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Biomedical subjects

M F Michel

Publications and source records attributed to M F Michel.

At least 163 records · Page 9Linked to original sources
PubMed1975

Induction of mutation in Staphylococcus aureus by ethylmethane sulphonate.

Staphylococcus aureus strains were treated with ethylmethane sulphonate with the object of obtaining mutants that differed from the wild type in one of the properties that might contribute to virulence. Mutants with isolated loss or deficient production of gamma-haemolysin, coagulase, leucocidin and staphylokinase were obtained. Changes in more than one property were often observed. The loss of delta-lysin production was always coupled with an appreciable reduction in P-V leucocidin production. With that exception, systematised combined loss of a restricted number of staphylococcal characteristics was not observed. Mutants that had lost all characteristics of S. aureus were phage-resistant. Isolated loss of staphylokinase production and deficient P-V leucocidin production were found to be due to the independent loss of two prophages.

Animals↗
PubMed1975

A study of virulence factors with induced mutants of Staphylococcus aureus.

The contribution of a number of extracellular products of Staphylococcus aureus to the virulence of the organism for mice was studied by comparing a wild-type strain with various mutants derived from it in three virulence tests: (1) subcutaneous and (2) intravenous challenge in normal mice, and (3) subcutaneous challenge in mice after total body X-irradiation. Mutants with lower production or non-production of coagulase, staphylokinase and leucocidin were just as virulent for mice as the wild type in all three tests. Unlike the wild type, mutants with low production or nonproduction of alpha-lysin never gave necrosis after subcutaneous injection in normal mice. One mutant with loss of delta-lysin and unaltered alpha-lysin production gave necrosis only when injected in high doses. Dermonecrosis seems to be caused by a combination of alpha- and delta-lysin. Intravenous injection of each of the two types of mutant in normal mice gave a lower mortality rate than that obtained with the wild type. Mutants with deficient alpha-lysin production, but not delta-lysin-deficient mutants, multiplied more slowly in the kidneys than the wild type under these conditions. alpha-Lysin appears to have a growth-enhancing effect for the organism in vivo, but delta-lysin does not. Differences in virulence between the wild type and mutants could not be demonstrated in irradiated mice.

Animals↗
PubMed1975

Activity of eight antimicrobial agents in vitro against N. Gonorrhoeae.

The sensitivity of four groups of gonococcal strains to ampicillin (Am), penicillin (P), tetracycline (T), rifampicin (Ri), spectinomycin (Sp), sulphamethoxazole (Su), trimethoprim (Tr), and a combination of Su and Tr in the ratio 5:1 (Su/Tr 5:1) has been determined. The various groups of strains were isolated from male civilians (MC), female civilians (FC), and sailors (S) in Rotterdam (R) in 1972, and from FC in Amsterdam (A) in 1967. The S-R strains, which may be regarded as mainly imported, were compared with the MC-R and FC-R (which may be considered as mainly of Dutch origin). Also investigated was whether the incidence of relative resistance to the antibiotics investigated among Dutch strains has changed in the period from 1967 to 1972. For this purpose, the FC-A and FC-R strains were compared. The MC-R and FC-R strains were also compared with one another. Finally, Spearman's rank correlation coefficient r were calculated between the sensitivity distributions for each pair of antibiotics investigated, for all strains. The S-R strains were significantly less sensitive to Am, P, T, Ri, and Tr than the MC-R and FC-R strains. Comparison of the FC-A and FC-R strains revealed that the FC-R strains were significantly less sensitive only to Su/Tr 5:1. A possible explanation for this finding is given. With the exception of one FC-A strain, all gonococcal strains were sensitive to Sp. High values of r (larger than or equal to 0.50) were found between Am and P, Am and T, and P and T for all groups of strains. The values of r between any pair of the antibiotics Am, P, T, Ri, and Tr (with the exception of the pair Am-P) were always highest for the S-R strains. High values of r (larger than or equal to 0.50) were found between Su and Su/Tr 5:1 for all groups of strains. The FC-A strains, unlike the R strains, gave low values of r between Su and Tr and between Tr and Su/Tr 5:1. A possible explanation for this is given. Finally, a hypothesis is put forward to explain the fact that no significant changes were found in the sensitivity of Dutch gonococcal strains to Am, P, T, Ri, Sp, Su, and Tr in the period from 1967 to 1972, while the S strains (which may be regarded as imported) showed a significantly higher percentage of strains relatively resistant to Am, P, T, Ri, and Tr.

Ampicillin↗
PubMed1974

Comparison of the titres of ASO, anti-DNase B, and antibodies against the group polysaccharide of group A streptococci in children with streptococcal infections.

Antibodies against the group polysaccharide of group A streptococci were estimated by means of a haemagglutination reaction. In this reaction human erythrocytes of blood group O were sensitized with polysaccharide esterified with myristoylchloride. The optimal conditions of the reactions were determined by varying the ester group content in the antigen and the amount of ester used for sensitization. The specificity of the reaction could be established by reacting sensitized erythrocytes with homologous and heterologous sera and by absorption experiments. Antistreptococcal group A polysaccharide titres (ASPAT) and antibody levels to streptolysine O and DNase-B were compared in a group of 52 children with proved streptococcal infection and in 52 age- and season-matched controls. Antibody levels were significantly higher in the patient group than in the controls. In the ASPAT there was clearly less overlap between patients and controls than in both other reactions. In the patient group the ASO titres were raised above normal in 27 cases (51.9%), anti-DNase-B titres in 18 (34.6%), and ASPAT in 40 (76.9%). Taken together the three reactions gave a positive score in 51 cases (98.1%) in the patient group against 17 cases (32.7%) in the controls. A positive antibody response is usually defined as a rise of two dilution increments between the acute and convalescent sera. According to this definition the ASPAT showed a response in 42%, ASO and/or DNase-B in 42%, and the three reactions taken together in 68% of paired sera from patients. It is believed the ASPAT will prove a welcome addition to the diagnostic outfit when the presence of streptococcal infection in children is considered.

Absorption↗