12, several standard methods and commercial systems have been developed for testing staphylococci
Although a penidllinase-resistant penicillin, such as methicillin, nafcillin, or oxacillin, is the mainstay of antistaphylococcal therapy, resistance is common.14 The primary mechanism for this resistance is production of an altered penicillin-binding protein (i.e., PBP 2a), which renders all currently available beta-lactams essen tially ineffective. Vancomycin is the most commonly used cell wall-active agent that retains activity and is an alternative drug for resistant strains. High-level resistance to vancomycin (minimal inhibitory concentrations
[MIC] > 8 pg/mL) has been described in six clinical S. aureus isolates and strains with MIC in the intermediate range (i.e., 8 to 16 pg/mL) have been encountered.13,22 TWo rdatively newer agents available for use against such resistant strains include linezolid and daptomyan. Because of the substantial clinical and public health impact of vancomycin resistance emerging among staphylococci, laboratories should have a heightened awareness of this resistance pattern.
Because Micrococcus spp. are rarely encountered in infections in humans, therapeutic guidelines and standardized testing methods do not exist (see Table 16-10). However, in vitro results indicate that these organisms generally appear to be susceptible to most beta-lactam antimicrobials.21
There are no approved antistaphylococcal vaccines. Health care workers identified as intranasal carriers of an epidemic strain of S. aureus are treated with topical mupirocin and, in some cases, with rifampin. Some physicians advocate the use of antibacterial substances such as gentian violet, acriflavine, chlorhexidine, or bacitracin to the umbilical cord stump to prevent staphylococcal disease in hospital nurseries. During epidemics, it is recommended that all full-term infants be bathed with 3% hexachlorophene as soon after birth as possible and daily thereafter until discharge.
áteenage male had a history of colitis, most likely Crohn's disease. He had difficulty controlling his disease with medical management and had been treated with parenteral nutrition and pain medication. He attends high school and is socially adjusted, even though bis illness has caused him to be small in stature. He lives •with his mother, who works for a veterinarian. The reason for this admission was abdominal discomfort and erythema at the exit site and along the tunnel of his central line. Blood cultures were collected, and both the ble d cultures and his catheter tip cultures grew a ptalase-positive, gram-positive cocci. The coagulase : f test was positive, but the slide and latex test for Coagulase were negative (See Procedure 13-11, Coagulase Test).
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