Comparison of Vogel-Johnson and Baird-Parker media for membrane filtration recovery of staphylococci in swimming pool water

Performance of CHROMagar Staph aureus and CHROMagar MRSA for detection of Staphylococcus aureus in seawater and beach sand--comparison of culture, agglutination, and molecular analyses

Beach seawater and sand were analyzed for Staphylococcus aureus and methicillin resistant S. aureus (MRSA) for samples collected from Avalon, and Doheny Beach, CA. Membrane filtration followed by incubation on CHROMagar Staph aureus (SCA) and CHROMagar MRSA (C-MRSA) was used to enumerate S. aureus and MRSA, respectively. Media performance was evaluated by comparing identification via colony morphology and latex agglutination tests to PCR (clfA, 16S, and mecA genes). Due to background color and crowding, picking colonies from membrane filters and streaking for isolation were sometimes necessary. The specificity of SCA and C-MRSA was improved if colony isolates were identified by the presence of a matte halo in addition to mauve color; however routine agglutination testing of isolates did not appear warranted. Using the appearance of a colony on the membrane filter in conjunction with isolate appearance, the positive % agreement, the negative % agreement, and the % positive predictive accuracy for SCA was 84%, 95%, and 99% respectively, and for C-MRSA it was 85%, 98%, and 92%, respectively. Sensitivity and specificity of SCA and C-MRSA with membrane-filtered beach samples were optimized through identification experience, control of filter volume and incubation time, and isolation of colonies needing further identification. With optimization, SCA and C-MRSA could be used for enumeration of S. aureus and MRSA from samples of beach water and sand. For the sites studied here, the frequency of detection of S. aureus ranged from 60 to 76% and 53 to 79% for samples of beach seawater and sand, respectively. The frequency of detection of MRSA ranged from 2 to 9% and 0 to 12% for samples of seawater and sand, respectively.

Ecology of Staphylococcus aureus isolated from various sites on dairy farms

The purposes of this study were to identify sources of Staphylococcus aureus on dairies and to determine whether S. aureus colonization of heifer body sites increases the risk of S. aureus IMI at parturition. In herds with high (> 10%) or low (< 3%) prevalence of S. aureus IMI, S. aureus was isolated from heifer teat skin, heifer external orifices, housing, feedstuffs, humans, nonbovine animals, air, and equipment. Additionally, in herds with high prevalence, S. aureus was isolated from bedding, insects, and water. The predominant sources of S. aureus for both groups were other IMI and heifer body sites. Heifers with prepartum lacteal secretions with S. aureus were at greater risk of S. aureus IMI at parturition than were prepartum heifers with lacteal secretions that were negative for S. aureus. Heifers with teat skin colonized by S. aureus were 3.34 times more likely to have S. aureus IMI at parturition than were noncolonized heifers. Overall, 35% of 700 heifers were colonized with S. aureus on a body site at least once. Although colonizations of most body sites appeared to be transient, a few heifers were colonized on the same site for 1 yr. Persistently colonized heifers may represent the primary reservoirs of S. aureus for other heifers.

Evaluation of a mannitol-salt-oxacillin-tellurite medium for the isolation of methicillin-resistant Staphylococcus aureus from contaminated sources

A mannitol-salt medium supplemented with 0.002% tellurite (MSOT) supported the growth of 104 of 109 strains of methicillin-resistant Staphylococcus aureus (MRSA) while suppressing 74 of 102 strains of mannitol-positive, methicillin-resistant coagulase-negative staphylococci. MSOT was equally or more sensitive and more differential than a similar formulation without tellurite for the isolation of MRSA from the skin and nares of hospitalized patients. Only S. haemolyticus produced dark gray-to-black colonies on MSOT similar to those of MRSA. MSOT is a useful adjunct to other nonselective culture formulations for the isolation of MRSA from contaminated sources.

Health effects of beach water pollution in Hong Kong

Prospective epidemiological studies of beach water pollution were conducted in Hong Kong in the summers of 1986 and 1987. For the main study in 1987, a total of 18741 usable responses were obtained from beachgoers on nine beaches at weekends. The study indicated the overall perceived symptom rates for gastrointestinal, ear, eye, skin, respiratory, fever and total illness were significantly higher for swimmers than non-swimmers; and the swimming-associated symptom rates for gastrointestinal, skin, respiratory and total illness were higher at 'barely acceptable' beaches than at 'relatively unpolluted' ones. Escherichia coli was found to be the best indicator of the health effects associated with swimming in the beaches of Hong Kong. It showed the highest correlation with combined swimming-associated gastroenteritis and skin symptom rates when compared with other microbial indicators. A linear relationship between E. coli and the combined symptom rates was established. Staphylococci were correlated with ear, respiratory and total illness, but could not be used for predicting swimming-associated health risks. They should be used to complement E. coli. The setting of health-related bathing-water quality standards based on such a study is discussed.

New screening test to determine the acceptability of 0.45-micron membrane filters for analysis of water

During routine membrane filter (MF) quality control testing, irregularities such as partial or complete inhibition of microbial growth at grid lines, abnormal spreading of colonies, growth in or along the grid lines, nonwetting areas, poor colony sheen and metallic sheen on the MF surface with mEndo agar, brittleness, decreased recovery, and severe wrinkling were observed with several lots of filters. To study these effects and to develop a more sensitive screening test for MF quality, we compared five different MFs with various types and degrees of defects by using five stock coliform cultures and five different media. Results showed that the Enterobacter aerogenes-tryptic soy agar test system detected more MF defects than any other combination did and was superior to the Escherichia coli-mFC agar American Society for Testing and Materials method for grid line inhibition. Filtered natural samples grown on the same media showed the same effects as were observed with the pure cultures. Poor colony sheen and sheen on the MF surface were best detected with Enterobacter aerogenes on mEndo agar. The use of tryptic soy agar and mEndo agar with this organism permitted the maximum detection of MF irregularities. Of the 142 MF lots tested by this method, 30% were acceptable, 10% were marginally acceptable, and 61% were unacceptable. This method provides a valuable screening test for determining the acceptability of 0.45-microm-pore-size MFs used for coliform and heterotroph analysis and may also be useful in conjunction with other methods.

Comparative studies of selective media for recovery of Staphylococcus aureus from natural waters

Several selective media currently used for the enumeration of Staphylococcus aureus from different sources were evaluated in order to establish their quantitative recovery, specificity and degree of selectivity, using different types of water samples. The highest selectivity and reliability in the enumeration of Staph. aureus from the samples was obtained on Borrego-Florido-Romero-0 (BFR-0) and KRANEP agars. The method that produced the highest recovery of Staph. aureus was BFR-0 agar with membrane filter and incubation at 36 degrees C for 48-72 h.

Design and performance of a new medium for the quantitative recovery of Staphylococcus aureus from recreational waters

Several reports have suggested that staphylococci, and especially Staphylococcus aureus, are useful indicators of pollution of recreational waters. The lack of a selective, accurate and reliable recovery system for the quantification of Staph. aureus from water has been the principal obstacle to the evaluation of their use as indicators. In this study, several inhibitory substances and different nutrient sources have been evaluated for the formulation of a new selective medium. The medium designed, BFR-0 agar, recovers more than 75% of staphylococci and allows Staph. aureus to be identified.

Rapid assay for in situ identification of coagulase-positive staphylococci recovered by membrane filtration from swimming pool water

A rapid, in situ thermonuclease test that identifies colonies of Staphylococcus aureus among staphylococci isolated from swimming pool water by membrane filtration recovery on various selective and differential media is described.

Evaluation of culture media for recovery of Staphylococcus aureus from swimming pools

Several selective media were evaluated for the primary isolation and enumeration of Staphylococcus aureus from halogenated indoor swimming pool waters. Standard plate counts of the viable population and total coliform densities were also determined to ascertain their value as indicator systems. All studies were done with membrane filters. The most selective, accurate, and reliable medium was Vogel-Johnson (VJ) medium supplemented with 0.5% pyruvate. This medium recovered two times more typical colonies than VJ medium alone, and subsequent identification of these well-defined black colonies proved that approximately 80% were S. aureus. The S. aureus recoveries correlated well with halogen levels and bather density use also. In contrast, VJ medium alone was 60% selective for S. aureus, and VJ medium supplemented with catalase did not increase either the percent recovery or the selectivity over that of VJ medium alone. Standard plate counts did not correlate with halogen levels, bather density, or total viable colonies. Coliforms were rarely recovered from indoor pool waters and were not considered to be useful indicators of water quality.