Colonizing Opportunistic Pathogens (COPs): The Beasts In All Of Us

COPs require new active and integrative surveillance programs

Enhanced surveillance of COPs can enable public health agencies to identify and control emerging COP clones more quickly than is currently possible. Because of the insidious nature of COP epidemics, active surveillance programs that monitor both COPs circulating among asymptomatic carriers in the community and COPs causing clinical infections are crucial. This work will require the development of new molecular methods and could be integrated into existing surveillance programs, such as the National Healthcare and Safety Network, FoodNet, PulseNet, and the National Antimicrobial Resistance Monitoring System [36–39]. Active surveillance of COPs can involve sentinel communities, households, or individuals who are recruited to provide samples from body sites where COPs reside, such as nasal swabs and stool specimens for culture-based and molecular analyses. Current surveillance programs could expand their monitoring to encompass COP clones in clinical infections and in environmental reservoirs. Linking these data could allow an early warning system on emerging COP clones and provide valuable information for tracing community- versus healthcare-associated COP clones. Incorporating whole-genome DNA sequencing can further resolve subtleties ranging from shifts in COP clonal populations to the loss and gain of resistance-encoding mobile genetic elements [40–42].

Both frank pathogens and COPs can cause foodborne zoonotic infections. Infections caused by frank pathogens, such as Salmonella enterica, Campylobacter jejuni, and E. coli 0157:H7 (Table 1), can quickly be recognized and controlled by tracing clusters of infections to a common source [43–45]. Foodborne COPs, such as K. pneumoniae and multidrug-resistant ExPEC, are known to contaminate meat products and can cause infections in consumers [46]; however, because they may persist indefinitely in exposed hosts before causing an infection, disease clusters can be dispersed in time and space, obscuring the source of the pathogen. In addition to the prolonged colonization period, once a foodborne COP successfully colonizes a person, it may also be transmitted person-to-person [47], spreading through the human population to a far greater extent than frank foodborne pathogens. All of this contributes to the challenge of estimating the disease burden of foodborne COPs.

A key target in active surveillance of COPs is the environmental reservoirs (e.g., air, food, and water) and nonhuman “co-host” species such as wild animals, companion animals, and livestock. The widespread use of antimicrobials in livestock [48] makes food animals an important target in monitoring novel resistance elements in COPs and emerging antibiotic-resistant COP clones—this is supported by the recent report of a mobile colistin-resistance element, mcr-1, among livestock in China [49]. We will need to monitor COPs throughout the livestock production system—from breeder farms to slaughter—to identify the origins and potential control points for emerging COPs from livestock. Other livestock products, such as wastes and meat, should be integrated into the active surveillance of COPs. Ideally, the active surveillance of environmental reservoirs should be coordinated with the sentinel community-based sites to maximize the integration across scales.