RESUMEN
The efficacy of Clausen, EE, Eugon, GN, Tergitol 7, lactose and nutrient broths as Salmonella preenrichment media was evaluated using 165 food samples with an incident contamination level ranging from 1.5 to 460 salmonellae/100 g. Replicate food samples (100 g) were preenriched in each of seven media (900 ml) for 6 h and 24 h at 35 C; various amounts (10, 1.0 and 0.1 ml) of preenriched cultures were selectively enriched in tetrathionate brilliant green (43 C) and selenite cystine (35 C) broths and plated on bismuth sulfite and brilliant green sulfa agars. Short (6 h) and 24-h preenrichment conditions resulted in 26 (16%) and 8 (5%) false negative results, respectively. Recovery of Salmonella from 6-h but not 24-h preenrichment cultures also varied directly with the portion of culture inoculated into selective enrichment broths. None of the preenrichment media tested performed satisfactorily at 6 h of incubation where levels of recovery ranged from 32 to 62%; at 24 h, good recovery was obtained with all media (95 to 100%) except EE broth (74%). The incidence of competitive flora was significantly higher on selenite + brilliant green sulfa than on tetrathionate + bismuth sulfite; transfer volumes (10 and 1.0 ml) and preenrichment media did not contribute significantly to the presence of non-salmonellae on plating media. Characteristics of preenrichment media were found to be less critical than preenrichment incubation time for effective recovery of Salmonella in foods and feed ingredients. The use of 1.0- rather than 10-ml preenrichment transfer volume is indicated because it proved to be completely reliable under our experimental conditions and reduced the cost of analyses.
RESUMEN
The efficacy of two methods for detection of Salmonella in 29 fish and 312 shellfish samples was evaluated, using replicate samples (100 g) of food homogenate. In method A, samples were preenriched 3 h in lactose broth, selectively enriched overnight in selenite cystine (35 C) and plated on brilliant green sulfa, xylose lysine desoxycholate and Hektoen enteric agar media. In method B, overnight nutrient broth cultures were enriched in tetrathionate brilliant green (43 C) and selenite cystine (35 C) broths and plated on brilliant green sulfa and bismuth sulfite agar media. Salmonella was recovered from seven (3%) shrimp samples of which six were detected by method B alone; the single positive sample detected by method A was negative by method B. Infected shrimp samples did not harbor coagulase-positive staphylococci, and aerobic plate counts ranged from 105 to 107 cells/g; two of the seven positive samples contained no detectable Escherichia coli . Our results suggest that short preenrichment incubation periods are not reliable and that tetrathionate brilliant green is superior to selenite cystine for effective recovery of Salmonella in shellfish. Coliforms are not reliable as an index of microbiological quality of fish and shellfish.
RESUMEN
Numbers of Staphylococcus aureus , Saccharomyces cerevisiae and Penicillium expansum in artificially contaminated pasta declined exponentially during storage at room temperature; corresponding D values ranged from 18-21 days, 40-45 days and 130-160 days. In contrast to the rapid death kinetics of Aspergillus repens and Escherichia coli , Streptococcus faecium survived after 180 days of storage. These results suggest that streptococci are more reliable than E. coli as indicators of fecal contamination in pasta. Detection of Salmonella infantis and Salmonella typhimurium after 360 days indicates that prolonged storage of pasta is not effective for decontamination of infected products.
RESUMEN
Inhibitory concentrations of 8 surfactants were determined for Salmonella typhimurium and Salmonella enteritidis . Pure culture work resulted in the exclusion of Tween 20, Teepol 610 and Brij 35 and retention of Tergitol-7 (T-7), Tween 80 (TW 80), Triton X-100 (TX), Myrj 52S (M), and Arlacel 80 + Tween 60 (AT) for a study on the quantitative recovery of Salmonella in 45 naturally contaminated fatty foods. Replicate food samples (100 g) were preenriched overnight at 35 C in nutrient broth supplemented with 3%(w/v) surfactant except AT (10%). Serial dilutions of preenrichment cultures were selectively enriched overnight in tetrathionate brilliant green (43 C) and selenite cystine (35 C) broths and streaked on bismuth sulfite and brilliant green sulfa agar media. Recovery with all test surfactants was comparable to that obtained with nutrient broth controls; of 270 preenrichment cultures tested, only 7 false-negative results attributable to TX (3), AT (2), M (1), and nutrient broth control (1) were obtained. None of the surfactants consistently yielded greater populations of Salmonella for given foods or food categories; median counts for preenrichment cultures were 104-105 salmonellae/ml for low and high moisture foods and 106-107 salmonellae/ml for animal feeds. These results suggest that use of surfactants to facilitate detection of Salmonella in fatty foods is not warranted.
RESUMEN
Refrigeration (4 C) of non-selective and selective enrichment broth cultures for 72 h did not markedly affect detection of Salmonella in 160 contaminated high and low moisture foods. Detection in refrigerated preenrichment (non-selective) broth cultures of poultry and high and low moisture foods was 90, 95 and 100%, respectively; homologous results for refrigerated selective enrichment broth cultures were 90, 100 and 100%. All but one of the 22 negative results were obtained with poultry and two of the six laboratories participating in poultry analysis contributed 19 of the 21 negative results. Refrigeration of broth cultures provides greater operational flexibility by increasing the number of days on which analyses can be initiated without engendering work outside a normal work week.