Activity of eight antibacterial agents on Staphylococcus epidermidis attached to Teflon catheters

Oral versus Intraperitoneal Application of Clindamycin in Tunnel Infections: A Prospective, Randomized Study in Capd Patients

Objective

To evaluate the potential superiority of either oral or intraperitoneal treatment of catheter tunnel infections (TI), using clindamycin as a first-Iine antibiotic and ultrasound as a diagnostic tool.

Design

This was a prospective, randomized study in continuous ambulatory peritoneal dialysis patients. From August 1993 until August 1995, 16 clinically and ultrasound-proven episodes of TI were randomly assigned to either an oral or an intraperitoneal (IP) treatment (100 patients, 1414 patient-months). Main criteria for TI diagnosis were purulent drainage from the exit site and/or a positive ultrasound (pericatheter fluid collection of at least 2 mm, 7.5 MHz transducer). Initially, clindamycin (20 mg/kg body weight) was given via the oral (three times per day) or intraperitoneal route (four times per day). In the case of incompatibility or resistance to clindamycin, either oxacillin orciprofloxacin were used orally or IP.

Results

Based on ultrasound criteria, the mean time until a ≥50% reduction of pericatheter abscess diameter was 26 days (median) (range: 8 28 days) in the oral, and 15 days (8 27 days) in the IP group (p ≤ 0.05). Showing no significant difference of pericatheter fluid at study entry with 4 mm (median) (range: 2 -6 mm) in the oral group and 4 mm (2 -4 mm) in the IP group, the IP treatment resulted in a decrease to 0 mm (0 2 mm) after 28 days (p < 0.05), while the diameter was still 2 mm (0 10 mm) (NS) in the oral group. Disappearance of exit-site infection was also somewhat earlier in the intraperitoneal group (51 vs 15 days, NS). Catheter removal had to be done once in the IP group and twice in the oral group within 6 months after study entry.

Conclusions

The results give evidence for greater efficacy of the IP application of clindamycin as a first -Iine antibiotic compared to the oral route for the treatment of tunnel infections.

Early planned removal versus expectant management of peripherally inserted central catheters to prevent infection in newborn infants

BACKGROUND

Duration of use may be a modifiable risk factor for central venous catheter-associated bloodstream infection in newborn infants. Early planned removal of peripherally inserted central catheters (PICCs) is recommended as a strategy to reduce the incidence of infection and its associated morbidity and mortality.

OBJECTIVES

To determine the effectiveness of early planned removal of PICCs (up to two weeks after insertion) compared to an expectant approach or a longer fixed duration in preventing bloodstream infection and other complications in newborn infants.

SEARCH METHODS

We searched of the Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 4), Ovid MEDLINE, Embase, Maternity & Infant Care Database, and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (until April 2018), and conference proceedings and previous reviews.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials that assessed the effect of early planned removal of umbilical venous catheters (up to two weeks after insertion) compared to an expectant management approach or a longer fixed duration in preventing bloodstream infection and other complications in newborn infants.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trial eligibility independently. We planned to analyse any treatment effects in the individual trials and report the risk ratio and risk difference for dichotomous data and mean difference for continuous data, with respective 95% confidence intervals. We planned to use a fixed-effect model in meta-analyses and explore potential causes of heterogeneity in sensitivity analyses. We planned to assess the quality of evidence for the main comparison at the outcome level using "Grading of Recommendations Assessment, Development and Evaluation" (GRADE) methods.

MAIN RESULTS

We did not identify any eligible randomised controlled trials.

AUTHORS' CONCLUSIONS

There are no trial data to guide practice regarding early planned removal versus expectant management of PICCs in newborn infants. A simple and pragmatic randomised controlled trial is needed to resolve the uncertainty about optimal management in this common and important clinical dilemma.

Intravascular Catheters and Biofilm Control

Intravascular catheters are the most common cause of nosocomially acquired bloodstream infections. Bacteria found adhering to the intraluminal surfaces of catheters are the principal source and cause of these infections. Adherent bacteria overtime are known to form multicellular communities which become encased within a three dimensional matrix of extracellular polymeric material known as biofilms, which are thought to be responsible for persistent infections. Consequently, a number of technologies have been developed to help prevent and control biofilms in intravascular catheters. One such approach involves impregnating catheter material with antimicrobial agents. Unfortunately these methods are not universally effective in preventing catheter-related biofilm infections. Technologies that utilise antimicrobials, as catheter locks have been shown to have more potential for preventing biofilm formation and reducing the incidences of catheter related bloodstream infections (CRBSI). This article discusses the significance of biofilms in intravascular catheters and determines whether the treatments available today are proving to be effective for controlling biofilms and draws attention to future avenues which are being investigated to control biofilms and therefore CRBSI.

Infection of totally implantable venous access devices: A review of the literature

Totally implantable venous access devices, or ports, are essential in the therapeutic management of patients who require long-term intermittent intravenous therapy. Totally implantable venous access devices guarantee safe infusion of chemotherapy, blood transfusion, parenteral nutrition, as well as repeated blood samples. Minimizing the need for frequent vascular access, totally implantable venous access devices also improve the patient's quality of life. Nonetheless, totally implantable venous access devices are not free from complications. Among those, infection is the most relevant, affecting patients' morbidity and mortality-both in the hospital or outpatient setting-and increasing healthcare costs. Knowledge of pathogenesis and risk factors of totally implantable venous access device-related infections is crucial to prevent this condition by adopting proper insertion bundles and maintenance bundles based on the best available evidence. Early diagnosis and prompt treatment of infection are of paramount importance. As a totally implantable venous access device-related infection occurs, device removal or a conservative approach should be chosen in treating this complication. For both prevention and therapy, antimicrobial lock is a major matter of controversy and a promising field for future clinical studies. This article reviews current evidences in terms of epidemiology, pathogenesis and risk factors, diagnosis, prevention, and treatment of totally implantable venous access device-related infections.

Evidence-Based Criteria for the Choice and the Clinical use of the Most Appropriate Lock Solutions for Central Venous Catheters (Excluding Dialysis Catheters): A GAVeCeLT Consensus

Background

The most appropriate lock solution for central venous access devices is still to be defined. GAVeCeLT – the Italian group for venous access devices – has developed a consensus on the evidence-based criteria for the choice and the clinical use of the most appropriate lock solution for central venous catheters (excluding dialysis catheters).

Method

After the constitution of a panel of experts, a systematic collection and review of the literature has been performed, focusing on clinical studies dealing with lock solutions used for prevention of occlusion (heparin, citrate, urokinase, recombinant tissue plasminogen activator [r-TPA], normal saline) or for prevention of infection (citrate, ethanol, taurolidine, ethylene-diamine-tetra-acetic acid [EDTA], vancomycin, linezolid and other antibiotics), in both adults and in pediatric patients. Studies on central lines used for dialysis or pheresis, on peripheral venous lines and on arterial lines were excluded from this analysis. Studies on lock solutions used for treatment of obstruction or infection were not considered. The consensus has been carried out according to the Delphi method.

Results

The panel has concluded that: (a) there is no evidence supporting the heparin lock; (b) the prevention of occlusion is based on the proper flushing and locking technique with normal saline; (c) the most appropriate lock solution for infection prevention should include citrate and/or taurolidine, which have both anti-bacterial and anti-biofilm activity, with negligible undesired effects if compared to antibiotics; (d) the patient populations most likely to benefit from citrate/taurolidine lock are yet to be defined.

Conclusions

The actual value of heparinization for non-dialysis catheters should be reconsidered. Also, the use of lock with substances with anti-bacterial and anti-biofilm activity (such as citrate or taurolidine) should be taken into consideration in selected populations of patients.

Antimicrobial-impregnated central venous catheters for prevention of catheter-related bloodstream infection in newborn infants

BACKGROUND

Central venous catheter-related bloodstream infection is an important cause of mortality and morbidity in newborn infants cared for in neonatal units. Potential strategies to prevent these infections include the use of central venous catheters impregnated with antimicrobial agents.

OBJECTIVES

To determine the effect of antimicrobial-impregnated central venous catheters in preventing catheter-related bloodstream infection in newborn infants.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 8), MEDLINE (1966 to September 2015), EMBASE (1980 to September 2015), CINAHL (1982 to September 2015), conference proceedings and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials comparing central venous catheters impregnated or coated with any antibiotic or antiseptic versus central venous catheters without antibiotic or antiseptic coating or impregnation in newborn infants.

DATA COLLECTION AND ANALYSIS

We extracted data using the standard methods of the Cochrane Neonatal Group, with independent evaluation of risk of bias and data extraction by two review authors.

MAIN RESULTS

We found only one small trial (N = 98). This trial found that silver zeolite-impregnated umbilical venous catheters reduced the incidence of bloodstream infection in very preterm infants (risk ratio 0.11, 95% confidence interval 0.01 to 0.87; risk difference -0.17, 95% CI -0.30 to -0.04; number needed to treat for benefit 6, 95% CI 3 to 25].

AUTHORS' CONCLUSIONS

Although the data from one small trial indicates that antimicrobial-impregnated central venous catheters might prevent catheter-related bloodstream infection in newborn infants, the available evidence is insufficient to guide clinical practice. A large, simple and pragmatic randomised controlled trial is needed to resolve on-going uncertainty.

Intravascular catheter-related infections

The introduction and subsequent widespread use of intravenous catheters have presented physicians a double-edged sword. Although safe and stable vascular access has become essential to modern medical practice, bloodstream infection involving these catheters (particularly central venous catheters [CVCs]) is a major cause of morbidity and mortality in the United States. In this comprehensive review, the author discusses the most common sources of catheter-related infections, current diagnostic and treatment methods, and graded evidence-based recommendations for prevention of these infections.

Antibiotic lock for the prevention of catheter-related infection in neonates

BACKGROUND

Use of a central venous catheter (CVC) in neonates is associated with an increase in nosocomial infection. Numerous strategies exist to prevent catheter-related bloodstream infection (CRBSI); however, CRBSI continues to be a major problem. Antibiotic locking catheters is a new and promising treatment that potentially prevents this severe condition.

OBJECTIVES

To assess the effectiveness of antibiotic lock versus no antibiotic lock or alternative antibiotic lock in the prevention of catheter-related infections in newborn infants of any gestational age during their initial stay in the neonatal unit and to study any relevant adverse effects from antibiotic lock therapy.

SEARCH METHODS

Methods followed those of the Cochrane Neonatal Review Group (CNRG). We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2014, Issue 5); MEDLINE (via PubMed); EMBASE (hosted by EBCHOST); CINAHL; abstracts from Pediatric Academic Societies, European Society for Paediatric Research and trials registries; and references cited in our short listed articles using keywords and MeSH headings, up to April 2015.

SELECTION CRITERIA

We considered all trials utilising random or quasi-random participant allocation. Participants included all newborn infants of any postmenstrual age who required any type of CVC. We compared an antibiotic lock technique with no antibiotic lock or placebo, such as heparinised saline, for any duration of time.

DATA COLLECTION AND ANALYSIS

We extracted data using the standard methods of the CNRG. Two review authors independently assessed the relevance and risk of bias of the retrieved records. We expressed our dichotomous results using risk ratio (RR) with their 95% confidence intervals (CIs). We assessed for heterogeneity using the I(2) statistic.

MAIN RESULTS

We included three trials (271 infants) in this review. Two of the three included studies had an overall low risk of bias and the remaining study had high risk of selection and performance biases. The use of an antibiotic lock decreased the incidence of confirmed catheter-related infection (typical RR 0.15, 95% CI 0.06 to 0.40; 3 studies, 271 infants) (high-quality evidence). The typical absolute risk reduction (ARR) was 18.5% and the number needed to treat for an additional beneficial outcome (NNTB) was 5. The effect of use of an antibiotic lock on suspected catheter infection was imprecise (typical RR 0.65, 95% CI 0.22 to 1.92) (moderate quality evidence). Confirmed and suspect infection rates combined were lower in the antibiotic lock group (absolute rates, RR 0.25, 95% CI 0.12 to 0.49; rate per 1000 catheter days, RR 0.17, 95% CI 0.07 to 0.40). The ARR was 20.5% and the NNTB was 5. None of the studies report resistance to the antibiotic used during the lock treatment. There was no significant difference in the detectable serum levels of antibiotic. When the data from two studies were pooled, there were significantly fewer episodes of hypoglycaemia in the treatment arm (typical RR 0.51, 95% CI 0.28 to 0.92). There was no statistically significant difference for mortality due to sepsis between the control and intervention group.

AUTHORS' CONCLUSIONS

Based on a small number of trials and neonates, antibiotic lock solution appeared to be effective in preventing CRBSI in the neonatal population. However, as each included study used a different antibiotics and antibiotic resistance could not be reliably assessed, the evidence to-date is insufficient to determine the effects of antibiotic lock on infections in neonates.

Prevalence of mutans streptococci isolated from complete dentures and their susceptibility to mouthrinses

The aims of this study were to evaluate the incidence of mutans streptococci (MS - sessile form) on complete maxillary dentures after use of a specific denture paste, and to determine the minimum inhibitory concentration (MIC) and maximum inhibitory dilution (MID) of 3 oral mouthrinses: Cepacol, Plax and Periogard. Seventy-seven complete denture wearers were randomly assigned into 2 groups, according to the product used for denture cleaning: Control group - conventional dentifrice (Kolynos-Super White); and Test group: experimental denture cleaning paste. Denture biofilm was collected at baseline and after 90 and 180 days after treatment by brushing the dentures with saline solution. After decimal serial dilution, samples were seeded onto agar sucrose bacitracin to count colonies with morphological characteristics of MS. MS identification was performed by the sugar fermentation tests. After this procedure, brain heart infusion broth (BHI) was added to oral mouthrinses (Plax, Cepacol e Periogard) and seeded on Petri dishes. The colonies were seeded using the Steers multiplier and, after the incubation, the MIC and MID of the mouthrinses were calculated. The results showed an incidence of 74.0% (n=57) of MS in the 77 complete dentures examined in the study, being 76.3% (n=29) of the Control group (conventional dentifrice) and 71.8% (28) of the Test group (experimental denture cleaning paste). In both groups, the number of positive cases for MS decreased from day 0 to day 180. In the Test group there was a slight decrease in the incidence of Streptococcus mutans 90 days after use of the experimental denture cleaning paste, which was not observed in the Control group. As regards to mouthrinses, for both groups, Periogard showed antimicrobial action with the highest dilution, followed by Cepacol and Plax. In conclusion, the incidence of MS in complete dentures was high and Periogard was the mouthrinse with the strongest antimicrobial action against MS. The experimental denture cleaning paste showed a slight action against S. mutans after 90 days of treatment.

Clinical practice guidelines for the diagnosis and management of intravascular catheter-related infection: 2009 Update by the Infectious Diseases Society of America

These updated guidelines replace the previous management guidelines published in 2001. The guidelines are intended for use by health care providers who care for patients who either have these infections or may be at risk for them.

Actividad y permeabilidad de linezolid y vancomicina en biocapas de Staphylococcus epidermidis

INTRODUCTION

The activity and capacity for penetration of linezolid and vancomycin were comparatively evaluated against Staphylococcus epidermidis biofilms.

METHODS

The activity of linezolid versus vancomycin was assessed against 24-hour S. epidermidis biofilms developed on silicon catheters. Penetration of the two antimicrobial agents was measured in biofilms developed on polycarbonate membrane filters. Penetration and activity were comparatively tested using S. epidermidis, slime-producing and non-slime-producing strains.

RESULTS

The activity of linezolid against S. epidermidis biofilms was significantly greater than that of vancomycin for both strains. Neither antimicrobial completely eradicated bacterial survival in 24-hour biofilms. Linezolid penetration in biofilms was greater than that of vancomycin for both S. epidermidis strains.

CONCLUSIONS

Linezolid showed higher in vitro activity than vancomycin against S. epidermidis biofilms on silicone catheters. This effect may be due to the capability of linezolid to cross the bacterial biofilm.

Antimicrobial locks: putting the lock on catheter infections

Infectious complications resulting from catheter use in the hemodialysis population remain as the significant cause of morbidity and mortality in this patient population. Because conservation of vascular access sites remains a therapeutic mainstay for chronic hemodialysis patients, clinical investigators have evaluated the safety and efficacy of catheter preservation with antimicrobial lock solutions instilled into the lumens of catheters to treat and prevent infectious complications. The recommended treatment of catheter-related bacteremia includes administration of systemic antibiotics with catheter removal. To date, 4 studies in the hemodialysis population have evaluated the use of systemic antibiotics with an antimicrobial lock solution for treatment of catheter-related bacteremias to amplify the success of catheter salvage. The use of antimicrobial lock solutions for the treatment of catheter-related bacteremia has resulted in successful catheter salvage in approximately 69% of patients, with the remainder requiring catheter removal following a lack of clinical improvement after 48 hours. The antimicrobial lock has also been studied as a prophylactic measure to prevent catheter-related bacteremia. Six studies in the hemodialysis population have evaluated the use of an antimicrobial lock for the prevention of catheter-related bacteremia with an overall 64%-100% reduction in the frequency of catheter-related bacteremia. Although the use of antimicrobial lock for prophylaxis has demonstrated efficacy in clinical trials, its long-term consequences, including potential impact on antimicrobial resistance, are unknown. The objectives of this review are to evaluate the current body of evidence espousing the utilization of an antimicrobial lock solution in tunneled cuffed and uncuffed catheters that are utilized during chronic intermittent hemodialysis.

Comparative in vitro efficacies of various catheter lock solutions

MEDTA (minocycline-edetate calcium disodium), taurolidine (2%)-polyvinylpyrolidine (5%) (T/PVP), and ethanol as potential catheter lock solutions have a unique mechanism of action, broad-spectrum activity, and anticoagulant properties. Traditional lock solutions minocycline (M), rifampin (R), ciprofloxacin (C), and vancomycin, except pharmacologic concentrations of C and R and of M and R, were less effective than MEDTA and T/PVP.

Lysostaphin disrupts Staphylococcus aureus and Staphylococcus epidermidis biofilms on artificial surfaces

Staphylococci often form biofilms, sessile communities of microcolonies encased in an extracellular matrix that adhere to biomedical implants or damaged tissue. Infections associated with biofilms are difficult to treat, and it is estimated that sessile bacteria in biofilms are 1,000 to 1,500 times more resistant to antibiotics than their planktonic counterparts. This antibiotic resistance of biofilms often leads to the failure of conventional antibiotic therapy and necessitates the removal of infected devices. Lysostaphin is a glycylglycine endopeptidase which specifically cleaves the pentaglycine cross bridges found in the staphylococcal peptidoglycan. Lysostaphin kills Staphylococcus aureus within minutes (MIC at which 90% of the strains are inhibited [MIC(90)], 0.001 to 0.064 microg/ml) and is also effective against Staphylococcus epidermidis at higher concentrations (MIC(90), 12.5 to 64 microg/ml). The activity of lysostaphin against staphylococci present in biofilms compared to those of other antibiotics was, however, never explored. Surprisingly, lysostaphin not only killed S. aureus in biofilms but also disrupted the extracellular matrix of S. aureus biofilms in vitro on plastic and glass surfaces at concentrations as low as 1 microg/ml. Scanning electron microscopy confirmed that lysostaphin eradicated both the sessile cells and the extracellular matrix of the biofilm. This disruption of S. aureus biofilms was specific for lysostaphin-sensitive S. aureus, as biofilms of lysostaphin-resistant S. aureus were not affected. High concentrations of oxacillin (400 microg/ml), vancomycin (800 microg/ml), and clindamycin (800 microg/ml) had no effect on the established S. aureus biofilms in this system, even after 24 h. Higher concentrations of lysostaphin also disrupted S. epidermidis biofilms.

The antibiotic-lock technique for therapy of 'highly needed' infected catheters

Catheter-related bacteremia is a major complication in patients with long-term surgically implanted central venous catheters, which are difficult and expensive to remove. Conventional treatment fails in a significant number of cases, resulting in removal of the device. The antibiotic-lock technique involves instilling a high concentration of antibiotic into the catheter lumen, and allowing it to remain for a period of time. Results of several open studies, mainly involving patients receiving home parenteral nutrition, indicate that this method may be regarded as an alternative to the conservative treatment of noncomplicated intraluminal catheter-related bacteremia, in which infection may be treated without catheter removal. However, many questions about this therapeutic method remain to be resolved, including appropriate concentration of antibiotics, duration of treatment, and whether or not concomitant systemic antibiotic therapy is necessary. Prospective studies comparing the antibiotic-lock technique with conventional treatment are needed.

Role of antibiotic prophylaxis for the prevention of intravascular catheter-related infection

Intravascular catheters have become essential tools for the management of patients in modern medical practice, but there are complications. In particular, catheter-related infection remains a major cause of nosocomial infection and primary septicemia. The development of preventive strategies to reduce the incidence of catheter-related infection is an important goal for all health providers. Over recent years, significant advances in prophylactic measures for the prevention of catheter-related infection have been made. This paper reviews strategies based on antibiotic prophylaxis such as systemic administration of antibiotics, application of antibiotic ointments to the skin insertion site as well as catheter flushing with antibiotics, the antibiotic-lock technique and the use of antimicrobial impregnated catheters.

Guidelines for the management of intravascular catheter-related infections

These guidelines from the Infectious Diseases Society of America (IDSA), the American College of Critical Care Medicine (for the Society of Critical Care Medicine), and the Society for Healthcare Epidemiology of America contain recommendations for the management of adults and children with, and diagnosis of infections related to, peripheral and nontunneled central venous catheters (CVCs), pulmonary artery catheters, tunneled central catheters, and implantable devices. The guidelines, written for clinicians, contain IDSA evidence-based recommendations for assessment of the quality and strength of the data. Recommendations are presented according to the type of catheter, the infecting organism, and the associated complications.

Intravascular catheter-related infections are a major cause of morbidity and mortality in the United States. Coagulase-negative staphylococci,Staphylococcus aureus, aerobic gram-negative bacilli, andCandida albicansmost commonly cause catheter-related bloodstream infection. Management of catheter-related infection varies according to the type of catheter involved. After appropriate cultures of blood and catheter samples are done, empirical iv antimicrobial therapy should be initiated on the basis of clinical clues, the severity of the patient's acute illness, underlying disease, and the potential pathogen (s) involved. In most cases of nontunneled CVC-related bacteremia and fungemia, the CVC should be removed.

Catheterization and urinary tract infections: microbiology

Patients with urinary catheters are a substantial proportion of the total patient population and catheter care is an important area of nursing practice. Urinary tract infection associated with catheterization is known to be the most common nosocomial (hospital-acquired) infection. Urinary tract infections can be caused by exogenous microorganisms or endogenous faecal or urethral microorganisms. The different microorganisms which are responsible for causing urinary tract infections have particular characteristics. Many microorganisms form a biofilm, a living layer of cells which stick to the surfaces of the catheter and the catheter bag. Biofilms not only lead to urinary tract infections, but also they are associated with encrustation and catheter blockage. The article considers the microorganisms implicated in catheter-associated urinary tract infections and aims to develop an increased awareness of the characteristics of different pathogens which could lead to enhanced nursing practice and improved patient care.

Microbial biofilms: their development and significance for medical device-related infections

Microbial adhesion and biofilm formation on medical devices represent a common occurrence that can lead to serious illness and death. The process by which bacteria and yeast colonize open and closed implants is fairly complicated and involves a series of steps commencing with deposition of host substances onto the material. Prevention and treatment of established biofilms with antimicrobial agents are difficult because the organisms are encased within a protected microenvironment. Efforts to reduce adhesion using specially developed materials, such as hydrophilic or heparin coated, have had modest success once applied to the patient. The reason, at least for the most part, is the diverse milieu into which devices are placed and the multitude of ways in which organisms can colonize surfaces. A better understanding of the process is required, and the knowledge gained must be used to devise new strategies as alternatives to the traditional employment of antibiotics. These new approaches may still use antibiotics but at different concentrations (low to prevent and high to treat infection) and in a different manner (perhaps spiked therapy in which there is a delay between doses to reduce the risk of drug resistance and impact on normal flora). The possibility of applying functional foods to patient management should also be pursued.

Antibiotic susceptibility assay for Staphylococcus aureus in biofilms developed in vitro

Four slime-producing isolates of Staphylococcus aureus were used in an antibiotic susceptibility assay for biofilms developed on 96-well polystyrene tissue culture plates. The study involved 11 antibiotics, two biofilm ages (6 and 48 h), two biofilm growth media (tryptone soy broth (TSB) and delipidated milk) and three antibiotic concentrations (4 x MBC, 100 mg/L and 500 mg/L). ATP-bioluminescence was used for automated bacterial viability determination after a 24 h exposure to antibiotics, to avoid biofilm handling. Under the conditions applied, viability in untreated biofilms (controls) was lower when biofilm growth was attempted in milk rather than in TSB. Various antibiotics had a greater effect on viability when used at higher (> or =100 mg/L) antibiotic concentrations and on younger (6 h) biofilms. Increased antibiotic effect was observed in milk-grown rather than TSB-grown biofilms. Phosphomycin and cefuroxime, followed by rifampicin, cefazolin, novobiocin, vancomycin, penicillin, ciprofloxacin and tobramycin significantly affected biofilm cell viability at least under some of the conditions tested. Gentamicin and erythromycin had a non-significant effect on cell viability. Transmission electron microscopy revealed that cells at the inner biofilm layers tend to remain intact after antibiotic treatment and that TSB-grown biofilms favoured a uniformity of cell distribution and increased cell density in comparison with milk-grown biofilms. A reduced matrix distribution and enhanced cell density were observed as the biofilm aged. The S. aureus biofilm test discriminated antibiotics requiring shorter (3 h or 6 h) from those requiring longer (24 h) exposure and yielded results which may be complementary to those obtained by conventional tests.

Antimicrobial substances and effects on sessile bacteria

Biofilms occur in natural aquatic ecosystems and on surfaces of biomaterials. They are generally associated with clinical infections predominantly of prosthetic hip joints, heart valves and catheters. Sessile microorganisms may be intimately associated with each other and to solid substratum through binding to and inclusion into exopolymer matrices on biofilms. The establishment of functional colonies within the exopolymeric matrices generate physico-chemical gradients within biofilms, that modify the metabolism and cell-wall properties of the microorganism. A consequence of biofilm growth is an enhanced microbial resistance to chemical antimicrobial agents and antibiotics. Investigations on the antimicrobial efficacy of antibiotics, antiseptics and antimicrobial heavy ions, however, gave controversial results. No single antimicrobial substance has been developed for the efficient eradication of adherent bacteria. This review elucidates the mechanisms of microbial resistance in biofilms and strategies for the prevention of biofilm development. Pharmacokinetical and pharmacodynamical issues for the screening of biofilm-active drugs are presented. Combinations of antistaphylococcal antibiotics with rifampin may be advantageous for preventing and curing biomaterial infections.

Killing effects of antibiotics and two-fold antimicrobial combinations on proliferating and non growing staphylococci

Antimicrobial agents are generally tested against bacteria in the log phase of multiplication to produce the maximal bactericidal effect. In case of foreign body infections, bacteria may multiply less optimally. We examined the effects of several classes of lipophilic antistaphylococcal agents to determine their antimicrobial activity towards coagulase-positive and coagulase-negative staphylococci during the non-growing and slowly growing phases. Only two-fold combinations containing rifampicin were bactericidal (3-log kill) against Staphylococcus aureus. This was in contrast to growing bacteria in the log phase, in which a variety of antibiotics produced relevant killing. Concerning the staphylococci examined, antibiotic killing was greatly dependent on the growth rate. Most of the two-fold combinations containing rifampicin showed additive and synergistic antibacterial activity both in growth and stationary states as measured by the killing kinetics. The theoretical and clinical implications of delayed killing by chemotherapeutic agents for established bacterial infections and infections involving foreign bodies are discussed. Antimicrobial combinations including rifampicin and a second lipophilic antistaphylococcal drug may be most promising and appropriate as coating substances for intravascular devices or for clinical application in cases of implant infections.

In vitro studies of pharmacodynamic properties of vancomycin against Staphylococcus aureus and Staphylococcus epidermidis

The bactericidal activities of vancomycin against two reference strains and two clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis were studied with five different concentrations ranging from 2x to 64x the MIC. The decrease in the numbers of CFU at 24 h was at least 3 log10 CFU/ml for all strains. No concentration-dependent killing was observed. The postantibiotic effect (PAE) was determined by obtaining viable counts for two of the reference strains, and the viable counts varied markedly: 1.2 h for S. aureus and 6.0 h for S. epidermidis. The determinations of the PAE, the postantibiotic sub-MIC effect (PA SME), and the sub-MIC effect (SME) for all strains were done with BioScreen C, a computerized incubator for bacteria. The PA SMEs were longer than the SMEs for all strains tested. A newly developed in vitro kinetic model was used to expose the bacteria to continuously decreasing concentrations of vancomycin. A filter prevented the loss of bacteria during the experiments. One reference strain each of S. aureus and S. epidermidis and two clinical isolates of S. aureus were exposed to an initial concentration of 10x the MIC of vancomycin with two different half-lives (t1/2s): 1 or 5 h. The post-MIC effect (PME) was calculated as the difference in time for the bacteria to grow 1 log10 CFU/ml from the numbers of CFU obtained at the time when the MIC was reached and the corresponding time for an unexposed control culture. The difference in PME between the strains was not as pronounced as that for the PAE. Furthermore, the PME was shorter when a t1/2 of 5 h (approximate terminal t1/2 in humans) was used. The PMEs at t1/2s of 1 and 5 h were 6.5 and 3.6 h, respectively, for S. aureus. The corresponding figures for S. epidermidis were 10.3 and less than 6 h. The shorter PMEs achieved with a t1/2 of 5 h and the lack of concentration-dependent killing indicate that the time above the MIC is the parameter most important for the efficacy of vancomycin.

Activity of glycopeptides in combination with amikacin or rifampin against Staphylococcus epidermidis biofilms on plastic catheters

The in vitro activity of vancomycin and teicoplanin (fourfold the MBC), alone and in combination with amikacin (16 mg/l) or rifampin (1 mg/l), against Staphylococcus epidermidis (slime-producing and non slime-producing strains) biofilms on different plastic catheters was evaluated. The addition of amikacin or rifampin significantly increased the activity of glycopeptides against sessile bacteria. With the slime-producing strain, these combinations were able to sterilize the surface of Vialon and polyvinylchloride catheters. It is concluded that the in vitro activity of glycopeptides against Staphylococcus epidermidis biofilms on plastic catheters can be increased by the addition of amikacin or rifampin.