, since the prothrombin time returns to baseline relatively slowly after therapy with vitamin K. Hemorrhage caused by beta-lactam-induced platelet dysfunction must be treated with platelet concentrates, since new platelets sufficient to correct the defect do not enter the circulation for several days after treatment with the offending drug is discontinued. The more desirable approach is to prevent hypoprothrombinemia by giving vitamin K prophylaxis and to avoid beta-lactams that impair platelet function in seriously ill patients at increased risk for bleeding.

Anti-Bacterial Agents↗

Electrochemiluminescence-based detection of beta-lactam antibiotics and beta-lactamases.

Bacterial resistance to clinically administered beta-lactam antibiotics is usually caused by beta-lactamases, enzymes that hydrolytically inactivate the antibiotics. This paper describes the use of electrogenerated chemiluminescence (ECL) to detect beta-lactam antibiotics and their hydrolysis by beta-lactamases. All 10 tested antibiotics were detected on the basis of their ability to participate in an ECL reaction with ruthenium(II) tris(bipyridine). In every case, antibiotic-promoted ECL changed when the antibiotic was hydrolyzed by beta-lactamases or NaOH. Standard curves of antibiotic concentration versus ECL intensity showed that antibiotics could be quantitated to low micromolar concentrations. Substrate profiles were generated for four beta-lactamases using six structurally diverse beta-lactam antibiotics. ECL-based antibiotic detection was accomplished in untreated whole milk, and beta-lactamases were detected in crude bacterial broth culture. Because several structurally diverse antibiotics were detectable by ECL, this method may become valuable for the detection of many or all beta-lactam antibiotics and their inactivation by beta-lactamases.

Anti-Bacterial Agents↗

Estimation of the molecular volumes of the reaction products between beta-lactam antibiotics and aminoglycoside antibiotics, and those of the degradation products of beta-lactam antibiotics by isotachophoresis.

The correlative equations between the molecular volume and the qualitative indication (hR) for beta-lactam antibiotics, the reaction products between beta-lactam antibiotics and kanamycin, and the degradation products of beta-lactam antibiotics were hR = 0.32 + 0.080 VA2/3//Z/(N = 15, r = 0.972 for penicillins) and hR = 0.04 + 0.072 VA2/3//Z/(N = 12, r = 0.987 for cephems). Where VA is van der Waals volume (A3/molecule), hR is the relative step height in the isotachopherogram, and Z is the electric change, respectively. According to these equations, the molecular volumes of the reaction products between beta-lactam antibiotics and the other aminoglycoside antibiotics, and those of the degradation products of beta-lactam antibiotics can be estimated from the value of hR. Also according to the step height in the isotachopherogram, the reaction products or the degradation products may be estimated directly when the electric charge is known. It was confirmed that a molecule of aminoglycoside antibiotics reacted with a molecule of beta-lactam antibiotics. Therefore, the inactivation of aminoglycoside antibiotics is much greater than for beta-lactam antibiotics when the clinical doses of these antibiotic combinations are used.

Aminoglycosides↗

In vitro susceptibility of Yersinia kristensenii strains to beta-lactam antibiotics.

The beta-lactam antibiotic susceptibility and beta-lactamase activity of 22 Yersinia kristensenii strains were determined in order to compare these properties with those reported for Y. enterocolitica. Carbenicillin, cephaloridine, cefoxitin and cefotaxime were the most active antimicrobial agents tested against Y. kristensenii. All strains were resistant to penicillin G, cephalothin, cephapirin and cephalexin. On the other hand, ampicillin and cefazolin activity could be considerated as intermediate. The influence of incubation temperature was also evaluated. All Y. kristensenii strains were more resistant at 22 degrees C than at 37 degrees C to beta-lactam antibiotics. Susceptibility to cefazolin was not affected by the incubation temperature. All Y. kristensenii strains produce beta-lactamase. The substrate profile of this enzyme is that of a cephalosporinase: its activity was highest on cephalothin, cephapirin, cephaloridine and cefazolin, while hydrolysis of ampicillin and carbenicillin was not detected. beta-Lactamase-resistant cefoxitin and cefotaxime were not hydrolysed. A correlation between beta-lactam antibiotic susceptibility and the hydrolysis rate of these antibiotics by beta-lactamase was observed, except for cephaloridine and cefazolin; these antibiotics were very good beta-lactamase substrates, but their MIC values were low.

Ampicillin↗

Analytical studies on beta-lactam antibiotics. II. Displacement effect of beta-lactam antibiotics on bilirubin bound to human serum albumin.

We established a method for determining the KD value as a measure of the bilirubin-displacing effect for drugs by using bilirubin oxidase, which is produced by Myrothecium verrucaria MT-1. This method makes it possible to conduct measurements of many beta-lactam antibiotics, including those which could not be determined by Brodersen's method. The KD values of latamoxef reported by many investigators based on Brodersen's method were higher than the true value owing to interaction of the drug with peroxidase and H2O2. Our KD value under the new enzyme conditions was 2.6 X 10(3). Little or no interaction of drug with the enzyme system was tentatively confirmed. Flomoxef, a newly developed drug, and 7432-S, under development in our company, had KD values of 0.4 X 10(3) and 2.8 X 10(3), respectively.

Anti-Bacterial Agents↗

Interactions of formylamino- and methoxy-substituted beta-lactam antibiotics with beta-lactamases.

Cephem and nocardicin-type monocyclic beta-lactam antibiotics with a formylamino substituent were highly resistant to hydrolysis by both penicillinases and cephalosporinases. Among antibiotics with a methoxy substituent, an N-sulfonated monocyclic beta-lactam antibiotic, sulfazecin was resistant to beta-lactamases, but cephem antibiotics were sensitive to the cephalosporinase of Enterobacter cloacae. The resistance of the antibiotics to the beta-lactamases depended primarily on the presence of the substituent, but affinity for the beta-lactamases was affected not only by the substituent but also by the presence of other side chains. Formylamino compounds and sulfazecin were as good inducers of beta-lactamases as semisynthetic 7-methoxycephalosporins, but naturally occurring 7-methoxycephalosporins were poor inducers. The inducer activities of the antibiotics were not necessarily related to their beta-lactamase stabilities. The stabilities of the compounds to the beta-lactamases were well reflected in their antibacterial activities against beta-lactamase producing bacteria.

Anti-Bacterial Agents↗

Intestinal uptake of dipeptides and beta-lactam antibiotics. I. The intestinal uptake system for dipeptides and beta-lactam antibiotics is not part of a brush border membrane peptidase.

The uptake of beta-lactam antibiotics into small intestinal enterocytes occurs by the transport system for small peptides. The role of membrane-bound peptidases in the brush border membrane of enterocytes from rabbit and pig small intestine for the uptake of small peptides and beta-lactam antibiotics was investigated using brush border membrane vesicles. The enzymatic activity of aminopeptidase N was inhibited by beta-lactam antibiotics in a non-competitive manner whereas dipeptidylpeptidase IV was not affected. The peptidase inhibitor bestatin led to a strong competitive inhibition of aminopeptidase N whereas the uptake of cephalexin into brush border membrane vesicles was only slightly inhibited at high bestatin concentrations (greater than 1 mM). Modification of brush border membrane vesicles with the histidine-modifying reagent diethyl pyrocarbonate led to a strong irreversible inhibition of cephalexin uptake whereas the activity of aminopeptidase N remained unchanged. A modification of serine residues with diisopropyl fluorophosphate completely inactivated dipeptidylpeptidase IV whereas the transport activity for cephalexin and the enzymatic activity of aminopeptidase N were not influenced. With polyclonal antibodies raised against aminopeptidase N from pig renal microsomes the aminopeptidase N from solubilized brush border membranes from pig small intestine could be completely precipitated; the binding protein for beta-lactam antibiotics and oligopeptides of apparent Mr 127,000 identified by direct photoaffinity labeling with [3H]benzylpenicillin showed no crossreactivity with the aminopeptidase N anti serum and was not precipitated by the anti serum. These results clearly demonstrate that peptidases of the brush border membrane like aminopeptidase N and dipeptidylpeptidase IV are not directly involved in the intestinal uptake process for small peptides and beta-lactam antibiotics and are not a constituent of this transport system. This suggests that a membrane protein of Mr 127,000 is (a part of) the uptake system for beta-lactam antibiotics and small peptides in the brush border membrane of small intestinal enterocytes.

Affinity Labels↗

Resistance to beta-lactam antibiotics.

beta-lactams have a long history in the treatment of infectious diseases, though their use has been and continues to be confounded by the development of resistance in target organisms. beta-lactamases, particularly in Gram-negative pathogens, are a major determinant of this resistance, although alterations in the beta-lactam targets, the penicillin-binding proteins (PBPs), are also important, especially in Gram-positive pathogens. Mechanisms for the efflux and/or exclusion of these agents also contribute, though often in conjunction these other two. Approaches for overcoming these resistance mechanisms include the development of novel beta-lactamase-stable beta-lactams, beta-lactamase inhibitors to be employed with existing beta-lactams, beta-lactam compounds that bind strongly to low-affinity PBPs and agents that potentiate the activity of existing beta-lactams against low-affinity PBP-producing organisms.

Anti-Bacterial Agents↗