Parenteral sparfloxacin compared with ceftriaxone in treatment of experimental endocarditis due to penicillin-susceptible and -resistant streptococci.

A new, investigational, parenteral form of sparfloxacin was compared with ceftriaxone in the treatment of experimental endocarditis caused by either of three penicillin-susceptible streptococci or one penicillin-resistant streptococcus. Both drugs have prolonged half-lives in serum, allowing single daily administration to humans. Sparfloxacin had relatively low MICs (0.25 to 0.5 mg/liter) for all four organisms and was also greater than or equal to eight times more effective than the other quinolones against 21 additional streptococcal isolates recovered from patients with bacteremia. Ceftriaxone MICs were 0.032 to 0.064 mg/liter for the penicillin-susceptible strains and 2 mg/liter for the resistant isolate. Both antibiotics resulted in moderate bacterial killing in vitro. Rats with catheter-induced aortic vegetations were inoculated with 10(7) CFU of the test organisms. Antibiotic treatment was started 48 h later and lasted either 3 or 5 days. The drugs were injected at doses which mimicked the kinetics in human serum produced by one intravenous injection of 400 mg of sparfloxacin (i.e., the daily dose expected to be given to human adults) and 2 g of ceftriaxone. Both antibiotics significantly decreased the bacterial densities in the vegetations. However, sparfloxacin was slower than ceftriaxone in its ability to eradicate valvular infection caused by penicillin-susceptible bacteria. While this difference was quite marked after 3 days of therapy, it tended to vanish when treatment was prolonged to 5 days. In contrast, sparfloxacin was very effective against the penicillin-resistant isolate, an organism against which ceftriaxone therapy failed in vivo. No sparfloxacin-resistant mutant was selected during therapy. Thus, in the present experimental setting, this new, investigational, parenteral form of sparfloxacin was effective against severe infections caused by both penicillin-susceptible and penicillin-resistant streptococci.

Effects of immunosuppressive drugs on T helper cells subsets and potential to promote tolerance in a stringent experimental transplantation model.

To achieve the goal of sustained donor-specifi c transplantation (Tx) tolerance, research efforts are now focusing on therapies based on specifi c cell subsets with regulatory properties. We and others have previously highlighted the therapeutic potential of naturally occurring CD4+CD25+Foxp3+ regulatory T cells (nTreg) in promoting long-term graft acceptance. Using more stringent experimental Tx models, we were however confronted to limitations. Indeed, while the transfer of antigenspecifi c nTreg promoted long-term MHC-mismatched skin allograft acceptance in lymphopenic mice in the absence of any immunosuppressive drug, allograft survival was only slightly prolonged when nTreg were transferred alone into non-lymphopenic mice. This suggested that in more stringent conditions, adjuvant therapies may be needed to effectively control alloreactive T cells (Teff). Whether and how the expansion of the Treg pool could be best combined with current immunosuppressive regimens in clinical settings remains to be defi ned. In this study, we have used in vitro assays and an in vivo skin Tx model to investigate the effects of various immunosuppressive drugs on the survival, proliferation and effector function of Teff and nTreg in response to alloantigens. Teff proliferation was inhibited in a dose-dependent manner by rapamycin and cyclosporine A, while anti-CD154 mAb only marginally affected Teff survival, proliferation and effector fucntion in vitro. Rapamycin promoted apoptosis of Teff as compared to nTreg that were more resistant in the presence of IL-2. In vivo, the transfer and/or expansion of Treg could be advantageously combined with rapamycin and anti-CD154 mAb treatment to signifi cantly prolong MHC-mismatched skin allografts survival in non-lymphopenic recipients. Taken together our data indicate that immunosuppressive drugs differentially target T-cell subsets and that some regimens could promote Treg expansion while controlling the Teff pool in response to alloantigens.

Leishmania braziliensis: partial control of experimental infection by interleukin-12 p40 deficient mice

Resistance to infection by Leishmania major has been associated with the development of a Th1 type response that is dependent on the presence of interleukin 12 (IL-12). In this work the involvement of this cytokine in the response to infection by L. braziliensis, a less virulent species in the mouse model, was evaluated. Our results show that while interferon (IFN-g) deficient (-/-) mice inoculated L. braziliensis develop severe uncontrolled lesions, chronic lesions that remained under control up to 12 weeks of infection were observed in IL-12p40 -/- mice. IL 12p40 -/- mice had fewer parasites in their lesions than IFN-g-/- mice. Lymph node cells from IL-12p40 -/- were capable of producing low but consistent levels of IFN-g suggestive of its involvement in parasite control. Furthermore, as opposed to previous reports on L. major-infected animals, no switch to a Th2 response was observed in IL-12p40 -/- infected with L. braziliensis.

The sexual behaviour of Panstrongylus megistus (Hemiptera: Reduviidae): an experimental study

The factors affecting the sexual behaviour of Panstrongylus megistus were studied under laboratory conditions. A general description of mating behaviour is presented for this species. The effect of the time elapsed after the first imaginal feeding on the mating frequency, the motivation of males to mate and the rejection behaviour by females, were analyzed. We also determined the number of copulas accepted by females of this species. Finally, the possible existence of a sexual chemical signal promoting male aggregation around mating couples was evaluated. Results showed that mating frequency increased with the time elapsed since the first adult meal. Despite the number of male copulatory attempts did not change as a function of time, the rejection behaviour of females became gradually less frequent. Females rejected mating by means of body flattening on the substrate, abdominal movements, evasion or stridulation. After a single copula, females did not usually accept to mate again. Neither male nor female aggregation around mating couples was observed, suggesting the absence of a sexual assembling pheromone in P. megistus.

Experimental lagochilascariosis: histopathological study of inflammatory response to larval migration in the Murine model

The goal of this study was to investigate the pattern of inflammatory response induced by Lagochilascaris minor in murine experimental model. For this purpose 115 mice were given 1000-3000 L. minor infective eggs "per os" and 51 uninfected mice were considered as controls. Four hours post-inoculation (PI), 3rd stage larvae were seen passing through the mucosa of terminal ends of small intestine. Six hours PI larvae were observed as an embolus inside the portal vein and also migrating through the liver parenchyma. During the first 24 h larvae-containing eggs of L. minor were observed in the lumen of intestinal tract. Two days PI larvae were seen migrating through lung parenchyma associated with an initial neutrophilic perivasculitis. From the 13th day of this experimental study, L. minor larvae were found mainly in skeletal muscles, in the center of granulomas. Concentric fibrosis with mixed inflammatory infiltrate involved the larvae after the 47th day PI, persistently. This experimental murine study with L. minor indicated that the 3rd stage larvae penetrated via ileum-cecal mucosa reaching the liver and probably other tissues through the hematogenic via. Throughout its pathway the larvae induced a granulomatous reaction, with abundant polimorphonuclear cells.

Experimental hepatic fibrosis due to Capillaria hepatica infection (differential features presented by rats and mice)

Rats and mice are among the most susceptible hosts for the helminth Capillaria hepatica. More information on the similarities and differences between the hepatic pathology presented by these two parasite hosts are needed, since they may represent good models for the study of hepatic fibrosis. Early changes are similar for both hosts and are represented by necro-inflammatory lesions around dead parasites and their eggs and diffuse and intense reactive hepatitis. Although worms remain alive longer in mice than in rats, hepatic changes are more rapidly and deeply modulated in the former, even leading to almost complete disappearance of fibrosis. As for the rats, the modulation of the focal lesions is followed by the formation of septal fibrosis, a process where fine and long fibrous septa appear connecting portal spaces and central veins in such a way as to form a final morphologic picture of cirrhosis. Hepatic functional changes usually present good correlations with the morphologic findings at the different phases of the infection evolution. Therefore C. hepatica infection in rats and mice represent two different models of hepatic fibrosis and these differences, if properly known and understood, can be explored to answer different questions regarding several aspects of hepatic fibrosis

Experimental kinetics of infection induced by Yersinia pseudotuberculosis isolated from stock animals

The course of in vivo infection of five isolates of Yersinia pseudotuberculosis was followed for three weeks in Swiss mice. The strains were isolated from diarrheic and normal feces and mesenteric lymph nodes of healthy and sick stock animals. Four strains of serogroup O:3 and one of serogroup O:1a, with and without the virulence plasmid, were inoculated intragastrically and intravenously in the mice. Groups of five animals were sacrificed at 6 h and 3, 6, 10, 15, and 21 days after inoculation, and organs and tissues were checked for possible macroscopic alterations. Development of infection was monitored at these times by performing viable bacterial counts in homogenates of selected tissues. The animals were cheked daily for clinical alterations. The results of the study showed that strains with the virulence plasmid infected organs and tissues at various times and at varying intensity by both routes of infection, the strain of type O:1a being the most invasive. Moreover, clinical and pathological alterations occurred only in animals inoculated with bacteria carrying the virulence plasmid, regardless of the route of infection.

Ceftriaxone acts synergistically with levofloxacin in experimental meningitis and reduces levofloxacin-induced resistance in penicillin-resistant pneumococci.

Ceftriaxone acted synergistically with levofloxacin in time-killing assays in vitro over 8 h against two penicillin-resistant pneumococcal strains (WB4 and KR4; MIC of penicillin: 4 mg/L). Synergy was confirmed with the chequerboard method, showing FIC indices of 0.25. In the experimental rabbit meningitis model, ceftriaxone (1x 125 mg/kg) was slightly less bactericidal (-0.30 Deltalog(10) cfu/mL(.)h) compared with levofloxacin (-0.45 Deltalog(10) cfu/mL(.)h) against the penicillin-resistant strain WB4. The combination therapy (levofloxacin and ceftriaxone) was significantly superior (-0.64 Deltalog(10) cfu/mL(.)h) to either monotherapy. In cycling experiments in vitro, the addition of ceftriaxone at a sub-MIC concentration (1/16 MIC) reduced levofloxacin-induced resistance in the two strains KR4 and WB4. After 12 cycles with levofloxacin monotherapy, the MIC increased 64-fold in both strains versus a 16-fold increase with the combination (levofloxacin + ceftriaxone 1/16 MIC). In both strains, levofloxacin-induced resistance was confirmed by mutations detected in the genes parC and gyrA, encoding for subunits of topoisomerase IV and gyrase, respectively. The addition of ceftriaxone suppressed mutations in parC but led to a new mutation in parE in both strains.