Antimicrobial susceptibility testing of Streptococcus pneumoniae: quality assessment results.

Six strains of Streptococcus pneumoniae were distributed to 405 United Kingdom laboratories who were asked to test the susceptibility of the strains to penicillin, tetracycline, chloramphenicol and erythromycin and to provide details of methodology to test the standards of susceptibility testing. High error rates were seen only in failure to detect moderate resistance to penicillin (12%) and resistance to chloramphenicol (16%). Increased error rates were associated with several methods or practices. These included the use of certain culture media; failure to standardise the inoculum; inoculation by loop rather than by swab; failure to use control organisms; failure to measure zone sizes; the use of discs containing a high content of penicillin to test susceptibility to penicillin, and the use of high content discs for testing erythromycin, tetracycline, and chloramphenicol.

Treatment of gonorrhea with clavulanate-potentiated amoxicillin (Augmentin).

One hundred sixty-one patients with culture-proved Neisseria gonorrhoeae infection were treated with a single oral dose of amoxicillin trihydrate (3 g) and potassium clavulanate (Augmentin, 0.25 g). Of 153 patients infected with non-penicillinase-producing strains of N. gonorrhoeae, 139 (91%) were cured, and five (62.5%) of eight patients infected with penicillinase-producing N. gonorrhoeae were cured. Augmentin was successful in eradicating N. gonorrhoeae from the rectum; 30 (97%) of 31 such infections were cured.

Growth of Candida species in liquid culture medium for Trichomonas vaginalis.

The growth of Candida spp from vaginal specimens in Bushby's liquid medium for T vaginalis was compared with that on Sabouraud's agar medium, and isolation was significantly greater in Bushby's medium (p less than 0.001). Isolations missed (4.43%) in Bushby's medium probably represented vaginal carriage of small numbers of Candida spp.

The epidemiological type identification of Serratia marcescens from outbreaks of infection in hospitals.

A study of serological, bacteriocine and phage typing of Serratia marcescens was made. Specific O-antisera of adequate titre were relatively simple to prepare but H-antisera exhibited many heterologous agglutination reactions amongst the type strains. Most of these cross-reactions were not reproduced when immobilization tests with H-sera were performed. Direct haemagglutination tests were used to establish the presence of fimbriae amongst the H-type strains and the results of agglutination tests with non-fimbriate variants of strains indicated that fimbrial antibody in high titre was present in some sera. Replicate typing of 100 pairs of cultures by the phage-typing method indicated that small variations in pattern were common and that larger variations occurred occasionally. Therefore differences in pattern of less than two strong reactions should not be taken as evidence that strains can be distinguished. Cultures of S. marcescens, 273 in total, from six outbreaks of infection in British and European hospitals were typed by O-serology, H agglutination and immobilization tests, phage typing and bacteriocine susceptibility by a cross-streaking method. The typability of strains by each method was high but the results suggested that no single method was sufficiently discriminating to be used alone for typing. Comparison of the H-type and typing patterns of members of the same O serogroup from incidents of infection showed that reliable results were obtained by H-typing or by phage and bacteriocine typing after the application of the appropriate 'difference' rule. The greatest discrimination between strains of the same O-group was obtained by the use of H-typing or phage typing.

The specificity of agglutination reactions of Pseudomonas aeruginosa with O antisera.

Polyagglutinable (PA) strains of Pseudomonas aeruginosa are agglutinated by more than one of the antisera prepared against antigenically unrelated O serogroups. They form c. 4% of strains--other than isolates from cystic-fibrosis units--submitted to us for typing. We were able to allocate 80% of PA strains to a single O serogroup by agglutination with typing sera that had been absorbed with the polyagglutinable strain SMC-247, or by co-agglutination tests with protein A-containing staphylococci coated with immunoglobulin from unabsorbed sera. Similar results were obtained by precipitation tests with crude bacterial extracts and unabsorbed sera, but these tests were less sensitive and less specific. Evidence is presented that PA antigen is a heat-stable cell constituent distinct from the O antigen. In rabbit antisera, anti-PA antibody is exclusively of the IgM class, but O antibody of both IgM and IgG classes is present.

A comparison of typing methods for Serratia marcescens.

A simple method for the bacteriocine typing of Serratia marcescens without the use of induction was sought. The results of a mutual inhibition experiment with 89 unrelated cultures indicated that a bacteriocine-susceptibility method would give more discrimination between strains than would a bacteriocine-production method. A cross-streaking technique for bacteriocine-susceptibility typing without previous induction was developed, and its performance was compared with that of another susceptibility-typing method in which cell-free lysates of the producer strains were obtained by induction with mitomycin C.Replicate typing of the same collection of cultures by both methods indicated that small variations in pattern were common and that larger variations occurred occasionally. Differences in pattern of less than two strong reactions in the mitomycin-C induction method, and of less than three strong reactions in the cross-streaking method, should therefore not be taken as evidence that strains can be distinguished.Sets of cultures of Ser. marcescens, 178 in total, from a number of supposed incidents of infection in hospitals, were used to evaluate the two bacteriocine-typing methods; all of the cultures were also O serogrouped. Comparison of the typing patterns of members of the same O serogroup from clear-cut incidents of infection confirmed that results of acceptable reliability could be obtained by either bacteriocine-typing method by the application of the appropriate ;difference' rule. When so interpreted, the cross-streaking method appeared to be slightly the more discriminatory.The greatest discrimination between strains was obtained by the use of a ;hierarchical' typing system in which the strains were first O serogrouped, and the cross-streaking method of bacteriocine typing was then used to make subdivisions within O serogroups.