refersto the large group of Gram-Negative bacteria. They include the widerange of harmless microorganisms that occur in the form of symbiontsas well as the commonly known harmful pathogens that includeEscherichia coli, Klebsiella, Salmonella and Yersinia pestis. Thereare other disease-causing bacteria in the group, which includeEnterobacter, Citrobacter and Proteus. It is the only family, whichrepresents the order Enterobacteriales class Gammaproteobacteria andthe phylum Proteobacteria.
Themembers of the family are rod-shaped and look likegray colonies when placed in blood agar. Like all otherproteobactercea, enterobacteria possess gram-negative stains. Inaddition, they ferment sugars, are facultative anaerobes and producelactic acid among other products. Unlike the anaerobic organisms, are seen in routine fecal specimen or culture. Itis because these cultures are typically grown under aerobicconditions. It is however no longer the case since the routinesamples is split into two major cultures. These are the aerobic andanaerobic (Brenner, Krieg & Staley 1108).
Someof them also reduce nitrate to nitrite. Majority of them move aboutusing their flagella although there are also some non-motile genera.They do not form spores and have varied catalase reactions (Levinson58).
Mostmembers of this family form a normal part of the flora that is foundwithin the gut region. They are mostly found in the small intestinesof animals and human beings although some of them are found in soiland water. It is in the sense that they can be considered to be amongthe enteric bacterial pathogens. Usually, they spot the digestivetrack as the most attractive place to colonize the human being or theanimal. Some of them serve useful functions while others are highlypathogenic (Williams et al., 2310).
Varioustests can be run to identify the different genera found under thisfamily. They include the methyl red test or the voges-proskauer test,which are part of the IMViC tests and depend on the digestion ofglucose. Both of them require the inoculation of MR-VP broth. Methylred test is conducted to test for the acid products using the methylred reagent. Voges-proskauer tests for acetylmethylcarbinolproduction using Baritt’s A and Baritt’s B reagents. The othersare Indole test and citric utilization test, which necessitate theuse of trypton broth or sulfide-indole motility medium and citraterespectively.
Indoletest is read after the addition of Kovac’s reagent while citrateutilization test is done on Simmons citrate agar. For Methyl red testand Indole test, the positive result is shown with a red layer, brownlayer for voges-proskauer test, and a blue color and growth forcitrate test. Negative results are shown with no color and anadditional lack of growth in citrate test.
Isolationand identification of specific enteric bacteria from fecal samples.
Perform gram stain
Culture on blood agar and aerobic condition
Culture on MacConkeys agar
Grow in 6.5% Nacl
Culture on Eosin Methyline blue agar
Escherichia coli (Green sream)
Perform wet mount
Culture on Nutrient agar
Aeroginos (Blue green pigment)aa
Brenner,J. Don, Krieg, R. Noel, and Staley, T. James in George M. Garrity,ed. The Gammaproteobacteria.Bergey`s Manual of Systematic Bacteriology 2B.New York: Springer. 2005. p. 1108.
Levinson,W. Reviewof Medical Microbiology and Immunology.San Francisco, California: Lange Medical Books/ McGraw-Hill MedicalPublishing Division. 2006.
Williams,K. P., Gillespie, J. J., Sobral, B. W. S., Nordberg, E. K., Snyder,E. E., Shallom, J. M., and Dickerman, A. W."Phylogeny ofGammaproteobacteria". Journalof Bacteriology. 2010.192 (9): 2305–2314