| Based on the gram stain morphology observed before, the possible presumptive identifications might include "gram positive cocci consistent with... | View Page |
| A gram stain of the serous exudate is shown in the photograph. The appropriate report would read: | View Page |
| The bacterial cells shown in the photograph were observed in a smear prepared from the colony shown before. Which of the following tests will help to affirm the identification of Staphylococcus aureus? | View Page |
| Staph aureus Mannitol The ability to grow in 6.5% NaCl and to produce acid from mannitol was once considered sufficient to identify S. aureus.Although other Staphylococcus species have these characteristics, mannitol salt agar, as shown here, can still be used for epidemiologic studies in suspected cases of S. aureus outbreaks.As shown in the photograph, the presence of colonies indicates the ability to grow on 6.5% NaCl; and, the yellow pigment of the colonies indicates acid production from mannitol. | View Page |
| MRSA Screen Perhaps the most efficient means for detecting methicillin-resistant staphylococci in clinical laboratories is the use of the agar dilution screening test.Illustrated in the photograph is a Mueller-Hinton agar plate containing 6ug/ml of oxicillin, previously inoculated with a strain of Staphylococcus aureus. Oxacillin is used as a marker for methicillin resistance because it is more stable in the agar medium. Growth on this screening medium is presumptive for methicillin resistance.Thus, in the presence of growth, as shown here, a follow-up MIC test must be performed to determine the exact level of resistance. | View Page |
| MRSA Disk Test The disk diffusion test can also be used in the detection of methicillin-resistant Staphylococcus aureus.Illustrated in the photograph is the surface of a Mueller-Hinton agar plate previously inoculated with a strain of S. aureus suspected of being methicillin-resistant. Although the zone of inhibition is at the borderline for resistance (18 mm); the presence of small colonies within the zone of inhibition (yellow arrows) indicates the presence of heteroresistant strains.The interpretation here, therefore, is "methicillin-resistant" staphylococci, even though the zone diameter appears to be adequate. The detection of the heteroresistant strains indicates that MIC studies are required. | View Page |
| Review 1 Francois P. Vaudaux P. Foster TJ. Lew DP.:
Host-bacteria interactions in foreign body infections.
Infection Control & Hospital Epidemiology. 17:514-20, 1996Persistent staphylococcal infections are a major medical problem, especially when they occur on implanted materials or intravascular catheters.This review describes some of the recently discovered molecular mechanisms of Staphylococcus aureus attachment to host proteins coating biomedical implants.These interactions involve specific surface proteins, called bacterial adhesins, that recognize specific domains of host proteins deposited on indwelling devices, such as fibronectin, fibrinogen, or fibrin.Elucidation of molecular mechanisms of S. aureus adhesion to the different host proteins may lead to the development of specific inhibitors blocking attachment of S. aureus, which may decrease the risk of bacterial colonization of indwelling devices. | View Page |
| Review 2 Hershow RC. Khayr WF. Smith NL.:
A comparison of clinical virulence of nosocomially acquired methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections in a university hospital (University of Illinois at Chicago).
Infection Control & Hospital Epidemiology. 13(10):587-93, 1992OBJECTIVES: To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) infections in 1989.DESIGN: A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. PARTICIPANTS: Forty-four adult patients with nosocomial S.aureus infections.RESULTS: The 22 MRSA-infected and 22 MSSA-infected persons were similar regarding mean age, gender, underlying diseases, and exposure to surgery. Before developing infection, MRSA-infected persons were more likely to have received antibiotics and to have stayed in the hospital > 2 weeks. Bacteremia was the most common presentation in the MRSA and MSSA groups (55% and 59%, respectively). Infectious complications and death were infrequent in both groups.CONCLUSIONS: MRSA and MSSA strains infect patients with similar demographic features and underlying diseases, but MRSA infections are significantly more common among patients with previous antibiotic therapy and a prolonged preinfection hospital stay. Clinical presentations and outcomes did not differ significantly between the 2 groups. Thus, similar to studies in the early 1980s, our findings do not suggest greater intrinsic virulence of MRSA. | View Page |
| Review 3 Ladhani S. Joannou CL. Lochrie DP. Evans RW. Poston SM.:
Clinical, microbial, and biochemical aspects of the exfoliative toxins causing staphylococcal scalded-skin syndrome.
Clinical Microbiology Reviews. 12:224-242, 1999The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body.The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood.Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases. | View Page |
| Factors predisposing to infections with methicillin resistant Staphylococcus aureus (MRSA) include: | View Page |
| Shown in the photograph is a close-in view of the colony growth after 48 hours incubation. Possible presumptive identifications suggested by the colonies observed include: | View Page |