Thursday, July 3, 2008

The role of Klebsiella pneumoniae as an opportunistic pathogen in paper industry.

Klebsiella pneumoniae is a common bacterium of the BERGEY's group "Gram-negative facultatively anaerobic rods", having motility by peritrichous flagella and being unable to perform oxidase test positively.

The former description indicates that we can set K.pneumoniae into the family Enterobacteriaceae with such, maybe better-known bacteria like Escherichia coli and Salmonella sp. They all have one distinct feature: they can grow either aerobically (= in an atmosphere containing oxygen) or anaerobically (= in an atmosphere without oxygen). The presence of two different energy metabolism, aerobic respiration and fermentation, allow this adaptation into two significantly different environments.

Klebsiella pneumoniae likes to live in wet environments and can use different sugars as the source of energy and carbon.

All these features of this bacterium declare its tendency to live in paper industry waters containing sugars from wood (waters originating mechanical pulp production; debarker waters; waste waters containing pulp mill effluents). The capability to use atmospheric nitrogen (N2) as the source of nitrogen (called nitrogen fixation) is also common among K.pneumoniae strains and gives to it good chances to compete with such microbes which are depending on organic nitrogen supply - which is often very poor in paper industry waters, having low N:C ratio.

What makes this peaceful situation more hazardous, are some other features of Klebsiella pneumoniae: its ability to produce exopolysaccharide capsel (= slime) and its resistance against several antibiotics. Optimal temperature for its growth is 35-37 oC which is responding to the body temperature of a man.

It has been described as an independent species already in 1885. Genus is named respecting famous Dr. Klebs, well-known microbiologist; name of this species comes from its ability to cause bacterial pneumoniae and other severe infections which may be fatal for weak persons (very young, very old or those having poor immune response like cancer patients). BROCK says: " ..the presence of bacteria in the blood is generally indicative of systemic infection. The most common pathogens found in blood include...enteric bacteria, especially Escherichia coli and Klebsiella pneumoniae...".

The physiological and biochemical features of K.pneumoniae strains isolated from patient samples and either from waste waters (DUFOUR & CABELLI 1976) or from paper industry processes (MENTU 1982) are very identical and the risk to be infected by this opportunistic pathogen is therefore obvious.

Finnish Work Environment Fund funded a research project in the beginning of 80's to investigate health risks, connected to the contaminated aerosols in the paper machine and debarker halls. K.pneumoniae was one of the microbes investigated in this research. The results of this extended project were published in Appl. Environ.Microbiology (SEPPO I. NIEMELÄ, PENTTI VÄÄTÄNEN, JUHA MENTU, ANTTI JOKINEN, PAAVO JÄPPINEN & PAAVO SILLANPÄÄ 1985). The writers said at the end of this article's Discussion: "...The lack of correlation between microbial incidence and occurrence of symptoms seems to indicate that permanent colonization of the process water microbes is not common or that the human pathogenity of these microbes is low. The microbes found in nasal cavities were evidently mostly transient. We conclude that the natural host defenses of the basically healthy adult worker population are normally effective enough to protect the workers from the the opportunistic pathogens present in the process waters and in the air of the paper mill environment. This does not preclude the possibility of a worker's becoming a host to a pathogenic microbe when the worker is in a subnormal state of health".

After 20 year from the publishing of this article, first cases of Legionella pneumophila infections, connected with paper industry, were found.

- Detailed list of references is not included in this article (to spare rows) but available on request from IM.

Pathogenic microbes in paper industry?

A paper industry professional (graduated in technical, not in any biological department) discussing with IM. - Every sentence in this story is fictional one (like they tend to tell at the end of many movies) but they base on those years (nearly 30), during which IM has been involved in P&P microbiology and they, in a way, are a condensate of frequent discussions about microbiological topics on the meetings and in the paper mills:

- You have told us that there may be over million living bacteria in every milliliter of white water inside a paper machine?
- Yes. High number of scientific reports by independent researchers can confirm it.
- What about viruses?
- Obviously there are viruses - but not those which are pathogenic to man. Viruses of paper industry will infect bacteria, they are called bacteriophages.
- What is the reason for the fact, there are no viral human pathogens?
- No significant source of those viruses - you can find them in waste waters of villages and big cities but, as you understand, people tend not to release their viruses into paper machine processes...and...
- And...?
- If there were viruses, pathogenic to man, they should have host cells...
- Wait a minute...bacterophages infect bacteria...
- You got it! And human viruses need human cells as hosts - they cannot reproduce themselves outside their host cells.
- Genetics..I know. And specified viruses to infect specified cells...
- Yes. They shall, in a way, "match" together.

A moment of silence. Fish are jumping on the lake, western horizon turns from yellow to darker shades.

- What about bacteria? If there really are so many there?
- That is a much longer story. We will discuss about hazards, caused by the bacteria, tomorrow morning.
- O.K. It is a late evening, sun has just gone down and..
- ...and the best time of the day for fishing!