Chronic granulomatous disease (CGD): in vitro enhancement of bactericidal activity of CGD phagocytes by rifampicin

In a series of 29 experiments on CGD patients, we have studied the in vitro bactericidal capacity of normal and CGD phagocytes against penicillin, streptomycin and rifampicin sensitive Staphylococcus aureus. The bactericidal activity of phagogyte preparations was tested at different intervals during a 21 hour incubation. The CGD-phagocyte bactericidy peaks after 90 min when penicillin is used; in contrast, a significant enhancement of the bactericidal activity is noted with rifampicin and best noted after 21 hours of incubation. To elucidate the mode of action of this antibiotic, a rifampicin resistant S. aureus was used in a series of experiments; The results point to a mixt type of action: antimicrobial and metabolic.     

Surface action of gentamicin on Pseudomonas aeruginosa

The mode of action of gentamicin has traditionally been considered to be at the 30S ribosomal level. However, the inhibition of bacterial protein synthesis alone appears to be insufficient to entirely explain the bactericidal effects. Bacteriolysis is also mediated through perturbation of the cell surface by gentamicin (J.L. Kadurugamuwa, J.S. Lam, and T.J. Beveridge, Antimicrob. Agents Chemother. 37:715-721, 1993). In order to separate the surface effect from protein synthesis in Pseudomonas aeruginosa PAO1, we chemically conjugated bovine serum albumin (BSA) to gentamicin, making the antibiotic too large to penetrate through the cell envelope to interact with the ribosomes of the cytoplasm. Furthermore, this BSA-gentamicin conjugate was also used to coat colloidal gold particles as a probe for electron microscopy to study the surface effect during antibiotic exposure. High-performance liquid chromatography confirmed the conjugation of the protein to the antibiotic. The conjugated gentamicin and BSA retained bactericidal activity and inhibited protein synthesis on isolated ribosomes in vitro but not on intact cells in vivo because of its exclusion from the cytoplasm. When reacted against the bacteria, numerous gentamicin-BSA-gold particles were clearly seen on the cell surfaces of whole mounts and thin sections of cells, while the cytoplasm was devoid of such particles. Disruption of the cell envelope was also observed since gentamicin-BSA and gentamicin-BSA-gold destabilized the outer membrane, evolved outer membrane blebs and vesicles, and formed holes in the cell surface. The morphological evidence suggests that the initial binding of the antibiotic disrupts the packing order of lipopolysaccharide of the outer membrane, which ultimately forms holes in the cell envelope and can lead to cell lysis. It is apparent that gentamicin has two potentially lethal effects on gram-negative cells, that resulting from inhibition of protein synthesis and that resulting from surface perturbation; the two effects in concert make aminoglycoside drugs particularly effective antibiotics.     

Staphylococcal cell wall: morphogenesis and fatal variations in the presence of penicillin

The primary goal of this review is to provide a compilation of the complex architectural features of staphylococcal cell walls and of some of their unusual morphogenetic traits including the utilization of murosomes and two different mechanisms of cell separation. Knowledge of these electron microscopic findings may serve as a prerequisite for a better understanding of the sophisticated events which lead to penicillin-induced death. For more than 50 years there have been controversial disputes about the mechanisms by which penicillin kills bacteria. Many hypotheses have tried to explain this fatal event biochemically and mainly via bacteriolysis. However, indications that penicillin-induced death of staphylococci results from overall biochemical defects or from a fatal attack of bacterial cell walls by bacteriolytic murein hydrolases were not been found. Rather, penicillin, claimed to trigger the activity of murein hydrolases, impaired autolytic wall enzymes of staphylococci. Electron microscopic investigations have meanwhile shown that penicillin-mediated induction of seemingly minute cross wall mistakes is the very reason for this killing. Such "morphogenetic death" taking place at predictable cross wall sites and at a predictable time is based on the initiation of normal cell separations in those staphylococci in which the completion of cross walls had been prevented by local penicillin-mediated impairment of the distribution of newly synthesized peptidoglycan; this death occurs because the high internal pressure of the protoplast abruptly kills such cells via ejection of some cytoplasm during attempted cell separation. An analogous fatal onset of cell partition is considered to take place without involvement of a detectable quantity of autolytic wall enzymes ("mechanical cell separation"). The most prominent feature of penicillin, the disintegration of bacterial cells via bacteriolysis, is shown to represent only a postmortem process resulting from shrinkage of dead cells and perturbation of the cytoplasmic membrane. Several schematic drawings have been included in this review to facilitate an understanding of the complex morphogenetic events.     

Protein-A-mediated targeting of bacteriochlorophyll-IgG to Staphylococcus aureus: a model for enhanced site-specific photocytotoxicity

A model for studying the efficiency of photodynamic action with a photosensitizer placed exclusively on the bacterial cell wall has been used. Bacteriochlorophyllide molecules, conjugated to rabbit immunoglobulin G (IgG), were synthesized. The conjugated pigment bacteriochlorophyll (Bchl)-IgG bound with high specificity to protein-A residues naturally exposed on the cell wall of the bacterium Staphylococcus aureus Cowan I. In bacterial suspensions the phototoxicity of the targeted conjugates (0.5-2.5 pigment per IgG molecule) was dose dependent (LD50 = 1.7 microM) in the presence of light (lambda > 550 nm) and inhibited by native IgG but not by ovalbumin, suggesting selective interaction with protein-A on the bacterial cell wall. No dark toxicity was noticed even with the highest conjugate concentration tested. In contrast, the photocytotoxicity of bacteriochlorophyll-serine (Bchl-Ser, LD50 = 0.07 microM) used as a nontargeted control was not inhibited by IgG. In spite of its lower apparent potency, Bchl-IgG was found to be 30 times more efficacious than Bchl-Ser: At LD50, only 66,000 Bchl-IgG molecules were bound per bacterium compared to 1,900,000 molecules of Bchl-Ser. The higher efficacy of Bchl-IgG is explained by its exclusive position on the bacterial cell wall. Consequently, photogeneration of oxidative species is confined to the cell wall and its vicinity, a seemingly highly susceptible domain for photodynamic action. In considering the design of cell-specific sensitizers for bacterial and cancer therapies, it would be beneficial to identify the more discretely sensitive subcellular domains as targets.     

Which conditions promote a remanent (persistent) bactericidal activity of chlorine covers?

The interaction of disinfectants containing active chlorine compounds (hypochlorite, chloramine T) with skin surfaces produces a so called chlorine cover which is a true chemical transformation of the protein matrix of the outermost horny skin layer by forming covalent N-Cl bonds. Though its intensity can easily be measured, the results on its remanent (persistent) bactericidal action until now have not been described consistently. While Gottardi and Karl observed a well-defined remanent action which correlated with the cover strength in the artificially with E. coli contaminated arm, Koller, Rotter, and Gottardi were not able to prove it, neither in artificially contaminated hands nor in the case of the resident bacterial colonization. To clarify these not consistent results, the bactericidal activity of chlorine covers on transient (dry contamination of the finger tips with Micrococcus luteus) as well as on resident colonization (after wearing gloves for 3 h) has been re-investigated using contact plates for recovering the bacteria. The results are showing that the remanent bactericidal action of chlorine covers strongly depends on the skin milieu, with moist conditions caused by sweat (surgical gloves) favoring the bactericidal activity. Elution experiments prove that protein constituents (detected by UV-spectrometry) continuously are transported to the skin-surface. It is obvious that the latter equilibrate with the chlorine cover by forming bactericidal N-Cl compounds with the effect that oxidation capacity fixed at the protein matrix is mobilized enabling the remanent bactericidal action.     

Effect of industrial contact with penicillin on the immunological reactivity of workers

Immunological examination of women occupied in production of penicillin revealed a decrease in the phagocytic activity of the blood neutrophiles and the bactericidal properties of the skin, an increase in the quantitative composition of the autoflora of the skin and changes in its biochemical properties. Correlation between the changes in the values of the natural non-specific immunity as dependent on the level of the contact with the antibiotic was shown.     

Decreased susceptibility to antibiotic killing of a stable small colony variant of Staphylococcus aureus in fluid phase and on fibronectin-coated surfaces

The frequency of small colony variants of staphylococci associated with persistent, antibiotic resistant and relapsing infections is probably underestimated. These variants demonstrate decreased metabolism, leading to slow growth, increased resistance to cell-wall-active antibiotics, and decreased uptake of aminoglycoside antibiotics. This altered phenotype arises from defects in menadione and haemin biosynthesis resulting in impaired electron transport and decreased ATP concentrations. The recent acquisition of a stable small colony variant (SCV strain JB1), generated from strain 6850 of Staphylococcus aureus, allowed us to study the susceptibilities to antibiotic killing of parent and variant strains. Because differences in susceptibilities have been found between unattached and surface-adherent organisms, we tested both strains in solid and fluid-phase assays. Suspensions of SCV strain JB1 exposed to 8 x MIC of either oxacillin, vancomycin or fleroxacin, exhibited lower reductions in viable counts than the parent strain 6850, especially when high bacterial concentrations (1-2 x 10(7) cfu/mL) of either strain were tested. Susceptibility to antibiotic killing of bacteria attached to fibronectin-coated coverslips was markedly influenced by their growing or nongrowing state on the surface. In the latter condition, surface-bound SCV organisms were highly resistant to the bactericidal action of oxacillin or vancomycin in contrast to the parental strain which was normally eliminated by each antimicrobial agent. In conclusion, the decreased susceptibility of the stable SCV strain of S. aureus to bactericidal concentrations of antibiotics may help to explain the persistence of such organisms in chronic infections.     

Effect of pre- and postnatal nicotine exposure on vasopressinergic system in rats

Intact mycobacteria and mycobacterial cell wall extracts have been shown to inhibit the growth of human and murine bladder cancer. Their mechanism of action is, however, poorly understood. Mycobacterium phlei mycobacterial cell complex (MCC) is a cell wall preparation that has mycobacterial DNA in the form of short oligonucleotides complexed on the cell wall surface. In this study, we have investigated the possibility that MCC has anti-cancer activity that is mediated by two different mechanisms--a direct effect on cancer cell proliferation and viability and an indirect effect mediated by the production of interleukin 12 (IL-12), a cytokine known to possess anti-cancer activity. We have found that, although MCC is a potent inducer of IL-12 and IL-6 synthesis in monocytes and macrophages either in vitro or in vivo, it is unable to induce the synthesis of either IL-12, IL-6 or granulocyte-macrophage colony-stimulating factor (GM-CSF) by the human transitional bladder cancer cell lines HT-1197 and HT-1376. MCC is not directly cytotoxic towards these cancer cells, but induces apoptosis as determined by nuclear DNA fragmentation and by the release of nuclear mitotic apparatus protein. Mycobacterium phlei DNA associated with MCC is responsible for the induction of apoptosis. Our results indicate that MCC directly effects bladder cancer cells by inhibiting cellular proliferation through the induction of apoptosis, and has the potential for an indirect anti-cancer activity by stimulating cancer-infiltrating monocytes/macrophages to synthesize IL-12.     

In vitro activities of oral beta-lactams at concentrations achieved in humans against penicillin-susceptible and -resistant pneumococci and potential to select resistance

The beta-lactam susceptibilities of 65 strains of Streptococcus pneumoniae for which penicillin MICs covered a broad range were assessed. The order of potency was amoxicillin (AMX) = amoxicillin-clavulanate (AMC) > penicillin G > cefpodoxime (CPO) > cefuroxime (CXM) > cefprozil > cefaclor > loracarbef > cefixime. No decrease in susceptibility was seen following repeated subculture of two penicillin-susceptible strains of S. pneumoniae in AMX, AMC, cefaclor, or loracarbef, whereas repeated exposure to CPO and CXM resulted in 4- to 32-fold decreases in susceptibility for both strains. When one of these strains was exposed to concentrations of CPO, CXM, AMX, and AMC achieved in the serum of humans following the administration of an oral dose, all agents were rapidly bactericidal, with no decrease in susceptibility up to 72 h. This was consistent with antibiotic concentrations exceeding the MICs for 100% of the dosing interval. For a penicillin-resistant strain, MICs were exceeded for 29% of the 12-h dosing interval for 500 mg of AMX, 42% of the interval for AMC with 875 mg of AMX and 125 mg of clavulanate (875/125 mg of AMC) 21% of the interval for 500 mg of CXM, and 0% of the interval for 200 mg of CPO. Consequently, only 875/125 mg of AMC produced a sustained bactericidal effect. A four- to eightfold reduction in susceptibility to CPO and CXM and cross-resistance with cefotaxime, but not penicillin or AMC, were selected following exposure to simulated serum CPO and CXM concentrations. In addition, AMX and AMC were the only agents which consistently produced a >99% reduction in bacterial numbers in time-kill studies using concentrations of antibiotic achieved in middle ear fluid for all three strains of penicillin-resistant S. pneumoniae tested.     

Inhibition of bacterial respiration by a low-molecular weight lectin, scyllin, from Scylla serrata crab hemolymph

Interaction of plant and/or invertebrate lectins with mammalian cells and different microorganisms is well known. In the present study, we have demonstrated that scyllin, a low molecular weight (MW 4000) lectin from the edible crab Scylla serrata hemolymph, purified by GalNAc-Sepharon affinity column followed by Mono-Q ion exchanger in FPLC exhibits antimicrobial activity against Bacillus cereus and Escherichia coli by inhibiting endogenous respiration as well as exogenous glucose oxidation. In both the cases oxygen consumption has been measured in an oxygraph. Scyllin has produced 50% inhibition of endogenous respiration at a concentration of 110 micrograms/ml and 125 micrograms/ml in B. cereus and E. coli respectively. It also reduced the exogenous glucose oxidation by 50% at a concentration of 12 micrograms/ml and 80 micrograms/ml respectively in B. cereus and E. coli. From the above study the mechanism of bacterial growth inhibitory property of scyllin is suggested though the other studies such as inhibition of nucleic acid biosynthesis, cell wall biosynthesis etc. to evaluate its total mode of inhibitory action are not yet obtained.     

The relationship between capillary and venous concentrations of the antimalarial drug lumefantrine (benflumetol)

The study aimed to determine the antibacterial therapy effective in the cure of endocarditis caused by Enterococcus faecalis resistant to clinically achievable levels of vancomycin. Isolation of the causative enterococcus had been achieved by direct inoculation of the resected valve into the culture medium in theatre. The patient was known to have had an aortic valve defect since childhood and had recently undergone splenectomy following trauma. Blood cultures were negative prior to valve replacement. A perivalvular abscess was noted at operation. In vitro minimal bactericidal results and serum activity were the basis of the postoperative choice of drugs. The minimal bactericidal level of teicoplanin was 250 micrograms/ml and that of amoxycillin 64 micrograms/ml. Neither is achievable with the advocated dosage. A combination of these two cell-wall-active agents successfully eliminated the infection. Acting at two different sites in the synthesis of the bacterial cell wall, teicoplanin and amoxycillin were found to be bactericidal in vitro at the trough levels of the antibiotics in the serum. The patient recovered fully.     

Penicillin-resistant mechanisms in Pseudomonas aeruginosa: binding of penicillin to Pseudomonas aeruginosa KM 338

A comparison of the binding of radioactive penicillin G to whole cells and the membrane fraction derived from Pseudomonas aeruginosa KM 338 was made. This organism has intrinsic resistance to penicillin. The binding to the membrane fraction which catalyzed peptidoglycan synthesis followed saturation type kinetics and saturation was achieved at approximately 2 nmol of penicillin G per ml, whereas binding to the whole cells was entirely of the nonsaturation type. The binding of carbenicillin to the membrane fraction was determined by competition between radioactive penicillin G and unlabeled carbenicillin for the binding sites. It was bound at the same sites in almost the same manner. When whole cells were pretreated with high concentration of unlabeled penicillin G or carbenicillin, the subsequent binding of radioactive penicillin G to the membrane fraction from carbenicillin-treated cells was entirely nonspecific, but with penicillin G-pretreated cells it was still specific. There was apparently specific binding of radioactive penicillin G to ethylenediaminetetraacetate-treated cells. P. aeruginosa KM 338 had an extremely low activity of beta-lactamase compared with other enzyme-producing organisms. This enzyme from P. aeruginosa KM 338 was of the cephalosporinase type. These data indicate that penicillin resistance of P. aeruginosa KM 338 may be a consequence of the development of a permeability barrier which prevents the antibiotic from reaching its sites of action in the cytoplasmic membrane.     

Radial glia and cell debris removal during lesion-regeneration of the lizard medial cortex

By challenging the efficiency of some of our most useful antimicrobial weapons, bacterial antibiotic resistance is becoming an increasingly worrying clinical problem. A good antibiotic is expected to exhibit a high affinity for its target and to reach it rapidly, while escaping chemical modification by inactivating enzymes and elimination by efflux mechanisms. A study of the behaviour of a beta-lactamase-overproducing mutant of Enterobacter cloacae in the presence of several penicillins and cephalosporins showed that the minimum inhibitory concentration (MIC) values for several compounds were practically independent of the sensitivity of the target penicillin binding protein (PBP), even for poor beta-lactamase substrates. This apparent paradox was explained by analysing the equation that relates the antibiotic concentration in the periplasm to that in the external medium. Indeed, under conditions that are encountered frequently in clinical isolates, the factor characterizing the PBP sensitivity became negligible. The conclusions can be extended to all antibiotics that are sensitive to enzymatic inactivation and efflux mechanisms and must overcome permeability barriers. It would be a grave mistake to neglect these considerations in the design of future antibacterial chemotherapeutic agents.     

Studies of the killing kinetics of benzylpenicillin, cefuroxime, azithromycin, and sparfloxacin on bacteria in the postantibiotic phase

Most antibiotics are known to be incapable of killing nongrowing or slowly growing bacteria with few exceptions. Bacterial cell division is inhibited during the postantibiotic phase (PA phase) after short exposure to antibiotics. Only scarce and conflicting data are available concerning the ability of antibiotics to kill bacteria in the PA phase. The aim of the present study was to investigate the killing effect of four different antibiotics on bacteria in the PA phase. A postantibiotic effect (PAE) was induced by exposing Streptococcus pyogenes and Haemophilus influenzae to 10x MICs of benzylpenicillin, cefuroxime, sparfloxacin, and azithromycin. The bacteria were thereafter reexposed to a 10x MIC of the same antibiotic used for the induction of the PAE at the beginning of and after 2 and 4 h in the PA phase. Due to a very long PAE, the bacteria in PA phase induced by azithromycin were also exposed to 10x MICs after 6 and 8 h. A previously unexposed culture exposed to a 10x MIC was used as a control. The results seem to be dependent on both the antibiotic used and the bacterial species. The antibiotics exhibiting a fork bactericidal action gave significantly reduced killing of the bacteria in PA phase (cefuroxime with S. pyogenes, P < 0.01, and sparfloxacin with H. influenzae, P < 0.001), which was restored at 4 h for cefuroxime with S. pyogenes. There was a tendency to restoration of the bactericidal activity also with sparfloxacin and H. influenzae, but there was still a significant difference in killing between the control and the test bacteria in PA phase at 4 h. However, in the combinations with a lesser bactericidal effect (benzylpenicillin with S. pyogenes and sparfloxacin with S. pyogenes), there was no difference in killing between the control and the test bacteria in PA phase. Azithromycin induced long PAEs in both S. pyogenes and H. influenzae and exhibited a slower bactericidal action on both the control and the bacteria in PA phase especially at the end of the PAE, when the killing was almost bacteriostatic. Our findings in this study support the concept that a long interval (> 12 h) between doses of azithromycin, restoring full bactericidal action, may be beneficial to optimize efficacy of this drug but is not necessary for the other antibiotics evaluated, since the bactericidal effect seems to be restored already at 4 h.     

Synthetic bactericidal peptide based on CAP37: a 37-kDa human neutrophil granule-associated cationic antimicrobial protein chemotactic for monocytes

CAP37 (cationic antimicrobial protein of molecular mass 37 kDa) is a multifunctional protein isolated from the granules of human neutrophils. It is antibiotic and chemotactic and binds lipopolysaccharide. A synthetic peptide, amino acid sequence NQGRHFCGGALIHARFVMTAASCFQ, based on residues 20-44 of CAP37 protein mimics its antibiotic and lipopolysaccharide binding action. Peptide 20-44, at the concentrations tested, has antibacterial activity against Salmonella typhimurium, Pseudomonas aeruginosa, Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus. The bactericidal action of the peptide was pH dependent, with maximum activity at pH 5.0 and pH 5.5 and decreased activity at pH 7.0. Various truncations, substitutions, and other modifications in the sequence deteriorate its activity. Free sulfhydryl groups and/or disulfide bridge formation are required for optimum antibiotic activity, since substitution of serines for, or alkylation of, cysteine residues 26 and 42 eliminates bactericidal activity. Evidently amino acids 20-44 represent an important, perhaps principal, antibacterial domain of CAP37. This peptide should provide new insight into the mechanism of antimicrobial activity of CAP37 and may serve as a model for new, useful, synthetic antibiotics.     

The evolution of virus-induced apoptosis

Viruses from several different families are able to exploit their host's cell death programmes so as to maximize viral fitness. Consideration of the evolution of such strategies has lead to the suggestion that the virus should inhibit apoptosis, in order to prolong the life of the cell and thereby maximize the number of progeny virions. The host, on the other hand, should stimulate apoptosis thereby inhibiting viral growth and blocking viral spread. For example, the function of the latent membrane protein I (LMPI) of the Epstein-Barr virus and the bcl-2 homologue gene A179L of African swine fever virus is to inhibit apoptosis. However, in other cases it is the virus that stimulates cell death or the host that benefits from inhibiting apoptosis, such as in fatal alphavirus encephalitis. This has been explained by assuming that virus-induced apoptosis in non-regenerating cells would be detrimental to the host. We present a mathematical framework for understanding virus-induced apoptosis which accounts for these two opposite solutions to virus infection with respect to the mode of virus replication and the life cycle of the target cell.     

Cell elongation and septation are two mutually exclusive processes in Escherichia coli

Bacterial rod morphogenesis was studied in synchronously growing cells of Escherichia coli C600 during the reshaping process that follows the removal of mecillinam, a beta-lactam antibiotic that specifically inhibits lateral wall formation of gram-negative rods and causes transition to coccal shape. Removal of mecillinam after 30 min of action did not affect the timing of subsequent cell division, but removal after 50 min delayed resumption of cell division for approximately one generation time. In order to study the interplay between lateral wall elongation and septum formation in determining and maintaining the bacterial rod shape, we evaluated the effect of re-adding mecillinam or of adding aztreonam (a specific inhibitor of septum formation) at various stages of the reshaping process. We conclude that mecillinam was active only during the reshaping process, while aztreonam was active only later when the cells were close to dividing again. These results provide further evidence for our previous proposal according to which elongation and septation are two alternating and competing events of the cell cycle and are linked to each other to force bacterial rods to grow to a given length.     

Curcumin, a natural plant phenolic food additive, inhibits cell proliferation and induces cell cycle changes in colon adenocarcinoma cell lines by a prostaglandin-independent pathway

Curcumin, the active ingredient of the rhizome of the plant turmeric (Curcuma longa Linn), a commonly used spice, prevents cancer in animal tumor models. Its mechanism of action is unknown; curcumin may act by inhibiting arachidonic acid metabolism. To explore the mechanism of curcumin's chemopreventive effect, we studied its role in proliferation and apoptosis in the HT-29 and HCT-15 human colon cancer cell lines. Curcumin dose-dependently reduced the proliferation rate of both cell lines, causing a 96% decrease by 48 hours. No apoptosis was detected. The antiproliferative effect was preceded by accumulation of the cells in the G2/M phase of cell cycle. The effect of curcumin was similar in both cell lines, which, however, differ in their ability to produce prostaglandins. We conclude that curcumin inhibits colon cancer cell proliferation in vitro mainly by accumulating cells in the G2/M phase and that this effect is independent of its ability to inhibit prostaglandin synthesis. The role of curcumin's antiproliferative effect in human colon cancer remains to be established.     

A YAC-based transcript map of human chromosome 9q22.1-q22.3 encompassing the loci for hereditary sensory neuropathy type I and multiple self-healing squamous epithelioma

The release of lipoteichoic acid (LTA) and teichoic acid (TA) from a Streptococcus pneumoniae type 3 strain during exposure to ceftriaxone, meropenem, rifampin, rifabutin, quinupristin-dalfopristin, and trovafloxacin in tryptic soy broth was monitored by a newly developed enzyme-linked immunosorbent assay. At a concentration of 10 microg/ml, a rapid and intense release of LTA and TA occurred during exposure to ceftriaxone (3,248+/-1,688 ng/ml at 3 h and 3,827+/-2,133 ng/ml at 12 h) and meropenem (2,464+/-1,081 ng/ml at 3 h and 2,900+/-1,364 ng/ml at 12 h). Three hours after exposure to rifampin, rifabutin, quinupristin-dalfopristin, and trovafloxacin, mean LTA and TA concentrations of less than 460 ng/ml were observed (for each group, P < 0.01 versus the concentrations after exposure to ceftriaxone). After 12 h of treatment, the LTA and TA concentrations were 463+/-126 ng/ml after exposure to rifampin, 669+/-303 ng/ml after exposure to rifabutin, and 1,236+/-772 ng/ml after exposure to quinupristin-dalfopristin (for each group, P < 0.05 versus the concentrations after exposure to ceftriaxone) and 1,745+/-1,185 ng/ml after exposure to trovafloxacin (P = 0.12 versus the concentration after exposure to ceftriaxone). At 10 microg/ml, bactericidal antibacterial agents that do not primarily affect cell wall synthesis reduced the amount of LTA and TA released during their cidal action against S. pneumoniae in comparison with the amount released after exposure to beta-lactams. Larger quantities of LTA and TA were released after treatment with low concentrations (1x the MIC and 1x the minimum bactericidal concentration) than after no treatment for all antibacterial agents except the rifamycins. This does not support the concept of using a low first antibiotic dose to prevent the release of proinflammatory cell wall components.