Comparative In Vitro Activity of Five Cephalosporins Against Lactobacilli

Of five parenteral cephalosporins tested against 43 lactobacilli, cephaloridine, cefazolin, and cefamandole were the most active inhibitory and bactericidal agents. Timed-kill analysis revealed a slow bactericidal effect, with significant declines in mean minimal bactericidal concentration values at 48 h versus 24 h.     

In Vitro Bactericidal Activity of Iclaprim in Human Plasma

This study evaluated the effect of human plasma on the in vitro bactericidal activity of the novel diaminopyrimidine iclaprim against methicillin (meticillin)-susceptible and -resistant Staphylococcus aureus strains. MICs and minimal bactericidal concentrations (MBCs) of iclaprim, with ∼93% protein binding, were similar in the absence and in the presence of 50% human plasma; MICs and MBCs ranged from 0.06 to 0.125 μg/ml. Furthermore, the activity of iclaprim was not affected by plasma, with ≥99.9% reduction in CFU after 5.0 to 7.6 h.Iclaprim is a novel dihydrofolate reductase inhibitor antibiotic that is under development for the treatment of hospitalized patients with severe infections caused by gram-positive pathogens, including Staphylococcus aureus, methicillin (meticillin)-resistant S. aureus (MRSA), and β-hemolytic streptococci (10, 11). Iclaprim has recently completed two pivotal phase III trials for the treatment of complicated skin and skin structure infections, including infections caused by MRSA. It has been shown to exhibit a rapid in vitro bactericidal activity against MRSA and vancomycin-nonsusceptible strains (11).Plasma protein binding is often, though not always, associated with a certain loss in in vitro microbiological activity. Despite the observation that iclaprim is ∼93% plasma protein bound, we have recently reported that the in vitro MIC of iclaprim is not affected by the presence of 50% human plasma (7). In contrast, the microbiological activity of fusidic acid (97 to 98% plasma protein bound) has been reported to be significantly affected by the addition of serum or blood to the test medium (4). The aim of this study was to determine the effect of human plasma on the bactericidal activity of iclaprim against S. aureus in comparison to the activity of teicoplanin and fusidic acid drugs with similar or higher protein binding (>90% and 97 to 98%, respectively) and vancomycin and linezolid with low reported protein binding (55% and 31%, respectively) (2).Ten methicillin-susceptible S. aureus (MSSA) and 10 MRSA strains were tested, including clinical isolates from different countries in Europe and North America and two type strains. MICs against iclaprim, teicoplanin, vancomycin, fusidic acid, and linezolid were determined by broth microdilutions in cation-adjusted Mueller-Hinton broth (CAMHB; Oxoid, Basingstoke, United Kingdom) with and without 50% pooled human plasma (PAA Laboratories GmbH, Pasching, Austria) following the standard CLSI protocol (3). Minimal bactericidal concentrations (MBCs) were determined via plating of aliquots on Mueller-Hinton agar taken from wells with no visual growth at 24 h, according to the CLSI guideline (9). To avoid the impact of potential drug carryover, cells grown with fusidic acid were washed twice with phosphate-buffered saline before plating (6). Washing did not affect the CFU counts. The rates of the bactericidal activities of iclaprim and vancomycin in the presence of 50% human plasma were assessed for one MSSA and four MRSA strains by time-kill methodology (9). The bacteria (∼1 × 10⁶ CFU/ml) were grown in 24-well plates containing 2 ml of CAMHB either with or without 50% human plasma and either containing no antibiotic (control) or containing iclaprim or vancomycin at 4× MIC, and the CFU/ml were determined. Samples were taken at 0, 2, 4, 6, 8, and 24 h, and appropriate dilutions were plated onto Mueller-Hinton agar to determine the CFU. Bactericidal activity was defined as a ≥3-log₁₀ CFU/ml reduction in bacterial density (i.e., ≥99.9% kill) compared with the level in the initial inoculum (9). Bacteria growing in the presence of plasma were sonicated briefly to disaggregate cellular clumps that can form in the presence of human plasma (Branson Sonifier 250; 30 s at 40% duty cycle and 40% capacity), which can result in an underestimation of CFU. The gentle sonication did not affect the viability of the cells.The activity of iclaprim was not affected by the presence of 50% human plasma, with MICs ranging from 0.06 to 0.125 μg/ml with and without 50% human plasma, in agreement with recently published data (7). Moreover, the MBCs of iclaprim were also not affected by the presence of human plasma. The MBC/MIC ratios ranged from 1 to 2 both in CAMHB and in the presence of 50% human plasma (Table ​(Table1).1). Therefore, iclaprim exhibited similar bactericidal activity irrespective of the presence or absence of 50% plasma according to MBC determinations. The activities of vancomycin and linezolid were also generally unaffected by the presence of human plasma, with similar MICs and MBCs in the presence and absence of 50% plasma (Table ​(Table1).1). Vancomycin was bactericidal and the MBC/MIC ratios ranged from 1 to 2, while linezolid was bacteriostatic (Table ​(Table1),1), which is in agreement with reported data (1, 12). The presence of plasma had a minimal effect on the activity of teicoplanin (Table ​(Table1).1). These data are in agreement with Dykhuizen et al., who reported similar MBCs of vancomycin and teicoplanin in the presence of 50% human serum (5). As expected from its high plasma protein binding, MICs for fusidic acid were 16- to 256-fold greater in the presence of plasma, which is in agreement with previously published data (4, 7). MBC ranges were 0.03 to >8 μg/ml in CAMHB and 8 to >128 μg/ml in the presence of 50% human plasma (Table ​(Table11).

TABLE 1.

Antibacterial activities of iclaprim and comparators against 20 isolates of S. aureus^a

In Vitro Antibody-Enzyme Conjugates with Specific Bactericidal Activity

IgG with antibacterial antibody opsonic activity was isolated from rabbit antisera produced by intravenous hyperimmunization with several test strains of pneumococci, Group A beta-hemolytic streptococci, Staphylococcus aureus, Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli. Antibody-enzyme conjugates were prepared, using diethylmalonimidate to couple glucose oxidase to IgG antibacterial antibody preparations. Opsonic human IgG obtained from serum of patients with subacute bacterial endocarditis was also conjugated to glucose oxidase. Antibody-enzyme conjugates retained combining specificity for test bacteria as demonstrated by indirect immunofluorescence. In vitro test for bactericidal activity of antibody-enzyme conjugates utilized potassium iodide, lactoperoxidase, and glucose as cofactors. Under these conditions glucose oxidase conjugated to antibody generates hydrogen peroxide, and lactoperoxidase enzyme catalyzes the reduction of hydrogen peroxide with simultaneous oxidation of I(-) and halogenation and killing of test bacteria. Potent in vitro bactericidal activity of this system was repeatedly demonstrated for antibody-enzyme conjugates against pneumococci, streptococci, S. aureus, P. mirabilis, and E. coli. However, no bactericidal effect was demonstrable with antibody-enzyme conjugates and two test strains of P. aeruginosa. Bactericidal activity of antibody-enzyme conjugates appeared to parallel original opsonic potency of unconjugated IgG preparations. Antibody-enzyme conjugates at concentrations as low as 0.01 mg/ml were capable of intense bactericidal activity producing substantial drops in surviving bacterial counts within 30-60 min after initiation of assay. These in vitro bactericidal systems indicate that the concept of antibacterial antibody-enzyme conjugates may possibly be adaptable as a mechanism for treatment of patients with leukocyte dysfunction or fulminant bacteremia.     

Comparative In Vitro Activity of Newer Cephalosporins Against Anaerobic Bacteria

The in vitro susceptibilities of 408 recent clinical isolates of anaerobic bacteria against cefaclor, cephalexin, cephalothin, cefazolin, cefamandole, and cefoxitin were compared by an agar dilution technique. Against gram-positive bacteria, especially peptococci, peptostreptococci, and propionibacteria, cephalexin and cefaclor were significantly less active than cephalothin (P < 0.05). Cephalexin was also less active than cephalothin against clostridia and lactobacillus (P < 0.05). Against gram-negative bacteria, major differences were observed primarily with Bacteroides fragilis, against which cephalexin, cefazolin and cefoxitin were all significantly more active than cephalothin (P < 0.001). At concentrations of 16 μg per ml, however, all cephalosporins showed high in vitro activity, except against Lactobacillus species and B. fragilis. Cephalothin, cefazolin and cefamandole were considerably more active against the former, whereas cefoxitin was distinctly more active against the latter.     

Susceptibility Breakpoints for Amphotericin B and Aspergillus Species in an In Vitro Pharmacokinetic-Pharmacodynamic Model Simulating Free-Drug Concentrations in Human Serum

Although conventional amphotericin B was for many years the drug of choice and remains an important agent against invasive aspergillosis, reliable susceptibility breakpoints are lacking. Three clinical Aspergillus isolates (Aspergillus fumigatus, Aspergillus flavus, and Aspergillus terreus) were tested in an in vitro pharmacokinetic-pharmacodynamic model simulating the biphasic 24-h time-concentration profile of free amphotericin B concentrations in human serum with free peak concentrations (fC_max) of 0.1, 0.3, 0.6, 1.2, and 2.4 mg/liter administered once daily. Drug concentrations were measured with a bioassay, and fungal growth was monitored for 72 h with galactomannan production. The fC_max/MIC corresponding to half-maximal activity (P₅₀) was determined for each species, and the percentage of target attainment was calculated for different MICs for the standard (1 mg/kg of body weight) and a lower (0.6-mg/kg) dose of amphotericin B with Monte Carlo simulation analysis. The fC_max/MICs (95% confidence intervals) corresponding to P₅₀ were 0.145 (0.133 to 0.158), 0.371 (0.283 to 0.486), and 0.41 (0.292 to 0.522) for A. fumigatus, A. flavus, and A. terreus, respectively. The median percentages of P₅₀ attainment were ≥88%, 47%, and 0% for A. fumigatus isolates with MICs of ≤0.5, 1, and ≥2 mg/liter, respectively, and ≥81%, 24%, and 0% and ≥75%, 15%, and 0% for A. flavus and A. terreus isolates with MICs of ≤0.25, 0.5, and ≥1 mg/liter, respectively. The lower dose of 0.6 mg/kg would retain efficacy for A. fumigatus, A. flavus, and A. terreus isolates with MICs of ≤0.25, ≤0.125, and ≤0.125 mg/liter, respectively. The susceptibility, intermediate susceptibility, and resistance breakpoints of ≤0.5, 1, and ≥2 mg/liter for A. fumigatus and ≤0.25, 0.5, and ≥1 mg/liter for A. flavus and A. terreus were determined for conventional amphotericin B with a pharmacokinetic-pharmacodynamic model simulating free-drug serum concentrations.     

Comparative In Vitro and Bactericidal Activity of Oxazolidinone Antibiotics Against Multidrug-Resistant Enterococci

Increasing resistance among enterococci poses a considerable therapeutic problem. In this study, we evaluated the comparative in vitro activity of two investigational oxazolidinone antibiotics, eperezolid and linezolid, versus clinical isolates of multidrug-resistant enterococci. One hundred isolates (16 Enterococcus faecalis, 69 E. faecium, 10 E. gallinarum, 2 E. casseliflavus, 1 E. avium, 1 E. hirae, and 1 E. raffinosus) evaluated were collected from diverse geographic areas in North America and Europe from 1991 to 1995. Eperezolid MIC₅₀ and MIC₉₀ were 1.0 μg/mL and 2.0 μg/mL (1.0–2.0 μg/mL range). Linezolid MIC₅₀ and MIC₉₀ were 2.0 μg/mL and 2.0 μg/mL (0.5–2.0 μg/mL range), respectively. MICs were the same at 10³ CFU/mL and 10⁸ CFU/mL initial inoculum. In time-kill experiments using 10 strains and concentrations of 4 μg/mL, 8 μg/mL, and 16 μg/mL (achievable serum concentrations) of eperezolid and linezolid, there was a 2 log₁₀ reduction of growth for 2 of 10 isolates tested using eperezolid and a 1 log₁₀ reduction for 50% of isolates with both agents. There was indifferent bactericidal killing when either oxazolidinone was combined with gentamicin, ampicillin, or streptomycin for isolates lacking these resistances. This study demonstrates these oxazolidinone agents to have excellent in vitro activity versus multidrug-resistant enterococci.     

Ceftaroline plus Avibactam Demonstrates Bactericidal Activity against Pathogenic Anaerobic Bacteria in a One-Compartment In Vitro Pharmacokinetic/Pharmacodynamic Model

Anaerobic pathogens are often associated with polymicrobial infections, such as diabetic foot infections. Patients with these infections are often treated with broad-spectrum, multidrug therapies targeting resistant Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus, as well as Gram-negative bacteria and anaerobes. The broad-spectrum, non-beta-lactam, beta-lactamase inhibitor avibactam has been combined with ceftaroline and may provide a single-product alternative for complicated polymicrobial infections. We compared the activity of ceftaroline-avibactam (CPA) to that of ertapenem (ERT) against common anaerobic pathogens in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Simulations of doses of ceftaroline-fosamil at 600 mg every 8 h (q8h) (maximum free drug concentration [fC_max], 17.04 mg/liter, and half-life [t_1/2], 2.66 h) plus avibactam at 600 mg q8h (fC_max, 11.72 mg/liter, and t_1/2, 1.8 h) and of ertapenem at 1 g q24h (fC_max, 13 mg/liter, and t_1/2, 4 h) were evaluated against two strains of Bacteroides fragilis, one strain of Prevotella bivia, and one strain of Finegoldia magna in an anaerobic one-compartment in vitro PK/PD model over 72 h with a starting inoculum of ∼8 log₁₀ CFU/ml. Bactericidal activity was defined as a reduction of ≥3 log₁₀ CFU/ml from the starting inoculum. Both CPA and ERT were bactericidal against all four strains. CPA demonstrated improved activity against Bacteroides strains compared to that of ERT but had similar activity against Finegoldia magna and P. bivia, although modest regrowth was observed with CPA against P. bivia. No resistance emerged from any of the models. The pharmacokinetics achieved were 92 to 105% of the targets. CPA has potent in vitro activity against common anaerobic pathogens at clinically relevant drug exposures and may be a suitable single product for the management of complicated polymicrobial infections.     

In Vitro Activity and Beta-Lactamase Stability of BL-S786 Compared with Those of Other Cephalosporins

In vitro activity of BL-S786, a new parenterally semisynthetic cephalosporin, was investigated against 570 bacterial isolates. BL-S786 inhibited most Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Salmonella. It inhibited some Enterobacter and indole-positive Proteus, but it was less active against these later species than was cefamandole, cefuroxime, or cefoxitin. It was not active against Serratia marcescens, Pseudomonas aeruginosa, or Bacteroides fragilis. BL-S786 was the least active new cephalosporin tested against staphylococci and was less active than cephalothin against streptococcal species. The activity of BL-S786 was not altered by the type of assay medium nor by 50% serum. The size of the test inoculum altered the minimal inhibitory and bactericidal concentrations for inhibition of some organisms, particularly those with Richmond type I β-lactamases. BL-S786 was not hydrolyzed by the R-factor-mediated, Richmond type III β-lactamase, but it was hydrolyzed by type I β-lactamases.     

Use of a Heavy Inoculum in the In Vitro Evaluation of the Anti-Staphylococcal Activity of 19 Cephalosporins

The in vitro activity of 19 cephalosporins against 105 clinical isolates of Staphylococcus aureus and S. epidermidis was determined by using a heavy inoculum, i.e., 10(8) to 10(9) organisms per ml, to maximally challenge the antibiotics. The anti-staphylococcal activities of cephaloridine and 87/312 were consistently decreased by the use of a heavy inoculum when compared with the activity obtained with two less-concentrated inocula. The activity of most of the other compounds was also decreased with the use of a heavy inoculum, but this was observed only with selected isolates. Cephapirin, cephalothin, and cefazaflur were the most active drugs against the methicillin-susceptible isolates. Cephaloridine, cefamandole, cefazaflur, and 87/312 had substantial activity against methicillin-resistant staphylococci even with heavy inocula. With the exception of cefaclor against S. aureus, the orally absorbed cephalosporins were generally one-half to one-sixteenth as active as the parenterally administered cephalosporins. The median minimal inhibitory concentrations of five of the 12 parenteral cephalosporins were lower with the methicillin-susceptible S. aureus than with the methicillin-susceptible S. epidermidis strains.     

In Vitro Activity and β-Lactamase Stability of Cefazaflur Compared with Those of β-Lactamase-Stable Cephalosporins

The in vitro activity of cefazaflur, a parenteral cephalosporin, was determined against 590 clinical isolates. Cefazaflur inhibited the majority of gram-positive cocci at concentrations below 1 mug/ml except for enterococci. The agent was as active as cefamandole or cefoxitin against most Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Although it inhibited a number of strains of Enterobacter, indole-positive Proteus, and Serratia resistant to cephalothin, it was much less active against these organisms than were cefamandole or cefoxitin.     

Ambush of Clostridium difficile Spores by Ramoplanin: Activity in an In Vitro Model

Clostridium difficile infection (CDI) is a gastrointestinal disease caused by C. difficile, a spore-forming bacterium that in its spore form is tolerant to standard antimicrobials. Ramoplanin is a glycolipodepsipeptide antibiotic that is active against C. difficile with MICs ranging from 0.25 to 0.50 μg/ml. The activity of ramoplanin against the spores of C. difficile has not been well characterized; such activity, however, may hold promise, since posttreatment residual intraluminal spores are likely elements of disease relapse, which can impact more than 20% of patients who are successfully treated. C. difficile spores were found to be stable in deionized water for 6 days. In vitro spore counts were consistently below the level of detection for 28 days after even brief (30-min) exposure to ramoplanin at concentrations found in feces (300 μg/ml). In contrast, suppression of spore counts was not observed for metronidazole or vancomycin at human fecal concentrations during treatment (10 μg/ml and 500 μg/ml, respectively). Removal of the C. difficile exosporium resulted in an increase in spore counts after exposure to 300 μg/ml of ramoplanin. Therefore, we propose that rather than being directly sporicidal, ramoplanin adheres to the exosporium for a prolonged period, during which time it is available to attack germinating cells. This action, in conjunction with its already established bactericidal activity against vegetative C. difficile forms, supports further evaluation of ramoplanin for the prevention of relapse after C. difficile infection in patients.     

In Vitro Bactericidal Effectiveness of Four Aminoglycoside Antibiotics

The antibacterial activity of four aminoglycoside antibiotics (gentamicin, Sch 13706, tobramycin, and sisomicin) was tested against eight gram-negative and three gram-positive species. A total of 323 strains were studied by the broth dilution technique. Tobramycin and sisomicin had greater bacteriostatic and bactericidal activity against Pseudomonas strains than did gentamicin and Sch 13706. Of the four antibiotics, sisomicin was most active against Klebsiella, Enterobacter, Escherichia coli, indole-negative and -positive Proteus, and Streptococcus pyogenes. Gentamicin was most effective against Serratia. A fourfold or greater difference existed frequently between the minimal inhibitory and bactericidal concentrations of all antibiotics against Enterobacter and Serratia. This difference was greatest with tobramycin. Staphylococcus aureus was highly susceptible, Providencia relatively resistant, and enterococcus uniformly resistant to the antibiotics studied. Agar diffusion susceptibility testing with gentamicin and tobramycin showed that organisms susceptible to less than 6.2 mug/ml usually yielded zones 17 to 26 mm in diameters. Zones of 15 to 16 mm represented intermediate susceptibility which varied with the organism and antibiotic. Several Serratia strains required 6.2 to 12.5 mug of gentamicin/ml or 25 to 50 mug of tobramycin/ml for bactericidal activity despite minimal inhibitory concentrations of 0.09 to 3.1 mug/ml and zone sizes greater than 13 and 17 mm, respectively. Studies with Enterobacter and tobramycin yielded similar results.     

Correlation of In Vitro Activity,Serum Levels,and In Vivo Efficacy of Posaconazole against Rhizopus microsporus in a Murine Disseminated Infection

A broth microdilution method was used to evaluate the in vitro activities of seven antifungal agents against 15 clinical strains of Rhizopus microsporus. Amphotericin B (AMB) and posaconazole (POS) were the most active drugs. In a model of disseminated R. microsporus infection in immunosuppressed mice, we studied the efficacy of POS administered once or twice daily against four of the strains previously tested in vitro and compared it with that of liposomal AMB (LAMB). LAMB was the most effective treatment for the two strains with intermediate susceptibility to POS. For the two POS-susceptible strains, LAMB and POS at 20 mg/kg of body weight twice a day orally showed similar efficacies. The in vivo efficacy of POS administered twice a day orally correlated with the in vitro susceptibility data and the serum drug concentrations.Zygomycosis is a frequently lethal invasive infection that occurs predominantly in immunocompromised patients (4), a population with a very poor prognosis and a high mortality rate (8). The clinical manifestations include rhino-orbito-cerebral, cutaneous, pulmonary, gastrointestinal, and disseminated infections (4). In a recent study in which a large number of clinical isolates of zygomycetes from different regions of the United States were molecularly identified, it was demonstrated that Rhizopus oryzae and Rhizopus microsporus were the most common species (3). Traditionally, amphotericin B (AMB) and, more recently, its lipid formulations are the front-line agents for the treatment of zygomycosis (4). Specifically, liposomal amphotericin B (LAMB) is less nephrotoxic than AMB and has better central nervous system penetration than AMB and the other lipid formulations (21). Posaconazole (POS) is a broad-spectrum triazole antifungal with a large volume of distribution into tissues (12). This drug has shown good in vitro activity against zygomycetes (1, 2) and has been used successfully as salvage therapy in some case reports and clinical trials of disseminated zygomycosis (8, 22, 23). However, its effectiveness remains controversial, since in experimental studies it has shown poor activity against R. oryzae, the main species causing zygomycosis (6, 9, 17). Several in vitro studies have shown that POS also exhibits significant activity against R. microsporus, another relevant clinical species (1, 2, 11), and a few clinical (14) and experimental (6) studies seem to demonstrate in vivo efficacy as well.In this study, after confirming the significant in vitro activity of POS and AMB, we evaluated the efficacy of POS against four strains of R. microsporus in a murine model of disseminated infection. Considering that antifungal susceptibility can differ substantially among different strains of a given species, which could explain the variable percentages of success demonstrated by POS and AMB in clinical trials (8, 18, 23), we tested multiple strains exhibiting various in vitro responses to obtain more-robust results.     

In Vitro Activity of BL-S640 Against Gram-Negative Bacilli and Staphylococcus aureus Compared with Activity of Four Other Semisynthetic Cephalosporins

The in vitro activity of BL-S640 (cefatrizine) was determined against 674 recent clinical isolates of Staphylococcus aureus and Enterobacteriaceae. Activity against S. aureus was less than that of cephapirin, cephalothin, and cefazolin, but greater than that of cephalexin. Activity against gram-negative isolates was variable: BL-S640 was slightly less potent than cefazolin against Escherichia coli and Klebsiella, but more active than the other compounds. As for the more resistant gram-negative genera, BL-S640 was significantly superior to the control cephalosporins. The effect of inoculum size on the antibacterial activity was moderate for most organisms except Enterobacter, Providencia stuartii, and indole-positive Proteus, the median minimal inhibitory concentrations of which were 6 to 27 times lower when determined with a 10(-4)-diluted culture compared with the undiluted one. The stability in aqueous solution at 37 C was remarkably high at the lower pH values, but low at the neutral point.     

Comparison of In Vitro Antibacterial Activity of Three Oral Cephalosporins: Cefaclor, Cephalexin, and Cephradine

Cefaclor, a new oral cephalosporin, was compared in vitro with cephalexin and cephradine against 233 organisms. Evaluations were performed in Mueller-Hinton and nutrient broth and agar using two inoculum sizes. In agar, cefaclor had greater antibacterial activity than either cephalexin or cephradine against isolates of Escherichia coli, Proteus mirabilis, Staphylococcus aureus, Klebsiella pneumoniae, and Salmonella typhi. All three drugs were relatively inactive against isolates of enterococci, Enterobacter species, and indole-positive Proteus. Cefaclor, however, did exhibit the greatest activity of the three antibiotics against these organisms. Although there was wide variability with respect to test parameters, the broth results generally paralleled the agar results. In nutrient broth a clear separation of the results with these three cephalosporins was seen with K. pneumoniae, E. coli, and S. typhi. Cefaclor was the most active, cephalexin had intermediate activity, and cephradine was the least active. From the data obtained in this in vitro study, it can be concluded that cefaclor, which has a substituted chloro group attached to the molecule, had increased antibacterial activity over cephalexin and cephradine. Comparative clinical trials with cefaclor will determine whether the differences outlined above are of clinical significance.     

In Vitro Bactericidal Capacity of Human Polymorphonuclear Leukocytes: Diminished Activity in Chronic Granulomatous Disease of Childhood

Diminished bactericidal capacity was found to be characteristic of polymorphonuclear leukocytes (PMN) from five children with the clinical syndrome of granulomatous disease of childhood. The PMN from these children demonstrated nearly normal phagocytic capacity, and the majority of viable bacteria, after 2 hours of incubation in the phagocytosis system, were found associated with leukocytes.The morphology of the unstimulated polymorphonuclear leukocytes from patients with chronic granulomatous disease was similar to those from normal persons of similar ages by light and electron microscopy. In addition, the total lysozyme and phagocytin activity of leukocyte extracts from these patients was similar to those from equal numbers of leukocytes from controls.A striking difference in the cytoplasmic response after phagocytosis characterized the PMN of the patients with granulomatous disease. Whereas degranulation, vacuole formation, and rapid bacterial digestion were the rule in the PMN from controls, little degranulation and persistence of intact bacteria in the cytoplasm characterized disease.The deficiency of bactericidal capacity and the minimal degranulation after active phagocytosis by the PMN of these children with an inherited syndrome suggest that separate metabolic processes are involved in phagocytosis and in intracellular digestion. Continuing study of the metabolic function of leukocytes from these children should provide an opportunity for increased understanding of the metabolic basis for degranulation and intracellular digestion in phagocytic cells.     

Antibiotic Activity against Naive and Induced Streptococcus pneumoniae Biofilms in an In Vitro Pharmacodynamic Model

Biofilms play a role in the pathogenicity of pneumococcal infections. A pharmacodynamic in vitro model of biofilm was developed that allows characterization of the activity of antibiotics against viability and biomass by using in parallel capsulated (ATCC 49619) and noncapsulated (R6) reference strains. Naive biofilms were obtained by incubating fresh planktonic cultures for 2 to 11 days in 96-well polystyrene plates. Induced biofilms were obtained using planktonic bacteria collected from the supernatant of 6-day-old naive biofilms. Biomass production was more rapid and intense in the induced model, but the levels were similar for both strains. Full concentration responses fitting sigmoidal regressions allowed calculation of maximal efficacies and relative potencies of drugs. All antibiotics tested (amoxicillin, clarithromycin, solithromycin, levofloxacin, and moxifloxacin) were more effective against young naive biofilms than against old or induced biofilms, except macrolides/ketolides, which were as effective at reducing viability in 2-day-old naive biofilms and in 11-day-old induced biofilms of R6. Macrolides/ketolides, however, were less potent than fluoroquinolones against R6 (approximately 5- to 20-fold-higher concentrations needed to reduction viability of 20%). However, at concentrations obtainable in epithelial lining fluid, the viabilities of mature or induced biofilms were reduced 15 to 45% (amoxicillin), 17 to 44% (macrolides/ketolides), and 12 to 64% (fluoroquinolones), and biomasses were reduced 5 to 45% (amoxicillin), 5 to 60% (macrolides/ketolides), and 10 to 76% (fluoroquinolones), with solithromycin and moxifloxacin being the most effective and the most potent agents (due to lower MICs) in their respective classes. This study allowed the ranking of antibiotics with respect to their potential effectiveness in biofilm-related infections, underlining the need to search for still more effective options.     

In Vitro Activities of Five Oral Cephalosporins Against Aerobic Pathogenic Bacteria

Cefaclor (Lilly 99638) and cefatrizine (BL-S640, SK&F 70771) are orally absorbed, broad-spectrum semisynthetic cephalosporins. They were compared in vitro with cephalexin, cephaloglycin, and cepharadine against a variety of aerobic pathogenic bacteria by an agar dilution procedure. Cefaclor and cefatrizine were found to be similar or superior to cephalexin, cephaloglycin, and cephradine in terms of activity against gram-positive cocci other than enterococci. Only cefatrizine demonstrated any potentially useful activity against some susceptible isolates of enterococci. Cefaclor and cefatrizine also were highly active, equally or more so than the other oral cephalosporins, against several gram-negative species including Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae. None of the cephalosporins were particularly active against Enterobacter cloacae. Both cefaclor and cefatrizine were active against Proteus mirabilis; cefatrizine was uniquely active against indolepositive Proteus species.