Stormwater, November/December 2003
The Journal for Surface Water Quality Professionals
STAPH AUREUS ANTIBIOTIC RESISTANT MICROBES IN SLUDGE/BIOSOLIDS
STORMWATER RUNOFF (CSOS TO POTWS!)
By Edward McGowan
Edward McGowan has a degree in medicine and a doctorate related to water-quality control.
I am a member of a multijurisdictional task group looking at issues related to biosolids,
stormwater, and wastewater. In a recent meeting of our task group, one of the members - a
wastewater engineer - raised an interesting question relating the survival of pathogens once
the material had left the sewer treatment works. The underlying issues involved in this
question are very similar for stormwater.
The essence of the question was related to the survival of genetic material - hence, an
analysis on the underlying issue of surviving multidrug (antibiotic)-resistant bacteria
(MDRB). The question went something like this: "If Staphylococcus aureus are found dead,
does that mean that the problem is solved?" The corollary: Are they dead, or merely in the
viable but nonculturable state, in a starvation arrested state, or killed from a starvation but
otherwise in a recoverable state by sudden nutrient excess in the culture? Additionally, there
are issues of the reuptake of naked DNA. Recently, in discussing mobile genetic elements
(MGEs), Nielsen and others (2000) demonstrated that DNA was well protected in dead cells
and that transforming activity remained. The survival of such material was found to be up to
two years. Additionally, these and similar papers demonstrate that growing plants, via their
roots, can transfer MGEs to bacteria. The reverse has also been widely demonstrated.
Thus, nonpathogens and nonbacteria can serve as reservoirs for maintaining resistance.
Pneumococci, for example, can take up naked DNA from the environment (natural
transformation from lysed bacteria). Thus, merely finding "dead" bacteria might be no
assurance that risk has reached acceptable levels. Further, from the classical work of
Griffith (a British medical officer who discovered in 1928 that pathogenic genetic information
was transferable from heat-killed bacteria cells to live ones, which provided the first
evidence that not only was genetic material heat-stable, but that pathogenesis could be
reclaimed from dead bacteria), we know that pathogens can regain virulence from dead
bacteria. Additionally, during the above-noted meeting, I mentioned some notes I had taken
during a recent medical grand rounds at our teaching hospital. The speaker, an expert on
infectious disease, indicated that there is strong medical evidence that about half of the
general, nonhospital-communityacquired skin infections in the greater Los Angeles area
are now caused by methicillin-resistant Staphylococcus aureus. The April 2003 issue of Skin
& Allergy News also had a front-page article on this topic since those in dermatology often
stand on the front lines. Prior to 1985, vancomycin resistance in human pathogens had not
been described in the literature. A decade later, more than one half of the hospitals in New
Jersey contained strains of vancomycin-resistant bacteria. By the end of 1998, one quarter
of enterococci isolated from intensive care units across the United States expressed
resistance to vancomycin. Recent publications in the medical literature discuss the cost of
drug-resistant bacteria. The annual cost in the US was estimated to be upward of $30 billion
annually (Dominguez, 2000). Current EPA Class B biosolids, which are applied to
agricultural lands, with the allowed fecal coliform counts of 2 x 10/6 per gram, might actually
constitute a large aliquot when containing MDRB. This is a worrisome situation when the
material is applied to areas with animal or vector access or stormwater runoff potential to
riparian areas or irrigation return.
These bacteria are thus able to colonize animals, including humans, through ingestion.
There are indications within the literature of E. coli O157:H7 being able to travel up the
vascular system in lettuce and celery (Solomon et al., 2002; Wachtel et al., 2002). Since
lettuce is eaten raw, the risk should be clear to most. One will remember that this bacteria
sent children and their parents desperately seeking new kidneys. Once ingested, the shiga
containing plasmids may be transferable to normal flora and later to pathogenic bacteria
found in humans or animals, making later treatment with particular antibiotics ineffective.
Additionally, one finds that there is a remultiplication of bacterial numbers within standing
sludge, biosolids, or compost. Thus, the current Part 503 limits on biosolid marker
organisms might have little bearing on the ultimate numbers. Stormwater managers need to
appreciate such issues. Even if these materials are composted prior to land application, the
issue might not be solved. During composting, the mesophiles can transfer genetic
information to thermophiles. The archaea, which are extreme thermophiles, are recognized
as a separate third domain of life together with the bacteria and eukarya.
Transfer of plasmids to bacteria from archaea has been demonstrated (Cannio et al., 2001;
Ruepp et al., 2000; Horiike et al., 2002; Cohen et al., 2003; Koonin et al., 2003). Thus, in
theory, it may be possible to develop an MDRB that can survive temperatures found within
composting. Furthermore, there is experimental evidence that even when disrupted by
radiation, these ancient organisms can reassemble (Jolivet et al., 2003; DiRuggiero et al.,
1997). This, from a theoretical perspective, raises questions of the eventual failure of
pasteurization. Hassen and others (2001) found that gram-positive bacteria, especially
micrococcus, spores of bacilli, and fungal propagules, survived and reached high
concentrations in compost. Not only that, "the appearance of gram-negative rods
(opportunistic pathogens) during the cooling phase may represent a serious risk for the
sanitary quality of the finished product intended for agronomic reuse."