Clinical impact of methicillin-resistant staphylococcus aureus on bacterial pneumonia: cultivation and 16S ribosomal RNA gene analysis of bronchoalveolar lavage fluid.

Toshinori Kawanami,Kentarou Akata,Shingo Noguchi,Kazumasa Fukuda,Hatsumi Taniguchi,Hiroshi Ishimoto,Hiroshi Mukae,Kei Yamasaki,Keisuke Naito,Takashi Kido,Kazuhiro Yatera

doi:10.1186/s12879-016-1493-3

Abstract

BackgroundDetermining whether methicillin-resistant Staphylococcus aureus (MRSA) is a true causative pathogen or reflective of colonization when MRSA is cultured from the respiratory tract remains important in treating patients with pneumonia.MethodsWe evaluated the bacterial microbiota in bronchoalveolar lavage fluid (BALF) using the clone library method with a 16S ribosomal RNA (rRNA) gene analysis in 42 patients from a pneumonia registry who had MRSA cultured from their sputum or BALF samples. Patients were divided into two groups: those treated with (Group A) or without (Group B) anti-MRSA agents, and their clinical features were compared.ResultsAmong 248 patients with pneumonia, 42 patients who had MRSA cultured from the respiratory tract were analyzed (Group A: 13 patients, Group B: 29 patients). No clones of S. aureus were detected in the BALF of 20 out of 42 patients. Twenty-eight of 29 patients in Group B showed favorable clinical outcomes, indicating that these patients had non-MRSA pneumonia. Using a microflora analysis of the BALF, the S. aureus phylotype was predominant in 5 of 28 (17.9 %) patients among the detected bacterial phylotypes, but a minor population (the percentage of clones ≤ 10 %) in 19 (67.9 %) of 28 patients. A statistical analysis revealed no positive relationship between the percentage of clones of the S. aureus phylotype and risk factors of MRSA pneumonia.ConclusionsThe molecular method using BALF specimens suggests that conventional cultivation method results may mislead true causative pathogens, especially in patients with MRSA pneumonia. Further studies are necessary to elucidate these clinically important issues.

Highlights

Determining whether methicillin-resistant Staphylococcus aureus (MRSA) is a true causative pathogen or reflective of colonization when MRSA is cultured from the respiratory tract remains important in treating patients with pneumonia
It is occasionally difficult to differentiate whether the detected MRSA is a true causative pathogen of pneumonia or only reflective of colonization when MRSA is cultured from the lower respiratory tract samples
Patients who had MRSA positively cultured from respiratory specimens were divided into two groups: groups: those treated with (Group A) consisted of patients that had been treated with anti-MRSA agents, and Group B included patients that had been treated without anti-MRSA agents, and the clinical features of these two groups were compared

Summary

Introduction

Determining whether methicillin-resistant Staphylococcus aureus (MRSA) is a true causative pathogen or reflective of colonization when MRSA is cultured from the respiratory tract remains important in treating patients with pneumonia. Patients with nosocomial pneumonia caused by methicillinresistant Staphylococcus aureus (MRSA) have been increasing over the past half century. It is occasionally difficult to differentiate whether the detected MRSA is a true causative pathogen of pneumonia or only reflective of colonization when MRSA is cultured from the lower respiratory tract samples. Physicians should carefully consider whether or not cultured MRSA is causative in each case because many patients fulfill these criteria and improve without anti-MRSA agents in real-world clinical settings. Differentiation of MRSA as a cause of pneumonia or merely colonization remains an important clinical issue and is of a particular interest in clinical settings

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