Schmidt-Malan, Suzannah M.

ABSTRACT Staphylococcal prosthetic joint infections (PJIs) are associated with biofilm formation, making them difficult to treat; if managed with debridement and implant retention, rifampin-based therapy is usually employed. Rifampin resistance potentially challenges PJI treatment. In investigating the effects of rifampin monotherapy on methicillin-resistant Staphylococcus aureus (MRSA) foreign-body osteomyelitis in rats, we previously demonstrated that rifampin resistance was selected but that it disappeared 14 days following rifampin monotherapy (1) and that rifampin resistance occurred less frequently following two rounds than following one round of rifampin monotherapy (2). Here, we compared rifampin monotherapy followed by rifampin-vancomycin combination therapy to rifampin-vancomycin combination therapy alone in experimental MRSA foreign-body osteomyelitis. Animals treated with rifampin monotherapy followed by rifampin-vancomycin combination therapy had decreased quantities of bacteria 14 days following treatment completion ( P = 0.034) compared to those in animals treated with combination therapy alone. Additionally, some isolates recovered from animals treated with combination therapy alone, although still susceptible to rifampin, had higher MIC, minimum biofilm-inhibitory concentration (MBIC), and minimum biofilm-bactericidal concentration (MBBC) values than those of the inoculating strain. This suggests that rifampin may remain a feasible treatment option in foreign-body-associated orthopedic infections following the selection of rifampin resistance.

ABSTRACT Foreign-body-associated infections are often difficult to treat, given that the associated microorganisms are in a biofilm state. Previously, we showed that a low-amperage direct electrical current (DC) reduces Propionibacterium acnes biofilms formed on implant-associated materials in vitro . In this study, low-amperage DC was compared to ceftriaxone treatment or no treatment in a novel rat femur model of foreign-body osteomyelitis. A platinum implant seeded with a P. acnes biofilm (10 7 CFU/cm 2 ) and 10 9 CFU of planktonic P. acnes was placed in the femoral medullary cavity. One week later, rats were assigned to one of three treatment groups: no treatment, ceftriaxone treatment, or 200-μA-DC treatment. After 2 weeks of treatment, there were fewer bacteria in the bones of the ceftriaxone group (3.06 log 10 CFU/g of bone [ P = 0.0209]) and the 200-μA-DC group (0.5 log 10 CFU/g [ P = 0.0015]) than in those of the control group (6.58 log 10 CFU/g). The DC-exposed animals exhibited fewer bacteria than the ceftriaxone-treated animals ( P = 0.0330). There were fewer bacteria on the implanted wires in the groups treated with ceftriaxone (0.1 log 10 CFU/cm 2 ) or a 200-μA DC (0.1 log 10 CFU/cm 2 ) than in the control group (2.53 log 10 CFU/cm 2 [ P , 0.0003 for both comparisons]). Low-amperage DC may be useful for treating, or aiding in the treatment of, foreign-body infections caused by P. acnes .

New strategies are needed for prevention of biofilm formation. We have previously shown that 24 hr of 2,000 µA of direct current (DC) reducesStaphylococcus epidermidisbiofilm formationin vitro. Herein, we examined the effect of a lower amount of DC exposure onS. epidermidis,Staphylococcus aureus,Escherichia coli,Pseudomonas aeruginosa,Propionibacterium acnes, andCandida albicansbiofilm formation. 12 hr of 500 µA DC decreasedS. epidermidis,S. aureus,E. coli, andP. aeruginosabiofilm formation on Teflon discs by 2, 1, 1, and 2 log10cfu/cm2, respectively (p<0.05). Reductions inS. epidermidis,S. aureus, andE. colibiofilm formation were observed with as few as 12 hr of 200 µA DC (2, 2 and 0.4 log10 cfu/cm2, resp.); a 1 log10 cfu/cm2reduction inP. aeruginosabiofilm formation was observed at 36 hr. 24 hr of 500 µA DC decreasedC. albicansbiofilm formation on Teflon discs by 2 log10 cfu/cm2. No reduction inP. acnesbiofilm formation was observed. 1 and 2 log10 cfu/cm2reductions inE. coliandS. epidermidisbiofilm formation on titanium discs, respectively, were observed with 12 hr of exposure to 500 µA. Electrical current is a potential strategy to reduce biofilm formation on medical biomaterials.

ABSTRACT Catheter-associated infections are difficult to treat with available antimicrobial agents because of their biofilm etiology. We examined the effect of low-amperage direct electrical current (DC) exposure on established bacterial and fungal biofilms in a novel experimental in vitro catheter model. Staphylococcus epidermidis , Staphylococcus aureus , Escherichia coli , Pseudomonas aeruginosa , and Candida parapsilosis biofilms were grown on the inside surfaces of polyvinyl chloride (PVC) catheters, after which 0, 100, 200, or 500 μA of DC was delivered via intraluminally placed platinum electrodes. Catheter biofilms and intraluminal fluid were quantitatively cultured after 24 h and 4 days of DC exposure. Time- and dose-dependent biofilm killing was observed with all amperages and durations of DC administration. Twenty-four hours of 500 μA of DC sterilized the intraluminal fluid for all bacterial species studied; no viable bacteria were detected after treatment of S. epidermidis and S. aureus biofilms with 500 μA of DC for 4 days.

ABSTRACT We examined the pharmacokinetic properties of vancomycin conjugated to a bone-targeting agent (BT) with high affinity for hydroxyapatite after systemic intravenous administration. The results confirm enhanced persistence of BT-vancomycin in plasma and enhanced accumulation in bone relative to vancomycin. This suggests that BT-vancomycin may be a potential carrier for the systemic targeted delivery of vancomycin in the treatment of bone infections, potentially reducing the reliance on surgical debridement to achieve the desired therapeutic outcome.

ABSTRACT Bacterial biofilms are difficult to treat using available antimicrobial agents, so new antibiofilm strategies are needed. We previously showed that 20, 200, and 2,000 μA of electrical current reduced bacterial biofilms of Staphylococcus aureus , Staphylococcus epidermidis , and Pseudomonas aeruginosa . Here, we tested continuous direct current at lower amperages, intermittent direct current, and combinations of surface materials (Teflon or titanium) and electrode compositions (stainless steel, graphite, titanium, or platinum) against S. aureus , S. epidermidis , and P. aeruginosa biofilms. In addition, we tested 200 or 2,000 μA for 1 and 4 days against biofilms of 33 strains representing 13 species of microorganisms. The logarithmic reduction factor was used to measure treatment effects. Using continuous current delivery, the lowest active amperage was 2 μA for 1, 4, or 7 days against P. aeruginosa and 5 μA for 7 days against S. epidermidis and S. aureus biofilms. Delivery of 200 μA for 4 h a day over 4 days reduced P. aeruginosa , S. aureus , and S. epidermidis biofilms on Teflon or titanium discs. A reduction of P. aeruginosa , S. aureus , and S. epidermidis biofilms was measured for 23 of 24 combinations of surface materials and electrode compositions tested. Four days of direct current delivery reduced biofilms of 25 of 33 strains studied. In conclusion, low-amperage current or 4 h a day of intermittent current delivered using a variety of electrode compositions reduced P. aeruginosa , S. aureus , and S. epidermidis biofilms on a variety of surface materials. The electricidal effect was observed against a majority of bacterial species studied.

ABSTRACT Orthopedic foreign body-associated infections are often treated with rifampin-based combination antimicrobial therapy. We previously observed that rifampin-resistant and methicillin-resistant Staphylococcus aureus (MRSA) isolates were present 2 days after cessation of rifampin therapy in experimental foreign body osteomyelitis. Unexpectedly, only rifampin-susceptible isolates were detected 14 days after the completion of treatment. We studied two rifampin-resistant isolates recovered 2 days after treatment and one rifampin-susceptible isolate recovered 14 days after treatment. Growing these isolates alone in vitro or in vivo demonstrated no fitness defects; however, in mixed culture, rifampin-susceptible bacteria outcompeted rifampin-resistant bacteria. In vivo , two courses of rifampin treatment (25 mg/kg of body weight every 12 h for 21 days) yielded a greater decrease in bacterial quantity in the bones of treated animals 14 days following treatment than that in animals receiving a single course of treatment ( P = 0.0398). In infections established with equal numbers of rifampin-resistant and rifampin-susceptible bacteria, one course of rifampin treatment did not affect bacterial quantities. Rifampin-resistant and rifampin-susceptible isolates were recovered both 2 days and 14 days following treatment completion; however, the proportion of animals with rifampin-resistant isolates was lower at 14 days than that at 2 days following treatment completion ( P = 0.024). In untreated animals infected with equal numbers of rifampin-resistant and rifampin-susceptible bacteria for 4 weeks, rifampin-susceptible isolates were exclusively recovered, indicating the outcompetition of rifampin-resistant by rifampin-susceptible isolates. The data presented imply that although there is no apparent fitness defect in rifampin-resistant bacteria when grown alone, they are outcompeted by rifampin-susceptible bacteria when the two are present together. The findings also suggest that selected rifampin resistance may not persist in initially rifampin-susceptible infections following the discontinuation of rifampin.