Factors Influencing the Occurrence of High Numbers of Iodine-Resistant Bacteria in Iodinated Swimming Pools

Previous studies have shown that bacteria maintained in a low-nutrient "natural" environment such as swimming pool water are much more resistant to disinfection by various chemical agents than strains maintained on rich media. In the present study a comparison was made of the chlorine (Cl2) susceptibility of hot-water tank isolates of Legionella pneumophila maintained in tap water and strains passaged on either nonselective buffered charcoal-yeast extract or selective differential glycine-vancomycin-polymyxin agar medium. Our earlier work has shown that environmental and clinical isolates of L. pneumophila maintained on agar medium are much more resistant to Cl2 than coliforms are. Under the present experimental conditions (21°C, pH 7.6 to 8.0, and 0.25 mg of free residual Cl2 per liter, we found the tap water-maintained L. pneumophila strains to be even more resistant than the agar-passaged isolates. Under these conditions, 99% kill of tap water-maintained strains of L. pneumophila was usually achieved within 60 to 90 min compared with 10 min for agar-passaged strains. Samples from plumbing fixtures in a hospital yielded legionellae which were "super"-chorine resistant when assayed under natural conditions. After one agar passage their resistance dropped to levels of comparable strains which had not been previously exposed to additional chlorination. These studies more closely approximate natural conditions than our previous work and show that tap water-maintained L. pneumophila is even more resistant to Cl2 than its already resistant agar medium-passaged counterpart.

mentioning

confidence: 99%

Enhanced chlorine resistance of tap water-adapted Legionella pneumophila as compared with agar medium-passaged strains

Kuchta¹,

States²,

McGlaughlin³

et al. 1985

“…Growth conditions can profoundly influence the susceptibility of microorganisms to disinfectants (4,6). We have previously shown that growth of Escherichia coli at submaximal rates due to nutrient limitation and at relatively low temperatures greatly increases the resistance of this bacterium to chlorine dioxide (3) and phenylphenol (1).…”

mentioning

confidence: 99%

Susceptibility of chemostat-grown Yersinia enterocolitica and Klebsiella pneumoniae to chlorine dioxide

Harakeh¹,

Berg²,

Hoff³

et al. 1985

The resistance of bacteria to antimicrobial agents could be influenced by growth environment. The susceptibility of two enteric bacteria, Yersinia enterocolitica and Klebsiella pneumoniae, to chlorine dioxide was investigated. These organisms were grown in a defined medium in a chemostat and the influence of growth rate, temperature, and cell density on the susceptibility was studied. All inactivation experiments were conducted with a dose of 0.25 mg of chlorine dioxide per liter in phosphate-buffered saline at pH 7.0 and 23°C. The results indicated that populations grown under conditions that more closely approximate natural aquatic environments, e.g., low temperatures and growth at submaximal rates caused by nutrient limitation, were most resistant. The conclusion from this study is that antecedent growth conditions have a profound effect on the susceptibility of bacteria to disinfectants, and it is more appropriate to use the chemostat-grown bacteria as test organisms to evaluate the efficacy of a certain disinfectant.

“…A number of other investigators have also reported that growth under low-nutrient conditions could stimulate resis- tance to disinfectant agents (3,4,8,9,11,12,19,22,29). In general, these previous studies suggested that naturally occurring organisms or those subcultured under conditions similar to their natural environment were the most resistant.…”

Section: Resultsmentioning

confidence: 98%

Impact of growth conditions on resistance of Klebsiella pneumoniae to chloramines

Stewart¹,

Olson²

1992

The resistance of Klebsiella pneumoniae to inorganic monochloramine (1.5 mg/liter; 3:1 C12:N ratio, pH 8.0) was examined in relation to growth phase, temperature of growth, and growth under decreased nutrient conditions. Growth phase did not impact resistance to chloramines. Mid-exponential and stationary-phase cells, grown in a yeast extract-based medium, had CT99 values and standard deviations of 4.8 + 0.1 and 4.6-+-0.2 mg. min/liter, respectively. Growth temperature did not alter chloramine resistance at short contact times. CT99 values of cells grown at 15 and 23°C were 4.5 + 0.2 and 4.6 + 0.2 mg. min/liter, respectively. However, at longer contact times, CT99.99 values of cells grown at 15 and 23°C were 14 and 8 mg. min/liter, respectively, suggesting a small resistant subpopulation for cells grown at the lower temperature. Growth under decreased nutrient conditions resulted in a concomitant increase in resistance to chloramines. When K. pneumoniae was grown in undiluted Ristroph medium and Ristroph medium diluted by 1:100 and 1:1,000, the CT99 values were 4.6 0.2, 9.6 0.4, and 24 + 7.0 mg-min/liter, respectively. These results indicate that nutrient availability has a greater impact than growth phase or growth temperature in promoting the resistance of K. pneumoniae to inorganic monochloramine.