Influence of Pregnancy on the Pathogenesis of Listeriosis in Mice Inoculated Intragastrically

Abstract

Pregnancy increases the risk of listeriosis, a systemic disease caused by Listeria monocytogenes. However, there is incomplete agreement on the reasons for this increased risk. We examined two features of listeriosis in gravid and nongravid female mice following intragastric (gavage) inoculation, namely, (i) disease severity (measured by lethality) and (ii) listerial infectivity (measured by liver and spleen colonization levels up to 120 h postinoculation). Two listerial strains of differing serotype (1/2a and 4nonb) were initially employed. Neither strain produced a lethal infection in nonpregnant female mice (dose range, 10 6 to 10 9 CFU/mouse), and only the 4nonb strain produced lethalities in pregnant mice (dose range, 10 6 to 10 8 CFU/mouse). The 4nonb strain also produced a higher level of liver and spleen colonization than the 1/2a strain following gavage administration. (The two strains showed similar levels of colonization if parenterally administered.) Both strains were equally capable of binding to and forming plaques upon cultured mouse enterocytes. The ability of the 4nonb strain to produce a lethal infection in pregnant animals did not correlate with an increased incidence or level of liver and spleen colonization over that in nonpregnant females. However, the lethality rate did correlate well with the rate at which embryos and their surrounding decidual covering became infected, suggesting that intrauterine infection could be responsible for the increased disease severity in the gravid females.

A Listeria monocytogenes Mutant Defective in Bacteriophage Attachment Is Attenuated in Orally Inoculated Mice and Impaired in Enterocyte Intracellular Growth

“…The L. monocytogenes strains and bacteriophage derivatives employed in this study are listed in Table 1. Our parental L. monocytogenes strain, F6214-1, is a spontaneous streptomycinresistant derivative of serotype 4nonb strain F6214 (18). Depending on the experimental situation, listerial strains were propagated at temperatures ranging from 22 to 44°C in either L broth (24) or brain heart infusion (BHI) broth or on those media supplemented with 1.5% agar.…”

“…42°C and at higher temperatures. Broth-grown bacteria destined for mouse inoculation were prepared as described by Hamrick et al (18). Where indicated, antibiotics were incorporated into the media at the following concentrations: streptomycin, 50 g/ml; nalidixic acid, 40 g/ml; erythromycin, 1 g/ml; lincomycin, 25 g/ml; chloramphenicol, 10 g/ml; and ampicillin, 100 g/ml.…”

“…The lesion in P35h4 expands the host range of P35 to include listerial serotypes other than serotype 1/2a, such as our serotype 4nonb strain (19). An L. monocytogenes strain F6214-1 Tn917 mutant bank was constructed as previously described (18). Bacteria exhibiting resistance to chloramphenicol, erythromycin, and lincomycin were screened for phage resistance by patching bacteria onto L agar plates overlaid with 3 ml of LCM soft agar containing 10 8 to 10 9 P35h4 phage per plate.…”

“…Cultured mouse enterocyte (MODE K [41]) monolayers were propagated as previously described (18). Listerial strains destined for tests of binding and plaque-forming ability were grown overnight in BHI broth at 31°C with shaking.…”

“…An aliquot of the culture was harvested by centrifugation (7,668 ϫ g for 10 min), and the cell pellet was resuspended in Dulbecco modified Eagle medium to obtain a final concentration of 1.5 ϫ 10 8 CFU/ml. The efficiencies with which the various listerial strains bound and formed plaques on MODE K cells were determined as previously described (18), except that plaque formation was assessed 48 h after binding in wells fixed with 100% methanol and stained with HEMA 3 solution II (Protocol; Fisher Scientific). Plaques were enumerated and plaque sizes (area in pixels) were determined using the AlphaImager 3300v2.03 spot denso analysis tool (Alpha Innotech Corp.).…”