A proteolytic transmembrane signaling pathway and resistance to beta-lactams in staphylococci.

beta-Lactamase and penicillin-binding protein 2a mediate staphylococcal resistance to beta-lactam antibiotics, which are otherwise highly clinically effective. Production of these inducible proteins is regulated by a signal-transducing integral membrane protein and a transcriptional repressor. The signal transducer is a fusion protein with penicillin-binding and zinc metalloprotease domains. The signal for protein expression is transmitted by site-specific proteolytic cleavage of both the transducer, which autoactivates, and the repressor, which is inactivated, unblocking gene transcription. Compounds that disrupt this regulatory pathway could restore the activity of beta-lactam antibiotics against drug-resistant strains of staphylococci.

The pharmacokinetics of teicoplanin in varying degrees of renal function.

The pharmacokinetics of teicoplanin, a new glycopeptide antibiotic with activity against aerobic gram-positive bacteria, were characterized after intravenous administration of a single 3 mg/kg dose in five healthy volunteers and six patients with various degrees of stable renal insufficiency. Serum and urine samples were collected during a 15-day period and drug concentrations were assayed microbiologically. The mean elimination half-life of teicoplanin was 162.6 +/- 69.8 hours in healthy volunteers and was prolonged with decreased renal function. The mean plasma and renal clearances of teicoplanin in healthy subjects were 11.4 +/- 1.5 ml/min and 10.0 +/- 1.0 ml/min, respectively. Both values decreased in patients with renal failure and correlated significantly with measured creatinine clearances (r2 = 0.938 and 0.884, respectively). A nomogram for dosage adjustment in patients with varying degrees of renal failure is presented.

Detection of proteinases in electrophoretograms of complex mixtures.

A simple, sensitive technique for detecting proteolytic enzyme zones on electrophoretograms by making contact print zymograms is described. The method is applicable to electrophoretograms prepared on a variety of support media, immunoelectrophoretograms or isoelectric focusing patterns on various media. The contact print zymograms are prepared by placing unfixed, unstained electrophoretograms in contact with a thin film of casein which has diffused into a layer of agarose supported by a hydrophilic polyester film. After staining the casein film with Coomassie blue, the proteolytic zones are detected as clear zones against a blue background. The method can detect as little as 9 ng of trypsin. The utility of the method is illustrated by detection of the proteinase enzymes in thermophilic actinomycete antigen preparations separated by polyacrylamide electrophoresis, crossed immunoelectrophoresis and isoelectric focusing on agarose and granulated dextran supports.

Effect of NaCl and nafcillin on penicillin-binding protein 2a and heterogeneous expression of methicillin resistance in Staphylococcus aureus.

Expression of methicillin resistance in heterogeneous strains of Staphylococcus aureus is enhanced by 2 to 5% NaCl in the medium and by selection with beta-lactam antibiotics. Resistance is associated with production of a penicillin-binding protein (PBP), PBP 2a, with low affinity for binding beta-lactam antibiotics. Therefore, the effects of NaCl and nafcillin on amounts of PBP 2a produced and its binding affinity were examined and correlated with expression of resistance. Nafcillin-triggered autolysis also was examined. No relationships between the level of resistance expressed and (i) relative amounts of PBP 2a, (ii) inducibility of PBP 2a by nafcillin, or (iii) binding affinity of nafcillin for PBP 2a were found. A protective effect of NaCl for the susceptible subpopulation, corresponding to inhibition of autolysis, was observed for heterogeneous strains. Even in the absence of NaCl, highly resistant cells were relatively tolerant to nafcillin-triggered autolysis. These results support the hypothesis that high levels of resistance require an additional factor besides PBP 2a. This factor may act within the autolytic pathway.

blaI and blaR1 regulate beta-lactamase and PBP 2a production in methicillin-resistant Staphylococcus aureus.

For Staphylococcus aureus, it is hypothesized that two genes located upstream of the beta-lactamase gene, blaZ, are required for the inducible expression of beta-lactamase. blaR1 is predicted to encode a signal-transducing membrane protein, and blaI is predicted to encode a repressor protein. These same two genes may also regulate the production of penicillin-binding protein 2a (PBP 2a), a protein essential for expression of methicillin resistance. To confirm that these two genes encode products that can control both beta-lactamase and PBP 2a production, blaI, blaR1, and blaZ with a 150-nucleotide deletion at the 3' end were subcloned from a 30-kb staphylococcal beta-lactamase plasmid and three beta-lactamase-negative strains of methicillin-resistant S. aureus were transformed with the recombinant plasmid containing that insert. The production of PBP 2a and a nonfunctional beta-lactamase was detected by fluorography and by immunoblots with polyclonal antisera directed against each of the proteins. Whereas the parent strains did not produce beta-lactamase and constitutively produced PBP 2a, PBP 2a and a truncated beta-lactamase were now inducible in the transformants. Therefore, two plasmid-derived genes regulate the production of both PBP 2a and beta-lactamase.

Cloning and sequence analysis of a class A beta-lactamase from Mycobacterium tuberculosis H37Ra.

A cosmid library from Mycobacterium tuberculosis H37Ra was introduced into Mycobacterium smegmatis, and eight recombinant clones with increased resistance to cefoxitin were identified. Isoelectric focusing detected an M. tuberculosis-derived beta-lactamase in one of these recombinant clones. A sequence analysis identified it as a class A beta-lactamase whose expression correlated with the increased resistance phenotype.

Value of serum tests in combined drug therapy of endocarditis.

Two in vitro tests, the serum killing level and the serum bactericidal rate assays, were evaluated for correlation with therapeutic efficacy in the rabbit model of Staphylococcus aureus endocarditis. Animals were treated with nafcillin alone and in combination with tobramycin or gentamicin. Both were effective therapies, but rapidity of vegetation sterilization by the single and combined regimens was shown by the serum bactericidal rate assay but not the serum killing level assay. As a direct measure of bactericidal activity in serum during therapy, the serum bactericidal rate assay may be a clinically useful supplemental test for providing information that the serum killing level assay cannot.

Evaluation of pefloxacin in experimental Escherichia coli meningitis.

The therapeutic efficacy of the fluoroquinolone pefloxacin mesylate was compared with those of cefotaxime and chloramphenicol in a rabbit model of Escherichia coli meningitis. The mean percent penetration (+/- the standard deviation) of pefloxacin (range, 1 to 30 mg/kg per h) into cerebrospinal fluid of infected rabbits was 51.3 +/- 14.0 compared with 11.1 +/- 1.0 for cefotaxime (100 mg/kg per h) and 22.3 +/- 1.5 for chloramphenicol (60 mg/kg per h). The rate of bacterial killing (delta log10 CFU/ml per h) did not change over a dosage range of 1 to 15 mg/kg per h (-0.37 +/- 0.15, 20% sterile). At 30 mg/kg per h, the rate achieved (-0.77 +/- 0.18, 100% sterile) was comparable to that of cefotaxime (-0.88 +/- 0.23, 100% sterile) and superior to that of chloramphenicol (-0.10 +/- 0.14, 0% sterile).

Serum bactericidal activity of rifampin in combination with other antimicrobial agents against Staphylococcus aureus.

Because rifampin-resistant strains of Staphylococcus aureus emerge during monotherapy with this drug, a search was made for potentially useful companion drugs. Bactericidal titers of spiked serum were determined, and time kill studies were performed for 10 strains of methicillin-susceptible S. aureus. We tested rifampin in combination with nafcillin, vancomycin, clindamycin, pefloxacin, ciprofloxacin, trimethoprim, teicoplanin, or erythromycin. The bactericidal activity of nafcillin, vancomycin, and teicoplanin was significantly reduced (P less than 0.05) when rifampin was added to the drug regimen. In contrast, the addition of rifampin to clindamycin or erythromycin significantly increased bactericidal activity as measured by both bactericidal titers in serum and 6-h killing rates (P less than 0.02). Bactericidal activity in serum was also increased by the addition of rifampin to trimethoprim, but rifampin-resistant strains emerged with this combination.

Serum bactericidal titer as a predictor of outcome in endocarditis.

A study was conducted in 89 rabbits with experimental aortic valve endocarditis caused by three different strains of Staphylococcus aureus to determine whether there was a correlation between the peak serum bactericidal titer of the four drugs tested and the vegetation titer. After four days of therapy both the rabbits with and those without sterile vegetations had median peak bactericidal titers of 1 : 8. The mean vegetation titers did not correlate with the mean bactericidal titers. The serum bactericidal test does not measure the relative rate of killing of the bacteria by the drugs. Although the test remains clinically useful for documentation of bactericidal activity, the minimum level of activity necessary for the test to serve as a predictor of outcome remains to be defined.

Kinetics of penicillin binding to penicillin-binding proteins of Staphylococcus aureus.

Reduced affinity of penicillin-binding proteins (PBPs) for binding penicillin has been proposed as a mechanism of beta-lactam antibiotic resistance in staphylococci. Penicillin binding by PBPs of three penicillin-susceptible and two penicillin-resistant strains of Staphylococcus aureus was studied in kinetic assays to determine rate constants, drug concentrations at which PBPs were bound and the relationship between concentrations that bound PBPs and concentrations that inhibited bacterial growth. PBPs 1 and 2 of the resistant strains exhibited slower acylation and more rapid deacylation than susceptible strains. In contrast PBP 4, a naturally low-affinity PBP, was modified such that it exhibited a lower rate of deacylation. The concentrations of penicillin at which modified PBPs were bound correlated with concentrations that inhibited growth of the resistant strains. Acquisition of penicillin resistance in these strains of S. aureus results, at least in part, from structural modifications affecting binding of multiple PBPs and appears to include recruitment of a non-essential PBP, PBP 4.

Altered production of penicillin-binding protein 2a can affect phenotypic expression of methicillin resistance in Staphylococcus aureus.

Altered production of penicillin-binding protein 2a (PBP 2a) may affect the phenotypic expression of resistance in methicillin-resistant Staphylococcus aureus (MRSA). COL, an MRSA strain that constitutively produces PBP 2a, was transformed with a recombinant plasmid containing the two beta-lactamase regulatory genes, blaI and blaR1, with either the beta-lactamase gene, blaZ, or a truncated blaZ. Both of the transformed MRSA strains now produced an inducible PBP 2a, and the MICs of nafcillin, methicillin, and imipenem for these strains were similar to those for the parental strain. A mutation in blaR1 that resulted in the complete repression of PBP 2a production altered the phenotypic expression of methicillin resistance in that strain, as evidenced by efficiency-of-plating experiments. Rather than being homogeneously resistant like COL, the blaR1 mutant strain now appeared to have a small resistant subpopulation. Gene products that regulate PBP 2a production may contribute to the organism's expression of methicillin resistance, but additional chromosomally located factors are required.

Comparative activity of CGP 31608, nafcillin, cefamandole, imipenem, and vancomycin against methicillin-susceptible and methicillin-resistant staphylococci.

The activity of CGP 31608 for 53 strains of Staphylococcus aureus and 48 strains of S. epidermidis, both methicillin susceptible and resistant, was compared with that of vancomycin, nafcillin, cefamandole, and imipenem. Microdilution MICs were determined in Mueller-Hinton broth with or without 2.5% NaCl at an inoculum of 3 x 10(5) CFU/ml with a 20-h, 37 degrees C incubation. The MICs of imipenem and CGP 31608 for methicillin-resistant strains were lower than the MICs of nafcillin or cefamandole for these strains; these differences diminished in the presence of 2.5% NaCl. Subpopulations were detected in strains of methicillin-resistant S. aureus and S. epidermidis that were resistant to all the beta-lactam antibiotics tested at 5 micrograms/ml. This resistant subpopulation produced progeny that were uniformly resistant to high concentrations of each of the beta-lactams.

Single, large, daily dosing versus intermittent dosing of tobramycin for treating experimental pseudomonas pneumonia.

Single, large, daily aminoglycoside doses in animals are less toxic than conventional dosing, and higher drug concentrations in vitro produce more-rapid bacterial killing. Thus, we compared various aminoglycoside dosing schedules in neutropenic (n = 153) and nonneutropenic (n = 192) guinea pigs with Pseudomonas aeruginosa pneumonia. Equivalent tobramycin dosages were given: 5 mg/kg every 4 h or 30 mg/kg every 24 h. Animals were serially killed during therapy, and quantitative lung cultures were performed. Bacterial titers in lungs dropped rapidly in all tobramycin-treated animals, both neutropenic and nonneutropenic, during the initial 16 h of therapy. In nonneutropenic guinea pigs, lung titers remained constant despite continued 4-h dosing. With subsequent 24-h dosing, titers continued to drop, and by 72 h there were a significant number of animals with sterile lungs (P less than .01). In neutropenic guinea pigs given tobramycin every 24 h, bacterial regrowth occurred; thus, therapy was ineffective. Adding mezlocillin, however, suppressed regrowth; thus, combination therapy was superior (P less than .05).

Single versus combination antibiotic therapy for pneumonia due to Pseudomonas aeruginosa in neutropenic guinea pigs.

Studies of therapy for experimental pneumonia due to Pseudomonas aeruginosa have failed to document beta-lactam-aminoglycoside synergy for most antibiotics examined, in contrast to results usually observed with pseudomonas infections at other sites. The neutropenic guinea-pig model of pseudomonas pneumonia was modified to resemble more closely therapy for clinical infections. Animals were treated 16 hr after infection with ticarcillin, azlocillin, ceftazidime, tobramycin, and netilmicin, alone and in combination. As predicted by in vitro synergy testing, in all cases combination drug therapy was more effective than the corresponding drugs given alone (P less than .05), as assessed by quantitative lung culture. Among single-drug regimens, those in which peak antibiotic levels did not exceed the minimal bactericidal concentration for the organism were significantly less effective. Resistance to aminoglycosides did not develop during therapy, and therefore, in this study does not explain the mechanism of synergy observed with beta-lactam antibiotics.

Activities of pefloxacin and ciprofloxacin in experimentally induced Pseudomonas pneumonia in neutropenic guinea pigs.

Pefloxacin and ciprofloxacin are two new quinoline carboxylic acid derivatives that have activity in vitro against a wide range of gram-negative bacteria, including Pseudomonas aeruginosa. Using a well-standardized model of Pseudomonas pneumonia in neutropenic guinea pigs, we tested the efficacy in vivo of these new agents. Both were highly effective in increasing survival and decreasing bacterial counts in the lungs of surviving animals. Pefloxacin and ciprofloxacin were significantly better (P less than 0.05) than aminoglycosides or beta-lactams tested in prior studies with this model, and they were as effective as combination therapy with aminoglycosides and beta-lactams. Resistance to either ciprofloxacin or pefloxacin did not emerge during the study period. Further studies with these drugs in the therapy of Pseudomonas sp. infections are warranted.

Characterization of precipitin response to Micropolyspora faeni in farmer's lung disease by quantitative immunoelectrophoresis.

Sera from 12 patients with farmer's lung disease (FLD) drawn during an acute episode and displaying precipitins to Micropolyspora faeni were analyzed by crossed immunoelectrophoresis with an intermediate gel combined with a rabbit reference precipitate system. Forty-six precipitin arcs were identified in the reference system, and FLD sera reacted with 36 of these antigens. The FLD sera displayed significantly more precipitates and higher precipitin scores when compared with sera from 16 precipitin-positive subjectw who did not have FLD. However, there was overlap between the 2 groups, and neither measurement distinguished the 2 persons who became ill after challenge from one person who did not. Three disease specific antigens were identified that may have special relevance for pathogenesis of disease. Ten exposure-relevant antigens were also identified. We propose that these antigens be important components of a standardized M. faeni antigen preparation.

Characterization of synthetic medium antigens of Micropolyspora faeni and Thermoactinomyces candidus.

A synthetic (Syn) medium was developed for growth of Micropolyspora faeni and Thermoactinomyces candidus, and optimum conditions for culture filtrate antigen production were found to be 3 days for T. candidus and 9 to 12 days for M. faeni. Appearance of proteolytic activity in the culture fluid supernatant coincided with a decrease in precipitating antigen content, protein content, and number of proteins on polyacrylamide gel electrophoresis (PAGE), probably as a result of proteolysis. The results suggest that protein content, number protein bands on PAGE, and proteolytic activity are predictive of precipitating antigen content. Antigens prepared in Syn medium were compared to those produced by the double-dialysis procedure and found to contain adequate amounts of antigenic material of sufficient quality to warrant clinical studies of their usefulness in the diagnosis of hypersensitivity pneumonitis.

Efficacy of ciprofloxacin for experimental endocarditis caused by methicillin-susceptible or -resistant strains of Staphylococcus aureus.

The efficacy of ciprofloxacin for experimental aortic valve endocarditis in rabbits infected by either a methicillin-susceptible or a methicillin-resistant strain of Staphylococcus aureus was compared with standard therapy of nafcillin or vancomycin, respectively. After 4 days of therapy, ciprofloxacin reduced the counts of organisms in aortic valve vegetations as effectively as the standard regimen for both susceptible and resistant strains. Mean concentrations of ciprofloxacin in serum achieved 1 h after a dose exceeded the MBC for each strain by twofold or less. In these experiments ciprofloxacin was as efficacious as standard regimens currently used to treat staphylococcal infections in humans.

Ciprofloxacin in experimental Pseudomonas aeruginosa meningitis in rabbits.

The potential of ciprofloxacin for the therapy of Pseudomonas aeruginosa meningitis was evaluated in an animal model by determining the penetration of the drug into CSF, its concentration-dependent killing characteristics in vivo, and its relative efficacy compared with ceftazidime and tobramycin. Meningitis was produced in 40 rabbits by intracisternal injection of 3 X 10(7) organisms. The drugs were administered intravenously over seven hours, and simultaneously serum and CSF samples were taken at 0, 1, 3, 5, and 7 h for determination of drug concentration and CSF bacterial counts. The percentage penetration of ciprofloxacin (18.4 +/- 12.3; mean +/- standard deviation) in infected rabbits was substantially increased over that found in uninfected rabbits (4.1 +/- 1.3). The rate of bacterial killing for animals treated with ceftazidime (100 mg/kg/h) and high doses of tobramycin (2.5 mg/kg/h) was -0.51 +/- 0.13 (log10 cfu/ml/h). This was similar to the rate of killing (-0.48 +/- 0.2) found when ciprofloxacin was infused at 5 mg/kg/h, a dose that produced a mean serum level of 6.7 +/- 4.6 mg/l, which corresponds to concentrations achievable in humans. As dosages were increased (15 and 30 mg/kg/h), the rate of bacterial killing also increased (-0.70 +/- 0.1 and -0.89 +/- 0.4 respectively; r = 0.7407; P less than 0.01). The drugs shows promise in the treatment of pseudomonas meningitis.