Opportunistic bacteria in implant infections Knowing them to plan their control - Editorial

Better general hygienic conditions, antibiotics, vaccines: these are the three factors of prevention and therapy that have eradicated many infective diseases, both of bacterial and of viral etiology, in the last two centuries. But infections are abreast of the times and seem unwilling to abandon us. Our times have witnessed great technological progress, with more and more frequent substitutions of tissues and organs, either bare or engineered with living cells. But prosthesis users are not only healthy people, such as athletes treated for sport traumas, or young women resorting to cosmetic surgery, but also and especially patients with impaired immunological defenses, who nowadays, because of the improvement in health conditions and medical progress, are more numerous and in need of implants, such as prostheses or artificial organs: the elderly, diabetics, oncologic patients, premature infants. Thus, here a new hazard emerges, bacterial opportunism: micro-organisms that, until few years ago, could be considered mere saprophytes, habitual guests of skin and mucosae, exhibit a peculiar attitude to cling to implant materials and to infect the surrounding peri-prosthesis tissues, often displaying an alarming antibiotic resistance. In this regard, two genera cover a special role, the genus Staphylococcus, enlisting numerous species usually characterized as saprophytic, and the genus Pseudomonas, with its diffuse nosocomial opportunistic pathogen species Pseudomonas aeruginosa. Staphylococcus aureus, Staphylococcus epidermidis and a number of other coagulase-negative staphylococci (CoNS) are progressively being indicated for their pathogenic potential. In this context, coagulase-negative staphylococci (CoNS) are playing a primary role. The large diffusion in the environment, also including human skin and mucosae, and the ability to colonize material surfaces forming protective biofilms, have led some members of this group of bacteria, among them in first place Staphylococcus epidermidis, to become very common nosocomial pathogens. New emerging staphylococcal species are progressively assuming a worrisome pathogenic behavior, affecting an ample population of hospitalized patients. The rapid adaptation of bacteria to new environmental niches, combined with the increased number of immunocompromised patients and with the large use of prosthetic materials, still steadily growing in many medical fields, will certainly favor the development of opportunistic infections caused by these staphylococci, determining the appearance of virulent pathogenic strains. Staphylococci, as other bacteria, have the possibility to exchange genetic material through mobile genetic elements, such as plasmids and transposons. Moreover, biofilms produced by Staphylococcus and Pseudomanas genera play an important role in the spread of antibiotic resistance. The high bacterial density and the accumulated mobile genetic elements within biofilms provide an ideal field for efficient horizontal gene transfer where bacteria can exchange plasmids by conjugation or by transposons carrying insertion elements. By these mechanisms, within polymicrobic biofilms, resistance and virulence factors may be passed among bacteria, transforming apathogenic to highly virulent strains both within and beyond species borders. Gene transfer between different species of Pseudomonas were shown to occur at a significantly higher rate in biofilms than under planktonic conditions. The prevalence of virulence and antibiotic resistance traits among opportunistic bacteria with different pathogenicity is currently analyzed by molecular methods, opening a new branch in the study of infectious diseases, molecular epidemiology. From these new studies, the concept emerges that minor staphylococcal species could represent important acceptors and reservoirs of antibiotic resistance genes and virulence factors. At the same time ...