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Phagocytosis by human polymorphonuclear leukocytes (PMNs) is an important host defense against infections caused by Staphylococcus aureus. Using an in vitro assay, we compared the opsonic requirements for phagocytic killing of prototype strains of encapsulated (type 1) and microencapsulated (type 5 and type 8) S. aureus by human PMNs. More than 85% of broth-grown, logarithmic-phase type 5 and 8 S. aureus organisms were killed by PMNs incubated with fresh normal human, rabbit, or guinea pig serum with complement activity. Under similar conditions, the highly encapsulated type 1 strain was not killed. Both encapsulated and microencapsulated strains were opsonized for phagocytosis by heat-inactivated serum raised in rabbits to killed bacteria. Opsonization by homologous serum was required for phagocytosis of the type 1 strain. In contrast, microencapsulated type 5 and 8 S. aureus organisms were killed by heat-inactivated rabbit serum raised to type 5, type 8, or nonencapsulated isolates; this result suggested that antibodies to the capsule or to cell wall components other than the capsule could opsonize these organisms for phagocytosis. The specificity of the assay was confirmed with capsule type 5-specific monoclonal antibodies, which were opsonic only for the type 5 S. aureus isolate. These studies indicate that, unlike the highly encapsulated type 1 strain, broth-grown microencapsulated S. aureus strains do not resist opsonophagocytic killing in vitro by normal serum.

Helicobacter hepaticus, which induces chronic hepatitis and typhlocolitis in susceptible mouse strains, produces a cytolethal distending toxin (CDT) consisting of CdtA, CdtB, and CdtC. AcdtB-deficientH. hepaticusisogenic mutant (HhcdtBm7) was generated and characterized for colonization parameters in four intestinal regions (jejunum, ileum, cecum, and colon) of outbred Swiss Webster (SW) mice. Inactivation of thecdtBgene abolished the ability of HhcdtBm7 to colonize female mice at both 8 and 16 weeks postinfection (wpi), whereas HhcdtBm7 colonized all of four intestinal regions of three of five males at 8 wpi and then was eliminated by 16 wpi. Wild-type (WT)H. hepaticuswas detected in the corresponding intestinal regions of both male and female mice at 8 and 16 wpi; however, colonization levels of WTH. hepaticusin the cecum and colon of male mice were approximately 1,000-fold higher than in females (P< 0.0079) at 16 wpi. Infection with WTH. hepaticus, but not HhcdtBm7, at 8 wpi was associated with significantly increased mRNA level of ileal and cecal gamma interferon (IFN-γ) in females (P< 0.016 and 0.031 between WTH. hepaticus-infected and sham-dosed females, respectively). In contrast, the mRNA levels of IFN-γ were significantly higher in the colon (P< 0.0079) and trended to be higher in the cecum (P< 0.15) in the HhcdtBm7-colonized male mice versus the sham-dosed controls at 8 wpi. In addition, mRNA levels of ileal IFN-γ were significantly higher in the control females than males at 8 wpi (P< 0.016). There were significantly higher Th1-associated immunoglobulin G2a (IgG2a), Th2-associated IgG1 and mucosal IgA (P< 0.002, 0.002, 0.002, respectively) responses in the mice infected with WTH. hepaticuswhen compared to HhcdtBm7 at 16 wpi. Colonic interleukin-10 (IL-10) expressions at 16 wpi were significantly lower in both female and male mice colonized by WTH. hepaticusor in males transiently colonized through 8 wpi by HhcdtBm7 versus control mice (P< 0.0159). These lines of evidence indicate that (i)H. hepaticusCDT plays a crucial role in the persistent colonization ofH. hepaticusin SW mice; (ii) SW female mice are more resistant toH. hepaticuscolonization than male mice; (iii) there was persistent colonization of WTH. hepaticusin cecum, colon, and jejunum but only transient colonization ofH. hepaticusin the ileum of female mice; (iv)H. hepaticuscolonization was associated with down-regulation of colonic IL-10 production.

Helicobacter mustelae , the gastric pathogen of ferrets, produces an array of surface ring structures which have not been described for any other member of the genus Helicobacter , including H. pylori . The unique ring structures are composed of a protein named Hsr. To investigate whether the Hsr rings are important for colonization of the ferret stomach, ferrets specific pathogen free for H. mustelae were inoculated with an Hsr-deficient mutant strain or the wild-type H. mustelae strain. Quantitative cultures from antral biopsy specimens obtained at 3, 6, and 9 weeks postinoculation demonstrated no significant difference in the levels of bacteria in the ferrets that received the Hsr-negative strain and the ferrets infected with the parent strain. However, when the ferrets were biopsied at 12 and 15 weeks and necropsied at 18 weeks after infection, the levels of bacteria of the Hsr-negative strain in the stomach antrum were significantly reduced. This decline contrasted the robust antral colonization by the wild-type strain. The Hsr-negative strain did not efficiently colonize the gastric body of the study ferrets. Histological examination at 18 weeks postinoculation revealed minimal gastric inflammation in the animals that received the mutant H. mustelae strain, a finding consistent with its waning infection status, whereas lesions characteristic of helicobacter infection were present in ferrets infected with the wild-type strain. Scant colonization by the Hsr-negative H. mustelae strain at the end of the 18-week study, despite initial successful colonization, indicates an inability of the mutant to persist, perhaps due to a specific host response.