Disseminated gonococcal infection in mice

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Growth of Neisseria gonorrhoeae in the female mouse genital tract does not require the gonococcal transferrin or hemoglobin receptors and may be enhanced by commensal lactobacilli

Neisseria gonorrhoeae is capable of utilizing a variety of iron sources in vitro, including human transferrin, human lactoferrin, hemoglobin, hemoglobin-haptoglobin complexes, heme, and heterologous siderophores. Transferrin has been implicated as a critical iron store for N. gonorrhoeae in the human male urethra. The demonstration that gonococci can infect the lower genital tracts of estradiol-treated BALB/c mice in the absence of human transferrin, however, suggests that other usable iron sources are present in the murine genital tract. Here we demonstrate that gonococcal transferrin and hemoglobin receptor mutants are not attenuated in mice, thereby ruling out transferrin and hemoglobin as essential for murine infection. An increased frequency of phase variants with the hemoglobin receptor "on" (Hg(+)) occurred in ca. 50% of infected mice; this increase was temporally associated with an influx of neutrophils and detectable levels of hemoglobin in the vagina, suggesting that the presence of hemoglobin in inflammatory exudates selects for Hg(+) phase variants during infection. We also demonstrate that commensal lactobacilli support the growth of N. gonorrhoeae in vitro unless an iron chelator is added to the medium. We hypothesize that commensal lactobacilli may enhance growth of gonococci in vivo by promoting the solubilization of iron on mucosal surfaces through the production of metabolic intermediates. Finally, transferrin-binding lipoprotein (TbpB) was detected on gonococci in vaginal smears, suggesting that although gonococci replicate within the genital tracts of mice, they may be sufficiently iron-stressed to express iron-repressible proteins. In summary, these studies support the potential role of nontransferrin, nonhemoglobin iron sources during gonococcal infection of the female genital tract.

Iron acquisition in the pathogenic Neisseria

Pathogenic Neisseria species need to obtain iron from the host to grow in vivo. Several iron-transport systems are known, and regulation of Neisseria iron-transport genes occurs via the transcriptional regulator Fur. There is evidence that the ability to transport iron is crucial to the survival of these organisms in vivo.

Effect of estrogen (17 beta-estradiol) on the susceptibility of mice to disseminated gonococcal infection

Studies of the effect of sex hormones on the susceptibility of mice to the disseminated gonococcal infection demonstrated significantly enhanced susceptibility of mice injected with estrogen (17 beta-estradiol). In mice treated with estradiol, bacteremia progressively developed within 12 h postinoculation and mice died within the next 6 h, whereas bacteremia in mice treated with progesterone was completely cleared within 3 h postinoculation. The administration of estradiol affected the function of polymorphonuclear leukocytes (PMN) responsible for eliminating gonococci, but the administration of progesterone did not. The bactericidal activity of PMN mediated by myeloperoxidase was affected by estradiol, but the capacity of PMN to release superoxide anion was not. Furthermore, peritoneal cell analysis demonstrated that the infiltration of PMN in the peritoneal cavity of estradiol-treated mice significantly decreased when mice were injected intraperitoneally with gonococci. These effects on PMN by estradiol may play an important role in the enhanced susceptibility of estradiol-treated mice to gonococcal infection.

Lethal Haemophilus influenzae type b infection in mice

Previous animal models of invasive Haemophilus influenzae type b (HITB) infection are characterized by a low mortality rate. We produced a highly lethal infection in CF1 mice using mouse passage, mucin, and hemoglobin to enhance infectivity. Infection by the intraperitoneal route was followed by progressive peritonitis and bacteremia with subsequent HITB infection of the brain and meninges, and death. Death occurred between eight and 72 hours after infection and was associated with 10(6) to 10(9) HITB per ml of blood and with 10(2) to 10(5) HITB per g of brain. Mucin-hemoglobin did not augment HITB growth, but impaired macrophage adherence to glass in vitro, without decreasing cellular viability. In vivo, mucin-hemoglobin decreased the rate of disappearance of 51Cr-labelled HITB from the blood by impairment of hepatic clearance. This technically simple and inexpensive model is useful for the study of HITB infections in which bacterial multiplication, invasion and host lethality are desired features.

Pathogenesis of atoxinogenic strains of gram--negative bacteria--a hypothesis

Textbooks of medical microbiology attribute to endotoxin a primary pathogenic role in diseases caused by nontoxinogenic gram negative bacteria. There is little experimental data to support this claim while some observations indicate the contrary. The possibility cannot be ignored that our understanding of the biological effects of endotoxin is based on the administration of endotoxin as a bolus rather than as a continuous release in small amounts over a period of hours or days as probably occurs during an infection. Results are described that clearly show how different the response can be under the two conditions. It is suggested, moreover, that mediators formed primarily by macrophages stimulated by endotoxin may contribute significantly to the pathogenesis of these diseases.

Effects of tampon components on growth and dissemination of Neisseria gonorrhoeae

Six components used in vaginal tampons were tested for their effects on a strain of Neisseria gonorrhoeae isolated from a patient with disseminated infection. Tampon components containing carboxymethyl cellulose or its derivative prolonged the in-vitro survival of gonococci and, when injected with mucin into mice, significantly (P less than 0.0001) increased the dissemination of gonococci from the peritoneal cavity. In contrast, a component extracted from rayon tampons reduced in-vitro survival and appeared to suppress gonococcal dissemination in mice. Since tampons are used by a large number of women at a time when the risk of developing complications from venereal infections are increased, their effects on potential urogenital pathogens warrant further study.

Induction of immunity against lethal Haemophilus influenzae type b infection by Escherichia coli core lipopolysaccharide

Efforts to prevent Haemophilus influenzae type b (HIB) infections in infancy have been hampered by the low immunogenicity of capsular polysaccharide vaccines in children younger than 18 mos. In searching for alternate immunogens, we have studied the protective potential of polysaccharide-poor, lipid-rich endotoxin (LPS) core in experimental HIB infections. Because all gram-negative bacteria have similar LPS core structures, we were able to use as vaccine the J5 mutant of Escherichia coli 0111, the LPS of which consists only of core components, and thus to avoid problems in interpretation arising from vaccine contamination with non-LPS HIB immunogens. Mice were given graded inocula of HIB and developed lethal infection analogous to human HIB disease when virulence was enhanced with mucin and hemoglobin. After active immunization with heat-killed E. coli J5, 40/50 (80%) of infected mice survived, compared with 14/50 (28%) of saline-immunized controls (P less than 0.005). Passive immunization with rabbit antiserum against E. coli J5 prevented lethal HIB infection when administered 24 or 72 h before or 3 h after infection. This protection was abolished by adsorption of antiserum with purified J5 LPS, with survival reduced from 14/24 to 0/24 (P less than 0.005). Furthermore, rabbit antiserum to purified J5 LPS gave just as potent protection against death as antiserum to whole J5 cells. These studies demonstrate that immunity to core LPS confers protection against experimental murine HIB infection and provide the framework for a new approach to prevention of human disease from HIB.

In vitro kinetics of phagocytosis and intracellular killing of gonococci by peritoneal macrophages from mice deficient in complement component 5

Unstimulated resident peritoneal macrophages were harvested from complement-sufficient (C5+) and complement-deficient (C5-) mice by peritoneal lavage and cultured for 14 h. Adherence to cover slips was determined, and the monolayer was infected with transparent T1 gonococci. At various times after infection, the macrophages were observed for both attachment and phagocytosis of the gonococci by scanning and transmission electron microscopy. this analysis indicated that C5+ macrophages were capable of immediate phagocytosis of gonococci, with maximal phagocytosis occurring by 60 to 90 min. In contrast, C5- macrophages had a greater lag time before initiation of phagocytosis; this event was started by 30 min and completed by 90 min. The intracellular gonococci which were phagocytized by either C5+ or C5- mice were completely killed after 30 min of incubation. It appears that C5- mice are at a disadvantage in the early kinetics of the phagocytosis of gonococci, but that this does not affect the ultimate intracellular destruction of gonococci.

Gonococcal infection in endotoxin-resistant and endotoxin-susceptible mice

The role of endotoxin responsiveness in defense against gonococcal infection was studied in endotoxin-resistant (C3H/HeJ) and endotoxin-susceptible (C3H/HeN) mice by using a model of disseminated gonococcal infection (DGI) and a model of gonococcal survival in the female genital tract to determine the ability of the mice to eliminate gonococci. The 50% lethal dose in the DGI model was 10(9.6) for C3H/HeJ mice and 10(5.2) for C3H/HeN mice. Levels of bacteremia during infection indicated the C3H/HeJ mice cleared large numbers of gonococci from their peripheral blood by 24 h post-inoculation but that C3H/HeN mice did not. Additionally, the peritoneal leukocyte response after intraperitoneal inoculation of gonococci was greater in C3H/HeJ mice than in C3H/HeN mice, which suggested that the ability to mount an inflammatory response to endotoxin may be important in defense against DGI. Besides being different in susceptibility to DGI, C3H/HeJ mice were found to be more resistant then C3H/HeN mice to genital colonization by gonococci. The resistance of C3H/HeJ mice to genital colonization by gonococci appeared to be due to both the high numbers of polymorphonuclear leukocytes in the genital secretion and the predominance of inhibitory gram-negative genital flora in that mouse strain.