COMPARISON OF PETRIFILM AEROBIC COUNT PLATES AND DE MAN–ROGOSA–SHARPE AGAR FOR ENUMERATION OF LACTIC ACID BACTERIA

Abstract

ABSTRACT This study aimed to compare Petrifilm aerobic count (AC) plates (3M Microbiology, St. Paul, MN) and de Man–Rogosa–Sharpe (MRS) agar for enumeration of lactic acid bacteria (LAB). The study was conducted with suspensions of 10 species of LAB prepared in reconstituted powdered milk. Raw milk samples, without any added bacteria, were also tested. For selective enumeration in Petrifilm AC plates, the suspensions of LAB and the raw milk samples were submitted to decimal dilutions in MRS broth prior to plating. Petrifilm AC and MRS agar plates were incubated in jars at 30C for 72 h, in microaerophilic conditions (Campygen, Oxoid, Basingstoke, U.K.). Differences in counts in the two culture media were not significant (P ≤ 0.05), regardless of the species of the LAB. Results presented high correlation indexes for both LAB suspensions (r = 0.9922, r2 = 0.9845, P = 0.00) and raw milk samples (r = 0.9841, r2 = 0.9685, P = 0.00). These results indicate that the advantages of using Petrifilm AC plates for a rapid enumeration in aerobic microorganisms can be extended for enumeration of LAB in foods. Their convenience is particularly interesting for testing fermented milk products.