A comparison of three semi-selective media for the isolation of methicillin-resistant Staphylococcus aureus

Abstract

Summary. During the 1980s the emergence of multiple antibiotic-resistant strains of Staphylococcus aureus posed new problems for infection control worldwide, many of which still remain. In investigations of outbreaks of infection, the laboratory has a key role in identifying infected or colonised patients and staff. The rapid isolation and accurate identification of the causative organisms are essential for the implementation of appropriate control measures. Speed and accuracy in identification, by colonial morphology, is often difficult to achieve in the presence of a mixed population of commensal bacteria.To this end, the sensitivity of three media for the isolation of methicillin-resistant S. aureus (MRSA) from simulated clinical specimens was compared. Initial colonial recognition of MRSA was enhanced on methicillin-milk agar when compared with that on other media.

Oral carriage of staphylococci in patients with rheumatoid arthritis

“…Staphylococcus aureus was present in the mouths of 14 agar with 5% defibrinated horse blood (Prolab (56%) of this group, a significantly greater rate of Diagnostics, Merseyside, UK ), mannitol salt agar colonization than the healthy adults (P < 0.01). Eleven (Prolab Diagnostics, Merseyside, UK ), milk agar [16 ] (78%) of those with oral carriage of S. aureus were also with no added methicillin and P agar [17], and incubated nasal carriers of the organism. Three patients in this at 37°C for 72 h. This extended incubation enhanced group were nasal carriers in the absence of oral carriage.…”

Cost-effectiveness of different MRSA screening methods

“…3 Colonies from MSA, unlike those from CBP, led to a false-negative result. Allen and co-workers 31 showed an interaction between the different microbial flora at a sampling site and the incubation media. For example, coliforms from perineal samples reduced the sensitivity for methicillin-blood agar, but not that of methicillin-milk agar or Chapman's medium.…”

“…For example, coliforms from perineal samples reduced the sensitivity for methicillin-blood agar, but not that of methicillin-milk agar or Chapman's medium. 31 The model was based on a scenario where all patients admitted to a high-risk ward, such as an ICU, were screened. A recent survey of ICUs found this to be common practice (Ms M. Carter, personal communication).…”

Soft Salt-Mannitol Agar–Cloxacillin Test: a Highly Specific Bedside Screening Test for Detection of Colonization with Methicillin-Resistant Staphylococcus aureus

“…Low-level MRSA colonization may be missed due to overgrowth of normal flora or the presence of a mixture of MRSA and methicillin-susceptible strains. Other protocols involve salt-mannitol agar containing methicillin or oxacillin as a screening medium (2,8,14,15,30). By using these selective and differential media, it is possible to increase the rate of recovery of MRSA isolates.…”