Stenotrophomonas

Stenotrophomonas

Class Gammaproteobacteria

Order Xanthomonadales

Family Xanthomonadaceae

Genus Stenotrophomonas

Reference BERGEY’S MANUAL OF By Talal alqahtan Systematic Bacteriology MRI institue Alex.

i

Stenotrophomonas

Straight or curved rods but not helical, 0.5-1.5 Mm, occur

singly or in pairs. Gram-negative bacterium, previously

known as Pseudomonas maltophilia Motile by two or more

polar flagella. Aerobic, having a strictly respiratory type of

metabolism with oxygen as electron acceptor. Nitrate is

reduced but it is not used as a nitrogen source for growth.

The colonies are yellow, greenish, or gray. The yellow color

is not due to carotenoids or xanthomonadins.The colonies

may turn a dark brown color with age.

Cells of Stenotrophomonas maltophilia strain ATCC13637T grown in nutrient broth. Phase contrast. Bar 5 Mm.

Stenotrophomonas maltophilia strain ATCC 13637T. Leifson flagella stain. Bar =5 Mm.

StenotrophomonasList of species of the genus Stenotrophomonas:-

1.Stenotrophomonas maltophilia

2.Stenotrophomonas africana

3. Stenotrophomonas nitritireducens

Chemical composition

Most studies on cell composition in this genus refer to

S.maltophilia. This species is resistant to EDTA

treatment, whereas P. aeruginosa and other species of

this genus were found to be particularly sensitive, due to

removal of components (metal ions, proteins,

lipopolysaccharides, lipids) from the outer membrane of

these organisms by the chelator

Both S. maltophilia and Xanthomonas have a lipid A

composition based on glucosamine, and similarities in

the LPS composition include a high content of

rhamnose, the presence of d-galacturonic acid, the

absence of a heptose, and a low KDO content.

An interesting feature of the LPS of S. maltophilia is

the presence of a pentose derivative identified as 3-O-

methyl-l-xylose, which is also found in unrelated species

such as Rhodopseudomonas viridis. Other observations

on the LPS structure and a possible basis for the

serological cross-reaction between Stenotrophomonas

and Brucella have been reported, as well as details of

the synthesis of the tetrasaccharide repeating unit of

Stenotrophomonas LPS.

Pigmentation

The colonies of S. maltophilia strains on various

complex and chemically defined media are often

yellowish. The color, which does not diffuse into the

medium, is not due to carotenoid pigments but perhaps

to flavins. Although characterization of the pigment is still

tentative, it is probably not a xanthomonadin (the

pigment characteristic of Xanthomonas) or a closely

related compound.

According to a published description (Hugh and

Gilardi,1980), the colonies of S. maltophilia

characteristically appear lavender- green in color on

blood agar media. A greenish discoloration erythrocytes

develops in the area of confluent growth, but there are

no signs of hemolysis around isolated colonies.

S.africana forms faint fluorescent green colonies on

trypticase soy agar and gray colonies on sheep blood

agar and on MacConkey agar at both 30 and 37C.

Nutrition and growth conditions

Many strains of Stenotrophomonas require the

addition of growth factors (methionine or cystine plus

glycine) for growth on chemically defined media.

A strong ammonia odor develops after growth on blood

agar medium .This property is absent from S. africana.

Studies on the nutrition of S. maltophilia have shown that

this species is not as nutritionally versatile as other

species of aerobic pseudomonads of the genus

Pseudomonas and other species formerly assigned to this genus This restricted nutritional capacity was the basis for the proposed new generic name

(Stenotrophomonas) .Metabolism Studies on many basic aspects of metabolism and

metabolic pathways in this group of bacteria are rather fragmentary. The strains of Stenotrophomonas species give a negative oxidase reaction, which is correlated with the lack of cytochrome c.

The metabolism of fructose involves the participation

of a phosphoenol-pyruvate (PEP) phosphotransferase

system.S. maltophilia is able to use lactose for growth, a

property very rare in other aerobic pseudomonads. In

the tyrosine biosynthetic pathway, both Pseudomonas

and Stenotrophomonas strains have a prephenate

activity linked to NAD; this activity is sensitive to

feedback inhibition in Stenotrophomonas but not in

Pseudomonas.

S. maltophilia is unable to use nitrate as a nitrogen

source, but it can reduce this anion to nitrite.

Phages and plasmids:-

The information available on these

subjects is scanty and fragmentary. The sensitivity of

Xanthomonas showed a major overlap with the

sensitivity of S. maltophilia among the various species

then assigned to the genus Pseudomonas.

This finding is a further confirmation of the phylogenetic

relationship between Xanthomonas a Stenotrophomonas

as members of the Gammaproteobacteria.

Some factors required for phage nucleic acid

replication may be conserved through evolution in some

groups of Gram-negative bacteria. One of the elements

required for in vitro replication of sex-specific single

stranded RNA coliphage Qb is the so-called host factor

(HF), which is a heat-resistant RNA-binding protein of

molecular weight 12,000, usually present in E. coli as a

hexamer. Cell extracts of members of rRNA similarity

groups I and V (Pseudomonas, Xanthomonas,

and Stenotrophomonas) had HF activity after heat

treatment.

Antigenic properties

A 30 kDa immunoglobulin binding protein was isolated

from S. maltophilia.

A serological classification of S.maltophilia strains based

on the heat-stable O antigens has been proposed,

extending the 15 serotypes defined by antisera in

previous investigation.The isolation of a membrane

protein capable of cross-reacting with the β subunit and

carboxyl tail of human pregnancy chorionic gonadotropin

(hCG s).

Antibiotic sensitivity

S. maltophilia is an increasingly important cause of hospital-

acquired infections in patients

The high frequency of detection of S. maltophilia as an opportunistic

pathogen and isolation from materials of clinical origin, has

prompted numerous studies on the susceptibility of the strains to

various antibiotics, as well as the intrinsic and exogenous conditions

that affect such sensitivity S. maltophilia is resistant to most ß-

lactam antibiotics, and the aminoglycosides and quinolones have a

modest activity. S.maltophilia is usually susceptible to trimethoprim-

sulfamethoxazole and ticarcillin-clavulanic acid

Pathogenicity for humans

S. maltophilia has been implicated as a direct agent

of disease and as the cause of secondary infections that

aggravate various human pathological conditions. It has

been identified in cystic fibrosis, cancer, meningitis, soft

tissue infections, septic bursitis, urinary tract infections,

bacteremia, endophthalmitis following surgical

procedures, and pneumonia.The literature records

concern for the emergence of the species as a

dangerous opportunistic pathogen

Lab.Diagnosis :-

S. maltophilia are slightly smaller (0.7–1.8 × 0.4–

0.7 micrometers) than other members of the genus.

They are motile due to polar flagella and grow well on

MacConkey agar producing pigmented colonies. S.

maltophilia are catalase-positive, oxidase-negative

(which distinguishes them from most other members

of the genus) and have a positive reaction for

extracellular DNase .

Colonies may be yellow or greenish yellow. Strongly

lipolytic. Gelatinase reaction positive. Ammonia

odor can be produced by colonies on blood agar

Methionine or cystine is required for growth, although

strains lacking this requirement may be isolated.

Biochemical Reaction

COLONIES OF STENOTROPHOMONAS MALTOPHILIA ON MACCONKEY AGAR, INCUBATION PERIOD 3 DAYS AT 30°-35°C

COLONIES OF STENOTROPHOMONAS MALTOPHILIA ON MUELLER-HINTON AGAR. CULTIVATION 72 HOURS, AEROBIC ATMOSPHERE, 28°C.

Screening for nutritional properties

A simple minimal medium that does not include

strong chelating compounds gives better results than

that of earlier formulations.Methionine (50 Mg/ml) should

be added from a sterile stock solution after the medium

has been autoclaved. Good heterotrophic growth can be

obtained by adding to the medium a single organic

compound as carbon and energy source to a final

concentration of 0.1%

Acid production from carbohydrates

The recommended medium gives clear and

reproducible results. It contains a small amount of

peptone, and ammonification does not interfere with the

acid production.

Hydrolysis of Tween 80

The test devised by Sierra (1957)

for the detection of lipolytic activity is very simple and the

results are clear. Sierra’ s medium3 contains Tween 80

and calcium chloride, and opacity formation around the

patches of growth or the individual colonies indicates

precipitation of calcium salts of the fatty acids liberated

by lipase

Nitrate reduction

Reduction of nitrate to nitrite can be

tested according to Lelliott et al. (1966).

Oxidase reaction:-

oxidase-negative (which distinguishes S.

maltophilia from most other members of the genus).

Gelatinase positive

Catalase Positive

Egg yolk reaction

The egg yolk test has been used for many years to

detect lecithinase production .However, the reaction is

quite complex, although the results are in most cases

clear and reproducible.

Nucleic acid hybridization

Several methods are in use. In some of them, one of

the DNA partners is immobilized on a membrane .More

stringent conditions are obtained by hybridization in

solution followed by hydrolysis of single strands using S1

nuclease.rRNA–DNA hybridization, as originally applied,

has been largely replaced by sequence studies of PCR-

amplified genes .