Uncertain; probably similar to those described tor
Similar to those described tor 5. epidermldis
Urinary tract infections in sexually active, young females; infections in sites outside urinary tract are not common
Unknown; probably of extremely low virulence
Usually considered contaminants of clinical specimens; rarely implicated as cause of infections In humans
spread to one or more internal organs including the respiratory tract. Furthermore, these serious infections have emerged more frequently among nonhospitalized patients and are associated with strains that produce the Panton-Valentine leukocidin (FVL) toxin. Also worrisome is that these serious "community-associated'' infections are frequendy mediated by methicillin-resistant S. aureus (community-acquired MRSA or CA-MRSA).
S. aureus can also produce toxin-mediated diseases, such as scalded skin syndrome and toxic shock syndrome. In these cases, the organisms may remain relatively localized, but production of potent toxins causes systemic or widespread effects. With scalded skin syndrome, which usually afflicts neonates, the exfoliatin toxins cause extensive sloughing of epidermis to produce a bumlike effect on the patient The toxic shock syndrome toxin (TSST-1) has several systemic effects, including fever, desquamation, and hypotension potentially leading to shock and death.
The coagulase-negative staphylococci, among which S. epidermidis is the most commonly encountered, are substantially less virulent than S. aureus and are opportunistic pathogens. Their prevalence as nosocomial pathogens is as much, if not more, related to medical procedures and practices than to the organism's capacity to establish an infection. Infections with S. epidermidis and, less commonly, S. haemolyticus and S. lugdunensis usually involve implantation of medical devices (see Table 16-2).5'20 This kind of medical intervention allows invasion by these normally noninvasive organisms. Two organism characteristics that do enhance the likelihood of infection include production of a slime layer or biofilm that facilitates attachment to implanted medical devices and the ability to acquire resistance to most of the antimicrobial agents used in hospital environments.3,4,7
Although most coagulase-negative staphylococci are primarily associated with nosocomial infections, urinary tract infections caused by S. saprophytics are dear exceptions. This organism is most frequendy associated with community-acquired urinary tract infections in young, sexually active females but is not commonly associated with hospital-acquired infections or any infections at non-urinary tract sites.
Because coagulase-negative staphylococci are ubiquitous colonizers, they are frequendy found as contaminants in clinical specimens. This fact, coupled with the emergence of these organisms as nosocomial pathogens, complicates laboratory interpretation of their clinical significance. When these organisms are isolated from clinical specimens, every effort should be made to substantiate their clinical relevance in a particular patient so that unnecessary work and production of misleading information can be avoided.
What, if any, virulence factors are produced by Micrococcus is not known. Because these organisms are rarely associated with infection, they are probably of low virulence.
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