Staphylococcus aureus AbcA transporter enhances persister formation under β-lactam exposure

We evaluated the role of Staphylococcus aureus AbcA transporter in bacterial persistence and survival following exposure to the bactericidal agents nafcillin and oxacillin at both the population and single-cell levels. We show that AbcA overexpression resulted in resistance to nafcillin but not oxacillin. Using distinct fluorescent reporters of cell viability and AbcA expression, we found that over 6-14 hours of persistence formation, the proportion of AbcA reporter-expressing cells assessed by confocal microscopy increased sixfold as cell viability reporters decreased. Similarly, single-cell analysis in a high-throughput microfluidic system found a strong correspondence between antibiotic exposure and AbcA reporter expression. Persister cells grown in the absence of antibiotics showed neither an increase in nafcillin MIC nor in abcA transcript levels, indicating that survival was not associated with stable mutational resistance or abcA overexpression. Furthermore, persister cell levels on exposure to 1×MIC and 25×MIC of nafcillin decreased in an abcA knockout mutant. Survivors of nafcillin and oxacillin treatment overexpressed transporter AbcA, contributing to an enrichment of the number of persisters during treatment with pump-substrate nafcillin but not with pump-non-substrate oxacillin, indicating that efflux pump expression can contribute selectively to the survival of a persister population.

Acetylenic spiroketal enol ethers from Artemisia rupestris and their synergistic antibacterial effects on methicillin-resistant Staphylococcus aureus

Synergistic bioassay-guided isolation of the extracts of Artemisia rupestris L, which belongs to the family Asteraceae, afforded two acetylenic spiroketal enol ethers, namely rupesdiynes A (1) and B (2). Their structures were determined based on spectroscopic analysis and experimental and calculated ECD investigations. The two compounds exhibited synergistic activity and were able to reduce the minimum inhibitory concentration (MIC) of oxacillin four-fold, with a fractional inhibitory concentration index (FICI) of 0.5 in combination with oxacillin against the oxacillin-resistant EMRSA-16. Biofilm formation inhibitory and Ethidium bromide (EtBr) efflux assay were further employed to verify the possible mechanism of the synergistic antibacterial effect. Additionally, molecular docking studies were conducted to investigate the binding affinities of the two compounds with penicillin-binding protein 2a (PBP2a) of EMRSA-16. Taken together, rupesdiynes A (1) and rupesdiyne B (2) showed moderate synergistic activity against EMRSA-16 with oxacillin via inhibiting biofilm formation and efflux pump activity, respectively.

Combining the dual antibacterial and regenerative activities of platelet-rich plasma with β-lactams to mitigate MRSA-infected skin wounds

The emergence of multidrug-resistant bacteria contributes to the necessity of developing novel infection treatment approaches. This study was designed to evaluate the antimicrobial and wound healing activities of platelet-rich plasma (PRP) in combination with β-lactams (ampicillin and/or oxacillin) for the application on methicillin-resistant Staphylococcus aureus (MRSA)-infected skin. PRP was collected from the peripheral blood of healthy donors. The anti-MRSA activity was tested through a growth inhibition curve, colony-forming unit (CFU), and SYTO 9 assay. The PRP incorporation lowered the minimum inhibitory concentration (MIC) of ampicillin and oxacillin against MRSA. The combination of β-lactams together with PRP showed a three-log CFU reduction of MRSA. The major components of PRP for eliminating MRSA were found to be the complement system and iron sequestration proteins, according to the proteomic analysis. The adhesive bacterial colony in the microplate was decreased from 2.9 × 107 to 7.3 × 105 CFU after the treatment of cocktails containing β-lactams and PRP. The cell-based study indicated that keratinocyte proliferation was stimulated by PRP. The in vitro scratch and transwell experiments revealed that PRP improved keratinocyte migration. In the MRSA-infected mouse skin model, PRP appeared to show a synergistic effect for wound area reduction by 39% when combined with β-lactams. The MRSA burden in the infected area was lessened two-fold after topical administration of the combined β-lactams and PRP. PRP inhibited macrophage infiltration in the wound site to shorten the inflammatory phase and accelerate the initiation of the proliferative phase. No skin irritation was detected with the topical delivery of this combination. Our findings suggested that β-lactams plus PRP was applicable to alleviate the problems associated with MRSA via dual antibacterial and regenerative activities.

Inhibition of peptidoglycan synthesis is sufficient for total arrest of staphylococcal cell division

Bacterial cell wall biosynthesis is the target of many important antibiotics. Its spatiotemporal organization is closely coordinated with cell division. However, the role of peptidoglycan synthesis within cell division is not fully understood. Even less is known about the impact of antibiotics on the coordination of these two essential processes. Visualizing the essential cell division protein FtsZ and other key proteins in Staphylococcus aureus, we show that antibiotics targeting peptidoglycan synthesis arrest cell division within minutes of treatment. The glycopeptides vancomycin and telavancin completely inhibit septum constriction in all phases of cell division. The beta-lactam oxacillin stops division progress by preventing recruitment of the major peptidoglycan synthase PBP2 to the septum, revealing PBP2 as crucial for septum closure. Our work identifies cell division as key cellular target of these antibiotics and provides evidence that peptidoglycan synthesis is the essential driving force of septum constriction throughout cell division of S. aureus.

The activity of 16 new hydantoin compounds on the intrinsic and overexpressed efflux pump system of Staphylococcus aureus

AIM

To evaluate a new series of 16 hydantoin derivatives for activity against the intrinsic and overexpressed efflux pumps of the ATTC 25923 Staphylococcus aureus and the clinical Staphylococcus aureus HPV-107 strain, respectively.

MATERIALS AND METHODS

The hydantoin compounds were evaluated for activity against the efflux pumps of the ATTC 25923 S. aureus and the clinical S. aureus HPV-107 strains by the aid of the automated ethidium bromide method. Compounds that inhibited the efflux pumps of either strain were evaluated for ability to reduce or reverse resistance of these strains to oxacillin.

RESULTS

Although most of the hydantoins inhibited the efflux pumps of the ATTC strain, none reduced the resistance of this strain to oxacillin. In contrast, the inhibition of the Qac efflux pump present in HPV-107 was inhibited to some degree, by much higher concentrations of the hydantoin compounds than that needed for similar activity against the ATTC strain; only hydantoin PI8a significantly reduced the minimum inhibitory concentration of oxacillin against the HPV-107 strain.

CONCLUSION

Hydantoin compound PI8a may have potential for therapy of a methicillin-resistant S. aureus infection whose multidrug-resistant phenotype is due to overexpression of an efflux pump.

Analysis of surface plasmon spectro-angular reflectance spectrum: real-time measurement, resolution limits, and applications to biosensing

A surface plasmon biosensing technique based on real-time measurement of the spectro-angular reflectance spectrum of a gold surface is presented. A significant improvement in refractive index resolution and drift compensation has been achieved for the spectro-angular technique to demonstrate a biosensing platform that is, in addition, applicable to plasmonic bandgap measurements. Instrumental improvements are detailed and constants for the model bovine serum albumin (BSA):oxacillin bioassay are presented.

[Diffusion and diffusion-osmosis models of the charged macromolecule transfer in barriers of biosystems]

Mathematical models of the transfer of charged macromolecules have been constructed on the basis of the classical equations of electromigration diffusion of Helmholtz-Smolukhovskii, Goldman, and Goldman-Hodgkin-Katz. It was shown that ion transfer in placental (mimicking lipid-protein barriers) and muscle barriers occurs by different mechanisms. In placental barriers, the electromigration diffusion occurs along lipid-protein channels formed due to the conformational deformation of phospholipid and protein molecules with the coefficients of diffusion D = (2.6-3.6) x 10(-8) cm2/s. The transfer in muscle barriers is due to the migration across charged interfibrillar channels with the negative diffusion activation energy, which is explained by changes in the structure of muscle fibers and expenditures of thermal energy for the extrusion of Cl- from channel walls with the diffusion coefficient D = (6.0-10.0) x 10(-6) cm2/s.

Comparison of beta-lactamases of classes A and D: 1.5-A crystallographic structure of the class D OXA-1 oxacillinase

The crystallographic structure of the Escherichia coli OXA-1 beta-lactamase has been established at 1.5-A resolution and refined to R = 0.18. The 28.2-kD oxacillinase is a class D serine beta-lactamase that is especially active against the penicillin-type beta-lactams oxacillin and cloxacillin. In contrast to the structures of OXA-2, OXA-10, and OXA-13 belonging to other subclasses, the OXA-1 molecule is monomeric rather than dimeric and represents the subclass characterized by an enlarged Omega loop near the beta-lactam binding site. The 6-residue hydrophilic insertion in this loop cannot interact directly with substrates and, instead, projects into solvent. In this structure at pH 7.5, carboxylation of the conserved Lys 70 in the catalytic site is observed. One oxygen atom of the carboxylate group is hydrogen bonded to Ser 120 and Trp 160. The other oxygen atom is more exposed and hydrogen bonded to the Ogamma of the reactive Ser 67. In the overlay of the class D and class A binding sites, the carboxylate group is displaced ca. 2.6 A from the carboxylate group of Glu 166 of class A enzymes. However, each group is equidistant from the site of the water molecule expected to function in hydrolysis, and which could be activated by the carboxylate group of Lys 70. In this ligand-free OXA-1 structure, no water molecule is seen in this site, so the water molecule must enter after formation of the acyl-Ser 67 intermediate.

Chemiluminescence detection coupled to high-performance frontal analysis for the determination of unbound concentrations of drugs in protein binding equilibrium

High-performance frontal analysis coupled with chemiluminescence detection (HPFA-CL) was developed for the determination of unbound oxacillin concentration in human serum albumin solution. The HPFA system consisted of an ISRP column and a mobile phase of 67 mM potassium phosphate buffer of pH 7.4 and ionic strength of 0.17. The luminol-H2O2-Co2+ system was used in the chemiluminescence detection. An enhancement of luminol chemiluminescence by oxacillin was investigated and employed for determining the concentration of oxacillin in the HPFA eluate. Sample solutions were directly injected onto the column; the drug was eluted as a zonal peak with a plateau region. The unbound drug concentrations were determined by using the height of the plateau. The results agreed with those obtained with conventional ultrafiltration-HPLC method. Good reproducibility was confirmed by the within run and between run RSD < or = 7.4%. HPFA-CL provided a selective method for determination of unbound drug concentration in protein binding equilibrium.

Oxacillin susceptibility testing of coagulase-negative staphylococci using the disk diffusion method and the Vitek GPS-105 card

One hundred and ninety-three isolates of coagulase-negative staphylococci (CoNS) were tested against oxacillin by agar dilution, disk diffusion, and Vitek (GPS-105 card), and the presence of the mecA gene determined by multiplex PCR. The results obtained by all testing methods were in agreement for 190 isolates. Two mecA-negative isolates (S. lugdunensis and S. haemolyticus) had MICs of < or = 0.25 microg/ml by agar dilution and Vitek but were resistant by disk diffusion. One mecA-positive isolate was resistant by Vitek and disk diffusion but had an agar dilution MIC of < or = 0.25 microg/ml. For the species of CoNS tested, oxacillin susceptibility results obtained with the Vitek GPS-105 card and disk diffusion correlated well with results obtained by National Committee for Clinical Laboratory Standards agar dilution and with the presence of the mecA gene.

Evaluation of an anti-PBP 2a slide latex agglutination test in coagulase-negative staphylococci isolated in Greek hospitals

Oxacillin resistance was examined in 258 coagulase-negative staphylococci from Greek hospitals. mecA DNA was detected in 168 isolates, which were also resistant to oxacillin by agar dilution and disk diffusion, according to the current NCCLS breakpoints. Both methods exhibited a relatively low specificity misclassifying 21 and 19 of the 90 mecA-negative isolates respectively as oxacillin resistant. In contrast, an anti-PBP 2a latex agglutination test, applied after induction by oxacillin, correctly classified 163 mecA-positive (sensitivity 97%) and 88 mecA-negative isolates (specificity 97.7%).

Investigation of oxacillin-hydrolyzing beta-lactamase in borderline methicillin-resistant clinical isolates of Staphylococcus aureus

BACKGROUND

Mechanisms of borderline resistance of Staphylococcus aureus to penicillinase-resistant penicillins (PRPs) may include hyperproduction of classical penicillinase and/or production of beta-lactamase hydrolyzing also PRPs.

METHODS

beta-Lactamase activity of whole cells and purified enzymes was estimated spectrophotometrically and in isolated cytoplasmic membranes by bioassay with Bacillus subtilis as test strain.

RESULTS

Out of 53 clinical isolates of S. aureus, 18 showed oxacillin MIC values from 0.5 to 2 microg/ml, which were reduced by sulbactam and/or clavulanic acid in the case of four isolates producing large quantities of inducible, type A beta-lactamase. Cytoplasmic membranes isolated from these strains showed oxacillin-hydrolyzing activity. One of these strains was grown also in the presence of globomycin, an antibiotic known to interfere with the anchorage of membrane lipoproteins; this treatment eliminated the oxacillin-hydrolyzing activity.

CONCLUSIONS

The resistance in these strains was due to a membrane-bound lipoprotein with oxacillin-hydrolyzing activity.

OXA-18, a class D clavulanic acid-inhibited extended-spectrum beta-lactamase from Pseudomonas aeruginosa

Clinical isolate Pseudomonas aeruginosa Mus showed resistance both to extended-spectrum cephalosporins and to aztreonam. We detected a typical double-disk synergy image when ceftazidime or aztreonam was placed next to a clavulanic acid disk on an agar plate. This resistance phenotype suggested the presence of an extended-spectrum beta-lactamase. Isoelectric focusing revealed that this strain produced three beta-lactamases, of pI 5.5, 7.4, and 8.2. A 2.6-kb Sau3A fragment encoding the extended-spectrum beta-lactamase of pI 5.5 was cloned from P. aeruginosa Mus genomic DNA. This enzyme, named OXA-18, had a relative molecular mass of 30.6 kDa. OXA-18 has a broad substrate profile, hydrolyzing amoxicillin, ticarcillin, cephalothin, ceftazidime, cefotaxime, and aztreonam, but not imipenem or cephamycins. Its activity was totally inhibited by clavulanic acid at 2 microg/ml. Hydrolysis constants of OXA-18 (Vmax, Km) confirmed the MIC results. Cloxacillin and oxacillin hydrolysis was noticeable with the partially purified OXA-18. The blaOXA-18 gene encodes a 275-amino-acid protein which has weak identity with all class D beta-lactamases except OXA-9 and OXA-12 (45 and 42% amino acid identity, respectively). OXA-18 is likely to be chromosomally encoded since no plasmid was found in the strain and because attempts to transfer the resistance marker failed. OXA-18 is peculiar since it is a class D beta-lactamase which confers high resistance to extended-spectrum cephalosporins and seems to have unique hydrolytic properties among non-class A enzymes.

Oxacillin-hydrolyzing beta-lactamase involved in resistance to imipenem in Acinetobacter baumannii

Acinetobacter baumannii strain A148, a clinical isolate resistant to imipenem (MIC = 32 mg l-1), synthesized two beta-lactamases with pIs 6.3 and > 9.2. The pI 6.3 enzyme hydrolyzed the penicillins, including isoxazoylpenicillins, first-, second- and, to a lesser extent, third-generation cephalosporins. It was inhibited by chloride ions and by the penem beta-lactamase inhibitor BRL 42715. Clavulanate was a weak inhibitor and EDTA did not affect the beta-lactamase activity. This enzyme also hydrolyzed imipenem with a catalytic efficiency (Kcat/Km) of 1500 mM-1 s-1. Moreover, this purified beta-lactamase produced a positive microbiological clover-leaf test with imipenem. Therefore, the pI 6.3 beta-lactamase was considered to be involved in the imipenem resistance of A. baumannii strain A148.

Mass spectral kinetic study of acylation and deacylation during the hydrolysis of penicillins and cefotaxime by beta-lactamase TEM-1 and the G238S mutant

The G238S substitution found in extended-spectrum natural mutants of TEM-1 beta-lactamase induces a new capacity to hydrolyze cefotaxime and a large loss of activity against the good substrates of TEM-1. To understand this phenomenon at the molecular level, a method to determine the acylation and deacylation elementary rate constants has been developed by using electrospray mass spectrometry combined with UV spectrophotometry. The hydrolysis of penicillins and cefotaxime by TEM-1 and the G238S mutant shows that the behavior of penicillins and cefotaxime is very different. With both enzymes, the limiting step is deacylation for penicillin hydrolysis, but acylation for cefotaxime hydrolysis. Further analyses of the G238S mutant show that the loss of activity against penicillins is due to a large decrease in the deacylation rate and that the increase in catalytic efficiency against cefotaxime is the result of a better Km and an increased acylation rate. These modifications of the elementary rate constants and the hydrolytic capacity in the G238S mutant could be linked to structural effects on the omega-loop conformation in the active site.

A survey of the kinetic parameters of class C beta-lactamases. Penicillins

The interaction between six class C beta-lactamases and various penicillins has been studied. All the enzymes behaved in a very uniform manner. Benzylpenicillin exhibited relatively low kcat. values (14-75 s-1) but low values of Km resulted in high catalytic efficiencies [kcat./Km = 10 X 10(6)-75 X 10(6) M-1.s-1]. The kcat. values for ampicillin were 10-100-fold lower. Carbenicillin, oxacillin cloxacillin and methicillin were very poor substrates, exhibiting kcat. values between 1 x 10(-3) and 0.1 s-1. The Km values were correspondingly small. It could safely be hypothesized that, with all the tested substrates, deacylation was rate-limiting, resulting in acyl-enzyme accumulation.

Inducible oxacillin-hydrolyzing beta-lactamase in a methylotrophic bacterium

A novel beta-lactamase (beta-lactam-hydrolase, EC 3.5.2.6) was detected in a culture of Pseudomonas C, an obligatory methylotroph. This is the first beta-lactamase discovered in a methylotrophic organism. The inducible cell-bound enzyme with broad-spectrum activity against penicillins, was purified 77-fold from cell extracts of the methanol-grown bacterium, and its molecular weight was estimated to be 30,000. As a group, the isoxazolyl penicillins are the favored substrates, while cephalosporins are resistant to hydrolysis and act as mild competitive inhibitors. The activity of this M-OXA beta-lactamase focused as a single band at an acidic pI value (5.5) similar to that of PSE- and TEM-type enzymes, but can be clearly distinguished from other OXA-type beta-lactamases, all of which focus in the alkaline region. The enzyme is coded by a non-transferable gene. Based on the sum of its physical and biochemical properties, the M-OXA beta-lactamase is distinguishable from all previously described beta-lactamases, although immunological studies revealed some cross reactivity with the plasmid mediated OXA-2 enzyme.

Antibiotic penetration into rabbit nucleus pulposus

A rabbit model was used to determine the penetration of four commonly used antibiotics (clindamycin, tobramycin, cephalothin, and oxacillin) into the nucleus pulposus after receiving an 8-hour course of intramuscular antibiotic injections. Clindamycin and tobramycin achieved therapeutic levels in the nucleus pulposus and both were present in greater than 50% of serum levels. Cephalothin was not detected in the nucleus pulposus and penetrated at less than 4% of serum levels at 1 hour after injection. The data were inconclusive regarding oxacillin penetration.

Comparative study of the effects of some inducers with or without protein binding properties on bioavailability of isoxazolylpenicillins in rats

The effect of various inducers with or without protein binding properties on serum levels and half life of Oxacillin, Cloxacillin and Dicloxacillin was studied. A total of 102 male rats classified in 3 "categories" according to the administered penicillin with 6 groups of rats in each of them were used. Each group was pretreated for 15 days with the following inducers: phenobarbital, diphenylhydantoin, diazepam, chlorpromazine and phenylbutazone. The control groups received saline. The d-glucaric acid concentration in the urine prior to and after the administration of inducers and the liver weight were taken as enzyme induction indices. The results showed a decrease of serum levels and half life of three penicillins with a negative correlation between urine d-glucaric acid and serum penicillin levels. Phenobarbital, diphenylhydantoin and chlorpromazine affected the 3 penicillins in the following statistically significant order: oxacillin, dicloxacillin, cloxacillin. Diazepam affected: cloxacillin, dicloxacillin, oxacillin, and phenylbutazone: dicloxacillin, cloxacillin and oxacillin. However all drugs finally produced a uniform effect on all 3 penicillins in the following decreasing order: phenobarbital (r = -0.910), diphenylhydantoin (r = -0.864), phenylbutazone (r = -0.851), chlorpromazine (r = -0.842) and diazepam (r = -0.821). For all inducers, the effect was most significant for oxacillin (r = -0.869), second most significant for dicloxacillin (r = -0.811) and finally for cloxacillin (r = -0.778). The results suggested an interaction of isoxazolylpenicillins and the above drugs.

Human vitreous levels of selected antistaphylococcal antibiotics

Staphylococcus epidermidis and S. aureus are the most common causes of bacterial endophthalmitis. A study of the penetration of selected antistaphylococcal antibiotics into human vitreous was undertaken in 58 patients. After 2-g intravenous doses of cephalothin, cefazolin, methicillin, oxacillin, or nafcillin were given to patients about to undergo vitreous surgery, mean vitreous levels for each antibiotic were as follows: cephalothin, 0.97 microgram/ml in diabetics and 0.69 microgram/ml in nondiabetics; cefazolin, 0.84 microgram/ml in diabetics and 1.6 microgram/ml in nondiabetics; methicillin, 2.56 micrograms/ml in diabetics and 2.64 micrograms/ml in nondiabetics; oxacillin, 0.62 microgram/ml in diabetics and 0.34 microgram/ml in nondiabetics; and nafcillin, 0.73 microgram/ml in diabetics and 0.75 microgram/ml in nondiabetics. Only cefazolin produced vitreous concentrations consistently above its minimum inhibitory concentration for 90% of S. epidermidis isolates. Staphylococcus aureus isolates were not similarly covered. There was a trend toward higher vitreous antibiotic concentrations in patients with proliferative vitreoretinopathy and rubeosis.

[Molecular mechanism of oxacillin interaction with human serum albumin studied by microcalorimetry]

Interaction of oxacillin, a semisynthetic penicillin, with human serum albumin (HSA) was studied by means of reaction isothermal and differential scanning microcalorimetry. The antibiotic bound with one primary and two secondary active protein sites. The first bound molecule of the drug had a significant effect on conformation of the biopolymer, which was evident from increased enthalpy and denaturation temperature of the complex as compared to pure HSA. However, the increased thermostability of the serum albumin on its association with oxacillin did not impair the cooperative nature of the thermal denaturation of globular protein. Analysis of the thermodynamic parameters of the complex formation suggested the presence of hydrophobic and electrostatic interactions. The role of electrostatic interaction increased with a decrease in the solution ionic strength.

[Penetration of ampicillin and oxacillin into the tissues of rats with aseptic inflammation]

Penetration of 2 penicillins with different indices of serum protein binding in the tissues of rats with aseptic inflammation was studied. The pharmacokinetics of both penicillins in the blood serum (total preparation) did not differ. However, the level of the ampicillin free fraction was much higher than that of oxacillin. In the inflammation exudate and inflamed tissues, the maximum concentrations of free ampicillin and the area below its pharmacokinetic curve were also higher than those of oxacillin. The rate of elimination of both antibiotics from the exudate was the same. The period of half elimination of the drugs from the exudate and inflamed tissue was significantly higher than the period of their half elimination from the blood serum. High positive correlation between the ampicillin levels in the blood serum and inflamed and intact tissues was shown. As for oxacillin, positive correlation between its levels in the blood serum and inflamed tissue was observed.

A model system to demonstrate that beta-lactamase-associated antibiotic trapping could be a potential means of resistance

Addition of beta-lactamase to cultures of antibiotic-sensitive Escherichia coli protected the bacteria against lysis induced by either a hydrolyzable (cephalothin) or relatively nonhydrolyzable (ceftriaxone) cephalosporin. The later addition of a nonhydrolyzable, non-lysis-inducing beta-lactam antibiotic (oxacillin), which had a higher affinity for the beta-lactamase than ceftriaxone, allowed the reversal of the protection and the onset of lysis. These results suggest that trapping of the antibiotic by the enzyme, without significant hydrolysis, is a reversible process that may play a role in the resistance of some gram-negative bacteria to third-generation cephalosporins.

Laboratory evaluation of the serum dilution test in serious staphylococcal infection

Four test media were studied to determine performance characteristics of serum dilution tests used to monitor antimicrobial therapy during serious Staphylococcus aureus infection being treated with highly protein-bound antibiotics. Serum inhibitory titers and serum bactericidal titers obtained with Mueller-Hinton broth supplemented with calcium and magnesium were 3- to 16-fold higher than titers obtained with whole human serum buffered with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES). In cation-supplemented Mueller-Hinton containing 5% albumin or in cation-supplemented Mueller-Hinton combined with an equal volume of human serum, titers were 2- to 5-fold higher than in whole human serum buffered with HEPES. Clinical or animal studies are needed to establish whether the higher titers observed with patient serum containing highly protein-bound drugs diluted in low protein-content media would foster inadequate dosage regiments. In the meantime, both infectious disease clinicians and microbiologists should be aware of this potential pitfall.

Effects of mezlocillin on the pharmacokinetics of oxacillin and dicloxacillin

The pharmacokinetics of oxacillin and dicloxacillin, with and without the coadministration of mezlocillin, were studied in 16 patients with normal or severely impaired renal function. After a single administration to patients in terminal renal failure a decrease in total oxacillin clearance from 279 to 159 ml/min/1.73 m2 and total dicloxacillin clearance from 249 to 43 ml/min/1.73 m2 was observed. After coadministration of mezlocillin total oxacillin clearance fell by 38% in all patients irrespective of their renal function. This was caused by a reduction in renal and non-renal elimination rather than by a change in the volume of distribution. With the exception of a minor reduction in renal excretion, the pharmacokinetics of dicloxacillin showed no significant changes. In terminal renal failure the oxacillin dose needs to be reduced by half only when combined with mezlocillin. For dicloxacillin, however, the same dosage adjustment is required irrespective of whether administration is single or combined.

Tn2011, a new transposon encoding oxacillin-hydrolyzing beta-lactamase

The type II penicillinase (oxacillin-hydrolyzing beta-lactamase, OXA-1) gene on plasmid Rms213 was transposed to various plasmids or to the host chromosome. The transposon bearing this gene, designated Tn2011, conferred resistance to ampicillin, streptomycin, sulfonamide, and mercuric chloride. By restriction endonuclease digestion and agarose gel electrophoresis, the molecular weight of Tn2011 was estimated to be 12.5 X 10(6). The transposition frequency of Tn2011 was about 10(-4) to 10(-5). The activity of type II penicillinase is related to the copy number of the replicon bearing Tn2011.

[Penetration of mezlocillin and oxacillin into the glandular and adipose tissue of the breast after simultaneous intravenous infusion. A pharmacokinetic study]

The concentrations of mezlocillin and oxacillin were measured after simultaneous intravenous infusion of 4 and 2 g respectively in serum, fat and mammary gland tissue of 35 patients. The maximum mean concentrations of mezlocillin were measured in serum with 281 micrograms/ml and in fat with 38 micrograms/g after the end of the infusion and in the mammary gland with 52.3 micrograms/g after 90 minutes. Mezlocillin concentrations of less than or equal to 2.0 micrograms/ml and g respectively were found after 6-8 hours after the end of the infusion. The maximum mean concentrations of oxacillin were measured in the serum with 107.8 micrograms/ml also after the end of the infusion, declining to levels less than or equal to 2.0 micrograms/ml within 6 hours. Measurable oxacillin-concentrations could not be found in the fat and in the tissue of mammary gland with the chosen dose. The clinical relevance of the results is discussed.

Ocular penetration of subconjunctival oxacillin, methicillin, and cefazolin in rabbits with staphylococcal endophthalmitis

The concentrations of oxacillin, methicillin, and cefazolin were examined in the infected eyes of pigmented rabbits with Staphylococcus aureus endophthalmitis after a subconjunctival dose of 100 mg. The three drugs had fairly similar ocular pharmacokinetics. The tissue concentration usually peaked within 30 min. Levels in the aqueous humor rose more slowly; the respective maximal concentrations of methicillin, oxacillin, and cefazolin were 72, 1,180, and 111 micrograms/ml. Oxacillin also produced the highest levels in the cornea. Penetration of the vitreous humor was poor with all three drugs, apparently owing to a diffusional barrier in the choroid-retina tissue complex. The respective median vitreous levels of methicillin, oxacillin, and cefazolin were 0.7, 0.6, and less than 0.8 micrograms/ml. These values are close to the concentrations usually required to inhibit S. aureus in vitro. Our results suggest that subconjunctival oxacillin achieves higher concentrations in anterior ocular tissues than do the other two drugs, but more aggressive approaches are necessary in treating endophthalmitis.

Effect of method of administration on extravascular penetration of four antibiotics

The effect of both method of drug administration and serum protein binding on antibiotic penetration into subcutaneous Visking chambers was studied in rabbits. Ampicillin and oxacillin were administered by either repeated intramuscular injection of 30 mg/kg every 4 h or by constant infusion of 7.5 mg/kg per h for 24 h. Gentamicin was given by intramuscular injection of 4 mg/kg every 4 h for 28 h and by constant infusion of 1 mg/kg per h for 24 h. Amikacin was given by intramuscular injection of 8 mg/kg every 4 h for 12 h and by constant intravenous infusion of 2 mg/kg per h for 12 h. Protein binding to rabbit serum was 73% for oxacillin, 9% for ampicillin, 19% for gentamicin, and 0% for amikacin. Chamber concentrations achieved for oxacillin, gentamicin, and amikacin were not significantly different for constant infusion versus intermittent administration. For ampicillin, chamber concentration was slightly higher by constant infusion than by intermittent administration (P less than 0.02). Fluctuations in drug concentration from peak to trough values in the chambers during the intermittent administration studies were markedly dampened when compared with serum fluctuations. This study demonstrates that whereas steady state is reached more rapidly by intermittent administration, the mean steady-state concentration of an antibiotic achieved at an extravascular site is the same or greater by constant infusion than by intermittent dosing. This is true for highly protein bound antibiotics as well as those with low serum protein binding.

Comparison of oral penicillinase-resistant penicillins: contrasts between agents and assays

We observed the comparative serum levels and mean peak serum antistaphylococcal activity in eight fasting adults who received 500 mg each of dicloxacillin, cloxacillin, oxacillin, and nafcillin. Dicloxacillin achieved higher and more prolonged serum levels and greater peak serum antistaphylococcal titers than the other drugs studied. The higher degree of protein binding of dicloxacillin was reflected in a greater disparity between the peak antistaphylococcal activity observed when dilutions were done in serum compared to broth. The lesser protein-bound penicillins showed less disparity, but this effect was offset by the higher serum levels obtained by dicloxacillin. The higher protein binding of dicloxacillin did not prevent its having equal or superior antistaphylococcal activity in serum when the drugs were given in equal doses.

A pharmacokinetic analysis program (multi) for microcomputer

A nonlinear least squares program (MULTI) for microcomputers was developed. The program is written in BASIC programming language. Four algorithms, (1) Gauss-Newton method, (2) damping Gauss-Newton method, (3) modified Marquardt method and (4) simplex method, can be used for nonlinear curve fitting in MULTI. Up to five pharmacokinetic equations, which are voluntarily defined by the user, are simultaneously fitted to observed time courses. The executions of MULTI are demonstrated for time courses of ampicillin and oxacillin in man.

Sodium oxacillin in the horse: serum, synovial fluid, peritoneal fluid, and urine concentrations after single-dose intramuscular administration

Six healthy adult mares were given a single dose (25 mg/kg of body weight) of sodium oxacillin IM. Oxacillin concentrations in serum, synovial fluid, peritoneal fluid, and urine were measured serially over a 48-hour period. The mean peak serum oxacillin concentration was 9.75 microgram/ml at 0.5 hour after injection. Mean peak oxacillin concentrations in synovial and peritoneal fluids were 1.45 microgram/ml and 2.60 microgram/ml at 1 hour and 2 hours, respectively. These concentrations decreased in parallel with serum values and were not measurable at 48 hours. Urine concentrations of oxacillin were high, with a mean peak concentration of 2,790.2 microgram/ml at 0.5 hour.

Transposition of the oxacillin-hydrolyzing penicillinase gene

We have found that the oxacillin-hydrolyzing penicillinase gene (oxa) encoded by plasmid RGN238 transposes to various plasmids in a recA background. We call this transposable element Tn2603. Tn2603 encodes the genes for streptomycin, sulfonamide, and mercury resistance in addition to the oxa gene. Tn2603 has a molecular size of 19.6 kilobase pairs and appears to be flanked by small inverted repeat sequences of about 200 base pairs long.

[Body pharmacokinetics of methicillin, oxacillin and cephaloridine in puerperal mastitis]

Mechanisms of absorption, distribution and excretion of methicillin, oxacillin and cephaloridin were studied in 46 women with postnatal mastitis (serous and infiltrative forms). The results obtained allow one to document different clinical efficiency of antibiotics in treatment of patients with postnatal mastitis. Poor efficiency of cephaloridin in therapy of mastitis was shown.

Identification of the active metabolites of the isoxazolylpenicillins by means of mass-spectrometry

Electron-impact mass-spectrometry of the methyl esters of the isoxazolylpenicillins and of their active metabolites showed the latter to be formed from their parent compounds by hydroxylation of the 5-methyl group.

[Phamacokinetics of methicillin, oxacillin and cephalosporin in the body of puerperae]

Features of absorption, distribution and excretion of methicillin, oxacillin and cephaloridine in 58 puerpera were studied. No complications were observed in the postnatal period of the puerpera. The results of the study of the antibiotic pharmacokinetics provided elaboration of the optimal regimen for the use of methicillin, oxacillin and cephaloridine in puerpera, i. e. I g intramuscularly every 6 hours.

Penetration of methicillin, oxacillin, and cephalothin into bone and synovial tissues

The penetrations of methicillin, oxacillin, and cephalothin into cortical bone and synovial tissues were studied 1 h after their intravenous administration in 105 patients having arthroplasty of the hip. Although the lowest serum levels were noted with cephalothin (P < 0.01), more patients receiving cephalothin achieved osseous drug levels inhibitory to staphylococci (P < 0.01). Differences in the penetration of the three agents into synovial tissues were not statistically significant.

Immunochemical comparison between an oxacillin-hydrolyzing penicillinase of Aeromonas hydrophila and those mediated by R plasmids

Antiserum against an oxacillin-hydrolyzing penicillinase of Aeromonas hydrophila did not show immunochemical cross-reaction with four oxacillin-hydrolyzing penicillinases mediated by R plasmids.

Inducible oxacillin-hydrolyzing penicillinase in Aeromonas hydrophila isolated from fish

An inducible penicillinase was shown to be present in a strain of Aeromonas hydrophila subsp. hydrophila isolated from freshwater fish. Enzyme induction was observed with benzylpenicillin or 6-aminopenicillanic acid, and the enzyme was cell bound. The penicillinase was purified 50-fold from a crude cell extract. The molecular weight was estimated to be 23,000 by gel filtration. The pH and temperature optima for the enzyme activity were 8.0 and 35 degrees C, respectively. The penicillinase showed a unique substrate profile by hydrolyzing oxacillin about twice as rapidly as benzylpenicillin. The enzyme activity was weakly inhibited by sodium chloride but was not affected by p-chloromercuribenzoate. The property of penicillinase production by the A. hydrophila strain could not be transferred to Escherichia coli and also could not be eliminated from the bacteria by ethidium bromide treatment.

An inducible beta-lactamase in a strain of Escherichia coli

The production of beta-lactamase (penicillin/cephalosporin beta-lactam amidohydrolase, E.C.3.5.2.6) was found to be inducible in a clinically isolated strain of Escherichia coli. This is the first report of an inducible beta-lactamase in E. coli. The optimal concentration of inducer was 400 mug/ml of ml of benzylpenicillin, or 800 mug/ml of 6-aminopenicillanic acid. About fiftyfold induction was achieved. Maximum induction took ninety minutes from the time of adding the inducer. Induction was abolished by the presence of chloramphenicol(10 mug/ml). The enzyme has a molecular wieght of 23,000, and is inhibited by rho-chloromercuribenzoate and by iodine. It is active against a wide range of substrates, including cephaloridine and cloxacillin.

[Pharmacokinetic investigations of the transfer of antibiotics into amniotic fluid. Part III: Oxacillin (author's transl)]

After intravenous administration of 2 g of Oxacillin to 12 gravidae at the end of their pregnancy short-interval tests were made of the Oxacillin levels in the mothers' serum and -- intra-amnionic catheter in position -- in the amniotic fluid. The following pharmaco-kinetic data were determined: fictitious initial Oxacillin level (79 mcg/ml), elimination constant (1,044 h-1), half-value of elimination (39,88 min), fictitious distribution volume (25,31), distribution coefficient (0,3617 ml/g), total clearance (26,431 l/h) and invasion constant (0,0084 h-1). All given data were statistically confirmed. For the para-placental passage of Oxacillin a permeability factor (chi) of 0,0084 was found. This factor indicates how easy Oxacillin passes trough the fetal membrane into the amniotic fluid. Ampicillin diffuses about 43 times and Cephalotin diffuses about 2,4 times better trough fetal membrane -- permeability factor 0,357 or 0,02 --, probably because of its weaker link to serum albumin. Under our conditions the amnionic levels reached 12 mcg/ml on the average. With 8-12 g Oxacillin daily bactericidal levels in the amniotic fluid are reached.