Particular attention should be given to this condition as it can progress very rapidly with complete corneal destruction occurring within 24–48 hour

Derivatives of prodigiosin have recently been found to have immunosuppressive properties and antitumor activity in vivo

capable of thriving in diverse environments, including water, soil, and the digestive tracts of various animals. [8] S marcescens has a predilection for growth on starchy foodstuffs, where the pigmented colonies are easily mistaken for drops of blood.

Some strains of S marcescens are capable of producing a pigment called prodigiosin, which ranges in color from dark red to pale pink,

Serratia are widespread in the environment, but are not a common component of the human fecal flora.

The most frequently observed infections were respiratory tract infection (32.5%) and keratitis/endophthalmitis (20.8%).

The organism has also been described as an important cause of ocular infection with high incidence in contact lens-related keratitis

Almost all isolates of S. marcescens secrete a pore-forming haemolysin, ShIA, that is associated with cell cytotoxicity and the release of inflammatory mediators. This cytotoxin is thought to assist in tissue penetration (43) and may be linked to the expression of an extensive host invasive pathogenic pathway involving bacterial swarming and quorum sensing (58, 61).

Results from a recent surveillance programme in the US and Europe, indicate that Serratia spp., accounts for an average of 6.5% of all Gram negative infection in Intensive Care Units (ranked 5th amongst Gram negative organisms in ICU) and an average of 3.5% in non-ICU patients (91). Currently Serratia is the seventh most common cause of pneumonia with an incidence of 4.1% in the US, 3.2% in Europe and 2.4% in Latin America (51), and the tenth most common cause of bloodstream infection with an incidence of 2.0% amongst hospitalized patients (2).

S. marcescensare uniformly resistant to a wide range of antibiotics including narrow-spectrum-penicillins and cephalosporins, cefuroxime, cephamycins, macrolides, tetracycline, nitrofurantoin and colistin

Serratia usually produce extracellular deoxyribonuclease (DNase), gelatinase and lipase and are resistant to the antibiotics colistin and cephalothin

Serratia marcescens is now recognized as an important opportunistic pathogen

Almost all strains of Serratia marcescens secrete a cytotoxin (7, 9–11, 34) that causes hemolysis of human and animal erythrocytes

These proteases play a prominent role inthe pathogenesis of experimental pneumonia(Lyerly and Kreger, 1983) and keratitis (Lyerlyet al., 1981).

Serratia marcescens was the most common organism isolated from the corneal scrapings and from the contact lenses.

Cephalothin was completely ineffective, and more than 90% of strains were resistant to ampicillin and tetracycline

S., marcescens from contact lens washing solutions containing chlorhexidine

outbreak

Infections caused by S. marcescens may be difficult to treat because of resistance to a variety of antibiotics, including ampicillin and first and second generation cephalosporins

It secretes extracellular chitinase; ' several proteases, a nuclease and a lipase [25], and produces a wetting agent or surfactant called 'serrawettin' which helps in the colonisation of surfaces

under extreme conditions, including in disinfectant [ 14, 151, antiseptics [ 161 and double- distilled water

there is a high risk of rapid growth in red blood cells stored at 4"C, as well as in platelet concentrates stored at 22"C

The important reservoirs in epidemics are the digestive tract, the respiratory tract, the urinary tracts and the perineum of neonates and the artificial nails of adults and health care workers.

S. marcescens may survive from 3 days to 2 month on dry, inanimate surfaces, and 5 weeks on dry floor Footnote 16. The organism may survive less than 4 days in a blood bag under aerobic conditions and 20 days in semi-anaerobic/anaerobic conditions Footnote 17. It has been also reported to survive in contact lens disinfectant (with chlorheximide), double-distilled water, non-medicated hand soap, but no duration has been reported for those cases Footnote 18-Footnote 20.

Ingestion of contaminated foods and direct contact

They are responsible for a variety of infections, including bacteremia, pneumonia, intravenous catheter-associated infections, osteomyelitis, endocarditis, and, rarely, endogenous and exogenous endophthalmitis

Many Serratia spp. isolates (39-73%) are resistant to gentamicin Footnote 7. They are all resistant to penicillins and cephalosporin.

Serratia spp. are usually susceptible to aminoglycosides, fluoroquinolones, and co-trimazole

The latter bacteria produce biofilms, which only consist of microcolonies of undifferentiated cells. Serratia spp. also produces β-lactamases

SERRATIA SPP.

marcescensS flexneri

Table1.1:COLONY MORPHOLOGY OF SERRATIAMARCESCENS OF VARIOUS MEDIA

S. marcescens is typically found in showers, toilet bowls, and around wetted tiles.

Positive. Immediately after the hydrogen peroxide solution had been added to a sample of the organism, it produced effervescence.

Negative. The sample on the cotton swab did not undergo a change in color several minutes after the reagent had been added.

Sorbitol – Positive. The organism is capable of fermenting sorbitol which results in the formation of acidic end products.

Lactose – Negative. The organism is not capable of fermenting lactose.

Indol formation – Negative. This indicates that the organism does not have the enzyme tryptophanase to metabolize tryptophan.

Glucose – Positive for the fermentation of glucose to produce acid, but negative for the production of gas.

Serratia marcescens was able to metabolize mannitol to produce acid, but gas was not produced.

Acid was produced causing a change in the color of the pH indicator to yellow, but no gas was produced. 

dark red colonies

bright, glossy red colonies on the TSA plate.

Results

Most S. marcescens strains are resistant to several antibiotics because of the presence of R-factors, which are a type of plasmid that carry one or more genes that encode resistance; all are considered intrinsically resistant to ampicillin, macrolides, and first-generation cephalosporins (such as cephalexin)

S. marcescens is a motile organism and can grow in temperatures ranging from 5–40 °C and in pH levels ranging from 5 to 9. It is differentiated from other Gram-negative bacteria by its ability to perform casein hydrolysis, which allows it to produce extracellular metalloproteinases which are believed to function in cell-to-extracellular matrix interactions. S. marcescens also exhibits tryptophan and citrate degradation.