Serratia marcescens - overview (2023)

Serratia wiltare Gram-negative, motile, non-endospore-forming, rod-shaped, gamma-proteobacteriaYersiniaceaeIn the order Enterobacteriaceae.

S. marcescensThe culprit for the discoloration of polenta (the blood-red color of polenta (a dish of boiled cornmeal)) was first discovered in 1819 by Venetian apothecary Bartolomeo Bizio in the Italian city of Padua. In 1823, he named this bacterium "Serratia wilt’ in memory of his late friend Serafino Serrati. Although the name was later changed toMirabilisandBacillus mirabilis,Serratia wiltThe species was reassigned in the 1920s.

It is now considered a member of the coliform group.S. marcescensHas been found to be an opportunistic pathogen, particularly in hospital settings, where it can cause a variety of diseases, includingurinary tract infection, wound infection, andbloodstream infection, although occasionally a benign commensal bacterium. It is a major problem in healthcare settings due to its ability to produce multiple virulence factors and resistance to multiple antibiotics.

ClassificationSerratia wilt

s positionSerratia wiltIn bacterial taxonomy is the topic of some discussion. In the past, it was classified as Enterobacteriaceae (even in Bergey's Handbook of Systematic Bacteriology), although other investigations indicated that it belonged to the Yersiniaceae family. In their 2006 book Serratia, Grimont and Grimont made one of the initial proposals for the transfer of Serratia from Enterobacteriaceae to Yersiniaceae. Later, in a 2013 study in the Journal of Clinical Microbiology, Serratia marcescens was more closely related to Yersinia than to other members of the Enterobacteriaceae family. Although taxonomically controversial, we classify Serratia in this note within the family Yersiniaceae.

HabitatSerratia wilt

• S. marcescensIt is a mesophilic saprophytic bacterium widely present in the environment. It is mainly found in wet and humid places such as bathrooms, washbasin and kitchen drain areas and other swampy areas where vegetation is rotting. It is also found in soil and is associated with insects, plants and animals including humans.
• In humans, mainly in hospitalized patients, they are present in the upper respiratory, urinary and gastrointestinal tracts.
• It is often seen in medical settings.S. marcescensOften found in healthcare settings on surfaces such as hospital equipment, sinks and floors, and in the skin and feces of healthcare workers. Biofilms are known to linger on surfaces, making their removal challenging using traditional cleaning techniques.

ShapeSerratia wilt

• They are rod-shaped (bacilli), inactive, non-endospore-forming bacteria. They are approximately 1 to 2 μm in length and 0.5 to 0.8 μm in diameter. (However, size may vary depending on growing conditions.)
• Microscopically, they are short, straight, or slightly curved rods; usually arranged in short chains.
• They are usually encapsulated. This capsule enhanced their biofilm-forming ability and increased virulence.
• one of the salient features ofS. marcescensis a prodigiosin pigment that produces a characteristic red pigmentation at room temperature. The pigment makes surfaces where bacteria grow red.

cultural characteristicsSerratia wilt

• Serratia wiltis a nonfastidious bacterium that grows on a variety of substrates. It occurs naturally in areas rich in organic substrates, such as decaying vegetation and food, in association with organisms as well as in places where harsh nutrients such as soil, bathroom tiles, distilled water, and some disinfectants are deficient. They are mesophilic bacteria that can grow in temperatures ranging from 5°C to 40°C; however, they grow at 37±2°C.
• Serratia wiltKnown for producing the bright red pigment prodigiosin. Although, this pigment can only be produced at room temperature, i.e. 20 to 30°C. Other than that, there are no other specific cultural traits.
• in the laboratory,Serratiamarcescens was isolated and grown on various general media such asNutrient Agar (NA),Tryptic Soy Agar (TSA),MacConkey Agar (MCA),Eosin Methylene Blue (EMB) Agar,Blood Agar (BA),Cetrimonium Agar (CA)wait. There are some selective and chromogenic media and BrillianceSerratiaAgar, ChromIDSerratiaAgar, caprylate-thallium (CT) mineral salt CT agar, etc.

cultural characteristicsSerratia wiltSome of these media are listed below:

1. Nutrient Agar (NA):

on nutrient agar,S. marcescensProduces smooth, round and raised non-lactose fermenting colonies approximately 2 to 4 mm in size. When grown at 20-30°C, red pigmentation may be observed after overnight (24 hr) incubation.

2. Tryptic Soy Agar (TSA):

On Tryptic Soy Agar,S. marcescensProduces smooth, round, moist and raised non-lactose fermenting colonies approximately 2 to 4 mm in size. A bright red prodigiosin can be observed when incubated at 20-30°C.

3. MacConkey Agar (MAC):

On MacConkey agar,S. marcescensProduces smooth, raised, round (2 to 4 mm) and non-lactose fermenting pink to red colonies.

4. Blood Agar (BA):

On MacConkey agar,S. marcescensProduces beta-hemolytic cells that are medium-sized (2 to 4 mm) round light gray colonies with a narrow hemolytic zone. Red production cannot be clearly seen in BA, however, the bacteria produce prodigiosin even in BA if incubated at or below 30°C.

5. Caprylate-cell agar medium (CT agar):

Is a highly selective and differentiated medium for isolationSerratiagenera and differentiate them into different species.SerratiaProduces small bluish-white colonies.S. marcescensA red pigment is produced at an appropriate temperature.

6. CHROMagar™ Serratia

It is a chromogenic medium used as a selective and differential chromogenic medium for isolation and initial identification.St. marcescens St. marcescensProduces round greenish-blue to metallic blue colonies approximately 2 mm in size.

biochemical properties ofSerratia wilt

General Biochemical Test Results

Carbohydrate Fermentation Test

Enzymatic Hydrolysis Test

Virulence factorsSerratia wilt

1. Extracellular enzymes:

Serratia wiltProduces many extracellular enzymes, such as lipases, proteases and DNases, which can damage host tissues and allow bacterial invasion.

2. Hemolysin:

hemolysin, aSerratia wilt, can lyse host cells including erythrocytes. Hemolysins can damage host tissues and contribute to the development of abscesses.

3. Lipopolysaccharide (LPS):

SomeSerratia wiltThe strain has an altered LPS structure that helps the bacteria become more virulent and avoid detection by the body's immune system. An LPS produced by Serratia marcescens triggers a host immune response and causes inflammation.

4. Siderophore:

Serratia wiltProduces siderophores, which help bacteria remove iron from host tissues and promote growth and survival. Serratiochelin, a siderophore produced by some strains of Serratia marcescens, can also increase the pathogenicity of the bacteria.

5. flagellum:

becauseSerratia wiltThere are flagella, which can pass through the host's tissues and evade the immune response. In addition, flagella can facilitate the adhesion of bacteria to host cells and contribute to the formation of biofilms.

pathogenesisSerratia wilt

Several virulence factors, including adhesins, biofilm formation, motility, and production of extracellular enzymes and exotoxins, areS. marcescens'Pathogenicity.S. marcescensAs a result of these virulence factors, they are able to colonize, persist and cause disease and tissue damage.

The pathogenesis varies according to the site of infection. However, the general pathogenesis can be summarized in the following steps:

Adhesion and colonization

S. marcescensAttachment to catheters or other medical devices in the body, or to cells and tissues of the host. Adhesins facilitate their attachment. Once attached, they rapidly multiply and colonize the attached surface.

biofilm formation

Serratia wiltBiofilms can form on the surfaces of a variety of medical devices and catheters. The formation of biofilms will allow them to attach more firmly to the host's surface, adapt to changing environments, and act as a barrier against certain host immune components.

infection development

onceS. marcescensAfter colonization and multiplication in host tissues, they begin to manifest clinically. The production of extracellular enzymes and exotoxins helps to damage the host's tissues and initiate infection. The pathogenesis varies according to the site of infection.

clinical manifestationsSerratia wilt

S. marcescensExhibits a wide range of clinical manifestations in humans. They are commonly reported in healthcare-associated infections; however, community-acquired infections are also common.S. marcescensare opportunistic pathogens, meaning they primarily infect people with compromised or weakened immune systems. some common diseases caused byS. marcescensIn humans it is listed as follows:

1. Urinary Tract Infection (UTI):

S. marcescensis a common pathogen of urinary tract infections, especially healthcare-associated urinary tract infections in patients with indwelling urinary catheters.

2. Respiratory Tract Infection (RTI):

For patients with compromised immune systems and/or underlying respiratory disease such as COPD,S. marcescensReported to cause pneumonia. In rare cases, community-acquired pneumonia has also been reported.

3. Wound infection:

Several cases of hospital-acquired soft-tissue infections, particularly surgical site infections in patients undergoing gastrointestinal and genitourinary surgery, have been associated withS. marcescens.

4. Bloodstream infection (BSI):

S. marcescensBSI can be caused in hospitalized patients with catheters, patients undergoing invasive medical treatments, and immunocompromised patients.

5. some peopleS. marcescens- Associated BSIs may also present with other conditions such as endocarditis, osteomyelitis, meningitis, etc. Meningitis is mainly seen in neonates and immunocompromised patients.

laboratory diagnosisSerratia wilt

Cultural identity and morphological identification

• In the laboratory, MacConkey and blood agar are commonly used for primary separationsS. marcescensfrom clinical specimens. Colony characteristics and red pigment production when cultured at 30 ℃⁰C was studied for initial identificationS. marcescens.
• On MAC agar medium, they produce medium-sized, round, smooth non-lactose fermenting colonies. In blood agar, a narrow zone of hemolysis is observed around off-white colonies of medium size (2 to 4 mm). They develop a red pigment when incubated at around 30°C⁰C。
• Microscopically, they appear as Gram-negative rod-shaped bacteria, often arranged in chains.

biochemical identification

• Isolated colonies are subjected to biochemical tests such as IMViC test, oxidase test, catalase test, urease test, TSI test, SIM test and other carbohydrate fermentation tests.
• API 20E Rapid System:

According to its biochemical characteristics,Serratia wiltCan be quickly identified using the commercial test suite API 20E system.

molecular identification

Serratia wiltPositive identification can be made in the laboratory using PCR-based techniques such as 16S rRNA gene sequencing and multilocus sequence typing.

Treatment programsSerratia wiltInfect

Antibiotics such as carbapenems, aminoglycosides, fluoroquinolones, and third-generation cephalosporins are commonly used to treatSerratia wiltInfect. However,Serratia wiltIsolates from various sources around the world have been found to be resistant to these drugs.

Antibiotic Resistance ProfilesSerratia wilt

• It is naturally resistant to many antibiotics.Serratia wiltResistance to other antibiotics is known to be acquired by a variety of methods, including mutation, horizontal gene transfer, and overexpression of efflux pumps. therefore,Serratia wiltInfections can be difficult to treat and antibiotics should be chosen based on susceptibility testing.
• Serratia wiltAlso known to produce various β-lactamases. Extended-spectrum beta-lactamases (ESBLs) are members of the class of beta-lactamases that hydrolyze and induce resistance to beta-lactam antibiotics such as penicillins and cephalosporinsSerratia wilt.also,Serratia wiltAbility to producecarbapenemaseconfers resistance to carbapenems such as KPC (Klebsiella pneumoniaecarbapenemase) and IMP (imipenemase).
• Serratia wiltThe recent emergence of multidrug-resistant and pan-drug-resistant (MDR and PDR, respectively) strains further limits the available treatments.

preventionSerratia wiltInfect

S. marcescensis an opportunistic pathogen primarily associated with healthcare-associated infections. infection fromS. marcescensIt can be prevented through practices such as good hand hygiene, environmental cleaning, contact precautions, disinfection, use of personal protective equipment, surveillance, education and training of healthcare workers, etc.

reference

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