Distribution de Pseudomonas aeruginosa et Aeromonas hydrophila dans les eaux de la nappe phréatique superficielle en zone équatoriale au Cameroun et relations avec quelques paramètres chimiques du milieu. Distribution of Pseudomonas aeruginosa and Aeromonas hydrophila hydrophila in groundwater in equatorial zone in Cameroon and relationships with some environmental chemical factors

Résumé

Une étude microbiologique et chimique a été menée pendant un an sur les eaux de sources et de puits de Yaoundé (Cameroun). Les analyses microbiologiques ont été faites suivant la technique des membranes filtrantes, et les analyses chimiques, suivant les techniques analytiques usuelles. Les abondances maximales mensuelles de Pseudomonas aeruginosa et de Aeromonas hydrophila varient respectivement de 1 à 22x10³ UFC.100 ml^-1 d'eau, et de 1 à 7,8x10³ UFC.100 ml^-1. Ces abondances bactériennes subissent d'amples fluctuations spatio-temporelles. Les eaux de sources et de puits analysées sont faiblement bicarbonatées, douces et présentent une minéralisation faible à moyenne. Le pH varie de 3 à 5 et les concentrations en CO₂ dissous, de 300 à 532 mg.l^-1. Un bon nombre des caractéristiques chimiques de ces eaux est relativement stable au cours du temps, en dépit des fluctuations spatiales apparentes. Le degré de corrélation entre les paramètres chimiques et la dynamique d'abondance des bactéries isolées, est hétérogène. Cela est nettement plus marqué dans les eaux de puits, en raison des conséquences de l'exploitation humaine de ces eaux, à l'origine d'apports allochtones divers.

Mots-clés:

• P. aeruginosa,
• A. hydrophila,
• environnement chimique,
• eau souterraine tropicale,
• Afrique

Abstract

bacteriological and chemical study was carried out on the waters of four springs and six wells over 13 months and 12 months, respectively, in the town of Yaounde and its environs in Cameroon. For these groundwater points the study analysed the importance of pH, electrical conductivity, dissolved oxygen and carbon dioxide, and some ions such as sodium, potassium, calcium, magnesium, chloride and bicarbonate, for communities of Pseudomonas aeruginosa and Aeromonas hydrophila. The two bacteria P. aeruginosa and A. hydrophila are considered opportunistic pathogens. Different groundwater points were chosen on the basis of their spatial distribution and the size of the human population using them. Microbiological analyses were carried out by membrane filtration and chemical analyses were performed using standard analytical techniques.

It has been noted that the monthly maximum abundance of P. aeruginosa and A. hydrophila varies from 1 to 22 x 10³ CFU per 100 ml and from 1 to 7.8 x 10³ CFU per 100 ml of water, respectively. These bacteria are sometimes rare and their abundance undergoes spatio-temporal fluctuations. The studied waters are slightly bicarbonate and soft, with a low to average level of mineralisation. The pH varied from 3 to 5 and the concentration of dissolved CO₂ from 300 to 532 mg/l. Most chemical characteristics were relatively stable with time, but exhibited apparent spatial fluctuations. The level of correlation between the chemical parameters and the abundance dynamics of P. aeruginosa and A. hydrophila is heterogeneous. Depending on the origin (well or spring) of water samples and minimising their spatial variations, samples were grouped into single biotopes (either mother well or mother spring) which were separated into compartments. A correlation test was then carried out using data obtained from 52 monthly-average samplings in the four compartments of mother-spring water, and using data obtained from 72 monthly-average samplings in the six compartments of mother-well water. From this it emerged (P < 0.001) that in springs increases in pH, electrical conductivity, and in concentrations of chloride, sodium, potassium, calcium, magnesium and dissolved oxygen favoured the development of P. aeruginosa and A. hydrophila. High concentrations of dissolved carbon dioxide reduced (P < 0.001) the abundance of these bacteria. In wells, the ecology of P. aeruginosa and A. hydrophila is relatively unstable in comparison with springs. The higher instability in well water is ascribed to an increase in the number of confounding factors, which make wells appear more vulnerable than springs. This leads to the multiplication of asymmetrical interaction networks affecting bacterial population dynamics.

Keywords:

• P. aeruginosa,
• A. hydrophila,
• chemical parameters,
• tropical groundwater,
• Africa