Horizontal transfer of the blaNDM-1 gene to Pseudomonas aeruginosa and Acinetobacter baumannii in biofilms.

Horizontal gene transfer has contributed to the global spread of the blaNDM-1 gene. Multiple studies have demonstrated plasmid transfer of blaNDM-1 between Gram-negative bacteria, primarily Enterobacteriaceae species, but conjugational transfer of natural blaNDM-1 plasmids from Enterobacteriaceae into Pseudomonas aeruginosa and Acinetobacter baumannii has not previously been shown. As P. aeruginosa and A. baumannii are both typically strong biofilm formers, transfer of natural blaNDM-1 plasmids could potentially occur more readily in this environment. To determine whether natural blaNDM-1 plasmids could transfer to P. aeruginosa or A. baumannii in biofilms, three clinical and environmental Enterobacteriaceae strains carrying NDM-1-encoding plasmids of different incompatibility types were mated with E. coli J53, producing E. coli J53- blaNDM-1 transconjugants. Subsequently, dual-species biofilms were created using the E. coli J53 transconjugants as plasmid donors and either P. aeruginosa or A. baumannii as recipients. Biofilm transfer of NDM-encoding plasmids to P. aeruginosa and A. baumannii was successful from one and two E. coli J53- blaNDM-1 transconjugants, respectively. This demonstrates the potential for the spread of blaNDM-1, genes to P. aeruginosa and A. baumannii in clinical and environmental settings.

Development and field evaluation of a method for detecting carbapenem-resistant bacteria in drinking water.

In this study, a fluorogenic heterotrophic plate count test for drinking water was modified in order to detect the presence of carbapenem-resistant bacteria. Antimicrobial agents and concentrations were selected based on recoveries of known carbapenem-resistant and carbapenem-susceptible strains inoculated into simulated samples. The modified method was field-tested on 19 drinking water samples from the New Delhi, India distribution system. Samples exhibiting fluorescence indicated bacterial growth in the presence of the supplemented antimicrobial agents, and organisms from these samples were cultured. Twenty-one Gram-negative isolates were identified from nine of the 19 samples and the meropenem minimum inhibitory concentrations were determined. Ultimately, eight carbapenem-resistant organisms were isolated from five sampling sites within the New Delhi water distribution system.

Shiga toxin-producing Escherichia coli (STEC) in Tennessee: surveillance and current clinical laboratory practices.

Since joining the Centers for Disease Control and Prevention's (CDC) Foodborne Diseases Active Surveillance Network (FoodNet) in 1999, Tennessee has conducted active surveillance for foodborne pathogens including Shiga toxin-producing E. coli (STEC). The number of STEC infections has increased in recent years in the United States, including Tennessee, due partly to changes in clinical laboratories practices including non-culture based testing methods. Despite increased reporting, STEC infections are likely under-recognized in Tennessee. A 2007 statewide laboratory survey indicated that less than half of clinical laboratories test for STEC on-site. Among these, only nine reported using non-culture based methods. Only one clinical laboratory reported simultaneous culture for STEC O157 and testing with an assay that detects Shiga toxins for non-O157 STEC as recommended by the CDC. Adoption of CDC recommendations coupled with timely and complete reporting will enhance public health surveillance, outbreak investigations and interventions to prevent STEC infection.

Evaluation of polymerase chain reaction for group B streptococcus detection using an improved culture method.

OBJECTIVE: The administration of antibiotic prophylaxis to laboring women who harbor Group B streptococci (GBS) depends on identification of carriers. We sought to evaluate the diagnostic accuracy of real-time polymerase chain reaction (PCR) for detection of GBS using a more stringent culture method. METHODS: Two swabs were used simultaneously to obtain rectovaginal GBS samples from consenting women. One swab was analyzed using a stringent, validated culture technology, which included direct plating onto selective agar and inoculation of a selective broth. The other swab was used for a commercial real-time PCR assay, which uses amplification to detect the presence of the cfb gene sequence of GBS DNA. We calculated the assay accuracy using sensitivity and specificity. RESULTS: A total of 233 samples were available. Both the culture and PCR methods were positive for 59 and negative for 157 patients. The culture method was positive and PCR was negative in 9 patients. The culture was negative and the PCR positive for 8 patients. The sensitivity of the PCR assay was 86.8% and specificity was 95.2%. The positive predictive value was 88.1% and the negative predictive value was 94.6%. CONCLUSION: Although a rapid PCR assay may be useful to determine GBS status in the urgent intrapartum setting, the false-negative rate of 13.2% for the real-time PCR assay prohibits its use for standard GBS screening in the office.