CTX-M and TEM as predominant types of extended spectrum beta-lactamases among Serratia marcescens isolated from solid organ recipients

Antibiotic-Resistant Infections and Treatment Challenges in the Immunocompromised Host

This article reviews antibiotic resistance and treatment of bacterial infections in the growing number of patients who are immunocompromised: solid organ transplant recipients, the neutropenic host, and persons with human immunodeficiency virus and AIDS. Specific mechanisms of resistance in both gram-negative and gram-positive bacteria, as well as newer treatment options are addressed elsewhere, and are only briefly discussed in the context of the immunocompromised host.

Serratia infections: from military experiments to current practice

Serratia species, in particular Serratia marcescens, are significant human pathogens. S. marcescens has a long and interesting taxonomic, medical experimentation, military experimentation, and human clinical infection history. The organisms in this genus, particularly S. marcescens, were long thought to be nonpathogenic. Because S. marcescens was thought to be a nonpathogen and is usually red pigmented, the U.S. military conducted experiments that attempted to ascertain the spread of this organism released over large areas. In the process, members of both the public and the military were exposed to S. marcescens, and this was uncovered by the press in the 1970s, leading to U.S. congressional hearings. S. marcescens was found to be a certain human pathogen by the mid-1960s. S. marcescens and S. liquefaciens have been isolated as causative agents of numerous outbreaks and opportunistic infections, and the association of these organisms with point sources such as medical devices and various solutions given to hospitalized patients is striking. Serratia species appear to be common environmental organisms, and this helps to explain the large number of nosocomial infections due to these bacteria. Since many nosocomial infections are caused by multiply antibiotic-resistant strains of S. marcescens, this increases the danger to hospitalized patients, and hospital personnel should be vigilant in preventing nosocomial outbreaks due to this organism. S. marcescens, and probably other species in the genus, carries several antibiotic resistance determinants and is also capable of acquiring resistance genes. S. marcescens and S. liquefaciens are usually identified well in the clinical laboratory, but the other species are rare enough that laboratory technologists may not recognize them. 16S rRNA gene sequencing may enable better identification of some of the less common Serratia species.

Extended-spectrum beta-lactamase-producing bacterial infections in adult solid organ transplant recipients

BACKGROUND

Limited research is available evaluating infections due to extended-spectrum β-lactamase (ESBL)-producing organisms in adult recipients of solid organ transplant (SOT).

OBJECTIVE

To evaluate clinical response and rate of recurrence of ESBL-producing organisms in 20 SOT recipients.

METHODS

In a retrospective case series, records of adult SOT recipients with an admitting diagnosis of infection and a positive culture for an ESBL-producing organism from January 2003 through August 2006 were reviewed.

RESULTS

Twenty patients met inclusion criteria. The median time to infection following transplant was 3.5 years (range 1-23 years). Overall, 85% of the patients received inadequate empiric antibiotic therapy, including ciprofloxacin or piperacillin/tazobactam, to manage their infection. Nineteen patients had clinical resolution; however, 12 patients required at least 1 readmission due to infection recurrence. One patient's death occurred during the study period. The median time to readmission for a recurrence was 41 days (18-455 days). All recurrent infections were caused by the same ESBL-producing pathogen and 10 of 12 (83%) infections occurred at the same site as the initial infection. Among patients with recurrent infections, 75% received inadequate empiric therapy upon readmission. All 12 patients with recurrent infections had successful clinical responses to both initial and recurrent infections.

CONCLUSIONS

The provision of inadequate empiric therapy for new and recurrent infections due to ESBL-producing pathogens was common in this study population. SOT recipients with a history of infection due to an ESBL-producing organism presenting with a new infection should receive adequate empiric therapy with a carbapenem agent until a definitive diagnosis can be established.

Serratia infections in a general hospital: characteristics and outcomes

We aimed to present our experience regarding infections caused by Serratia spp. in a region with relatively high antimicrobial resistance rates. We retrospectively reviewed the databases of the microbiological laboratory of the University Hospital of Heraklion, Crete (2/2004-12/2009). A total of 77 patients [67.5% men, mean age ± standard deviation (SD) = 56.9 ± 24.5 years) were identified; 37.7% were outpatients. Sixty-five (84.4%) of the 77 included patients had a Serratia marcescens isolate; the remaining 12 patients had a non-marcescens Serratia spp. The most frequently observed infections were respiratory tract infection (32.5%) and keratitis/endophthalmitis (20.8%). Seventy-three (94.9%) patients were cured. Four deaths were observed; three of them were considered as attributed to the Serratia infection. No difference was found regarding the characteristics and outcomes between patients with Serratia marcescens and non-marcescens infections. In addition, antipseudomonal penicillins and their combinations with beta-lactamase inhibitors, as well as carbapenemes, and fluoroquinolones exhibited high antimicrobial activity against both the tested Serratia marcescens and non-marcescens isolates. Our study adds useful information regarding the characteristics and outcomes of patients with Serratia infection, as well as the susceptibilities of the respective Serratia marcescens and non-marcescens isolates, in a region with relatively high levels of antimicrobial resistance.