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[The lymphocyte proliferative response to Staphylococcus aureus antigen in mice with an opposite susceptibility to staphylococcal infection].

The difference between the proliferative response of spleen cells to S. aureus cytoplasmic antigen on days 5 and 9 of the infectious process was shown in experiments of CBA and C3HA mice, opposite in their susceptibility to systemic staphylococcal infection. Hybrid mice F1 (CBA x C3HA) inherited a high level of proliferative response on day 5 (as in resistant CBA mice) and its low level on day 9 (as in susceptible C3HA mice). These data on genetic differences in proliferative response to S. aureus cytoplasmic antigen were confirmed in the test of the proliferation of lymph node lymphocytes taken from mice of these lines immunized with the above-mentioned antigen in Freund incomplete adjuvant into the pad of their paws 14 days before the test.

Animals↗

[Therapeutic effect of some antibiotics on experimental staphylococcal infection and its correlation with in vitro activity of antibiotics in sub-inhibitory concentration against Staphylococcus aureus strains].

The aim of the study was to demonstrate of whether the therapeutic effects of antibiotics depend on their in vitro activity in sub-inhibitory concentrations against staphylococci. Cloxacillin, gentamicin and lincomycin were used in the study. Groups of S. aureus strains, containing 6 strains with similar MIC values each but different sensitivity to sub-inhibitory antibiotic concentrations (sub-MIC) were selected (a total of 36 trains): i. strains increasing their sensitivity to phagocytosis and bactericidal activity of rabbit leukocytes after incubation with an antibiotic in 0.1 MIC concentration, ii. strains with sensitivity to the above factors unaffected by incubation with an antibiotic in 0.5 MIC concentration. The doses of staphylococci causing death of 90-100% of Swiss albino mice 10 days after i.p. infection were determined. The injected doses (LD 90-100) and various doses of antibiotics were used to determine ED50 values as well as the survival rate of the mice with experimental staphylococcal infections after treatment with these antibiotics. It was demonstrated that effective doses (ED 50) of the antiboitics were significantly lower when the antibiotics were administered once to mice infected with strains S. aureus sensitive to sub-MIC concentrations of the investigated antibiotics than for mice infected with strains resistant to their sub-MIC concentrations. Similar correlations were observed in mice which were given the antibiotics several times (for 7 days): the percentage of the surviving mice was higher in the group infected with sub-MIC sensitive strains. The therapeutic effect of cloxacillin, gentamicin and lincomycin demonstrated a significant correlation with the S. aureus strains used to induce the infections and their sensitivity, or lack of sensitivity in vitro, to phagocytosis and bactericdal activity of leukocytes in the presence of antibiotics in sub-MIC concentrations.

Animals↗

In vitro study of the potential role of quinupristin/dalfopristin in the treatment of catheter-related staphylococcal infections.

The susceptibility of clinical isolates of methicillin-susceptible and -resistant staphylococci from cancer patients with central venous catheter bacteremia to quinupristin/dalfopristin, a semisynthetic streptogramin, was determined in vitro. Susceptibility of these isolates to nine other antistaphylococcal antibiotics was also determined for comparison. A total of 197 staphylococcal strains were tested from 1983 to 1992. Quinupristin/dalfopristin was bactericidal against all isolates, independent of their resistance to methicillin. Its activity was similar to that of vancomycin but superior to that of teicoplanin. Quinupristin/dalfopristin may prove to be an important addition to our armamentarium against catheter-related staphylococcal infections.

Anti-Bacterial Agents↗

[Evaluation of the use of rifampin combinations in severe staphylococcal infections. Apropos of the selection of 7 resistant mutants].

Selection of rifampicin-resistant Staphylococcus aureus has been described in vitro and in vivo when this compound is given as monotherapy or orally. That this occurrence may be prevented by combination antibiotic therapy is generally accepted. We report 25 cases of severe staphylococcal infection treated by a synergistic association of rifampicin with an aminoglycoside, vancomycin, or a macrolide. Therapy failed as a result of selection of the same rifampicin-resistant Staphylococcus aureus (serotype and lysotype) in seven cases. This finding may be explained by insufficient diffusion or inactivation of the other antibiotic in the infection site.

Adolescent↗

Epidemiological and biological characteristics of methicillin-resistant staphylococcal infections in a Mexican hospital.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide since 1960. However, there is little information concerning methicillin-resistant coagulase-negative staphylococci (MRCNS) infections. METHODS: In order to study the clinical and epidemiological characteristics of methicillin-resistant staphylococci (MRS) infections and to determine the relationship between MRS and both synergistic hemolysis (SH) and slime production (SP), a laboratory-based survey and non-matched case-control study were carried out at a tertiary-care center in Mexico City. In regard to patients, from May 1991 to October 1992, 46 cases of MRS infection and 86 patients (controls) infected by methicillin-susceptible staphylococci (MSS) were included. Clinical and epidemiologic variables were analyzed. The isolates were identified and tested for antimicrobial susceptibility by standard methods. An MIC of oxacillin > or = 8 micrograms/mL was defined as an MRS. RESULTS: During the study, 94 nosocomial staphylococcal infections were diagnosed: S. aureus, 35 and CNS, 59; 43 (45.7%) by MRS (rate of MRS infections was 1.12 per 100 in-patients); 2 MRSA; 41 MRCNS, and only 19 were symptomatic. Three infections were community-acquired, including one MRSA and two MRCNS. After multivariate analysis, the significant risk factors were previous antimicrobial therapy (p = 0.013) and catheter-related (p = 0.009) and urinary-tract source (p = 0.0001). Forty-nine percent of MRS showed SH while only 15% of MSS (p < 0.001) showed SH, especially in 10/10 MR-S. hemolyticus. Additionally, 48% of MRCNS showed SP, as did 18% of MSCNS (p = 0.019), particularly in 15/20 MR-S. epidermidis. Of all MRS isolates, 38% showed a homogeneous phenotype, a trait associated with multi-drug resistance (p < 0.01) and SH (p < 0.001). CONCLUSIONS: CNS predominated as the cause of MRS infections in our setting. The homogenous phenotype was associated with SH and multi-drug resistance.

Adolescent↗

Contribution of T cell-mediated immunity to the resistance to staphylococcal infection.

Abscess formation in nude mice after subcutaneous inoculation of Staphylococcus aureus (S. aureus) was more extensive and prolonged as compared with that in phenotypically normal littermates. Abscess formation in nude mice was augmented markedly by whole-body irradiation. Not only T cell-mediated immunity but also radiosensitive, nonimmune phagocytosis appear to contribute to the resistance against staphylococcal infection.

Abscess↗

Vancomycin therapy of severe staphylococcal infections.

Vancomycin, introduced clinically about 30 years ago, has been used widely over the past decade because of the increasing incidence of methicillin-resistant staphylococci. Its bactericidal action, high and prolonged blood levels, the lack of development of resistant strains, and decreased adverse reactions with the more purified preparation now available, make it an excellent agent for staphylococcal infections due to strains resistant to the beta-lactam antibiotics. Recent articles reviewing the efficacy of vancomycin are summarized.

Aminoglycosides↗

[Chemotherapeutic activity of lytic enzymes in experimental staphylococcal infection].

It was shown possible to use lytic enzymes from Streptomyces recifensis subsp. lyticus 2435 for chemotherapeutic purposes. After fractionation with ammonium sulfate or chromatographic purification on sephadex G-75, the enzymatic preparations were found to be complex and contain a number of proteinases and lytic endopeptidases. They were highly active in vitro in lysing thick staphylococcal suspensions. The local use of the preparations provided a favourable therapeutic effect on a model of experimental staphylococcal infection of albino mice and rats. It was evident from rapid arrest of the inflammatory process or earlier maturation and opening of abscesses and their cicatrization. The contribution of nonlytic proteinases to the process is not excluded.

Animals↗

Treatment of experimental staphylococcal infection with rifampin.

Bacteria surviving within leukocytes are protected from the lethal action of high concentrations of most antibiotics, which may explain, in part, the failure of bactericidal antibiotics to eradicate staphylococci from abscesses. Since rifampin is unique in its ability to kill intraleukocytic bacteria, the efficacy of this drug was tested in the treatment of staphylococcal infections in mice. Groups of mice infected intravenously with Staphylococcus aureus were treated with rifampin (20 mg/kg), procaine penicillin (937.5 mg/kg), or methicillin (200 mg/kg). All untreated mice died with disseminated visceral abscesses. After 10 days of therapy, survival in groups treated with penicillin and methicillin was 16 and 20%, respectively, whereas with rifampin it was 80% (P < 0.0005). Antibiotic concentrations in the serum of mice treated with penicillin, methicillin, or rifampin were bactericidal for the strain of S. aureus used. Serial bacterial counts of kidney, lung, and spleen homogenates showed that neither penicillin nor methicillin was able to eradicate staphylococci, whereas rifampin completely sterilized those organs in many mice. When abscess contents and infected peritoneal washings were incubated with high concentrations of penicillin, methicillin, or rifampin, only rifampin killed all of the bacteria. The capacity of rifampin to eradicate staphylococci from pus in vitro and from abscesses in mice appears to be related to the ability of rifampin to kill intraleukocytic bacteria.

Animals↗