Beta-lactam activity against penicillin-resistant Streptococcus pneumoniae strains exhibiting higher amoxicillin versus penicillin minimum inhibitory concentration values: an in vitro pharmacodynamic simulation.

BACKGROUND: Activity of simulated serum concentrations after oral therapy with 400 mg cefditoren pivoxil b.i.d., 500 mg cefuroxime axetil b.i.d. and 875/125 mg amoxicillin/clavulanic acid b.i.d. and t.i.d. regimens was explored over 24 h against Streptococcus pneumoniae. METHODS: Computerized pharmacodynamic simulations were performed against strains with penicillin/amoxicillin/cefuroxime/cefditoren minimum inhibitory concentrations (MICs, microg/ml) and serotypes: strain 1 (0.25/0.12/1/0.12; serotype 6A), strain 2 (2/4/ 2/0.25; serotype 6B), strain 3 (4/16/4/0.5; serotype 14), and strain 4 (4/16/8/1; serotype 14). RESULTS: Bactericidal activity (> or =3 log(10) reduction) at 12 and 24 h was obtained against all strains with cefditoren, against strains 1 and 2 with cefuroxime and amoxicillin/clavulanic acid t.i.d., but only against strain 1 with amoxicillin/clavulanic acid b.i.d.. Bactericidal activity at 24 h was related to T > MIC of >30% dosing interval, 1.7-2.0 log(10) reductions with T > MIC of 20-30%, and <1 log(10) reduction or regrowth with T > MIC of 0%. CONCLUSIONS: It is difficult to achieve pharmacodynamic coverage and bactericidal activity by physiological concentrations of oral beta-lactams against penicillin-resistant pneumococcal strains exhibiting higher amoxicillin versus penicillin MICs. Cefditoren may offer alternatives.

Inhibition of peptidoglycan hydrolase activity in vivo and in vitro by energy uncouplers in Escherichia coli.

The effects of energy uncouplers on in vivo and in vitro peptidoglycan hydrolase activities in Escherichia coli were determined. Sodium azide, potassium cyanide, and carbonyl cyanide m-chlorophenylhydrazone all inhibited ampicillin-induced lysis of exponential phase cultures, even when they were added to lysis-committed cultures. These energy uncouplers also inhibited the solubilization of radiolabeled peptidoglycan by bacterial suspensions that had been treated with 5% trichloroacetic acid by the method of Hartmann et al.3 to activate the peptidoglycan hydrolases. Therefore, the in vivo and in vitro activities of peptidoglycan hydrolases in E. coli are dependent on membrane energization.

Antagonism between penicillin and erythromycin against Streptococcus pneumoniae: does it exist?

Penicillin and erythromycin are commonly used for the treatment of serious infections caused by Streptococcus pneumoniae and combined as empiric therapy of community-acquired pneumonia. A concern about potential antagonism between these drugs prompted a protocol designed to test the hypothesis in timed kill curve experiments with several interpretive criteria applied. Four clinical isolates of S.pneumoniae from the United States referred to the SENTRY Antimicrobial Surveillance Program and one QC strain (ATCC 49619) were tested. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined for each isolate using reference dilution methods (NCCLS). Penicillin MBC results matched very closely to the MIC values. Penicillin and erythromycin were tested at clinically relevant concentrations of 10 and 1 microg/ml, respectively, alone and in combination. Interpretations were calculated comparing the penicillin + erythromycin killing effect versus penicillin or erythromycin rates tested alone. There was consistent bactericidal activity against S. pneumoniae by each drug alone and combined over the monitored five-hour period, except for an erythromycin induced-resistant isolate. Drug interactions ranged from synergy to antagonism, depending on the criteria applied. Antagonism risk of macrolide-penicillin combinations appeared to be minimal and method-dependent by in vitro tests.

The effect of phenobarbital on autonomic function and epileptogenic activity induced by the hippocampal injection of penicillin in cats.

This study addressed whether penicillin-induced epileptiform discharges in the right hippocampus produced associated autonomic dysfunction. The study also examined the effect of phenobarbital on the heart rate and blood pressure changes that were induced by the epileptiform discharges. The delay in onset of epileptiform activity at the site of injection ranged from 1 second to 16 minutes, and consisted of interictal discharges or ictal discharges. With the onset of epileptiform activity, blood pressure and heart rate increased significantly from control (P < .05). Electrocardiogram alterations included: P-R interval changes; increased P-wave amplitude; QRS complex changes; T-wave inversion; and ST elevation. Phenobarbital 20 mg/kg intravenously suppressed the epileptogenic activity and depressed the blood pressure and heart rate below control (P < .05). In an additional series of experiments, penicillin G injected into the right hippocampus in five cats produced epileptiform activity and increased the blood pressure and the heart rate significantly from the control (P < .05). Phenobarbital (20 mg/kg, intravenously, and 40 mg/kg, intravenously) also prevented the penicillin-induced epileptiform activity. Phenobarbital (40 mg/kg, intravenously) reversed the effect of penicillin on the blood pressure and heart rate, to levels significantly below that of control (P < .05). Phenobarbital diminished both epileptiform activity and autonomic dysfunction. The autonomic dysfunction related to epileptiform activity induced by focal hippocampal administration of penicillin was similar to that induced by the intravenous administration of pentylenetetrazol.

Suppression of the thermosensitive replication phenotype of the derivative plasmid of pI9789::Tn552 in Staphylococcus aureus may involve integration of the plasmid into the host chromosome.

Plasmid-chromosome co-integration was found to be the mechanism of choice to overcome thermosensitivity of replication of the plasmid pS1 in PS80d and RN4220 strains of Staphylococcus aureus. The integration of the plasmid was sometimes accompanied by deletion of a specific section of the plasmid pS1 in PS80d. Growth of bacteriophage on strains containing the integrated plasmid and the subsequent use of the phage in transduction gave transductants containing plasmids that had regained their replication thermosensitivity. These plasmids had not acquired any detectable chromosomal DNA. The 16-kb EcoRI fragment of the PS80d chromosome that hybridizes to pS1 is the target for recombination in many cases, but apparently other sites are also used. This fragment contains sequence homologous to parts of the transposon Tn552 and it is probable that site-specific recombination is involved in the integration. The possible mechanisms for the integrations and the deletions are discussed.

Carbamazepine suppresses synchronized afterdischarging in disinhibited immature rat hippocampus in vitro.

Bath application of therapeutic concentrations of the anticonvulsant carbamazepine suppressed penicillin-induced synchronized afterdischarging in immature rat CA3 hippocampal pyramidal cells. Afterdischarging was completely abolished in all preparations at a concentration of 30 microM (IC50 = 8.5 +/- 1.4 microM; mean +/- S.E.M.). The duration of the preceding epileptiform burst was not altered at this concentration and was diminished by only 24.4 +/- 1.2% at a supratherapeutic concentration of 100 microM. These results suggest that a carbamazepine-sensitive neurophysiological mechanism distinct from those responsible for epileptiform burst generation plays a key role in the generation of afterdischarges in developing hippocampus.

Influence of morphine and cyclazocine on the cortical epileptic foci in rabbits.

The effects of morphine, cyclazocine and naloxone on penicillin- and strychnine-induced epileptic foci were studied in rabbits. The intracortical injection of penicillin (75, 150 and 300 units) elicited isolated spikes followed by repeated ictal events. The application of strychnine (0.062 and 0.125%) over the cortical surface of one side induced appearance of ipsilateral spiking spreading to the contralateral cortex. Administration of morphine (0.25-0.75 mg/kg i.v.) or cyclazocine (0.05-3.0 mg/kg i.v.) inhibited the occurrence or the duration of the EEG and motor manifestations induced by penicillin (75 and 150 units) and strychnine (0.062 and 0.125%), while it did not influence the effect of 300 units of penicillin. High doses of morphine (up to 10 mg/kg i.v.) failed to affect the epileptic responses to penicillin and strychnine and at the same time significantly reduced the pO2 in arterial blood. Naloxone per se potentiated the effects of the lower doses of penicillin and strychnine. Only at very high doses (20 mg/kg i.v.) displayed a weak antagonism towards the anticonvulsant effect of the two opiates. A full antagonism is only observed towards the effect of cyclazocine (2 mg/kg i.v.) administered after penicillin. Present data provide additional evidence of the heterogeneity of regulation by opioids of convulsive phenomena. One can hypothesize that the anticonvulsant effect of the two opiate agonists is mediated by naloxone-insensitive opiate receptors, while the proconvulsant-convulsant effect of naloxone might be related to an inhibition of GABA and glycine-mediated transmission.

The anticonvulsive action of adenosine: a postsynaptic, dendritic action by a possible endogenous anticonvulsant.

Neural afterdischarges generated in the presence of penicillin or low extracellular calcium concentrations were found to be inhibited by adenosine in the rat hippocampus in vitro. This anticonvulsant effect of adenosine is observed in the absence, as well as in the presence, of chemical synaptic transmission and apparently occurs at a postsynaptic site which is most sensitive in the apical dendritic region of the CA1 pyramidal cells. The methylxanthine theophylline antagonizes the effect of adenosine; and, the anticonvulsant action of the L-isomer of the adenosine analogue phenylisopropyladenosine (PIA) is substantially more potent than the D-isomer, findings which are characteristic of an A1 type adenosine receptor. The endogenous release of adenosine may therefore serve to tonically reduce the tendency for repetitive discharge in CA1 pyramidal cells via an interaction with a high affinity A1 receptor which appears to be preferentially localized in the apical dendrites.

In vitro antagonism between beta-lactam and macrolide in Streptococcus pneumoniae: how important is the antibiotic order?

We found that the in vitro interaction between penicillin or cefotaxime and erythromycin against Streptococcus pneumoniae varies depending on the order of antibiotic exposure. Time-kill experiments were performed with penicillin, cefotaxime, erythromycin and different order combinations of both beta-lactams with erythromycin. The mean difference between the colony count at 0 and 6h for penicillin, cefotaxime and erythromycin tested separately was 3.5 log cfu/mL, 2.4 and 1.5 respectively for susceptible strains. The mean difference for the combination of beta-lactam and erythromycin studied simultaneously was 1.8 log cfu/mL for these strains. The association of penicillin or cefotaxime with erythromycin added two hours later showed an activity similar to those of beta-lactam alone (mean difference was 3.0 for this association with penicillin and 2.5 with cefotaxime). Therefore, the antagonistic effect of macrolide activity could be less important if erythromycin was administrated after beta-lactam.

The excitatory amino acid antagonist amino-phosphono-valeric acid (APV) provides protection against penicillin-induced epileptic activity in the rat.

The effects of intraperitoneal injection of 2-amino-5-phosphono-valeric acid (APV) on EEG-monitored penicillin-induced epileptic activity in rats were evaluated. A significant decrease in the frequency of spikes occurred with low APV dosages (10 and 20 mg/kg), while an almost complete disappearance of spike activity was observed at higher APV doses (40 and 160 mg/kg). Our data suggest that excitatory amino acids play a relevant role in penicillin-induced epileptic activity in rats.

Antiseizure activity of insulin: insulin inhibits pentylenetetrazole, penicillin and kainic acid-induced seizures in rats.

The present study was undertaken to evaluate the antiseizure activity spectrum of insulin against various behavioral seizure models in rats. Insulin was injected intraperitoneally (i.p.) at a test dose of 1 U/kg. Dextrose (3 g/kg) was administered simultaneously with insulin to counteract its hypoglycemic effect and induce a normoglycemic state. Insulin was found to significantly decrease the incidence, intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by pentylenetetrazole (60 mg/kg i.p.) and significantly decrease the intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by penicillin (2000 U/intracerebrocortical). Insulin was not only found to prolong the latency of all the seizure components but was found to reduce the incidence of focal myoclonic twitches and generalized tonic-clonic convulsions induced by kainic acid (12 mg/kg i.p.) as well. Insulin was shown to be ineffective to suppress ouabain (5 micrograms/intracerebroventricular) induced seizures. These findings indicate that insulin possesses a broad spectrum of antiseizure activity in rats. Interaction with brain Na(+)-K(+)-ATPase has been discussed as a possible mechanism of action.

Inhibition of penicillin-induced EEG discharges by low doses of morphine or naloxone in the rabbit. Evidence for a possible non-opioid receptor-mediated mechanism at the sensorimotor cortex.

In rabbits, pretreatment by intravenous (IV) and intracortical (IC) routes with low doses of morphine (250 micrograms/kg IV or 60 pmoles/rabbit IC) and naloxone (1-50 micrograms/kg IV or 0.3 pmoles/rabbit IC) antagonizes the EEG and behavioural seizures due to the IC injection of penicillin (150 Units) at the level of the sensorimotor cortex. Pretreatment with naloxone (20 micrograms/kg IV) did not alter the anticonvulsant effect of morphine (250 micrograms/kg IV). The similar anticonvulsant effect of the two drugs together with the absence of any antagonism by naloxone on the effect of morphine seem to suggest that both drugs act through a non-opioid receptor-mediated mechanism. Further, in light of the low effective doses of the drugs and of the absence of any additive effect after their combined administration, one might speculate that morphine and naloxone do not act through different pharmacological receptors. However, the presence of distinct EEG patterns with either morphine or naloxone, injected IC and IV, in animals fully protected against penicillin-induced seizures, does not seem to be in favour of the latter possibility.

Enzymatic studies on the mechanism of action of cefoxitin. Correlation between the affinities of cefoxitin to penicillin-binding proteins and its rates of inhibition of the respective penicillin-sensitive reactions in E. coli.

The affinities of cefoxitin, a cephamycin antibiotic, to penicillin-binding proteins of Escherichia coli were reexamined using a recently developed method for separating penicillin-binding proteins. The inhibitions by this antibiotic of four measurable penicillin-sensitive enzymatic reactions, the reactions of D-alanine carboxypeptidases IA and IB, cross-bridge formation and concomitant release of D-alanine, were also measured. An approximate correlation was found between the affinities of cefoxitin to the penicillin-binding proteins responsible for these reactions and its rates of inhibition of the respective penicillin-sensitive reactions.

[The postantibiotic effect of amoxicillin/clavulanic acid on Streptococcus pneumoniae strains of different serotypes and penicillin sensitivity]. / Efecto postantibiótico de amoxicilina/acido clavulánico en cepas de Streptococcus pneumoniae de diferente serotipo y sensibilidad a penicilina.

Amoxicillin and clavulanic acid, combined in a 4:1 ratio, caused a significant (longer than 0.5 hours) postantibiotic effect (PAE) for the S. pneumoniae stains tested. These strains were from a different serotype (3, 6 and 9) and also had different susceptibility to penicillin. The duration of the PAE depended both on the strain and the amoxicillin/clavulanic acid concentration used. It is significant that for the serotype 9 strain, which was both penicillin and amoxicillin resistant, the duration of the PAE was between 1.5 and 2.2 hours. These results agree with those observed by other authors as to the effectiveness of amoxicillin/clavulanic acid against S.pneumoniae.

[Use of nicotinamide and pyridoxal-5-phosphate to treat experimental epilepsy]. / Primenenie nikotinamida i piridoksal'-5-fosfata dlia kupirovaniia éksperimental'noi épilepsii.

In experiments on cats it was shown that nicotinamide injected intravenously in a dose of 300 to 500 mg per kg body weight depressed singular epileptic foci and groups of foci with synchronized activity induced in the animals' brain cortex by application of strychnine (0.1 ml of 3% solution). The vitamin was also effective, though to a lesser degree, in depressing foci induced by application of penicillin (2% solution). Pyridoxal-5-phosphate (Pyr-5-Ph) injected intravenously in a dose of 10 mg/kg depressed singular foci and groups of foci with synchronized activity induced by application of 2% solution of penicillin, but was less effective in depressing strychnine-induced foci. Combined application of both drugs even in lower doses (nicotinamide, 200 mg/kg; Pyr-5-Ph, 5 mg/kg) resulted in depression of groups of epileptic foci induced by combined application of strychnine and penicillin. Mechanisms of the effects discovered are discussed. A question on possible use of combined nicotinamide and pyridoxal-5-phosphate in the treatment of epilepsy is raised.

[Depression of penicillin-evoked seizure discharges of cerebrospinal neurons by magnesium ions]. / Ugnetenie ionami magniia vyzvannykh penitsillinom sudorozhnykh razriadov spinnomozgovykh neironov.

In experiments on narcotized spinal cats perfusion of the lumbosacral segments of the spinal cord with penicillin (50 mmol/l) containing artificial cerebrospinal fluid led to the appearance of spontaneous negative small potentials in the dorsal roots and spontaneous repetitive bursts of impulses in the ventral roots of the perfused segments. The epileptogenic activity of penicillin was reduced or completely blocked if administration of the penicillin containing cerebrospinal fluid was preceded by 20-30 minute perfusion of the central canal of the lumbosacral segments with cerebrospinal fluid containing a high concentration of magnesium ions.

[Expression, purification and application of bla(TEM-116) extended-spectrum beta-lactamase].

To produce TEM-116 extended-spectrum beta-lactamase (ESBL) from recombinant bacteria in a cost-effective way, we purified and renatured the recombinant TEM-116 ESBL from the inclusion bodies by Ni(2+)-NTA affinity and gel filtration chromatography through subcloning the bla(TEM-116) into expression vector pET28a(+), transforming into Escherichia coli BL21(DE3) and inducing with IPTG. We characterized the purified protein that had the molecular weight of 30 kDa and specific activity of 476 IU/mg. The recombinant TEM-116 ESBL showed higher efficiency in eliminating penicillin and cephalosporin in vitro and in vivo. Specifically, the recombinant TEM-116 ESBL could eliminate 7000 mg penicillin G (PG) when used at 10.0 IU in 1 L fermentation medium. When used at 320.0 IU, it could also degrade a mix of PG, ampicillin and cefazolin each at 200 mg in 1 L of urine. In milk, 1.0-2.5 IU of the recombinant enzyme could remove 80 U/L of PG. The recombinant enzyme was fully active at the temperature ranged from 4 degrees C to 37 degrees C. Furthermore, the recombinant enzyme used at 2.0x10(4)-2.3x10(4) IU/(kg bw) (body weight) eliminated 8.0x10(4)-9.1x10(4) microg/(kg bw) PG in mouse models in vivo. The recombinant TEM-116 ESBL has the potential as a tool enzyme in food and environmental protection to eliminate harmful residues of antibiotics.