Lactobacillus acidophilus exerted antagonistic actions on growth of Staphylococcus aureus, Salmonella typhimurium, enteropathogenic Escherichia coli, and Clostridium perfringens when grown with each in associative cultures. S. aureus and C. perfringens were more sensitive to the inhibition than were S. typhimurium and E. coli. The amount of the antagonism produced varied among strains of L. acidophilus and could not be directly related to amounts of acid produced; hydrogen peroxide produced by the lactobacilli appeared to be partially responsible for the antagonistic interaction. The inhibitory effect was produced also under anaerobic conditions in a pre-reduced medium.

A PCR identification of methicillin-resistant Staphylococcus aureus (MRSA), obviating the need for subculture on agar media, was investigated. The combination of MRSA detection by mecA femB PCR with prior enrichment in selective broth was tested for 439 swabs. PCR identified 36 MRSA-positive samples, in concordance with conventional methods.Accurate and rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) in clinical specimens is essential for timely decisions on isolation procedures and effective antimicrobial chemotherapy. Numerous approaches that improve turnaround time for the identification of MRSA have been described. Fluorescence tests (14), PCR assays (4), or penicillin-binding protein 2a (PBP2a) antibody agglutination tests have been described elsewhere (12). Yet, these require subculture on solid media, and many are unable to determine species and methicillin susceptibility at the same time. A simultaneous test of methicillin resistance and species confirmation by a mecA femB duplex PCR has been proposed elsewhere (16). The mecA gene encodes the extra PBP2a, which is unique to methicillin-resistant staphylococci. The femB gene codes for an enzyme important in cross-linking peptidoglycan in various different Staphylococcus spp. The specificity of the femB PCR primers used for DNA amplification of the species S. aureus has been demonstrated previously (8).This study describes the performance of this technique in a clinical setting of moderate MRSA endemicity where large numbers of screens need to be processed on a daily basis. Moreover, the robustness of the test was investigated by determining the number of false-positive readings due to coamplification of femB and mecA from methicillin-susceptible S. aureus (MSSA) and methicillin-resistant coagulase-negative staphylococci (R-CNS) coexisting at the sample site (C. M.

No abstract

Production of heat resistant proteases by psychrotrophs growing in milk, resistance of such proteases to ultrahigh temperature treatments and action of these enzymes on milk were studied. All of the psychrotrophs obtained from raw milk produced proteases that survived 149 C for 10s. Seventy to ninety percent of the raw milk samples contained psychrotrophs capable of producing heat resistant proteases. The protease chosen as a model was resistant to heat treatments at 110 to 150 C, and the inactivation parameters suggested that thermal destruction of heat resistant proteases would damage the milk severely. The casein content and pH of normal milk were suitable for protease action, and the protease was quite active at normal and elevated room temperatures. The protease rapidly spoiled sterile milk with the development of bitter flavor, clearing, or coagulation; and the susceptibility of sterile milk to protease increased during storage of the milk.

Lactobacillus species normally found in the intestinal tract of humans varied in the ability to deconjugate bile acids, whereas laboratory strains of Lactobacillus acidophilus deconjugated both glycocholate and taurocholate. All isolates of L. acidophilus from human feces deconjugated taurocholate, whereas only one of six deconjugated glycocholate. None of 13 isolates identified as L. casei deconjugated taurocholate, whereas 9 deconjugated glycocholate. The deconjugating system of L. acidophilus appeared to be constitutive, required low oxidation-reduction potential, and was most active at pH 6. No degradation beyond deconjugation was detected.

No abstract

No abstract

More than 90% of the surviving cells of Escherichia coli NCSM were injured after freezing in water at-78 C. Injury was determined by the ability of cells to form colonies on Trypticase soy agar with yeast extract but not on violet red-bile agar and deoxycholate-lactose agar. Exposure of the injured cells to Brilliant Green-bile broth and lauryl sulfate broth prevented subsequent colony formation on Trypticase soy agar with yeast extract. The freeze-injury could be repaired rapidly in a medium such as Trypticase soy broth with yeast extract (TSYB). The repaired cells formed colonies on violet red-bile agar and deoxycholate-lactose agar and were not inhibited by Brilliant Green-bile broth and lauryl sulfate broth. At least 90% of the cells repaired in TSYB within 30 min at 20 to 45 C and began multiplication within 2 h at 25 C. When the cells were frozen in different foods, 60 to 90% of the survivors were injured. Repair of the injured cells occurred in foods during 1 h at 25 C, but generally repair was greater and more reproducible when the foods were incubated in TSYB. The study indicated that the repair of freeze-injured coliform bacteria should be accomplished before such cells are exposed to selective media for their enumeration.