Modulation of bacteriolysis by cooperative effects of penicillin-binding proteins 1a and 3 in Escherichia coli

Transcriptional Modulation of Penicillin-Binding Protein 1b, Outer Membrane Protein P2 and Efflux Pump (AcrAB-TolC) during Heat Stress Is Correlated to Enhanced Bactericidal Action of Imipenem on Non-typeable Haemophilus influenzae

Objective: The purpose of the present study was to investigate the penicillin binding proteins (PBPs), drug influx and efflux modulations during heat stress and their effects on the bactericidal action of imipenem on non-typeable Haemophilus influenzae (NTHi).

Methods: The two NTHi clinical isolates (GE47 and GE88, imipenem MICs by E-test > 32 μg/mL) examined in this study were collected at Geneva University Hospitals. The imipenem killing activity was assessed after incubation of the NTHi strains at either 37 or 42°C for 3 h with increasing concentrations of imipenem. The detection of PBPs was carried out by Bocillin-FL. Global transcriptional changes were monitored by RNA-seq after pre-incubation of bacterial cells at either 37 or 42°C, and the expression levels of relevant target genes were confirmed by qRT-PCR.

Results: Quantitation of NTHi viable cells after incubation with 0.25 μg/mL of imipenem for 3 h revealed more than a twofold decrease in GE47 and GE88 viable cells at 42°C as compared to 37°C. Transcriptome analysis showed that under heat stress conditions, there were 141 differentially expressed genes with a | log2(fold change)| > 1, including 67 up-regulated and 74 down-regulated genes. The expression levels of ponB (encoding PBP1b) and acrR (regulator of AcrAB-TolC efflux pump) were significantly increased at 42°C. In contrast, the transcript levels of ompP2 (encoding the outer membrane protein P2) and acrB gene (encoding AcrB) were significantly lower under heat stress condition.

Conclusion: This study shows that the transcriptional modulation of ponB, ompP2, acrR, and acrB in the heat stress response is correlated to enhanced antimicrobial effects of imipenem on non-typeable H. influenzae.

Morphological and ultrastructural changes in bacterial cells as an indicator of antibacterial mechanism of action

Efforts to reduce the global burden of bacterial disease and contend with escalating bacterial resistance are spurring innovation in antibacterial drug and biocide development and related technologies such as photodynamic therapy and photochemical disinfection. Elucidation of the mechanism of action of these new agents and processes can greatly facilitate their development, but it is a complex endeavour. One strategy that has been popular for many years, and which is garnering increasing interest due to recent technological advances in microscopy and a deeper understanding of the molecular events involved, is the examination of treated bacteria for changes to their morphology and ultrastructure. In this review, we take a critical look at this approach. Variables affecting antibacterial-induced alterations are discussed first. These include characteristics of the test organism (e.g. cell wall structure) and incubation conditions (e.g. growth medium osmolarity). The main body of the review then describes the different alterations that can occur. Micrographs depicting these alterations are presented, together with information on agents that induce the change, and the sequence of molecular events that lead to the change. We close by highlighting those morphological and ultrastructural changes which are consistently induced by agents sharing the same mechanism (e.g. spheroplast formation by peptidoglycan synthesis inhibitors) and explaining how changes that are induced by multiple antibacterial classes (e.g. filamentation by DNA synthesis inhibitors, FtsZ disruptors, and other types of agent) can still yield useful mechanistic information. Lastly, recommendations are made regarding future study design and execution.

Biological characterization of Pseudomonas aeruginosa endotoxin released by antibiotic treatment in vitro

The supernatants taken from Pseudomonas aeruginosa cultures in human sera or chemically defined M9 medium in the presence of ceftazidime (CAZ) contained high levels of endotoxin, while those of imipenem (IPM) yielded relatively lower levels of endotoxin. The membrane-filtered supernatants were used as a source of endotoxin and the biological activities of the endotoxin were examined in comparison with those of hot-phenol water-extracted LPS. The CAZ-released endotoxin preparation contained large amounts of protein. The protein, however, appeared to lack significant endotoxic activity through the endotoxin-protein component, since the endotoxin did not show any toxic effect in D(+)-galactosamine (GaIN)-sensitized C3H/HeJ mice in vivo or macrophage activation in vitro. The activities of CAZ- and IPM-released endotoxins as assessed by chromogenic Limulus amebocyte coagulation test were fundamentally identical to those of purified P. aeruginosa LPS and Escherichia coli LPS, since their regression lines were parallel. The biological effects of CAZ-released endotoxin, such as lethal toxicity in GaIN-sensitized mice, in vitro induction of TNF and NO production by peritoneal macrophages, and MAP-kinase activation in macrophages of LPS-responsive C3H/He and LPS-low responsive C3H/HeJ mice, were similar to those of the LPS. Macrophage activation by CAZ-released endotoxin as well as LPS was mainly dependent on serum factors and CD14 antigen. Polymyxin B blocked the activity. These findings indicate that the endotoxic activity of CAZ-released endotoxin is due primarily to LPS (lipid A), although such preparations contain a high level of protein released from or produced by the organisms. Finally, the possibility that the treatment of P. aeruginosa infection with some kind of antibiotics may induce endotoxic shock was suggested in a mouse model.

The clinical significance of endotoxin released by antibiotics: what is the evidence?

Basic investigations indicate variation among antibiotics in their propensity to release endotoxin from bacterial cells. Evidence for the clinical significance of this phenomenon includes: anecdotal reports; studies evaluating changes in endotoxin levels in response to antibiotics in a variety of infectious diseases; two studies which have prospectively evaluated changes in endotoxin levels in response to different antibiotics and correlated the changes with the patients' clinical course; and one study which evaluated differences in mortality in injured patients based on the endotoxin-releasing potential of antibiotics they received. These studies suggest: (i) different types of antibiotics do induce differing levels of endotoxin release during treatment of bacterial infections in humans; (ii) such antibiotic-associated endotoxin release probably does have a biologic consequence; and (iii) this biologic consequence is possibly of clinical relevance. However, the data are not sufficient to advocate changes in current antibiotic prescribing or dosing decisions. Rather, a variety of in vitro and in vivo experiments as well as clinical studies are advocated.

The release of endotoxin, TNF and IL-6 during the antibiotic treatment of experimental Gram-negative sepsis

To evaluate the role of different antibiotics in the release of endotoxin and the production of tumor necrosis factor-α (TNF) and interleukin 6 (IL-6) during the treatment of experimental Escherichia coli septical peritonitis, we obtained serial blood samples from septic rats treated with placebo, ceftazidime, aztreonam or imipenem. We also studied the effect of taurolidine, given alone or in combination with aztreonam, on the release of endotoxin and IL-6. Despite decreasing levels of viable counts after treatment with ceftazidime, aztreonam or imipenem, levels of free endotoxin increased in all animals. We did not notice any significant differences in the extent of plasma endotoxin release between the different treatment groups. However, we did find significant differences in the IL-6 production between the different treatment groups. After 2 h of treatment, IL-6 levels had increased in all animals with the highest levels in the imipenem treated animals, whereafter IL-6 levels decreased again in the rats treated with imipenem or ceftazidime, while in the rats treated with placebo or aztreonam IL-6 levels further increased. This increase in IL-6 levels was associated with acute mortality. In all antibiotic treated animals TNF levels significantly decreased during therapy. After 2 h of treatment TNF levels were the highest in the imipenem treated rats. The high levels of TNF and IL-6 at t = 2 in the imipenem group were thought to be the result of early bacterial lysis, while the late increase in IL-6 levels in the aztreonam treated animals was thought to be the result of the formation of long bacterial filaments in the abdominal cavity. In the present study, treatment with taurolidine could not prevent or inhibit the release of endotoxin or IL-6, but taurolidine, alone or in combination with aztreonam, unexpectedly caused a dramatic increase in IL-6 levels which was associated with an increased acute mortality. We conclude that antibiotics can cause the release of endotoxin in spite of decreasing levels of bacteremia in vivo. It is suggested that circumstances in which antibiotic-induced filamentation occurs are also conditions that yield excessive (local) LPS release. Our data also suggest that there is a lack of relationship between plasma free endotoxin levels and mortality and that the most important inflammatory compartment was the abdominal cavity in this model.

Endopeptidase-mediated beta lactam tolerance

In many bacteria, inhibition of cell wall synthesis leads to cell death and lysis. The pathways and enzymes that mediate cell lysis after exposure to cell wall-acting antibiotics (e.g. beta lactams) are incompletely understood, but the activities of enzymes that degrade the cell wall ('autolysins') are thought to be critical. Here, we report that Vibrio cholerae, the cholera pathogen, is tolerant to antibiotics targeting cell wall synthesis. In response to a wide variety of cell wall--acting antibiotics, this pathogen loses its rod shape, indicative of cell wall degradation, and becomes spherical. Genetic analyses revealed that paradoxically, V. cholerae survival via sphere formation required the activity of D,D endopeptidases, enzymes that cleave the cell wall. Other autolysins proved dispensable for this process. Our findings suggest the enzymes that mediate cell wall degradation are critical for determining bacterial cell fate--sphere formation vs. lysis--after treatment with antibiotics that target cell wall synthesis.

Differences in neutrophil death among beta-lactam antibiotics after in vitro killing of bacteria

Antibiotic therapy is an essential treatment for gram-negative bacterial infections. Antibiotic-induced endotoxin release and subsequent production of inflammatory cytokines reportedly depend on the type of antibiotic action. This study examined the effects of various beta-lactam antibiotics on cell death of human polymorphonuclear neutrophils (PMNs) cocultured with Escherichia coli (E. coli) in vitro. E. coli morphology after antibiotic treatment was determined. PMNs and E. coli were cocultured with antibiotics for 0, 4, or 12 h. Levels of endotoxin and cytokines (TNF-alpha, IL-1beta, and IL-6) in the supernatants were measured. The filtrates of antibiotic-treated E. coli supernatants were cocultured with PMNs for 0, 4, or 12 h. In all experiments, ampicillin (ABPC), cefazolin sodium (CEZ), cefoperazone sodium (CPZ), latamoxef sodium (LMOX), imipenem (IPM), and polymyxin B sulfate (PLB) were used at 30 microg/mL. PMNs were isolated from healthy volunteers. PMN cell death was assessed by flow cytometry and light microscopy. ABPC, CEZ, CPZ, and LMOX, which induce bacterial filament formation with lysis, caused PMN necrosis when cocultured with E. coli. In contrast, IPM, which induces bacterial spheroplast formation with lysis, caused PMN apoptosis. Levels of endotoxin, TNF-alpha and IL-6 in the supernatants with IPM and PLB were significantly lower than in those with other beta-lactam antibiotics. The filtrates of IPM- and PLB-treated E. coli supernatants induced PMN apoptosis, whereas those treated with other beta-lactam antibiotics increased PMN necrosis. Beta-lactam antibiotics have different impacts on the types of PMN cell death after E. coli killing. Underlying mechanisms and the clinical relevance of IPM-induced PMN apoptosis in severe gram-negative infection warrant further investigation.

Morphological changes and lysis induced by beta-lactams associated with the characteristic profiles of affinities of penicillin-binding proteins in actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae, which was formerly classified in the genus Haemophilus, is a pathogen causing swine pleuropneumonia. We found that aspoxicillin showed strong activity and that meropenem had better lytic activity against this pathogen. In the present study, we for the first time identified penicillin-binding proteins (PBPs) of A. pleuropneumoniae in order to elucidate the relationship between the antibacterial and lytic activities of beta-lactam antibiotics and affinities of the PBPs. The competitive assay using (3)H-labeled benzylpenicillin revealed seven PBPs in A. pleuropneumoniae; they were determined to be PBPs 1a, 1b, 2, 3, 4, 5, and 6, and the molecular masses of these PBPs were estimated to be 92, 80, 76, 72, 50, 44, and 30 kDa, respectively, by comparison with those of Haemophilus influenzae. Our detailed analysis of the affinities of the PBPs of A. pleuropneumoniae and of the bacterial lysis kinetics for several beta-lactam antibiotics revealed that the strong antibacterial activity of aspoxicillin against this strain could be related to the higher affinity of PBP 3 and that preferential inactivation of PBP 1b could cause rapid lysis.

Potent bacteriolytic activity of ritipenem associated with a characteristic profile of affinities for penicillin-binding proteins of Haemophilus influenzae

Ritipenem is highly bacteriolytic against Haemophilus influenzae. Bacterial lysis was shown after treatments with ritipenem and cefsulodin at their MICs and after treatments with fropenem and cefdinir at four times their MICs, indicated by decreases in the culture turbidities and by morphological changes of the destroyed cells. These beta-lactams were preferentially bound to penicillin-binding protein (PBP) 1b. Ritipenem, fropenem, and cefsulodin exhibited poor affinities to PBPs 3a and 3b, but cefdinir showed high affinities to these PBPs. Microscopic examinations revealed that selective PBP 3 inhibitors, such as aztreonam and cefotaxime, inhibited lysis induced by ritipenem. These results suggest that the preferential inactivation of PBP 1b could be essential to induce the lysis of H. influenzae cells and that binding to PBPs 3a and 3b may interfere with lysis.

New criteria for selecting the proper antimicrobial chemotherapy for severe sepsis and septic shock

The mortality rate resulting from severe bacterial sepsis, particularly that associated with shock, still approaches 50% in spite of appropriate antimicrobial therapy and optimum supportive care. Bacterial endotoxins that are part of the cell wall are one of the cofactors in the pathogenesis of sepsis and septic shock and are often induced by antimicrobial chemotherapy even if it is administered rationally. Not all antimicrobial agents are equally capable of inducing septic shock; this is dependant on their mechanism of action rather than on the causative pathogen species. The quantity of endotoxin released depends on the drug dose and whether filaments or spheroplast formation predominates. Some antibiotics such as carbapenems, ceftriaxone, cefepime, glycopeptides, aminoglycosides and quinolones do not have the propensity to provoke septic shock because their rapid bactericidal activity induces mainly spheroplast or fragile spheroplast-like bacterial forms.

Antibiotic-induced release of bacterial cell wall components in the pathogenesis of sepsis and septic shock: a review

This article reviews the new criteria for selecting the proper antimicrobial agent and dosage regimen for standard treatment of severe sepsis, with the intention of preventing septic shock. After introducing new concepts on the pathogenesis of sepsis and septic shock, the authors analyze the parameters of betalactam antibacterial activity, the antibiotic-induced release of bacterial endotoxin and the interrelationships between pharmacokinetics and pharmacodynamics of antibiotics in the search for an optimum dosage regimen of antimicrobial mono- or polytherapy for severely ill septic patients admitted to the intensive care unit.

Biological characterization of endotoxins released from antibiotic-treated Pseudomonas aeruginosa and Escherichia coli

The supernatants taken from Pseudomonas aeruginosa and Escherichia coli cultures in human sera or chemically defined M9 medium in the presence of ceftazidime (CAZ) contained high levels of endotoxin, while those taken from the same cultures in the presence of imipenem (IPM) yielded a very low level of endotoxin. The biological activities of endotoxin in the supernatants were compared with those of phenol water-extracted lipopolysaccharide (LPS). The endotoxin released from the organisms as a result of CAZ treatment (CAZ-released endotoxin) contained a large amount of protein. The protein, however, lacked endotoxic activity, since the endotoxin did not show any in vivo toxic effects in LPS-hyporesponsive C3H/HeJ mice sensitized with D-(+)-galactosamine (GalN) or any activation of C3H/HeJ mouse macrophages in vitro. The activities of CAZ- and IPM-released endotoxin (as assessed by a chromogenic Limulus test) were fundamentally the same as those of P. aeruginosa LPS, since their regression lines were parallel. The CAZ-released endotoxin was similar to purified LPS with respect to the following biological activities in LPS-responsive C3H/HeN mice and LPS-hyporesponsive C3H/HeJ mice: lethal toxicity in GalN-sensitized mice, in vitro induction of tumor necrosis factor- and NO production by macrophages, and mitogen-activated protein kinase activation in macrophages. The macrophage activation by CAZ-released endotoxin as well as LPS was mainly dependent on the presence of serum factor and CD14 antigen. Polymyxin B blocked the activity. These findings indicate that the endotoxic activity of CAZ-released endotoxin is due primarily to LPS (lipid A).

Protective effects of a human 18-kilodalton cationic antimicrobial protein (CAP18)-derived peptide against murine endotoxemia

CAP18 (an 18-kDa cationic antimicrobial protein) is a granulocyte-derived protein that can bind lipopolysaccharide (LPS) and inhibit various activities of LPS in vitro. The present study examined the protective effect of a synthetic 27-amino-acid peptide (CAP18(109-135)) from the LPS-binding domain of CAP18 against antibiotic-induced endotoxin shock, using highly LPS-sensitive D-(+)-galactosamine (D-GalN)-sensitized C3H/HeN mice. The antibiotic-induced endotoxin (CAZ-endotoxin) was prepared from the culture filtrate of Pseudomonas aeruginosa PAO1 exposed to ceftazidime (CAZ). Injection of CAP18(109-135) protected the mice injected with LPS or CAZ-endotoxin from death and lowered their tumor necrosis factor (TNF) levels in serum in a dose-dependent manner. Treatment with CAZ caused death of the D-GalN-sensitized P. aeruginosa PAO-infected mice within 48 h, while injection with CAP18(109-135) rescued the mice from death. In the mice rescued from death by injection with CAP18(109-135), endotoxin levels in plasma and TNF production by liver tissues were decreased but the numbers of viable infecting bacteria in their blood were not decreased significantly and remained at the levels in CAZ-treated mice. These results indicate that CAP18(109-135) is capable of preventing antibiotic-induced endotoxic shock in mice with septicemia and that the effect is due to its LPS-neutralizing activity rather than to its antibacterial activity.

Antibiotic-induced lipopolysaccharide (LPS) release from Salmonella typhi: delay between killing by ceftazidime and imipenem and release of LPS

It has been suggested that the antibiotic-induced release of lipopolysaccharide (LPS) is an important cause of the development of septic shock in patients treated for severe infections caused by gram-negative bacteria. Beta-lactam antibiotics change the integrity of the bacterial cell envelope by binding to penicillin-binding proteins (PBP) in the membrane and thus may affect the amount of LPS that is released and the kinetics of that release. In this respect, ceftazidime at intermediate concentrations binds with a high affinity to PBP 3 and PBP 1a and thus can induce filament formation in addition to killing, whereas imipenem preferentially binds to PBP 2 and PBP 1b, leading to spheroplast formation and rapid cell lysis. We investigated the effects of these antibiotics on the killing and the release of the radioactively labelled LPS of Salmonella typhi Ty 21A. A mathematical model was developed to calculate the delay between bacterial killing and LPS release, designated the lag time. At antibiotic concentrations inducing equal killing, the amount of LPS released was the same for both antibiotics. Only after 6 h of incubation at antibiotic concentrations above 0.5 microg/ml, the amount of 3H-LPS released was slightly higher (approximately 1.2-fold) in incubations with ceftazidime than in those with imipenem, and the maximum releases of the total label were 33.2% +/- 0.89% and 27.1% +/- 0.45%, respectively. Despite the clear concentration-dependent effect on the bacterial killing and subsequent LPS release, the lag time was independent of the antibiotic concentration. For ceftazidime as well as imipenem the lag time amounted to approximately 60 min. In conclusion, our findings imply that the mechanism of antibiotic-induced LPS release is independent of the PBP affinities for these beta-lactam antibiotics. Furthermore, once the organism is killed by either imipenem or ceftazidime, the rate of LPS release from S. typhi does not differ according to the antibiotic with which the organism is killed, and there is little difference in the relative amount of LPS released.

In vivo TNF induction by culture supernatants of antibiotic-treated Escherichia coli 07:K1. Role of antibiotic class and concentration

Antibiotics may cause an excess release of lipopolysaccharide (LPS) from bacteria and thereby promote the production of tumour necrosis factor (TNF). TNF was measured in the serum of Swiss mice challenged with filtered supernatant of Escherichia coli O7:K1 that had been exposed to various antibiotics in vitro. Expressed as a function of a standardized number of cells remaining after 6 h of exposure to gentamicin, ceftazidime, ciprofloxacin or imipenem, TNF leves associated with antibiotic exposure always exceeded those of controls. However, if differences in the remaining number of bacteria were not taken into account, TNF induction by supernatant of control untreated cultures was greater than that elicited by supernatant from any of the antibiotic-treated cultures. With the exception of imipenem, low-dose antibiotic exposure (0.5 x MIC) invariably induced higher TNF levels than did high-dose exposure (10 x MIC). Considerable antibiotic class- and concentration-related differences were noted. LAL equivalent amounts of LPS released by different antibiotics may diverge in their capacity to induce TNF. Our results do not support the notion that the use of rapidly bactericidal and lytic antibiotics should be avoided.

Target for bacteriostatic and bactericidal activities of beta-lactam antibiotics against Escherichia coli resides in different penicillin-binding proteins

The relationship between cell-killing kinetics and penicillin-binding protein (PBP) saturation has been evaluated in the permeability mutant Escherichia coli DC2 in which the antimicrobial activity of beta-lactams has been described as being directly related to the extent of saturation of the PBP target(s). Saturation of a single PBP by cefsulodin (PBP 1s), mecillinam (PBP 2), and aztreonam (PBP 3) resulted in a slow rate of killing (2.5-, 1.5-, and 0.8-log-unit decreases in the number of CFU per milliliter, respectively, in 6 h). Saturation of two of the three essential PBPs resulted in a marked increase in the rate of killing, which reached the maximum value when PBPs 1s and 2 were simultaneously saturated by a combination of cefsulodin and mecillinam (4.7-log-unit decrease in the number of CFU per milliliter in 6 h). Inactivation of all three essential PBPs by the combination of cefsulodin, mecillinam, and aztreonam further increased the killing kinetics (5.5-log-unit decrease in the number of CFU per milliliter), and this was not significantly changed upon additional saturation of the nonessential PBPs 5 and 6 by cefoxitin. Similar relationships between PBP saturation and killing kinetics were obtained with imipenem and meropenem at concentrations which inhibited only one PBP (PBP 2), only two PBPs (PBP 1s and 2), or all three essential PBPs. Saturation of one or more PBPs also resulted in a different rate of bacteriolysis, the highest rate being obtained by the cefsulodin-mecillinam combination and by 5 micrograms of either imipenem or meropenem per ml. All of these conditions caused saturation of PBP 2 and saturation or extensive binding of PBP 1s. However, none of these conditions caused determined the fastest possible rate of killing, which occurred only when all three essential PBPs were saturated. It was concluded that the actual killing effect of beta-lactams is reflected by killing rates that approach the fastest possible rate for the given microorganism and that the targets for the bactericidal activity are precisely those PBPs whose saturation or binding occurs under conditions.

Molecular basis of the efficacy of cefaclor against Haemophilus influenzae

Cefaclor sustained its inhibitory activity against a beta-lactamase-producing strain of Haemophilus influenzae. Although a relatively high permeability coefficient was calculated for ampicillin compared with that calculated for cefaclor, the resulting periplasmic concentration of cefaclor was 5.7 times that of ampicillin. The efficacy of cefaclor may be due to its higher beta-lactamase resistance, which allows it to achieve a greater periplasmic concentration and adequate binding to crucial penicillin-binding proteins.

Effects of different types and combinations of antimicrobial agents on endotoxin release from gram-negative bacteria: an in-vitro and in-vivo study

Total and free endotoxin release in time from cultures of Escherichia coli by different antibiotics was studied in vitro for 4 h in relation to the antibiotic effect on viable counts and morphological features of the test cultures. The most rapid fall in viable counts was seen after treatment with imipenem or the combination of imipenem with tobramycin, accompanied by an early, but minimal increase (1.8-fold) of the total (free plus cell-bound) endotoxin level at 1 h. Total endotoxin levels increased approximately 5-fold upon incubation with ceftazidime, tobramycin or the combination of tobramycin with cefuroxime, whereas incubation with cefuroxime or aztreonam alone caused a late 22-and 49-fold increase in total endotoxin, respectively, at 4 h. In chloramphenicol treated cultures there was still an increase in viable counts during therapy, resulting in an ultimately 78-fold increase of mean levels of total endotoxin. Free endotoxin levels increased approximately 6-fold within 1 h upon treatment with imipenem, alone or in combination with tobramycin, or ceftazidime as the result of rapid lysis of bacteria. Treatment with cefuroxime or aztreonam induced a relatively late but much higher release of free endotoxin (118-and 222-fold, respectively), which was due to the formation of long filamentous structures during the first 2 h of incubation and eventually cell lysis. Both tobramycin and the combination of tobramycin with cefuroxime caused a more gradual rise in free endotoxin, with a +/- 15-fold increase in free endotoxin at 4 h. In chloramphenicol treated cultures, as in the control cultures, the level of free endotoxin remained proportional to the amount of viable organisms. We also studied plasma endotoxin levels in 20 patients with septic shock. 10 out of these 20 patients had a detectable endotoxemia (greater than 5 ng/l) on admission. We describe the patterns of plasma endotoxin in these patients during the first 24 h of antibiotic treatment. We conclude that, in the in-vitro study, values of total endotoxin, free endotoxin, and the rate of release of endotoxin varies with the antibiotic used. We also demonstrate that in patients under treatment for septic shock endotoxin release can be related to the administration of antibiotics.

Haemophilus influenzae penicillin-binding proteins 1a and 3 possess distinct and opposite temperature-modulated penicillin-binding activities

Upon investigation of penicillin-binding proteins (PBPs) in Haemophilus influenzae strains, five H. influenzae and seven other Haemophilus strains were tested for whole-cell penicillin binding at either 37 or 42 degrees C. Binding of [35S]penicillin G to H. influenzae PBPs 3a and 3b was drastically reduced at 42 degrees C, while PBP 1a showed a temperature-modulated increase in penicillin binding. Further investigation revealed that growth at 42 degrees C causes altered electrophoretic mobility of PBP 3a on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and that cell labeling performed at 42 degrees C showed the differential penicillin binding to target proteins. All Haemophilus spp. tested showed a similar temperature modulation of penicillin binding. Growth measurement and cell viability studies performed at 42 degrees C permitted correlation of PBP 3 temperature sensitivity to H. influenzae resistance to moxalactam at 42 degrees C, and the probable correlation of PBP 1a increased penicillin binding to the more rapid antibacterial activity of penicillin G against H. influenzae at 42 degrees C. Microscopic examination of Haemophilus cells grown at 42 degrees C revealed filamentous cell formation, supporting a role of PBP 3 in the septation process. Results of this study demonstrate that wild-type H. influenzae strains (and possibly all other Haemophilus spp.) possess PBPs 1a and 3, which have distinct and opposite temperature-modulated penicillin-binding activities.