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.     

Oxidation of Methionine by Human Polymorphonuclear Leukocytes

Studies of the photosensitized oxidation have demonstrated that photodynamic oxidation of methionine is mediated by singlet oxygen (¹O₂). In this study, we demonstrated that phagocytosing human polymorphonuclear leukocytes (PMN), but not resting PMN, oxidized both intracellular and extracellular methionine to methionine sulfoxide. N-ethylmaleimide, which inhibits phagocytosis and cellular metabolism, inhibited the oxidation of methionine. Neutrophils from patients with chronic granulomatous disease did not oxidize methionine even in the presence of phagocytosis. The oxidation of methionine by phagocytosing normal PMN was inhibited by ¹O₂ quenchers, (1.4-diazabicyclo-[2,2,2]-octane, tryptophan, NaN₃), myeloperoxidase (MPO) inhibitors (NaN₃, KCN) and catalase. In contrast, superoxide dismutase, ethanol, and mannitol had no effect. Furthermore, ¹O₂ quenchers did not interfere with the production of superoxide (O₂⁻) by phagocytosing PMN. The combination of catalase and SOD did not enhance the inhibition of methionine by phagocytosing PMN. On the other hand, deuterium oxide stimulated the oxidation of methionine by PMN almost 200%.     

Quantitative Iodination of Human Blood Polymorphonuclear Leukocytes

Abstract. It was shown by Pincus and Klebanoff that a correlation existed between leukocytic iodination measured in vivo and microbicidal leukocytic activity. We have analysed the results of this test in relation to time and in the presence of variable quantities of polymorphonuclear leukocytes (PMN). The values observed per time and PMN unit proved to be equivalent in the presence of 2. 5 × 10⁵ PMN or 5. 0 × 10⁵ PMN per 0.5 ml of incubation medium, measured after 10, 20 and 30 minutes or in the presence of 1. 0 × 10⁶ PMN, measured after 10 minutes. That is to say iodination is proportional to leukocyte concentration and incubation time. Increase of either the quantity of cells or the incubation time, beyond the area we defined, reduce iodination per cell and per unit of time. Concerning the patients with an insufficient iodination, we have studied 2 parameters in the presence of 5. 0 × 10⁵ PMN:1) initial iodination measured after 10 and 20 minutes and 2) stability of iodination measured after 60 minutes. These two parameters were equally affected in two cases with myelofibrosis, 3 patients with acquired refractory anaemia, one with chronic lymphoid leukaemia, one with erythroleukaemia, one with hairy cell leukaemia, one with systemic mastocytosis and almost complete myeloperoxidase deficiency, one with sickle cell disease, two with liver diseases and two with chronic myeloid leukaemia. The iodination at the 60th minute was more affected than at the 10th minute with a patient with myelofibrosis and 4 other patients with acquired refractory anaemias. The significance of these differences is not well understood; however the meaning of the decrease in the iodination of whatever type is that a PMN anomaly exists directly related to the myeloperoxidase H₂O₂ halogenation system, or to one of the stages of engulfment and/or metabolic events preceeding it and leading to the production of H₂O₂. This test, with the alterations we introduced, is suggested as a test for detection of functional PMN abnormalities.     

Inactivation of Glycogen Phosphorylase of Human Polymorphonuclear Leukocytes

Glycogen phosphorylase of human polymorphonuclear leukocytes is dephosphorylated during incubation of a gel-filtered cell extract. The dephosphorylated enzyme (b form) retains 25 per cent of the activity of the phosphoenzyme (a form) when measured without AMP but at high glucose-1-phosphate concentrations. The ratio of activity -AMP/+AMP for the a enzyme is 0.8–1.0 and for the b enzyme 0.2. Leukocyte phosphorylase is not activated by -SH groups, but the b enzyme is stimulated by 0.4 mol/1 Na₂ sO₄. The phosphatase which catalyzes the conversion of phosphorylase a to b is inhibited by glucose-1-phosphate and AMP both at 14°C and 25°C. Glucose counteracts the AMP inhibition but not the glucose-1-phos-phate inhibition at both temperatures. Glucose alone had no effect at 25°C, but it accelerated the phosphatase reaction at 14°C. Glucoses-phosphate or glycogen alone or in the presence of AMP or glucose-1-phos-phate did not affect the phosphatase reaction. From previous and present experiments it is concluded that the phosphorylase of human polymorphonuclear leukocytes is closely related to liver phosphorylase and that the inactivation of the enzyme is mainly controlled by AMP and glucose.     

Increased Production and Expression of Tissue Thromboplastin-Like Procoagulant Activity In Vitro by Allogeneically Stimulated Human Leukocytes

Intravascular coagulation, thrombosis, and fibrin deposition often produce tissue damage in allogeneic inflammatory reactions such as allograft rejection. The mechanisms which initiate blood clotting in these reactions are poorly understood. We find that allogeneic stimulation of human leukocytes in vitro increases production and expression of tissue thromboplastin-like activity. In our experiments mixed leukocyte cultures (MLC) of cells from allogeneic (unrelated) donors produced and expressed more procoagulant activity than control cultures of cells from each donor alone. After 7 days, allogeneic MLC had 5- to 50-fold more total procoagulant activity than controls, as shown by assaying lysed whole cultures. Additionally, allogeneic MLC had 8- to 240-fold more procoagulant activity expressed on leukocyte surfaces and in culture supernates than controls after 7 days, as shown by assaying intact whole cultures and cell-free supernates. These increases were largely accounted for by gains in the amounts of procoagulant activity produced and expressed per cell in MLC as compared to controls. Controls and MLC produced and expressed considerable amounts of procoagulant activity during the 1st day of culture, and there were no differential effects of allogeneic stimulation on day 1. However, after day 1, the total amount of procoagulant activity produced and the amount expressed declined steadily in controls, nearly reaching preculture levels by day 7. In contrast, the total amount of procoagulant activity in allogeneic MLC remained high, and the amount of activity expressed on cell surfaces and in supernates increased severalfold by day 7. MLC of syngeneic (identical twin) cells produced and expressed the same amount of activity as controls over a 7-day period, whereas MLC of cells from each twin and an allogeneic donor produced and expressed more activity than controls (at least 9- and 35-fold more, respectively). Thus, increases of procoagulant activity production and expression were found only in MLC of genetically dissimilar cells. Therefore, these increases must have resulted from allogeneic stimulation.     

Bactericidal Activity of Cephalosporins in an In Vitro Model Simulating Serum Levels

The bactericidal activity of cefazolin, cephaloridine, and cephalothin in a simulated intramuscular study (500 mg) and a simulated intravenous drip infusion study (2 g/2 h) is reported. In both model systems, the bactericidal activity of cefazolin surpassed that of cephalothin, and there were certain differences between cefazolin and cephaloridine in the simulated intramuscular study when human serum was used as a medium. In a routine reference static system, the drug levels were constant at the simulated peak level of each cephalosporin by both routes. In this system the three cephalosporins were equal in activity. In a third experiment, the effect of drug concentrations and exposure time on bactericidal activity of the cephalosporins was studied. The bactericidal activity of cephaloridine was the strongest of the three drugs when exposure time was 2 h and drug concentration was less than four times the minimal inhibitory concentration. At concentrations above four times the minimum inhibitory concentration, all three cephalosporins were equal in activity when the exposure time was 2 h.     

The Anticoagulant Activity of Lysosomal Cationic Proteins from Polymorphonuclear Leukocytes

A cationic protein fraction from rabbit polymorphonuclear leukocyte lysosomes has been shown to exert a potent anticoagulant effect on human blood in vitro. The anticoagulant activity is detectable in the whole blood clotting time, the recalcification time of platelet-rich plasma, the prothrombin time, the partial thromboplastin time, and the thromboplastin generation test. The lysosomal cationic proteins do not inhibit any of the known specific procoagulants. They appear to inhibit clotting by blocking the formation of intrinsic thromboplastin possibly by interfering with the role of phospholipids in the reaction involving Factors V and X and calcium.     

Chronic Granulomatous Disease: The European Experience

CGD is an immunodeficiency caused by deletions or mutations in genes that encode subunits of the leukocyte NADPH oxidase complex. Normally, assembly of the NADPH oxidase complex in phagosomes of certain phagocytic cells leads to a “respiratory burst”, essential for the clearance of phagocytosed micro-organisms. CGD patients lack this mechanism, which leads to life-threatening infections and granuloma formation. However, a clear picture of the clinical course of CGD is hampered by its low prevalence (~1250,000). Therefore, extensive clinical data from 429 European patients were collected and analyzed. Of these patients 351 were males and 78 were females. X-linked (XL) CGD (gp91^phox deficient) accounted for 67% of the cases, autosomal recessive (AR) inheritance for 33%. AR-CGD was diagnosed later in life, and the mean survival time was significantly better in AR patients (49.6 years) than in XL CGD (37.8 years), suggesting a milder disease course in AR patients. The disease manifested itself most frequently in the lungs (66% of patients), skin (53%), lymph nodes (50%), gastrointestinal tract (48%) and liver (32%). The most frequently cultured micro-organisms per episode were Staphylococcus aureus (30%), Aspergillus spp. (26%), and Salmonella spp. (16%). Surprisingly, Pseudomonas spp. (2%) and Burkholderia cepacia (<1%) were found only sporadically. Lesions induced by inoculation with BCG occurred in 8% of the patients. Only 71% of the patients received antibiotic maintenance therapy, and 53% antifungal prophylaxis. 33% were treated with γ-interferon. 24 patients (6%) had received a stem cell transplantation. The most prominent reason of death was pneumonia and pulmonary abscess (18/84 cases), septicemia (16/84) and brain abscess (4/84). These data provide further insight in the clinical course of CGD in Europe and hopefully can help to increase awareness and optimize the treatment of these patients.     

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.     

Chemiluminescence of Human and Canine Polymorphonuclear Leukocytes in the Absence of Phagocytosis

Polymorphonuclear leukocytes (PMNs) have increased oxidative metabolism during phagocytosis and emit light (chemiluminescence, CL) as a result of metabolic activation. The present study examined PMN CL in the absence of phagocytosis using sodium fluoride (NaF), a nonparticulate agent and known stimulator of cellular oxidative metabolism. Normal human and canine PMNs were assayed in a CL spectrometer which permitted continuous sample mixing and constant temperature regulation during CL measurement. PMNs treated with 20 mM NaF demonstrated maximum CL responses of 10,000-20,000 cpm above background, 13-17 min after addition of NaF at 37 degrees C. Temperature regulation of reaction mixtures was found to be a critical factor in assaying PMN CL responses to NaF, because a small decrease in temperature (i.e. 1.5 degrees C) substantially depressed and delayed the CL response. Superoxide anion production correlated closely with CL responses in NaF-treated human PMNs. CL responses were completely suppressed in the presence of the oxidative metabolic inhibitors, iodoacetamide, and N-ethylmalemide; and were partially suppressed in the presence of either superoxide dismutase or sodium azide.CL responses of NaF-treated PMNs were significantly lower than responses generated by PMNs phagocytizing opsonized yeast. When NaF was evaluated for its effect on light generation from a singlet oxygen dependent CL reaction, it was found that NaF did not quench singlet oxygen light. This study demonstrates that PMN CL can occur in the absence of phagocytosis, and it proposes that a nonphagocytic PMN CL assay may be useful in evaluating leukocyte metabolic defects.     

Effect of Aminoglycosides on the Chemotactic Response of Human Polymorphonuclear Leukocytes

Leukocyte chemotaxis was inhibited 9.6% compared with control in the presence of 10 μg of gentamicin per ml and 10.5% when exposed to 20 μg of amikacin per ml. However, cells incubated with an injectable form of gentamicin, containing preservatives, were inhibited an additional 25.8% relative to cells incubated with pure gentamicin.     

A Review of Chronic Granulomatous Disease

Chronic granulomatous disease (CGD) is a primary immunodeficiency caused by defects in any of the five subunits of the NADPH oxidase complex responsible for the respiratory burst in phagocytic leukocytes. Patients with CGD are at increased risk of life-threatening infections with catalase-positive bacteria and fungi and inflammatory complications such as CGD colitis. The implementation of routine antimicrobial prophylaxis and the advent of azole antifungals has considerably improved overall survival. Nevertheless, life expectancy remains decreased compared to the general population. Inflammatory complications are a significant contributor to morbidity in CGD, and they are often refractory to standard therapies. At present, hematopoietic stem cell transplantation (HCT) is the only curative treatment, and transplantation outcomes have improved over the last few decades with overall survival rates now > 90% in children less than 14 years of age. However, there remains debate as to the optimal conditioning regimen, and there is question as to how to manage adolescent and adult patients. The current evidence suggests that myeloablative conditioning results is more durable myeloid engraftment but with increased toxicity and high rates of graft-versus-host disease. In recent years, gene therapy has been proposed as an alternative to HCT for patients without an HLA-matched donor. However, results to date have not been encouraging. with negligible long-term engraftment of gene-corrected hematopoietic stem cells and reports of myelodysplastic syndrome due to insertional mutagenesis. Multicenter trials are currently underway in the United States and Europe using a SIN-lentiviral vector under the control of a myeloid-specific promoter, and, should the trials be successful, gene therapy may be a viable option for patients with CGD in the future.     

Cephanone: In Vitro Antibacterial Activity and Pharmacology in Normal Human Volunteers

Cephanone, a new 3-heterocyclic-thiomethyl cephalosporin antibiotic, was found to have an antibacterial spectrum similar to that of cephalothin. The compound was active in vitro against a variety of gram-positive and gram-negative bacteria. All strains of Staphylococcus aureus tested were inhibited by concentrations of 6.2 mug or less of cephanone per ml. Beta-hemolytic group A streptococci and pneumococci were exquisitely sensitive. Among strains of Escherichia coli and Klebsiella sp., 83 and 82%, respectively, were inhibited by 3.1 mug or less of cephanone per ml. Excellent serum concentrations of the antibiotic were obtained after parenteral administration. Peak concentrations of 38 and 81.2 mug/ml were achieved in the serum after intramuscular and intravenous doses of 1 g of cephanone, respectively. The serum concentrations of cephanone fell gradually during the 12 hr after administration. Very high concentrations of cephanone were found in the urine.     

X-linked Inheritance in Females with Chronic Granulomatous Disease

Chronic granulomatous disease in males is familial and its transmission is is usually clearly x-linked. The mode of inheritance in females with the syndrome is unknown and the carrier state difficult to identify. Defective polymorphonuclear leukocyte bactericidal activity in this disease is associated with an absence of the respiratory burst generated in stimulated phagocytes and may be detected by the chemiluminescence assay. Polymorphonuclear leukocytes from three of four females with chronic granulomatous disease had extremely low chemiluminescence production, their asymptomatic mothers had intermediate values, and their fathers were normal. Polymorphonuclear neutrophils of two affected males in these kinships generated no chemiluminescence, whereas two of seven female relatives had intermediate values, and all nonaffected males had normal values. In the three families in which leukocytes were studied by nitroblue tetrazolium reduction, two populations of neutrophils were demonstrated for the female patients and/or their mothers. The wide phenotypic variability for clinical disease, evidence of two leukocyte populations in the patients or their mothers, and low but detectable leukocyte chemiluminescence in the affected females is consistent with the Lyon hypothesis of x-chromosome inactivation in these families. The findings suggest an x-linked inheritance in these females with chronic granulomatous disease.     

Phagocytic Function of Polymorphonuclear Leukocytes in Rheumatic Diseases

Phagocytosis of yeast particles by peripheral blood and synovial fluid neutrophils was compared in the sera and synovial fluids from 16 osteoarthritis, 23 rheumatoid arthritis, and 12 miscellaneous arthritis patients. Phagocytosis by normal peripheral blood neutrophils was decreased equally and significantly in all synovial fluids. All synovial fluid neutrophils demonstrated decreased phagocytic capacity in all media. Rheumatoid arthritis synovial fluid neutrophils showed significantly less phagocytosis than miscellaneous arthritis synovial fluid neutrophils. Normal peripheral blood neutrophils which in vitro had previously ingested monosodium urate crystals or oil red O, subsequently exhibited a normal yeast phagocytic capacity. Normal peripheral blood neutrophils, which had ingested preformed immunoglobulin G-rheumatoid factor complexes exhibited significantly less yeast phagocytic capacity than control cells or cells preincubated with the individual complex components. There was a significant correlation between the log of the reciprocal of the rheumatoid factor titer in sera used to produce complexes and the phagocytic capacity exhibited by test neutrophils. Ingestion of immunoglobulin G-rheumatoid factor complexes may be important in the production of the cellular phagocytic defect which this study has demonstrated in rheumatoid arthritis synovial fluid neutrophils.     

In Vitro Activity of Antimicrobial Agents on Legionnaires Disease Bacterium

Six isolates of Legionnaires disease bacteria were tested for their susceptibility to 22 antimicrobial agents. The most active agent was rifampin (minimal inhibitory concentration, 相似文献   

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.