Experimental endogenous endophthalmitis caused by Haemophilus influenzae type b

A Case of Endophthalmitis After Bilateral Medial Rectus Recession

A 9-month-old male infant with a history of Down syndrome underwent bilateral medial rectus recession. Two weeks postoperatively, he developed leukocoria of the left eye with a white opacity posterior to the lens, numerous undulations, necrosis, and hemorrhages in the retrolental space. His contralateral eye had white retinal lesions nasally. Ultrasound examination of the left eye showed a funnel retinal detachment, loculated debris, and a small, central, hyperechoic area concerning for calcification. He underwent enucleation because retinoblastoma could not be definitively ruled out. Given this patient's low visual potential, enucleation was a definitive and safe treatment option. Ocular pathology showed significant inflammation and necrosis. There was an area of scleral perforation by a suture adherent to the retina and vitreous, surrounded by inflammatory cells. This case uniquely demonstrates pediatric endophthalmitis following strabismus surgery, secondary to scleral perforation confirmed by histopathological analysis. Care must be taken during scleral passage of sutures to prevent inadvertent scleral perforation and the potential complication of endophthalmitis. [J Pediatr Ophthalmol Strabismus. 2017;54:e37-e41.].

Complex role of hemoglobin and hemoglobin-haptoglobin binding proteins in Haemophilus influenzae virulence in the infant rat model of invasive infection

Haemophilus influenzae requires an exogenous heme source for aerobic growth in vitro. Hemoglobin or hemoglobin-haptoglobin satisfies this requirement. Heme acquisition from hemoglobin-haptoglobin is mediated by proteins encoded by hgp genes. Both Hgps and additional proteins, including those encoded by the hxu operon, provide independent pathways for hemoglobin utilization. Recently we showed that deletion of the set of three hgp genes from a nontypeable strain (86-028NP) of H. influenzae attenuated virulence in the chinchilla otitis media model of noninvasive disease. The present study was undertaken to investigate the role of the hgp genes in virulence of the wild-type serotype b clinical isolate HI689 in the infant rat model of hematogenous meningitis, an established model of invasive disease requiring aerobic growth. Bacteremia of high titer and long duration (>14 days) and histopathologically confirmed meningitis occurred in >95% of infant rats challenged at 5 days of age with strain HI689. While mutations disrupting either the Hgp- or Hxu-mediated pathway of heme acquisition had no effect on virulence in infant rats, an isogenic mutant deficient for both pathways was unable to sustain bacteremia or produce meningitis. In contrast, mutations disrupting either pathway decreased the limited ability of H. influenzae to initiate and sustain bacteremia in weanling rats. Biochemical and growth studies also indicated that infant rat plasma contains multiple heme sources that change with age. Taken together, these data indicate that both the hgp genes and the hxuC gene are virulence determinants in the rat model of human invasive disease.

Hemophilus influenzae meningitis in the rat: behavioral, electrophysiological, and biochemical consequences

Hemophilus influenzae is the most common cause of bacterial meningitis in children, and a high percentage of survivors are at risk for long-term sequelae. To explore the mechanisms responsible for these sequelae, a neonatal rat model was used to define the behavioral, electrophysiological, and biochemical changes following meningitis. Three days after inoculation of 6-day-old rats with a minimum of 1 X 10(7) colony-forming units of a virulent Hemophilus influenzae, type b, cerebrospinal fluid and blood were cultured to confirm the presence of meningitis and bacteremia, respectively. At this time, forebrain norepinephrine and dopamine levels were significantly elevated in meningitic rats when standardized on a wet-weight basis. No changes in brain serotonin or heart norepinephrine levels could be found in the 9-day-old rats. No residual changes were found in steady-state concentrations of norepinephrine or dopamine in surviving adult rats. However, survivors that had had meningitis as neonates showed significant impairment in active and passive avoidance learning tasks and demonstrated a significantly higher level of activity during a habituation period in circular photocell activity cages. No change in the flinch-jump threshold was detected. Brainstem auditory evoked potentials showed delays of various waves in 3 of 10 Hemophilus influenzae type b-treated adult rats tested. These rats also exhibited markedly augmented locomotory responses to d-amphetamine (1 mg/kg), suggesting a long-lasting perturbation of central monoamine neuronal transmission.

Metastatic bacterial endophthalmitis: a contemporary reappraisal

Metastatic bacterial endophthalmitis remains a challenge to the clinician despite the success of antibiotics in reducing its frequency and severity. Controversy currently surrounds the management of this condition because of uncertainty about the value of and indications for vitreous surgery. We review 72 cases of metastatic endophthalmitis from the past decade, including five not previously published. The spectrum of causative bacteria changed significantly during this period, with displacement of meningococcus by Bacillus cereus as the most frequently reported agent and an increasing incidence of infection by organisms of low pathogenicity in immunologically compromised hosts. We propose a new classification scheme for metastatic endophthalmitis based on the location (anterior or posterior segment) and extent (focal or diffuse) of the primary intraocular infection. Focal and anterior cases appear to have a good prognosis, while posterior diffuse disease nearly always leads to blindness. Our analysis of outcomes suggests that systemic antibiotics are more valuable in metastatic than in postoperative or traumatic endophthalmitis and that intraocular antibiotic injection and vitrectomy make only a limited contribution to successful treatment in metastatic infection. We recommend a clinical approach to metastatic endophthalmitis that minimizes exposure of patients to the risks of invasive procedures.

Intra-ocular and CNS listeriosis following systemic infection in Wistar rats with chronic serum sickness

The relationship of immune complex deposits and cell-mediated immunity to the occurrence of ocular and brain listeriosis following a low (0.007-0.03 LD50) intraperitoneal challenge was investigated in 68 Wistar rats with chronic experimental serum sickness and 68 normally resistant controls. The induction of chronic serum sickness involved long continued immunization with bovine serum albumin which resulted in a high level of immune complex entrapment in both the ciliary processes (92%) and choroid plexus (74%) of eye and brain. The extensive immune deposits were associated with a high (23%) incidence of CNS listeriosis and a much lower rate (5.9%) of ocular listeriosis. The difference in incidence could not be related to impaired cell-mediated immunity based on cultural data in liver and spleen. The results seem to indicate that the eye is less vulnerable to systemic listerial infection in chronic immune complex disease despite comparable immune complex entrapment in the ciliary processes and choroid plexus. The findings reflect biologically significant differences between eye and brain that influence their respective vulnerability to systemic Listeria, an opportunistic bacterium, of clinical importance in patients with chronic immunological disorders.

Further studies on the immunology of the infant rat experimental model of Haemophilus influenzae type B meningitis

An age-related acquisition of anticapsular (AC) antibodies to Haemophilus influenzae b (HIb) did not occur in rats; this result corrects a previous spurious observation from this laboratory. Purified HIb polysaccharide was found to be totally non-immunogenic over a wide range of doses in infant and adult rats, with or without booster immunizations. Killed HIb was also totally non-immunogenic. Only about one-quarter of survivors of infantile HIb disease made an AC antibody response. In an attempt to observe “immune paralysis”, survivors of infantile HIb disease were immunized with live HIb at age 8 weeks. This immunization resulted in significantly fewer AC antibody responders in the survivors than in the controls. However, immunization of survivors with killed HIb produced significantly greater responders in survivors than in controls. In order to determine whether passive protection from HIb disease could be achieved by non-capsular antibodies, survivors' offspring were studied and found to be protected from infantile HIb disease due to bactericidal (BA) antibodies that were probably not directed at the capsular polysaccharide. Using the BA assay, differences were observed between two HIb strains, presumably due to differences in non-capsular antigens.

The infant rat experimental model of HIb disease appears to have only limited value in the study of AC antibody responses since infant rats differ from infant humans in several respects. The model may be more useful in studying the immunology of non-capsular HIb antigens including their role in protective immunity and possible differences in these antigens among strains of HIb.

Significance of noncapsular antigens in protection against experimental Haemophilus influenzae type b disease: cross-reactivity

A bacterial strain, tentatively identified as an Actinobacillus species, was found to asymptomatically colonize the pharynx of some rats and to bear cell wall antigens which cross-react with noncapsular antigens of Haemophilus influenzae type b (HIb). The cross-reacting antigens appeared to be a heterogeneous mixture with varying molecular size and charge. The antigenic moieties are probably carbohydrate in nature. Antisera raised with this strain had both immunochemical and biological (bactericidal, opsonizing, and protective against experimental infection) activity against HIb. These findings lend further evidence to the idea that noncapsular antigens are important in the induction of resistance to HIb disease. The findings also raise the possibility of using bacteria which cross-react with noncapsular antigens for immunization against HIb disease in humans through nasopharyngeal or enteric colonization.

Age-related susceptibility to Pseudomonas aeruginosa ocular infections in mice

The susceptibility of newborn and infant mice to eye infection by Pseudomonas aeruginosa was studied in 5-, 10-, 15- to 16-, and 21-day-old mice. In the first of three age-related susceptibility experiments, inoculation of P. aeruginosa under the unopened eyelids of infant (5- and 10-day-old) mice in the absence of prior corneal wounding resulted in acute infection and rapid death of many of the animals. However, endophthalmitis was observed in about 30% of bacteremic animals that survived to age 14 to 15 days. In the second experiment, 15- to 16-day-old mice whose eyes were open received P. aeruginosa topically onto either wounded or unwounded corneas. At least 50% of the mice that received both corneal wounding and the bacteria exhibited keratitis, endophthalmitis, and subsequent phthisis bulbi. None of the infected mice died of bacteremia. In addition, mice infected in the absence of corneal wounding did not exhibit any eye damage. In the third experiment, the wounded-cornea responses of 21-day-old mice to P. aeruginosa were more variable. Thirty seven percent of the mice exhibited an intermediate response of decreased eye size and cataracts which was not observed in 15- to 16-day-old mice, 32% recovered spontaneously, and 29% exhibited complete shrinkage of the infected eyes. The variability of the latter responses may reflect a transitional maturation period of natural immunity to the organism in some of the animals, since all 4- to 6-week-old adult mice respond routinely to ocular wounding and similar infections with the organism by undergoing a spontaneous resolvable keratitis (3 to 4 weeks).

Effect of neonatal gastrointestinal colonization with cross reacting Escherichia coli on anticapsular antibody production and bacteremia in experimental Haemophilus influenzae type b disease of rats

Neonatal gastrointestinal colonization of newborn rats with Escherichia coli 075:K100:H5, cross-reactive with the capsular polysaccharide of Haemophilus influenzae type b, was harmless but failed to stimulated detectable ( greater than 200 ng/ml) serum anticapsular antibodies. Neonatally colonized rats, when challenged at age 13 weeks by intraperitoneal inoculation of H. influenzae b, showed no difference in the frequency, magnitude, or duration of bacteremia or in the postinfection anticapsular antibody response when compared with saline-fed controls. However, neonatally colonized rats challenged at age 4 weeks had a significantly decreased incidence of sustained bacteremia and/or endophthalmitis when compared with controls. This decreased frequency of disease correlated with a significant increase in postinfection serum anticapsular antibodies. Neonatal gastrointestinal colonization with cross-reacting E. coli appears to "prime" the young host to respond to infection with H. influenzae b with an anticapsular antibody response that protects against sustained H. influenzae b bacteremia and its complications.

Immunology of the infant rat experimental model of Haemophilus influenzae type b meningitis

The age-related acquisition of serum anticapsular and bactericidal antibodies to Haemophilus influenzae type b observed in rats was similar to that of humans. The antigenic source for this "natural" immunity was not identified since neither pharyngeal infection with H. influenzae b nor enteric colonization by cross-reacting bacteria was detected. Infant rats surviving H. influenzae b bacteremia failed to respond immunologically to the capsular polysaccharide. However, surviving rats demonstrated no impairment of immune responsiveness to this antigen after subsequent immunization with live bacteria in adulthood. In passive protection experiments, antibodies directed against the type b capsular polysaccharide represented the major protective specificity. However, a small protective effect of antibodies to noncapsular antigens also appeared to have been demonstrated.