Comparison of four hippurate hydrolysis methods for identification of thermophilic Campylobacter spp.

The test for hippurate hydrolysis is critical for separation of Campylobacter jejuni and C. coli strains. Glycine and benzoic acid are formed when hippurate is hydrolyzed by C. jejuni. The test used in most laboratories is one of several variations of the ninhydrin tube test described by Hwang and Ederer (M. Hwang and G. M. Ederer, J. Clin. Microbiol. 1:114-115, 1975) for detection of glycine. We evaluated three modifications of the Hwang and Ederer method and the gas-liquid chromatographic (GLC) method described by Kodaka et al. (H. Kodaka, G. L. Lombard, and V. R. Dowell, Jr., J. Clin. Microbiol. 16:962-964, 1982) for detecting benzoic acid. Campylobacter strains comprised 22 C. jejuni, 11 C. coli, and 8 C. laridis strains. The species identification of each strain was confirmed by DNA relatedness. All strains of C. jejuni were positive and all strains of C. coli and C. laridis were negative by the GLC method for detecting hippurate hydrolysis, whereas three strains of C. jejuni gave negative or variable results in the tube tests. The GLC method is more sensitive than the tube methods for detecting hippurate hydrolysis and should be used on cultures yielding variable or questionable test results.

Comparison of gauze swabs and membrane filters for isolation of Campylobacter spp. from surface water.

The epidemiology of Campylobacter jejuni indicates that waterborne transmission is important; the organism has been isolated from seawater, fresh water, and estuarine sites. Membrane filtration, with and without use of an enrichment broth, has been the most common method for isolating C. jejuni from water. We evaluated two methods for isolating C. jejuni from water: membrane filtration and gauze filtration. The membrane filters evaluated included 0.22- and 0.45-micron-pore Millipore filters (Millipore Corp., Bedford, Mass.), 0.2- and 0.4-micron-pore Nuclepore filters (Nucleopore Corp., Pleasanton, Calif.), and a 0.45-micron-pore Zetapor filters (AMF Cuno, Meridian, Conn.). The gauze filters included both Moore and Spira swabs. Of the membrane filters evaluated, the 0.45-micron-pore Millipore and Zetapor filters were the most sensitive for recovery of C. jejuni from seeded waters. The 0.45-micron-pore Millipore filter placed in Oosterom broth was better for recovery of C. jejuni from seeded stationary surface waters than either the Spira or Moore swab. However, the 0.45-micron-pore Millipore filter placed on a plate or in enrichment broth was equivalent to the Spira gauze swab when used to examine water from Atlanta area streams. C. jejuni organisms were isolated from 9 of 24 surface water samples representing 5 of 12 streams.

Microbiological Profile and Storage Temperatures of Egyptian Rice Dishes.

Cooked rice and other dishes containing rice (172 samples) were tested for aerobic colony count (30°C), Salmonella , Shigella , Staphylococcus aureus , and presumptive Bacillus cereus . Salmonella was isolated from a sample of Oriental rice that was prepared in a five-star hotel kitchen. Shigella was isolated from a sample of boiled rice from a four-star hotel kitchen. Nineteen percent of the samples were contaminated by S. aureus , and 73% of these contained more than 103/g. Forty percent of the samples were contaminated by B. cereus , 31% of these contained more than 103/g. Rice was more frequently stored at safe temperatures (>55°C) in four- and five-star hotels than in any other type of establishment or that which was sold by street venders. Aerobic colony counts (30°C) per g were usually quite low when rice was held at temperatures of 55°C or higher. These counts generally became progressively higher as the temperature decreased, often reaching quantities exceeding 106 when temperatures were 44°C or below. This was particularly so when the temperature range was 25-34°C. These counts were lower for fried and Oriental rice than for boiled rice, rice and vegetables, kushari (a mixture of rice, macaroni and lentils), and rice and shirea (thin, wheat macaroni).

Microbiological Profiles of Egyptian Raw Vegetables and Salads.

Two hundred-fifty samples of raw vegetables and salads that were collected from hotels, restaurants, small foodservice shops, markets and street vendors in Egypt were tested for Salmonella , Shigella and aerobic colony (30°C) count. Thirty-six of these samples were tested for Staphylococcus aureus . Salmonella was isolated from two samples of green leafy vegetables (greens) and one sample of mixed salad that most likely contained greens. Shigellae were isolated from one sample of greens, one sample of parsley, and three samples of mixed salads. Most samples of raw vegetables and salads were at either room or outside temperature just before sampling. Eighty percent of the samples had aerobic colony counts of more than 106 CFU/g. Three of 36 samples contained ca. 1 × 103 S. aureus /g.

Microbiological Profiles and Storage Temperatures of Egyptian Fish and Other Sea Foods.

Raw and cooked fish and other sea foods (108 samples) were collected from hotels of different classes, restaurants, markets, street vendors, and small cook-shops and analyzed for common foodborne pathogens. Salmonellae were isolated from two samples of raw shrimp, but not from raw fish and other seafoods. Shigella was isolated from one sample of raw fish and from two samples of raw shrimp. Vibrio parahaemolyticus was isolated from three raw fish samples and one raw shrimp sample. Forty-eight percent of samples of raw fish, 30% of samples of raw shrimp, and a sample of raw mussels and a sample of crab contained Staphylococcus aureus . Cooked products were free from salmonellae, shigellae and V. parahaemolyticus , but approximately 1/3 of these contained S. aureus , which suggests contamination after cooking. Aerobic colony count (30°C) of cooked fish and shellfish dishes was more than a million organisms/g. Such large numbers of microorganisms on cooked products suggests either a prolonged holding time or gross contamination after cooking.