Haru Kato

Relapses or reinfections: Analysis of a case of Clostridium difficile-associated colitis by two typing systems

Immunoblotting and pulsed-field gel electrophoresis of Clostridium difficile isolates were employed to differentiate reinfection by a newly acquired strain from relapse by an original strain in a 10-year-old patient with four episodes of C. difficile-associated colitis. Immunoblot typing demonstrated subserogroup K-1 of serogroup K for the first and second organisms, subserogroup A-1 of serogroup A for the third organism, and subserogroup G-4 of serogroup G for the fourth organism. PFGE analysis revealed consistent results with immunoblot analysis except that the strains from the fourth episode, whose DNA constantly degraded, were nontypable by this method. Five separate isolates of C. difficile from a specimen of each episode showed identical PFGE patterns, indicating that infections of multiple strains probably did not occur in this patient. These typing results suggested that the second episode after a 17-day course of vancomycin therapy represented a relapse by the strain causing the first episode, and that the third and fourth episodes after tapering vancomycin therapy were reinfections by other strains. Both immunoblot and PFGE typing systems are promising tools for analyzing recurrence of C. difficile infection.

Detection of Bacteroides fragilis in clinical specimens by polymerase chain reaction amplification of the neuraminidase gene

The polymerase chain reaction (PCR) was used in an attempt to detect Bacteroides fragilis by amplifying a segment of the gene encoding B. fragilis neuraminidase. Forty-five reference strains representing 45 species and 113 clinical isolates were tested. Only B. fragilis was PCR positive, except for Bacteroides merdae ATCC 43184, which gave a band by ethidium bromide staining that showed no signal by Southern hybridization. Using a protocol that employed DNA extraction by Sepa Gene kit and a highly sensitive digoxigenin-chemiluminescence detection system, detection of B. fragilis by PCR was in complete agreement with culture results for 44 clinical specimens from which a wide range of aerobic and anaerobic organisms and fungi were recovered.

Comparative In Vitro Activity of AM-1155, a New Quinolone, against Anaerobic Bacteria

AM-1155 is a new fluoroquinolone; its chemical structure is shown in figure 1. The molecular weight of this compound is 402.42g. Although many studies have investigated the activity of new quinolones against aerobic bacteria (Fuchs et al. 1991; Neu et al. 1992), few have examined their activity against anaerobic bacteria. We evaluated the in vitro activity of AM-1155 against obligate anaerobic bacteria and a fastidious facultative anaerobe, Gardnerella vaginalis (Gibbs et al. 1987). We also compared its activity with those offive other fluoroquinolones and cefmetazole.

Molecular Detection and Identification of Anaerobic Bacteria

Anaerobic bacteria are organisms which are inactivated by exposure to air, and some species grow very slowly. Thus, they are good candidates for direct detection and culture confirmation using molecular diagnostic techniques. In clostridial species, polymerase chain reaction (PCR) amplification techniques have been used to demonstrate a segment of the gene encoding neurotoxins, enterotoxins, or cytotoxins. Using these techniques,Clostridium botulinum strains were directly isolated and toxin-typed from food samples.Clostridium tetani strains were identified, and toxigenicClostridium difficile strains and enterotoxin-producingClostridium perfringens strains were either confirmed in culture studies or directly detected from stool or food specimens. Among nonclostridial anaerobic bacteria,Propionibacterium acnes, Mobiluncus, gram-negative periodontal pathogens includingPorphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Bacteroides forsythus, Bacterioides fragilis and enterotoxin-producingB. fragilis, Fusobacterium prausnitzii (a common constituent of fecal flora), andBilophila wadsworthia have been studied on a molecular level using oligonucleotide probes and PCR methods. Universal PCR primers may be the choice for differentiation of anaerobes which are commonly found in polymicrobial infections and quantitative nucleic acid amplification technology has been used extensively in these situations. However, some studies lack a sufficient number of strains tested to evaluate the reliability of these molecular methods. The accumulation of additional data using these techniques is crucial to their widespread use or to estimate their limitations.