FLAVOBACTERIUM

I – GENERAL CHARACTERISTICS:

For years, the genus Flavobacterium presented very heterogeneous: indeed he gathered gram-negative bacilli or positive, stationary or mobile, to ciliature peritrichous, bacilli whose only common property was yellow pigmentation of their cultures.

In the latest edition of “Bergey’s Manual of Systematic Bacteriology,” 1984, the genus Flavobacterium was redefined as comprising “Gram-negative bacilli, 0.5 to 1-3 microns (in liquid medium, the presence of greater length of bacilli 5 | Jm), do not form spores, strictly aerobic, (strictly respiratory type of metabolism) oxidase (+), catalase (+), still and devoid of gliding motility and not swarming like Cytophaga ” .

Stem environmental grow between 5 and 30 ° C, most strains of human origin also grow at 37 ° C. Colonies are translucent, sometimes opaque, round, 1 to 2 mm in diameter, slightly convex or slightly, smooth, shiny. The colonies are pigmented yellow, orange or yellow-orange (non-diffusible pigment whose production is favored by a temperature of 15-20 ° C, by daylight and by the use of casein circles, milk or starch) or are not pigmented.Chemo-organotrophic, the majority of the strains are proteolytic hydrolyze gelatin and casein, produce DNase.Nitrates are generally not reduced. Species produce indole.

The Flavobacterium have habitat soil and water: they are also found in raw meat, milk and other foods in the hospital environment and in various samples of human origin.

The base content (G + C%) of the DNA is between 31 and 42 mol%.

F. brief was proposed by Holmes and Owen as the type species of the genus Flavobacterium replacing F. aquatile.According to these authors, F. aquatile is not representative of all species of the genus Flavobacterium and is more akin to Cytophaga as Flavobacterium.

Other Flavobacterium species and the corresponding type strains are respectively:

F. balustinum (syn. Flavobacterium group IIb), F. meningosepticum most important species medically, F. odoratum, F. multivorum (syn. IIk group biovar 2), F. spiritovorum.

II – F. meningosepticum:

A – Morphology and cropping characters:

Gram-negative bacilli, short, sometimes very short (0.4-0.5 x 0.7-2 um), thin or fairly thin, with tendency to polymorphism: the presence of long forms and often flexuous, long bacilli the more numerous than the broth cultures are older.

About 20% of strains of F. meningosepticum do not grow on the medium Drigalski; others develop there giving colonies lactose (-), round, about 1.5 to 2 mm after 48 h at 30 ° C. The vast majority of crops are apigmentées or appear very pale pink color when the fee to the platinum loop; the others are yellow-orange light. ASD environments and Hajna-Kliger, some cultures F. meningosepticum have a mucoid.

B – Clinical significance and sensitivity to antibiotics:

In the newborn, mostly premature, F. meningosepticum is sepsis agent and extremely serious meningitis, with frequent fatal or leaving significant sequelae (hydrocephalus). In adults, the infections are essentially iatrogenic.

F. meningosepticum is resistant to many antibiotics usually active against Gram-negative bacilli (beta-lactams, aminoglycosides, tetracycline, colistin, trimethoprim, furans …) and usually has a “paradoxical” sensitivity to antibiotics in only active principle on gram-positive bacteria (novobiocin, vancomycin, erythromycin, spiramycin, lincomycin, clindamycin …). The genus Flavobacterium is great heterogeneity from the point of view of antibiotype: some strains are sensitive to ureidopenicillins, ciprofloxacin, co-trimoxazole, we encounter strains resistant to imipenem.

III – OTHER SPECIES FLAVOBACTERIUM:

F. odoratum, F. and F. Brief II f are sometimes isolated from urine, F. II f genitals, F. odoratum pus diverse, and F. II bcatheters, syringes, medical or surgical use equipment in hospitals.

The sensitivity of these species is close to that of F. meningosepticum except F. odoratum which is very durable.

Achromobacter – Alcaligenes

The taxonomic position of the species of these genera is still uncertain and the current description of Bergey’s Manual does not allow to give a practical presentation of these species that are found in certain pathological products and hospital equipment.

Differential diagnosis arises with various species: Bordetella bronchiseptica, P. acidovorans, P. testosteroni, P. alcaligenes, P. pseudoalcaligenes, Agrobacterium.

We limit ourselves to a simplified description of these species without considering the incessant taxonomic revisions due to their limited interest in the differential diagnosis in routine clinical bacteriology.

A – Alcaligenes:

The type species is A. faecalis (Castellani and Chalmers, 1919). The genus Alcaligenes includes gram-negative bacilli, oxidase (+), a mobile peritrichous ciliature. But it must be emphasized that cilia may be “degenerate” leaving only one or two side or polar flagella. Staining flagella (Method of Rhodes) is essential to guide the diagnosis and to avoid confusion with Pseudomonas Heterotrophic freshwater species are alone considered.:

– TO. faecalis (A. odoriferous equated with A. faecalis)

– A. denitrificans (A. xylosoxidans subsp denitrificans subsp xylosoxidans and assimilated to xylosoxidans..)

– A. piechaudii.

The optional marine and autotrophic species show no interest

Medical bacteriology.

Alcaligenes, isolated from water and soil, is common in the hospital environment.

Their natural pathogenicity is zero, but because of their resistance to antibiotics and antiseptics usual, these germs can cause contamination of drug solutions and localized secondary infections in hospitals.

A simplified bacteriological diagnosis can be made in the following diagram (supplemented by a auxanogramme)

Absence of pigment, gelatinase, of decarboxylases.

Antibiotic sensitivity differs little from that of Pseudomonas and action of aminoglycosides is variable.

B – Achromobacter:

The genus Achromobacter group of Gram-negative bacilli, oxidase (+) at ciliature peritrichous, oxidative various carbohydrates and not producing 3-cétolactose from lactose. The classification of this kind is controversial.

Two species are recognized by the “Center for Disease Control” (CDC):

A. xylosoxidans and Achromobacter sp Vd group.

The natural habitat of these organisms is poorly understood. They would be part of the endogenous flora of the colon and are isolated from different sources and hospitable environment. They can be isolated in various pathological products and sometimes have real clinical significance in nosocomial infections (meningitis, bacterial, …) in immunocompromised patients.

Bacteriological diagnosis retains the oxidation of xylose by 99% of the strains. Xylosoxidans and the hydrolysis of urea by Achromobacter sp Vd group.

Achromobacter is sensitive to carboxypénicillines, to acyluréidopénicillines (aziocilline, piperacillin), certain third-generation cephalosporins (cefoperazone, ceftazidime, …) and cotrimoxazole.

AGROBACTERIUM

This genus has long been considered plant pathogen (eg Agrobacterium tumefaciens) tumor agent of the collar (crown gall), root proliferation (hairy root).

The habitat of these bacteria is the ground. A species may have a medical interest:

A. radiobacteï (not pathogenic for plants).

Isolated hospital strains have different biotypes, with three main characters: esculin (+), urease (+), ONPG (+). These are motile cilia in peritrichous often degenerate with few flagella.

They can contaminate and be isolated in various disease products, their clinical significance is difficult to establish even when positive blood culture.

XANTHOMONAS

The genus Xanthomonas was created to group of plant pathogenic bacteria neighboring yellow pigmentedPseudomonas. This kind contained sixty species whose distinction was made ​​on the basis of their pathogenic power vis-à-vis a given plant.

The latest edition of “Bergey’s Manual” recognizes five main species:

X. campestris, X. fragariae, X. albilineans, X. axonopodis, X. ampelina.

Pseudomonas maltophilia has been transferred to the genus Xanthomonas.

A – Body type:

Gram-negative bacilli, mobile monotriche by a polar eyelash.

B – Cropping characters:

Bacteria chemo-organotrophic apparently undemanding but not absolutely prototrophic. Optimum temperature 25 to 30 ° C. Xanthomonas produce a yellow pigment, but there are exceptions. Originally defined as carotenoid nature, it would actually xanthomonadin = aryl-polyene bromine, soluble in organic solvents. On nutrient agar containing glucose, some strains produce a “slime” abundant.

C – biochemical characters:

Oxidase (-) sometimes weakly positive

Catalase (+)

Frequently lipolytic, proteolytic, pectolytic and / or amylolytic.

Simple biochemical characteristics of X. maltophilia are given in the table of chapter 22 Pseudomonas.

D – Medical Interest:

Clinical bacteriology significance of the isolation of plant pathogenic Xanthomonas is still obscure. This is mainly a problem of differential diagnosis may possibly arise in the laboratory. The involvement of these opportunistic bacteria Xanthomonas like to be demonstrated.

X. maltophilia has been described in 1961 by Hugh and Ryschenkow. Despite its special nutrient requirements and in particular auxotrophy vis-à-vis methionine, this ubiquitous bacterium is isolated from vegetables, bananas, cotton seed, bean pods, tobacco plants, and even drinking water , stagnant water, sewage water, water streams and rivers, water from groundwater, contaminated milk, soil from the oil fields.

In the hospital environment it occurs in distilled water, water incubators, nebulizers, humidifiers. X. maltophilia is the second non-fermenting bacterium related to Pseudomonas isolated in order of frequency in a laboratory medical bacteriology after P. aeruginosa. The usual sources of isolation in humans are the airways, wounds, blood, urine, butX. maltophilia may be in multiple other sites: liquids, ascites, pericardial, pleural, CSF, lymph, leg ulcers, dialysis fluids … It’s usually a commensal organism that is part of the transient flora inpatient, it is becoming more common in cystic fibrosis.

X. maltophilia is the agent of opportunistic infections: endocarditis, septicemia, lobar pneumonia, bronchopneumonia, aspiration pneumonia, urinary tract infections, conjunctivitis, meningitis, wound superinfection, various suppurations.

Twenty-six serotypes 0 have recently been described and could be used for epidemiological studies.

X. maltophilia is often characterized by high natural resistance vis-à-vis beta-lactam associated with low membrane permeability. It has chromosomal and plasmid beta-lactamases. The existence of at least 2 inducible chromosomal beta-lactamases (LI Zn – penicillinase and L2 – cephalosporinase containing a serine in the active site) already provides the hydrolysis of several beta-lactams making difficult the choice of antibiotic therapy.

We must remember that it is still resistant to imipenem. 2nd generation quinolones can be active but variably.