A diverse range of life forms exists deep below Earth's surface, scientists have concluded, but they survive at an incredibly slow pace. Long-lived bacteria, reproducing only once every 10, years, have been found in rocks 2. The discoveries raise questions about how life persists in such extreme conditions. Scientists from the Integrated Ocean Drilling Program have announced the findings at the Goldschmidt conference , a meeting of more than 4, geochemists, in Florence, Italy.
Fumio Inagaki of the Japan Agency for Marine-Earth Science and Technology, reported that the microbes exist in very low concentrations, of around 1, microbes in every tea spoon full of rock, compared with billions or trillions of bacteria that would typically be found in the same amount of soil at Earth's surface. Alongside the simple single-celled organisms prokaryotes found in the deep rocks, Tim Engelhardt of the University of Oldenburg, Germany, showed that viruses are even more abundant, outnumbering microbes by more than 10 to one, with that ratio increasing with depth.
Speaking to BBC News, Dr Engelhardt said of these viruses: "They are quite stable in these sediments, especially as the metabolic rates of the cells are so low, and they exist in sediments up to million years old. The number of microbes was so low that the distances between them were much greater than those of communities at Earth's surface, so the scientists were surprised to find that they could support a virus' life cycle. This category comprises of diverse organisms from molds and mildews , to yeasts and mushrooms.
So, while some can be life-threatening, there are still plenty of strains we have found uses for. Scientifically known as Stachybotrys chartarum, black mold is a common household growth, found practically anywhere moisture can build-up.
Porous surfaces such as windows sills, tile grout, carpets, and drywall make perfect environments for black mold to reproduce and release its toxic spores.
Instead, in a lack of moisture, black mold will revert to a dormant state that can be reactivated when environments become favourable. So technically, survival on surfaces are indefinite without external interference.
Disinfectants are your weapons of choice when dealing with black mold in a household, as it causes respiratory issues when spores are inhaled. A microscopic fungus that lives on the dead cells of hair, toenails, and skin. With at least four strains, most common infections stem from Trichophyton rubrum. This is because the fungi are particularly suited for warm and moist environments. Almost as well adapted as bacteria, protozoans have little preference in their habitat. Existing in fresh water, brackish, saltwater, soils, mosses, and even hot springs.
The presence of moisture is all that is needed; however, several protozoan species have remarkably displayed adaptive techniques for dry climates. Cryptosporidium is a parasitic protozoon that makes its home in surface water reservoirs.
While symptoms vary for each host, Cryptosporidium predominantly causes diarrhea and, in some cases, respiratory cryptosporidiosis persistent coughing. The germ itself is usually contracted through contaminated food, water, or fecal matter exposure. Symptoms will appear anywhere between 1 to 12 days and last for two weeks.
Wash hands thoroughly and disinfect surfaces with bleach to avoid the spread of contamination. A very common type of single-celled protozoan parasite, toxoplasmosis is an infection that occurs from eating undercooked contaminated food , exposure to infected cat feces, and in some cases, transmission from mother-to-child during pregnancy. Information from textbooks was also included, even if the chapter itself did not contain experimental evidence. At least two of the investigators decided on the relevance of each report.
Reports were not blinded to the investigators so that they knew the names of the authors of all studies. For a clinically relevant summary, all nosocomial pathogens were grouped according to their importance in causing hospital-acquired hand-transmitted infections [ 7 ] and according to their mode of nosocomial transmission [ 8 ]. The range of the reported duration of persistence was used as the principle outcome of the search for each nosocomial pathogen. In addition, parameters with potential influence on persistence were evaluated in all experimental studies.
In general, there was no obvious difference in survival between multiresistant and susceptible strains of Staphylococcus aureus and Enterococcus spp. Only in one study was such a difference suggested, but the susceptible strains revealed a very brief survival as such [ 10 ].
These species are found among the most frequent isolates from patients with nosocomial infections [ 11 ]. Overall, gram-negative bacteria have been described to persist longer than gram-positive bacteria [ 12 , 13 ]. Humid conditions improved persistence for most types of bacteria, such as Chlamydia trachomatis [ 14 ], Listeria monocytogenes [ 15 ], Salmonella typhimurium [ 15 ], Pseudomonas aeruginosa [ 16 ], Escherichia coli [ 17 ], or other relevant pathogens [ 18 , 19 ].
Only Staphylococcus aureus was found to persist longer at low humidity [ 16 ]. Low temperatures, e. The type of test material does not reveal a consistent result.
Although some investigators report that the type of material has no influence on the persistence [ 25 , 26 ], other authors described a longer persistence on plastic [ 27 , 28 ], and others yet see a survival advantage on steel [ 29 ].
Other factors were rarely investigated and hence provide inconsistent results. Longer persistence has been described with higher inocula [ 28 ], in the presence of protein [ 13 ], serum [ 13 , 24 ], sputum [ 30 ], or without dust [ 10 ]. Persistence of other yeasts was described to be similar Torulopsis glabrata 5 months or shorter Candida parapsilosis 14 days. The presence of serum or albumin, a low temperature, and high humidity have been described as leading to longer persistence [ 31 ].
Most viruses from the respiratory tract such as corona- , coxsackie- , influenza virus, SARS , or rhino virus can persist on surfaces for a few days. Viruses from the gastrointestinal tract, such as astro virus, HAV , polio- and rota virus persist for approximately 2 months. The influence of humidity on persistence has been described inconsistently.
For entero- [ 32 ] and rhino virus [ 33 ], high humidity was associated with longer persistence. For aden o- [ 32 , 34 ], rota- [ 36 , 37 ], and polio virus [ 34 , 35 ], conflicting results were reported. For most viruses, such as astro- [ 38 ], adeno- [ 34 ], polio virus [ 34 ], HSV [ 34 ], and HAV [ 35 ], low temperature is associated with a longer persistence. Inconsistent results are also reported for the influence of type of material. Some authors described that the type of material did not affect the persistence of echo- [ 39 ], adeno- [ 39 - 41 ], parainfluenza- [ 39 ], rota virus [ 41 ], RSV [ 39 ], polio- [ 41 ] or noro virus [ 42 ].
Other investigators found that persistence was favored on non-porous surfaces for influenza virus [ 43 ], on formica and gloves for RSV [ 44 ], and on a telephone receiver for FCV [ 45 ].
Other parameters for a longer persistence of viruses include the presence of fecal suspension [ 38 ] and a higher inoculum [ 46 ]. Cryptosporidium species have been reported to survive on dry surfaces for only 2 hours [ 47 ]. The most relevant nosocomial pathogens can persist on dry inanimate surfaces for months. In addition to the duration of persistence, some studies have also identified factors influencing persistence.
High humidity e. A few studies also suggest that a higher inoculum is associated with longer persistence. The type of surface material and the type of suspension medium, however, reveal inconsistent data. Overall, a high inoculum of the nosocomial pathogen in a cold room with high relative humidity will have the best chance for long persistence. In most reports with experimental evidence, persistence was studied on dry surfaces using artificial contamination of a standardized type of surface in a laboratory.
In most studies, bacteria were prepared in broth, water or saline. Viruses were usually prepared in a cell culture medium [ 48 ]. The main advantage is that the environmental conditions are consistent regarding temperature and air humidity.
In addition, the effect of temperature or relative humidity can only be determined under controlled conditions, which are much easier to ensure in the laboratory. However, this may not always reflect the clinical situation, in which surfaces can be simultaneously contaminated with various nosocomial pathogens and different types of body fluids, secretions etc. Yet the question remains: what is the clinical evidence for the role of surfaces in nosocomial infections?
In hospitals, surfaces with hand contact are often contaminated with nosocomial pathogens [ 49 - 51 ], and may serve as vectors for cross transmission. A single hand contact with a contaminated surface results in a variable degree of pathogen transfer. Transmission to hands was most successful with Escherichia coli , Salmonella spp. Contaminated hands can transfer viruses to 5 more surfaces [ 58 ] or 14 other subjects [ 59 ].
Contaminated hands can also be the source of re-contaminating the surface, as shown with HAV [ 55 , 58 ].
The main route of transmission is via the transiently contaminated hands of the healthcare worker [ 60 - 62 ]. An outbreak of nosocomial infections due to Acinetobacter baumannii in a neurosurgical intensive care unit may serve as an example. A direct correlation was found between the number of environmental isolates obtained during screening and the number of patients who were colonized or infected with the same strain during the same calender month [ 63 ]. During outbreaks, the environment may play a significant role for transmission of nosocomial pathogens, as suggested by observational evidence.
This has been described for various types of microorganisms, such as Acinetobacter baumannii [ 64 - 66 ], Clostridium difficile [ 67 - 69 ], MRSA [ 65 , 70 ], Pseudomonas aeruginosa [ 4 , 65 ], VRE [ 65 , 71 - 77 ], SARS [ 78 , 79 ], rota- [ 80 , 81 ], and noro virus [ 82 ].
However, the evidence to support a role of environmental contamination is not equally strong for all types of nosocomial pathogens. For Clostridium difficile , MRSA, and VRE, data are stronger than for other pathogens, such as Pseudomonas aeruginosa or Acinetobacter baumannii , of which multiple types were detected in the environment, and which did not always correlate with the acquired strain [ 83 ]. The role of surface disinfection for the control of nosocomial pathogens has been a contentious issue for some time [ 3 ].
Routine treatment of clean floors with various types of surface disinfectants some of them had rather poor bactericidal activity has been described to have no significant impact on the incidence of nosocomial infections [ 84 ]. Disinfection of surfaces in the immediate environment of patients, however, has been described to reduce acquisition of nosocomial pathogens such as VRE [ 85 ] or Acinetobacter baumannii [ 86 ].
It is therefore advisable to control the spread of nosocomial pathogens at least in the direct inanimate environment of the patient by routine surface disinfection. Most nosocomial pathogens can persist on inanimate surfaces for weeks or even months. Our review supports current guidelines which recommend a disinfection of surfaces in specific patient-care areas in order to reduce the risk of transmission of nosocomial pathogens from inanimate surfaces to susceptible patients.
KG, Hamburg, Germany. All authors contributed to the conception, review of studies, and analysis of data. All authors were involved in drafting and revising the manuscript. All authors approved the final version of the manuscript. National Center for Biotechnology Information , U. BMC Infect Dis.
Published online Aug Author information Article notes Copyright and License information Disclaimer. Corresponding author. Axel Kramer: ed. Received Apr 26; Accepted Aug This article has been cited by other articles in PMC. Abstract Background Inanimate surfaces have often been described as the source for outbreaks of nosocomial infections.
Methods The literature was systematically reviewed in MedLine without language restrictions. Results Most gram-positive bacteria, such as Enterococcus spp. Conclusion The most common nosocomial pathogens may well survive or persist on surfaces for months and can thereby be a continuous source of transmission if no regular preventive surface disinfection is performed. Background Within the global infection control community, there is an ongoing controversy about the appropriate treatment of inanimate surfaces in hospitals in order to prevent transmission of nosocomial pathogens within an institution.
Methods Search strategy The literature was systematically reviewed in MedLine on the internet homepage of the National Library of Medicine without language restrictions. Selecting studies All reports with experimental evidence on the duration of persistence of a nosocomial pathogen on any type of inanimate surface were included. Interpretation of studies For a clinically relevant summary, all nosocomial pathogens were grouped according to their importance in causing hospital-acquired hand-transmitted infections [ 7 ] and according to their mode of nosocomial transmission [ 8 ].
Results Persistence of bacteria Most gram-positive bacteria, such as Enterococcus spp. Table 1 Persistence of clinically relevant bacteria on dry inanimate surfaces. Type of bacterium Duration of persistence range Reference s Acinetobacter spp. Open in a separate window. Table 2 Persistence of clinically relevant fungi on dry inanimate surfaces.
Type of fungus Duration of persistence range Reference s Candida albicans 1 — days [31, 53, 99, ] Candida parapsilosis 14 days [] Torulopsis glabrata — days [31]. Persistence of viruses Most viruses from the respiratory tract such as corona- , coxsackie- , influenza virus, SARS , or rhino virus can persist on surfaces for a few days.
Persistence of other nosocomial pathogens Cryptosporidium species have been reported to survive on dry surfaces for only 2 hours [ 47 ]. Discussion The most relevant nosocomial pathogens can persist on dry inanimate surfaces for months. Figure 1. Common modes of transmission from inanimate surfaces to susceptible patients. Conclusion Most nosocomial pathogens can persist on inanimate surfaces for weeks or even months. Authors' contributions All authors contributed to the conception, review of studies, and analysis of data.
Table 3 Persistence of clinically relevant viruses on dry inanimate surfaces. Acknowledgements The authors declare that they have no acknowledgements.
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