Prospective addition of  -lactamase to blood culture medium

Abstract

Summary. The value of adding P-lactamase to bottles of blood-culture medium before their distribution to wards was investigated. Significantly more bottles containing P-lactamase were culture-positive than those without (p < 0.002). In another series, when the enzyme was added to both bottles in each set there was no significant difference in isolation rates between the two bottles. The groups of organisms which were isolated more readily when P-lactamase was present were staphylococci and streptococci. Storage of P-lactamase (Genzyme broad-spectrum mixture) in bloodculture medium at room temperature resulted in rapid loss of cephalosporinase activity, whereas little decline in penicillinase activity was noted over a period of 118 days.

False penicillin resistance in Neisseria meningitidis following direct susceptibility tests from blood cultures

“…3 It is not known how common this practice is in the UK, but it is not widespread in the USA. 4 Little has recently been published on the use of -lactamases in blood culture media, particularly in automated blood culture systems, but one study 5 demonstrated that the addition of -lactamases increased the isolation rates of organisms from blood significantly in clinical practice, although N meningitidis did not feature in that series. It is perhaps surprising that no clinical study has investigated the eVect of adding -lactamases to blood cultures from patients with invasive meningococcal disease treated with benzylpenicillin before admission to hospital.…”