Klebsiella – Enterobacter – Serratia

In the group Klebsiella – Enterobacter – Serratia says KES gathered Enterobacteriaceae that share the following characteristics:

1 / The Voges-Proskauer (VP) is positive.

This reaction is to demonstrate the production of acetylmethylcarbinol (or acetoin) by the bacteria. It is very specific.A positive VP means that the strain has a particular metabolic pathway for the fermentation of hexoses, the butylèneglycolique path.

2 / These are Opportunistic Bacterial Pathogens.

Low virulence by themselves, they meet little Extramural practice.

Opportunistic, they are responsible for nosocomial infections in hospital patients debilitated: cirrhosis, diabetes, burns, cancer, aged, resuscitation sick infants.

3 / These species are often resistant to multiple antibiotics. The frequency with which they occur is even greater than the selection pressure of broad-spectrum antibiotics is high.

Bacteriological characteristics that distinguish the types forming the KES group are shown in Table I.

TABLE I: main distinguishing features between Klebsiella, Enterobacter, Serratia and Hafina
TABLE I: main distinguishing features between Klebsiella, Enterobacter, Serratia and Hafina



Klebsiella Enterobacteriaceae are always immobile, generally having a capsule and ferment many carbohydrates.They possess neither ODC, or DHA, or tryptophan deaminase (TDA), or lipase and do not produce H2S.

Klebsiella - Enterobacter - Serratia
Klebsiella – Enterobacter – Serratia

The classification of different species of Klebsiella is discussed.

Nevertheless 6 species are usually recognized:

– Four species are pathogenic for humans K. pneumoniae(type species), K. oxytoca, K. ozaenae and K.rhinoscleromatis.

Two species are found in the environment and are rarely pathogenic, it is K. and K. terrigena planticola which will not be described here.



K. pneumoniae and K. oxytoca are the most commonly encountered species. They are frequently isolated from water, soil and plants. They are present in the fecal flora of humans and are often commensal of the skin, mucous membranes and respiratory tract.

The patients become infected either with their own stem or with strains causing small hospital outbreaks. They are then manuportées of sick sick.


K. pneumoniae, by far the most frequently encountered, and K. oxytoca were isolated mainly from acute or subacute pulmonary disease, as well as urinary tract infections, hepatobiliary or pus diverse.

Due to the weakness land on which they grow, Klebsiella septicemia have a very poor prognosis.

K. ozaenae is virtually isolated as chronic respiratory infections.

It is rarely isolated from urine or blood cultures. It is the same for K. rhinoscleromatis which is rarely found in France.It is most common in Africa.

The role of K. ozaenae as etiologic agent ozena and that of K. rhinoscleromatis as rhinoscleroma agent are imperfectly established.


A – Appearance of colonies:

On usual media, Klebsiella give after incubation for 24 hours at 37 ° C colonies generally lactose (+), round, 3 to 4 mm diameter, curved, mucous membranes and having a tendency to confluence.

This mucoid, in relation with the usual presence of a more or less large capsule, is sometimes observed with otherEnterobacteriaceae including E. some strains al.

B – species Diagnosis:

Useful biochemical characters diagnosis are shown in Table II:

K. pneumoniae is VP (+), ONPG (+), LDC (+) and attacks the glucose by producing a lot of gas.

K. oxytoca is distinguished by indole production.

K. ozaenae is VP (-), ONPG (+) and malonate (-)

K. rhinoscleromatis is VP (-), ONPG (-) and LDC (-)

TABLE II main characters for the diagnosis of the genus Klebsiella
TABLE II main characters for the diagnosis of the genus Klebsiella

C – Differential diagnosis:

The majority of the strains K. pneumoniae urease (+) in the middle “uréeindole”. Urease strains (-) of K. pneumoniaeare sometimes confused with Enterobacter aerogenes which differs in mobility and ODC (Table III).

TABLE III: differential characters of K. pneumoniae and E. aerogenes
TABLE III: differential characters of K. pneumoniae and E. aerogenes

D – Epidemiological Markers:

Their research is done by specialized laboratories to rule out or confirm the existence of epidemic nosocomial infections in hospitals.

– The capsular typing. This is the most discriminating method. There are 77 capsular antigens K. The determination of these antigens is primarily through the swelling reaction of the capsule or reaction Neufeld, in the presence of the corresponding immum serum.

The biotypie. It is less efficient. Eight biotypes can be distinguished by the study of three characters: sorbose, dulcitol and d-tartrate.


Klebsiella have a natural resistance to ampicillin and carbenicillin. They are normally sensitive to cephalosporins.Recently characterized enzyme CTX-1 (TEM 3, K. pneumoniae) and SHV-2, make them resistant strains ureidopenicillins to all cephalosporins (except cephamycines) and monobactam. These new beta-lactamase plasmid is strongly inhibited by clavulanic acid. In K. oxytoca, beta-lactamase extended spectrum has a chromosomal support, is inhibited by clavulanic acid.

Most strains hosts R plasmids that make them resistant to many antibiotics. The treatment can not do without a susceptibility on which it is necessary to test the latest antibiotics.



Enterobacter are VP Enterobacteriaceae (+), neighboring Klebsiella they are distinguished by their mobility, for the presence of ODC, sometimes of ADH and the lack of urease. TDA, DNase, producing indole and H2S are negative.

The classification of Enterobacter was subject to many changes. We indicate in the table below the names of the species encountered in medical bacteriology.

Klebsiella, Serratia

The type species is E. cloacae. It is also the most frequently encountered.

The species Hafnia alvei is now classified in the genus Hafnia she is the only representative.

The plant pathogenic Enterobacteriaceae Erwinia are not encountered in medical bacteriology.


Enterobacter are commensal gut of humans and animals. They are found in the water, on the ground, on the skin and mucous membranes. These are bacteria hospitalism.


These opportunistic pathogenic bacteria may be responsible for septicemia, meningitis, urinary tract infections, neonatal infections and various suppurations.


The biochemical characteristics that distinguish the species encountered clinically are shown in Table IV.

It should be noted that the colonies of E. sakazakii are pigmented yellow. A yellow pigment can also be produced by strains of E. agglomerans. The latter species is heterogeneous and consists of several biotypes.

E. gergoviae has urease.

E. asburiae is motionless, RM (+), malonate (-), rhamnose (-).

TABLE IV characteristics of different species of Enterobacter
TABLE IV characteristics of different species of Enterobacter


Enterobacter are often very resistant to antibiotics. E. cloacae has a natural resistance to ampicillin and cephalothin.A significant percentage of strains resistant to carbenicillin, gentamicin, tetracycline, chloramphenicol, sulfonamides and trimethoprim. Sensitivity ureido-penicillins, third generation cephalosporins, aminoglycosides and quinolones should be determined by susceptibility testing.

Some strains of E. cloacae initially sensitive to cefotaxime can become resistant to third generation cephalosporins during treatment with one of these cephalosporins. It is either the induction of chromosomal cephalosporinases, or selecting a mutant derepressed producing high level this cephalosporinase.

The enzyme in question is a beta-lactamase Class 1 Richmond and Sykes. Recently it inactivates molecules except imipenem. It is not inhibited by clavulanic acid. Induction can be detected by placing a antibiogram cefoxitin disk, very inductive, beside a cefotaxime disc.

This resistance mechanism, common in E. cloacae, can also be encountered in the main species ofEnterobacteriaceae except E. coli and Shigella and in Pseudomonas aeruginosa.



Serratia are generally mobile Enterobacteriaceae. They sometimes give pigmented colonies red. VP are (+), ONPG (+), and produce numerous extracellular enzymes. They have no ADH or ADD or urease and do not produce H ^ O.

Eight species are currently recognized:

S. marcescens, S. liquefaciens (previously classified as Enterobacter), S. plymuthica, S. rubidaea, S. odorifera andS.fîcaria, S.fonticola and S. entomophila.


Serratia are environmental bacteria found on the ground and on the plants. S. marcescens is a ubiquitous species that is the only play an important role as an opportunistic pathogen. Pigmented strains are common in nature, but rarely isolated in a hospital; non-pigmented strains are frequently isolated in hospital. They are much more resistant to antibiotics.

Serratia are the most resistant to physical and chemical agents Enterobacteriaceae. They can survive for months in distilled water and multiply in antiseptic solutions: quaternary ammonium compounds, chlorhexidine. They grow well at 4 ° C. Are killed by heat or bleach. Hospital infections can be related to antiseptics or contaminated bottles but hand transmission seems the most common.


Serratia are not pathogenic to healthy subjects. Today, they are responsible for hospital infections sometimes epidemic, especially S. . marcescens The location of the infection depends on the nature of the activity of hospital service: UTI after instrumental maneuvers; respiratory infections due to the use of artificial ventilation or aerosol devices; secondary infections of wounds by contaminated antiseptic; sepsis complicating the preceding or subsequent infections with the use of catheters.

Outside of hospital acquired infections, serious infections Serratia (endocarditis, osteomyelitis) were observed among heroin. S. plymuthica S.fîcaria and have no known pathogenicity for humans.


Some strains of S. marcescens, usually isolated from the environment and humans, produce a red pigment, prodigiosin. Most strains of S. marinorubra and S. plymuthica produces a pink or red pigment.

Most strains of Serratia overlooks antibiogram a zone of inhibition around the colistin with regrowth “rosette” around the disk. This may sometimes be observed with other bacterial species.

The distinctive features of the different Serratia species are shown in Table V. It should be noted that:

S. marcescens is raffinose (-) and arabinose (-), S. liquefaciens adonitol is (-), arabinose (+), 5. rubidaea is ODC (-) and sorbitol (-), S. odorifera produces indole.

TABLE V: distinctive characteristics of different species of Serratia
TABLE V: distinctive characteristics of different species of Serratia

For epidemiological studies, it is possible to characterize the strains of S. marcescens by biotypie or serotyping.


Serratia are among the more antibiotic resistant bacterial species. They have a natural resistance to cephalothin, colistin and tetracyclines. Some strains are resistant to cephalosporins 3rd generation or by producing a cephalosporinase, either by reduction of the permeability.

Among Serratia strains virtually “resistant to all” can meet. They pose difficult therapeutic problems.


This type consists of a single species, Hafnia alvei, previously designated as Enterobacter alvei.

Normal host of the digestive tract of humans and animals, H. alvei can be isolated during opportunistic infections.

H. biochemical characters alvei, including VP, are more consistently positive after incubation at 22 ° C than at 37 ° C.H. alvei is mobile at 22 ° C and often still at 37 ° C. The following reactions are positive: LDC, ODC, ONPG (exceptions), arabinose, mannitol H.. alvei is sometimes confused with H2S negative Salmonella.