Confronting the complexities of the new century, clinicalmicrobiology (CM) is developing in various directions.According to its original meaning, CM primarily deals withthe aetiological diagnosis of human and animal infections, andit also goes as far as to suggest the possible outcome of theinfectious process in any individual patient for whom a givenantimicrobial treatment is considered. Since the early phasesof CM, these tasks and their accomplishment havealways followed, and have been regulated by, Koch’s classicpostulates.Because, by definition, infectious diseases may be trans-mitted from a patient to a novel subject, CM, by its ownnature, has a public health (PH) dimension. Nobody wouldargue against this PH dimension in the hospital setting,where CM does indeed play a key role in preventing andcontrolling hospital-acquired infections [1,2]. Nonetheless,one should consider that hospitals are not isolated institu-tions but are ecologically (and epidemiologically) linked withother hospitals and long-term-care facilities, and with an‘infectable’ community at large. A considerable body ofevidence has now confirmed the extent to which any intra-hospital microbiological event may have wide-ranging PHconsequences in several external compartments, fromneighbouring wards to the entire extra-hospital community.Conversely, any biological change occurring anywhere out-side the hospital—from the emergence of new pathogensor novel antibiotic resistance mechanisms, to demographicchanges in the human or animal population, to micro-variations or macro-variations in the climate, to the use ofantibiotics in the food chain—will sooner or later impacton the ecology of CM within the hospital [3]. Thus, inrecent years, hospital-based CM specialists have been moreand more frequently involved in initiatives aimed at under-standing and controlling phenomena such as the widespreaddissemination of microbial clones endowed with particularvirulence or antimicrobial resistance, or the dynamicsof mobile genetic elements involved in either antibioticresistance or virulence, or aimed at establishing theextra-hospital origin of new microorganisms, or monitoringand controlling the use of antimicrobial drugs or vaccines[4,5]. In all of these initiatives, CM specialists have moreoften than not held a leading position.All of this can be regarded as PH microbiology (PHM), inwhich activities such as elucidating the population structureof a collection of clones, classifying plasmids, transposons orintegrons, or identifying novel b-lactamases are not aimed atimproving the diagnosis and therapy of individual infectedpatients, but can be seen—and are fully justified—in theframework of a PH perspective [4,6]. The current involve-ment of CM in diagnosing the new A(H1N1) influenza cases,sequencing viral genomes, tracing the origin of the strain andmonitoring the emergence of resistance to antiviral agents isa prominent example of PHM.One should be aware that two opposite forces, onepositive and one negative, are currently driving the PHdimension of CM. On the one hand, PHM is being nour-ished by the multiple networks of hospital CM laboratoriesenrolled in national and international surveillance pro-grammes, representing, to date, the only feasible way ofobtaining comprehensive data about the epidemiology,ecology and evolution of infectious diseases [7]. On theother hand, participation of individual hospitals in thesePHM activities is constantly at risk of being no longer fun-ded—or even of being frankly opposed—by hospital man-agement teams facing continuous budget restrictions, withthe justification that these tasks should be performed bycentral reference laboratories, or alternatively funded as‘research projects’ by either national or international fund-ing agencies.A realistic view of the current PHM landscape could beoutlined as follows:1. The complexity and the spatial–temporal variability ofmicrobiological events that might be significant for PHinterventions both require a broad network of estab-lished sampling and surveillance sites, and this can becurrently accomplished only by recruiting CM laborato-ries based in the individual hospitals (which frequentlyalso cover the community department). The emergence