Benedict L. Wasilauskas

An analysis of Streptococcus pneumoniae identification using biochemical and serological procedures

Five methods for identification of Streptococcus pneumoniae were evaluated with stock strains representing all 83 capsular types and 130 fresh clinical isolates of alpha-hemolytic streptococci. The identification methods included bile solubility, optochin sensitivity, countercurrent-immunoelectrophoresis (CIEP), and coagglutination (CoA) using laboratory-prepared reagents (LPR) and the Phadebact Pneumococcus Test (Phadebact). The Quellung reaction was performed on the 83 capsular types of S. pneumoniae and on the clinical isolates that produced serological cross reactions with the three serological tests and those that were bile-soluble and optochin-sensitive. All 83 pneumococcal types were in complete agreement with each of the different test methods. Of the 130 alpha-hemolytic streptococci, 26 were identified as S. pneumoniae, and 104 isolates were identified as viridans streptococci using biochemical, physiologic, Quellung, or mouse virulence tests. All 104 viridans streptococci were bile-insoluble and optochin-resistant; however, 63 reacted with either one, both, or all three serological methods. Our data suggest that bile solubility and optochin tests are more reliable for pneumococcal identification than serological methods currently available.

Effectiveness of cefotaxime alone and in combination with desacetylcefotaxime against Bacteroides fragilis

The synergistic activity of the combination cefotaxime-desacetylcefotaxime (CTX/dCTX) was compared to the effectiveness of seven other antimicrobial agents: cefoxitin (CFOX), cefotetan (CTAN), ceftizoxime (CTIZ), chloramphenicol (CLOR), clindamycin (CLIND), metronidazole (METR), and ampicillin-sulbactam (A/S) tested against 100 clinical isolates belonging to the Bacteroides fragilis group. All tests were performed using the NCCLS reference agar-dilution method. The overall susceptibility of these organisms to CTX/dCTX was 84% compared to CFOX at 78% or CTAN at 66%. The other antimicrobials inhibited greater than 90% of these isolates. There was no difference between the susceptibility rates of CTX/dCTX and CTX with the B fragilis (85%) or B. distasonis (75%) strains. Bacteroides thetaiotaomicron showed a 11% greater susceptibility to CTX/dCTX than to CTX. Of the 100 isolates tested, 40% showed either synergy or partial synergistic interactions between CTX and dCTX. Most of the isolates showed indifference (52%), while 8% demonstrated antagonism; a relatively unique finding to date.

A comparison of antibiotic susceptibility profiles using single and multiple isolates per patient.

We compared the antibiogram statistics generated by including all clinical isolates to those obtained by tabulating no more than one isolate of a particular organism from a given patient. We found that 48.3% of the isolates presented multiple occurrences in individual patients but found no practical differences in the profiles obtained by the two methods. We also tabulated the occurrence of minimum inhibitory concentration (MIC)-distinct organisms among the sets of multiple isolates of E. coli and of S. aureus and found that only 20.9% of those isolates represented duplicate organisms by MIC profile. This heterogeneity of MIC sensitivity that occurs in multiple isolates from individual patients was not expected but provides an explanation for the lack of difference between the two methods of tabulating antibiotic susceptibility statistics.

Presumptive Identification of the Bacterium Escherichia Coli by High Performance Liquid Chromatography

Abstract The potential of high performance liquid chromatography (HPLC) for bacterial identification has been explored employing Escherichia coli (E. coli) as an example. E. coli produced a distinct pattern of changes in the media, different from several other organisms. These changes are time dependent and inversely related to media concentration and can be detected after one hour incubation. Some of these changes have been subjected to chemical analysis and it was found that E. coli rapidly degraded tryptophan and produced indole. The ratio of tryptophan to phenylalanine in the media served as a good index for bacterial growth. Different isolates of E. coli showed the same metabolic pattern. Although other bacteria are capable of degrading tryptophan, they produced a different pattern. HPLC appears to have a potential for rapidly identifying bacterial isolates and may provide a useful tool for use in microbiology laboratories.

Comparative in vitro Activity of 5 Cephalosporins with Other Antibiotics Tested against 887 Recent Clinical Isolates

Five cephalosporins including 3 newer agents were tested along with several aminoglycosides, penicillins and other antimicrobials against 887 recent clinical bacterial isolates. Of the newer cephalosporins, cefotaxime appeared to be the most effective against gram-negative bacilli. However, with gram-positive cocci, cephalothin seemed to be the most effective cephalosporin. Superior antipseudomonal activity still resides with the aminoglycosides although moxalactam and cefotaxime appeared to offer some alternatives.