16 MODERN FOOD MICROBIOLOGY Table 21 Subclasses of the to Which Man y Foodborne era Belong.Campylobacter and Helicobacter Belong to the 8-Subclass Alpha Beta Gamma Acetobacter Acidovorax Acinetobacte Asaia ne Aeromona imonas luconobacter Comamonas acteriodes acoccu cter Flavobacterium Pandorae alomo onas(plant pathogens) Telluria Pseudoalteromonas udomona Wautersia ium Xylophilus hewanella otrophomonas Xanthomonas Xylella Gram-negative bacteria.The class is divided into five subclasses designatedB.,etcThe sub classes are defined on the basis of their 16S rRNA sequences. By extensive use of signature ns)of diff ent proteins,an evolutionary relati ot th acteria h propose en sugge fo siti (e.g Micm rim Rubrobacter).and then by Dei us.Ther N three gr ups that are not foodborne (not listed here).and then the Proteobceri with and followed by a,B,andy It has been stressed that these groups are related to each other in a linear rather than a tree-like manner.20 It can be seen from Table 2-1 that most foodborne bacteria (especially foodbome the -ubc The earliest prokaryoem r.Som that the bacterial ger ran this list with those in Table 22 e bacicawhat prrec oblematic si the list may be expected to change as more phylogenetic data are employed
16 Modern Food Microbiology Table 2–1 Subclasses of the Proteobacteria to Which Many Foodborne Genera Belong. Campylobacter and Helicobacter Belong to the δ-Subclass Alpha Beta Gamma Acetobacter Acidovorax Acinetobacter Asaia Alcaligenes Aeromonas Brevundimonas Burkholderia Alteromonas Devosia Chromobacterium Azomonas Gluconobacter Comamonas Bacteriodes Paracoccus Delftia Carnimonas Pseudoaminobacter Hydrogenophaga Enterobacteriaceaea Sphingomonas Janthinobacterium Flavobacterium Xanthobacter Pandoraea Halomonas Zymomonas Pseudomonas (plant pathogens) Moraxella Ralstonia Plesiomonas Telluria Pseudoalteromonas Variovorax Pseudomonas Vogesella Psychrobacter Wautersia Photobacterium Xylophilus Shewanella Stenotrophomonas Vibrio Xanthomonas Xylella aInclude Escherichia, Citrobacter, Salmonella, Shigella, Proteus, Raoultella, Proteus, Klebsiella, Edwardsiella, etc. Gram-negative bacteria.43 The class is divided into five subclasses designated α, β, γ , etc. The subclasses are defined on the basis of their 16S rRNA sequences.54–56 By extensive use of signature sequences (conserved inserts and deletions) of different proteins, an evolutionary relationship of the Proteobacteria has been proposed.20 It has been suggested that the first eubacteria were low G + C Gram positives (e.g., Clostridium, Bacillus, Lactobacillus), followed by high G + C Gram positives (e.g., Micrococcus, Propionibacterium, Rubrobacter), and then by Deinococcus-Thermus. Next arose three groups that are not foodborne (not listed here), and then the Proteobacteria with and σ followed by α, β, and γ . 20 It has been stressed that these groups are related to each other in a linear rather than a tree-like manner.20 It can be seen from Table 2–1 that most foodborne bacteria (especially foodborne pathogens) belong to the γ -subclass. The earliest prokaryotes are estimated to have arisen 3.5–3.8 billion years ago.20 Some of the important genera known to occur in foods are listed below in alphabetical order. Some are desirable in certain foods; others bring about spoilage or cause gastroenteritis. It should be noted that the bacterial genera in this list along with those in Table 2–2 are now somewhat problematic since most were defined largely on phenotypic data. They are placed here mainly on historical reports but the list may be expected to change as more phylogenetic data are employed
Taxonomy,Role,and Significance of Microorganisms in Foods 17 Bacteria Proteus Hafnia Kocuria Serratia Campylobacter Mon Paenibacillus Molds altemaria Penicillium Mucor Xeromvces Yeasts Cryptococcus Protozoa ytica Toxoplasma gondii Giardia lamblia PRIMARY SOURCES OF MICROORGANISMS FOUND IN FOODS The genera and species previously listed are among the most important normally found in food products.Each genus has its own particular nutritional requirements.and each is affected in predictable ways by the parameters of its environment.Eight environmental sources of organisms to foods are listedbelowand theselong with the generaofbacteriaand protozoanotedare presentednTable 2-2 source envionments. that inhabit both have a lot cteria and th ion oft ung and later enter water bodies when it rains.They also enter water when rainwater flows over soils into bodies of water.Aquatic organisms can be deposited onto soils through the actions of cloud formation and subsequent rainfall.This common cycling results in soil and aquatic organisms being one and the same to a large degree.Some aquatic organisms,however,are unable topersist in soils.especially those that are indigenous to marine waters.Alreromonas spp.are aquatic forms that require seawater salinity
Taxonomy, Role, and Significance of Microorganisms in Foods 17 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 PRIMARY SOURCES OF MICROORGANISMS FOUND IN FOODS The genera and species previously listed are among the most important normally found in food products. Each genus has its own particular nutritional requirements, and each is affected in predictable ways by the parameters of its environment. Eight environmental sources of organisms to foods are listed below, and these, along with the genera of bacteria and protozoa noted, are presented in Table 2–2 to reflect their primary food-source environments. Soil and Water. These two environments are placed together because many of the bacteria and fungi that inhabit both have a lot in common. Soil organisms may enter the atmosphere by the action of wind and later enter water bodies when it rains. They also enter water when rainwater flows over soils into bodies of water. Aquatic organisms can be deposited onto soils through the actions of cloud formation and subsequent rainfall. This common cycling results in soil and aquatic organisms being one and the same to a large degree. Some aquatic organisms, however, are unable to persist in soils, especially those that are indigenous to marine waters. Alteromonas spp. are aquatic forms that require seawater salinity
爻×× ×××× ××××××× × ×× ××爻炎炎××× X X ××X×××× ×X××× x×x ×交× ×爻×x炎×爻×爻××爻爻爻交××× 爻炎×支× XXX
Table 2–2 Relative Importance of Eight Sources of Bacteria and Protozoa to Foods Soil and Food Gastrointestinal Food Animal Animal Air and Organisms Water Plants/Products Utensils Tract Handlers Feeds Hides Dust Bacteria Acinetobacter XX X X X X Aeromonas XXa X Alcaligenes X X XX X Alteromonas XXa Arcobacter X Bacillus XXb X X X X X XX Brochothrix XX X Brevibacillus X X X Burkholderia XX Campylobacter XX X Carnobacterium XXX Citrobacter X XX X XX Clostridium XXb X X X X X X XX Corynebacterium XX b X X X XX Enterobacter X XX X X X Enterococcus X X X XX X X X X Erwinia X XX X Escherichia X X XX X Flavobacterium X XX X Hafnia X X XX Kocuria X X X X XX Lactococcus XX X X X Lactobacillus XX X X X Leuconostoc XX X X X Listeria X XX X X X Micrococcus X X X X X X XX Mycobacteriumc X Moraxella X X X Mycobacterium 18
××××× + ×爻× ××× ×××交×交×交××××××爻 ××××× × ××爻×爻××××××爻 爻×× × 炎×××炎炎××××炎炎××炎炎炎 O L O 19
Paenibacillus XX X X XX Pandoraea X Pectobacterium X XX Pantoea XX X Pediococcus XX X X X Proteus X X XX X X Pseudomonas XX X X X X Psychrobacter XX X X X Salmonella XX XX Serratia X X X X XX Shewanella X X Sphingomonas X X Shigella XX Stenotrophomonas X XX Staphylococcus X XX X Vagococcus XX XX Vibrio XX X Weissella XX X Yersinia XX X Protozoa C. cayetanensis XX X C. parvum XX X X E. histolytica XX X X G. lamblia XX X X T. gondii X XX Note: XX indicates a very important source. aPrimarily water bPrimarily soil. cNontuberculous. 19
20 MODERN FOOD MICROBIOLOGY water has beeni ontamination of fresh Plants and Plant Products.It may be assumed that many or most soil and water organisms con- taminate plants.However,only a relatively small number find the plant environment suitable to their overall well-being.Those that persist on plant products do so by virtue of a capacity to adhere to plant surfaces so that they are not easily washed away and because they are able to obtain their nutritional requirements.Notable among these are the lac c acid bactera and some yeasts.Among others that are plants are bacteral ant pathogens in t cterum,Cur of molds ingal pathogens among several Whn vegctables are harvested in ners ade oneocind some or all of the surface organisms on the products to contaminate contact surfaces.As more and more vegetables are placed in the same containers.a normalization of the microbiota would be expected to occur.In a similar way.the cutting block in a meat market along with cutting knives and grinders are conadmsamplesnd thisprceadsto buildup oforanimsthussng fairly cons ant lever c of meat-borne organisms The in when P lluted water i ens such as salmonellae.Any or all of the Enterobacteriaceae may be expected in fecal wastes,along with intestinal pathogens,including the five protozoal species already listed. Food Handlers.The microbiota on the hands and outer garments of handlers generally reflect the environment and habits of individuals,and the organisms in question may be those from soil,water. dust.and er environmer source sources al e thos the mouth. on the Animal Fe This is a sou salmonellae to poultry and other farm animals.In the case of some silage it is a known source of listeria monocytogenes to dairy and meat animals The organisms in dry animal feed are spread throughout the animal environment and may be expected to occur on animal hides Animal Hides.In the case of milk cows,the types of organisms found in raw milk can be areflection of the biota of the sare n wed in milking and of the gene of such a the ud hide,organismscan contaminate the Air and Dust.Although most of the rganisms listed in Table 2-2 may at times be found in air and dust in a food-processing operation.the ones that can persist include most of the Gram-positive organisms listed.Among fungi,a number of molds may be expected to occur in air and dust,along with some yeasts.In general,the types of organisms in air and dust would be those that are constantly reseeded to the environment.Air ducts are not unimportant sources. SYNOPSIS OF COMMON FOODBORNE BACTERIA These synopses are provided to give the reader glimpses of bacterial groups that are discussed throughout the textbook.They are not meant to be used for culture identifications.For the latter,one or
20 Modern Food Microbiology for growth and would not be expected to persist in soils. The bacterial biota of seawater is essentially Gram-negative, and Gram-positive bacteria exist there essentially only as transients. Contaminated water has been implicated in Cyclospora contamination of fresh raspberries. Plants and Plant Products. It may be assumed that many or most soil and water organisms contaminate plants. However, only a relatively small number find the plant environment suitable to their overall well-being. Those that persist on plant products do so by virtue of a capacity to adhere to plant surfaces so that they are not easily washed away and because they are able to obtain their nutritional requirements. Notable among these are the lactic acid bacteria and some yeasts. Among others that are commonly associated with plants are bacterial plant pathogens in the genera Corynebacterium, Curtobacterium, Pectobacterium, Pseudomonas, and Xanthomonas; and fungal pathogens among several genera of molds. Food Utensils. When vegetables are harvested in containers and utensils, one would expect to find some or all of the surface organisms on the products to contaminate contact surfaces. As more and more vegetables are placed in the same containers, a normalization of the microbiota would be expected to occur. In a similar way, the cutting block in a meat market along with cutting knives and grinders are contaminated from initial samples, and this process leads to a buildup of organisms, thus ensuring a fairly constant level of contamination of meat-borne organisms. Gastrointestinal Tract. This biota becomes a water source when polluted water is used to wash raw food products. The intestinal biota consists of many organisms that do not persist as long in waters as do others, and notable among these are pathogens such as salmonellae. Any or all of the Enterobacteriaceae may be expected in fecal wastes, along with intestinal pathogens, including the five protozoal species already listed. Food Handlers. The microbiota on the hands and outer garments of handlers generally reflect the environment and habits of individuals, and the organisms in question may be those from soil, water, dust, and other environmental sources. Additional important sources are those that are common in nasal cavities, the mouth, and on the skin, and those from the gastrointestinal tract that may enter foods through poor personal hygiene practices. Animal Feeds. This is a source of salmonellae to poultry and other farm animals. In the case of some silage, it is a known source of Listeria monocytogenes to dairy and meat animals. The organisms in dry animal feed are spread throughout the animal environment and may be expected to occur on animal hides. Animal Hides. In the case of milk cows, the types of organisms found in raw milk can be a reflection of the biota of the udder when proper procedures are not followed in milking and of the general environment of such animals. From both the udder and the hide, organisms can contaminate the general environment, milk containers, and the hands of handlers. Air and Dust. Although most of the organisms listed in Table 2–2 may at times be found in air and dust in a food-processing operation, the ones that can persist include most of the Gram-positive organisms listed. Among fungi, a number of molds may be expected to occur in air and dust, along with some yeasts. In general, the types of organisms in air and dust would be those that are constantly reseeded to the environment. Air ducts are not unimportant sources. SYNOPSIS OF COMMON FOODBORNE BACTERIA These synopses are provided to give the reader glimpses of bacterial groups that are discussed throughout the textbook. They are not meant to be used for culture identifications. For the latter, one or