Staphylococcal Infections
2.21.1 STAPHYLOCOCCUS AND ENVIRONMENT (FIGURE )
As previously mentioned, staphylococci are also inhabitants of soil environment. Their soil permanent association with diverse types of bacteria may convey a variety of genetic characteristics, including antibiotic resistance. Polak and Novick (1982) showed that a common plasmid found in bacilli and
therefore a carrier of airborne bacteria. Bananaet al.(2001) foundS. aureusas one of the most frequently isolated dust microorganisms originating from soil, which probably may explain its prevalence in human nostrils. These authors also reported its high prevalence in cinema halls (25.35%) and residential areas (18.75 %) alluding to potential cross-contamination by air-borne particles.
Most species of staphylococci are harmless and inherent in the normal flora of human and animal skin and mucous membranes. Among other species of this genus,S. aureus is also a persistent commensal Figure 2.21.1. Staphylococcispp. environmental behavior and transmission
Table 2.21.1 Some important characteristics ofStaphylococcusspecies.
Resistance Coagulase
Species Host Novobiocin Polymyxin B Methicillin
S. aureus Animals, Humans – + + +
S.epidermidis Humans – + + –
S. haemolyticus Humans, Apes, Lemurs – – d –
S. lugdunensis Humans, Goats – d ? +
S. schleiferi subsp.
schleiferi
Humans – – + +
S. saprophyticus Humans + – ? –
S. intermedius Dogs, Humans – – + +
S. hyicus Turkey, Swine, Cattle – + ? +
dVariable
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organism of the anterior nares in 20%–40% of humans without any clinical symptoms (Wertheimet al., 2005). Nevertheless, nasal carriage seems to be a major risk factor for successive infections. The asymptomatic human group includes non- and intermittent carriers, both at low risk of reinfection.
Ruimy et al. (2010) investigate different risk factors such as age, gender, underlying comorbidities, household sharing, smoking, hospital admission, contact with animals, antibiotics use and genetic polymorphism, that may explain the colonization variability ofS. aureusin an isolated group of humans (Wayampi Amerindians living in an isolated village in the Amazonian forest). Based on bivariate analyses adjusted by Holm’s test for multiple testing, the most significant and predominant factor involved was found to be the genetic variability among the group individuals.
Staphylococci ubiquity in the environment had been presented by Murrellet al.(2003) who surveyed ticks, lice and fleas for their microbial flora, in Australia. Staphylococci of the subspecies (Staphylococcus succinus, S. saprophyticus, S. xylosus, Staphylococcus sciuri, S. lugdunensis, S. warneri, S. saccharolyticus, S. capitus, S. caprae, S. epidermidis and others) had been isolated from most of the tested ticks and lice beside a large variety of other bacteria. S. aureus was absent, but S. intermediuswas isolated from ticks. Graham et al.(2009) collected flies near broiler chicken houses and screened for antibiotic-resistant bacteria carried by these insects. The authors reported on enterococci (to be discussed further) and staphylococci (S. aureus, S. xylosus, S. saprophyticus, and S. epidermidis) that harbor antibiotic resistance [the most common reported resistance gene was: erm (A), erythromycin-resistance]. Their study strongly suggests that flies can exercise as vectors and contribute to human exposures through antibiotic-resistant bacteria (present in their digestive tracts and their external surface) dispersal when in close contact with intensive poultry production areas (Nmorsi et al., 2007). The staphylococcal carrier role of the house fly was also supported by a study in peninsular Malaysia that showed a large bacterial diversity harbored by flies, revealing among other things that carrier state is horizontal and not vertical with these “hiking”bacteria (Nazni et al. 2005). Similar results with carrier flies were also obtained in Burkina Faso, in a nearby vending area close to waste and sewage, which provided food and harborage for these insects (Barro et al., 2006). Cutaneous staphylococci (60%
penicillin-resistant) possible direct transmission by flies has been also reported, based on the observation that Hippelates flies feed on purulent skin lesions (Allen and Taplin, 1974).
Additional arthropods such as mosquitoes, Tenebrionid beetles, flies, German cockroaches, wasps, ants, spiders, non-biting midges, moths, beetles isolated from a health care facility, were also shown to harbor gram-positive bacteria (13% prevalence) while among staphylococci S. hominiswas the dominant one, displaying multiple-antibiotic resistance (Sramovaet al., 1992).
An interesting study was published by Robacker and Flath (1995) in which they showed that S. aureus grown in tryptic soy broth cultures produced volatile compounds that attract fruit flies. Odor production is one of the mechanisms by which, in a close ecosystem, a sessile organism can communicate with another motile organism and associate with it, therefore suggesting a possible bacterial transmission by these flies.
With regard to arthropods, one should remember at this point the potential use of greenbottle fly larvae to heal wounds infected withS. aureusand MRSA strains in severe cases, where antibiotics are useless (so called“maggot therapy”) (Bexfieldet al., 2004; Bruggmannet al., 2006). Parket al.(2010) reported on antibacterial acitivity of ethanol and water extracts from fly maggots against methicilline-resistant S. aureus(MRSA).
There is still a debate on the benefit of this therapeutic method, but it became increasingly clear that these larvae are of a beneficial potential. From the evolutionary point of view, it is very logical that larvae should
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On the subject of plants,Staphylococcus aureuswas reported to be strongly inhibited by plants hormones such as IAA, indolebutyric acid (IBA), naphthaleneacetic acid (NA), 2,5-dichlorophenoxyacetic acid (2,5-D)(Bouillenne and Bouillenne-Walrand, 1951). This phenomenon is probably linked to a possible double role of these hormones. The authors recommended use of plant hormones in controlling human cutaneous infections. Historically, is well known in traditional medicine the use of plants to combat skin infections and various diseases (Navarroet al., 1996).
Bischoffet al.(2004) showed that infection with rhinovirus enhances the spread of coagulase-negative staphylococci through increased colonization of the latter due to nasal tissue damage inflicted by this virus.
However, this problem can be easily solved by simple means such as: surgical scrubs, gowns and masks that are excellent barriers against bacteria spread (Bischoffet al., 2007).
In New Zealand, researchers reported on methicillin-resistantS. aureusisolates, the British epidemic MRSA 15 strain (EMRSA-15) from dogs, cats, cow’s milk and anterior nares of a healthy hospital staff member involved in animal care. The authors concluded that “MRSA can cause clinically overt and difficult-to-treat infections in animals in New Zealand and the rapid emergence of EMRSA-15 as the dominant MRSA strain in humans, resulted in infection spillover to animals”. This conclusion is also supported by an old study performed on wild boars and domestic pigs, where the authors reported on an unusual discovery that staphylococci were absent in all wild boars’ fecal samples when living in their natural environment. As the specific habitat of staphylococci is in man and wild boars are the ancestors of domestic pigs, it is very plausible that humans are the origin of S. aureusin these animals as well other pets domesticated for thousands of years (van Dijck & van de Voorde, 1979; Morgan, 2008;
Leonard and Markey, 2008; Guardabassiet al., 2003).
In a recent review, Loeffler and Lloyd (2010) raised the same concept of community-acquired MRSA rising number of cases, pointing in the direction of animals as the reservoir of this pathogen.
According to the numerous publications on staphylococci isolation from water resources, it is evident that beside their presence in the bodies of water they will also be closely related to aquatic life. Indeed, fish surface seems to containS. aureus naturally able to produce enterotoxins and infect humans coming in contact with it (Simon and Sanjeev, 2007). Yamazakiet al.(1992) showed slight staphylococcal growth on fish surface (fillets of walleye pollack) when packed in 100% CO2in gas-impermeable pouches and preserved at 0°C for 20 days.
The potential of staphylococci to survive in sea water was presented by Bochet et al. (2008) who described two patients with a skin infection caused by community-acquired methicillin-resistant Staphylococcus aureus(CA-MRSA) identical strains, when practicing scuba dive in the Philippines. The authors pointed to the scuba diving equipment as a possible new mode of acquisition of CA-MRSA.
In a periurban area of Niger, a survey on the presence ofS. auruesin milk and on udder was carried out during two seasons: dry and rainy.Staphylococcus aureus, coagulase-negative staphylococci (CNS) and environmental microorganisms were detected in significantly more samples during the rainy season (55.2%, p,0.05) than during the dry season (27.1%). The authors did not explain this variation however, speculatively it might be that the rainy season higher prevalence might be attributed to wash out of animal skin bacteria (know to contain staphylococci) and further contamination of udder and milk.
Finally, in relation to more unconventional environments, a specialS. haemolyticusstrain was isolated from larval guts of the oil flyHelaeomyia petroleiknown to grow exclusively submerged in oil, where they ingest large quantities of oil and asphalt. This S. haemolyticus strain was able to tolerate excessive concentrations of solvents such as 100% toluene, benzene, andp-xylene on plate overlays and saturating levels of these solvents in monophasic liquid cultures (Nielsen et al., 2005). The elucidation of this extreme bacterial tolerance was based on increased membrane fluidity via fatty acid composition once the bacterium is exposed to various solvents, a system much different from the gram-negative bacteria
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mechanism of solvent resistance. In this case, we can merely speculate on the environmental advantage of the above attribute, such as the role of bacterial efflux pumps that are also linked to cross-resistance to antibiotics (Fernandes et al., 2003), commensalism with higher organisms (e.g., larvae), collective defense through biofilm formation or just an opportunistic saprophyte.
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