Utility of Gram Staining for Evaluation of the Quality of Cystic Fibrosis Sputum Samples

Abstract

The microscopic examination of Gram-stained sputum specimens is very helpful in the evaluation of patients with community-acquired pneumonia and has also been recommended for use in cystic fibrosis (CF) patients. This study was undertaken to evaluate that recommendation. One hundred one sputum samples from CF patients were cultured for gram-negative bacilli and examined by Gram staining for both sputum adequacy (using the quality [Q] score) and bacterial morphology. Subjective evaluation of adequacy was also performed and categorized. Based on Q score evaluation, 41% of the samples would have been rejected despite a subjective appearance of purulence. Only three of these rejected samples were culture negative for gram-negative CF pathogens. Correlation between culture results and quantitative Gram stain examination was also poor. These data suggest that subjective evaluation combined with comprehensive bacteriology is superior to Gram staining in identifying pathogens in CF sputum.Gram staining is considered key in the workup of sputum from patients with pneumonia and other lower respiratory tract infections (10). Unfortunately, sputum samples are often contaminated with saliva and resident oropharyngeal microbial flora. This contamination can be quantified by evaluating Gram-stained sputum samples for polymorphonuclear leukocytes and squamous epithelial cells. The resulting objective measure, called the quality (Q) score, has been validated and recommended for use in evaluating the quality of the specimen (1).Cystic fibrosis (CF) lung infections are chronic and polymicrobial, occasionally marked by exacerbations accompanied by increased, purulent sputum production and systemic symptoms. Antibiotic treatment based on sputum culture results is a mainstay of CF management. The specific use of the Gram stain for evaluating the adequacy of sputum samples from patients with CF has also been recommended (4). In addition, past literature reports excellent sensitivity, specificity, and predictive values of examination of the morphology of bacteria seen in Gram-stained specimens compared with microbiological culture techniques for the prediction of specific organisms in CF sputum samples (11).At the Therapeutic Development Network (TDN) Core Microbiology Laboratory, we have had experience processing thousands of CF respiratory samples. It is the impression of the technologists at the bench that the Q score of the Gramstained specimen is less useful than subjective evaluation of the specimens for adequacy. In addition, because specimens are solubilized and diluted prior to plating on selective media (2), it is rare that organisms are detected by Gram staining and not cultured from the sample. To validate these impressions, we performed a prospective study to compare the objective scoring (Q score) and Gram stain evaluation with subjective characterization of purulence and quantitative culture results. MATERIALS AND METHODSStudy design. The present study was a substudy in the investigation of tobramycin-containing media fo...

Antibiogram Pattern of <i>Moraxella catarrhalis</i> Isolates in Acute Exacerbation Chronic Obstructive Pulmonary Disease

“…Apart from immunocompromised patients, the recovery rate of M. catarrhalis in smokers is high as compared to non-smokers and ex-smokers with underlying AECOPD. This observation concurs with those of previous investigators who have stated that cigarette smoking and tobacco smoke exposure could exacerbate the COPD state [5,[8][9][10] . In line with others, we observed that 1 90% of M. catarrhalis isolates produced ␤ -lactamase [11,12] .…”

“…AECOPD patients fulfilled the diagnostic criteria of COPD J44.x according to the 10th edition of the International Classification of Diseases guidelines. Sputum specimens were collected and cultured on 5% sheep blood agar and chocolate agar and incubated in a CO 2 environment for 24-48 h. Based on microscopy, only specimens representative of the lower respiratory tract were used [5] . M. catarrhalis isolates obtained were tested for sensitivity to ␤ -lactam antibiotics, a combination of ␤ -lactam and clavulanic acid, macrolides and quinolones.…”

Pulmonary exacerbations in cystic fibrosis with negative bacterial cultures

“…Culture positive samples were more likely to contain polymorphonuclear cells or bacteria, suggesting that inadequacy of samples may have contributed to negative culture findings. However, gram stain evaluation has been shown to have poor correlation with culture results for CF sputum samples 34. Culture interference by antibiotics is a valid concern in our study, given the high number of patients on antibiotics at the time of admission.…”

Bacteriology in acute exacerbation of chronic obstructive pulmonary disease in patients admitted to hospital

“…Microscopy was performed on Gramstained smears, and sputum was cultured on 5% horse blood agar and chocolate agar and incubated in CO 2 for 24Á48 h. The isolates were tested for sensitivity to beta-lactams, combination of betalactam and clavulanic acid, macrolides and quinolones. Based on the microscopy, only specimens representative for lower respiratory tract were used [19].…”