Pauline K. W. Yu

Comparative In Vitro Activity of Three Aminoglycosidic Antibiotics: BB-K8, Kanamycin, and Gentamicin

Kanamycin, BB-K8, and gentamicin were tested in parallel against 1,037 bacterial strains isolated from clinical material. The activity of BB-K8 at 20 μg/ml was comparable to that of gentamicin at 8 μg/ml against Pseudomonas aeruginosa and against Enterobacteriaceae, with the exception of gentamicin-resistant strains of Proteus rettgeri and Providencia stuartii, in which case the activities of BB-K8 and kanamycin were the same. BB-K8 exhibited little or no activity against streptococci. The activity of BB-K8 was affected by pH and inoculum size. A regression graph for inhibition data with a 10-μg disk of BB-K8 was developed, and synergistic activity of penicillin and BB-K8 against Streptococcus faecalis was tested.

Results of a 6-Month Survey of Stool Cultures for Escherichia coli O157:H7

Escherichia coli O157:H7 is a recently recognized enteric pathogen that causes acute hemorrhagic colitis. Although the infection is usually self-limited, it may be complicated by hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. At our institution, stool specimens are now routinely cultured for this organism. To determine the prevalence of E. coli O157:H7-associated diarrhea in our patient population, we surveyed all submitted stool cultures for 6 months for this organism. Specimens were screened for non-sorbitol fermenting E. coli and confirmed by slide-agglutination and immobilization testing. Of 2,164 specimens, 10 yielded E. coli O157:H7. It was the fourth most common bacterial stool pathogen found. Bloody diarrhea and abdominal pain were the most common symptoms of the infected patients. E. coli O157:H7 causes sporadic infections in our patient population and should be considered in the differential diagnosis of acute hemorrhagic colitis.

Interpretation of the Disk Diffusion Susceptibility Test for Amikacin: Report of a Collaborative Study

Because excessively high rates of false resistance have been encountered with the 10-μg amikacin disk in diffusion susceptibility tests, a study was performed to examine existing zone diameter interpretative criteria and to compare the accuracy of 10- and 30-μg amikacin disks by the error rate-bounded classification scheme. Although current zone diameter interpretative criteria eliminate false susceptibles, there is an unacceptably high rate of false resistants. This problem can be resolved in most instances by revising the zone diameter interpretative criteria for the 10-μg disk (resistant, ≤9 mm; indeterminate, 10 to 11 mm; susceptible, ≥12 mm) or, preferably, by replacing the 10-μg disk with a 30-μg disk and adopting new interpretative criteria (resistant, ≤14 mm; indeterminate, 15 to 16 mm; susceptible, ≥17 mm). Because of significant differences in performance among media, it is necessary to include Pseudomonas aeruginosa ATCC 27853 among controls routinely tested and to exclude from use lots of Mueller-Hinton agar yielding results outside the 75% tolerance (90% confidence) limits for amikacin.

Evaluation of TestPack Strep A for the Detection of Group A Streptococci in Throat Swabs

The performance of TestPack Strep A (Abbott Laboratories), a rapid enzyme immunoassay, was compared with a culture-based method for the detection of group A streptococci in 648 throat swabs. The rapid test correctly detected 99 of the 128 positive and 511 of the 520 negative specimens, a sensitivity of 77% and a specificity of 98%. Although highly specific, TestPack Strep A is less sensitive than culture techniques for the detection of group A streptococci in throat swabs.

In vitro antibacterial activity of spectinomycin.

The in vitro inhibitory and bactericidal activities of spectinomycin hydrochloride were tested against a variety of bacteria. The antibiotic was inhibitory at 31.2 μg/ml to most strains of Escherichia coli, Klebsiella, Enterobacter, and Staphylococcus epidermidis. Concentrations of antibiotic exhibiting bactericidal activity exceeded the inhibitory concentration by at least fourfold. Regression graphs were plotted for results obtained with 30-, 100-, 200-, and 300-μg spectinomycin discs; tentative interpretative standards are proposed.

In Vitro Evaluation of a Semisynthetic Derivative of Gentamicin B (SCH 21420)

The activities of Sch 21420 and amikacin were compared in vitro against 448 clinical bacterial isolates and against 82 gentamicin-resistant isolates of gram-negative bacilli. At 1 μg/ml, Sch 21420 was more active than amikacin against most Enterobacteriaceae but less active against Pseudomonas aeruginosa. Activity of these antibiotics against gentamicin-resistant organisms varied according to the species examined.

Comparison of In Vitro Antibacterial Activities of Gentamicin and Verdamicin

The in vitro activities of verdamicin and gentamicin were studied in parallel against 1,049 bacterial isolates. Verdamicin demonstrated activity similar to that of gentamicin against members of the family Enterobacteriaceae and against Pseudomonas aeruginosa at 2 and 8 μg/ml, respectively. Proteus rettgeri and Providencia stuartii were notably more susceptible to verdamicin. The new aminoglycoside was also highly active against staphylococci but was not effective against group D streptococci.

Direct Microscopic Examination of Specimens

Direct microscopic examination of stained or unstained wet mount preparations or fixed stained smears of clinical material can often provide the etiological diagnosis of an infectious process (Table 2–1) and the opportunity to initiate appropriate therapy before the results of cultures become available.

Direct Examination of Specimens

Direct examination of clinical material can often provide the etiological diagnosis of an infectious process (Table 2-1) and the opportunity to initiate appropriate therapy before the results of cultures become available.

Aerobic and Facultatively Anaerobic Bacteria

Bacteria are identified whenever their presence is considered clinically significant. Isolates, therefore, from normally sterile sites require identification and antimicrobial susceptibility testing. Those without recognized clinical importance from sites normally harboring indigenous flora (Table 1–1) seldom require identification. Indeed, reporting normal flora may be highly misleading since specific identification by the laboratory would generally appear to ascribe clinical importance to any organisms reported. For this reason, reports of throat cultures can usually be limited to whether or not group A streptococci are present, and reports of stool cultures can be limited to whether or not recognized enteric pathogens are present. No useful purpose is served by identifying and reporting organisms indigenous to the oropharynx or gastrointestinal tract, despite the fact that their isolation from other sites may be clinically significant. By the same token, when cultures fail to yield recognized pathogens, the report should clearly state that cultures were negative for the specific pathogens sought (e.g., Salmonella, Shigella, Yersinia, and Campylobacter fetus in feces) rather than simply to report the cultures were negative.