Publisher Summary Thousands of identification methods for medically important bacteria have been described in the chapter. The overwhelming majority represent modifications of tests discovered in the first half of this century, when the foundation of modern taxonomy was laid. Selection of the best of these methods or replacement of an old test with an improved one requires extensive comparative trials. In choosing methods, an enormous number of commercial reagents, dehydrated or complete media and multitest systems also have to be considered. In general, any method is satisfactory that gives accurate and reproducible results. Tests used in routine clinical and public health bacteriology should be suitable for a tolerably rapid and reliable identification. To determine their characteristics, bacteria must be grown in pure culture, which is a group of organisms that have developed from a single cell or from a single clump of similar cells.

1 Classical and Rapid Identification Methods for Medically Important Bacteria

Bacterial decomposition of urea has been especially useful in distinguishing between members of the Proteus group and other fecal organisms encountered in stool examinations. Originally, the reactions of these organisms on urea were determined by the use of sterile urine as a culture medium, and only recently have media of known composition been employed (Rustigian and Stuart, 1941). Of the media of known composition, those of Rustigian and Stuart and of Ferguson and Hook (1943) have been found suitable to differentiate between Proteus and other organisms believed to be urease-negative. In considering the formulae of the two media mentioned, it is obvious that the medium of Ferguson and Hook (urea, 2 per cent; phosphate buffer; NaCl, 0.5 per cent; and ethyl alcohol, 1.0 per cent) is of such a nature that only an organism capable of utilizing urea as a sole source of nitrogen would grow. The possibility therefore arises that this medium would not detect organisms which could hydrolyze urea but which could not utilize the liberated ammonia as a source of nitrogen. In such a case, no growth would occur, and the organism would be considered urease-negative. The medium of Rustigian and Stuart (urea, 2 per cent; yeast extract, 0.01 per cent; and phosphate buffer), because of the extremely small amount of nutritive material present, also is subject to the same theoretical limitations, particularly in view of the fact that an organism incapable of utilizing ammonia is probably forced to use the yeast extract not only as a nitrogen source but also as a carbon source. If these materials are exhausted before the organism shows appreciable growth, its ability to hydrolyze urea cannot be adequately determined. The high buffer capacity of the medium would also mask slight urease activity if such an organism were capable of initial growth in the medium. These two media, however, as stated by the authors, were designed for the detection of Proteus organisms, and for this purpose they are well suited. It was thought possible, however, that if a medium were devised which eliminated the necessity of an organism's utilizing ammonia as a sole source of nitrogen, other organisms of the fecal group could be detected which would hydrolyze urea.

Urea Decomposition as a Means of Differentiating Proteus and Paracolon Cultures from Each Other and from Salmonella and Shigella Types.

This review presents the current taxonomy of the genera Proteus, Providencia, and Morganella, along with the current methods for the identification of each species within the three genera, incorporating both conventional biochemical and commercial methods. While all of these organisms are ubiquitous in the environment, individual case reports and nosocomial outbreak reports that demonstrate their ability to cause major infectious disease problems are presented. Lastly, anticipated antimicrobial susceptibility patterns are reviewed. Many of these organisms are easily controlled, but the advent of newer and more powerful antimicrobial agents has led to some problems of which laboratorians need to be aware.

Classification, Identification, and Clinical Significance of Proteus, Providencia, and Morganella

Luria explored the question of bacterial hybridization only briefly, but established that these two types of intestinal bacteria
 could mate and produce hybrids possessing characteristics of each. This had implications for laboratory diagnosis, raising
 the possibility that a hybrid possessing Shigella's pathogenic qualities could test as an E. coli, or vice-versa.

Hybridization between Escherichia coli and Shigella.

Although the first Aeromonas strain was described by Zimmermann as early as in 1890, it took 60 years until Caselitz established human pathogenicity of strains then called "Vibrio jamaicensis". Since then, and especially in the last 10 years, there have been increasing numbers of reports on different infections caused by members of the genus Aeromonas. These include sepsis; meningitis; cellulitis; necrotizing fasciitis; ecthyma gangrenosum; pneumonia; peritonitis; conjunctivitis; corneal ulcer; endophthalmitis; osteomyelitis; suppurative arthritis; myositis; subphrenic abscess; liver abscess; cholecystitis and/or ascending cholangitis; urinary tract infection; endocarditis; ear, nose, and throat infections; balanitis; etc. The role of Aeromonas in gastrointestinal disease is very controversial. Increasing epidemiological data suggest that these organisms play a major role in enteric infections, but so far enteropathogenicity has not been demonstrable in experiments where volunteers were given high numbers of Aeromonas possessing different virulence factors. Virulence factors include hemolysin(s), enterotoxin(s), hemagglutinins, invasivity, and others; but these are not found more frequently in strains isolated from patients with diarrhea than from healthy controls. Whether there is a correlation between species and disease remains to be elucidated and requires more information about the taxonomy of this genus.

Aeromonas as a human pathogen.

In the bacteriological laboratories of Brown University and the Connecticut State Department of Health, Bureau of Laboratories, we have been engaged in a systematic study of the biochemical and serological relationships of the coliform and related bacteria since April 1937. During this time over 12,000 normal and aberrant coliform cultures have been isolated. The IMViC reactions and in addition cellobiose fermentation were determined for all these cultures. A wide variety of biochemical types were encountered ranging from those positive in all five tests to a few weakly positive in only one of the IMViC tests. The ability of more than 3,500 of these cultures to ferment glucose, lactose, sucrose, salicin, maltose and mannitol was determined. Normal coliform cultures negative in sucrose or salicin or both were commonly found. Strains failing to ferment maltose were not anticipated but several were isolated from widely different sources. Mannitol fermentation appeared to be a constant characteristic of normal coliforms but among the last 500 isolations two, otherwise normal, mannitol-negative strains were obtained. Coliform cultures fermenting lactose slowly or not at all, but normal in other respects, were frequently encountered. We have obtained from both rapid and slow lactose-fermenting coliforms variants which were anaerogenic in lactose only or in all carbohydrates. Some of these variants have remained constant for 2 years, one for more than 3 years. In addition motile and nonmotile, indolepositive cultures were found which produced no gas from carbohydrates when originally isolated. Many such cultures would be classed as Eberthella or Shigella, particularly when the fermentation of lactose, sucrose or salicin was slow or absent. After varying periods of laboratory cultivation many of these strains produced gas. Cultures that appeared to be non-gas-forming but which could not be identified as known Eberthella or Shigella have been included in the paracolon group since they could be anaerogenic variants of coliforms. These exceptions and others are a serious handicap to the practical bacteriologist because strains not infrequently defy classification in any of the recognized sections of the coliform group. The tendency to disregard such exceptions for the most part is justifiable but occasionally this might be a mistake. Stuart, Mickle and Borman (1940) proposed the term \"aberrant\" coliforms for cultures not fermenting lactose, producing acid only, or requiring more than 48 hours for the production of 20 per cent gas when the unusual fermenting characteristics of such strains are relatively stable. Aberrant coliforms are frequently isolated from such sources as water with an excellent sanitary survey, soils from rigidly

Biochemical and Antigenic Relationships of the Paracolon Bacteria.

At the Third International Congress for Microbiology St. John-Brooks and Rhodes1 suggested a simplification of the taxonomy of the Proteus genus. On the basis of maltose fermentation and indol production 3 species were set up in the genus, indologenes (vulgaris), morganii, and anindologenes (mirabilis). Proteus americanus and Proteus ammoniœ were considered variants of anindologenes. Proteus hydrophilus, Proteus pseudovaleriei, and Proteus icthyosmius were excluded from the genus on the basis of their ability to ferment mannitol.The decomposition of urea with formation of ammonia is one of the major criteria for the determination of the Proteus group (Bergey).2 This phenomenon, however has received relatively little attention, particularly when recent additions have been made to this genus. From a review of the literature it appears that the action on urea of Proteus morganii, Proteus hydrophilus, Proteus icthyosmius, and Proteus bombycis is unknown.Investigators, with few exceptions, have used sterile ur...

http://ebm.sagepub.com/content/47/1/108.full.pdf

Decomposition of Urea by Proteus

Recently Cope and Kilander1 described 83 strains isolated from gastroenteritis patients, contacts and foodhandlers with suggestive or definite history of enteric disorders as “atypical enteric orga...

Taxonomic Relationships in the Genus Proteus

Pathogenicity, Antigenic Relationships and Evolutionary Trends of Shigella alkalescens.

Eijkman Relationships of the Coliform and Related Bacteria.

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