The Genus Serratia

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232 F. Grimont and P.A.D. Grimont CHAPTER 3.3.11 Gas Production Gas production differentiates Serratia marcescens from S. liquefaciens—S. proteamaculans better when glucose agar is used than when a liquid medium with a Durham inverted tube is used (Grimont et al., 1977b). Glucose agar consists of nutrient agar (meat extract [Liebig], 3 g; yeast extract [Difco], 10 g; agar [BBL], 15 g; distilled water to 1 liter; pH 7.4) supplemented with 1% (wt/vol) glucose. Dispense into tubes (160 × 10 mm). Autoclave 20 min at 120°C, cool at 50°C, and inoculate before the agar sets. Tubes are examined for bubbles of gas for up to 3 days. β-Xylosidase The method of Brisou et al. (1972) for demonstrating β-xylosidase can conveniently be adapted for use with sterile microculture plates. Aqueous (1% wt/vol) p-nitrophenyl-β-xyloside is dispensed into the wells in 0.05-ml amounts, followed by 0.05 ml of a fresh bacterial suspension in 0.25 M phosphate buffer, pH 7. Plates are examined for a yellow color after 24 h. Identification of Serratia at the Genus Level Members of the genus Serratia share the characteristics defining the family Enterobacteriaceae. Only occasionally can a nitrate-negative strain be isolated. The properties that best define the genus Serratia are listed in Table 3. Although lipase activity on tributyrin or corn oil is listed, S. odorifera strains are only weakly lipolytic. A weak urease activity, lack of motility, or presence of a capsule are occasionally observed. Serratiae are clearly differentiated from Klebsiella spp., Enterobacter aerogenes, and E. cloacae by production of gelatinase, lipase, DNase, and by growth on caprate or caprylate as sole carbon source. Some soft-rot Erwinia spp. produce extracellular proteinase and DNase, but these strains are pectinolytic and lack glucose and gluconate dehydrogenases (Grimont et al., 1977b). Identification of Serratia Species The characteristics best allowing identification of each Serratia species are given in Tables 4 and 5. Carbon source utilization tests are invaluable for unambiguous identification. Indole production by S. odorifera is not reproducibly observed when peptone water is used. A defined medium containing trytophane (e.g., “urée-indole” medium, Diagnostics Pasteur, Marnes-la- Coquette, France; or the indole test in API 20E strips) gives consistently positive results with this species. With the use of classical tests (Ewing, 1986), S. plymuthica may be confused either with Table 3. Characteristics defining the genus Serratia. a Positive characteristics of all species of the genus Serratia b Motile rods Growth at 20°C in 1 day Growth at pH 9 Growth with 4% NaCl Growth on minimal medium without addition of growth factor Acid from maltose Acid from mannitol Acid from salicin Acid from trehalose ONPG c hydrolyzed Glucose oxidized to gluconate d Gluconate oxidized to 2-ketogluconate Carbon source utilization tests: N-acetylglucosamine, cisaconitate, 4-aminobutyrate, citrate, fructose, galactose, galacturonate, gluconate, glucose, glucuronate, glycerol, m-inositol, 2-ketogluconate, L-malate, maltose, mannitol, mannose, putrescine, ribose, trehalose Additional positive characteristics of Serratia species other than S. fonticola b Voges-Proskauer test (Richard) Lipase (tributyrin, corn oil) Growth on caprylate-thallous agar DNase Proteinase(s) Negative characteristics of all species of the genus Serratia b Urease (Ferguson) H2S from thiosulfate Phenylalanine/tryptophane deaminase Polygalacturonidase Amylase (4-day reading) β-Glucuronidase Carbon source utilization tests: 5-aminovalerate, mcoumarate, ethanolamine, glutarate, histamine, L-sorbose, tryptamine Sodium ion requirement Anaerobic growth with KClO3 Additional negative characteristics of Serratia species other than S. fonticola Acid from dulcitol Carbon source utilization tests: dulcitol, 3-phenylpropionate a Taken from Grimont et al., 1977b, and unpublished observations. b More than 90% of the isolates of each species give the same reaction. c ONPG, ortho-nitrophenyl-galactoside. In the presence of pyrroloquinoline quinone. S. proteamaculans, S. liquefaciens, S. rubidaea, or Enterobacter agglomerans. In the past, S. plymuthica had been identified as “atypical S. liquefaciens” (negative for lysine and ornithine decarboxylase) or atypical S. rubidaea (sorbitol positive). The species S. odorifera can also be recognized in a number of “rhamnose-positive S. liquefaciens” strains. Carbon source utilization
CHAPTER 3.3.11 The Genus Serratia 233 Table 4. Differential characteristics of Serratia species. Characteristic S. marcescens Red pigment d − v v − − − − Potato-like odor − − − v + + − − Good growth at 5°C − + + − + + + + Good growth at 40°C + − − v ND ND + ND Indole − − − − + − − − Tetrathionate reduction d + − − − − − + Gas from glucose agar − + v − − − − v β-Xylosidase − − v + + v − + Oxidation of: Glucose to gluconate (without cofactor) b + − v + + + + − 2-Ketogluconate to 2,5-diketogluconate + d − − − − − − Acid from: Adonitol v − − + (+) + + + L-Arabinose − + + + + + − + Lactose d v (+) + (+) v − + D-Melibiose − + + + + + − + D-Raffinose d + + + d + −+ L-Rhamnose − − − − + + − v D-Sorbitol + + d − + + − + Sucrose + + + + d + + − D-Xylose − + + + + + d d Lysine decarboxylase + + − d + − − + Ornithine decarboxylase + + − − d − − + Arginine decarboxylase − d − − − − − − Tween 80 hydrolysis + + + + − + + + Carbon source utilization: Adonitol + d − + + + + + L-Arabinose − + + + + + − + D-Arabitol − − − + − + d + L-Arabitol + − − − + + d + Betaine − − v + − − − − Dulcitol − − − − − − − + meso-Erythritol d − − + d + −+ Maltitol − + + + − + − v Melezitose − + + d − + − − D-Melibiose − + + + + + − + Palatinose − + + + − + − + Quinate d − + (+) − + d − L-Rhamnose − d − − + + − + D-Sorbitol + + v − + + − + Sucrose + + + + d + + − D-Tartrate − − − d d − − v Tricarballylate − − − d − − − v Trigonelline d − − + + v − − a The liquefaciens group or complex includes S. liquefaciens, S. proteamaculans, and S. grimesii. Without addition of pyrroloquinoline quinone. All species produce gluconate from glucose in the presence of pyrroloquinoline quinone. b Symbols: +, positive for 90% or more strains in 2-day reading; −, negative for 90% or more strains in 4-day reading; d, test used to differentiate biotypes; v, variable reactions; ( ), 4-day reading; ND, not determined. tests can help to sort out these “atypical” strains: after examining more than 5,000 Serratia strains, we have found no S. liquefaciens, no S. grimesii, and no S. plymuthica strains that were able to grow on adonitol and erythritol and no S. rubidaea strains able to grow on sorbitol as sole carbon source. “liquefaciens group” a S. plymuthica S. rubidaea S. odorifera S. ficaria Identification of Serratia Biogroups and Biotypes S. entomophila S. fonticola Biotypes in Serratia marcescens, S. proteamaculans, S. plymuthica, and S. rubidaea were first defined by numerical taxomony (Grimont et al., 1977b). We recognize 18 biotypes in S. marce-
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