To study the possible in¯uence of intestinal micro-organisms on the course of strongyloidiasis in mice, a method was developed to obtain axenic infective larvae of Strongyloides venezuelensis. Cultured larvae from conventional mice were treated with sodium hypochlorite 0.25% for 10 min, washed in distilled water and then exposed to various combinations of antibiotics for 30 or 60 min. Success was achieved with a combination of penicillin 180 mg=L and ceftazidime 1 mg=ml. Decontamination of the larvae was determined by aerobic and anaerobic culture and by inoculation into gnotobiotic mice. Viability was established by subcutaneous inoculation of larvae into germ-free and conventional mice. Preliminary results showed that gnotobiotic mice were more susceptible than conventional mice to infection with axenic S. venezuelensis larvae as judged by faecal egg excretion, recovery of worms in the small intestine and histopathological examination of the duodenal mucosa. These results suggest that the normal intestinal¯ora protects the host against experimental infection with S. venezuelensis.

In order to better understand experimental strongyloidiasis in small New World primates, and to evaluate aspects of reinfection and immunosuppression induced by glucocorticoids, nine specimens of Callithrix penicillata (Primates: Cebidae) were administered (by subcutaneous injection, sc) 3000 infective larvae of a strain of Strongyloides venezuelensis (Rhabditida: Strongyloididae) that had been maintained in successive passages through AKR/J mice since 1987. The mean prepatent period was 5.6 ± 0.7 days post-infection (DPI). The mean patent period of infection among the untreated animals (marmosets 1-7) was 123.4 ± 61.4 DPI. Two animals (marmosets 8 and 9) received dexamethasone (2.5 mg/kg, sc) for five consecutive days starting on the 20th day after infection, but this treatment did not alter the course of the infection, and the patent period for these animals was 100.5 ± 58.7 DPI (59 and 142, respectively). Stool examination showed that the highest quantities of parasite eggs were expelled between the 8th and 19th days after inoculation of the larvae. Thereafter, there was a gradual reduction in the number of parasite eggs in feces of all marmosets. During the chronic phase of the infection, before completely negative parasitological findings were obtained, the parasitological examinations were intermittently positive. Reinfection of three of these animals did not result in new positive examinations. However, given the receptiveness of these animals to initial infection with S. venezuelensis and their similarities to human beings, it is proposed that C. penicillata could be used as a nonhuman primate model for experimental strongyloidiasis.

Camundongos da linhagem AKR/J infectados pelo Strongyloides venezuelensis e tratados com Ceftazidima, Dexametasona ou com ambas as drogas foram sacrificados no terceiro, sétimo e décimo segundo dia após infecção. Pulmões e intestino delgado foram processados para histologia. Verificaram-se, nos pulmões dos quatro grupos infectados, infiltrados inflamatórios (neutrófilos e mononucleares) no terceiro dia após a infecção. No sétimo e décimo segundo dia após a infecção, o processo inflamatório se torna reduzido nos animais controle e tratados com antimicrobiano, mas não nos animais imunossuprimidos (com ou sem tratamento com antimicrobiano). A análise da mucosa duodenal confirmou a presença de parasitos em todos os grupos de animais. No 7º dia após a infecção, foram observadas alterações significativas no duodeno dos grupos controle (infectados) e dos infectados e tratados com antimicrobiano, com presença de infiltrado inflamatório, constituído de mononucleares e eosinófilos na mucosa, associada a uma maior quantidade de parasitos, principalmente na região do epitélio e sub-epitélio. Os outros dois grupos (camundongos infectados e imunossuprimidos com ou sem antimicrobiano), não apresentaram processo inflamatório. A mucosa apresentou células caliciformes menos evidentes, sugerindo uma redução de produção de muco. No décimo segundo dia da infecção, os grupos não tratados e tratados apenas com antimicrobiano apresentaram um número reduzido de parasitos e um discreto processo inflamatório no duodeno, enquanto os grupos tratados com imunossupressor (com ou sem antimicrobiano) mostraram presença de um maior número do parasito no duodeno. A permanência da infecção do S. venezuelensis foi mais prolongada nos animais imunossuprimidos em relação aos demais grupos, permanecendo até o 490dia após infecção. Os resultados indicam que a interferência dos tratamentos no equilíbrio da microbiota intestinal favoreceu o parasitismo pelo S. venezuelensis.

Prevotella intermedia is a component of the indigenous microbiota but is also responsible for anaerobic infections of the gastrointestinal tract and oral cavity. The aim of the present study was to investigate the influence of oxidative stress on the in vivo pathogenicity of P. intermedia. Germ-free mice were challenged intraperitoneally with parental (wt) or oxidative stress adapted (aero) strains. Bacterial virulence was evaluated by histopathology, hyperaemia and blood analysis [C-reactive protein (CRP), serum albumin and white blood cells (WBCs)], 3 and 10 days after challenge. CRP levels and WBC count were higher in animals challenged with the aero strain, and the albumin level was lower in this group, only 10 days after infection (P<0.05). Body weight gain was significantly reduced whereas hyperaemia and ratios of spleen/organ weight were increased in animals challenged with the aero strain (P<0.05). The liver of animals challenged with the aero strain showed hyperaemia, vasodilatation as well as an increase in the number of inflammatory cells and liver/organ weight ratio (P<0.05). Similar, but more discrete, alterations were observed in the small intestine of animals challenged with the aero strain. Studies on stress responses of this putative pathogen may help to better understand the aggressive potential and virulence markers of anaerobic bacteria.

The aim of this study was to identify phenotypic changes in a laboratory-derived strain of ertapenem-resistant Escherichia coli (Ec-ERT) when compared to its susceptible parent strain (Ec-WT). In both strains, we assessed both the effects of ertapenem via time-kill curves and the occurrence of cross resistance with other beta-lactams. The strains were compared based on growth pattern, biochemical-physiological profile and changes in the subproteome using 2D-DIGE followed by MALDI-TOF/TOF MS. To assess virulence, we employed a murine model of intraperitoneal infection in which we investigated the invasiveness of both strains. Growth persistence of the laboratory-derived resistant strain was observed via the time-kill curve assay, but cross resistance was not observed for other beta-lactams. We also observed a slower growth rate and changes in the biochemical and physiological characteristics of the drug-resistant bacteria. In the resistant strain, a total of 51 protein spots were increased in abundance relative to the wild-type strain, including an outer membrane protein A, which is related to bacterial virulence. The mouse infection assay showed a higher invasiveness of the Ec-ERT strain in relation to the Ec-WT strain. In conclusion, the alterations driven by ertapenem in E. coli reinforce the idea that antimicrobial agents may interfere in several aspects of bacterial cell biology, with possible implications for host-bacteria interactions.