Serratia spp. is a group of gram negative bacteria, categorized under the wider group of Enterobacteriaceae. A Serratia infection is an infection caused by this bacterial species, that can affect almost every system in humans, including the urinary tract, respiratory tract, meninges, wounds, heart and abdomen.
Due to the fact that bacteria belonging to the Serratia spp. class can affect a multitude of organs, a Serratia infection can lead to symptoms that vary and are categorized depending on the affected system.
Urinary tract infections (UTIs) are amongst the most common types of infection caused, and patients usually present with symptoms typically expected in a UTI. These include dysuria, fever, hematuria and abnormally frequent urination. Prior instrumentation of the urinary tract or surgical procedures are reported in up to 50% of the patients diagnosed with a Serratia urinary tract infection; patients suffering from diabetes mellitus or renal failure are at a greater risk of developing such an infection.
Infections of the respiratory tract can also be caused by a bacterium of the Serratia species, especially in patients affected by chronic pulmonary conditions, such as chronic obstructive pulmonary disease (COPD). The infection may progress to pneumonia, although this is an uncommon occurrence. Typical symptoms of pneumonia include thoracic pain, cough, fever, hypotension, dyspnea and pseudo hemoptysis [1] [2].
Serratia spp can also cause cerebral abscesses or meningitis. Underlying conditions such as sepsis in neonates and children and open trauma, as well as invasive procedures (neurosurgery, lumbar puncture), increase the risk for such a central nervous system infection [3]. Symptoms elicited by a Serratia meningitis encompass lethargy, cephalalgia, vomiting, a decreased level of consciousness, and even coma.
Serratia can also be responsible for infections of the abdominal cavity, such as abdominal abscesses or peritonitis. Fever, malaise, abdominal discomfort or pain are the symptoms expected in the case of an intra-abdominal infection; peritonitis should be suspected in patients presenting with severe abdominal pain, high fever, and chills. Peritoneal dialysis may be complicated by peritonitis caused by Serratia bacterium [4].
Intravenous drug use, intra-articular injections, open trauma or surgery can lead to osteomyelitis and arthritis due to a Serratia colonization. Osteomyelitis induces symptoms such as pain, edema, and erythema in the affected region, fever, and chills, whereas arthritis leads to painful and inflamed joints. Chronic granulomatous disease in infants is frequently complicated by osteomyelitis due to Serratia [5].
Finally, Serratia spp. may be responsible for various other types of human infections. Patients may present with otalgia and otorrhea due to otitis media; with fever, respiratory compromise, hypotension and, in a comatose state in generalized sepsis. Soft tissues are also susceptible to Serratia infections and patients may present with infected scars, phlebitis, and cellulitis. Women who breastfeed may report their breastmilk turning pink, which is a typical symptom of Serratia postpartum mastitis [6] [7].
Given that the clinical presentation of a Serratia infection is extremely variable, the workup involved is non-specific and guided by the particular symptoms with which each patient presents.
Generally, blood samples should be taken and a complete blood count is expected to illustrate leucocytosis with distinctive neutrophilia, anemia and more than 10% of immature neutrophils. Leukopenia can be observed but is a rather uncommon laboratory result. A complete biochemical profile should also be carried out, in order to evaluate creatinine, glucose, urea and electrolyte levels.
A culture and antibiogram are mandatory in order to accurately diagnose a Serratia infection. The most common bacterial subtype isolated is S. marcenscens [8]. Blood, fluid from effusions, abscesses, catheters or IV fluids that are potentially contaminated all constitute good samples for a culture.
If meningitis is suspected, a lumbar puncture should be performed. A cerebrospinal fluid analysis will reveal pleocytosis of a polynuclear morphology, low glucose, and high protein levels. Respiratory infections are primarily investigated with a chest radiograph. An ultrasonographic (US) or computerized tomography (CT) scan can be used to detect possible intra-abdominal abscesses and echocardiography can be employed to detect valvular abnormalities consistent with endocarditis.