News Update on Bacterial Population: May 2020

Mechanical reduction of the bacterial population in the root canal by three instrumentation techniques

The in vitro reduction of the bacterial population in the root canal by the mechanical action of instrumentation and irrigation was evaluated. Root canals inoculated with a Enterococcus faecalis suspension were instrumented using hand Nitiflex files, Greater Taper (GT) files, and Profile 0.06 taper Series 29 rotary instruments. Irrigation was performed using sterile saline solution. Root canals were sampled before and after instrumentation. In the group of the Nitiflex files, samples were also taken after each file size. After serial dilution, samples were plated onto Mitis-Salivarius agar, and the colony forming units grown were counted. All techniques and instruments tested were able to reduce significantly the number of bacterial cells in the root canal. Instrumentation to a Nitiflex #30 was significantly more effective than GT files. There were no significant differences when comparing the effects of the Profile instrument #5 with either the GT files or the Nitiflex #30. Enlargement to a Nitiflex #40 was significantly more effective in eliminating bacteria when compared with the other techniques and instruments tested (p < 0.05). The results of this study showed that the instrumentation and irrigation can mechanically remove more than 90% of bacterial cells from the root canal. [1]

Raw Cow Milk Bacterial Population Shifts Attributable to Refrigeration

We monitored the dynamic changes in the bacterial population in milk associated with refrigeration. Direct analyses of DNA by using temporal temperature gel electrophoresis (TTGE) and denaturing gradient gel electrophoresis (DGGE) allowed us to make accurate species assignments for bacteria with low-GC-content (low-GC%) (<55%) and medium- or high-GC% (>55%) genomes, respectively. We examined raw milk samples before and after 24-h conservation at 4°C. Bacterial identification was facilitated by comparison with an extensive bacterial reference database (∼150 species) that we established with DNA fragments of pure bacterial strains. Cloning and sequencing of fragments missing from the database were used to achieve complete species identification. Considerable evolution of bacterial populations occurred during conservation at 4°C. TTGE and DGGE are shown to be a powerful tool for identifying the main bacterial species of the raw milk samples and for monitoring changes in bacterial populations during conservation at 4°C. The emergence of psychrotrophic bacteria such as Listeria spp. or Aeromonas hydrophila is demonstrated. [2]

Bacterial Population Dynamics in Three Anopheline Species: The Impact on Plasmodium Sporogonic Development

The functional role of bacteria in the midgut of adult mosquitoes is unknown. In this study, we examined the population dynamics of midgut bacteria of laboratory reared Anopheles stephensi, An. gambiae, and An. albimanus. Mosquito midguts were dissected under sterile conditions and examined for the presence of bacteria using standard microbiologic techniques. Ninety percent and 73% (n = 30) of newly emerged An. gambiae and An. stephensi, respectively, harbored bacteria. In contrast, only 17% (n = 23) of An. albimanus harbored any bacteria. The bacterial population increased 11–40-fold in the presence of a blood meal, but then decreased to pre-blood meal levels in 3–5 days. Pseudomonas cepacia, Enterobacter agglomerans, and Flavobacterium spp. were found in all three anopheline species. Midgut bacteria were acquired both transtadially and through the sugar meal. Transtadial transmission was demonstrated by successfully passaging Escherichia coli HS5 from the larval to the adult stage. However, midgut bacteria were acquired more efficiently through the sugar meal than through transtadial passage. An increase in midgut bacterial counts after mosquitoes were exposed to a bacteria/sugar suspension significantly reduced oocyst infection rates and densities in Plasmodium falciparum-infected mosquito cohorts. Since bacteria occur naturally in wild mosquitoes, it may be possible to modify anopheline vector competence using introduced or indigenous bacteria. [3]

Population Dynamics and Diversity of Endophytic Bacteria Associated with Soybean (Glycine max (L) Merril)

Aim: Endophytic bacterial population and their diversity in soybean were investigated.

Study Design: Endophytic population was assessed during different growth stages of soybean (CV JS 335) viz., vegetative and reproductive stages.

Place and Duration of Study: Microbiology Research Laboratory, Department of Microbiology, R. A. Mahavidyalaya, Washim (MS), India, during the cultivation period of June-December 2010.

Methodology: Healthy plants of soybean were screened from the different locations of Washim district (M. S., India). Samples represent each growth stage viz., vegetative (V1-V5) and reproductive (R1-R8) were collected. Population densities were expressed as log10 colony forming units (CFU) g-1 fresh weight. The isolates were identified to genus level according to Bergey’s Manual of Determinative Bacteriology on the basis morphological, cultural and biochemical characteristics. [4]

Identification of Bacterial Population of Activated Sludge Process and Their Potentials in Pharmaceutical Effluent Treatment

Aims/objectives: The cognition about microbial population of activated sludge and their treatment potential will be very useful for industrial wastewater treatment plant operation.

Methodology: In this study microbial population of activated sludge process that was used for pharmaceutical wastewater has been investigated. Sampling was done from return sludge line and after serial dilution 1500 plates were studied. Methods for separating the bacteria from wastewater was pour plate method. All bacterial samples were purified using nutrient Agar and Macconkey Agar culture. Bacteria were separated from return sludge line and classified into 3 groups after biochemical tests and morphological analysis, These include positive bacteria of Bacillus genus, Pseudomonas aeruginosa and Flavobacterium. [5]


[1] Siqueira Jr, J.F., Lima, K.C., Magalhães, F.A., Lopes, H.P. and de Uzeda, M., 1999. Mechanical reduction of the bacterial population in the root canal by three instrumentation techniques. Journal of Endodontics, 25(5), pp.332-335.

[2] Lafarge, V., Ogier, J.C., Girard, V., Maladen, V., Leveau, J.Y., Gruss, A. and Delacroix-Buchet, A., 2004. Raw cow milk bacterial population shifts attributable to refrigeration. Appl. Environ. Microbiol., 70(9), pp.5644-5650.

[3] Pumpuni, C.B., Demaio, J., Kent, M., Davis, J.R. and Beier, J.C., 1996. Bacterial population dynamics in three anopheline species: the impact on Plasmodium sporogonic development. The American journal of tropical medicine and hygiene, 54(2), pp.214-218.

[4] Dalal, J. and Kulkarni, N. (2013) “Population Dynamics and Diversity of Endophytic Bacteria Associated with Soybean (Glycine max (L) Merril)”, Microbiology Research Journal International, 3(1), pp. 96-105. doi: 10.9734/BMRJ/2013/2302.

[5]  Meherdad, F., Naser, G., Fazel, N., Joubani Mohammad, N.-, Rabiollah, F. and Joorshari Esmaeil, R. (2014) “Identification of Bacterial Population of Activated Sludge Process and Their Potentials in Pharmaceutical Effluent Treatment”, Biotechnology Journal International, 4(3), pp. 317-324. doi: 10.9734/BBJ/2014/7913.

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