Chapter V: Classification

The arrangement of living organisms in groups according to their resemblances and the adoption of _fixed names_ is of the greatest advantage in their scientific study. For animal forms and for the higher plants this classification is gradually becoming standardized through the International Congress of Zoölogists and of Botanists respectively. Unfortunately, the naming of the bacteria has not as yet been taken up by the latter body, though announced as one of the subjects for the Congress of 1916 (postponed on account of the war). Hence there is at present no system which can be regarded as either fixed or official.

Since Müller’s first classification of “animalcules” in 1786 numerous attempts have been made to solve the problem. Only those beginning with Ferdinand Cohn (1872-75) are of any real value. As long as bacteria are regarded as plants it appears that the logical method is to follow the well-established botanical principles in any system for naming them. Botanists depend on morphological features almost entirely in making their distinctions. The preceding chapters have shown that the minute plants which are discussed have very few such features. They are, to recapitulate, _cell wall_, _protoplasm_, _vacuoles_, _metachromatic granules_, _capsules_, _flagella_, _spores_, _cell forms_ and _cell groupings_. Most bacteria show not more than three or four of these features, so that it is impossible by the aid of morphology alone to distinguish from each other the large number of different kinds which certainly exist. In the various systems which are conceded to be the best these characteristics do serve to classify them down to genera, leaving the “species” to be determined from their _physiological_ activities. One of these systems was adopted by the laboratory section of the American Public Health Association and by the Society of American Bacteriologists and was practically the standard in this country until superseded by the Society’s own classification. It is that of the German Bacteriologist Migula and is given below for comparison. Since practically the entire discussion in this book is concerned with the first three families the generic characteristics in these only will be given. The full classification as well as a thorough discussion of this subject is given in Lafar’s _Handbuch_, whence the following is adopted:

ORDER I. Eubacteria.

Cells without nuclei, free from sulphur granules and from bacteriopurpurin (p. 112); colorless, or slightly colored.

1. Family: COCCACEÆ (Zopf) Migula, all cocci.

{Genus 1. _Streptococcus_ Billroth:
{ division in one plane only (Fig. 49).
Non-flagellated, { „ 2. _Micrococcus_ (Hallier) Cohn:
Non-motile { division in two planes only (Fig. 50).
{ „ 3. _Sarcina_ Goodsir:
{ division in three planes only (Fig. 51).

{ „ 4. _Planococcus_ Migula:
Flagellated, { division in two planes only.
motile { „ 5. _Planosarcina_ Migula:
{ division in three planes only.

2. Family: BACTERIACEÆ Migula, all bacilli.

Genus 1. _Bacterium_ (Ehrenberg) Migula: no flagella; non-motile.
„ 2. _Bacillus_ (Cohn) Migula: flagella peritrichic (Fig. 52).
„ 3. _Pseudomonas_ Migula: flagella at the end:
monotrichic, lophotrichic, amphitrichic (Fig. 53).

3. Family: SPIRILLACEÆ Migula, all spirilla.

{Genus 1. _Spirosoma_ Migula:
{ non flagellated; non-motile.
{ „ 2. _Microspira_ (Schrœter) Migula:
Cells stiff { flagella one to three at the end (Fig. 54).
{ „ 3. _Spirillum_ (Ehrenberg) Migula:
{ flagella more than three
{ at the end (Fig. 55).

Cell flexible { „ 4. _Spirochæta_ Ehrenberg:
{ motile; no flagella (Fig. 56).

4. Family: CHLAMYDOBACTERIACEÆ.

Cells cylindrical in long threads and surrounded by a sheath. Reproduction also by gonidia formed from an entire cell.

Genus 1. _Chlamydothrix_ Migula (Fig. 57).
„ 2. _Crenothrix_ Colin (Fig. 58).
„ 3. _Pragmidiothrix_ Engler.
„ 4. _Spherotilus_ (including Cladothrix).

ORDER II. THIOBACTERIA: SULPHUR BACTERIA.

Cells without a nucleus, but containing sulphur granules, may be colorless or contain bacteriopurpurin and be colored reddish or violet.

1. Family BEGGIATOACEÆ.

Genus 1. _Thiothrix_ Winogradsky.

„ 2. _Beggiatoa_ Trevisan. Of interest since it is without a
sheath, is motile, but without flagella (Fig. 59).

2. Family RHODOBACTERIACEÆ.

This has five subfamilies and twelve genera, most of which are due to the Russian bacteriologist Winogradsky who did more work than anyone else with the sulphur bacteria.

THE CLASSIFICATION OF THE SOCIETY OF AMERICAN BACTERIOLOGISTS.

The Committee on Classification of the Society of American Bacteriologists at the meeting held in December, 1919, submitted its final report. This report has not been formally adopted as a whole, but in all probability will be substantially as outlined below. This outline does not attempt to give the detailed characterizations of the different groups as defined by the committee, but does show the names to be applied to the commoner organisms. These organisms are included in the 4th and 5th orders. Details of the first three orders have not been worked out. They are listed merely for completeness.

CLASS SCHIZOMYCETES.

Unicellular, chlorophyl-free plants, reproducing by transverse division (some forms by gonidia also).

ORDERS:

A. Myxobacteriales--Cells united during vegetative stage into
a pseudo-plasmodium which passes over into a highly developed
cyst-producing resting stage.

B. Thiobacteriales--Sulphur bacteria.

C. Chlamydobacteriales--Iron bacteria and other sheathed bacteria.

D. Actinomycetales--Actinomyces, tubercle and diphtheria bacilli.

E. Eubacteriales--All the other common bacteria.

GENERA OF ORDERS D AND E.

D. ACTINOMYCETALES--
FAMILY I. ACTINOMYCETACEÆ Buchanan, 1918.
Genus 1. _Actinobacillus_, Brampt, 1900.
Type species, _Actinobacillus lignieresi_ Brampt, 1900.
Genus 2. _Leptotrichia_ Trevisan, 1879.
Type species, _Leptotrichia buccalis_ (Robin, 1847) Trevisan.
Genus 3. _Actinomyces_ Harz, 1877.
Type species, _Actinomyces bovis_ Harz.
Genus 4. _Erysipelothrix_ Rosenbach, 1909.
Type species, _Erysipelothrix rhusiopathiæ_ (Kitt, 1893)
Rosenbach, swine erysipelas.
FAMILY II. MYCOBACTERIACEÆ Chester, 1897.
Genus 1. _Mycobacterium_ Lehmann and Neumann, 1896.
Type species, _Mycobacterium tuberculosis_ (Koch, 1882) L.
and N.
Genus 2. _Corynebacterium_ Lehmann and Neumann, 1896.
Type species, _Corynebacterium diphtheriæ_ (Loeffler, 1882)
L. and N.
Genus 3. _Fusiformis_ Hoelling, 1910.
Type species, _Fusiformis termitidis_ Hoelling. Vincent’s
angina.
Genus 4. _Pfeifferella_ Buchanan, 1918.
Type species, _Pfeifferella mallei_ (Loeffler, 1896) Buchanan.
Glanders bacillus.

E. EUBACTERIALES
FAMILY I--NITROBACTERIACEÆ--Proto- or autotrophic for N
or C and sometimes for both (except Acetobacter).
TRIBE I--NITROBACTEREÆ--autotrophic for C.
Genus 1. _Hydrogenomonas_ Jensen, 1909.
Type species, _Hydrogenomonas pantotropha_ (Kaserer, 1906)
Jensen; oxidizes free H.
Genus 2. _Methanomonas_ Jensen, 1909.
Type species, _Methanomonas methanica_ (Söhngen) Jensen;
oxidizes CH₄.
Genus 3. _Carboxydomonas_ Jensen, 1909.
Type species, _Carboxydomonas oligocarbophila_ (Beijerinck
and Van Delden, 1903) Jensen; oxidizes CO.
Genus 4. _Acetobacter_ Fuhrman, 1905.
Type species, _Acetobacter aceti_ (Thompson, 1852) Fuhrman;
oxidizes alcohol to acetic acid.
Genus 5. _Nitrosomonas_ Winogradsky, 1892.
Type species, _Nitrosomonas europoea_ Winogradsky; oxidizes
ammonia or ammonium salts to nitrous acid,
hence nitrites.
Genus 6. _Nitrobacter_ Winogradsky, 1892.
Type species, _Nitrobacter Winogradskyi_ Committee of 1917;
oxidizes nitrous acid (nitrites)
to nitric acid (nitrates).
TRIBE II--AZOTOBACTEREÆ--prototrophic for N.
Genus 7. _Azotobacter_ Beijerinck, 1901; large, free-living,
aerobic N absorbers.
Type species, _Azotobacter chroococcum_ Beijerinck.
Genus 8. _Rhizobium_ Frank, 1889.
Type species, _Rhizobium leguminosarum_ Frank; root tubercle
bacteria of legumes.
FAMILY II--PSEUDOMONADACEÆ, Committee of 1917.
Genus 1. _Pseudomonas_ Migula, 1894.
Type species, _Pseudomonas violacea_ (Schroeter, 1872) Migula.
FAMILY III--SPIRILLACEÆ Migula, 1894--all spiral bacteria.
Genus 1. _Vibrio_ Müller, 1786, emended by E. F. Smith, 1905.
Type species, _Vibrio choleræ_ (Koch, 1884) Schroeter, 1886.
Genus 2. _Spirillum_ Ehrenberg, 1830, emended Migula, 1894.
Type species, _Spirillum undula_ (Müller, 1786) Ehrenberg.
FAMILY IV--COCCACEÆ Zopf, 1884, emended Migula, 1894--all cocci.
Tribe I--NEISSEREÆ.
Genus 1. _Neisseria_ Trevisan, 1885.
Type species, _Neisseria gonorrhoeae_ Trevisan.
Tribe II--STREPTOCOCCEÆ Trevisan, 1889.
Genus 2. _Diplococcus_ Weichselbaum, 1886.
Type species, _Diplococcus pneumoniae_ Weichselbaum.
Genus 3. _Leuconostoc_ Van Tieghem, 1878.
Type species, _Leuconostoc mesenterioides_ (Cienkowski) Van
Tieghem.
Genus 4. _Streptococcus_ Rosenbach, 1884; emended Winslow
and Rogers, 1905.
Type species, _Streptococcus pyogenes_ Rosenbach.
Tribe III--MICROCOCCEÆ Trevisan, 1889.
Genus 5. _Staphylococcus_ Rosenbach, 1884; animal parasites.
Type species, _Staphylococcus aureus_ Rosenbach.
Genus 6. _Micrococcus_ Cohn, 1872, emended Winslow and Rogers,
1905. Facultative parasites or saprophytes.
Type species, _Micrococcus luteus_ (Schroeter, 1872) Cohn.
Genus 7. _Sarcina_ Goodsir, 1842, emended Winslow and
Rogers, 1905.
Type species, _Sarcina ventriculi_ Goodsir.
Genus 8. _Rhodococcus_ Zopf, 1891, emended Winslow and
Rogers, 1905; cocci with red pigment.
Type species, _Rhodococcus rhodochrous_ Zopf.
FAMILY V--BACTERIACEÆ Cohn, 1872, emended by Committee of 1917;
bacilli without spores not above included.
Tribe I--CHROMOBACTEREÆ Committee of 1919; producing red or
violet pigment, mainly water forms.
Genus 1. _Erythrobacillus_ Fortineau, 1905.
Type species, _Erythrobacillus prodigiosus_
(Ehrenberg, 1848) Fortineau.
Genus 2. _Chromobacterium_ Bergonzini, 1881.
Type species, _Chromobacterium violaceum_ Bergonzini.
Tribe II--ERWINEÆ Committee 1919; plant pathogens.
Genus 3. _Erwinia_ Committee 1917.
Type species, _Erwinia amylovora_ (Burrill, 1883) Committee
1917.
Tribe III--ZOPFEÆ Committee of 1919; Gram +, no pigment,
non-carbohydrate-fermenting.
Genus 4. _Zopfius_ Wenner and Rettger, 1919.
Type species, _Zopfius zopfii_ (Kurth) Wenner and Rettger.
Tribe IV--BACTEREÆ Committee of 1919; Gram -, carbohydrate
fermenters.
Genus 5. _Proteus_ Hauser, 1885; liquefy gelatin.
Type species, _Proteus vulgaris_ Hauser.
Genus 6. _Bacterium_ Ehrenberg, 1828, emended Jensen, 1909;
liquefy gelatin rarely.
Type species, _Bacterium coli_.
Tribe VI--LACTOBACILLEÆ Committee of 1919; Gram +, high acid,
thermophils.
Genus 7. _Lactobacillus_ Beijerinck, 1901.
Type species, _Lactobacillus caucasicus_ (Kern?) Beijerinck;
Bulgarian bacillus.
Tribe VI--PASTEURELLEÆ Committee of 1919; organisms of
hemorrhagic septicemia.
Genus 8. _Pasteurella_ Trevisan, 1888.
Type species, _Pasteurella cholerae-gallinarum_
(Flügge, 1886); Trevisan.
Tribe VII--HEMOPHILEÆ Committee of 1917; require hemoglobin for
growth.
Genus 9. _Hemophilus_ Committee of 1917.
Type species, _Hemophilus influenzae_ (Pfeiffer, 1893)
Committee of 1917.
FAMILY VI--BACILLACEÆ Fischer, 1895. Spore forming rods.
Genus 1. _Bacillus_ Cohn, 1872; aerobic, no change of form
around the spore.
Type species, _Bacillus subtilis_ Cohn.
Genus 2. _Clostridium_ Prazmowski, 1880; anaërobic, frequently
enlarged around spore.
Type species, _Clostridium butyricum_ Prazmowski.

As compared with Migula’s classification it is to be noted that there are 38 genera listed by the Committee instead of 13 in the same general groups.

The following list of _Genera conservanda_ submitted by the Committee was formally adopted by the Society and these are therefore its official names for the organisms included in these genera.

_Acetobacter_ Fuhrman
_Actinomyces_ Harz
_Bacillus_ Cohn
_Bacterium_ Ehrenberg
_Chromobacterium_ Bergonzini
_Clostridium_ Prazmowski
_Erythrobacillus_ Fortineau
_Leptotrichia_ Trevisan
_Leuconostoc_ Van Tieghem
_Micrococcus_ Cohn
_Rhizobium_ Frank
_Sarcina_ Goodsir
_Spirillum_ Ehrenberg
_Staphylococcus_ Rosenbach
_Streptococcus_ Rosenbach
_Vibrio_ Müller

_It is greatly to be desired that the Society’s Classification when finally completed shall become the standard in the United States at least._

_Such names as have been adopted by the Society are used throughout this work._

The Committee also submitted the following artificial key for determining the genera in the two orders _ACTINOMYCETALES AND EUBACTERIALES_:

A--Typically filamentous forms _Actinomycetacae_
B--Mycelium and conidia formed _Actinomyces_
BB--No true mycelium
C--Cells show branching
D--Gram negative _Actinobacillus_
DD--Gram positive _Erysipelothrix_
CC--Cells never branch. Gram positive threads later fragmenting
into rods _Leptotrichia_
AA--Typically unicellular forms (though chains of cells may occur)
B--Cells spherical--_COCCACEÆ_
C--Parasitic forms (except Leuconostoc), cells generally grouped
in pairs or chains, never in packets, generally active
fermenters.
D--Cells in flattened coffee-bean-like pairs, gram -.
_Neisseria_
DD--Not as D
E--Saprophytes in zoögloea masses in sugar solutions.
_Leuconostoc_
EE--Not as E. Gram +.
F--Cells in lanceolate pairs or in chains. Growth on
media not abundant.
G--Cells in lanceolate pairs. Inulin generally fermented.
_Diplococcus_
GG--Cells in chains. Inulin not generally fermented.
_Streptococcus_
FF--Cells in irregular groups. Growth in media fairly
vigorous. White or orange pigment.
_Staphylococcus_
CC--Saprophytic forms. Cells in irregular groups or packets,
not in chains. Fermentative powers low.
D--Packets _Sarcina_
DD--No packets.
E--Yellow pigment _Micrococcus_
EE--Red pigment _Rhodococcus_
BB--Rods:
C--Spiral rods
D--Short, comma-like rods. One to three flagella.
_Vibrio_
DD--Long spirals. Five to twenty flagella. _Spirillum_
CC--Straight rods.
D--No endospores.
E--Rods of irregular shape or showing branched or filamentous
involution forms.
F--Cells irregular in shape. Staining unevenly. Animal
parasites.
G--Acid fast _Mycobacterium_
GG--Not acid fast.
H--Cells elongated, fusiform _Fusiformis_
HH--Cells not elongated, sometimes branching.
I--Gram positive. Slender, sometimes club-shaped.
_Corynebacterium_
II--Gram negative. Rods sometimes form threads.
Characteristic honey-like growth on potato.
_Pfeifferella_
FF--Cells staining unevenly but with branched or filamentous
forms at certain stages. Never acid fast.
Not animal parasites.
G--Metabolism simple, growth processes involving oxidation
of alcohol or fixation of free N (latter in symbiosis
with green plants).
H--Cells minute. Symbiotic in roots of legumes.
_Rhizobium_
HH--Oxidizing alcohol. Branching forms common.
_Acetobacter_
GG--Not as G. Proteus-like colonies.
H--Not attacking carbohydrates _Zopfius_
HH--Fermenting glucose and sucrose at least.
_Proteus_
EE--Regularly formed rods.
F--Metabolism simple, growth processes involving oxidation
of C, H, or their simple compounds or the fixation
of free N.--_NITROBACTERIACEÆ._
G--Fixing N or oxidizing its simple compounds.
H--Fixing N, cells large, free in soil _Azotobacter_
HH--Oxidizing N compounds.
I--Oxidizing NH₄ compounds _Nitrosomonas_
II--Oxidizing nitrites _Nitrobacter_
GG--Not as G.
H--Oxidizing free H _Hydrogenomonas_
HH--Oxidizing simple C compounds, not free H.
I--Oxidizing CO _Carboxydomonas_
II--Oxidizing CH₄ _Methanomonas_
FF--Not as F.
G--Flagella usually present, polar--_PSEUDOMONADACEÆ_
_Pseudomonas_
GG--Flagella when present peritrichic--_BACTERIACEÆ_
H--Parasitic forms showing bi-polar staining.
_Pasteurella_
HH--Not as H.
I--Strict parasites growing only in presence
of hemoglobin
_Hemophilus_
II--Not as I.
J--Water forms producing red or violet pigment.
K--Pigment red _Erythrobacillus_
KK--Pigment violet _Chromobacterium_
JJ--Not as J.
K--Plant pathogens _Erwinia_
KK--Not plant pathogens.
L--Gram +, forming large amount of acid
from carbohydrates, sometimes CO₂,
never H _Lactobacillus_
LL--Gram -, forming H as well as CO₂ if
gas is produced _Bacterium_
DD--Endospores present--_BACILLACEÆ_
E--Aerobes, rods not swollen at sporulation. _Bacillus_
EE--Anaërobes, rods swollen at sporulation. _Clostridium_