Keratotomy model of pseudomonas keratitis: gentamicin chemotherapy

BACKGROUND

Chemotherapy of bacterial keratitis requires frequent application of antibiotic drops. Collagen shields containing antibiotics could reduce the need for frequent antibiotic application. To determine the effect of gentamicin-containing collagen shields and gentamicin drops on Pseudomonas keratitis, a new keratotomy model of infection was employed.

METHODS

Model--contact lenses (58% water content) presoaked in 1% bovine serum albumin and exposed to 10(8) colony forming units per mL of Pseudomonas aeruginosa strain 27853, were found to reproducibly retain 5.9 (log base 10) colony-forming units. Rabbit corneas were scarified centrally with two perpendicular intersecting diamond knife cuts (5 mm x 5 mm x 0.2 mm), and bacteria-impregnated contact lenses were positioned and held in place for 24 hours with partial tarsorrhaphies. Treatment--Fourteen hours after lens removal (38 hours after infection), corneas were treated for 8 hours with collagen shields hydrated in saline (control), or shields impregnated with 800 micrograms gentamicin during manufacture, or one drop every 30 minutes of fortified gentamicin drops (14 mg/mL). The rabbits were killed and corneas collected for bacterial enumeration after 8 hours of treatment (46 hours after infection).

RESULTS

Model--Slit-lamp examination and microbiologic confirmation showed uniformity of keratitis in all eyes. Treatment--Corneas treated with saline (controls) contained 6.4 (log base 10) Pseudomonas. Corneas treated with gentamicin-impregnated collagen shields (total drug = 800 micrograms) and fortified gentamicin drops (total drug = 21 mg) showed a reduction in viable bacteria of 2 logs and 6 logs, respectively, relative to the control.

CONCLUSIONS

In this new model of Pseudomonas keratitis, the amount of gentamicin introduced into collagen shields during manufacture effectively reduced bacterial growth in infected rabbit corneas. However, larger amounts of drug applied as fortified drops on a frequent dosing schedule were more effective by a factor of three. Treatment of keratitis with antibiotic-impregnated collagen shields may reduce the need for very frequent application of topical drops, but may be more effective with topical drop supplementation to increase the amount of drug available over the course of therapy.

Latency-associated transcripts in corneas and ganglia of HSV-1 infected rabbits

Herpes simplex virus (HSV) establishes latent infection in the sensory neuron and possibly in non-neuronal tissue, particularly the cornea. During latency only one region of the HSV genome is transcribed, producing RNAs known as latency associated transcripts (LAT). The gene for LAT overlaps with the HSV gene for the protein ICPO in the downstream regions of both genes. Latency can occur in the absence of LAT. This study reports the detection of ICPO/LAT and thymidine kinase (TK) gene fragments by the polymerase chain reaction in DNA extracted from the corneas and trigeminal ganglia of latently infected rabbits. Both genes were detected in four of four trigeminal ganglia tested and in three of five corneas tested. More importantly, this study reports the first detection of LAT in RNA extracted from 9% of corneas from latently infected rabbits (n = 22) by the polymerase chain reaction. LAT was detected in RNA from 100% of the corresponding trigeminal ganglia (n = 22). Although LAT is not essential for latency, it remains the only known molecular marker for latent HSV infections. Detection of LAT in these rabbit corneas suggests that HSV latency may occur in this non-neuronal tissue and that reactivation from non-neuronal tissue may occur at a low frequency in animals in which HSV latency has been established.

Successful treatment of methicillin-resistant Staphylococcus aureus Keratitis with topical ciprofloxacin

Ciprofloxacin is a new quinolone antibiotic with a broad spectrum of activity against most aerobic gram-positive and gram-negative bacteria. Topical ciprofloxacin (3 mg/ml) was used to treat bacterial keratitis caused by methicillin-resistant strains of Staphylococcus aureus in two patients. Both corneal ulcers had been previously treated with other antibiotics without success. Topical ciprofloxacin was curative in both cases. The authors recommend the use of topical ciprofloxacin for methicillin-resistant S. aureus keratitis.

Clinical effects of daily methamphetamine administration

This study investigated alterations in the disposition and pharmacodynamics of methamphetamine HCl after daily administration. Six male paid volunteers familiar with the use of amphetamines participated. Each subject was administered 10 mg of methamphetamine HCl as a slow-release preparation (Desoxyn Gradumets) at 9 a.m. for 13 consecutive days (days 2-14 of the study). On days 1 and 15 the subjects were challenged with 10 mg of oral deuterated methamphetamine HCl. Deuterated drug was used to differentiate plasma concentrations of challenge doses from those of daily doses. The heart rate, subjective perception of "high," and plasma concentrations of methamphetamine were examined on days 1 and 15. Repeated ANOVA measures indicate that a significant decrease in heart-rate acceleration in response to methamphetamine challenge occurred on day 15 [F(1,5) = 8.26, p less than or equal to 0.035]. However, no significant change in either the subjective ratings of "high" or the plasma concentrations of deuterated methamphetamine occurred. These findings indicate that the disposition of methamphetamine and its subjective effects were not altered by this period of daily exposure to a low dose of the drug. In contrast, tolerance to the heart-rate accelerating effect was observed.

Cardiovascular and respiratory response to static exercise in the newborn kitten

Muscle contraction produces a reflex increase in blood pressure, heart rate, and minute ventilation in adults. To evaluate the role of this reflex in newborns, we compared the blood pressure, heart rate, and ventilatory responses to static contraction of the hindlimb muscles in sedated newborn and adult felines. The reflex response to muscle contraction was compared with the baroreflex, the chemoreceptor reflex, and the response to maximal stimulation of sciatic nerve afferents. With muscle contraction, newborn systolic blood pressure increased by 8.5 +/- 2.6%, which was significantly less than the adult response of 15.9 +/- 1.8% (p less than 0.025). Heart rate response to muscle contraction was less in newborns compared with adults, increasing by 1.4 +/- 0.5 and 8.3 +/- 1.3%, respectively (p less than 0.025). In contrast to heart-rate and blood-pressure responses, ventilatory responses to muscle contraction were similar in both age groups, increasing by 34 +/- 20 and 34 +/- 10% in newborns and adults, respectively. With stimulation of sciatic nerve afferents and with hypoxemia, blood pressure and heart rate increased similarly in both newborns and adults. When the baroreflex was elicited, heart rate decreased similarly in both age groups. We conclude that newborn cats have a reduced heart rate and blood pressure response to muscle contraction compared with the adult. We speculate that the postnatal development of this reflex is due to maturation of integrative and modulatory mechanisms in the CNS.

Time-saving formats for patient care planning in outpatient surgery units

Due to the frequent patient turnover and the fast pace of an outpatient surgery unit, time is limited for developing an individual plan of care. Other factors making this task more complex are related to brief nursing observations and unclear patient expectations. Care plans are now mandated in the outpatient areas at Central Baptist Hospital in Lexington, KY. The plans need to be realistic, comprehensive, and timesaving, yet generic. A checklist format, which is described in this article, was the solution.

Intrathecal serotonin attenuates the pressor response to static contraction

We tested the hypothesis that intrathecal injection of serotonin onto the lumbosacral spinal cord of chloralose-anesthetized cats attenuates the pressor response to static contraction of the triceps surae muscles. Serotonin (10 micrograms) significantly attenuated the contraction-induced reflex increases in mean arterial pressure but not in ventilation. This attenuation of the reflex pressor response to static contraction by serotonin was prevented by prior intrathecal injection of mianserin hydrochloride, a serotonergic receptor antagonist. In addition, the reflex pressor response to contraction was significantly attenuated by intrathecal injection of carboxamidotryptamine maleate, a 5-HT1 agonist but not by DOI-hydrochloride, a 5-HT2 agonist. We conclude that stimulation of 5-HT1 receptors in the lumbosacral spinal cord attenuates the reflex pressor response to static muscular contraction.

Ocular herpes simplex virus reactivation in mice latently infected with latency-associated transcript mutants

A mouse model for ocular reactivation of herpes simplex virus type 1 (HSV-1) was modified and used to study the effect of strain difference on the frequency of ocular HSV reactivation. Outbred male NIH white mice were immunized with 1.0 ml of anti-HSV serum with a neutralizing titer of 1:400 24 hr before infection and bilaterally infected at 10(5) plaque-forming units/eye with one of three HSV-1 strains: 17 Syn+, LAT+ (XC-20), or LAT- (X10-13). Latency-associated transcripts (LAT) are produced by strain 17 Syn+ and LAT+ but not by LAT-. The primary infection was monitored by ocular swabbing for HSV. Reactivation was induced by intravenous (i.v.) injection of cyclophosphamide (5 mg) followed 24 hr later by i.v. dexamethasone (0.2 mg). These drugs significantly reduced the white cell count between 0 and 6 days post-administration. The eyes were swabbed for 7 consecutive days to monitor reactivation, and HSV-1 reactivation was induced at the following frequencies in individual eyes: 17 Syn+ (32.5%), LAT+ (18.5%), and LAT- (2.5%) (P less than or equal to 0.002). Co-culture of trigeminal ganglia was done, and random isolates were checked to ascertain their identity. The HSV was recovered from individual trigeminal ganglia at the following frequencies: 17 Syn+ (83%), LAT+ (100%), and LAT- (67%) (P less than or equal to 0.091). These results confirm that the mouse can be used as a reactivation model for ocular HSV infection and that the presence of LAT facilitates reactivation in vivo in the mouse.

Screening for alcoholism in a psychiatric hospital

The prevalence of alcoholism is generally underestimated in patients in private practices, general hospitals and psychiatric institutions. Even though the World Health Organization has advocated the concurrent use of laboratory test results and questionnaires for screening, these methods are seldom used together. In this study, patients admitted consecutively to the North Bay Psychiatric Hospital were screened for alcoholism using the Michigan Alcoholism Screening Test (MAST) and gamma-glutamyl-transferase plasma level. Unexpectedly, 56.7% of the entire sample were identified as possible alcoholics; of these, 73.5% were men and 26.5% were women. When rates for men and women were looked at separately, it was found that 66.2% of the men and 40.6% of the women were alcoholic. Participants who tested positive on one or both of the screening tests were offered a more complete evaluation of their drinking behaviour. A diagnosis of alcoholism was confirmed in 88.2% of the patients who agreed to participate further. The question remains whether the high prevalence rates found are a function of the particular sample studied (i.e., patients in a hospital which typically serves a socially disadvantaged sector of the population) or reflects a feature of the general population in this catchment area. A study is currently underway in general hospitals of North Eastern Ontario in an attempt to answer this question.

Attenuating effects of intrathecal clonidine on the exercise pressor reflex

We tested the hypothesis that intrathecal injection of clonidine, an alpha 2-adrenergic agonist, attenuated the reflex cardiovascular and ventilatory responses to static muscular contraction in cats. Before clonidine (1 microgram in 0.2 ml), contraction-induced reflex increases (n = 10) in mean arterial pressure and ventilation averaged 25 +/- 3 mmHg and 359 +/- 105 ml/min, respectively, whereas after clonidine these increases averaged 8 +/- 4 mmHg and 200 +/- 114 ml/min, respectively (P less than 0.05). Clonidine had no effect on the heart rate response to contraction. Intrathecal injection of yohimbine (10 micrograms; n = 5), an alpha 2-adrenergic antagonist, but not prazosin (10 micrograms; n = 3), an alpha 1-adrenergic antagonist, prevented the attenuating effects of clonidine on the reflex pressor and ventilatory responses to contraction. Our findings were not due to the spread of clonidine to the medulla, because the reflex pressor and ventilatory responses to contraction were not attenuated by injection of clonidine (1 microgram) onto the medulla (n = 3). In addition, our findings were not due to a clonidine-induced withdrawal of sympathetic outflow, because intrathecal injection of clonidine (1 microgram) did not attenuate increases in arterial pressure and ventilation evoked by high-intensity electrical stimulation of the cut central end of the sciatic nerve (n = 5). Furthermore, our findings were not due to a local anesthetic action of clonidine, because application of this agent to the dorsal roots had no effect on the discharge of group IV muscle afferents. We conclude that stimulation of alpha 2-adrenergic receptors in the spinal cord attenuates the reflex pressor and ventilatory responses to static contraction.

Vasoactive intestinal peptide antagonist retards the development of neonatal behaviors in the rat

Based on the demonstrated neurotrophic activity of VIP in vitro, a recently designed VIP antagonist was used to assess the role of this neuropeptide in the behavioral development of rats. Rats received daily subcutaneous injections from birth to day 14. Observations of developmental milestones/behaviors were made daily for 21 days. Of the measures of behavioral development tested, the time to surface right on day 4 and the day of onset for forelimb placing, hindlimb placing, forelimb grasping and air righting were significantly retarded by the antagonist. Cotreatment with VIP prevented the antagonist-induced delay. These results suggest that VIP activity is important in the development of select complex motor behaviors.

Clinical effects of methamphetamine vapor inhalation

Despite the increasing popularity of crystalline methamphetamine ("ice") vapor inhalation, no investigations have reported drug plasma concentrations and effects. Under controlled laboratory conditions, six subjects were studied. Plasma concentrations of methamphetamine were determined, and subjective and cardiovascular effects were measured. Methamphetamine appeared in plasma rapidly, increased slowly over the next four hours and then progressively declined. The dose of methamphetamine administered produced modest ratings of subjective drug effects, and moderate changes in cardiovascular parameters. Both subjective and cardiovascular effects rapidly decreased despite the presence of sustained concentrations of methamphetamine in plasma.

The effect of HSV multiplication rate on antiviral drug efficacy in vitro

HSV-1 multiplication rates have been shown to vary in different tissues and the rate of multiplication may correlate with susceptibility to antiviral chemotherapy. Herpetic stromal keratitis is a necrotizing condition refractive to antiviral therapy and this lack of antiviral efficacy in stromal disease may be the result of very low rates of viral replication in the corneal stromal keratocytes. In this study, we investigated the efficacy of antiviral drugs in an in vitro system in which the virus multiplication rate is slow. In this system, the reduced rate of virus multiplication is achieved by a reduction in the incubation temperature. Vero cells were infected at one of several multiplicities of infection with McKrae strain HSV-1 and incubated for 24, 48, or 72 h at 26 or 36.5 degrees C in the presence or absence of trifluridine (50 micrograms/ml) or acyclovir (20 micrograms/ml). Both drugs suppressed viral replication at 36.5 degrees C. However, under some specific sets of conditions, trifluridine was not effective in suppressing viral replication in cells incubated at 26 degrees C. At this temperature, viral replication and cell metabolism are slowed to a pace which may be similar to that which occurs in corneal stromal keratocytes in vivo. Acyclovir significantly reduced HSV-1 replication under all conditions at 26 degrees C, indicating that the antiviral activity of this compound is effective in cells whose metabolic rate is slow and in which viral replication is taking place slowly.

The coincidence of HSV-1 ocular cultures with HSV-1 corneal epithelial defects in rabbits after experimental penetrating keratoplasty

Penetrating keratoplasty (PKP) in conjunction with postoperative corticosteroids may reactivate latent herpes simplex virus type 1 (HSV-1) to cause persistent postoperative epithelial defects. The clinical diagnosis of HSV keratitis after penetrating keratoplasty is difficult because the postoperative appearance may be nondendritic and, therefore, not characteristic of HSV-1 infection. Presently, the most reliable method to diagnose HSV-1 under these conditions is to culture eyes for the presence of HSV-1. To determine the coincidence of positive HSV-1 ocular cultures with HSV-1 epithelial defects, 15 rabbits (20 eyes) latently infected with HSV-1 underwent autograft PKP with postoperative corticosteroids. Daily ocular cultures and slit-lamp examinations were performed on postoperative days 1-8 and 10. Viral shedding occurred in 15 of 19 (79.0%) of the eyes postoperatively. Superficial punctate keratopathy (SPK) was observed in 19 of 19 (100%) of the eyes and coincided with positive HSV-1 cultures 24% of the time. Dendritic lesions were observed in three of 19 (15.8%) of the eyes; the dendrites coincided with positive HSV-1 cultures 60% of the time. Finally, epithelial ulcers were seen in eleven of 19 (57.9%) of the eyes, thus coinciding with HSV-1 positive cultures 29% of the time. The greatest coincidence of positive HSV-1 cultures with nondendritic epithelial lesions occurred on postoperative day number 4. The results suggest that an epithelial lesion following PKP and postoperative corticosteroids could represent HSV infection, even if a single HSV ocular culture is negative.

The efficacy of topical ciprofloxacin and norfloxacin in the treatment of experimental Pseudomonas keratitis

An aminoglycoside-resistant strain of Pseudomonas aeruginosa was injected intrastromally into the corneas of rabbits, and keratitis was allowed to develop over a 22-h period. Rabbits were treated with either 0.75% ciprofloxacin, 1% norfloxacin, or 1.36% tobramycin administered topically every 15 min for 1 h and then every 30 min for the following 3 h. All therapy ceased 26 h postinoculation. Rabbits were killed 1 h after the treatment, and the number of bacteria per cornea were quantified in terms of bacterial colony-forming units. Aqueous humor specimens were obtained from rabbits receiving norfloxacin and ciprofloxacin, and bioassays were performed to determine drug concentration. Ciprofloxacin caused a 5 log reduction in the number of bacterial colony-forming units, as compared with untreated controls (p less than 0.0001); it also produced a significantly greater reduction in bacterial colony-forming units than either norfloxacin or fortified tobramycin drops (p less than 0.0001). Norfloxacin produced a 2 log reduction in bacterial colony-forming units, as compared with untreated controls (p less than 0.0001). The mean aqueous concentration of norfloxacin (7.5 micrograms/ml) was substantially less than that achieved by ciprofloxacin (30.5 micrograms/ml). We conclude that ciprofloxacin may be a useful broad spectrum, topical chemotherapeutic agent in the therapy of aminoglycoside-resistant P. aeruginosa keratitis.

The role of pneumolysin in ocular infections with Streptococcus pneumoniae

Pneumolysin, a cytolytic protein produced by Streptococcus pneumoniae, has many properties which suggest it may be an important virulence factor in pneumococcal ocular infections. To directly test this possibility, we have constructed pneumolysin-negative strains of S. pneumoniae and compared their virulence with that of the wild type in a rabbit model of intracorneal infection. A pneumolysin-negative strain produced by chemical mutagenesis (probably a point mutant) was found to be no less virulent than the parent strain. However, a strain bearing a deletion in the pneumolysin gene showed greatly reduced virulence. This strain produced less pathology while showing significantly higher bacterial counts. These results suggest that a property of the pneumolysin molecule other than its cytolytic (hemolytic) activity may be involved in its pathogenic mechanism of action. This property may be the ability to activate complement, known to be a function of pneumolysin, which results in influx of PMNs, reducing the bacterial counts but also producing tissue damage.

Quinolones in collagen shields to treat aminoglycoside-resistant pseudomonal keratitis

Rabbit corneas were infected with a tobramycin-resistant (minimum inhibitory concentration, 31.25 micrograms/ml) strain of Pseudomonas aeruginosa 27853 (10(3) colony-forming units) and were treated 22 hours later with collagen corneal shields hydrated in either 25 mg/ml ciprofloxacin, 40 mg/ml norfloxacin, 40 mg/ml tobramycin, or deionized water. Shields were removed at 26 hours postinfection, and 1 hour later, corneas were harvested for bacterial enumeration. Application of shields hydrated in ciprofloxacin reduced the number of viable bacteria per cornea approximately 4 log units compared with the application of shields containing tobramycin or deionized water (P less than 0.0001). Use of shields hydrated in norfloxacin reduced the number of P. aeruginosa organisms by greater than 2 log units compared with shields containing tobramycin or deionized water (P less than 0.0001). Ciprofloxacin was significantly more effective than norfloxacin in reducing the number of bacteria per cornea (P less than 0.0001). There was no significant difference in the number of bacteria recovered from corneas treated with tobramycin or deionized water (P less than 0.56).

Ciprofloxacin iontophoresis for aminoglycoside-resistant pseudomonal keratitis

Studies using ciprofloxacin for the therapy of experimental aminoglycoside-resistant keratitis caused by Pseudomonas aeruginosa were conducted using transcorneal iontophoresis as the drug-delivery system. Corneas infected with P. aeruginosa ATCC 27853/pMG6 were treated 22 hours postinfection with ciprofloxacin delivered by iontophoresis (0.8 mA X 10 min), mock iontophoresis (eyecup with no current), or frequently applied topical drops. Iontophoresis of 10 mg/ml or 25 mg/ml of ciprofloxacin significantly reduced the number of viable bacteria per cornea by more than 5 log units compared with untreated controls (P less than 0.0001). Five hours after the initiation of treatment, mock iontophoresis (10 mg/ml or 25 mg/ml) or 11 applications of topical ciproflaxicin drops (7.5 mg/ml) decreased the viable bacteria relative to the untreated controls by 5 log units (P less than 0.0001). One treatment with an eyecup was as effective as 11 treatments with topical drops (P greater than 0.75). One hour after treatment with iontophoresis or mock iontophoresis of 10 mg/ml of ciprofloxacin, aqueous humor concentrations were 83.75 +/- 8.85 micrograms/ml and 24.87 +/- 4.0 micrograms/ml (mean +/- standard error of the mean), respectively. One hour after the last of five applications of 7.5 mg/ml of ciprofloxacin (every 15 min for 1 hr) the aqueous humor concentration was 4.2 +/- 1.14 micrograms/ml. These results show the value of ciprofloxacin in treating aminoglycoside-resistant infections caused by P. aeruginosa and suggest that ciprofloxacin can be efficiently delivered by iontophoresis.

Role of iron and ferritin in MR imaging of the brain: a study in primates at different field strengths

The authors measured in vivo signal intensity on magnetic resonance (MR) images and postmortem iron concentrations in the brains of three young and two old rhesus monkeys. T2-weighted MR imaging was done at 0.5, 1.5, 2.0, and 4.7 T. Relative assessment of iron concentration was made from the optical density of brain sections stained with the Perls' method intensified with diaminobenzidine. MR imaging and optical density measurements were made in the centrum semiovale (white matter) and in four gray matter areas: the insular cortex, caudate nucleus, putamen, and globus pallidus, the latter three of which accumulate significant iron deposits with age. High optical density and decreased signal intensity were found in these areas, and the inverse correlation between gray matter/white matter signal ratio and optical density was in good agreement with the theory of T2 shortening caused by diffusion of water through magnetic inhomogeneities. However, the dependence of T2 shortening on field strength was not quadratic, as expected for paramagnetic iron, but instead showed a marked leveling off at higher field strengths. This magnetic "saturation" is explainable by antiferromagnetism and superparamagnetism of the ferritin core and has been observed in ferritin solutions at low temperatures. Similar observations at body temperature are needed before the iron-ferritin explanation for T2 shortening can be considered proved.