Modelling the interaction between the host immune response, bacterial dynamics and inflammatory damage in comparison with immunomodulation and vaccination experiments.

The immune system is a complex system of chemical and cellular interactions that responds quickly to queues that signal infection and then reverts to a basal level once the challenge is eliminated. Here, we present a general, four-component model of the immune system's response to a Staphylococcal aureus (S. aureus) infection, using ordinary differential equations. To incorporate both the infection and the immune system, we adopt the style of compartmenting the system to include bacterial dynamics, damage and inflammation to the host, and the host response. We incorporate interactions not previously represented including cross-talk between inflammation/damage and the infection and the suppression of the anti-inflammatory pathway in response to inflammation/damage. As a result, the most relevant equilibrium of the system, representing the health state, is an all-positive basal level. The model is able to capture eight different experimental outcomes for mice challenged with intratibial osteomyelitis due to S. aureus, primarily involving immunomodulation and vaccine therapies. For further validation and parameter exploration, we perform a parameter sensitivity analysis which suggests that the model is very stable with respect to variations in parameters, indicates potential immunomodulation strategies and provides a possible explanation for the difference in immune potential for different mouse strains.

Resistance class 1 integron in clinical methicillin-resistant Staphylococcus aureus strains in southern China, 2001-2006.

As a novel antibiotic resistance determinant, investigation of the occurrence and characteristics of class 1 integron was performed on nosocomial methicillin-resistant Staphylococcus aureus (MRSA) strains sampled during 2001-2006. Seventy-six out of 179 (42.5%) of the tested strains were found to carry class 1 integrons, with four unique arrays of gene cassettes detected. This is the first report of the comprehensive identification and typing of class 1 integrons in clinical MRSA isolates over a 6-year period, representing the first evidence for class 1 integrons as possible antibiotic resistance determinants in clinical MRSA strains.

The high-affinity phosphate transporter Pst in Proteus mirabilis HI4320 and its importance in biofilm formation.

Proteus mirabilis causes urinary tract infections (UTIs) in individuals requiring long-term indwelling catheterization. The pathogenesis of this uropathogen is mediated by a number of virulence factors and the formation of crystalline biofilms. In addition, micro-organisms have evolved complex systems for the acquisition of nutrients, including the phosphate-specific transport system, which has been shown to be important in biofilm formation and pathogenesis. A functional Pst system is important during UTIs caused by P. mirabilis HI4320, since transposon mutants in the PstS periplasmic binding protein and the PstA permease protein were attenuated in the CBA mouse model of UTI. These mutants displayed a defect in biofilm formation when grown in human urine. This study focuses on a comparison of the proteomes during biofilm and planktonic growth in phosphate-rich medium and human urine, and microscopic investigations of biofilms formed by the pst mutants. Our data suggest that (i) the Deltapst mutants, and particularly the DeltapstS mutant, are defective in biofilm formation, and (ii) the proteomes of these mutants differ significantly from that of the wild-type. Therefore, since the Pst system of P. mirabilis HI4320 negatively regulates biofilm formation, this system is important for the pathogenesis of these organisms during complicated UTIs.

Complicated catheter-associated urinary tract infections due to Escherichia coli and Proteus mirabilis.

Catheter-associated urinary tract infections (CAUTIs) represent the most common type of nosocomial infection and are a major health concern due to the complications and frequent recurrence. These infections are often caused by Escherichia coli and Proteus mirabilis. Gram-negative bacterial species that cause CAUTIs express a number of virulence factors associated with adhesion, motility, biofilm formation, immunoavoidance, and nutrient acquisition as well as factors that cause damage to the host. These infections can be reduced by limiting catheter usage and ensuring that health care professionals correctly use closed-system Foley catheters. A number of novel approaches such as condom and suprapubic catheters, intermittent catheterization, new surfaces, catheters with antimicrobial agents, and probiotics have thus far met with limited success. While the diagnosis of symptomatic versus asymptomatic CAUTIs may be a contentious issue, it is generally agreed that once a catheterized patient is believed to have a symptomatic urinary tract infection, the catheter is removed if possible due to the high rate of relapse. Research focusing on the pathogenesis of CAUTIs will lead to a better understanding of the disease process and will subsequently lead to the development of new diagnosis, prevention, and treatment options.

Experimental osteomyelitis: what have we learned from animal studies about the systemic treatment of osteomyelitis?

Clinical trials of systemic antibiotic treatment of osteomyelitis are difficult to perform for many reasons, such as low incidence rate of osteomyelitis, variety of anatomic locations, stage and etiologic agents. In this article, we reviewed the experimental studies on osteomyelitis available in the English medical literature since 1968, to ascertain their actual and potential impact on the treatment of human osteomyelitis. Major results are summarized and topics of major interest, such as reproducibility of animal models, predictive value of animal models, correlation of pharmacokinetics between different animals and humans, and the correlation of outcome between animal and clinical studies are discussed. Most of the reviewed animal models are reproducible and dependable. However, establishing the right dose regimen in animals appeared a critical factor, which might undermine the predictive value of the experimental study. Due to difficulties in comparing results of animal and human studies, the predictive value of animal studies about osteomyelitis is still unclear. However, animal models gave valuable information to the clinician for choosing the minimal duration of antibiotic treatment. Even though the use of antibiotic combinations was associated with better outcome in the majority of animal studies, such a finding seems to have limited impact on clinical practice.

Effect of farnesol on Staphylococcus aureus biofilm formation and antimicrobial susceptibility.

Staphylococcus aureus is among the leading pathogens causing bloodstream infections able to form biofilms on host tissue and indwelling medical devices and to persist and cause disease. Infections caused by S. aureus are becoming more difficult to treat because of increasing resistance to antibiotics. In a biofilm environment particularly, microbes exhibit enhanced resistance to antimicrobial agents. Recently, farnesol was described as a quorum-sensing molecule with possible antimicrobial properties. In this study, the effect of farnesol on methicillin-resistant and -susceptible strains of S. aureus was investigated. With viability assays, biofilm formation assessment, and ethidium bromide uptake testing, farnesol was shown to inhibit biofilm formation and compromise cell membrane integrity. The ability of farnesol to sensitize S. aureus to antimicrobials was assessed by agar disk diffusion and broth microdilution methods. For both strains of staphylococci, farnesol was only able to reverse resistance at a high concentration (150 microM). However, it was very successful at enhancing the antimicrobial efficacy of all of the antibiotics to which the strains were somewhat susceptible. Therefore, synergy testing of farnesol and gentamicin was performed with static biofilms exposed to various concentrations of both agents. Plate counts of harvested biofilm cells at 0, 4, and 24 h posttreatment indicated that the combined effect of gentamicin at 2.5 times the MIC and farnesol at 100 microM (22 microg/ml) was able to reduce bacterial populations by more than 2 log units, demonstrating synergy between the two antimicrobial agents. This observed sensitization of resistant strains to antimicrobials and the observed synergistic effect with gentamicin indicate a potential application for farnesol as an adjuvant therapeutic agent for the prevention of biofilm-related infections and promotion of drug resistance reversal.

Comparative evaluation of oral levofloxacin and parenteral nafcillin in the treatment of experimental methicillin-susceptible Staphylococcus aureus osteomyelitis in rabbits.

Methicillin-susceptible Staphylococcus aureus (MSSA) is the most common pathogen recovered from osteomyelitis patients. The current standard therapeutic method for acute phase osteomyelitis is parenteral antibiotic therapy. However, parenteral administration has negative aspects, such as secondary infection, patient inconvenience and high cost. The use of single oral antibiotic therapy may alleviate these problems. Therefore, the purpose of this study was to compare the effectiveness of standard once per day dosing of oral levofloxacin with a standard parenteral antibiotic regimen (nafcillin four times daily) for the treatment of experimental MSSA osteomyelitis in rabbits. Nearly all tibias from untreated infected controls (n = 27) revealed positive cultures (93%) for S. aureus, while the levofloxacin-treated group (n = 20) demonstrated significantly lower percentages of S. aureus infection (50%). The infected tibias of the nafcillin-treated group (n = 20) demonstrated significantly lower percentages (10%) of infected tibias than either the controls or the levofloxacin-treated groups (P < 0.05). The inferior efficacy of levofloxacin may have been due to the pharmacokinetic profile of this fluoroquinolone. The serum kinetics demonstrated that following single dose administration, levofloxacin was almost undetectable after 12 h. Studies in which levofloxacin is dosed every 12 h or given at increased doses in order to obtain bactericidal concentrations throughout the treatment regimen are needed.

Prevention of diseases caused by Staphylococcus aureus using the peptide RIP.

Staphylococcus aureus causes many diseases including cellulitis, keratitis, osteomyelitis, septic arthritis and mastitis. The heptapeptide RIP has been shown to prevent cellulitis in mice, which was induced by S. aureus strain Smith diffuse. Here we show that RIP can also significantly reduce the overall pathology and delay the onset of disease symptoms in several other models of S. aureus infections, including: keratitis (tested in rabbits against S. aureus 8325-4), osteomyelitis (tested in rabbits against S. aureus MS), mastitis (tested in cows against S. aureus Newbould 305, AE-1, and environmental infections) and septic arthritis (tested in mice against S. aureus LS-1). These findings substantiate that RIP is not strain specific in its inhibitory activity and that RIP is an effective inhibitor of bacterial pathology at multiple body sites following diverse routes and doses of administration. These findings strongly evidence the potential value of RIP as a chemotherapeutic agent.

Bone and joint infections in the elderly: practical treatment guidelines.

Two types of haematogenous osteomyelitis that are seen in the elderly are vertebral and long bone osteomyelitis. Osteomyelitis secondary to contiguous foci of infection can occur in older adults without vascular insufficiency (secondary to pressure ulcers) or with vascular insufficiency due to diabetes mellitus or peripheral vascular disease from atherosclerosis. Most cases of osteomyelitis can be reasonably treated with adequate drainage, thorough debridement, obliteration of dead space, wound protection, and antimicrobial therapy. Patients are initially given a broad spectrum antimicrobial that is changed to specific antimicrobial therapy based on meticulous bone cultures taken at debridement surgery or from deep bone biopsies. Surgical management is often required in the treatment of osteomyelitis and includes adequate drainage, extensive debridement of all necrotic tissue, obliteration of dead spaces, stabilisation, adequate soft tissue coverage, and restoration of an effective blood supply. Bone repair and bone mineral density may be significantly retarded and may be corrected by eliminating risk factors, supplementing the diet with calcium, bisphosphonates, and/or vitamin D, and treating with testosterone and/or estrogen when deficient. Sodium fluoride treatment and anabolic steroids may be used as alternatives. Septic arthritis is a medical emergency, and prompt recognition and rapid and aggressive treatment are critical to ensuring a good prognosis. The treatment of septic arthritis includes appropriate antimicrobial therapy and joint drainage. Adverse effects of prescribed antibacterials occur more often in the elderly patient than in young adults. The physician can help to minimise the incidence of adverse effects and improve outcomes by being aware of the principles of clinical pharmacology, the characteristics of specific drugs, and the special physical, psychological and social needs of older patients.

Antimicrobial treatment of chronic osteomyelitis.

Chronic osteomyelitis has been a difficult problem for patients and the treating physicians. Appropriate antibiotic therapy is necessary to arrest osteomyelitis along with adequate surgical therapy. Factors involved in choosing the appropriate antibiotic(s) include infection type, infecting organism, sensitivity results, host factors, and antibiotic characteristics. Initially, antibiotics are chosen on the basis of the organisms that are suspected to be causing the infection. Once the infecting organism(s) is isolated and sensitivities are established, the initial antibiotic(s) may be modified. In selecting specific antibiotics for the treatment of osteomyelitis, the type of infection, current hospital sensitivity resistance patterns, and the risk of adverse reactions must be strongly appraised. Antibiotic classes used in the treatment of osteomyelitis include penicillins, beta-lactamase inhibitors, cephalosporins, other beta-lactams (aztreonam and imipenem), vancomycin, clindamycin, rifampin, aminoglycosides, fluoroquinolones, trimethoprim-sulfamethoxazole, metronidazole, and new investigational agents including teicoplanin, quinupristin/dalfopristin, and oxazolidinones. Traditional treatments have used operative procedures followed by 4 to 6 weeks of parenteral antibiotics. Adjunctive therapy for treating chronic osteomyelitis may be achieved by using beads, spacers, or coated implants to deliver local antibiotic therapy and/or by using hyperbaric oxygen therapy (once per day for 90-120 minutes at two to three atmospheres at 100% oxygen).

Oral rifampin plus azithromycin or clarithromycin to treat osteomyelitis in rabbits.

A rabbit model for Staphylococcus aureus osteomyelitis was used to compare 28-day combination antibiotic therapy using oral rifampin (40 mg/kg, twice daily) plus oral azithromycin (50 mg/kg, once per day), oral clarithromycin (80 mg/kg, twice daily), or parenteral nafcillin (30 mg/kg, four times daily). The left tibial metaphysis of New Zealand White rabbits was infected with Staphylococcus aureus. Grades 3 to 4 osteomyelitis (according to the Cierny-Mader classification system) development in the rabbits was confirmed radiographically. After antibiotic therapy regimens of 28 days, all tibias from controls that were infected but left untreated (n = 10) revealed positive cultures for Staphylococcus aureus at a mean concentration of 2.8 x 10(4) colony forming units/g bone. The rifampin plus clarithromycin (n = 15) and rifampin plus azithromycin (n = 15) groups showed significantly lower percentages of positive Staphylococcus aureus infection (20% and 13.3%, respectively) and bacterial concentrations (3.5 x 10(1) and 1.75 x 10(1) colony forming units/g bone, respectively). The osteomyelitic tibias of the nafcillin plus rifampin treated group (n = 7) showed no detectable Staphylococcus aureus infection (significantly lower than controls). The differences observed for bone bacterial concentrations and sterilization percentages between the antibiotic treated groups were not statistically significant. Although fluoroquinolones (including ofloxacin and ciprofloxacin) are the agents usually prescribed with rifampin, increasing resistance has been observed. Although macrolides traditionally are not used in the treatment of osteomyelitis, the results of this study indicate that azithromycin and clarithromycin may be attractive partners for rifampin for the treatment of Staphylococcus aureus osteomyelitis in humans.

Skeletal scintigraphy with technetium-99m-tetraphenyl porphyrin sulfonate for the detection and determination of osteomyelitis in an animal model.

UNLABELLED: This article explores the accumulation of 99mTc-tetraphenyl porphyrin sulfonate (TPPS4) at inflammatory sites, especially osteomyelitis, and compares the results with 111In Cl3 and 111In-WBC in an animal model. METHODS: Osteomyelitis was induced in 12 New Zealand white rabbits by injecting staphylococcus aureus in the left tibia. Three weeks later, radiographs confirmed the disease. Two hours later, after injection of 74 MBq 99mTc-TPPS4, scintiphotos of the lower extremities were acquired and repeat scintiphotos were obtained 24 hr after injection of 5.55 MBq 111In Cl3. After these studies, 24- and 48-hr scintiphotos of the lower extremities were acquired after injecting 5.55 MBq 111In-labeled WBC. RESULTS: The left tibia averaged three times the uptake with 99mTc-TPPS4 compared with right tibia; with 111In Cl3 and 111In WBC the ratios are two times. These three radiopharmaceuticals reveal positive images, but the image quality using 99mTc-TPPS4 is better, as would be expected from the more favorable physical characteristics of 99mTc and the higher uptake. CONCLUSION: The traditional combination of three-phase bone and 67Ga-citrate scintigraphy can be replaced by a single injection of 99mTc-TPPS4 with imaging as early as 2 hr. Finally, the use 99mTc-TPPS4 should result in a substantial reduction in radiopharmaceutical cost.

In vivo reduction of bacterial populations in the urinary tract of catheterized sheep by iontophoresis.

PURPOSE: Iontophoresis kills microbes in vitro and, therefore, may be a useful method for eliminating microbial populations associated with catheter-induced urinary tract infections in vivo. MATERIALS AND METHODS: Catheters were modified to deliver current to platinum electrodes in the catheter tip. Female sheep were catheterized with this iontophoretic catheter and left ambulatory. In 5 sheep (experimental group) 400 microA was applied to the catheter and withheld in 4 sheep (control group) for 20 to 21 days. The animals were then sacrificed. During the study, types and concentrations of bacteria, and physical and chemical characteristics of the urine samples were determined. RESULTS: Throughout the study, bacteria levels were reduced in urinary tracts of the experimental group (10(3) to 10(4) microbes per ml.) compared with the control group (10(7) microbes per ml.), without extensive alterations to urine chemistry or the sheep urinary tract. CONCLUSIONS: Since iontophoresis safely reduced bacterial populations in catheterized sheep, this technology may reduce or eliminate nosocomial, catheter-induced urinary tract infections in humans.

Quantification, qualification, and microbial killing efficiencies of antimicrobial chlorine-based substances produced by iontophoresis.

The dependence of microbial killing on chloride ions present in solutions undergoing iontophoresis is addressed. A 400-microA current was applied to vials containing synthetic urine or saline, and the production of chlorine-based substances (CBSs) was detected by the N,N-diethyl-p-phenylene diamine colorimetric method. It was found that as the time of current application increased, the total concentration of CBSs also increased. The iontophoretic current converted (through oxidation) chloride ions present in the solutions into CBSs such as free chlorine, chlorine dioxide, chlorite, monochloramine, and dichloramine (the last two were produced by iontophoresis only when nitrogenous substances were present in the solution). Two of the CBSs (free Cl and ClO2), when they were separately added back to microbial suspensions (approximately 3 x 10(5) CFU/ml) at the same concentrations at which they were detected in either 0.46% (wt/vol) NaCl solution or synthetic urine iontophoresed for 4 h at 400 microA, reduced or eliminated bacterial genera and a fungus. However, when free Cl and ClO2 were jointly added back to microbial suspensions, bacterial and fungal killing was synergistic and more rapid and complete than when these chlorine-based biocides were added separately. Therefore, iontophoresis of solutions containing chloride ions produces chlorine-based biocides that are responsible for the antimicrobial effect of iontophoresis.