Nursery Outbreak of Pseudomonas aeruginosa : Epidemiological Conclusions from Five Different Typing Methods

Abstract

In April 1971, nine cases of Pseudomonas aeruginosa septicemia occurred in a high-risk nursery. The epidemiology of the outbreak was studied by pyocin production, pyocin sensitivity, serological typing, antibiotic susceptibility, and phenotypic properties such as colonial morphology, pigment, and hemolysis. Ten isolates of P. aeruginosa were recovered from 9 newborn infants and from 13 environmental sources. Twenty-one of the 23 isolates had identical pyocin production patterns against 60 different indicator strains and were of the same serotype. These 21 isolates were designated as the “outbreak strain”; the other 2 isolates had no epidemiological significance. The results of pyocin sensitivity, antibiotic susceptibility tests, and phenotypic properties were dissimilar. They would yield incorrect epidemiological conclusions if used alone. The outbreak strain dissociated in vitro and these phenotypic changes accounted for the variable results by the latter three typing methods. Although the precise mode of introduction of the organism into the nursery could not be determined in retrospect, the epidemiological data strongly suggested that one infant contracted a P. aeruginosa infection, and this strain spread throughout the nursery by means of contaminated resuscitation equipment.

Epidemiology of Pseudomonas aeruginosa infections: determination by pyocin typing

“…It may be possible to combine pyocin typing with other methods, e.g., serology, antibiotic sensitivity or biotype. This has been reported by several investigators (2,3,23). Type differences or similarities of antibiotic sensitivity should be investigated.…”

“…The median percent inhibition was 39.4%. To minimize intertest vari- 3,1976 ations, nine indicator strains were omitted from the procedure. Criteria for discarding indicator strains were poor reproducibility and formation of inhibition zones that were ill defined and difficult to interpret.…”

“…2 Present address: Department of Surgery, Medical School of Ohio at Toledo, Toledo, Ohio 43614. alone (23). There have been studies using two or more methods (2,3). Various methods have been proposed based on either pyocin production or pyocin sensitivity of isolates (7,11,12,24).…”

Core Genome Multilocus Sequence Typing and Antibiotic Susceptibility Prediction from Whole-Genome Sequence Data of Multidrug-Resistant Pseudomonas aeruginosa Isolates

“…Medical microbiologists have used a variety of tools to determine the relatedness of P. aeruginosa isolates in suspected outbreaks. Early studies using phenotypic traits such as pyocin production, serologic studies, and antibiograms eventually gave way to pulsed-field gel electrophoresis (PFGE) ( 7 ). Alternate molecular methods have been proposed and evaluated over the past two decades, including multilocus sequence typing (MLST), multiple locus variable number tandem-repeat analysis (MLVA), microarrays, and mass spectrometry; however, PFGE remained the most discriminatory method ( 8 – 14 ).…”