Pseudomonas, Stenotrophomonas, Acinetobacter, and Other Nonfermentative Gram-Negative Bacteria and Medically Important Anaerobic Bacteria in Transplant Recipients

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Despite the overall decline in the frequency of documented gram-negative infections in transplant recipients receiving antimicrobial prophylaxis, the proportion of these infections caused by nonfermentative gram-negative bacilli (NFGNB) is increasing. Pseudomonas aeruginosa is the most common species of NFGNB isolated from such patients, from both monomicrobial and polymicrobial infections. The spectrum of infection caused by P. aeruginosa is wide, and involvement of multiple organ systems is not uncommon. Resistance to multiple agents expected to have activity against P. aeruginosa has become a significant problem and, to some extent, has spurred the development of novel antimicrobial agents. Other important NFGNB include Stenotrophomonas maltophilia, Acinetobacter species, and, to a lesser extent, Achromobacter species, Alcaligenes species, nonaeruginosa Pseudomonas species, and Chryseobacterium species. As with P. aeruginosa, resistance to multiple agents is a common thread with these organisms as well. Infections with these organisms are associated with substantial morbidity and mortality. Consequently, in addition to appropriate antimicrobial therapy, infection control and antimicrobial stewardship are important tools in combating the development and spread of infections caused by NFGNB. Anaerobic organisms, on the other hand, are isolated much less frequently, generally from mixed or polymicrobial infections. Although they are frequently co-pathogens in this setting, their importance should not be underestimated.