Wolfgang Kohnen

Detection of antibiotic‐resistant bacteria and their resistance genes in wastewater, surface water, and drinking water biofilms

Abstract In view of the increasing interest in the possible role played by hospital and municipal wastewater systems in the selection of antibiotic-resistant bacteria, biofilms were investigated using enterococci, staphylococci, Enterobacteriaceae, and heterotrophic bacteria as indicator organisms. In addition to wastewater, biofilms were also investigated in drinking water from river bank filtrate to estimate the occurrence of resistant bacteria and their resistance genes, thus indicating possible transfer from wastewater and surface water to the drinking water distribution network. Vancomycin-resistant enterococci were characterized by antibiograms, and the vanA resistance gene was detected by molecular biology methods, including PCR. The vanA gene was found not only in wastewater biofilms but also in drinking water biofilms in the absence of enterococci, indicating possible gene transfer to autochthonous drinking water bacteria. The mecA gene encoding methicillin resistance in staphylococci was detected in hospital wastewater biofilms but not in any other compartment. Enterobacterial ampC resistance genes encoding beta-lactamase activities were amplified by PCR from wastewater, surface water and drinking water biofilms.

Infections Associated with Medical Devices Pathogenesis, Management and Prophylaxis

The insertion or implantation of foreign bodies has become an indispensable part in almost all fields of medicine. However, medical devices are associated with a definitive risk of bacterial and fungal infections. Foreign body-related infections (FBRIs), particularly catheter-related infections, significantly contribute to the increasing problem of nosocomial infections. While a variety of microorganisms may be involved as pathogens, staphylococci account for the majority of FBRIs. Their ability to adhere to materials and to promote formation of a biofilm is the most important feature of their pathogenicity. This biofilm on the surface of colonised foreign bodies is regarded as the biological correlative for the clinical experience with FBRI, that is, that the host defence mechanisms often seem to be unable to handle the infection and, in particular, to eliminate the microorganisms from the infected device. Since antibacterial chemotherapy is also frequently not able to cure these infections despite the use of antibacterials with proven in vitro activity, removal of implanted devices is often inevitable and has been standard clinical practice. However, in specific circumstances, such as infections of implanted medical devices with coagulase-negative staphylococci, a trial of salvage of the device may be justified. All FBRIs should be treated with antibacterials to which the pathogens have been shown to be susceptible. In addition to systemic antibacterial therapy, an intraluminal application of antibacterial agents, referred to as the ‘antibiotic-lock’ technique, should be considered to circumvent the need for removal, especially in patients with implanted long-term catheters.To reduce the incidence of intravascular catheter-related bloodstream infections, specific guidelines comprising both technological and nontechnological strategies for prevention have been established. Quality assurance, continuing education, choice of the catheter insertion site, hand hygiene and aseptic techniques are aspects of particular interest. Furthermore, all steps in the pathogenesis of biofilm formation may represent targets against which prevention strategies may be directed. Alteration of the foreign body material surface may lead to a change in specific and nonspecific interactions with micro-organisms and, thus, to a reduced microbial adherence. Medical devices made out of a material that would be antiadhesive or at least colonisation resistant would be the most suitable candidates to avoid colonisation and subsequent infection. Another concept for the prevention of FBRIs involves the impregnation of devices with various substances such as antibacterials, antiseptics and/or metals. Finally, further studies are needed to translate the knowledge on the mechanisms of biofilm formation into applicable therapeutic and preventive strategies.

Development of a long-lasting ventricular catheter impregnated with a combination of antibiotics

A ventricular silicone catheter impregnated with a combination of rifampin and a quinolone was developed in order to prevent ventricular shunt related infections. As model substance for the quinolones we used sparfloxacin, because of its specific physicochemical properties resulting in a quantitative detection also in the presence of a second antibiotic. In our study we focused especially on an optimization of the antibiotic release out of the impregnated catheters in order to develop long lasting devices with a broad antimicrobial spectrum. A release-optimized catheter was tested with an in vitro colonization test and additionally with a method developed to examine the spread of bacteria on a catheter surface. In vitro experiments showed that the impregnated catheters reduce the colonization with Staphylococcus epidermidis for at least 1 year and prevent the spread of bacteria along the catheter surface.

A silicone ventricular catheter coated with a combination of rifampin and trimethoprim for the prevention of catheter-related infections.

So-called antiinfective catheters which are generated by incorporation of antimicrobial substances into polymers appear to be effectful devices in the prevention of catheter related infections. Such devices mainly act by prevention of bacterial colonization of the catheter surface rather than by inhibition of adherence. In a preceding study, we developed a rifampin-containing silicone catheter for the prevention of ventricular shunt infection. In the present study, this work was continued with a combination of antimicrobials incorporated in silicone ventricular catheters to reduce the risk of rifampin resistance and to expand the antimicrobial spectrum. We found that the drug release kinetics could be greatly influenced by the incorporation conditions. It was possible to incorporate an optimal antibiotic combination of rifampin and trimethoprim into the polymer resulting in defined release rates and a defined total release. A catheter loaded with this combination showed an excellent reduction of the colonization with Staphylococcus aureus (99.97% reduction within 3 hours) under in-vitro conditions.

In vitro efficacy of a Hydrophilic Central Venous Catheter Loaded with Silver to Prevent Microbial Colonization

A method was developed to load the surface of a central venous catheter with silver to prevent bacterial colonization. Silver confers a broad antimicrobial activity with a relatively low risk of resistance. Catheters were incubated with a silver nitrate solution in different concentrations. The solvent, incubation temperature and incubation period were varied to examine the influence on the catheter loading. With increasing incubation temperature, time and concentration of silver nitrate, higher rates of silver elution were observed by atomic absorption spectroscopy. Furthermore, by using ethanol-water as a solvent instead of pure water, the amount of silver bound to the catheter surface was enhanced. The release of silver from the catheter surface is mainly controlled by first order kinetics. Antimicrobial efficacy of the modified catheter, in comparison to unloaded catheters, was tested in a stationary and a dynamic model with different microorganisms. Adherence experiments with Candida albicans showed almost complete inhibition of growth during a period of 72 hours, including initial adherence. While initial adherence of bacteria could not be prevented, these experiments showed an excellent reduction of bacterial colonization. In a perfusion model, adhesion of E. coli could be reduced for at least seven days. Further studies are planned to examine prolonged antimicrobial effects.

Changing Material Surface Chemistry for Preventing Bacterial Adhesion

Since the initial step in the pathogenesis of catheter related infections is the adhesion of bacteria to the polymer, prevention of bacterial adherence should be an ideal way to avoid foreign body infections.21 A scientific understanding of the interactions between microorganisms and commonly used polymers is the basis of any effective development of devices with antiinfective surfaces. Thus Ferreiros et al. studied the in vitro adhesion of twenty nine Staphylococcus epidermidis strains to Teflon, polyethylene and polycarbonate.11 It was found that all strains showed a high adhesion to polymers with a high surface free energy. Reid et al. investigated the adhesion of microorganisms to urinary catheter surfaces.40 They found Lactobacillus acidophilus adhesion correlated with substratum surface tension, whereas adherence of a S. epidermidis strain did not. Escherichia coli adhered very poorly to all polymers tested. A correlation between surface tension of different synthetic polymers used for medical purposes and staphylococci was also observed in a study conducted by us:33 bacterial attachment decreased with increasing surface tension of synthetic materials.

Microbial contamination of anesthetic syringes in relation to different handling habits

This single-center study prospectively assessed the microbial contamination of anesthetic syringes handled perioperatively under different conditions. We documented high rates of bacterial contamination, with strong but statistically nonsignificant differences between handling groups. Our results identify skin contact as the main source of contamination, and thus we emphasize the impact of proper hand hygiene.

Patients with Rheumatic Diseases do not have an Increased Risk of MRSA Carrier Status

IntroductionThe aim of this study was to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) both in rheumatologic and non-rheumatologic rehabilitation centers. In addition, we sought to evaluate the practice value of existing screening recommendations of the German Commission for Hospital Hygiene and Infection Prevention (KRINKO).MethodsThe analysis was performed in four rehabilitation clinics (rheumatology, psychosomatic medicine, oncology, and cardiology) with at least 200 patients per clinic tested for MRSA.ResultsNine (1.1%) of the 842 patients were colonized with MRSA. Only five of them should have been tested according to the commission’s recommendations. The prevalence was 0.5% (n = 207) in rheumatologic, 0.9% (n = 224) in psychosomatic, 1.4% (n = 209) in oncologic and 1.5% (n = 202) in cardiologic patients. We found a greater exposure to risk factors in cardiologic and oncologic patients. Among patients with carrier status, a higher percentage was exposed to three potential risk factors not applied by the commission.ConclusionsThe prevalence of MRSA in our cohort correlates with data from previous studies. The low percentage among rheumatologic patients suggests that they are not more likely to reveal MRSA carrier status than other patient groups and that long-term immunosuppression does not necessarily represent a risk factor for MRSA colonization. Since only five out of nine patients with carrier status would have been detected following the recommendations of the KRINKO, further studies on potential risk factors are warranted.