Microbiology of parapharyngeal abscesses in adults: in search of the significant pathogens

Tejs Ehlers Klug,Mirjana Ninn-Pedersen,Anne-Louise Christensen,Helle Døssing,Pernille Hahn,Simon Fuglsang,Søren Pauli,Anette Kjeldsen,Camilla Andersen,Maria Rusan,Sophie Mikkelsen,Thomas Greve,Christian Danstrup,Niels Krintel Petersen

doi:10.1007/s10096-021-04180-y

Abstract

We aimed to describe the microbiology of parapharyngeal abscess (PPA) and point out the likely pathogens using the following principles to suggest pathogenic significance: (1) frequent recovery, (2) abundant growth, (3) growth in relative abundance to other microorganisms, (4) percentage of the isolates recovered in both absolute and relative abundance, (5) more frequent recovery in PPA pus compared with tonsillar surface and tissue. Comprehensive bacterial cultures were performed on specimens obtained from adult patients (n = 60) with surgically verified PPA, who were prospectively enrolled at five Danish ear-nose-throat departments. The prevalent isolates (in PPA pus) were unspecified anaerobes (73%), non-hemolytic streptococci (67%), Streptococcus anginosus group (SAG) (40%), Corynebacterium spp. (25%), Neisseria spp. (23%), Fusobacterium spp. (22%), Fusobacterium necrophorum (17%), Prevotella spp. (12%), and Streptococcus pyogenes (10%). The bacteria most frequently isolated in heavy (maximum) growth were unspecified anaerobes (60%), SAG (40%), F. necrophorum (23%), and Prevotella spp. (17%). The predominant microorganisms (those found in highest relative abundance) were unspecified anaerobes (53%), SAG (28%), non-hemolytic streptococci (25%), F. necrophorum (15%), S. pyogenes (10%), and Prevotella spp. (10%). Four potential pathogens were found in both heavy growth and highest relative abundance in at least 50% of cases: F. necrophorum, Prevotella spp., SAG, and S. pyogenes. SAG, Prevotella spp., F. necrophorum, S. pyogenes, and Bacteroides spp. were recovered with the same or higher frequency from PPA pus compared with tonsillar tissue and surface. Our findings suggest that SAG, F. necrophorum, Prevotella, and S. pyogenes are significant pathogens in PPA development.

Highlights

Parapharyngeal abscess (PPA) refers to a collection of pus located laterally or posteriorly to the pharyngeal constrictor muscle
Based on extensive cultures from PPA aspirates obtained with a focus to minimize the contamination from surrounding tissues, a polymicrobial aerobic and anaerobic flora was found in the vast majority (93%) of PPAs, and the most frequently recovered bacteria were non-hemolytic streptococci and unspecified anaerobes
To further pinpoint the likely pathogens and deduct the massive commensal flora of the pharynx, we (1) calculated the percentage of each bacterial strain, which was most commonly recovered in both absolute and relative abundance and (2) compared the findings in PPA pus with tonsillar tissues and surface swabs. These analyses suggested that the Streptococcus anginosus group, F. necrophorum, Prevotella spp., and S. pyogenes were the major pathogens

Summary

Introduction

Parapharyngeal abscess (PPA) refers to a collection of pus located laterally or posteriorly to the pharyngeal constrictor muscle. PPAs are reported as extensions of peritonsillar abscesses (PTA) [2,3,4,5]. As with other neck abscesses derived from upper airway mucosa (i.e., PTA), a polymicrobial mixture of aerobes and anaerobes can be grown from PPA pus, when appropriate culture methods are applied [6, 7]. These polymicrobial infections derived from areas that are heavily colonized raise the following questions: which bacteria are significant pathogens, which are merely non-pathogenic bystanders, and which. The few previous studies focusing on the microbiology of PPA in adults were all retrospective, and reported findings in routine cultures, and no attempts were made to analyze the significance of the recovered bacteria [2, 5, 8, 9]

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