Combination trochanteric arrest and intertrochanteric osteotomy for Perthes' disease

A significant complication associated with femoral varus osteotomy (FVO) is trochanteric overgrowth and concomitant abductor weakness. We identified 28 patients who underwent unilateral FVO for Perthes' disease, had a healed femoral head on their latest radiograph, and had at least 2.1 years of follow-up. The patients were divided into two groups; group 1: patients who did not receive prophylactic trochanteric arrest (TA) at the time of FVO; group 2: patients who did receive TA. Clinical parameters were quantified using objective measurements and a scoring system for reported symptoms. At postoperative follow-up, group 2 had greater articulotrochanteric distance (ATD), better range of motion, less abductor weakness, less pain, and superior activity levels. These differences were statistically significant. This study demonstrates that when properly performed with respect to indications and timing, the combination of TA and FVO provides an effective means of managing Perthes' disease when "head at risk" signs are present. The authors include a detailed discussion of surgical technique.

Rapid determination of logarithmic partition coefficients between n-octanol and water using micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) was evaluated as a rapid screening tool for the determination of logarithmic partition coefficients between n-octanol-water (log P(OW)). The technique is performed by electrochromatographing a mixture of standards of known log P(OW). The logarithmic capacity factor of each standard was plotted against its log P(OW) to form a linear calibration curve for a given set of chromatographic conditions. The log P(OW) of an unknown is calculated by using its chromatographically determined capacity factor and extracting the log P(OW) value from the calibration curve. The method was evaluated with a set of model compounds with known log P(OW). The accuracy of the method was examined and found to be within the limits required for screening purposes. The correlation of log P(OW) values determined using HPLC and MECC for some novel compounds was examined. This technique allows the screening of log P(OW) at a rate of four samples per hour with minimal sample requirements (< microgram) and with extremely small solvent waste generated.

Bactericidal activity of the new 4-quinolones DU-6859a and DV-7751a

The bactericidal activity of two new 4-quinolones, DU-6859a and DV-7751a, was investigated against strains of Escherichia coli, Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae and Enterococcus faecalis. DU-6859a and DV-7751a were more bactericidal than any 4-quinolone tested previously. Furthermore, DU-6859a was unique among 4-quinolones in being able to kill Ent. faecalis after incubation for only 3 h in nutrient broth. The bactericidal mechanisms of DV-7551a were similar to those of other 4-quinolones, but, uniquely, DU-6859a possessed additional bactericidal mechanisms against both Str. pneumoniae and Ent. faecalis. This may explain the unusually potent bactericidal activity of this agent against these species. These results show that DU-6859a is a unique extended-spectrum 4-quinolone, which should prove to be superior to established 4-quinolones.

Validity of newborn oscillometric blood pressure

The objective of this study was to determine the validity of oscillometric blood pressure in relation to arterial blood pressure. Thirty-one newborns were studied. Clinical characteristics, complications, and treatment interventions were documented. Arterial pressure (every 2 sec) and oscillometric pressure (every 3 min) were concurrently recorded for 1-2 h. Serial observations of oscillometric pressure followed the trend of arterial pressure in the individual newborn. However, the study averaged oscillometric pressures were lower than the arterial pressures: systolic, by 1 mmHg; mean, by 5.3 mmHg (p < 0.0001); and diastolic, by 4.6 mmHg (p < 0.0001). The variance of individual, 15-min averaged, and 1-h averaged observations of oscillometric pressure in relation to arterial pressure was examined. Variance for individual observations may be large. The least variance of oscillometric pressure was in the 1-h averaged mean pressure, in which the difference was +/- 2 mmHg in 77% and +/- 4 mmHg in 95% of observations. Clinical characteristics, with the exception of birth weight and treatment interventions, did not affect the variance of oscillometric pressure. This study implies that the offset in relation to arterial pressure should be established for each oscillometric pressure monitoring system. Hourly averaged mean oscillometric pressure is satisfactory for many newborn assessments and management circumstances. However, arterial pressure may be necessary to accurately document transient hypertension or hypotension or an unstable blood pressure.

An investigation of the effects of water velocity on inorganic phosphorus influx to a sediment

Measurements of the net influx of soluble reactive phosphorus (SRP), to a river bed-sediment, illustrate the importance of the water velocity and hydrodynamics in controlling the transfer rates. Experiments are reported using a characterised bed-sediment, with associated fauna, contained in a flowing-water channel. The results show a systematic increase in the net influx of SRP with increasing water velocity. A mathematical description of the influx was sought by modelling the experimental results using the Elovich equation, a boundary-layer model and a parabolic rate equation. In fact all three kinetic equations produce a good representation of the experimental data and it is concluded that further research is needed, in well-defined hydrodynamic conditions, to distinguish between the boundary-layer model and the parabolic equation. The boundary-layer model leads to an inverse relationship between the boundary-layer thickness (z/microm), and the water velocity (v/cm s(-1), viz z approximately 2500/v). In comparison, the parabolic equation of the form: influx of SRP (mol m(-2) = kp [SRP-EPC0]2, where EPC0 is the concentration at which the influx is zero prior to the sorption of phosphorus by the sediment and kp is the rate constant which leads to a velocity dependence, kp* = 0.714v + 1 where kp* is the reduced rate constant, kp* = kp(v)/kp(0). The semi-empirical Elovich equation in the form: influx of SRP (mol m(-2)) = (1/b) ln(1 + abt) where a and b are the Elovich parameters and t the time, gives a convenient description of the net influx of SRP to bed-sediments downstream of a point-source of pollution. The parameters calculated from the results obtained from the experimental channel are used to estimate the SRP flux to the sediment for a distance of up to 5 km downstream of a point-input of SRP.

Ranitidine bismuth citrate and ranitidine do not affect gastric emptying of a radio-labelled liquid meal

Ranitidine bismuth citrate, a new chemical entity which is a salt complex of ranitidine and bismuth citrate, is being developed for the treatment of relapse of benign gastric and duodenal ulcer and eradication of Helicobacter pylori. The aim of the present study was to establish whether ranitidine bismuth citrate (800 mg) or ranitidine hydrochloride (300 mg) have any effect on gastric emptying of a liquid meal using gamma scintigraphy. On three separate occasions, each of twelve subjects received a single oral tablet of 800 mg ranitidine bismuth citrate, 300 mg ranitidine hydrochloride or placebo in random order. Thirty minutes after dosing each subject was given 375 ml of 99mTc-DTPA (diethylene triaminepentaacetic acid) labelled Clinifeed-ISO. The primary endpoint was the time to 50% gastric emptying (t50%). The proportion of the meal remaining was summarised by weighted mean proportion of the meal remaining in the stomach over 0-60 min and 0-180 min, separately. No differences were observed for t50%, weighted mean 0-60 min, and weighted mean 0-180 min between any two treatments. In man, we have detected no significant effect of single oral doses of ranitidine bismuth citrate 800 mg or ranitidine hydrochloride 300 mg on the rate of gastric emptying of a liquid meal when compared with placebo.

Activity of 4-quinolones against Pseudomonas aeruginosa

The minimum inhibitory concentrations (MICs), bactericidal activities and mechanisms of action of ofloxacin (CAS 82419-36-1), levofloxacin (CAS 100986-85-4) and ciprofloxacin (CAS 86393-32-0) were investigated against Pseudomonas aeruginosa. All three 4-quinolones were found to possess higher MICs against Pseudomonas aeruginosa than against other Gram-negative bacteria. Despite this, however, all three drugs were more rapidly bactericidal and produced a greater level of kill against Pseudomonas aeruginosa than against any other bacterial species previously tested. Thus MIC tests cannot be used to predict the bactericidal activity of 4-quinolones. Furthermore, MIC tests showed ciprofloxacin to be more potent than ofloxacin or levofloxacin against Pseudomonas aeruginosa. However, bactericidal tests showed levofloxacin to be about 10 times more bactericidal than either ciprofloxacin or ofloxacin. Thus MIC tests cannot predict the relative bactericidal potency of 4-quinolones against Pseudomonas aeruginosa. Therefore, MIC tests should not be used as the sole measure for the efficacy of 4-quinolones, as is often the case. Surprisingly, the characteristic biphasic dose response curve, normally shown by 4-quinolones against other bacteria, was absent when Pseudomonas aeruginosa was tested. This unusual effect was explained by the presence of bactericidal mechanism B associated with the unique loss of bactericidal mechanism A at high 4-quinolone concentrations. This loss of bactericidal mechanism A may explain the recent high incidences of chromosomally-mediated 4-quinolone resistance with Pseudomonas aeruginosa because it may be easier for Pseudomonas aeruginosa to mutate to resist one mechanism of action than to mutate to resist two or more mechanisms of action.

Micellar electrokinetic capillary chromatography with in situ charged micelles: 3. Evaluation of alkylglucoside surfactants as anionic butylboronate complexes

This article represents an extension to a new approach introduced very recently by our laboratory for the control of the surface charge density as well as the hydrophobic character of micellar phases used in micellar electrokinetic capillary chromatography (MECC). The approach is based on the complexation of polyolic surfactants, e.g., alkylglucosides, with butylboronate to form in situ branched, anionic surfactants. The butylboronate can also incorporate into the micelle via its alkyl tail and acts as a "class I" organic additive that mainly modifies the micelle by decreasing the critical micellar concentration, i.e., increasing the hydrophobic character of the micelle, while exhibiting little influence on the aqueous phase. The net result is an in situ charged micellar entity whose hydrophobic character is dynamically altered. The alkylglucoside-butylboronate micellar phases yielded high separation efficiencies and proved useful in the separation of charged and neutral herbicides as well as the chiral separations of medicarpins and precursors, and dansylated D and L-amino acids in the presence of native or modified cyclodextrin chiral selectors.

Comparative pharmacokinetics of bismuth from ranitidine bismuth citrate (GR122311X), a novel anti-ulcerant and tripotassium dicitrato bismuthate (TDB)

GR122311X (ranitidine bismuth citrate, Glaxo Group Research Ltd.) is a salt of ranitidine with a complex of bismuth and citric acid which is being developed for the treatment of peptic ulceration. In this study, 4 groups of 12 healthy male subjects were dosed for 10 days with either GR122311X 500 mg bid (301 mg bismuth per day), GR122311X 1.0 g bid (602 mg bismuth per day), tripotassium dicitrato bismuthate (TDB, DeNoltab, Gist Brocades Ltd., Weybridge, England) 240 mg bid (431 mg bismuth per day) or placebo. After the last dose the geometric mean for Cmax for 500 mg bid of GR122311X was 5 ng.g-1, for 1.0 g bid GR122311X it was 12 ng.g-1 and it was 21 ng.g-1 for 240 mg TDB bid. The corresponding trough plasma levels were 2 ng.g-1, 4 ng.g-1 and 4 ng.g-1, respectively. The AUC over a dosing interval after the last dose (AUC tau) were 34 ng.h.g-1, 71 ng.h.g-1 and 79 ng.h.g-1, respectively. The bismuth urinary recoveries over the last dosing interval (Ae tau) were 97 micrograms, 227 micrograms and 309 micrograms, respectively, which is less than 1% of the administered doses. The renal clearance of bismuth was less than the glomerular filtration rate. After adjustment for bismuth dose, the Cmax for GR122311X 500 mg was 35% that of TDB, while for GR122311X 1.0 g the Cmax was 42% that of TDB. Similar differences were observed for Ae tau. In conclusion bismuth pharmacokinetics after oral administration of GR1223311X exhibited lower Ae tau and Cmax, with a much narrower Cmax range than those observed for TDB.

Post-antibiotic effects of cefdinir on Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Streptococcus pyrogenes

The post-antibiotic effects (PAEs) of a new cephalosporin, cefdinir, were determined against a range of organisms using a viable counting technique. Cefdinir exerted considerable PAEs against Staphylococcus aureus and Streptococcus pyogenes, but no overall post-antibiotic inhibition of growth was detected against Escherichia coli or Klebsiella pneumoniae. Exposure to cefdinir made the gram-negative organisms susceptible to the washing procedure used for drug removal, but this was followed by rapid recovery of viability in drug-free broth.

Development of physical fitness standards for Canadian Armed Forces older personnel

The purpose of the study was to develop a minimum physical fitness standard for Canadian Forces personnel, 35 years and older, based on common criteria for physically demanding tasks. A random sample of 100 men and 76 women performed the Exercise Prescription (EXPRES) test and five physically demanding tasks that simulate common military tasks, while restricted, for safety reasons, to 90% maximal predicted heart rate. Results indicated poor predictive power, as variances ranged from 5 to 55% between EXPRES fitness scores and task performance. With approval from an expert panel, the 75th percentile score for each task was selected as the cutting criterion. The passing-group data were converted to Z-scores in order to determine the 5th percentile from each EXPRES item: these scores became the EXPRES fitness standard. The minimum fitness standard had a greater impact on women than on men but was representative of the passing groups for both sexes.

4-Quinolone bactericidal mechanisms

The bactericidal activity of nalidixic acid against Escherichia coli strain KL16 in nutrient broth was abolished by the addition of rifampicin. Cells suspended in phosphate-buffered normal saline (PBS) were also not killed by nalidixic acid. Experiments with modern 4-quinolones showed their activities varied according to the conditions under which they were tested. Rifampicin did not affect the concentration at which ofloxacin became bactericidal in nutrient broth, but did limit the extent of ofloxacin-induced death. However, rifampicin produced a 10-fold increase in the concentration at which ciprofloxacin became bactericidal in nutrient broth, and completely abolished the bactericidal activity of norfloxacin. Unlike nalidixic acid all of the modern 4-quinolones killed cells suspended in PBS. Based on these results it was possible to differentiate 3 processes by which 4-quinolones induced death. Mechanism A was only active against dividing bacteria and required RNA and protein synthesis; it was therefore not active against bacteria suspended in PBS and was inhibited in nutrient broth by the addition of rifampicin. Mechanism B required neither RNA nor protein synthesis and was also active against non-dividing bacteria; it was therefore not inhibited by rifampicin nor by suspending bacteria in PBS. Mechanism C killed non-dividing bacteria, but required protein and RNA synthesis: it therefore functioned in PBS, but was inhibited by rifampicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Function of the SOS process in repair of DNA damage induced by modern 4-quinolones

The recA13 mutant of Escherichia coli strain K-12, which lacks recombination and SOS error-prone DNA repair is hypersensitive to nalidixic acid and to the newer 4-quinolones ciprofloxacin, norfloxacin and ofloxacin. However, whereas recombination-proficient but SOS repair-deficient strains, such as those carrying the lexA3 or recA430 alleles are no more sensitive to nalidixic than the lexA+ recA+ parent, they are more sensitive to the newer quinolones, although not as sensitive as the recA13 derivative. Nalidixic acid possesses only bactericidal mechanism A (which requires RNA and protein synthesis and is only effective on actively dividing cells), whereas the newer 4-quinolones exhibit additional mechanisms B (which does not require RNA and protein synthesis and is effective on bacteria unable to multiply) and C (which requires RNA and protein synthesis but does not depend on cell division). Results obtained with bacteria suspended in phosphate-buffered saline, which inhibits mechanism A, and with bacteria suspended in nutrient broth plus rifampicin, which inhibits mechanisms A and C, showed that the lexA3 mutant was still more sensitive than the lexA+ parent under these conditions. The results suggest that, unlike bactericidal mechanism A, DNA damage that results from bactericidal mechanisms B and C of the newer 4-quinolones is subject to SOS error-prone (mutagenic) repair.

Post-antibiotic effects of ofloxacin on Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, and Streptococcus pyogenes

A viable counting technique was used to determine the post-antibiotic effect (PAE) of ofloxacin against four bacterial species, treated with either once of four times the minimum inhibitory concentration for 1 or 3 h. Similar to the results obtained previously with ciprofloxacin, ofloxacin gave PAE values with Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. Cell division of Klebsiella pneumoniae was inhibited on removal of ofloxacin, but no clear PAE was demonstrated with this species because once replication recommenced, the mean generation times of drug-treated cultures were much shorter than those of untreated controls. Therefore, although the results obtained with ciprofloxacin and ofloxacin imply a consistency of PAE for 4-quinolones within a species, the response to DNA damage induced by 4-quinolones is multifaceted and species dependent. 4-quinolones inhibit both DNA replication and cell division, whilst at the same time stimulating DNA repair pathways. Thus, in some cases PAEs result from an increased post-treatment lag phase which may be followed by nearly normal multiplication, whereas in other cases a long lag may be followed by abnormally rapid cell division, with the generation times of treated cultures being shorter than those of corresponding drug-free controls. The PAE of a drug-induced lag may thus be masked by rapid cell division once growth resumes.

Mechanisms of antimicrobial resistance and implications for epidemiology

The development of antibacterial agents has provided a means of treating bacterial diseases which were, previously, often fatal in both man and animal and thus represents one of the major advances of the 20th century. However, the efficacy of these agents is increasingly being compromised by the development of bacterial resistance to the drugs currently available for therapeutic use. Bacterial resistance can be combated in two ways. New drugs to which bacteria are susceptible can be developed and policies to contain the development and spread of resistance can be implemented. Both strategies require an understanding of the mechanisms of drug resistance, its epidemiology and the role of environmental factors in promoting resistance. Over the past thirty years our knowledge of bacterial resistance has increased dramatically mainly due to new technology that has become available. Bacteria are able to resist antibacterials by a variety of mechanisms: for example, altering the target to decrease susceptibility to the antibacterial, inactivating or destroying the drug, reducing drug transport into the cell or metabolic bypass. These drug resistance determinants are mediated via one of two distinct genetic mechanisms, a mutation in the bacterial chromosome or by a transmissible element; either a plasmid or a transposon. Significant differences exist between these two types of drug resistance as transmissible resistance, which is mainly plasmid-mediated, permits intraspecies and even interspecies transfer to occur. In contrast, chromosomal resistance can only be passed on to progeny. Transmissible antibacterial resistance is the major cause of concern as it can lead to the rapid spread of antibacterial resistance and has proven difficult, if not impossible, to eradicate. Furthermore, plasmids and transposons can code for multiple antibiotic resistance as well as virulence genes. Antibacterials for which transferable resistance has been identified include most commonly used antibacterials such as beta-lactams, aminoglycosides, macrolides, sulphonamides, tetracyclines, chloramphenicol and trimethoprim. One notable exception is the 4-quinolones for which plasmid-mediated resistance has yet to be identified.

Capillary zone electrophoresis of biological substances with fused silica capillaries having zero or constant electroosmotic flow

A series of capillary surface modifications entailing multilayered coatings were introduced and evaluated in capillary zone electrophoresis of biological substances, e.g., proteins, peptides, oligosaccharides and nucleotides. In one set of surface modifications, large molecular weight hydroxypropyl cellulose afforded "zero" flow capillaries, which were used as precursors for developing anodal flow capillaries. When "zero" flow capillaries were further functionalized with a charge polyethyleneimine layer to which a top polyether layer was covalently attached, the resulting anodal electroosmotic flow was relatively weak due to the high viscosity of the coated wall imparted by the hydroxypropyl cellulose layer. Capillaries with relatively strong and constant anodal electroosmotic flow were best achieved when the inner capillary surface was first chemically derivatized with methylated (i.e., quaternarized) polyethyleneimine hydroxyethylated. This hydroxylated and permanently charged polymeric coating yielded constant anodal flow regardless of electrolyte pH. The hydroxyl groups of the charged polymeric coating permitted the covalent attachment of polyether chains, which minimized electrostatic interaction between the positive charges of the polymeric layer and oppositely charged biopolymers. Under these conditions, rapid transport of acidic biopolymers past the detection point in the separation capillary could be achieved, and relatively high plate counts were obtained.

The association between preterm newborn hypotension and hypoxemia and outcome during the first year

Ninety-eight newborn infants, less than 34 weeks at birth, were studied to examine the relationship between newborn hypotension and hypoxemia and brain damage. Heart rate, blood pressure and oxygen tension were recorded continuously during the 96 h following delivery. Outcome measures included neuropathology in children who died, and motor and cognitive development at one year corrected age in children who survived. There were 22 children with a minor and 27 with a major abnormal outcome. There was a relationship between newborn hypotension, newborn hypoxemia and low birth weight, and a major abnormal outcome. The probability of a major abnormal outcome increased from 8% in newborns with no hypotension or hypoxemia, to 53% in children with both hypotension and hypoxemia. These findings support the contention that combinations of sustained newborn hypotension and hypoxemia are important factors in the development of brain damage, accounting for a major abnormal outcome.

Studies in capillary zone electrophoresis with a post-column multiple capillary device for fraction collection and stepwise increase in electroosmotic flow during analysis

A new approach involving the stepwise increase in electroosmotic flow during analysis in capillary zone electrophoresis is introduced and evaluated in the rapid separations of proteins and peptides. The stepwise increase in electroosmotic flow is based on the principle of coupled capillaries in series having different flow characteristics, a concept that was introduced recently by our laboratory. To produce stepwise changes in electroosmotic flow during analysis, a post-column multiple capillary device, which allowed the switching between several coupled capillary systems, was designed and constructed in-house. The utility of the multiple capillary device was also demonstrated and extended to fraction collection of separated analytes in short capillary segments. The fraction collection in capillaries facilitated the quantitative transfer of the collected fractions to high performance liquid chromatography (HPLC) for further analysis or to mass spectrometry (MS) for structural determination. The off-line combination of capillary zone electrophoresis with HPLC or MS utilized commercial instruments without the need of expensive interfacing designs.

Middle cerebral artery blood flow velocity in the newborn following delivery

Ninety-five normally grown term and preterm newborns were examined to determine the means and prediction limits of cerebral blood flow velocity following delivery and to examine the relationship of systemic blood pressure to cerebral blood flow velocity. Doppler blood flow velocity was observed during the four days following delivery. Continuous measures of blood pressure and heart rate were recorded concurrently. Mean peak systolic and end diastolic blood flow velocity immediately following delivery was 43.2 and 9.3 cm/sec for term newborn, and 31.8 and 3.3 cm/sec for preterm newborn. During the 24 h following delivery there was no change of peak systolic blood flow velocity but a two to three fold increase of end diastolic blood flow velocity in the term and preterm newborn. The reference limits for peak systolic and end diastolic blood flow velocity provide criteria to define abnormal increases and decreases of blood flow velocity. During the 24 h following delivery, increasing diastolic blood pressure was associated with increasing end diastolic blood flow velocity independent of birth weight and time following delivery. Also there was a significant correlation between systemic pressure pulsatile index and middle cerebral artery blood flow velocity pulsatile index. Thus systemic blood pressure pulsatility must be recognized as distinct from other intracerebral influences on cerebral blood flow velocity regulation in the newborn.

Studies on mutational cross-resistance between ciprofloxacin, novobiocin and coumermycin in Escherichia coli and Staphylococcus warneri

Nalidixic acid resistant mutants of Escherichia coli KL16 were tested against ciprofloxacin, coumermycin and novobiocin. The mutants gyrA, nalB and nal-24 were more resistant than KL16 to ciprofloxacin, whereas the nal-31 strain was hypersensitive. Only the nalB mutant was more resistant to novobiocin than KL16, but gyrA, nal-31 and nal-24 mutants were more sensitive to coumermycin than KL16. Newly-isolated novobiocin-resistant mutants of KL16 were not cross-resistant to coumermycin or ciprofloxacin. Some coumermycin-resistant mutants were cross-resistant to novobiocin but not ciprofloxacin, whereas mutants resistant to novobiocin and ciprofloxacin were isolated at higher coumermycin concentrations. Two types of Staphylococcus warneri mutant were isolated on media containing novobiocin or coumermycin. Each was resistant to both coumarins, but one was highly resistant to novobiocin and the other to coumermycin. High level resistance to both coumarins was unstable. E. coli mutants differed in susceptibility to bactericidal concentrations of ciprofloxacin, and S. warneri mutants behaved similarly. These results suggest the modes of action of the coumarins are not identical.

Contributions of post-antibiotic lag and repair-recovery to the post-antibiotic effects of ciprofloxacin on Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Streptococcus pyogenes

A viable counting technique was used to determine the post-antibiotic effect (PAE) of ciprofloxacin against four bacterial species, treated with either one or four times the minimum inhibitory concentration for 1 or 3 h. PAE were demonstrated with Escherichia coli, Staphylococcus aureus or Streptococcus pyogenes after exposure to either concentration for both times. No clear PAE was demonstrated for Klebsiella pneumoniae after any treatment. In some cases, PAE was due to an increased post-treatment lag phase, which was followed by nearly normal multiplication, whereas in other cases a long lag was followed by abnormally rapid cell division, with the generation times of treated cultures being much less than those of the corresponding drug-free controls. This is evidence of recovery of cells that have completed DNA repair. S. aureus, E. coli and K. pneumoniae all exhibited evidence of this type of repair even though K. pneumoniae gave no significant PAE. However, the post-treatment generation times of S. pyogenes, which produced the greatest PAE, gave no evidence of such repair. It is concluded that PAEs may result from a variety of factors.