Serratia

Classi©cation. Serratia species are classiŠed in the tribe Klebsielliae within the family Enterobacteriaceae along with several other genera, including Klebsiella, Enterobacter, Hafnia, and Pantoea. Serratia marcescens is the most important cause of human disease amongst all species recovered from clinical specimens. The S. liquefaciens group (consisting of S. liquefaciens sensu stricto, S. proteamaculans, and S. grimesii) and S. rubidaea are less common but well-documented causes of human disease. Other Serratia species that may occasionally cause human disease include S. fonticola and S. odorifera, whereas S. ureilytica, S. quinivorans, S. plymuthica, S. entomophila, and S. ƒcaria are predominantly environmental organisms and are rare causes of human disease.1,2

Epidemiology. Serratia spp. may be found broadly in the environment. They are commonly present in water sources and may also be found colonizing plants, animals, and insects. Although widely recognized as an important contemporary cause of human disease, Serratia spp. have only been considered to be signiŠcant pathogens for the past half century.3,4 Outbreaks of nosocomial urinary tract infections received attention in the 1950s, and clinical case reports and series of invasive infections with Serratia spp. were reported with increasing frequency over the subsequent decades.3,4 At present, Serratia spp., most commonly S. marcescens, are

widely recognized agents causing serious hospital-acquired infections, including pneumonia, wound infection, bloodstream infection, and urinary tract infection. Contemporary, hospital-based series and surveillance surveys indicate that Serratia spp. cause approximately 1%–2% of hospitalacquired infections overall, with a higher proportion observed in critically ill patients.5-8

The ability of Serratia spp., and in particular S. marcescens, to cause large hospital-and healthcare-associated outbreaks is widely recognized. Most other members of the Enterobacteriaceae family are frequently found in the normal intestinal ³ora, but this does not appear to be the case with Serratia spp., where most infections are believed to be exogenously acquired. Serratia spp. have a notable ability to contaminate ³uids and devices, and represent the most commonly reported cause of outbreaks due to contaminated blood products.9,10 Numerous large hospital outbreaks with Serratia spp. have been reported, with sources related to contaminated parenteral infusions and injections, particularly due to multiple use of single-dose vials11-17; environmental sources, such as contaminated faucets, air conditioners, and respiratory equipment18-22; and non-antimicrobial-containing soaps.23,24 Patient-to-patient transmission is believed to occur primarily by healthcare workers as a result of inadequate hygiene practices.25,26

But exposure to contaminated substances and inadequate hygiene practices aside, patient-related risk factors for nosocomial infections due to Serratia spp. are multifold

88.1 Introduction ................................................................................................................................................................... 1037 88.1.1 ClassiŠcation and Epidemiology ....................................................................................................................... 1037 88.1.2 Clinical Features and Pathogenesis ................................................................................................................... 1038 88.1.3 Laboratory Diagnosis ........................................................................................................................................ 1039

88.1.3.1 Phenotypic Techniques ....................................................................................................................... 1039 88.1.3.2 Molecular Techniques ......................................................................................................................... 1040

88.2 Methods ..........................................................................................................................................................................1041 88.2.1 Sample Preparation .............................................................................................................................................1041 88.2.2 Detection Procedures ......................................................................................................................................... 1042

88.2.2.1 IdentiŠcation ....................................................................................................................................... 1042 88.2.2.2 Antibiotic Resistance Gene Detection ................................................................................................ 1044 88.2.2.3 Genotyping.......................................................................................................................................... 1045

88.3 Conclusion and Future Perspectives .............................................................................................................................. 1045 References ............................................................................................................................................................................... 1046

and largely similar to those for other major nosocomial pathogens. These are not limited to prolonged stays, admission to intensive care units (ICU), broad-spectrum antimicrobial use, and the use of devices and catheters.27 It has been recognized that Serratia spp. have a propensity to cause infections in patients admitted to neonatal ICUs, with the associated major risk factors of low birth weight, prematurity, and mechanical ventilation.28 In adult ICUs, neurosurgical and burn patients appear to be at increased risk.