Currently, there is a clamour about the health hazards posed by the condition of the South Coast Sewerage System. Indeed, the acting Chief Medical Officer (CMO) is on record as having stated that microbial assays of potable water and the environment were found to be negative for enteric organisms.
His position was augmented by the Massy’s Group of Companies in the print media. In the latter case, the group claimed to have engaged the services of a firm and that between the firm and local Government departments, the area surrounding its supermarket was being disinfected thrice daily (I will deal with this practice later on).
In all instances according to Massy, no indicator of pathogenic enteric organisms were detected. No mention was made of viral or protozoan pathogenic causative agents of cholera, hepatitis, and dysentery and so on.
Since the above pronouncements, the CMO has now acknowledged that there are 35 cases of gastroenteritis. Prior to this acknowledgement, it was reported in the local print media that there were 12 cases of gastroenteritis in the affected area and that fish had died.
Having admitted that there were cases of gastroenteritis, the CMO must concede that there has been some type of contamination on the South Coast. He is now disputing the American claim that sewage has been discharged into the sea (I will deal with this later).
The following is written in the public interest. Let me start by saying that the authorities dealing with microbial assays are either remarkably mistaken or else they have been placed under gag orders. The absence of disease-causing agents signifies nothing, as I will now show. The assays alluded to above did not indicate the assay protocols used. The public is told assays were done, nothing found; end of story.
Let me point out here that the microbial media used and protocol conditions all have a bearing on the detection rates. This particularly so under the following conditions:
1. The causative agent is present in the environment in trace amounts. For example, testing seawater. If there is one organism per cubic metre of seawater, one has to do lots of sampling.
2. Causative agent has been exposed to hostile environment and has been injured, thereby requiring special enumerating media and conditions. For example, “enteric (gut) organisms, including coliforms, are generally adapted to relatively high nutrient and solute concentrations, but low oxygen concentrations due to the nature of their natural habitat and when exposed to oxygen, show an increase loss of viability”. Roslev, P. 2004. “Effect of oxygen on survival of fecal pollution indicators in drinking water”. Journal of Applied Microbiology .96:5: 938-945.
3. The type of storage medium/diluent used. For example, if samples of salted fish are placed in sterile distilled water, lysis of microbial cells occur resulting in death, since cell have been moved from salt environment to a non-salt environment. As a result, no microorganisms will be detected.
4. The timing and frequency of sampling. If sampling is done immediately after disinfecting, obviously there will be fewer organisms detected. Massy did not specify when sampling was done.
5. The causative agent is present as an aerosol and sampling is done on solids and water only. Since vehicles passed through the area, one would expect aerosols to form and the wide distribution of the causative agent.
The practice of frequently exposing a microbial population to disinfectants is a hostile action. This type of activity is referred to as selective pressure and causes the microbes to undergo mutations and to develop resistance to antibiotics (if the hostile agents are antibiotics) or resistance to the disinfectant as the case maybe. If the microorganisms are exposed to moist, solid surfaces such as is the case of the local sewerage, biofilm forms.
A biofilm is a thin layer of densely packed microorganisms encapsulated within an aqueous matrix of proteins, nucleic acid and polysaccharides. These characteristics, combined with strong cohesive properties and sophisticated collaboration, make biofilms highly resistant to conventional cleansing agents such as biocides and disinfectants.
The CMO is making a lot of noise about the America’s claim that raw sewerage has been discharged into the sea. I wonder if the CMO has ever heard of the terms in geography “surface run-off and percolation”. With all the rain the country has been experiencing recently and the lack of gutters on the roads, surely one would expect some kind of discharge into the sea.
For his information, the Americans can use remote sensing from aircraft or from space to detect microbial growth in the oceans.
Using algorithms, the biochemical signals of a particular organism can be used to detect its presence from space.
In any event, the DNA profile of microbes present in the sewage can be extracted and compared with the DNA of the microbes isolated from the 35 suspected cases of gastroenteritis.
– ROBERT D. LUCAS, PH.D, food biotechnologist