Bacteriophage typing of gram-negative rod-shaped bacteria

The State of the Art in Biodefense Related Bacterial Pathogen Detection Using Bacteriophages: How It Started and How It's Going

Accurate pathogen detection and diagnosis is paramount in clinical success of treating patients. There are two general paradigms in pathogen detection: molecular and immuno-based, and phage-based detection is a third emerging paradigm due to its sensitivity and selectivity. Molecular detection methods look for genetic material specific for a given pathogen in a sample usually by polymerase chain reaction (PCR). Immuno-methods look at the pathogen components (antigens) by antibodies raised against that pathogen specific antigens. There are different variations and products based on these two paradigms with advantages and disadvantages. The third paradigm at least for bacterial pathogen detection entails bacteriophages specific for a given bacterium. Sensitivity and specificity are the two key parameters in any pathogen detection system. By their very nature, bacteriophages afford the best sensitivity for bacterial detection. Bacteria and bacteriophages form the predator-prey pair in the evolutionary arms race and has coevolved over time to acquire the exquisite specificity of the pair, in some instances at the strain level. This specificity has been exploited for diagnostic purposes of various pathogens of concern in clinical and other settings. Many recent reviews focus on phage-based detection and sensor technologies. In this review, we focus on a very special group of pathogens that are of concern in biodefense because of their potential misuse in bioterrorism and their extremely virulent nature and as such fall under the Centers for Disease and Prevention (CDC) Category A pathogen list. We describe the currently available phage methods that are based on the usual modalities of detection from culture, to molecular and immuno- and fluorescent methods. We further highlight the gaps and the needs for more modern technologies and sensors drawing from technologies existing for detection and surveillance of other pathogens of clinical relevance.

Development of a new set of phages as an epidemiological marker in Staphylococcus epidermidis causing nosocomial infections

We describe the isolation of a new set of phages for typing Staphylococcus epidermidis. One hundred and eighty-two phages were obtained from S. epidermidis strains of human origin. Twelve phages were selected according to their potency and their lytic activity studied. Twenty phages of the Dean and Williams' set were also studied. Phage-typing was undertaken at 100 x RTD, 1000 x RTD and after heat treatment at 48 degrees C. When the two sets of phages were compared separately similar figures were obtained. When the two typing sets were combined, the percentage of typability for the 182 bacterial strains increased to 29.1% using 1000 x RTD and to 75.3% after heat treatment.

Conventional typing methods

Clinical microbiologists normally identify important isolates to the level of species and determine their susceptibility to antibiotics. These activities generate a species identification and provide some differentiation below the level of species in the form of a biotype and an antibiogram. Most other typing methods should be reserved for special studies or to investigate possible infection problems or outbreaks. Specialized techniques should usually be done in reference laboratories. These include serotyping, (complete antigenic analysis), bacteriophage susceptibility, and bacteriocin production or susceptibility.