THE SIGNIFICANCE OF VARIOUS ORGANISMS OF FAECAL ORIGIN IN FOODS AND DRINKING WATER

The species accuracy of the Most Probable Number (MPN) European Union reference method for enumeration of Escherichia coli in marine bivalves

Continuous European Union programmes with specified methods for enumeration of Escherichia coli in bivalves for human consumption are currently running. The objective of this research was to examine the species accuracy of the five times three tube Most Probable Number (MPN) EU reference method used for detection of E. coli in marine bivalves. Among 549 samples of bivalves harvested from Norwegian localities during 2014 and 2015, a total number of 200 bacterial isolates were prepared from randomly selected culture-positive bivalves. These presumptive E. coli isolates were characterized biochemically by the Analytical Profile Index (API) 20E, as well as by Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). The majority of isolates (90%) were identified as E. coli, by both API 20E and MALDI-TOF MS. Ten isolates (5%) were identified as Klebsiella pneumoniae, while one isolate was identified as K. oxytoca by both methods, whereas three isolates were identified as Acinetobacter baumannii, Citrobacter braakii, and Enterobacter cloacae, respectively. The identification of the remaining six isolates were not in compliance between the two methods.

Seven-hour fluorescence in situ hybridization technique for enumeration of Enterobacteriaceae in food and environmental water sample

AIMS

A fluorescent in situ hybridization (FISH) technique using an Enterobacteriaceae-specific probe (probe D) to target 16S rRNA was improved in order to enumerate, within a single working day, Enterobacteriaceae present in food and environmental water samples.

METHODS AND RESULTS

In order to minimize the time required for the FISH procedure, each step of FISH with probe D was re-evaluated using cultured Escherichia coli. Five minutes of ethanol treatment for cell fixation and hybridization were sufficient to visualize cultured E. coli, and FISH could be performed within 1 h. Because of the difficulties in detecting low levels of bacterial cells by FISH without cultivation, a FISH technique for detecting microcolonies on membrane filters was investigated to improve the bacterial detection limit. FISH with probe D following 6 h of cultivation to grow microcolonies on a 13 mm diameter membrane filter was performed, and whole Enterobacteriaceae microcolonies on the filter were then detected and enumerated by manual epifluorescence microscopic scanning at magnification of x100 in ca 5 min. The total time for FISH with probe D following cultivation (FISHFC) was reduced to within 7 h. FISHFC can be applied to enumerate cultivable Enterobacteriaceae in food (above 100 cells g-1) and environmental water samples (above 1 cell ml-1).

CONCLUSIONS

Cultivable Enterobacteriaceae in food and water samples were enumerated accurately within 7 h using the FISHFC method.

SIGNIFICANCE AND IMPACT OF THE STUDY

A FISHFC method capable of evaluating Enterobacteriaceae contamination in food and environmental water within a single working day was developed.

Enterococci in milk and milk products

Enterococci are widely distributed in nature. They gain entry into milk and milk products through the water supply, equipment, and insanitary and unhygienic conditions of production and handling. They have been incriminated as direct or indirect agents of disease. The evidence concerning their involvement is only circumstantial. These reports are also disputed as the disease symptoms have not been experimentally induced in animal models. However, there is sufficient evidence to indicate that prolific growth of enterococci in foods may lead to formation of clinically significant levels of pressor amines. These amines are very thermostable and therefore remain active even after heat processing, which eliminates all viable streptococci. These pressor amines may be involved in the onset of migraine attacks and produce hypersensitive crises in psychiatric patients who are being treated with monoamine oxidase inhibitors for depression.

Enumeration and speciation of group D streptococci from above and below a sewer outfall, their susceptibilities to six antibiotics and a comparison with clinical isolates

Isolates of group D streptococci from above and below a sewer outfall and a series of clinical isolates have been speciated to sub-species level. From below the sewer outfall, Streptococcus faecalis var. faecalis predominates whereas above the outfall, S. faecium var. casseliflavus predominates. S. faecalis var. faecalis, S. faecalis var. liquefaciens and S. faecalis var. zymogenes were the predominant sub-species in the clinical isolates where S. faecium var. casseliflavus was virtually absent. S. faecalis var. liquefaciens and S. faecalis var. zymogenes were uncommon in the environmental isolates. S. faecium and S. durans were more abundant in the environmental than in the clinical isolates. The use of group D streptococci as indicators of faecal pollution would seem more suited to higher, rather than lower, levels of pollution. A statistically significant increase in resistance to antibiotics (ampicillin, penicillin, streptomycin, gentamicin, erythromycin and tetracycline) was seen in isolates from below the outfall compared with those from above and a further significant increase was seen in the clinical isolates compared with the former. Resistance to tetracycline was most common and ampicillin was the only antibiotic tested to which no resistance was detected. Multiple antibiotic resistance was rare in the environmental isolates. Even in moderately polluted water, there is not a large pool of antibiotic resistance.

Sorbitol-fermenting bifidobacteria as specific indicators of human faecal pollution

Bifidobacteria were consistently present in the faeces of both man and pigs but only occasionally in the faeces of cattle and sheep, and they were not isolated from faecal samples from other animals; total counts of bifidobacteria were obtained by membrane filtration with YN-17 medium, a modification of Resnick and Levin's YN-6 medium. Mannitol-fermenting strains of bifidobacteria were isolated from both human and animal faeces, but sorbitol-fermenting strains were obtained only from human samples. These sorbitol-fermenting strains were identified as either Bifidobacterium adolescentis or B. breve and their numbers were obtained by membrane filtration of Human Bifid Sorbitol agar (HBSA). Sorbitol-fermenting bifidobacteria are specific indicators of human faecal pollution of waters and wastewaters.

Multiple antibiotic resistance indexing of Escherichia coli to identify high-risk sources of fecal contamination of foods

Escherichia coli isolates taken from environments considered to have low and high enteric disease potential for humans were screened against 12 antibiotics to determine the prevalence of multiple antibiotic resistance among the isolates of these environments. It was determined that multiple-antibiotic-resistant E. coli organisms exist in large numbers within the major reservoirs of enteric diseases for humans while existing in comparatively low numbers elsewhere. These differences provide a method for distinguishing high-risk contamination of foods by indexing the frequency with which multiple-antibiotic-resistant E. coli organisms occur among isolates taken from a sample.

Enterobacteriaceae associated with meats and meat handling

The source of Enterobacteriaceae on meats was shown to be associated with the meat-handling work surfaces in two packing plants studies. A total of 2,343 Enterobacteriaceae were isolated and identified from meat samples and work surfaces at the packing plants and at the retail facilities. Escherichia coli biotype I and Serratia liquefaciens were detected at all stages of meat handling, indicating that they may be present in meats throughout the meat-handling system. Enterobacter agglomerans and S. liquefaciens were the predominant Enterobacteriaceae at the retail level, but they had limited indicator potential for sanitation and hygiene, Klebsiella pneumoniae was a frequent isolate among Enterobacteriaceae from meats and meat-handling surfaces in the packing plants but not at the retail level, indicating that this organism might signal unhygienic handling of meats at the retail level.

On the transformation of coliform types, proper and irregular forms

Physiological changes have been induced in strains of E. coli I and its irregular forms, using a basal synthetic medium and addition of sodium pyruvate, or glucose, or yeast extract, or peptone. Changes in biochemical patterns, using the IMViC reactions plus growth at 44.5 degrees C, were induced, thus brining transformations between the regular types and irregular forms. Ultra-violet irradiation of E. coli I for 90 seconds may turn it into a methyl-red negative strain, while education of E. coli III for producing acid and gas at 44.5 degrees C was possible. Thus, E. coli I could be transformed to give the same reactions as the untyped form 1 of Geldreich (1966) through U.V. irradiation, while E. coli III may give the biochemical reactions of E. coli I via heat-resistance and training in MacConkey broth. The relationship between regular and irregular coliforms was also verified by phage typing. The results obtained were discussed both qualitatively, using "lytic activity", and quantitatively in terms of "efficiency of plating", especially with sewage-derived phages and irregular coliforms.