Elimination of intraluminal colonization by antibiotic lock in silicone vascular catheters.

An in vitro model was designed to evaluate the efficacy of instilled antimicrobials to reduce or eliminate intraluminal microbial colonization. Minimal inhibitory concentration and minimal bactericidal concentration activity of appropriate test anti-infectives were determined using standard methodology against clinically derived and reference test strains commonly associated with catheter-related infection. Drug activity was validated by bioassay for the test anti-infectives. Reference and clinical test strains were inoculated to the intraluminal surface of silicone catheter segments and incubated for 30 min, after which the inoculum was replaced with total parenteral nutrition (TPN) solution and reincubated for 12 h. For 7 d, instillation of antibiotic and TPN solution was alternated every 12 h to simulate clinical conditions. On days 1, 4, and 7, catheter segments were rinsed, bisected, and sonicated for quantitative plate count to determine mean microbial counts per centimeter of catheter surface. Catheter segments were also prepared for scanning electron microscopy. A significant decrease in staphylococcal intraluminal colonization after instillation of nafcillin, ceftriaxone, gentamicin, and vancomycin was demonstrated (P < 0.001). Aztreonam, ceftriaxone, and gentamicin completely eliminated gram-negative catheter colonization (P < 0.001). Yeast was eradicated from the internal catheter surface after treatment with amphoteracin B, and fluconazole significantly decreased intraluminal colonization (P < 0.001). Results show a significant decrease in staphylococcal, gram-negative, and fungal intraluminal colonization after instillation of appropriate antimicrobial. In vitro results support early clinical success using this technique. Future studies are warranted to identify optimal drug concentrations and dosing intervals.

Surgical sepsis: constancy of antibiotic susceptibility of causative organisms.

BACKGROUND: It is well documented that antibiotic therapy exerts selective pressure on bacteria. Conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. It has been postulated that human intestinal reservoirs facilitate communication of transposons that can transfer resistance determinants among various bacterial species. METHODS: This study examined the susceptibilities of organisms isolated from infected abdomens to a number of antibiotic agents during a 12-year time interval. Analysis included 1102 isolates recovered from 255 specimens, representing the following genera: Bacteroides, Clostridium, Gemella, Fusobacterium, Peptostreptococcus, Porphyromonas, Prevotella, Enterococcus, Staphylococcus, Streptococcus, Pseudomonas, and Enterobacteriaceae. Strains were tested against beta-lactam agents, beta-lactams in combination with beta-lactamase inhibitors, first, second, and third generation cephalosporins, aminoglycosides, clindamycin, metronidazole, chloramphenicol, and imipenem. RESULTS: The results indicated that during a time period of more than a decade essentially no change occurred in the antibiotic susceptible fraction of all species tested. CONCLUSIONS: Abdominal sepsis is caused by leakage of endogenous intestinal flora. This study suggests that the intestinal flora is not permanently affected by short-term antibiotic therapy and that older antibiotics are appropriate first-line therapeutic agents for community-acquired infections caused by normal intestinal flora.

Microflora of abdominal sepsis by locus of infection.

Specimens from 152 abdominal infections were examined to determine which groups of endogenous bacteria participate in infection emanating from different sites in the gastrointestinal tract. A notable finding was the predominance of anaerobic microflora from infections of ischemic versus perforated small bowel. Empiric antibiotic treatment for ischemic bowel should include focused coverage for anaerobes.

Microbroth versus agar dilution for susceptibility testing of fluoroquinolones and other agents against anaerobic bacteria.

Agar dilution and microbroth dilution methods appear equally acceptable for susceptibility testing of anaerobes against temafloxacin and ciprofloxacin. Most major discrepancies occurred with strains whose MIC was near the breakpoint. These results suggest that method variation will not be a significant factor in the susceptibility testing of anaerobic bacteria against other fluoroquinolone agents.

Enzymatically active Peptostreptococcus magnus: association with site of infection.

Fifty-four strains of Peptostreptococcus magnus (11 were recovered from abdominal infections, 18 were from nonpuerperal breast abscesses, and 21 were from diabetic foot infections; the type strain and three other strains were from the American Type Culture Collection, Rockville, Md.) and the type strain of Peptostreptococcus micros were tested for their ability to produce various enzymes, including catalase, hippurate hydrolase, serine dehydratase, threonine dehydratase, collagenase, gelatinase, alkaline phosphatase, and esterase C4. The data were analyzed by cluster analysis. The results showed that all but one strain could be assigned to either of two distinct, valid clusters. The first cluster of 11 strains was composed of strains that were relatively inactive, having produced one or two of the eight strain-dependent enzymes. The second was a large cluster of strains (n = 43) that were considerably more active, all having produced at least three enzymes; the vast majority of strains (89%) produced four or more enzymes. The unclustered strain produced one enzyme that was different from that produced by the strains in the first cluster. The chi 2 test of homogeneity applied to the clustering solution indicated that greater enzyme activity was significantly associated with the site of infection (P less than 0.001). The more enzymatically active P. magnus strains were recovered significantly more often from nonpuerperal breast abscesses and diabetic foot infections than they were from abdominal infections. These results may provide insight into the nature of certain polymicrobial soft tissue infections and suggest that (i) P. magnus may participate more in nonpuerperal breast and diabetic foot infections than in abdominal infections and that (ii) peptostreptococcal production of proteolytic enzymes may have an important adjunctive effect on the pathogenesis of certain soft tissue infections.

Anaerobic pathogenesis: collagenase production by Peptostreptococcus magnus and its relationship to site of infection.

Fifty isolates of Peptostreptococcus magnus from intraabdominal sepsis, nonpuerperal breast abscess, and diabetic foot infections were examined for collagenase activity using bovine type I collagen. Collagenase production was detected in a higher percentage of strains from nonpuerperal breast and diabetic foot specimens (P less than .001). This enzyme may be responsible for P. magnus playing a more central role in the pathogenesis of nonpuerperal breast abscess and diabetic foot disease than in intraabdominal sepsis.

Streptococcus milleri group (Streptococcus anginosus): recovery from intra-abdominal and soft tissue sites.

One hundred thirty-three Streptococcus milleri group (S. anginosus) isolates were recovered from 487 surgical patients. The streptococci were recovered from 33 percent of intra-abdominal infection cultures (84/257). 22 percent of samples from penetrating visceral trauma (19/86), 52 percent of perirectal abscess specimens (13/25), 13 percent of nonpuerperal breast abscess cultures (8/60), and 15 percent of diabetic foot lesions (9/59). Ninety-eight percent of the S. milleri (131/133) were recovered as companion flora in polymicrobial cultures. The organisms were highly susceptible to the beta-lactam antibiotics. The precise pathogenic role of the S. milleri group (S. anginosus) is unknown. However, intrinsic virulence may be expressed in patients with severe infection or other predisposing factors.

The nonpuerperal breast infection: aerobic and anaerobic microbial recovery from acute and chronic disease.

Sixty breast culture specimens were obtained by needle aspiration from 54 women and 2 men. A total of 221 microbial isolates were obtained from 52 culture-positive samples. Aerobes alone were recovered from 11 patients while 5 were culture-positive for anaerobes only. Thirty-six patients harbored mixed aerobic and anaerobic microbial flora, and the anaerobic gram-positive cocci were the predominant isolates recovered. The mean microbial recovery for patients with an acute abscess was 2.9 isolates, while in patients with chronic infections the mean microbial recovery was 5. The anaerobic populations outnumbered facultative isolates by two to one, and 34% of anaerobic isolates were recovered from subculture. These findings demonstrate that, contrary to previous reports, nonpuerperal breast infections involve a mixed infection that is primarily anaerobic.

Anastomotic femoral pseudoaneurysm: an investigation of occult infection as an etiologic factor.

Occult infection was investigated as an etiologic factor in the formation of femoral anastomotic pseudoaneurysms associated with prosthetic vascular grafts. Forty-five femoral pseudoaneurysms with no clinical evidence of infection 10 to 173 months after prosthetic graft placement were consecutively studied. The explanted Dacron or explanted polytetrafluoroethylene graft material was cultured in trypticase soy broth and ultrasonically oscillated to remove adherent bacteria. All patients were treated by excision of the pseudoaneurysm and surrounding perigraft capsule and in situ replacement with an interposition prosthetic graft. Thirty-two bacterial isolates were recovered from 27 (60%) of the specimens, with coagulase negative staphylococci (Staphylococcus epidermidis S. warneri, S. hominis, S. capitis) accounting for 24 of the recovered species. No infection of the replacement graft developed in any patient and no recurrent pseudoaneurysms were observed. Bacterial colonization may occur at implantation or during subsequent procedures when the prosthetic graft is exposed. This chronic infection can be diagnosed by means of sensitive culture techniques that dislodge adherent bacteria from the graft surface. On grounds of the observations reported in this study, there appears to be suggestive evidence that an occult infectious process may be one of the factors that play a role in the development of some femoral anastomotic pseudoaneurysms.

Sequential analysis of staphylococcal colonization of body surfaces of patients undergoing vascular surgery.

Slime-producing coagulase-negative staphylococci are pathogens in vascular surgery by virtue of their ability to adhere to and persist on prosthetic graft material. Inguinal and abdominal skin sites were cultured in 41 patients upon hospitalization, and slime production and antimicrobial susceptibility were assessed in all recovered staphylococcal isolates. Twenty-one patients eventually underwent lower-extremity revascularization. In the operative population, cultures were also obtained on the day of surgery and fifth postoperative day. All 21 patients received perioperative cefazolin. Of 327 coagulase-negative staphylococci recovered, Staphylococcus epidermidis (47%), S. haemolyticus (21%), and S. hominis (10%) were the predominant isolates. Slime-producing coagulase-negative staphylococci were recovered from 17 of 21 patients at admission but only from 8 of 21 patients on day 5 postoperation (P less than 0.05). S. epidermidis isolates demonstrated increasing multiple resistance from admission to 5 days postoperation to methicillin, gentamicin, clindamycin, erythromycin, and trimethoprim-sulfamethoxazole (P less than 0.05). All coagulase-negative staphylococcal isolates were susceptible to ciprofloxacin and vancomycin. Slime-producing capability was not associated with increased methicillin resistance for the recovered isolates. The data demonstrate that patients enter the hospital colonized with slime-producing strains of coagulase-negative staphylococci and that during hospitalization the staphylococcal skin burden shifts from a predominately susceptible to a resistant microbial population, which may enhance the importance of slime production as a risk factor in lower-extremity revascularization.

The efficacy of oral antimicrobials in reducing aerobic and anaerobic colonic mucosal flora.

We investigated the impact of intestinal antisepsis on the colonic mucosa-associated flora. Four groups of dogs were studied: group A received no bowel preparation, group B received a three-day clear-liquid diet, group C underwent mechanical cleansing of the bowel, and group D had mechanical cleansing followed by oral neomycin and erythromycin. Mucosal biopsy specimens were obtained for bacteriologic and scanning electron microscopic (SEM) studies. No significant difference in recovery of mucosal bacteria was observed between groups A and B. A significant decrease in recovery of aerobes was observed in group C, and a significant decrease in both aerobes and anaerobes was observed in group D compared with group A; Enterobacteriaceae and Bacteroides were either eliminated or greatly reduced. The SEM analysis of group D revealed a marked decrease in mucosa-associated microflora compared with groups B and C. Oral neomycin-erythromycin produced a significant quantitative reduction in the colonic mucosa-associated bacterial population, including the potentially pathogenic Escherichia coli and Bacteroides fragilis group isolates. These mucosa-associated bacteria are a likely source of contamination of the abdominal cavity and wound at the time of colon surgery.

A prospective study of the microflora of nonpuerperal breast abscess.

The majority of reports concerning nonpuerperal breast abscess (NPBA) identify aerobic and facultative bacterial isolates as the predominant flora in this disease. In the present study, fine-needle aspiration was performed in 29 women with NPBA; 12 (41%) of the patients had a history of chronic NPBA. The mean age of patients was 39.2 years. The aspirated material was cultured both anaerobically and aerobically. A total of 108 bacterial strains were recovered from 32 specimens; two specimens yielded no bacterial growth. A mean of 3.6 different bacteria were recovered from each culture-positive specimen. Anaerobic recovery outweighed aerobic-facultative recovery by a factor of 2:1. Significantly, 37 strains (five aerobes and 32 anaerobes) were harvested only from enriched broth subcultured for four to 14 days after initial culture processing. Coagulase-negative staphylococci (60% of total aerobes) and peptostreptococci (47% of total anaerobes) were the predominant bacterial isolates. These findings indicate that NPBA is due to a mixed flora with a major anaerobic component. Furthermore, the results suggest that routine cultures often overlook the involvement of anaerobes in these infections.

Comparative in vitro beta-lactam activity against aerobic and anaerobic surgical isolates.

The comparative in vitro activity of cefoxitin, piperacillin, cefotetan, and ceftizoxime was compared against 843 surgical microbial isolates. All compounds exhibited excellent activity against the streptococcal isolates. Antimicrobial activity was poor for Staphylococcus aureus and S. epidermidis. Cefotetan activity against the Enterobacteriaceae was comparable to ceftizoxime (greater than 95% susceptible). Resistance rates of 0, 1, 5, and 2% were observed with cefoxitin, piperacillin, cefotetan, and ceftizoxime against the anaerobic cocci and anaerobic gram-positive non-spore-forming rods. Ninety-six and ninety-nine percent of the clostridial strains were susceptible to cefotetan and piperacillin, respectively. Piperacillin, cefotetan, and ceftizoxime exhibited similar activity against Bacteroides fragilis (resistance less than 10%). Cefotetan and cefoxitin exhibited poor activity against Bacteroides distasonis, B. ovatus, and B. thetaiotaomicron. Antimicrobial activities were comparable for the four drugs against other Bacteroides and Fusobacterium species. The results demonstrate that all four compounds exhibited broad antimicrobial activity against facultative and obligate anaerobic surgical isolates from intraabdominal and soft tissue infections.