Mark S. Rouse

Influence of referral bias on the apparent clinical spectrum of infective endocarditis

PURPOSE To assess the effect of referral bias on the clinical spectrum of infective endocarditis. PATIENTS AND METHODS We performed a retrospective study comparing a population-based cohort of incidence cases from Olmsted County, Minnesota, with a cohort of referred cases from the practice of the Mayo Clinic during the period from 1970 to 1987. RESULTS In the community cohort, age was an important risk factor for acquiring endocarditis (incidence rate ratio 8.8:1 for age 65 years or older versus age less than 65 years), but episodes in elderly patients were underrepresented in the referral practice. The proportion of cases due to Staphylococcus aureus was greater in the community than in the referral practice (p less than 0.02), while a trend toward overrepresentation of enterococcal endocarditis was seen in the referral population (p = 0.057). Symptom duration prior to diagnosis was significantly shorter in the community. Overall, measures of in-hospital morbidity and mortality were similar in the two populations, but advanced age was associated with adverse outcome in the community cohort. CONCLUSION The clinical spectrum of infective endocarditis may be distorted by referral. The increased risk of endocarditis in the elderly underscores the importance of adherence to recommendations for prophylaxis in this patient population.

Ciprofloxacin Inhibition of Experimental Fracture-Healing*

Background: Fluoroquinolones, such as ciprofloxacin, have an adverse effect on growing cartilage and endochondral ossification in children. This study was carried out to determine whether ciprofloxacin also has an adverse effect on the healing of experimental fractures. Methods: Sixty male 300-gram Wistar rats were divided equally into three groups, which received ciprofloxacin, cefazolin, or no treatment for three weeks, beginning seven days after production of a closed, nondisplaced, bilateral femoral fracture. The serum concentrations of the ciprofloxacin and the cefazolin were 2.4 and 146 micrograms per milliliter, respectively. Radiographic, histological, and biomechanical studies were used to evaluate fracture-healing. Results: Radiographs revealed significantly more advanced healing of the control fractures compared with the fractures in the ciprofloxacin-treated group (average stage, 2.1 compared with 1.5, p = 0.01). The cefazolin-treated group was not different from the controls with respect to radiographic healing (average stage, 1.8 compared with 2.1, p = 0.18). Torsional strength-testing of fracture callus exposed to ciprofloxacin revealed a 16 percent decrease in strength compared with the controls (284 compared with 338 newton-millimeters, p = 0.04) and a 49 percent decrease in stiffness (twenty compared with thirty-nine newton-millimeters per degree, p = 0.001). The biomechanical strength in the cefazolin-treated group was not different from that of the controls. Fracture calluses in the animals treated with ciprofloxacin showed abnormalities in cartilage morphology and endochondral bone formation and a significant decrease in the number of chondrocytes compared with the controls (0.77 x 104 compared with 1.3 x 104 cells per square millimeter, p = 0.004). Conclusions: These data suggest that experimental fractures exposed to therapeutic concentrations of ciprofloxacin in serum demonstrate diminished healing during the early stages of fracture repair. The administration of ciprofloxacin during early fracture repair may compromise the clinical course of fracture-healing.

Bacteremia Due to Viridans Group Streptococci with Diminished Susceptibility to Levofloxacin among Neutropenic Patients Receiving Levofloxacin Prophylaxis

Despite the use of levofloxacin prophylaxis during the neutropenic period after autologous peripheral blood stem cell transplantation, viridans group (VG) streptococcal bacteremia developed in 6 (16.2%) of 37 patients who underwent transplantation between 1 January and 25 February 2001 at the Mayo Clinic in Rochester, Minnesota. All 6 patients presented with fever and mucositis after a mean of 4.5 days of neutropenia, and 3 developed septic shock. All 6 VG streptococcal isolates from these patients exhibited distinct patterns on pulsed-field gel electrophoresis. All isolates had diminished susceptibility to levofloxacin, 5 to gatifloxacin, and 4 to moxifloxacin. Quinolone resistance was associated with mutations in the quinolone resistance-determining region of GyrA and (for 1 isolate) of ParC. The use of levofloxacin may select VG streptococci with diminished susceptibility to levofloxacin and other quinolones with enhanced activity against gram-positive organisms and, therefore, may not be optimal for preventing VG streptococcal bacteremia in neutropenic patients.

Evaluation of Caspofungin and Amphotericin B Deoxycholate against Candida albicans Biofilms in an Experimental Intravascular Catheter Infection Model

Candida albicans biofilms complicate the treatment of infected implanted intravascular devices because of decreased antifungal susceptibility. In our investigation, 48 rabbits with experimental central venous catheter C. albicans infection were equally allocated to a control arm or to receive amphotericin B deoxycholate or caspofungin treatment while undergoing systemic and intraluminal lock therapy for 7 days. C. albicans was cultured from catheters from all control rabbits, from 3 that received amphotericin B, and from 0 that received caspofungin. Differences in colony counts were detected between the control and amphotericin (P<.001) and control and caspofungin (P<.001) arms. Caspofungin may be useful in the treatment of C. albicans biofilm-associated intravascular catheter infections, which warrants further study.

The Electricidal Effect: Reduction of Staphylococcus and Pseudomonas Biofilms by Prolonged Exposure to Low-Intensity Electrical Current

ABSTRACT The activity of electrical current against planktonic bacteria has previously been demonstrated. The short-term exposure of the bacteria in biofilms to electrical current in the absence of antimicrobials has been shown to have no substantial effect; however, longer-term exposure has not been studied. A previously described in vitro model was used to determine the effect of prolonged exposure (i.e., up to 7 days) to low-intensity (i.e., 20-, 200-, and 2,000-microampere) electrical direct currents on Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis biofilms. Dose- and time-dependent killing was observed. A maximum of a 6-log10-CFU/cm2 reduction was observed when S. epidermidis biofilms were exposed to 2,000 microamperes for at least 2 days. A 4- to 5-log10-CFU/cm2 reduction was observed when S. aureus biofilms were exposed to 2,000 microamperes for at least 2 days. Finally, a 3.5- to 5-log10-CFU/cm2 reduction was observed when P. aeruginosa biofilms were exposed to electrical current for 7 days. A higher electrical current intensity correlated with greater decreases in viable bacteria at all time points studied. In conclusion, low-intensity electrical current substantially reduced the numbers of viable bacteria in staphylococcal or Pseudomonas biofilms, a phenomenon we have labeled the “electricidal effect.”

Levofloxacin and trovafloxacin inhibition of experimental fracture-healing.

We previously have shown that experimental fractures exposed to ciprofloxacin have diminished fracture healing. The purpose of this study was to assess the effect of levofloxacin and trovafloxacin on experimental fracture healing to test the hypothesis that diminished fracture healing is a quinolone class effect. Sixty-one male Wistar rats were divided into three groups, which received 25 mg/kg of levofloxacin twice daily for 3 weeks, 35 mg/kg of trovafloxacin twice daily for 3 weeks, or no treatment, beginning 7 days after production of closed, nondisplaced, bilateral femoral fractures. The mean peak serum concentrations of levofloxacin and trovafloxacin drawn 30 minutes after administration were 6.9 and 7.0 μg/mL, respectively. Radiographic, histologic, and biomechanical studies were used to evaluate fracture healing. Torsional strength testing of fracture callus exposed to levofloxacin and trovafloxacin revealed a decrease in strength (299 and 257 N-mm, respectively) as compared with controls (364 N-mm). Radiographs revealed significantly more advanced healing in control animals (Goldberg score of 2.1) compared with the fractures in the rats treated with levofloxacin and trovafloxacin (Goldberg score of 1.5 in both groups). Fracture calluses in the animals treated with levofloxacin and trovafloxacin showed a lower histologic grade (5.3 and 3.5, respectively) as compared with control animals (7.5) representing a less mature callus with the presence of more cartilage and less woven bone. These data suggest that experimental fractures systemically exposed to levofloxacin or trovafloxacin have diminished healing during the early stages of fracture repair. The administration of quinolones during early fracture repair may compromise fracture healing in humans.

Effect of Electrical Current on the Activities of Antimicrobial Agents against Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis Biofilms

ABSTRACT Bacterial biofilms are resistant to conventional antimicrobial agents. Prior in vitro studies have shown that electrical current (EC) enhances the activities of aminoglycosides, quinolones, and oxytetracycline against Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus epidermidis, Escherichia coli, and Streptococcus gordonii. This phenomenon, known as the bioelectric effect, has been only partially defined. The purpose of this work was to study the in vitro bioelectric effect on the activities of 11 antimicrobial agents representing a variety of different classes against P. aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA), and S. epidermidis. An eight-channel current generator/controller and eight chambers delivering a continuous flow of fresh medium with or without antimicrobial agents and/or EC to biofilm-coated coupons were used. No significant decreases in the numbers of log10 CFU/cm2 were seen after exposure to antimicrobial agents alone, with the exception of a 4.57-log-unit reduction for S. epidermidis and trimethoprim-sulfamethoxazole. We detected a statistically significant bioelectric effect when vancomycin plus 2,000 microamperes EC were used against MRSA biofilms (P = 0.04) and when daptomycin and erythromycin were used in combination with 200 or 2,000 microamperes EC against S. epidermidis biofilms (P = 0.02 and 0.0004, respectively). The results of these experiments indicate that the enhancement of the activity of antimicrobial agents against biofilm organisms by EC is not a generalizable phenomenon across microorganisms and antimicrobial agents.

Improved survival in experimental sepsis with an orally administered inhibitor of apoptosis

The pathophysiology of sepsis involves excessive lymphocyte apoptosis, which correlates with adverse outcomes, and disordered cytokine production, which may promote host injury. As the protease inhibitor (PI) class of antiretroviral agents is known to prevent apoptosis in vitro, we evaluated their effect on survival, lymphocyte apoptosis, and consequent cytokine production in mice with sepsis induced by cecal ligation and perforation. Mice pretreated with PIs have improved survival (67%; P<0.0005) compared with controls (17%) and a significant (P<0.05) reduction in lymphocyte apoptosis. Even mice receiving therapy beginning 4 h after perforation demonstrated improved survival (50%; P<0.05) compared with controls. PI therapy is also associated with an increase in the Th1 cytokine TNF‐a (P<0.05) early in sepsis and a reduction in the Th2 cytokines IL‐6 and IL‐10 (P<0.05) late in sepsis; despite no intrinsic antibacterial effects, PI also reduced quantitative bacterial blood cultures. The beneficial effects of PI appear to be specific to lymphocyte apoptosis, as lymphocyte‐deficient Rag1—/— mice did not experience benefit from treatment with PI. Thus, inhibition of lymphocyte apoptosis by PI is a candidate approach for the treatment of sepsis.— Weaver, J. G. R., Rouse, M. S., Steckelberg, J. M., Badley, A. D. Improved survival in experimental sepsis with an orally administered inhibitor of apoptosis. FASEB J. 18, 1185–1191 (2004)

The electricidal effect is active in an experimental model of Staphylococcus epidermidis chronic foreign body osteomyelitis.

ABSTRACT Treatment with low-amperage (200 μA) electrical current was compared to intravenous doxycycline treatment or no treatment in a rabbit model of Staphylococcus epidermidis chronic foreign body osteomyelitis to determine if the electricidal effect is active in vivo. A stainless steel implant and 104 CFU of planktonic S. epidermidis were placed into the medullary cavity of the tibia. Four weeks later, rabbits were assigned to one of three groups with treatment administered for 21 days. The groups included those receiving no treatment (n = 10), intravenous doxycycline (n = 14; 8 mg/kg of body weight three times per day), and electrical current (n = 15; 200 μA continuous delivery). Following treatment, rabbits were sacrificed and the tibias quantitatively cultured. Bacterial load was significantly reduced in the doxycycline (median, 2.55 [range, 0.50 to 6.13] log10 CFU/g of bone) and electrical-current (median, 1.09 [range, 0.50 to 2.99] log10 CFU/g of bone) groups, compared to the level for the control group (median, 4.16 [range, 3.70 to 5.66] log10 CFU/g of bone) (P < 0.0001). Moreover, treatment with electrical current was statistically significantly more efficacious (P = 0.035) than doxycycline treatment. The electricidal effect (the bactericidal activity of low-amperage electrical current against bacterial biofilms) is active in vivo in the treatment of experimental S. epidermidis chronic foreign body osteomyelitis.

Reevaluation of Streptococcus bovis Endocarditis Cases from 1975 to 1985 by 16S Ribosomal DNA Sequence Analysis

ABSTRACT Studies that detected an association between Streptococcus bovis endocarditis and colon carcinoma have not taken into account the recently identified genetic diversity among organisms historically classified as S. bovis. With near full-length 16S ribosomal DNA sequence analysis, organisms cultured from the blood of endocarditis patients at the Mayo Clinic from 1975 to 1985 and previously identified as S. bovis or streptococcus group D nonenterococci were shown to represent S. bovis biotypes I (11 isolates) and II/2 (1 isolate), S. salivarius (1 isolate), and S. macedonicus (1 isolate). Two of the S. bovis biotype I cases were associated with colon cancer. Whether S. bovis biotype II or other organisms closely related to and historically identified as S. bovis (e.g., S. macedonicus) are associated with malignant (or premalignant) colon lesions in humans remains to be definitively determined.