Drug Repurposing for Candidate SARS-CoV-2 Main Protease Inhibitors by a Novel In Silico Method

The SARS-CoV-2 outbreak caused an unprecedented global public health threat, having a high transmission rate with currently no drugs or vaccines approved. An alternative powerful additional approach to counteract COVID-19 is in silico drug repurposing. The SARS-CoV-2 main protease is essential for viral replication and an attractive drug target. In this study, we used the virtual screening protocol with both long-range and short-range interactions to select candidate SARS-CoV-2 main protease inhibitors. First, the Informational spectrum method applied for small molecules was used for searching the Drugbank database and further followed by molecular docking. After in silico screening of drug space, we identified 57 drugs as potential SARS-CoV-2 main protease inhibitors that we propose for further experimental testing.

Clinical determinants for the recovery of fungal and mezlocillin-resistant pathogens from bile specimens

We conducted a retrospective analysis of all bile specimens obtained for routine cultures from January 1995 through December 1999 at our tertiary care hospital. Results of microbiologic testing were linked to clinical parameters gathered by means of chart review. A total of 722 isolates were cultured from 345 of 454 bile specimens obtained from 288 individual patients. Prior receipt of a >7-day course of antibiotics (odds ratio [OR], 5.7), extensive leukocytosis (leukocyte count, >20,000 cells/microL) on admission (OR, 7.8), endoscopic or percutaneous biliary manipulation during the previous 14 days (OR, 2.9), and treatment in an internal medicine ward (OR, 2.5) were independent factors significantly associated (Pless-than-or-eq, slant.05) with recovery of Candida species from bile specimens. Culture of mezlocillin-resistant bacteria from bile specimens was independently associated with the specimen having been obtained >1 week after admission (OR, 3.8), lack of history of endoscopic biliary drainage (OR, 3.2), and high serum aspartate aminotransferase levels (>72 U/L) on admission (OR, 2.6). Prospective studies are warranted to evaluate accordingly adjusted empiric therapies for biliary infections.

In vitro activity of mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid against Borrelia burgdorferi

The in vitro susceptibility profile of Borrelia burgdorferi is not yet well defined for several antibiotics. Our study explored the in vitro susceptibility of B. burgdorferi to mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid. Minimal inhibitory concentrations (MICs) and minimal borreliacidal concentrations (MBCs) were measured using a standardised colorimetric microdilution method and conventional subculture experiments. MIC values were lowest for mezlocillin (MIC(90), < or =0.06 mg/l) and meropenem (MIC(90), 0.33 mg/l). Vancomycin (MIC(90), 0.83 mg/l) was less effective in vitro. Borreliae proved to be resistant to aztreonam (MIC(90), >32 mg/l), teicoplanin (MIC(90), 6.6 mg/l), ribostamycin (MIC(90), 32 mg/l), and fusidic acid (MIC(90), >4 mg/l). The mean MBCs resulting in 100% killing of the final inoculum after 72 h of incubation were lowest for mezlocillin (MBC, 0.83 mg/l). This study gathered further data on the in vitro susceptibility patterns of the B. burgdorferi complex. The excellent in vitro effectiveness of acylamino-penicillin derivatives and their suitability for the therapy of Lyme disease is emphasised.

Characterization of an In vitro-selected amoxicillin-resistant strain of Helicobacter pylori

An amoxicillin-resistant (Amox(r)) strain of Helicobacter pylori was selected for by culturing an amoxicillin-sensitive (Amox(s)) strain in increasingly higher concentrations of amoxicillin, resulting in a 133-fold increase in MIC, from 0.03 to 0.06 microg/ml to 4 to 8 microg/ml. This resistance was stable upon freezing for at least 6 months and conferred cross-resistance to seven other beta-lactam antibiotics. beta-Lactamase activity was not detected in this Amox(r) strain; however, analysis of the penicillin-binding protein (PBP) profiles generated from isolated bacterial membranes of the Amox(s) parental strain and the Amox(r) strain revealed a significant decrease in labeling of PBP 1 by biotinylated amoxicillin (bio-Amox) in the Amox(r) strain. Comparative binding studies of PBP 1 for several beta-lactams demonstrated that PBP 1 in the Amox(r) strain had decreased affinity for mezlocillin but not significantly decreased affinity for penicillin G. In addition, PBP profiles prepared from whole bacterial cells showed decreased labeling of PBP 1 and PBP 2 in the Amox(r) strain at all bio-Amox concentrations tested, suggesting a diffusional barrier to bio-Amox or a possible antibiotic efflux mechanism. Uptake analysis of (14)C-labeled penicillin G showed a significant decrease in uptake of the labeled antibiotic by the Amox(r) strain compared to the Amox(s) strain, which was not affected by pretreatment with carbonyl cyanide m-chlorophenylhydrazone, eliminating the possibility of an efflux mechanism in the resistant strain. These results demonstrate that alterations in PBP 1 and in the uptake of beta-lactam antibiotics in H. pylori can be selected for by prolonged exposure to amoxicillin, resulting in increased resistance to this antibiotic.

In-vitro susceptibilities of species of the Bacteroides fragilis group to newer beta-lactam agents

The in-vitro activities of imipenem and four beta-lactam-beta-lactamase inhibitor combinations were tested against 816 strains of the Bacteroides fragilis group, and compared with other anti-anaerobic agents. None of the strains was resistant to metronidazole, and only one was resistant to chloramphenicol. Mezlocillin and piperacillin were moderately active, while clindamycin was the least active. Rates of resistance varied between various species. The new beta-lactam agents tested showed excellent activity; piperacillin-tazobactam and imipenem were the most active. The emergence of strains that are resistant to these agents, observed in this study, suggests there is a need to perform periodic antimicrobial susceptibility tests.

Influence of ciprofloxacin and other antimicrobial drugs on different Escherichia coli strains in continuous-flow cultures under aerobic and anaerobic conditions

In continuous-flow culture, long generation times and high bacterial counts favour survival of bacteria. A chemotherapeutic agent that achieves a bactericidal effect under these circumstances can therefore be seen as highly effective. In our continuous-flow culture we obtained bactericidal effects with ciprofloxacin 1-2 mg/L, cefotaxime 4 mg/L and mezlocillin 32 mg/L. These effects were seen irrespective of whether conditions were aerobic or anaerobic. There were no significant differences between monocultures and mixed cultures simulating faecal flora with the various Escherichia coli strains tested. Cefotaxime had an initial effect but an increase in counts was then observed as a result of regrowth of E. coli survivor strains in aerobic monoculture and mixed cultures. Mezlocillin was completely bactericidal in monocultures, but regrowth occurred in mixed cultures under anaerobic conditions. Neither the bacterial composition of this culture nor the resistance pattern explained this regrowth. These results were observed in long-term experiments followed for up to 7 days. We conclude that the antibiotics tested are highly effective against E. coli under unfavourable conditions simulating in-vivo situations.

Microflora-associated defense stimulating factors

Mucosal surfaces are habitats for the physiological microflora and are closely related to the mucosal immune compartment (mucosa-associated lymphoid tissue, MALT). Recently, considerable evidence has accumulated showing that various members of the physiological microflora liberate low molecular weight substances which, apparently, are essential for the adequate immune response of the host. Antibiotic decontamination (e.g. of the BALB/c mouse gastrointestinal tract) results in a lack of generation of immunopriming microbial substances leading to immunosuppression. Biochemical analysis of the microbial substances revealed reproducible chromatographic fractions which selectively influence maturation, proliferation and activation of mononuclear immune cells.

Evaluation of 500 gram negative isolates to determine the number of major susceptibility interpretation discrepancies between the Vitek and MicroScan Walkaway for 9 antimicrobial agents

Although the Vitek and MicroScan Walkaway are two of the most commonly used automated antimicrobial susceptibility test systems, few studies have been performed comparing discrepancies between these systems. In this study, 500 Gram negative clinical isolates were tested against ampicillin, ampicillin/sulbactam, ticarcillin, ticarcillin/clavulanate, imipenem, ciprofloxacin, norfloxacin, mezlocillin, and piperacillin to determine the number of major interpretation discrepancies between the two systems. The 500 isolates consisted of 100 isolates each of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis and Enterobacter species. Each isolate was tested simultaneously in both systems using the same standardized inoculum. Eighty-four major discrepancies occurred, of which 48 were reproducible. The reproducible discrepancy rate, for the 4,500 isolate/antimicrobic combinations tested, was 48 of 4500 (1.06%). The rate for individual antimicrobics varied from 17 of 500 (3.4%) for ampicillin to no discrepancies for ticarcillin or ciprofloxacin. Of the 48 reproducible discrepancies, 44 (92%) were Vitek resistant, MicroScan susceptible. Fifteen (31%) of the Vitek and 21 (44%) of the MicroScan results were confirmed by broth microdilution. Disk diffusion results were in agreement with 15 (31%) of the Vitek and 21 (44%) of the MicroScan results. Twelve (25%) of the broth microdilution and 12 (25%) of the disk diffusion results were intermediate. The broth microdilution and disk diffusion results for the 48 isolates with reproducible discrepancies were in agreement more often with MicroScan. However, there was less very major error comparing the Vitek results for these isolates to the broth microdilution and disk diffusion. Overall, the result of this evaluation indicate that the number of major interpretation discrepancies between the two systems is minimal for the isolate/antimicrobic combinations tested.

Comparison of the pharmacokinetic and pharmacodynamic activity of piperacillin and mezlocillin

STUDY OBJECTIVE

To compare serum bactericidal activity over time and pharmacokinetics resulting from single doses of piperacillin (PIP) and a single dose of mezlocillin (MEZ).

DESIGN

Open-label, randomized, three-way crossover study.

SETTING

Hartford Hospital Clinical Research Center.

PATIENTS

Nine healthy volunteers.

INTERVENTIONS

Subjects received single doses of PIP 3 and 4 g/70 kg, and a single dose of MEZ 5 g/70 kg.

MEASUREMENTS AND MAIN RESULTS

Test organisms were two clinical isolates of Pseudomonas aeruginosa. Pharmacodynamic analysis revealed that PIP 4 g had 2- to 3-fold higher peak serum bactericidal activity at the end of infusion and 4- to 5-fold higher activity at 0.5 hour than did MEZ 5 g, and also provided approximately 1 hour additional activity over MEZ 5 g. Pharmacokinetic analysis revealed that serum concentrations resulting from PIP 4 g remained above the minimum inhibitory concentration of our test strains almost twice as long as MEZ 5 g.

CONCLUSION

Since mezlocillin 5 g every 8 hours is currently proving to be effective at many institutions, and since piperacillin 4 g demonstrates superior pharmacokinetic and pharmacodynamic activity, we believe that piperacillin 4 g every 8 hours could be used instead, with resulting cost savings.

[Immunomodulating effects of antibiotics influencing digestive flora]

Mucosal surfaces are habitats of the physiological microflora and are closely related to the mucosal immune compartment (mucosa-associated lymphoid tissue, MALT). Recently, considerable evidence has been accumulated showing that various members of the physiological microflora liberate low molecular weight peptides which, apparently, are essential for adequate immune responses of the host. Antibiotic decontamination (e.g. of the BALB/c-mouse intestinal tract) results in a lack of generation of immunopriming microbial peptides leading to immunosuppression. Biochemical analysis of the peptides revealed reproducible chromatographic fractions which selectively influence maturation, proliferation, and activation of lymphatic cells.

Enterococcus faecalis: in vitro activity of antimicrobial drugs, singly and combined, with and without defibrinated human blood, against high-level-gentamicin-resistant isolates

Teicoplanin (4 micrograms/ml) combined with 4 micrograms/ml of ampicillin, mezlocillin, and piperacillin, respectively, proved more efficacious than vancomycin (4 micrograms/ml) combined with the three beta-lactam antibiotics against three representative clinical isolates of Enterococcus faecalis that showed high-level-gentamicin resistance (HLGR). In the presence of 65% (v/v) of fresh defibrinated human blood, teicoplanin (4 micrograms/ml) alone afforded significant bactericidal activity, but failed to completely sterilize assay tube contents, whereas teicoplanin combined with any of the three beta-lactam antibiotics consistently and completely killed HLGR E. faecalis inocula.

Beta-lactam antibiotics inhibit agonist-stimulated platelet calcium influx

beta-lactam antibiotics cause platelet dysfunction with reversible agonist-receptor inhibition, irreversible [14C]-penicillin binding, and inhibition of agonist-stimulated elevation in cytosolic Ca2+ ([Ca2+]i), occurring after 24 h exposure in vitro and after in vivo treatment. We investigated beta-lactam antibiotic-induced inhibition of rises in [Ca2+]i stimulated by thrombin, sodium arachidonate or A23187 to determine whether Ca2+ influx or intracellular release was primarily affected. The mean rise in [Ca2+]i, measured with fura-2-AM, was inhibited 43.7-84.1% by penicillin when the extracellular Ca2+ concentration ([Ca2+]e) was 1 mM, but was significantly less inhibited when [Ca2+]e was < 1 microM. NiCl2 (2 mM), that blocks Ca2+ influx, caused inhibition comparable to penicillin. MnCl2 (1 mM), that quenches the intracellular fura-2 signal, significantly decreased the rise in 1 mM [Ca2+]i when [Ca2+]e was 1 mM, but did not increase the inhibition caused by penicillin. Penicillin did not inhibit the rise in [Ca2+]i stimulated by inositol-1,4,5-trisphosphate or GTP gamma S. Therefore, beta-lactam antibiotics inhibit agonist-induced elevations of [Ca2+]i primarily through inhibition of Ca2+ influx, which probably accounts for the irreversible inhibition of platelet function seen after prolonged in vitro or in vivo treatment.

Patterns of multiple resistance to antibiotics in gram-negative bacteria demonstrated by factor analysis

Principal component analysis was used to demonstrate the main associations between patterns of resistance to antibiotic drugs in 670 gram-negative bacteria consecutively isolated from blood cultures over a period of two years. Six factors were derived, which accounted for 84% of the total variance of the original matrix. Each factor represented an association between resistance to certain antibiotics as follows: factor 1: aztreonam, third generation cephalosporins and aminoglycosides; factor 2: first and second generation cephalosporins; factor 3: tetracycline and chloramphenicol; factor 4: ampicillin and ureidopenicillins; factor 5: trimethoprim/sulfamethoxazole; factor 6: fluoroquinolones. On two-way analysis of variance the difference in the factor scores was significant between bacteria for all factors except factor 5. The difference in factor scores between community and hospital acquired strains was significant only for factors 1, 2 and 6. Only the score of factor 6 showed a clear trend to increase with time during the two-year study period. Patients who were treated with antibiotics prior to bacteremia had higher scores for all factors, the difference being most marked in patients treated with fluoroquinolones. Factor analysis can be used to describe phenotypic associations between resistance to antibiotics, and the factor score used to compare groups of isolates and to demonstrate temporal and other trends.

Antibacterial and mezlocillin-enhancing activity of pure human pancreatic fluid

The majority of deaths in severe pancreatitis are the result of superinfection of necrotic tissue. The pathogen most commonly responsible for such infections is Escherichia coli. Antibiotic prophylaxis would appear a logical precaution. The antibacterial drugs of choice should possess two basic characteristics: they must be active against the flora responsible for the infections and must be capable of penetrating into the pancreas at adequate minimum inhibitory concentrations (MICs). Mezlocillin--which is active against E. coli--has been shown to possess the latter requisite, but achieving therapeutic concentrations requires administration at high doses. In the present study, pure human pancreatic fluid showed properties similar to those observed in the dog against E. coli (bacterial colony growth 100 times lower than in a control culture) and produced a 75% reduction in mezlocillin MICs against this organism. These enhancing characteristics might make the commonly used doses sufficient for prophylactic purposes.

Antimicrobial activity of isepamicin (SCH21420, 1-N-HAPA gentamicin B) combinations with cefotaxime, ceftazidime, ceftriaxone, ciprofloxacin, imipenem, mezlocillin and piperacillin tested against gentamicin-resistant and susceptible gram-negative bacilli and enterococci

Isepamicin, formerly SCH21420 or 1-N-HAPA gentamicin B, is an aminoglycoside that was tested alone or in combination with one of seven broad spectrum drugs against 80 clinical isolates. Half of the strains were gentamicin-resistant but only one isolate (1.3%) was resistant to isepamicin. The broadest spectrum comparison drugs tested alone (ciprofloxacin at 3.8% resistance and imipenem at 5.0% resistance) were associated with the lowest synergy rates when combined with isepamicin. The rank order of synergy (complete or partial) was; cefotaxime = ceftazidime = ceftriaxone = mezlocillin = piperacillin (75% to 80%) greater than imipenem (66%) greater than ciprofloxacin (38%). Isepamicin/ampicillin combinations produced synergistic killing of those enterococci not having high-grade resistance to gentamicin or kanamycin. Enterococcus faecium strains were also refractory to isepamicin/ampicillin synergy. Isepamicin appears to be widely useable against gentamicin-resistant gram-negative bacilli either alone or combined with most commonly used broad spectrum beta-lactams.

[The effect of sulbactam on the in vitro activity of mezlocillin, piperacillin and cefotaxime]

The in vitro activity of mezlocillin (MZL, CAS 51481-65-3), piperacillin (PIP, CAS 61477-96-1) and cefotaxim (CTX, CAS 63527-52-6) alone and in combination with sulbactam (SBT; CAS 68373-14-8) against mezlocillin-resistant pathogens was determined in a multicenter study. A total of 870 strains were investigated (481 Enterobacteriaceae, 57 Pseudomonas aeruginos, 41 Acinetobaster spp., 194 Bacteroides fragilis, and 97 Staphylococcus spp.). Determinations of MIC were performed according to DIN-guidelines (agar-dilution method for aerobes and microbroth-dilution method for anaerobes). Sulbactam was added in fixed concentrations of 5 mg/l and 10 mg/l. In all sulbactam-combinations examined mean MIC as well as MIC50 and MIC90 were reduced compared to the respective values for the antibiotics alone. Consequently, percentages of susceptible strains increased significantly: i.e. for Enterobacteriaceae: MZL 1% vs. MZL + 10 mg/l SBT 53%; PIP 4% vs. PIP + 10 mg/l SBT 54%; CTX 52% vs. CTX + 10 mg/l SBT 68%. The effect of sulbactam was most pronounced in Bacteroides spp. with an increase in susceptible strains from 2% to 97% for MZL, from 6% to 95% for PIP and from 7% to 98% for CTX. The results indicate that by adding sulbactam the in vitro activity of mezlocillin, piperacillin and cefotaxim against resistant pathogens is augmented significantly. In addition, the spectrum of antibacterial activity is extended to anaerobic pathogens such as Bacteroides spp. The availability of sulbactam as a monosubstance for combination with various beta-lactam-antibiotics thus represents a useful improvement of therapeutic options in bacterial infections.

[The effect of some antibiotics on primary antibody response]

In this study, effect of four broad spectrum antibiotics (sodium cefoperazone, sulbactam-ampicillin, mezlocillin, rifamycin) on primary antibody response. Therefore, sheep red blood cells were injected into total 25 rabbits in control and experiment groups. Hemolysin levels were titrated in serum specimens prepared from blood specimens taken before the experiment and taken three weeks after the last antigen injection. It was found that statistically significant in all the experiment groups rather than control (p less than 0.05).

[In vitro activity of beta-lactam antibiotics in combination with sulbactam against enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter. Results of a multicenter study]

The in vitro antimicrobial activity of ticarcillin (TICAR), mezlocillin (MEZLO), piperacillin (PIPER), cefoperazone (CPZ), cefotaxime (CTX) and ceftazidime (CAZ), alone and in combination with 8 micrograms/ml of sulbactam (SULB), was studied by agar dilution against TICAR resistant strains isolated in 8 hospitals over a period of 3 months in 1989 (747 enterobacteria, 110 Ps. aeruginosa and 48 Acinetobacter sp.). SULB did not modify the activity of beta-lactam antibiotics against Ps. aeruginosa. The 6 beta-lactam antibiotics SULB combinations were only active for 27% of Acinetobacter SULB sensitive. SULB restored the activity of: MEZLO, PIPER, CPZ in Enterobacteria producing a penicillinase; PIPER, CTX and CAZ in Enterobacteria producing a broad-spectrum beta-lactamase; MEZLO, PIPER, CTX and CAZ in M. morganii producing a derepressed cephalosporinase.

Effect of daptomycin, metronidazole and mezlocillin combinations on mixed bacterial cultures involving facultative and anaerobic bacteria

The in vitro activities of different daptomycin concentrations in combination with metronidazole (4 mg/l) or/and mezlocillin (8 mg/l) were investigated on mixed bacterial cultures involving gram-positive facultative cocci. Bacteroides fragilis group strains and Escherichia coli. When Streptococcus faecalis alone or together with E. coli was cultured with B. thetaiotaomicron the colony counts of the latter were 4 log units higher after incubation in the presence of daptomycin and metronidazole than when it was cultured alone. After the addition of mezlocillin, this effect disappeared and all 3 strains were killed. When the same antibiotic combinations were used in the presence of beta-lactamase producing Staphylococcus aureus, the activity of mezlocillin was decreased significantly. The colony counts of the co-cultured B. thetaiotaomicron and E. coli proved to be 2 log and 6 log higher, respectively, than those observed after they were cultured alone. The antimicrobial susceptibilities of the clinical isolates tested here in mixed cultures of up to 3 strains were modified significantly by interactions between the strains and the antibiotics used.

In vitro activity against clinically important gram-positive and gram-negative bacteria of sulbactam, alone and in combination with ampicillin, cefotaxime, mezlocillin, and piperacillin

The in vitro effects of the single agents, and the synergistic/antagonistic action of three different combinations of ampicillin (AMP, CAS 69-53-4), cefotaxime (CTX, CAS 63527-52-6), mezlocillin (MEZ, CAS 51481-65-3), and piperacillin (PIP, CAS 61477-96-1) with the beta-lactamase inhibitor sulbactam (SUL, CAS 68373-14-8) were determined against 675 gram-positive and gram-negative, both aerobic and anaerobic bacteria. All the combinations of sulbactam and the antibiotics (1: 1, 1:2 and 1:4) exhibited very similar synergistic action. The percentage of the total strains tested for which synergistic activity was found was 51% with SUL + AMP (1:1), 24% with SUL + CTX (1:1), 31% with SUL + MEZ (1:1), and 28% with SUL + PIP (1:1). A fourfold or greater reduction of MIC's in the comparison with the antibiotics alone was found with 23% of the total strains tested for the SUL + AMP, with 9% of the strains tested with SUL + CTX, with 11% of the strains tested with SUL + MEZ, and with 15% of the strains tested with the SUL + PIP-combination. In the presence of sulbactam, 18% of the strains tested showed a significant reduction in the number of resistant strains with ampicillin, 7% with cefotaxime, 16% with mezlocillin, 14% with piperacillin, and in parallel there was an increase in the number of fully susceptible strains (shift from resistant or moderately sensitive to sensitive) by about 14%. In comparison with the antibiotic alone, the most marked reductions in the number of resistant strains on combination with sulbactam were as follows (the percentage of reduction is shown in brackets): for SUL + AMP and Acine-tobacter spp. (39% fewer resistant strains). Citrobacter spp. (-60%), Enterobacter aerogenes (-48%), Klebsiella oxytoca (-49%), Klebsiella pneumoniae (-63%), Morganella morganii (-74%), and Proteus vulgaris (-55%); for SUL + CTX and Acinetobacter spp. (-38%), Enterobacter cloacae (-6%), Klebsiella pneumoniae (-16%), Serratia marcescens (-9%), and Bacteroides fragilis (-31%); for SUL + MEZ and Acinetobacter spp. (-68%), Citrobacter spp. (-27%), Enterobacter spp. (-23%), Klebsiella pneumoniae (-32%), and Serratia marcescens (-19%); for SUL + PIP and Acinetobacter spp. (-41%), Citrobacter spp. (-30%), Klebsiella spp. (-30%), and Serratia marcescens (-33%).

In vitro comparison of mezlocillin and piperacillin plus tobramycin or gentamicin versus 100 gram-negative nosocomial bloodstream isolates

We compared the in vitro activity of mezlocillin and piperacillin, alone and in combination with tobramycin or gentamicin, against clinical isolates of gram-negative bacilli from hospitalized patients with 100 distinct episodes of nosocomial bacteremia. The minimum inhibitory concentrations (MICs) necessary to inhibit 50% and 90% of isolates showed that piperacillin was most active against Pseudomonas aeruginosa. The MIC needed to inhibit 90% of isolates also showed that mezlocillin was more active against Enterobacter cloacae. Activities of the two acylaminopenicillins were comparable against the rest of the isolates. Combining the acylaminopenicillins with either gentamicin or tobramycin decreased the MICs fourfold or more for both combinations. Synergy occurred more frequently with mezlocillin-gentamicin (12%), followed by piperacillin-tobramycin (9%), mezlocillin-tobramycin (6%), and piperacillin-gentamicin (5%). Antagonism for Enterobacteriaceae isolates was observed most frequently with the combination of piperacillin plus tobramycin (20%), followed by mezlocillin plus tobramycin (17.6%), piperacillin plus gentamicin (12.9%), and mezlocillin plus gentamicin (8.2%). There are very few differences in the activities of mezlocillin and piperacillin combined with either gentamicin or tobramycin versus nosocomial gram-negative bloodstream isolates.

Beta-lactam antibiotic-induced platelet dysfunction: evidence for irreversible inhibition of platelet activation in vitro and in vivo after prolonged exposure to penicillin

beta-Lactam antibiotics cause platelet dysfunction with bleeding complications. Previous in vitro studies documented reversible inhibition of agonist-receptor interaction. This mechanism is inadequate to explain the effect of beta-lactam antibiotics in vivo. Platelet function does not return to normal immediately after drug treatment, implying irreversible inhibition of platelet function. We report here evidence of irreversible platelet functional and biochemical abnormalities after in vitro and in vivo exposure to beta-lactam antibiotics. Irreversible binding of [14C]-penicillin (Pen) occurred in vitro. After 24 hours' in vitro incubation with 10 to 20 mmol/L Pen, or ex vivo after antibiotic treatment, irreversible functional impairment occurred; but no irreversible inhibition of alpha 2 adrenergic receptors, measured with [3H]-yohimbine, or high-affinity thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors, measured with agonist [3H]-U46619 and antagonist [3H]-SQ29548, occurred. However, low-affinity platelet TXA2/PGH2 receptors were decreased 40% after Pen exposure in vitro or in vivo, indicating irreversible membrane alteration. Two postreceptor biochemical events were irreversibly inhibited in platelets incubated with Pen for 24 hours in vitro or ex vivo after antibiotic treatment. Thromboxane synthesis was inhibited 28.3% to 81.7%. Agonist-induced rises in cytosolic calcium ([Ca2+]i) were inhibited 40.1% to 67.5% in vitro and 26.6% to 52.2% ex vivo. Therefore, Pen binds to platelets after prolonged exposure, resulting in irreversible dysfunction attributable to inhibition of TXA2 synthesis and impairment of the rise in [Ca2+]i. The loss of low-affinity TXA2/PGH2 receptors suggests that the primary site of action of these drugs is on the platelet membrane.

Aztreonam susceptibility testing. A retrospective analysis

Aztreonam is a structurally and immunologically unique beta-lactam antibiotic with activity exclusively against aerobic gram-negative micro-organisms. Between 1983 and 1988, its antimicrobial spectrum was evaluated against more than 5,800 fresh clinical isolates at a 300-bed community teaching hospital. Only 1.1 percent of Enterobacteriaceae isolates were resistant to aztreonam over the five-year study period, an incidence similar to that observed with aminoglycoside antibiotics. Aztreonam was found to be more active than third-generation cephalosporins and comparable with mezlocillin against Enterobacter spp., Morganella, and Citrobacter freundii. Although aztreonam was somewhat less active against nonfermenting gram-negative bacilli, such as Pseudomonas and Acinetobacter, overall more than 90 percent of Pseudomonas aeruginosa isolates were susceptible. Ceftazidime was the most active beta-lactam tested against nonfermenters. Against aerobic gram-positive cocci, aztreonam possessed no clinically useful activity. No significant change in susceptibility to aztreonam was observed over the five-year study period for Enterobacteriaceae. For third-generation cephalosporins, however, a trend toward increased resistance was noted, particularly for Enterobacter spp. and C. freundii. A 50 percent increase in resistance to aztreonam was observed over the five-year study period for nonfermenters, particularly P. aeruginosa and Acinetobacter anitratus. Similar increases in resistance were seen with other beta-lactams and gentamicin. Based on its potent in vitro activity, aztreonam appears to be a useful agent and a desirable alternative to aminoglycoside antibiotics for the treatment of pure aerobic gram-negative bacillary infections, or as a component in combination therapy against mixed infections.

Digestive tract microflora liberates low molecular weight peptides with immunotriggering activity

Antibiotic digestive tract decontamination in BALB/c-mice resulted in a significant reduction of peritoneal macrophage function and lymphocyte proliferation. Considerable evidence has accumulated showing that certain species of the indigenous gastrointestinal (GI)-tract microflora, e.g. Bacteroides sp., Clostridium sp., Lactobacillus sp., and Propionibacterium sp., liberate low molecular weight peptides which are able to trigger basic immune responses. Eradication of the GI-tract microflora apparently results in a lack of peptide production correlating to immunosuppression in experimental BALB/c-mice. Substitution of peptides in GI-tract decontaminated mice reconstituted macrophage function as well as proliferation of lymphatic tissue.

Evolution of antimicrobial susceptibility in isolates of the Bacteroides fragilis group in Spain

The species included in the Bacteroides fragilis group are the most frequent nontoxigenic anaerobic bacteria pathogenic to humans. The emergence and increase of resistance to antibiotics among this group make surveillance and state-of-the-art knowledge important. We studied the evolution of resistance to antibiotics in B. fragilis group organisms isolated at the University Clinical Hospital at Salamanca, Spain, from 1975 to 1987. No resistance to imipenem, chloramphenicol, or metronidazole was detected. The frequency of resistance to clindamycin was in the range of 6%-7%. Resistance to moxalactam, cefoxitin, mezlocillin, and piperacillin has increased steadily and is currently approximately 20%-25%.

[In vitro interaction of mezlocillin with fluorouracil and mitomycin]

The interaction of mezlocillin (Baypen) with either fluorouracil (5-fluorouracil, 5-FU) or mitomycin was tested in vitro by incubating colorectal carcinoma cell line HT 29 with varying concentrations of mezlocillin, 5-FU, mitomycin and the combinations of mezlocillin + 5-FU and mezlocillin + mitomycin. Inhibition of colony growth in soft agar of treated compared with untreated cells was used as an in vitro response parameter. Concentration ranges were representative for regional chemotherapy with mitomycin or 5-FU and perioperative antibiotic therapy with mezlocillin. Mezlocillin, 5-FU and mitomycin showed dose-dependent inhibition of colony growth. Mezlocillin produced a maximal toxicity of 16% at 1000 micrograms/ml. Toxicity of 5-FU was reduced by addition of mezlocillin. The increase of colony growth after coincubation of mezlocillin with 5-FU (compared to cells treated with 5-FU alone) at a mezlocillin concentration of 10 micrograms/ml was 47% to 116%, at 100 micrograms/ml 44% to 132%, depending on the 5-FU test concentrations. The 5-FU toxicity in some instances was nearly abolished. There was no interaction between mezlocillin and mitomycin. The interference of mezlocillin with 5-FU-toxicity should be respected in case of combined perioperative antitumor and antibiotic therapy with 5-FU mezlocillin. Similar interactions with related antibiotics cannot be excluded.

Comparison of in vitro susceptibilities among gram-negative rods

The activity of mezlocillin, azlocillin and piperacillin was compared using 100 clinical isolates of gram-negative rods. Overall piperacillin had the highest activity with 72 per cent sensitive strains; mezlocillin, 66 per cent, and azlocillin, 57 per cent. In the group of Pseudomonas aeruginosa, however, mezlocillin showed distinctly lower activity than both piperacillin and azlocillin.

Dactimicin, a new aminoglycoside: in vitro activity, post-antibiotic effect and interaction with other antibiotics

The in vitro activity of the new aminoglycoside dactimicin in comparison to amikacin was tested alone and in combination with piperacillin, mezlocillin and ceftazidime against freshly isolated clinical pathogens. Dactimicin was more active than amikacin against Enterobacter cloacae, Providencia rettgeri and Salmonella spp., and less active than amikacin against Escherichia coli, Pseudomonas aeruginosa and Acinetobacter anitratus. Using the checkerboard technique, the combination of either dactimicin or amikacin with the other drugs was shown to result in synergistic interaction against most of the 23 strains tested. Dactimicin-ceftazidime and amikacin-ceftazidime were the most effective combinations, demonstrating synergism against 91% and 95% of the isolates respectively. Antagonism was not encountered. Using the time-kill method, synergism was seen in most cases, indifference rarely being seen; antagonism was not observed. Dactimicin induced a post-antibiotic effect which ranged from 1 h for Enterobacter cloacae to 2.4 h for Escherichia coli. An average post-antibiotic effect of 0.6 h was also seen when dactimicin was combined with piperacillin, mezlocillin and ceftazidime. The findings indicate that dactimicin compares favorably in vitro with amikacin and suggest that clinical trials with this drug alone or in combination are warranted.

Influence of coadministration on the pharmacokinetics of mezlocillin and cefotaxime in healthy volunteers and in patients with renal failure

The pharmacokinetic disposition of cefotaxime, desacetyl cefotaxime, and mezlocillin after the administration of each drug singly and in combination was examined in eight healthy volunteers and in five anuric patients with end-stage renal disease (ESRD). In the presence of ESRD, the total body clearance of cefotaxime decreased from 256.7 +/- 41.5 to 65.4 +/- 42.0 ml/min, and its elimination half-life (t1/2) increased from 1.1 to 3.6 hours as compared with healthy volunteers. Concomitant administration of mezlocillin in healthy volunteers decreased the total body clearance of cefotaxime by 42% and increased its steady-state volume of distribution. This reduction in clearance was reflected by a decrease in both renal and nonrenal clearances. In the presence of ESRD, coadministration of mezlocillin increased the t1/2 of cefotaxime to 5.8 hours. Desacetyl cefotaxime accumulated in ESRD with a prolongation of its elimination t1/2 to 18.7 hours from 1.7 hours in healthy volunteers. Desacetyl cefotaxime peak plasma concentrations occurred later with the combination regimen in the presence of ESRD. The clearance of mezlocillin was reduced and t1/2 prolonged in ESRD from 194.6 +/- 31.9 to 76.4 +/- 38.8 ml/min and 1.4 to 2.3 hours, respectively. Concomitant administration of cefotaxime did not alter the pharmacokinetics of mezlocillin. These data suggest that in the presence of normal renal function, lower doses of cefotaxime may be adequate to maintain similar cefotaxime plasma concentrations when mezlocillin is coadministered compared to when cefotaxime is given alone. Additional pharmacodynamic and clinical studies with this combination are warranted to further elucidate the clinical impact of this pharmacokinetic interaction.

Study of in vitro antibacterial activity of 19 antimicrobial agents against Pseudomonas aeruginosa

The in vitro antibacterial activity of 19 antimicrobial agents against 40 strains of P aeruginosa was studied. The 19 antimicrobial agents included 7 semisynthetic penicillins, 6 third generation cephalosporins, 5 aminoglycosides and 1 quinolone agent. The minimal inhibition concentrations (MIGs) were measured by the serial dilution on solid agar. Ceftazidime was the most active in 19 antimicrobial agents again P aeruginosa (MIC50: 1 microgram/ml, MIC90: 2 micrograms/ml) Amikacin and ofloxaxin followed it in activity. Acylureido-penicillins, such as azlocillin, furbenicillin and piperacillin were highly active against P aeruginosa, which could inhibit, 92.5%, 90% and 85% of these strains at a concentration of 8 micrograms/ml. Cefsulodine and cefoperazone were also active against the same strains, inhibiting 92.5% and 99% of the strains at a concentration of 8 micrograms/ml. The potency of the agents mentioned above against P. aeruginosa was similar to that of aminoglycosides. The drug susceptibility of 10 strains isolated in our hospital was compared with that of 29 strains of other hospitals in Beijing. The MICS of 5 penicillins and 3 cephalosporins against the isolates of our hospital was higher than that of other hospitals, suggesting that the susceptibility of beta-lactam antibiotics against isolates of our hospital was lower. The effects of combined use of azlocillin with oxacillin and piperacillin with ofloxacin against 4 strains of carbenicillin-resistant P aeruginosa was studied using check-board testing. The synergy and partial synergy were observed in both combinations.

Effect of antibiotics on laser-induced thrombus formation in rat mesenteric arterioles

Antibiotics were tested in a thrombosis model, in which thrombi are produced in small rat mesenteric arterioles. An interference contrast system based on a Leitz Orthoplan microscope, was used to visualize thrombus formation. Vascular lesions were produced with a Coherent CR-2 supergraphite ion laser (argon laser) in arterioles of 25-35 microns diameter. Cefmenoxim, cefotaxim (i.v.) and cephalexin orally at doses of 20 and 40 mg/kg and gentamycin 10 and 20 mg/kg (i.v.) had a marked and significant antithrombotic effect. Even more effective were cefoperazon and lamoxactam 20 and 40 mg/kg (i.v.) and tobramycin 10 and 20 mg/kg (i.v.). Azlocillin, cefoxitin, mezlocillin or spectinomycin (20 mg/kg i.v.) and penicillin or piperacillin (50 mg/kg i.v.) also showed a significant antithrombotic effect, which, however, disappeared on doubling of the applied dose.

Studies on the synergism of sulbactam and beta-lactam antibiotics under in vitro conditions and in healthy volunteers after intravenous administration. Antibacterial activity in vitro, compatibility and pharmacokinetics of the drugs in combination

Sulbactam, a new beta-lactam inhibitor, increased the in vitro activity of cefotaxime, mezlocillin and piperacillin against 803 clinical bacterial isolates. The synergism of sulbactam and these antibiotics was particular marked against 467 beta-lactamase positive strains, both aerobic and anaerobic. In the presence of sulbactam the mean minimal inhibitory concentrations (MICs) of the antibiotics against beta-lactamase positive bacteria were greatly reduced: with cefotaxime by 58%, with mezlocillin by 64% and with piperacillin by 70%. Sulbactam alone at low concentrations inhibited the growth of only a few strains (Neisseria spp., Acinetobacter spp.). The inhibitor proved to be very stable in infusion media under a variety of conditions and was compatible in vitro with 14 different beta-lactam antibiotics. The pharmacokinetics profiles of sulbactam and the antibiotics cefotaxime, mezlocillin and piperacillin were similar after infusion to healthy volunteers. The relevant pharmacokinetic parameters of the single substances were essentially unchanged when administered in combination. The general similarity between the pharmacokinetics of sulbactam and of the beta-lactam antibiotics appears to be an essential precondition for the therapeutic success of such a synergistic combination. Thus the physicochemical and pharmacological properties of sulbactam apparently permit flexible dosage in combination with different penicillins or cephalosporins and sulbactam can be administered as non-fixed combination in the clinical treatment of bacterial infections.

Intestinal microflora of BALB/c-mice and function of local immune cells

BALB/c-mice were treated for 7 days with oral nonabsorbable dosages of mezlocillin to achieve digestive tract decontamination. Such a procedure resulted in rapid eradication of most species of aerobic and anaerobic intestinal microflora. Various functions of peritoneal macrophages (e.g. chemiluminescence response, chemotactic motility, bactericidal and cytostatic ability) and lymphocyte proliferation were decreased in decontaminated animals as compared to non-treated controls.

Cefoperazone plus mezlocillin for empiric therapy of febrile cancer patients

Two dosing regimens of cefoperazone plus mezlocillin were compared in a prospective, randomized trial for therapy of febrile cancer patients. The two regimens were 5 g mezlocillin plus 2 g cefoperazone intravenously every four hours (higher dose) or 3 g mezlocillin plus 1 g cefoperazone intravenously every four hours (lower dose). Although the overall response rate was higher with the higher dose regimen (78 percent versus 66 percent, p = 0.04), the two regimens were comparable in patients with documented infections (72 percent versus 68 percent). Likewise, the two regimens were equally effective against those infections in which the pathogen could be determined (82 percent versus 82 percent). Serum bactericidal titers of at least 1:32 against a known pathogen were associated with a higher response rate than were titers of less than 1:32, but the higher dose regimen did not result in higher serum bactericidal titers. Hypoprothrombinemia was a side effect, especially with the higher dose regimen, before prophylactic vitamin K was routinely administered to patients. Since there were no major benefits with the use of the higher dose regimen of mezlocillin plus cefoperazone, the lower dose regimen is more appropriate for routine usage.

[Ciprofloxacin in combination with other antimicrobial substances]

The antibacterial activity of ciprofloxacin, either alone or in combination with azlocillin, imipenem, mezlocillin or tobramycin, was tested against enterococcus and pseudomonas species. No synergy or antagonism was found by means of the checkerboard titration method used. Subsequently, the bactericidal activity of ciprofloxacin (2 x minimal inhibitory concentration, MIC), azlocillin, imipenem, mezlocillin or tobramycin (2 x MIC) either alone or in combination (1 x MIC each of each substance) was tested against individual strains. No reduction of bactericidal activity in comparison with the effect of the single substances at higher concentration was found, even though the concentrations of each substance were halved. An antagonism is unlikely when ciprofloxacin is combined with one of the beta-lactams studied or with tobramycin. More likely is a slight synergistic effect.

Evaluation of the Cobas Bact automated system for susceptibility testing of Enterobacteriaceae, Pseudomonas aeruginosa, and Enterococcus faecalis to azlocillin, mezlocillin, and ciprofloxacin compared to NCCLS and DIN standards

The aim of automated susceptibility testing systems like the Cobas Bact is to provide the clinicians with rapid and reliable results for the care of patients and to decrease the work load in microbiological laboratories. Because data about accuracy on mezlocillin, azlocillin and ciprofloxacin were lacking, we investigated 184 bacterial strains and compared the results of the Cobas Bact susceptibility testing to standardized agar dilution and agar diffusion methods. Essential correlations for all methods compared exceeded 90% for the three chemotherapeutics and all species investigated, with the exception of Pseudomonas aeruginosa. On an average only 1.5% very major errors were observed with the several species of Enterobacteriaceae, whereas P. aeruginosa and Enterococcus faecalis were characterized by the complete absence of very major errors when Cobas Bact was correlated to NCCLS agar diffusion.

Bactericidal activity and killing rate of serum in volunteers receiving pefloxacin alone or in combination with ceftazidime, piperacillin or mezlocillin against Pseudomonas aeruginosa

The activity of the combination of pefloxacin with ceftazidime, piperacillin, or mezlocillin was compared to the activity of the same antibiotics given alone, by measurement of serum bactericidal titres and the rate of killing of ten strains of Pseudomonas aeruginosa. Three groups of five volunteers each received pefloxacin (12 mg/kg iv) with or without ceftazidime, piperacillin or mezlocillin (25 mg/kg iv). Serum samples were obtained at the end of the infusion. The mean serum concentration of pefloxacin at this time was 13.9 mg/l (3.2, S.D.). The activity of each of the three combinations was identical to the corresponding activity of the beta-lactam alone. However, the emergence of resistance to pefloxacin was prevented by ceftazidime (five out of five strains), and piperacillin (two out of five strains). We conclude that combinations of pefloxacin with beta-lactam antibiotics may not increase efficacy against P. aeruginosa.

A comparison of the in-vitro activity of seventeen antibiotics against Streptococcus faecalis

The in-vitro activity of seventeen antibiotics against 177 clinical strains of Streptococcus faecalis was evaluated. Ampicillin and mezlocillin were the most active beta-lactams tested (geometric mean MICs, 0.61 and 0.74 mg/l, respectively). Aminoglycosides showed poor activity and 22.6% of the strains were resistant to 2000 mg/l of streptomycin. No correlation was observed between MICs of gentamicin and streptomycin. Moderate activity was observed when testing norfloxacin and ciprofloxacin. Teicoplanin and co-trimoxazole were extremely active, showing geometric mean MICs of 0.59 and 0.08 mg/l respectively. All strains were susceptible to vancomycin and teicoplanin.

Antibiotic treatment, intestinal aerobic microflora and experimental sarcoma L-1 growth in Balb/c-mice

The present paper deals with the influence of a 10 days treatment with mezlocillin, piperacillin, cefotaxime, clindamycin or gentamicin on the endogenous intestinal microflora of Balb/c-mice and on the local growth of sarcoma L-1 tumor. Clindamycin and gentamicin demonstrated no influence, whereas cefotaxime and piperacillin caused the eradication of gram-negative resp. gram-positive bacteria but these antibiotics didn't produce a growth inhibition of local L-1 sarcoma tumor. The oral or parenteral application of mezlocillin (a 3 days treatment was sufficient) eradicated the complete aerobic and anaerobic intestinal microflora. This effect was significantly correlated with an increase of the cecum weight and the inhibition of local tumor growth. Possible mechanisms of these effects are discussed.