Antibiotic resistance pattern and visual outcome in experimentally-induced Staphylococcus epidermidis endophthalmitis in a rabbit model

OBJECTIVE

To study whether the clinical outcome of Staphylococcus epidermidis-induced endophthalmitis in rabbits is related to the antibiotic resistance pattern of the infecting strain.

DESIGN

Experimental animal study.

PARTICIPANTS

The right eyes of 36 New Zealand white albino rabbits were inoculated with strains of S. epidermidis that displayed various patterns of antibiotic resistance.

METHODS

There were 12 rabbits in each of three study groups: fully antibiotic susceptible (FS), partially antibiotic resistant (PR), and multiresistant (MR). Five days after inoculation, the eyes were enucleated and prepared for histologic studies.

MAIN OUTCOME MEASURES

Comparisons among the three groups were made based on electroretinographic (ERG) findings, histologic evaluation by a masked observer, and clinical examination.

RESULTS

Electroretinographic findings on all rabbits were made by an unmasked observer. At 30 hours after inoculation, the ERG was diminished to 65% of normal for group FS, compared with a flat ERG waveform for groups PR (P < 0.05) and MR (P < 0.05). The ERG waveform was flat for all three groups at 72 hours after inoculation. Histologic evaluation by use of a histologic score revealed that the degree of inflammation and destruction of the retina was less for group FS (n = 10) compared with groups PR (n = 8) and MR (n = 8). Clinical examination revealed that there was a trend of less ocular inflammation for group FS compared with groups PR and MR.

CONCLUSIONS

In a rabbit model of S. epidermidis-induced endophthalmitis, antibiotic-susceptible strains caused less inflammation and destruction of the infected retina than did antibiotic-resistant strains.

[3-D ultrasound. Initial experiences in various eye diseases]

BACKGROUND

Studies have confirmed three-dimensional (3-D) ultrasound as a practical diagnostic tool in examining the eye and orbit and suggest its routine clinical use.

MATERIALS AND METHODS

3-D ultrasound was prospectively performed in 46 patients (46 eyes) with various ocular diseases. In six large choroidal melanomas the tumor volume were measured by 3-D ultrasound and compared to that measured by MRI and to that calculated by a theoretical formula. To assess the reproducibility of volumetry by 3-D ultrasound the volumes of such three intraocular tumors were measured ten times using ten different virtual sectioning planes and a section thickness of 0.5 mm and/or 1.0 mm.

RESULTS

3-D ultrasound allows the precise assessment of complex three-dimensional structures. Choroidal melanoma volumes measured by 3-D ultrasound, MRI, and theoretical calculation were in the same range.

CONCLUSION

Intraocular tumor volume can be measured well by 3-D ultrasound,which may be of clinical importance in follow-up examinations.

[Sterilization of phacoemulsification and vitrectomy instruments. Contamination and evaluation]

BACKGROUND

Contamination of automated surgical equipment is widely disregarded as a potential source of perioperative infection. We investigated the possibility of contamination of the aspiration fluid by the vacuum control manifold (VCM). The normal, unsterile internal VCM was compared with a modified external VCM that was regularly disinfected.

MATERIALS AND METHODS

We investigated 37 aspiration fluid specimens from routine cataract and vitrectomy operations performed with automated evacuation systems. There were 25 specimens from three automated evacuation systems equipped with an internal VCM (experimental groups) and 12 specimens from one system equipped with a modified external VCM (control group). No hygiene procedures were used with the hidden internal VCM, but the modified external VCM was regularly rinsed and filled with 70% isopropanol overnight. Specimens were collected under sterile conditions, centrifuged, cultured for bacterial growth on blood agar and MacConkey agar for 24-48 h at 37 degrees C, and analyzed microbiologically.

RESULTS

Aspiration fluids of irrigation/aspiration systems used for intraocular surgery were found to be severely contaminated with bacteria originating from the VCM. In all aspiration fluid specimens from internal VCM systems, 2(+)-4+ bacterial growth was found. Stenotrophomonas maltophilia (17), Comamonas acidovorans (8), and Agrobacterium radiobacter (13) were found most frequently. All specimens from the modified external VCM system remained sterile. There was a significant difference with regard to the frequency of contamination of the aspiration fluid between experimental and control groups (P = 0.0001, chi 2).

CONCLUSIONS

We found that the aspiration fluid of common phaco- and vitrectomy systems was strongly contaminated by bacteria originating from the internal VCM. The technical modification of an external VCM allows easy disinfection and prevents contamination of the aspiration fluid.

Growth of postnatal rat retina in vitro. Development of neurotransmitter systems

In this study, we demonstrate that explanted neonatal rat retina can be maintained in culture for periods up to 3 weeks. The cultured retinas displayed a distinct layering that was almost identical to litter-matched retinas of the same age, but the majority of the ganglion cells did not survive and photoreceptor outer segments did not develop properly. Distinct synaptophysin immunoreactivity was expressed in both the inner and outer plexiform layers of cultured retina and the pattern mimicked that one observed in vivo. After 2-3 weeks in vitro, the inner retina expressed immunoreactivities to various components of the cholinergic and nitrergic transmitter systems, including nitric oxide activated cyclic GMP immunoreactivity. The investigated cell populations displayed similar distribution patterns as in situ, but morphological differences appeared in vitro. Such differences were mainly observed as irregularities in the arborization patterns in the inner part of the inner plexiform layer. We suggest that these discrepancies may arise as a result of reduced ganglion cell survival. Our observations demonstrate that some neurotransmitter systems develop in vitro and their neural circuitry appears similar to the in vivo situation. The presence of synapses, receptor proteins and transmitter substances implies that neural communication can occur in cultured retinas.

Automated surgical equipment requires routine disinfection of vacuum control manifold to prevent postoperative endophthalmitis

PURPOSE

Contamination of automated surgical equipment is a potential source of postoperative endophthalmitis. The effect of disinfecting the unsterile vacuum control manifold (VCM) on contamination of the aspiration fluid was studied.

DESIGN

Comparative prospective microbiologic contamination study. SPECIMENS AND CONTROLS: The 37 aspiration fluid specimens studied or examined consisted of 25 from three automated evacuation systems equipped with an internal VCM (experimental groups) and 12 from one system equipped with a modified external VCM (control group). In addition, the tubings of two internal VCMs were investigated.

METHODS

We investigated aspiration fluid specimens from routine cataract and vitrectomy operations performed with automated evacuation systems. After tracing the source of contamination to the internal VCM, the system was modified, creating an external VCM with the possibility for disinfection, and the study was continued. Whereas no sterilizing rinsing procedures were applied to the hidden internal VCM, the modified external VCM was regularly rinsed and filled overnight with 70% isopropanol. All samples were collected under sterile conditions, centrifuged, and cultured for bacterial growth on blood agar and MacConkey agar for 24 to 48 hours at 37 degrees C. The samples of the two internal VCMs were cultured for fungi as well.

MAIN OUTCOME MEASURES

Bacterial growth was quantified, and bacteria and fungi were isolated and identified according to standard microbiologic procedures.

RESULTS

In all aspiration fluid specimens from internal VCM-systems, 2+ to 4+ bacterial growth was found. Pseudomonas-related genera (Stenotrophomonas maltophilia, 17x; Comamonas acidovorans, 8x; Chryseomonas spp., 3x), Agrobacterium radiobacter (1 3x), Flavobacterium spp. (3x), and Micrococcus luteus (7x) were found most frequently. The tubing of the two VCMs contained biofilms exhibiting several of these bacteria and fungi. All specimens from the modified external VCM-system remained sterile. There was a significant difference with regard to the frequency of contamination of the aspiration fluid between the experimental and control groups (chi-square: P = 0.0001).

CONCLUSIONS

The technical modification described herein allows facile hygienic measures, by which contamination of aspiration fluid by the VCM can be eliminated, which otherwise can be a significant source of contamination.

[Bacterial keratitis. Microbiological analysis as a principle for therapeutic recommendations]

PURPOSE

The study presented differentiates between the aetiological agents of bacterial keratitis in patients with and without a history of contact lens wear. Based on these results, recommendations are given for optimal antibiotic primary therapy.

PATIENTS AND METHODS

Swabs and corneal scrapings were taken from 218 patients referred to the University Eye Hospital in Munich with a diagnosis of bacterial keratitis from 1989 to 1997. Ninety-two of these patients had a history of contact lens wear; 126 had none. The germs were isolated and identified by staining and microscopy. Observing polymicrobial growth in 51 patients, a total of 275 germs was isolated.

RESULTS

The most frequent pathogens were Staphylococcus epidermidis (44%), S. aureus (18%), Streptococcus spp. (10%), Propionibacterium acnes (7%) and Pseudomonas aeruginosa (6%). Gram-negative germs were nearly exclusively isolated from contact lens wearers, gram-positive germs were predominant in non-contact lens wearers.

CONCLUSION

Keratitis in patients with a history of contact lens wear is often caused by aggressive gram-negative germs. Those cases should immediately be treated with quinolones and erythromycin. In keratitis caused by gram-positive pathogens, a combination with aminoglycosides and erythromycin is sufficient.

[Bacterial keratitis in patients with and without contact lens anamnesis]

BACKGROUND

The study shows differences between contact lens wearers and patients without history of contact lenses regarding the spectrum of etiological agents in bacterial keratitis. Based on microbiological analysis, there are given recommendations for an optimal initial antibiotic treatment in both groups.

MATERIAL AND METHODS

From 1989 to 1997 smears, scrapings and corneal biopsies were taken from 218 patients with bacterial keratitis. The causing pathogens were isolated on directly inoculated culture media and identified by staining and microscopy. The resistance pattern of a total of 275 germs was analysed for different antibiotics.

RESULTS

The most frequently isolated germs were Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus spp., Propionibacterium acnes and Pseudomonas aeruginosa. Whereas sensitive gram-positive germs were predominating in contact lens wearers as well as in non-contact lens wearers, multiresistant gram-negative germs could nearly exclusively be isolated from contact lens wearers. Frequently administered antibiotics like aminoglycosides and quinolones are effective in infections caused by Staphylococcus spp., but increasing resistance could be seen to Streptococcus spp. In this case, erythromycin is very sensitive. Gram-negative germs like Pseudomonas aeruginosa are sensitive to quinolones and some aminoglycosides (e.g. tobramycin).

CONCLUSION

In contact lens wearers, more aggressive germs have to be considered than in non-contact lens wearers. In such cases, frequently administered antibiotics like amino-glycosides are not effective. To cover problematic gram-negative germs we recommend the application of quinolones alternating with erythromycin. The latter one is more effective than quinolones and aminoglycosides in case of Streptococcus spp. co-involvement.

CuZn superoxide dismutase transgenic retinal transplants

BACKGROUND

The morphology of retinal transplants is believed to depend on the extent of mechanical disruption of the donor tissue during the surgical procedure and on local factors of the host environment. We hypothesized that oxidative stress during donor tissue preparation and implantation further affects transplant development and investigated the effects of CuZn superoxide dismutase (SOD) overexpression on the survival and morphological development of mouse embryonic retinal transplants.

METHODS

Retinae and livers from embryonic day 14-15 SOD overexpressing transgenic mice and CBA control mice were harvested under sterile conditions. In order to identify transgenic mouse embryos, the embryonic livers were analyzed via nondenaturing gel-electrophoresis for the presence of the human SOD protein. Neural retinae were transplanted as fragmented tissue into the subretinal space of albino BALB/c mice. At 4-8 weeks following transplantation, the grafted eyes were fixed in Bouin's solution and processed for histological analysis.

RESULTS

Both SOD transgenic and control retinal transplants had developed all retinal layers except for a ganglion cell layer and exhibited a similar extent of rosette formation. Computer-assisted, quantitative assessment of retinal graft volumes revealed a significant, around 58% increase in size of SOD transgenic transplants compared with controls.

CONCLUSIONS

Enhanced intracellular SOD levels do not seem to influence retinal transplant morphology as detected by light microscopy. However, volumes of the SOD transgenic transplants were found to be increased compared to control grafts.

[Choroid neovascularization in age-related macular degeneration. Correlation of histological and fluorescence angiography findings]

BACKGROUND

Recent studies have raised confusion about the fluorescein angiographical and histopathological correlation of CNV.

MATERIAL AND METHODS

The preoperative fluorescein angiograms of four patients with subfoveal CNV due to ARMD extracted by pars plana vitrectomy were classified as wellor ill-defined CNV and were correlated to the histopathologically (in serial sections) verrified CNV-location (subneuroretinal (= type II according to Gass) versus sub-RPE (type I according to Gass)).

RESULTS

The locations of all four CNV could be classified by histopathological landmarks as there were RPE, BLD/drusen, and inner Bruchs membrane. Angiographically welldefined membranes were type II membranes according to Gass, whereas the ill-defined membrane represented type I. The CNV with well- and ill-defined borders consisted of type II and type I parts according to Gass.

CONCLUSION

We find subneuroretinal locations of the well-defined CNV examined (type II membranes according to Gass). Correspondingly, ill-defined CNV or ill-defined parts of a CNV seem to be beneath the RPE (type I). The correlation of fluorescein angiography and histopathology should be studied in greater numbers of well- and ill-defined CNV.

[Coagulase-negative staphylococci in normal and chronically inflamed conjunctiva]

This study examines the prevalence of coagulase-negative Staphylococcus species in normal and mildly inflamed conjunctiva, their sensitivity to antibiotics, and their relationship to the remaining flora.

PATIENTS AND METHODS

In 99 patients including 9 HIV-positives in an early stage of the infection, 100 conjunctival swabs were taken and microbiologically investigated for bacteria and fungi. Thirty-four were from healthy eyes. 40 were from patients with chronic (n = 28) and unspecific (n = 12) conjunctivitis, 17 were from patients with a variety of outer inflammatory ocular conditions, and 9 were from the HIV group from uninfected (n = 6) and infected (n = 3) conjunctivae. Samples from each patient were collected with three moistened cotton swabs and directly inoculated onto five different agars, followed by immersion into three specific culture broths. Staphylococci were identified species-wise, the other microorganisms genus-wise. Sensitivity to a broad spectrum of antibiotics was determined by agar diffusion tests.

OUTCOME

Staphylococci were found in 89%, which was the highest prevalence genus-wise. Of those, coagulase-negative species accounted for 86%, while coagulase-positive Staphylococcus aureus was isolated in 12% of all swabs. In the 86 smears positive for coagulase-negative staphylococci, 151 different strains were isolated. In these strains, resistance to the 13 tested antibiotics varied from 0% for vancomycin to 66% for penicillin. Strains which were isolated from patients with chronic conjunctivitis showed a greater range of resistance than those from normal flora, with significant levels for ciprofloxacin, gentamycin and kanamycin (Mann-Whitney) U-test: P < 0.05). All except six strains of staphylococci were identified strains represented ten species, of which Staphylococcus epidermidis was most prevalent (74%), but only made up 70% of all isolated strains of the coagulase-negative staphylococci. Staphylococcus aureus and gram-negative bacteria were found significantly more commonly in patients which chronic conjunctivitis than in healthy eyes, while coagulase-negative species of the Micrococcaceae family were significantly more prevalent in the healthy than in the chronically inflamed conjunctiva (chi-square: P < 0.05).

CONCLUSION

The conjunctiva can simultaneously host several stems of coagulase-negative staphylococci, which differ in regard to species and resistance to antibiotics. This variety might indicate a microbiological balance of the conjunctiva and be reduced in chronic inflammatory conditions. In patients with chronic conjunctivitis the risk for multiresistant coagulase-negative staphylococci is increased.

[No detection of mycoplasma in 205 conjunctival swabs]

Mycoplasma is known to cause pulmonary and urogenital infections in humans. A pathogenicity for the human eye never has been assessed, although they have been observed in the peripheral eye in a few cases of acute and non-specific conjunctivitis, in patients with Reiter's disease and in newborns. Due to the absence of cell walls, mycoplasma is only sensitive to a few antibiotics. Therefore, we presume that mycoplasma has a role in non-specific and chronic conjunctivitis. It is conceivable that in HIV-positive patients the risk of opportunistic colonization of the conjunctiva by mycoplasma is increased. PATIENTS AND METHODS. Between January and December 1992, 205 conjunctival swabs of 151 patients were prospectively analyzed for mycoplasma. The group contained 51 HIV-infected patients (94 swabs). A total of 85 swabs were from non-irritated eyes and the remaining (120) from peripherally inflamed eyes, mainly diagnosed as non-specific or chronic conjunctivitis (75 swabs). Specimen were obtained from the inferior fornix conjunctivae by use of a moistened cotton swab, which was directly immersed in culture broth. For subsequent culture, we used a liquid and a solid mycoplasma medium to differentiate Mycoplasma hominis, Mycoplasma fermentans and Ureaplasma urealyticum. In 77 swabs, a second sample was taken, which was investigated at the Institute for Poultry Diseases of the Ludwig Maximilians University, Munich. OUTCOME. None of 205 swabs, including the 77 samples tested in parallel, gave positive results for mycoplasma. Six cases were positive for bacteria and five cases for fungi. CONCLUSION. In adult patients at the Munich University Eye Hospital with either non-irritated eyes or non-specific and chronic conjunctivitis, no mycoplasma could be detected. With regard to HIV infection, there is no indication that mycoplasma plays a role in opportunistic infections of the conjunctiva.