Serratia species are opportunistic gram-negative bacteria classified in the tribe Klebsielleae and the large family Enterobacteriaceae. Serratia are widespread in the environment, but are not a common component of the human fecal flora.
Serratia marcescens is the primary pathogenic species of Serratia. Rare reports have described disease resulting from infection with Serratia plymuthica, Serratia liquefaciens, Serratia rubidaea, Serratia odorifera, and Serratia fonticola.
Some strains of S marcescens are capable of producing a pigment called prodigiosin, which ranges in color from dark red to pale pink, depending on the age of the colonies. The chemical structure of prodigiosin has been unveiled. Serratia are capable of thriving in diverse environments, including water, soil, and the digestive tracts of various animals. S marcescens has a predilection for growth on starchy foodstuffs, where the pigmented colonies are easily mistaken for drops of blood.
In 1819, Bartolomeo Bizio, a pharmacist from Padua, Italy, discovered and named S marcescens when he identified the bacterium as the cause of a miraculous bloody discoloration in a cornmeal mush called polenta. Bizio named Serratia in honor of an Italian physicist named Serrati, who invented the steamboat, and Bizio chose marcescens (from the Latin word for decaying) because the bloody pigment was found to deteriorate quickly.
Since 1906, physicians have used S marcescens as a biological marker for studying the transmission of microorganisms because, until the 1950s, this bacterium was generally considered a harmless saprophyte. Only since the 1960s has S marcescens been recognized as an opportunistic pathogen in humans.
Derivatives of prodigiosin have recently been found to have immunosuppressive properties and antitumor activity in vivo[11, 12] and are also currently being considered as a candidate treatment for Chagas disease.
It appears that at least some Serratia isolates interfere with macrophage function or viability. In the hospital, Serratia species tend to colonize the respiratory and urinary tracts, rather than the gastrointestinal tract, in adults.
Serratia infection is responsible for about 2% of nosocomial infections of the bloodstream, lower respiratory tract, urinary tract, surgical wounds, and skin and soft tissues in adult patients. An outbreak of S marcescens bloodstream infections was identified in patients receiving contaminated bags of parenteral nutrition. Outbreaks of S marcescens meningitis, wound infections, and arthritis have occurred in pediatric wards.
Serratia infection has caused endocarditis and osteomyelitis in people addicted to heroin.
Cases of Serratia septic arthritis have been reported in outpatients receiving intra-articular injections.
An outbreak of meningitis caused by S marcescens in patients who had undergone spinal anaesthesia for caesarean section has been ascribed to contaminated medications used for this purpose.
Serratia species are responsible for 1.4% of nosocomial bloodstream infections.
The yearly incidence of Serratia bacteremia is 1.03 per 100,000 population, with 47% of episodes having their onset in the community.
The prevalence of Serratia species as a cause of nosocomial infections is diminishing, but these bacteria are still able to cause hospital outbreaks, especially in intensive care units.
In the University Hospital of Heraklion, Crete, S marcescens was isolated in 65 (84.4%) of 77 patients with Serratia infection; the remaining 12 patients had infection with a nonmarcescens Serratia species. The most frequently observed infections were respiratory tract infection (32.5%) and keratitis/endophthalmitis (20.8%).
In a population-based study of Serratia bacteremia, the 7-day and 6-month mortality rates were 5% and 37%, respectively.
Serratia meningitis and Serratia endocarditis carry a high mortality rate.
Serratia species cause less than 6% of cases of hospital-acquired bacterial pneumonia.
S marcescens causes 11% of burn-related surgical wound infections.
Most (68%) episodes of Serratia bacteremia occur in males.
Outbreaks of Serratia infection occur in neonates and infants. In adults, most Serratia infections are isolated, but occasional nosocomial outbreaks occur.
Patients with Serratia sepsis may present with fever, chills, shock, and respiratory distress.
Approximately 30-50% of patients with Serratia urinary tract infections are asymptomatic. Symptoms may include fever, frequent urination, dysuria, pyuria, or pain upon urination.
In 90% of cases, patients have a history of recent surgery or instrumentation of the urinary tract.
Important risk factors for with Serratia urinary tract infections include diabetes mellitus, urinary tract obstruction, and renal failure.
Patients with Serratia respiratory tract infection are usually are colonized with Serratia species after instrumentation (eg, ventilation, bronchoscopy), especially those with chronic obstructive pulmonary disease.
Serratia pneumonia may develop, but this is rare. Patients with pneumonia may have fever, chills, productive cough (sometimes with pseudohemoptysis[21, 22] ), hypotension, dyspnea, and/or chest pain.
Serratia meningitis or cerebral abscesses may develop in premature children and neonates with prior sepsis. Patients who have experienced head trauma or have undergone neurosurgery, lumbar puncture, or even epidural injections are at risk of developing meningitis or cerebral abscess.
The symptoms are those of gram-negative meningitis (eg, headache, fever, vomiting, stupor, coma).
Patients with Serratia intra-abdominal infections may present with biliary drainage, hepatic abscess, pancreatic abscess, and peritoneal exudate. Serratia peritonitis can complicate peritoneal dialysis.
Serratia osteomyelitis and arthritis may develop following hematogenous spread in persons who are addicted to intravenous drugs or may be caused exogenously by surgery, open trauma, or intra-articular injection. S marcescens osteomyelitis is a common presentation of chronic granulomatous disease in infancy.
Patients with Serratia endocarditis may present with fever, petechiae, and, occasionally, embolic complications (eg, stroke, arterial emboli).
Patients with Serratia ocular infections present with keratitis or endophthalmitis.
Patients with Serratia soft-tissue infections may have surgical scars, cellulitis, phlebitis, or skin infections.
Patients with Serratia otitis media present with earaches, hearing loss, and ear discharge.
Serratia parotitis is rare.
Pink hypopyon in the absence of hyphema may suggest S marcescens endophthalmitis.
Breast milk can turn pink with Serratia postpartum mastitis.[27, 28]
The main risk factor for Serratia sepsis/bacteremia is hospitalization. Placement of intravenous, intraperitoneal, or urinary catheters and prior instrumentation of the respiratory tract have been identified as risk factors among inpatients.
Other risk factors include cardiac valve replacement, transfusions, and the use of contaminated intravenous infusions. An outbreak of bacteremia was caused by pooling the residual contents of preservative-free epoetin vials for later use. Another outbreak was traced to tampering with an infused narcotic by a hospital employee. A multistate outbreak of S marcescens bloodstream infection was linked to contaminated intravenous magnesium sulfate distributed in the United States by a compounding pharmacy.
Contamination of a faucet resulted in 2 cases of bacteremia during an outbreak of 10 S marcescens infections in an intensive care unit.
Ninety percent of patients with Serratia urinary tract infection have a history of recent surgery or instrumentation of the urinary tract.
Important risk factors include diabetes mellitus, urinary tract obstruction, and renal failure.
Serratia respiratory tract infection may develop after instrumentation (eg, ventilation, bronchoscopy), especially in patients with chronic obstructive pulmonary disease. During an outbreak of S marcescens infections traced to a contaminated faucet (including consumption of tap water from the faucet) in an intensive care unit, 9 patients developed respiratory tract infection (8 developed septic bronchitis; 1 developed empyema), while another 9 patients developed only S marcescens colonization of the respiratory tract.
Serratia meningitis or cerebral abscess may develop in premature children and neonates with prior sepsis. Serratia meningitis may also develop in adults who have experienced head trauma or have undergone neurosurgery, epidural injection, or lumbar puncture.
Osteomyelitis or arthritis can be hematogenous in people addicted to intravenous drugs, or can be caused exogenously by surgery, open trauma, or intraarticular injection.
Although Serratia endocarditis tends to appear in intravenous drug abusers, it usually involves aortic or mitral valves.
Serratia infection frequently causes nonulcerating bacterial keratitis, which is associated with wearing rigid or soft contact lenses.
Serratia endophthalmitis usually occurs after eye surgery.
Bacterial parotitis may develop in individuals with prior sialectasia.
Poorly healing skin ulcers in combination with S marcescens infections at multiple sites are typical in young adults with chronic granulomatous disease. Dermal abscesses and skin ulcers in the legs have appeared after a toe-web infection.
See the list below:
Perform chest radiography in patients with suspected pneumonia or with respiratory distress.
Abdominal ultrasonography or CT scanning is used to rule out obstructive hydronephrosis or intra-abdominal abscesses (eg, hepatic, pancreatic).
Transthoracic or transesophageal echocardiography may reveal valvular vegetations and valvular or paravalvular regurgitation.
Perform spinal CT scanning or MRI if spondylitis is suspected.
Lumbar puncture should be performed in all patients with suspected meningitis. Signs of increased intracranial pressure (focal neurologic abnormalities, seizure, altered mental status) should prompt evaluation with CT scanning prior to puncture to exclude cerebral abscess or mass lesion.
Antibiotic therapy is the primary treatment in most patients with Serratia infection. Home therapy is an option in patients who are clinically stable.
Purulent collections (abscesses) may require drainage.
Consult a cardiac surgeon if considering valve replacement in patients with infective endocarditis.
In a possible nosocomial outbreak of Serratia infection, strain typing may assist the epidemiologic investigation.
S marcescens is naturally resistant to ampicillin, macrolides, and first-generation cephalosporins. In Taiwan, 92% of the strains are resistant to cefotaxime, but 99% are still susceptible to ceftazidime. Extended spectrum beta-lactamases are produced by most S marcescens strains. International data on antimicrobial susceptibility of Serratia and other nosocomial isolates have been published.[36, 37]
Serratia infections should be treated with an aminoglycoside plus an antipseudomonal beta-lactam, as the single use of a beta-lactam can select for resistant strains. Most strains are susceptible to amikacin, but reports indicate increasing resistance to gentamicin and tobramycin. Quinolones also are highly active against most strains.
Cefepime may be a reasonable option for the treatment of infections with Serratia strains that produce AmpC β-lactamase.
Definitive therapy should be based on the results of susceptibility testing because multiresistant strains are common.
Clinical Context: For pseudomonal infections and infections due to multidrug-resistant gram-negative organisms.
Clinical Context: Fourth-generation cephalosporin. Gram-negative coverage comparable to ceftazidime but has better gram-positive coverage (comparable to ceftriaxone). Cefepime is a zwitter ion; rapidly penetrates gram-negative cells. Best beta-lactam for IM administration. Poor capacity to cross blood-brain barrier precludes use for treatment of meningitis.
Clinical Context: Bactericidal activity results from inhibition of cell wall synthesis and is mediated through ertapenem binding to penicillin-binding proteins. Stable against hydrolysis by various beta-lactamases including penicillinases, cephalosporinases, and extended-spectrum beta-lactamases. Hydrolyzed by metallo-beta-lactamases.
Clinical Context: Preferred aminoglycoside. Usually synergistic with antipseudomonal beta-lactams. Use both in combination, pending results of susceptibility testing. For gram-negative bacterial coverage of infections resistant to gentamicin and tobramycin. Effective against Pseudomonas aeruginosa. Irreversibly binds to 30S subunit of bacterial ribosomes. Blocks recognition step in protein synthesis. Causes bacterial growth inhibition.
Clinical Context: Usually synergistic with amikacin. Use both in combination, pending results of susceptibility testing. A monobactam that inhibits cell wall synthesis during bacterial growth. Active against gram-negative bacilli.
Clinical Context: Preferred therapy for Serratia meningitis. Bactericidal broad-spectrum carbapenem antibiotic that inhibits cell wall synthesis. Effective against most gram-positive and gram-negative bacteria. Has increased activity against gram-negative bacteria and slightly decreased activity against staphylococci and streptococci compared to imipenem.
Clinical Context: Comparable in activity to meropenem.
Clinical Context: Greatest anti-P aeruginosa activity among the quinolones. May be particularly useful for isolates resistant to the aminoglycosides.
Empiric antimicrobial therapy should cover all likely pathogens in the context of the clinical setting.
Remove or change catheters suspected of being contaminated with Serratia bacteria.
Avoid reusing single-use vials, and reject possibly contaminated intravenous fluids.
Avoid using soaps or disinfectants that may be contaminated.
Avoid using tap water for administration of medication orally or via a nasogastric tube in critically ill patients.
Use disposable ECG leads.
Emphasize standard precautions. Hospital employees should wash their hands before and after contact with patients. The most common mechanism of Serratia transmission in nosocomial outbreaks is through soiled hands. Long-term carriage of an epidemic strain of S marcescens on the hands of a health care worker has been described.
Intravenous lines should be removed as soon as possible.
Severe Serratia infection (bacteremia) carries a mortality rate of 26%. Among survivors, the prognosis for complete recovery is good.
S marcescens endophthalmitis carries a poor prognosis in terms of maintaining vision.