Susceptibility testing of Propionibacterium acnes comparing agar dilution with E test.

Propionibacterium acnes has been identified as a significant agent of nosocomial infections, including endophthalmitis. Data concerning susceptibility of P. acnes to newer beta-lactam antibiotics and fluoroquinolones are limited. Recent reports suggest that quinolones have activity against these organisms sufficient to warrant further study. We undertook a study to select appropriate antimicrobial agents for use in a rabbit model of P. acnes endophthalmitis. We compared the antibiotic susceptibilities of P. acnes by using the National Committee for Clinical Laboratory Standards method of agar dilution with the E test. Thirteen clinical isolates obtained from eye specimens and three American Type Culture Collection control strains were tested against 14 antibiotics. All the clinical isolates were susceptible by both methods to piperacillin, piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, cefotaxime, cefotetan, ceftriaxone, cefoxitin, and imipenem in addition to clindamycin but were resistant to metronidazole. The clinical P. acnes isolates also displayed high-level susceptibility to ciprofloxacin, sparfloxacin, and ofloxacin. Almost all the P. acnes strains demonstrated E-test MICs within 2 dilutions of the MICs observed by the agar dilution method. Those few strains for which discrepancies were noted exhibited E-test susceptibilities three- to fivefold dilutions lower than the agar dilution method susceptibilities but only with ampicillin-sulbactam, ticarcillin-clavulanate, and/or clindamycin. On the basis of our study, all of clinical eye isolates were susceptible to these newer antimicrobial agents and the two methods demonstrated similar susceptibility patterns.

Odontogenic infection secondary to Leuconostoc species.

Leuconostoc species are gaining importance as pathogenic organisms. We present the first case of odontogenic infection caused by Leuconostoc spp. Isolates initially identified as streptococci were found to be vancomycin resistant. Rigorous bacteriologic investigation subsequently classified these organisms as Leuconostoc mesenteroides.

Microbiology of indwelling central intravascular catheters.

Indwelling central-line catheters (n = 502) from 362 patients in intensive care units were analyzed prospectively. The skin site, 6-cm-distal and -proximal subcutaneous segments of the catheter, exudates, and blood were cultured. Semiqualitative roll plate cultures of the catheter segments were followed by broth cultures and examined for 72 h. All isolates were identified, and susceptibilities were determined. Line infections, defined clinically, yielded 22 different microbial species; 10 different species were recovered from colonized lines. Of the Staphylococcus epidermidis isolates recovered, 39% occurred singly and 21% occurred in combination with other microorganisms; Enterococcus faecalis, S. hominis, and Pseudomonas aeruginosa were next in frequency of isolation. Line infections also yielded other staphylococci, viridans group streptococci, several members of the family Enterobacteriaceae, acinetobacters, anaerobic bacteria, Candida spp., and Aspergillus fumigatus. While S. epidermidis was also the most frequent isolate among the line colonizers, different species and different frequencies of isolation were found among this group. The study showed that the distal catheter segment broth culture was the best predictor of clinical line infections; in addition, gram-negative bacteria were isolated only from the catheters of patients with overt infections.

Clinical laboratory challenges in the recognition of Leuconostoc spp.

Vancomycin-resistant Streptococcus salivarius-like bacteria were isolated from the blood and gastrostomy tube of a 6-month-old child during vancomycin therapy for Staphylococcus epidermidis central venous catheter-associated bacteremia. The isolates produced D-(-)-lactate and ethanol from glucose, hydrolyzed esculin, and produced no ammonia from arginine, thus fulfilling the major criteria as Leuconostoc spp. The enzymatic profile of the bacteria suggested that they were not lactobacilli or streptococci. Resistance to vancomycin and penicillin tolerance were noted. The formula fed through the gastrostomy tube was suspected as the vehicle that transmitted the organism to the patient. Penicillin and tobramycin therapy was used successfully.

Nosocomial urinary tract infection with a slowly growing, fastidious Escherichia coli.

Escherichia coli recovered from a nosocomially acquired urinary tract infection required 48 h of incubation on blood agar and did not grow on other routine clinical laboratory media. This bacterium dissociated readily into three colony types, all of which were confirmed as E. coli by DNA hybridization studies. Preliminary studies indicate a prolonged lag phase that could not be corrected by the addition of a variety of peptones and yeast extracts. Better growth was achieved by the addition of 10% horse serum.

Production of cephalosporin C by Paecilomyces persicinus P-10.

After the growth of Paecilomyces persicinus P-10 in a glucose-peptone medium, filtrates were collected and analyzed for antibiotic antivity. Activities against Salmonella gallinarum ATCC 3030 and Alcaligenes faecalis ATCC 8750 (penicillin N-resistant strain) were obtained. Part of the former activity was readily inactivated by penicillinase. The fraction active against A. faecalis was isolated by passage through Amberlite XAD-2 and Amberlite IRA-68. The powder eventually obtained was subjected to paper chromatography followed by bioautography, and the activity obtained corresponded to that of a sample of cephalosporin C. Thin-layer chromatography was also employed to verify the presence of cephalosporin C in the P-10 powder. The active solids were further purified by means of paper chromatography in a solvent system consisting of n-butanol-acetic acid-water (60:15:25, vol/vol). The material obtained from this procedure yielded an infrared absorption spectrum identical to that of cephalosporin C. Similarly, the ultraviolet absorption of the purified preparation coincided with that of cephalosporin C. Exposure of the purified solids to cephalosporinase resulted in rapid inactivation of the antibiotic. In addition to penicillin N and cephalosporin C, filtrates of P. persicinus P-10 also contained deacetylcephalosporin C, deacetoxycephalosporin C, and cephalosporin P.