Spheroplasts of Haemophilus influenzae induced by cell wall-active antibiotics and their effect upon the interpretation of susceptibility tests.

The interpretation of in vitro susceptibility tests of Haemophilus influenzae performed by the agar or broth dilution methods with Levinthal enrichment was found to be markedly influenced by the production of spheroplasts by this species. Using an inoculum of 10(7) organisms/ml, this phenomenon was frequently evident macroscopically as a haziness on agar substrates and in broths containing cell wall-acting agents, such as ampicillin, cephalothin, and penicillin, but was not noted with chloramphenicol. Phase-contrast microscopic examination of the haze from these sources revealed numerous spherical bodies in contrast to the typical cocco-bacillary forms observed in growth controls. With this inoculum size, minimal bactericidal concentrations could not be determined since subculture of 0.1 ml of the hazy broths or the surface haze onto chocolate agar resulted in most instances in the development of a small number of colonies which, upon smear and gram stain, revealed typical Haemophilus morphology. An inoculum of 10(4) organisms/ml abolished the haziness on agar surfaces and in broths and resulted in clear-cut end points. Also, although spherical bodies were still present, they were distinctly less in number as contrasted to tests performed with an inoculum of 10(7) organisms/ml. It is recommended that minimal inhibitory concentration end points in antibiotic susceptibility tests be determined by microscopic, rather than macroscopic, observation of the growth milieu to determine the presence or absence of morphologically typical bacilli which, when observed, is indicative of true in vitro resistance.

Simple method for rapid determination of antibiotic blood levels.

A simple method for the rapid determination of antibiotic blood levels is described. Results are readily obtainable within 4 to 6 hr. The reported procedure is based upon determination of the highest dilution of a patient's serum capable of inhibiting dextrose fermentation by a standardized inoculum of a staphylococcus strain or of an Escherichia coli strain, when colymycin or polymyxin are involved, as compared to previously determined endpoints in this regard of defined concentrations of the different antibiotics dissolved in normal human serum. Excellent correlation was observed with 36 serum specimens that contained different antimicrobial agents in varied concentrations when simultaneously assayed by the standard method and the subject procedure of this report.

Electronic data processing system for the clinical microbiology laboratory.

Owing to the increased volume of laboratory services and the shortage of skilled medical microbiologists who presently spend up to 30% of their time in clerical matters, pragmatic applications of electronic sorting techniques and computers should be considered to alleviate this problem. Moreover, surveillance of the hospital community, with particular reference to changing patterns of microbial resistance and the distribution of potentially infectious pathogens, requires detailed information which can be readily supplied by electronic sorting analysis. Mark-sense and prescored Port-A-Punch IBM cards were used to: (i) analyze antibiotic susceptibility data; (ii) tabulate total test loads according to conditions set down by the American Society for Clinical Pathologists; and (iii) to prepare a bacteriological report on the surveillance of hospital infections. After proper sorting and analysis, the cards also serve as a convenient reference file in the laboratory for pertinent information recorded by either blackening the appropriate areas (mark-sense style) or pushing out the preperforated rectangular holes with a simple inexpensive board and stylus (Port-A-Punch). No one scheme can fulfill the requirements of all laboratories or purposes, but ideas contained herein might serve as starting points for the design of similar systems in other laboratories.