Recovery Of Coliforms Research Articles

Aggregative Swab Sampling Method for Romaine Lettuce Show Similar Quality and Safety Indicators and Microbial Profiles Compared to Composite Produce Leaf Samples in a Pilot Study.

Composite produce leaf samples from commercial production rarely test positive for pathogens, potentially due to low pathogen prevalence or the relatively small number of plants sampled. Aggregative sampling may offer a more representative alternative. This pilot study investigated whether aggregative swab samples performed similarly to produce leaf samples in their ability to recover quality indicators (APCs and coliforms), detect Escherichia coli, and recover representative microbial profiles. Aggregative swabs of the outer leaves of romaine plants (n = 12) and composite samples consisting of various grabs of produce leaves (n = 14) were collected from 60 by 28 ft sections of a one-acre commercial romaine lettuce field. Aerobic plate counts were 9.17 ± 0.43 and 9.21 ± 0.42 log(CFU/g) for produce leaf samples and swabs, respectively. Means and variance were not significantly different (p = 0.38 and p = 0.92, respectively). Coliform recoveries were 3.80 ± 0.76 and 4.19 ± 1.15 log(CFU/g) for produce leaf and swabs, respectively. Means and variances were not significantly different (p = 0.30 and p = 0.16, respectively). Swabs detected generic E. coli in 8 of 12 samples, more often than produce leaf samples (3 of 14 positive, Fisher's p = 0.045). Full-length 16S rRNA microbial profiling revealed that swab and produce leaf samples did not show significantly different alpha diversities (p = 0.75) and had many of the most prevalent bacterial taxa in common and in similar abundances. These data suggest that aggregative swabs perform similarly to, if not better than, produce leaf samples in recovering indicators of quality (aerobic and coliform bacteria) and food safety (E. coli), justifying further method development and validation.

MICROBIOLOGICAL QUALITY OF LEAFY GREEN VEGETABLES GROWN IN THE TOLUCA VALLEY

The intake of fresh fruits and vegetables has increased in recent years, as have outbreaks of foodborne illnesses associated with these products. The risk of microbiological hazards in vegetables can occur from the field to the table. The main sources of contamination are agricultural soil and irrigation water, which can affect product quality and be a reservoir of foodborne pathogenic bacteria. This research analysed the microbiological quality of green leafy vegetable crops: spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.) and coriander (Coriandrum sativum L.), grown in the valley of Toluca. The presence of microorganisms indicating microbiological contamination (mesophilic bacteria, total coliforms, faecal coliforms and Escherichia coli, Salmonella and Listeria) was evaluated in plants, water and soil. Sampling, processing, isolation and bacterial identification were performed in accordance with Mexican Official Standards and the FDA Bacteriological Analytical Manual. The recovered bacteria were subjected to biochemical tests, serotyping and PCR. Microbial counts were present in 100 % of the samples tested. The spinach culture had higher recovery of mesophilic bacteria and total coliforms, while the lettuce culture presented higher values for the faecal coliform group. The results indicated higher microbiological contamination in water and soil > 250 CFU for mesophilic bacteria, total coliforms and faecal coliforms, respectively. The microbiological counts of the three cultures were found within the maximum limits established by Mexican regulations. However, the presence of faecal coliforms, which included E. coli bacteria of serotype O105 ab flagellar, compromises the quality of the product and poses a risk to the health of the consumer.

Development of a wild-type Escherichia coli environmental bloom model to evaluate alternatives to formaldehyde fumigation in broiler chicken hatch cabinets

Horizontal transmission of opportunistic Escherichia coli during hatch can have detrimental effects on early performance, particularly as pioneer colonizers. Commercially, formaldehyde is often applied in the United States to combat the bacterial bloom that occurs inside of the hatching environment. The purpose of these experiments was to develop a replicable E. coli horizontal challenge model to evaluate alternatives to formaldehyde sanitation applied to the hatching environment. In experiment 1, two trials were conducted for 2 wild-type (WT) E. coli isolates (isolate 1 [I1] or isolate 2 [I2]) to determine the appropriate in ovo challenge dose and day of embryogenesis (DOE) for challenge administration. In experiment 1 trial 1, the most appropriate inoculation dose and time point were determined to be 102 cfu/embryo on DOE 19. Experiment 1 trial 2 evaluated whether placement of seeder (direct-challenged) embryos with contact (indirect-challenged) embryos during hatch affected contact hatchability. Trial 2 showed no differences in hatchability between groups. A 7-day experiment (experiment 1 trial 2) was conducted to evaluate the effects of I1 or I2 on horizontal transmission, gram-negative bacterial (GNB) recovery from the gastrointestinal tract (GIT), and impact on BW gain (BWG). Compared with the negative control, seeder, and contact chicks challenged with I1 or I2, we observed increased (P < 0.05) GNB recovered from GIT on the day of hatch. There was a marked (P < 0.05) reduction in 7-day BWG between the I1 indirect-challenged group and the negative control group. To further validate the model, 2 7-day trials (experiment 2, experiment 3) were conducted to evaluate the effects of formaldehyde fumigation on coliform recovery from the hatching environment and on early performance using I1 for the challenge. Isolate 1 positive control hatchers had increased levels of circulating coliforms compared with the negative control and formaldehyde-treated hatchers, although there was no significant impact on performance induced by challenge or formaldehyde treatment in experiment 2 or experiment 3. These data provide a potential model for investigations related to horizontal transmission of WT E. coli at a low dose on DOE 19 to promote simulated commercially relevant bacterial blooms under laboratory conditions.

Injured coliforms in swimming pools : How big a threat?

A swimming pool is an important leisure facility, but it can harbor injured cells creating potential health hazards. Disinfection of swimming pools can cause bacterial injury, when cells are exposed to a suboptimal concentration of disinfectants. Possible pathogenic bacteria can enter into an injured state, for example, Escherichia coli, Klebsiella spp, and Enterococcus faecalis. Injured bacteria can retain their pathogenicity and virulence and they may recover causing diseases. To assess the presence of injured coliforms in swimming pools based on differential plating media. This study compared the difference in recovery of coliforms between two differential media, one designed for recovery of injured coliforms (HiCrome ECC selective agar and the other is CHROMagar ECC). A total of 120 samples were collected from 10 semi-public swimming pools with sporadic distribution around Alexandria, Egypt, and included in this study. Five pools were used for swim training, 4 were used for both training and recreational swimming and one was used for children only. The recovery medium (HiCrome ECC selective agar) detected 1.47 and 2.54 times total coliforms and E. coli, respectively, as CHROMagar ECC. The compliance of samples per fresh water swimming pool Egyptian standard in total coliforms and E. coli fell from 54.10% when examined by CHROMagar ECC medium to 35% by HiCrome ECC selective medium. The current findings may not be universal to all swimming pools but may be applicable to ones where the physicochemical properties of their water induce coliform injury. Results suggest that the use of media that detect injured yet viable coliforms will give a more sensitive and representative guidance about the quality of examined water and will assist in the treatment and decontamination of swimming pools.

Injured coliforms in swimming pools : How big a threat?

A swimming pool is an important leisure facility, but it can harbor injured cells creating potential health hazards. Disinfection of swimming pools can cause bacterial injury, when cells are exposed to a suboptimal concentration of disinfectants. Possible pathogenic bacteria can enter into an injured state, for example, Escherichia coli, Klebsiella spp, and Enterococcus faecalis. Injured bacteria can retain their pathogenicity and virulence and they may recover causing diseases.To assess the presence of injured coliforms in swimming pools based on differential plating media.This study compared the difference in recovery of coliforms between two differential media, one designed for recovery of injured coliforms (HiCrome ECC selective agar and the other is CHROMagar ECC). A total of 120 samples were collected from 10 semi-public swimming pools with sporadic distribution around Alexandria, Egypt, and included in this study. Five pools were used for swim training, 4 were used for both training and recreational swimming and one was used for children only.The recovery medium (HiCrome ECC selective agar) detected 1.47 and 2.54 times total coliforms and E. coli, respectively, as CHROMagar ECC. The compliance of samples per fresh water swimming pool Egyptian standard in total coliforms and E. coli fell from 54.10% when examined by CHROMagar ECC medium to 35% by HiCrome ECC selective medium.The current findings may not be universal to all swimming pools but may be applicable to ones where the physicochemical properties of their water induce coliform injury. Results suggest that the use of media that detect injured yet viable coliforms will give a more sensitive and representative guidance about the quality of examined water and will assist in the treatment and decontamination of swimming pools.

Drip Line Flushing with Chlorine May Not Be Effective in Reducing Bacterial Loads in Irrigation Water Distribution Systems

Irrigation water distribution systems are used to supply water to produce crops, but the system may also provide a protected environment for the growth of human pathogens present in irrigation water. In this study, the effects of drip tape installation depth and sanitization on the microbial quality of irrigation groundwater were evaluated. Drip tape lines were installed on the soil surface or 5 or 10 cm below the soil surface. Water samples were collected from the irrigation source and the end of each drip line every 2 weeks over an 11-week period, and the levels of Escherichia coli, total coliforms, aerobic mesophilic bacteria, and enterococci were quantified. Half of the lines installed at each depth were flushed with sodium hypochlorite for 1 h during week 6 to achieve a residual of 10 ppm at the end of the line. There was a statistically significant (P = 0.01) effect of drip tape installation depth and sanitizer application on the recovery of E. coli, with increased levels measured at the 5-cm depth and in nonsanitized lines, although the levels were at the limit of detection, potentially confounding the results. There was no significant effect of drip tape depth on total coliforms, aerobic mesophiles, or enterococci. In contrast, a statistically significant increase (P < 0.01) in the recovery of total coliforms was recorded from the ends of lines that received chlorine. This may be indicative of shedding of cells owing to degradation of biofilms that formed on the inner walls of the lines. These findings emphasize the need to better understand conditions that may lead to corrosion and increases in bacterial loads inside drip lines during flushing. Recommendations to growers should suggest collecting groundwater samples for testing at the end of drip lines rather than at the source. Guidelines on flushing drip lines with chlorine may need to include water pH monitoring, a parameter that influences the corrosive properties of chlorine.

Validation of a Novel Rinse and Filtration Method for Efficient Processing of Fresh Produce Samples for Microbiological Indicator Enumeration

Several methods have been described to prepare fresh produce samples for microbiological analysis, each with its own advantages and disadvantages. The aim of this study was to compare the performance of a novel combined rinse and membrane filtration method to two alternative sample preparation methods for the quantification of indicator microorganisms from fresh produce. Decontaminated cantaloupe melons and jalapeño peppers were surface inoculated with a cocktail containing 10(6) CFU/ml Escherichia coli, Salmonella Typhimurium, and Enterococcus faecalis. Samples were processed using a rinse and filtration method, homogenization by stomacher, or a sponge-rubbing method, followed by quantification of bacterial load using culture methods. Recovery efficiencies of the three methods were compared. On inoculated cantaloupes, the rinse and filtration method had higher recovery of coliforms (0.95 log CFU/ml higher recovery, P = 0.0193) than the sponge-rubbing method. Similarly, on inoculated jalapeños, the rinse and filtration method had higher recovery for coliforms (0.84 log CFU/ml higher, P = 0.0130) and E. coli (1.46 log CFU/ml higher, P < 0.0001) than the sponge-rubbing method. For jalapeños, the rinse and filtration method outperformed the homogenization method for all three indicators (0.79 to 1.71 log CFU/ml higher, P values ranging from 0.0075 to 0.0002). The precision of the three methods was also compared. The precision of the rinse and filtration method was similar to that of the other methods for recovery of two of three indicators from cantaloupe (E. coli P = 0.7685, E. faecalis P = 0.1545) and was more precise for recovery of two of three indicators from jalapeño (coliforms P = 0.0026, E. coli P = 0.0243). Overall, the rinse and filtration method performed equivalent to, and sometimes better than, either of the compared methods. The rinse and filtration method may have logistical advantages when processing large numbers of samples, improving sampling efficiency and facilitating microbial detection.

Tu2033 Role of Methionine Adenosyltransferase 2β in Resveratrol's Biological Activities in Liver Cancer Cells

1.20x105cfu/ml (range=0-8.6x105cfu/ml) (p,0.01 by Wilcoxon Rank Sum test for matched pairs). Interestingly, in the rats followed for 30 additional days, the stool Staphylococcal counts continued to drop to near non-detectable levels. In the case of coliforms, atbaseline, rats had a median of 1.86x104cfu/ml. By day 10 of rifaximin, stool coliform counts dropped to 2.2x103cfu/mL (P,0.01, Wilcoxon Rank sum test for matched pairs). However, complete recovery of stool coliforms was seen by 3 days after cessation of therapy. After dissection, coliforms were rare in the duodenum and jejunum as expected in normal animals. However, rifaximin did not affect the large number of coliforms in the colon. Using qPCR for total bacteria, only the duodenum demonstrated a significant reduction in bacteria (P=0.05). Interestingly, there was a trend for continued decline in bacteria in the duodenum even after cessation of rifaximin (P=0.08). Conclusions: Rifaximin has no durable effect on stool colonic coliform bacteria although durable reductions in stool Staphylococcal species are seen. Using qPCR, rifaximin has a durable effect on the total flora of the duodenum in normal rats.

Tu2032 VSL#3 Probiotic Treatment Prevents Ritonavir-Induced Gastrointestinal Barrier Dysfunction and Dyslipidemia in Mice

1.20x105cfu/ml (range=0-8.6x105cfu/ml) (p,0.01 by Wilcoxon Rank Sum test for matched pairs). Interestingly, in the rats followed for 30 additional days, the stool Staphylococcal counts continued to drop to near non-detectable levels. In the case of coliforms, atbaseline, rats had a median of 1.86x104cfu/ml. By day 10 of rifaximin, stool coliform counts dropped to 2.2x103cfu/mL (P,0.01, Wilcoxon Rank sum test for matched pairs). However, complete recovery of stool coliforms was seen by 3 days after cessation of therapy. After dissection, coliforms were rare in the duodenum and jejunum as expected in normal animals. However, rifaximin did not affect the large number of coliforms in the colon. Using qPCR for total bacteria, only the duodenum demonstrated a significant reduction in bacteria (P=0.05). Interestingly, there was a trend for continued decline in bacteria in the duodenum even after cessation of rifaximin (P=0.08). Conclusions: Rifaximin has no durable effect on stool colonic coliform bacteria although durable reductions in stool Staphylococcal species are seen. Using qPCR, rifaximin has a durable effect on the total flora of the duodenum in normal rats.

Effect of Long-Term Freezing and Freeze–Thaw Cycles on Indigenous and Inoculated Microorganisms in Dewatered Blackwater

Wastewater treatment in many Arctic regions is inadequate, even nonexisting. Natural freezing of wastewater in those areas may be beneficial for reduction of microorganisms. The aim of this study was to investigate the effect of long-term freezing, and repeated freezing and thawing, on indigenous coliforms, fecal streptococci, and antibiotic-resistant (AR) bacteria, and inoculated Salmonella Enteriditis and E. coli bacteriophage ΦX174 in dewatered blackwater. At the end of the long-term freezing experiment (10 months), an MPN recovery study was done, including the microbial groups that had shown the largest reduction, using tryptone soy broth at incubation temperatures of 10 and 20 °C overnight for the coliforms and AR bacteria, and buffered peptone water at incubation temperature of 37 °C for 18-20 h for Salmonella. Fecal streptococci were more resistant to long-term freezing than the coliform group. Total number of AR bacteria decreased slowly but constantly over the 10-month freezing period. Salmonella rapidly decreased and were nondetectable within a week but exhibited some recovery after 10 months of freezing, whereas limited or no recovery of coliforms and AR-bacteria was detected. Bacteriophages showed limited reduction during the long-term freezing. Repeated freezing and thawing increased the reduction of all tested microbial groups markedly.

Sampling method and location affect recovery of coliforms and Escherichia coli from broiler carcasses

Two experiments were conducted, the first to determine whether numbers of recovered bacteria differed due to sampling method used or due to location on carcass sampled (breast or leg quarters) and the second to determine if numbers of bacteria differed between the front (ventral) and back (dorsal) side of the carcass. In both experiments, eviscerated broiler carcasses were obtained from a commercial processing plant just before the final inside-outside bird washer. In experiment 1, carcasses (3 in each of 4 replicate trials) were separated into leg quarters and breast quarters (n = 48) and either rinsed or ground and stomached for microbiological sampling. In experiment 2, for 3 replicate trials of 4 carcasses each, necks, wings, and legs were manually removed; the remaining trunks were cut through the sides to produce front (ventral) and back (dorsal) halves (n = 24); and then rinsed. For both experiments, coliforms and Escherichia coli were enumerated. In experiment 1, significantly higher numbers (P < 0.05) of coliforms and E. coli were recovered by rinsing than by grinding from both breast and leg quarters. Leg quarters were found to have higher bacterial numbers than breasts from grind samples, but no quarter differences were found for rinse samples. In experiment 2, higher (P < 0.05) numbers of coliforms and E. coli were recovered from the dorsal carcass half compared with the ventral half. Bacterial counts of broiler carcasses are affected by both the sampling method used and by carcass location sampled.

Comparison between Colifast® Milk and the standard method for the detection of coliforms in pasteurised milk

Colifast® Milk is a rapid screening test for the detection of total coliforms in milk based upon the measurement of change in fluorescence during an incubation period, due to the targeted -D-galactosidase activity on 4-methyl-umbelliferone--D-galactoside contained in a selective growth medium. In this work, 800 samples of homogenised pasteurised milk, with different fat content (1.5 and 3.5%) and contaminated with various concentrations of coliforms (from 0.03 to > 10000 CFU·mL -1 ), were analysed in order to compare the results obtained by Colifast ® Milk with those by the standard method. The effect of the incubation temperature (30 and 39 °C) was also investigated. For the totality of samples the correspondence between coliform counts obtained by the two methods was 64% (r 2 = 0.743; P = 0.88). The performance of Colifast ® Milk was notably affected by the level of contamination, since for samples with coliforms > 10 CFU·mL -1 the correspondence between the two methods achieved 86% (r2 = 0.837; P = 0.94) whereas for samples with coliforms 10 CFU·mL -1 it fell to 42% (r 2 = 0.073; P = 0.33). Fat content also influenced the response of the Colifast ® system since the correspondence decreased from 80% (r 2 = 0.767; P = 0.91) for semi-skimmed milk to 48% (r2 = 0.724; P = 0.63) for whole milk. Incubation at 30 °C improved the recovery of coliforms by Colifast ® Milk as the correspondence between values obtained with the two methods reached 72% (r 2 = 0.760; P = 0.89) if compared with 56% (r 2 = 0.735; P = 0.87) when the incubation temperature was 39 °C. Under these operating conditions the sensitivity showed by the fluorometric method appeared to be not sufficient for the detection of coliforms in pasteurised milk. Colifast ® Milk / coliform / method / milk

Development of a Thin Tube Cultivation Method for Determining Coliform Counts in Milk

A new rapid coliform-monitoring method using thin tube cultivation (TTC) was developed. One hundred microliters of modified selective medium (1.5% agar) and 100μl of sample were mixed in thin cultivation tubes, yielding a semisolid mixture of 0.75% agar. The tubes were incubated at 37°C and checked for a positive reaction (gas production from lactose fermentation and color changes from acid production) at 30-min intervals. The positive reaction times for TTC were compared with actual coliform numbers. The first experiment was performed to validate the TTC method using pure coliform cultures (the Escherichia coli group, the Enterobacter cloacae group, and the Klebsiella pneumoniae group). The results indicated that the TTC method saved about 10 to 14 h of incubation time compared with the conventional plating method. When coliforms were present in small numbers, such as 1 to 1.5 log10 CFU/ml, the TTC method detected their presence within 10 h. When highly contaminated samples were assayed (6 log10 CFU/ml), the TTC method detected the presence of coliforms within 4 to 5 h. In a food system experiment, pasteurized skim milk inoculated with a coliform mixture was assayed by the TTC method. The coliforms in the milk were quickly detected, resulting in a savings of 11 to 14 h compared with the conventional plating method. Cold-injured coliforms were studied to evaluate the TTC system. The recovery and estimation of injured coliforms by the TTC method strongly agree with those of the conventional plating method. The TTC system was also applied to ascertain the levels of natural coliforms in noninoculated milk. The TTC system reduced incubation times by about 11 to 14 h compared with the conventional plating method. According to these data, this method is a rapid, simple, accurate, and economical way to monitor and estimate total coliforms in milk.

Comparison of Methods for Determining Coliform and Escherichia coli Levels in Apple Cider

The main objective of this research was to determine the easiest and most reliable media for enumerating coliform bacteria and Escherichia coli levels in apple cider. During the autumn of 1994 a total of 59 apple cider samples were collected directly from 12 cider producers and were assessed for bacterial levels and pH. Plate count agar was used to determine heterotrophic bacteria levels. Coliform levels were determined using three different media: violet red bile agar (VRBA), Petrifilm High Sensitivity Coliform Count Plates (PHSCCP), and Trypticase soy agar with a VRBA overlay (TSA/VRBA) for attempted recovery of coliforms injured by the low pH of the apple cider. Eosin methylene blue agar (EMBA) and Petrifilm E. coli Count Plates were used to screen cider samples for E. coli. Apple cider had an average pH of 3.34 ± 0.08. Heterotrophic bacterial levels ranged from 2.30 to 7.11 log CFU/ml. All cider samples contained coliform bacteria with levels varying greatly; on the different media, we found the following: on VRBA, <1.00 to 4.37 log CFU/ml; on TSA/VRBA, 1.20 to 4.40 log CFU/ml; and on PHSCCP, < 1.00 to 4.56 log CFU/ml. Coliform levels were most easily determined in apple cider by using PHSCCP. However TSA/VRBA proved to be more reliable; coliform detection was significantly (P < 0.05) increased. EMBA was ineffective for screening apple cider for E. coli, with the low pH of the cider producing many false-positive results. E. coli was only recovered by using Petrifilm E. coli Count Plates with one of the 59 samples positive for E. coli (non-O157:H7) at a level of 10 CFU/ml.

Use of two formulations of Colilert and QuantiTray ™ for assessment of the bacteriological quality of water

The use of standard Colilert (IDEXX) for the detection of coliforms and E. coli in potable water has been studied. In a large survey, Colilbert recovered E. coli from similar numbers of samples to membrane filtration whilst recovery of coliforms was higher with Colilert. Further experiments to study the sensitivity of the two methods using pure cultures, showed that there was no significant difference in their ability to recover E. coli. Studies on a newly developed form of Colilert (Colilert 18) which is said to give results within 18 h showed that there was no significant difference between the two forms of the product. Use of the Colilert 18 in a quantitative format using QuantiTray™ showed that the product gave similar quantitative results to membrane filtration, but was easier to read and was less time consuming. Subculture of a proportion of positive samples demonstrated that there was no need to confirm results obtained with the Colilert/QuantiTray ™ system. The results of this study suggest that both formulations of Colilert are suitable alternatives to the United Kingdom membrane filtration method for monitoring the bacteriological quality of drinking water.

Impact of chlorine injury on reaction kinetics of coliforms and E. coli in colisureTM and LTB

This study compared a chromogenic and fluorogenic substrate based medium, Colisure, with the conventional fermentation based medium, lauryl tryptose broth (LTB), for the recovery of chlorine-injured and non-injured coliforms and E. coli. Mixed natural populations of coliforms from sewage, with and without chlorine exposure, and untreated surface water samples were examined following a USEPA established procedure. Colisure and LTB were examined after 20, 24, 28 and 48h incubation and reactions verified. There were slight increases in positive reactions over time with unchlorinated samples, for which the two media gave similar kinetic patterns. The increases over time with chlorinated samples were much greater than with unchlorinated samples. LTB gave significantly lower total positive responses and had a more pronounced lag period than did Colisure. Total coliform bacteria from surface water samples gave somewhat different reactions with more of an increase with time. Colisure recovered comparable or higher numbers of total coliforms and E. coli in 20–28h than LTB after 48h. These results confirm that Colisure gives improved recovery of chlorine-injured total coliforms and E. coli under conditions simulating treated drinking and source water, resulting in a more realistic estimate of the actual population of indicator bacteria in public water supplies.

Recovery of coliform bacteria from rural groundwater supplies using reduced oxygen concentrations during incubation.

The effect of decreased oxygen concentration during incubation of M-Endo medium on detection of coliforms from rural groundwater supplies was examined. Incubation oxygen concentrations of 0¿(anaerobic GasPak), 4, 8, and 21% (atmospheric) were examined. Our findings point to several advantages of using anaerobic incubation for the isolation of coliforms: (i) higher verification rates with concomitant decreases in occurrence of false-positive coliforms; (ii) overall reduction in growth of nonsheen colonies; and (iii) reduction in colony size for nonsheen organisms, thereby minimizing crowding effects and facilitating enumeration of coliform colonies. However, these advantages were not sufficient to permit increased recovery of total coliforms as compared with aerobic incubation. In addition, the increased frequency of detecting false-negative coliforms during anaerobic incubation is a disadvantage to this method. While detection of total coliforms was reduced under conditions of anaerobiosis,the detection of fecal coliforms and (or) E. coli was not impeded.

Impact of chlorine injury on reaction kinetics of coliforms and E. coli in colisure™ and LTB

This study compared a chromogenic and fluorogenic substrate based medium, Colisure, with the conventional fermentation based medium, lauryl tryptose broth (LTB), for the recovery of chlorine-injured and non-injured coliforms and E. coli. Mixed natural populations of coliforsns from sewage, with and without chlorine exposure, and untreated surface water samples were examined following a USEPA established procedure. Colisure and LTB were examined after 20, 24, 28 and 48h incubation and reactions verified. There were slight increases in positive reactions over time with unchlorinated samples, for which the two media gave similar kinetic pattems. The increases over time with chlorinated samples were much greater than with unchlorinated samples. LTB gave significantly lower total positive responses and had a more pronounced lag period than did Colisure. Total coliform bacteria from surface water samples gave somewhat different reactions with more of an increase with time. Colisure recovered comparable or higher numbers of total coliforms and E. coli in 20–28h than LTB after 48h. These results confirm that Colisure gives improved recovery of chlorine-injured total coliforms and E. coli under conditions simulating treated drinking and source water, resulting in a more realistic estimate of the actual population of indicator bacteria in public water supplies.

Interlaboratory evaluation of MI agar and the US Environmental Protection Agency-Approved Membrane Filter Method for the recovery of total coliforms and Escherichia coli from drinking water

A new membrane filter (MF) medium, MI agar, recently validated for use in recovering chlorine-damaged total coliforms (TC) and Escherichia coli from drinking water, was compared to the US Environmental Protection Agency (EPA)-approved MF method (mEndo agar and nutrient agar supplemented with 4-methylumbelliferyl-β- d-glucuronide) in a collaborative study. Six wastewater-spiked Cincinnati tap water samples, containing three different concentrations of E. coli (≤ 10, 11–30, and >30 E. coli/100 ml), were analyzed concurrently by 19 geographically dispersed laboratories. Results showed that although the overall recoveries of TC and E. coli with MI agar were 12% and 26% greater, respectively, than those of the approved method, the differences were not statistically significant (α=0.05). However, the overall recovery of background/non-coliforms by the new method, 5% of the mEndo agar recovery, was significantly lower ( P=0.0009). Since the results of this study show MI agar to be equal to or better than the current method, it meets the criteria for routine compliance monitoring of drinking water.

Microbial Safety and Quality and Protein Integrity of Shrimp Sold in Shops in Riyadh, Saudi Arabia

The microbial safety and quality were assessed of shrimp from fish shops located in five separate zones in Riyadh City, Saudi Arabia. Protein hydrolysis of the shrimp was determined as a function of microbial growth by using an isoelectric focusing technique. A resuscitation culture step also was assessed and compared with direct plating on selective media for detection of the coliform group and fecal enterococci. The results of this study indicated high (6.23 to 7.23), moderate (4.10 to 5.94), and low (3.49 to 3.94 log CFU/g) ranges of psychrotrophic counts in 23.3, 60, and 16.7% of the samples, respectively. Statistical analysis showed significant (P < 0.05) differences in the psychrotrophic counts among the zones tested, with the highest counts being in the western and central zones, and the lowest counts in the northern zone. Similar results were obtained with coliform, fecal enterococci, and staphylococci counts. Use of the resuscitation step resulted in significantly (P < 0.05) higher recovery of coliforms and fecal enterococci. Band intensities of the sarcoplasmic proteins, as shown in the gel electrophoresis, were faint in samples with higher counts and comparatively intense in the ones with lower counts, indicating a clear relationship between product degradation and microbial load.