Taxonomy of Microorganisms in Foods. Doç. Dr. Arzu Çağrı Mehmetoğlu

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1 Taxonomy of Microorganisms in Foods Doç. Dr. Arzu Çağrı Mehmetoğlu

2 Classification of Microorganisms Each microorganism has only one officially accepted name by international agreement M.O. are named according to a system of binomial classification Each composed of two words Must follow certain rules of Latin Grammar The first name of genus name, capitalized The second word is the species name, never capitalized All genus, species, and strain names are italicized (or underlined) Such as Saccharoymycess cerevisiae

3 Classification of Microorganisms A microbial species (spp.) can be divided into several subspecies (subsp.) according to differences in characteristics Lactococcus lactis subsp. lactis Lactococcus lactis subsp. cremoris Subspecies used to differentiate strains by specific characters and named as serovar for antigenic reaction; biovar for producing a specific metabolite; phagovar for sensitive to a specific phage.

4 Such classification has not taxonomic importance but can have practical usefulness Lactococcus lactis subsp. lactis biovar. diacetylactis This strain produces diacetylactis Each strain of species can be further named with a specific strain number Pediococcus acidilactici LB923

5 The genuses can be represented collectively using family name plural adjective suffix aceae Salmonella, Escherichia, Klebsiella in Enterobactericaceae The species and the strain in a genus can be represented collectively, using either spp. After genus name Lactibacillus spp. or plural forms of the genus lactobacilli

6 An organism s name can include some information about the organism s properties For example: Staphylococcus aureus Was named for its shape (Coccus) Arrangement (stapylo, grape like clusters) For the gold color of colony (aureus, gold)

7 When the name of the same species is written more than once in article, both genus and species name is written completely for the first time and abbreviate the genus name in text written in the text Listeria monocytogenes; L. monocytogenes Leu. mesenteroides, Lb. bulgaricus

8 Latin Lesson Many words in microbiology have stem word with a Latin ending Be aware of this when using singular or plural words Eg. The singular ending for bacillus, fungus, nuclues and coccus is «-us» ; the plural is «-i», hence bacilli, cocci, etc.

9 bacillus bacilli Coccus Cocci

10 The singular bacterium, flagellum and medium where «-um» is the singular; the plural is «-a», hence bacteria, flagella, media medium media flagellum flagella

11 Food Pre-Enrichment Selective Enrichment Selective/Differential Plating Bacterial Isolate

12 Classical Tests for Differentiating Food- Associated Bacteria Shape, size Gram stain Spore Formation Aerobic vs. anaerobic Catalase test Oxidase test Colonia morphology Physiological test Biochemical pathways/enzyme activities

13 Shape, size

14 Gram stain

15 Spore formation

16 Aerobic vs. anaerobic Aerobes require oxygen Obligate anaerobes can not grow in presence of oxygen Facultative anaerobes can grow in presence and absence of oxygen

17 Catalase test Heme-containing enzyme found in most bacteria 2H 2 O 2 2H 2 O +O 2 Detected by adding 3%H 2 O 2 to microbial colony and visualizing white foaming Catalase negative bacteria are usually anaerobic Catalase negatives include Streptococcus, Lactobacillus, Enterococcus, Leucocnostoc, Lactobacillus and Clostridium

18 Oxidase test Capacity of a microbe to oxidize aromatic p- aminodimethylaniline to yield a color end product Relates closely with high cytochrome oxidase activity of bacteria such as Pseudomonas

19 Colonial morphology

20 Physiological tests ph Temperature Salt concentration Water activity

21 Biochemical pathways/enzyme activities Key metabolic pathways Substrate utilization Enzyme activities can be determined using various differential media or colorimetric reactions Baird parker agar- Clostridium perfringens Clear zone-lipase, protease Opeque zone within clear zone-lecithinase

22 Modern Approaches for Differentiating Food-Associated Bacteria Serology the diagnostic identification of antibodies in the serum Bacteriophage typing Molecular figerprinting

23 Food Pre-Enrichment Selective Enrichment Selective/Differential Plating Bacterial Isolate

24 Bacterial İsolate Gram + Gram

25 Bacterial Isolate Gram + Gram Rod Coccus Rod Coccus

26 Bacterial Isolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facultative Aerobe Anaerobe Anaerobe

27 Bacterial Isolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facul Anerobe Aerobe Anaerobe Pseudomonas Flavobacterium Morexalla Psychrobacter Acetobacter Gluconobacter Xanthomonas

28 Gram Negative Aerobic Rods Pseudomonas Flavobacterium Morexalla Psychrobacter Acetobacter Gluconobacter Xanthomonas

29 Bacterial Isolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facul Anerobe Aerobe Anaerobe Pseudomona Flavobacterium Oxidase - Oxidase + Morexalla Psychrobacter Acetobacter Gluconobacter Xanthomonas

30 Bacterial Isolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facul Anerobe Aerobe Anaerobe Pseudomona Flavobacterium Oxidase - Oxidase + Morexalla Psychrobacter Acetobacter Gluconobacter Citrobacter Enterobacter Klebsiella Serratia Hafnia Erwinia Xanthomonas Escherichia Salmonella Yersinia Proteus Shigella

31 Oxidase-, Gram-, Facultative Anaerobe (Family Enterobacteriacae) Citrobacter Enterobacter Klebsiella Serratia Hafnia Erwinia Many of these are found in the gut But also in environment Some are true pathogens Some can cause «opportunistic infectiouns» (e.g. From wounds)

32 Oxidase-, Gram-, Facultative Anaerobic rods Escherichia Salmonella Yersinia Proteus Shigella

33 Bacterial İsolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facul Anerobe Aerobe Anaerobe Pseudomona Flavobacterium Oxidase - Oxidase + Morexalla Psychrobacter Acetobacter Gluconobacter Citrobacter Enterobacter Klebsiella Serratia Hafnia Erwinia Vibrio Campylobacter Aeromonas Xanthomonas Escherichia Salmonella Yersinia Proteus Shigella

34 Gram -, Oxidase + Facultatively Araerobic Curved Rods Vibrio Campylobacter Aeromonas

35 Bacterial İsolate Gram + Gram Rod Coccus Rod Coccus Aerobe Facul Anerobe Aerobe Anaerobe Pseudomona Flavobacterium Oxidase - Oxidase + Morexalla Psychrobacter Acetobacter Gluconobacter Citrobacter Enterobacter Klebsiella Serratia Hafnia Erwinia Vibrio Campylobacter Aeromonas Halobacterium Halococcus Veillonella Xanthomonas Escherichia Salmonella Yersinia Proteus Shigella

36 Gram Negative Cocci Aerobic Halobacterium Halococcus Anaerobic Veillonella

37 Bacterial İsolate Gram + Gram Rod Coccus Rod Coccus Aerobes Facul anaerobes anaerobes aerobes Facul anaerobes anaerobes Bacillus Corynebacterium Lactobacillus Listeria Brochothrix Clostridium Fructobacillus, Leuconostoc, Oenococcus, Weissella Leuconostoc, Pediococcus, Lactococcus, Streptococcus, Enterococcus Staphylococcus

38 the important genera known to occur in foods Bacteria Acinetobacter, Erwinia, Proteus Aeromonas, Escherichia, Pseudomonas Alcaligenes, Flavobacterium, Psychrobacter Arcobacter, Hafnia, Salmonella Bacillus, Kocuria, Serratia Brevibacillus, Lactococcus, Shewanella Brochothrix, Lactobacillus, Shigella Burkholderia, Leuconostoc, Sphingomonas Campylobacter, Listeria, Stenotrophomonas Carnobacterium, Micrococcus, Staphylococcus Citrobacter, Moraxella, Vagococcus Clostridium, Paenibacillus, Vibrio Corynebacterium, Pandoraea, Weissella Enterobacter, Pantoea, Yersinia Enterococcus, Pediococcus Molds Alternaria, Colletotrichum, Penicillium Aspergillus, Fusarium, Rhizopus Aureobasidium, Geotrichum, Trichothecium Botrytis, Monilia, Wallemia Byssochlamys, Mucor, Xeromyces, Cladosporium Yeasts Brettanomyces/Dekkera, Issatchenkia Schizosaccharomyces Candida, Kluyveromyces, Torulaspora Cryptococcus, Pichia, Trichosporon Debaryomyces, Rhodotorula, Yarrowia Hanseniaspora, Saccharomyces, Zygosaccharomyces Protozoa Cryptosporidium parvum, Entamoeba histolytica Toxoplasma gondii, Cyclospora cayetanensis, Giardia lamblia

39 Acinetobacter (A ci ne to bac ter; Gr. akinetos, unable to move) Gram-negative rods strict aerobes young cultures-rod-shaped cells old cultures -coccoid-shaped cells distributed in soil and water be found on many foods, especially refrigerated fresh products

40 Aeromonas (ae ro mo nas; gas producing) aquatic Gram-negative rods produce gas from the fermented sugars They are normal inhabitants of the intestines of fish some are fish pathogens Some possesses pathogenic properties

41 Alcaligenes (al ca li ge nes; alkali producers) ferment sugars but instead produce alkaline reactions Nonpigmented Raw milk, poultry products, and fecal matter are common sources

42 Alteromonas (al te ro mo nas; another monad) marine and coastal water inhabitants that are found in and on seafoods; all species require seawater salinity for growth They are Gram-negative motile rods strict aerobe

43 Arcobacter (Ar co bac ter; L. arcus, bow) Gram-negative curved S-shaped rods - similar to the campylobacters except they can grow at 15 C and are aerotolerant found in poultry, raw milk, shellfish, and water; and in cattle and swine products oxidase- and catalase-positive cause abortion and enteritis in some animals

44 Bacillus (ba cil lus) Gram-positive spore-forming rods aerobes most - mesophiles, psychrotrophs thermophiles also exist The genus contains only two pathogens: B. anthracis (cause of anthrax) and B. cereus B. subtilis -rope disease in bread

45 Brevibacillus (Bre vi ba cil lus) these organisms found in soil and water, common on plants, and in air, and dust. Gram positive

46 Brochothrix (bro cho thr ix; Gr. brochos, loop; thrix, thread) Gram-positive nonspore forming Shape: exponential-phase cells are rods, older cells are coccoids, a feature typical of coryneforms common on processed meats and on fresh and processed meats that are stored in gasimpermeable packages at refrigerator temperatures They do not grow at 37 C.

47 Campylobacter (cam py lo bac Gram-negative ter; Gr. campylo, curved) spirally curved rods They are microaerophilic to anaerobic Common in poultry Pathogens

48 Carnobacterium (car no bac terium; L. carnis, of flesh-meat bacteria) Gram positive, catalase-negative rods They are heterofermentative, most grow at 0 C and none at 45 C. Gas is produced from glucose by some species They are found on vacuum-packaged meats and related products, as well as on fish and poultry meats

49 Citrobacter (cit ro bac ter) enteric bacteria slow lactose-fermenting Gram-negative rods All members can use citrate as the sole carbon source C. freundii is the most dominant species in foods

50 Clostridium (clos tri di um; Gr. closter, a spindle) anaerobic spore-forming rods Some causes disease in humans C. perfringens, C. botulinium Mesotrophic, psychrotrophic, and thermophilic species/strains exist their importance in the thermal canning of foods

51 Corynebacterium (co ry ne bac ter i um;gr. coryne, club) This is one of the true coryne form genera of Gram-positive, rod-shaped bacteria sometimes involved in the spoilage of vegetable and meat products. C. diphtheriae, causes diphtheria in humans.

52 Enterobacter (en te ro bac ter) enteric Gram-negative bacteria Facultative anaerob E. aerogene and E. cloacae-clinicaly important urinary and respiratory tracts infection

53 Enterococcus (en te ro coc cus) Gram-positive ovoid cells occur singly, in pairs, or in short chains Actic acid bacteria Difficult to distinguish from Streptococci Found in human intestine

54 Erwinia (er wi ni a) Gram-negative enteric rods especially associated with plants

55 Escherichia (esch er i chi a) Those strains that cause foodborne gastroenteritis E. coli- fecal coliform E. coli O157:H7-a sistemic pathogen

56 Flavobacterium (fla vo bac te ri Gram-negative rods um) association with plants Some are mesotrophs, others are psychrotrophs, cause spoilage of refrigerated meats and vegetables.

57 Hafnia (haf ni a) Gram-negative enteric rods Facultative anaerob the spoilage of refrigerated meat and vegetable products

58 Lactobacillus (lac to ba cil lus) Gram-positive, catalase-negative rods often occur in long chains microaerophilic, many true anaerobic strains exist, especially in the colon and the rumen. Most found on vegetables, with some of the other lactic acid bacteria Their occurrence in dairy products is also common. Many fermented products are produced, common on refrigerator-stored, vacuum-packaged meats

59 Lactococcus (lac to coc cus) The nonmotile Gram-positive, catalase-negative, spherical, or ovoid cells, that occur singly, in pairs, or as chains. They grow at 10 C but not at 45 C, l-lactic acid is the predominant end-product of fermentation.

60 Leuconostoc (leu co nos toc; lactic acid bacteria. colorless nostoc) Gram-positive, catalase-negative cocci that are heterofermentative. These cocci are typically found in association with the lactobacilli.

61 Listeria (lis te ri a) This genus of six species of Gram-positive, nonsporing rods is closely related to Brochothrix. L. monocytogenes pathogen Menengites abortion

62 Micrococcus (mi cro coc cus) Gram-positive and catalasepositive cocci inhabitants of mammalian skin, dairy products can grow in high NaCl M. luteus and M. lylae are the only two micrococcal species.

63 Moraxella (mo rax el la) short Gram-negative rods Their metabolism is oxidative they do not form acid from glucose

64 Pediococcus (pe di o coc cus; coccus growing in one plane) These homofermentative cocci are lactic acid bacteria P. acidilactici, a common starter species It can grow in 18% NaCl responsible for the fermentation of cabbage

65 Proteus (pro te us) These enteric Gram-negative rods are aerobes They are typical of enteric bacteria in being present in the intestinal tract of humans and animals. They may be isolated from a variety of vegetable and meat products, especially those that undergo spoilage at temperatures in the mesophilic range

66 Pseudomonas (pseu do mo nas; false monad) These are typical soil and water bacteria they are widely distributed among fresh foods, especially vegetables, meats, poultry, and seafood products Spoilage bacteria

67 Salmonella (sal mon el la) Gram-negative enteric bacteria human pathogens two species with those that affect humans placed in the species Salmonella enterica. The serotypes (serovars) of more than 2,400 are listed as follows: Salmonella enterica serotype Newport, or Salmonella Newport

68 Serratia (ser ra ti a) These Gram-negative rods that belong to the family Enterobacteriaceae aerobic and proteolytic, and they generally produce red pigments on culture media S. liquefaciens is the most prevalent of the foodborne species; it causes spoilage of refrigerated vegetables and meat products.

69 Shewanella (she wa nel la). They are Gram-negative, straight or curved rods, nonpigmented, motile by polar flagella They are oxidase positive All are associated with aquatic or marine habitats

70 Shigella (shi gel la). human enteropathogens

71 Staphylococcus (staph y lo coc cus; grape-like coccus). These Gram-positive, catalase-positive cocci include S. aureus, which causes several disease syndromes in humans, including foodborne gastroenteritis.

72 Vibrio (vib ri o) Gram-negative straight or curved rods are members of the family Vibrionaceae. Several species cause gastroenteritis and other human illness;

73 Weissella (Weiss ella, after N.Weiss) This genus of lactic acid bacteria All produce gas from carbohydrates.

74 Yersinia (yer si ni a) This genus includes the agent of human plague, Y. pestis, at least one species that causes foodborne gastroenteritis, Y. enterocolitica.

75 SYNOPSIS OF COMMON GENERA OF FOODBORNE MOLDS Molds are filamentous fungi that grow in the form of a tangled mass that spreads rapidly The total of the mass or any large portion of it is referred to as mycelium. Mycelium is composed of branches or filaments referred to as hyphae. multiply by ascospores, zygospores, or conidia. The some ascospores -heat resistance.

76 The taxonomic positions of the genera Division: Zygomycota Class: Zygomycetes (nonseptate mycelium, reproduction by sporangiospores, rapid growth) Order: Mucorales Family: Mucoraceae Genus: Mucor Rhizopus Thamnidium Division: Ascomycota Class: Plectomycetes (septate mycelium, ascospores produced in asci usually number 8) Order: Eurotiales Family: Trichocomaceae Genus: Byssochlamys Emericella Eupenicillium Eurotium

77 Division: Deuteromycota (the imperfects, anamorphs; perfect stages are unknown) Class: Coelomycetes Genus: Colletotrichum Class: Hypomycetes (hyphae give rise to conidia) Order: Hyphomycetales Family: Moniliaceae Genus: Alternaria Aspergillus Aureobasidium (Pullularia) Botrytis Cladosporium Fusarium Geotrichum Helminthosporium Monilia/Sclerotinium Penicillium Stachybotrys Trichothecium

78 Alternaria Septate mycelia with conidiophores and large brown conidia are produced. They cause brown to black rots of apples, and figs. Stem-end rot and black rot of citrus fruits This is a field fungus that grows on wheat. Also found on red meats. Some species produce mycotoxins

79 Aspergillus Chains of conidia are produced. The aspergilli appear yellow to green to black on a large number of foods. Black rot of peaches, citrus fruits, and figs Some species cause spoilage of oils, such as palm, peanut, and corn. A. oryzae -the shogu fermentation A. soyae koji fermentation. A. glaucus - katsuobushi, a fermented fish product. A. glaucus A. restrictus group contains storage fungi that invade seeds, soybeans, and common beans. A. niger produces β-galactosidase, glucoamylase, invertase, lipase, and pectinase: A. oryzae produces α-amylase. Several species produce aflatoxins, and others produce ochratoxin A and sterigmatocystin

80 Botrytis Long, slender, and often pigmented conidiophores Mycelium is septate; conidia are borne on apical cells and are gray in color, B. cinerea is the most common in foods. -the cause of gray mold rot of apples, pears, raspberries, strawberries, grapes, blueberries, citrus

81 Byssochlamys The ascomycete Byssochlamys produces open clusters of asci, each of which contains eight ascospores. their heat resistance, resulting in spoilage of some high-acid canned foods. they can tolerate low oxidation reduction potential (Eh) values. Some are pectinase producers, B. fulva and B. nivea spoil canned and bottled fruits B. fulva possesses a thermal D value at 90 C between 1 and 12 minutes

82 Cladosporium Septate hyphae with dark, tree-like growth is smooth and olive colored to black Some conidia are lemon shaped C. herbarum produces black spot on beef and frozen mutton. Some spoil butter and margarine, and some cause restricted rot of stone fruits and black rot of grapes. They are field fungi that grow on barley and wheat grains. C. herbarum and C. cladosporiodes are the two most predominant on fruits and vegetables.

83 Fusarium Extensive mycelium is produced - cottony with tinges of pink, red, purple, or brown. Septate fusiform to sickle-shaped conidia (macroconidia) are produced. cause brown rot of citrus fruits and pineapples and soft rot of figs. As field fungi, some grow on barley and wheat grains.

84 Geotrichum These yeast-like fungi are usually white. The hyphae are septate, and reproduction occurs by vegetative hyphae. G. candidum is the most important species in foods. It is variously referred to as dairy mold because it imparts flavor and aroma to many types of cheese, machinery mold because it builds up on food contact equipment in food-processing plants, especially tomato canning plants. They cause sour rot of citrus fruits and peaches and the spoilage of dairy cream. They are widespread and have been found on meats and many vegetables. Some participate in the fermentation of gari.

85 Monilia/Sclerotinium Pink, gray, or tan conidia are produced. They produce brown rot of stone fruits such as peaches. Monilina sp. causes mummification of blueberries.

86 Mucor Nonseptate hyphae are produced that give rise to sporangiophores that bear columella with a sporangium at the apex. No rhizoids or stolons are produced by members of this large genus. Cottony colonies are often produced. The conditions described as whiskers of beef and black spot of frozen mutton are caused by some species. At least one species, M. miehei, is a lipase producer. It is found in fermented foods, bacon, and many vegetables. One species ferments soybean whey curd.

87 Penicillium When conidiophores and conidia are the only reproductive structures present It produces heat-resistant spores. Typical colors on foods are blue to bluegreen. Blue and green mold rots of citrus fruits and blue mold rot of apples, grapes, pears One species, P. roqueforti, produces blue cheese. Some species produce citrinin, yellow rice toxin, ochratoxin A, rubratoxin B, and other mycotoxins

88 Nonseptate hyphae are produced that give rise to stolons and rhizoids. Sporangiophores typically develop in clusters from ends of stolons at the point of origin of rhizoids. Rhizopus

89 Rhizopus R. stolonifer is by far the most common species in foods. Sometimes referred to as bread molds, they produce watery soft rot of apples, pears, stone fruits, grapes, figs, and others. Some cause black spot of beef They may be found on bacon and other processed meats. Some produce pectinases, and R. oligosporus is important in the production of oncom, bongkrek, and tempeh.

90 Thamnidium Produce small sporangia borne on highly branched structures. T. elegans is the only species, and it is best known for its growth on refrigerated beef where its characteristic growth is described as whiskers. It is less often found in decaying eggs.

91 Trichothecium Septate hyphae -long, slender, and simple conidiophores T. roseum is the only species, and it is pink in color and causes pink rot of fruits. It also causes soft rot of cucurbits and is common on barley, wheat, corn, and pecans. Some produce mycotoxins

92 SYNOPSIS OF COMMON GENERA OF FOODBORNE YEASTS Yeasts are unicellular fungi Can produce mycelia Yeasts can be differentiated from bacteria by their larger cell size and their oval, elongate, elliptical, or spherical cell shapes. Typical yeast cells range from 5 to 8 μm in diameter, with some being even larger. Older yeast cultures tend to have smaller cells. divide by budding or fission.

93 Yeasts can grow over wide ranges of acid ph and in up to 18% ethanol. Many grow in the presence of 55 60% sucrose. Many colors are produced by yeasts, ranging from creamy, to pink, to red. The asco- and arthrospores of some are quite heat resistant.

94 The taxonomy of 15 or so foodborne genera Division: Ascomycotina Family: Saccharomycetaceae (ascospores and arthrospores formed; vegetative reproduction by fission or budding) Subfamily: Nadsonioideae Genus: Hanseniaspora

95 Subfamily: Saccharomycotoideae Genus: Debaryomyces Issatchenkia Kluyveromyces Pichia Saccharomyces Torulaspora Zygosaccharomyces Subfamily: Schizosaccharomycetoideae Genus: Schizosaccharomyces Division: Deuteromycotina Family: Cryptococcaceae (the imperfects ; reproduce by budding) Genus: Brettanomyces Candida Cryptococcus Rhodotorula Trichosporon

96 Brettanomyces These asporogenous yeasts form ogival cells and terminal budding, produce acetic acid from glucose only under aerobic conditions. B. intermedius is the most prevalent, and it can grow at a ph as low as 1.8. They cause spoilage of beer, wine, soft drinks, and pickles, and some are involved in after fermentation of some beers and ales. D. bruxellensis is involved in some sourdough fermentations, and it contributes to biogenic amines in red wines.

97 Candida The generic name means shining white, and cells contain no carotenoid pigments. Members of this genus are the most common yeasts in fresh ground beef and poultry, and C. tropicalis is the most prevalent in foods in general. Some members are involved in the fermentation of cacao beans, as a component of kefir grains, and in many other products, including beers, ales, and fruit juices.

98 Cryptococcus They are asporogenous, reproduce by multilateral budding, and are nonfermenters of sugars. They are hyaline and red or orange, and they may form arthrospores. They have been found on plants, in soils, on strawberries and other fruits, marine fish, shrimp, and fresh ground beef.

99 Debaryomyces These ascosporogenous yeasts sometimes produce a pseudomycelium and reproduce by multilateral budding. They are one of the two most prevalent yeast genera in dairy products. D. hansenii represents most prevalent foodborne species. It can grow in 24% NaCl and at an aw as low as It forms slime on wieners, grows in brines and on cheeses, and causes spoilage of orange juice concentrate and yogurt.

100 Hanseniaspora They exhibit bipolar budding, and, consequently, lemon shaped cells are produced. The asci contain two to four hat-shaped spores. Sugars are fermented, and they can be found on a variety of foods, especially figs, tomatoes, strawberries, citrus fruits, and the cacao bean fermentation.

101 Issatchenkia Members of this genus produce pseudomycelia and multiply by multilateral budding. They typically form pellicles in liquid media. dominant on a wide variety of foods.

102 Kluyveromyces These ascospore-forming yeasts reproduce by multilateral budding, and the spores are spherical. K. marxianus is one of the two most prevalent yeasts in dairy products. Kluyveromyces spp. produce β-galactosidase and are vigorous fermenters of sugars, including lactose. involved in the fermentation of kumiss It is also used for lactase production from whey and as the organism of choice for producing yeast cells from whey. They are found on a wide variety of fruits, and K. marxianus causes cheese spoilage.

103 Pichia They reproduce by multilateral budding, Pichia spp. typically form films on liquid media and are known to be important in producing indigenous foods in various parts of the world. Some have been found on fresh fish and shrimp they are known to grow in olive brines and to cause spoilage of pickles and sauerkraut.

104 Rhodotorula They reproduce by multilateral budding and are nonfermenters. R. Glutinis and R. mucilaginosa are the two most prevalent species in foods. They produce pink to red pigments, and most are orange or salmon pink in color. The genus contains many psychrotrophic species/strains that are found on fresh poultry, shrimp, fish, and beef. Some grow on the surface of butter.

105 Saccharomyces These ascosporogenous yeasts multiply by multilateral budding They are diploid and do not ferment lactose. SAll bakers, brewers, wine, and champagne yeasts are S. cerevisiae. They are found in kefir grains and can be isolated from a wide range of foods, such as dry-cured salami and numerous fruits. S. cerevisiae rarely causes spoilage.

106 Schizosaccharomyces They are regarded as being only distantly related to the true yeasts. S. pombe is the most prevalent species; it is osmophilic and resistant to some chemical preservatives.

107 Torulaspora Multilateral budding is the method of reproduction with spherical spores in asci. They are strong fermenters of sugars, T. delbrueckii is the most prevalent species.

108 Trichosporon These nonascospore-forming oxidative yeasts multiply by budding and by arthroconidia formation. They produce a true mycelium, and sugar fermentation is absent or weak. They are involved in cacao bean and idli fermentations and have been recovered from fresh shrimp, ground beef, poultry, frozen lamb, and other foods. T. pullulans is the most prevalent species, and it produces lipase.

109 Yarrowia they are common on fruits, vegetables, meats, and poultry.

110 Zygosaccharomyces Multilateral budding is the method of reproduction, and the bean-shaped ascospores formed are generally free in asci. Most are haploid and they are strong fermenters of sugars. Z. rouxii is the most prevalent species, and it can grow at an aw of 0.62, Some are involved in shoyu and miso fermentations, and some are common spoilers of mayonnaise and salad dressing, especially Z. bailii, which can grow at a ph of 1.8