ANAEROBES IN PLEUROPULMONARY INFECTIONS

Antimicrobial resistance pattern of anaerobic bacteria causing lower respiratory tract infections

BACKGROUND

Anaerobes are normal flora of the human body. However, they can cause serious infections in humans. Anaerobic bacteria are known to cause respiratory infections like pneumonia and acute exacerbation of chronic lower airway infections. These are often missed due to the complexity of their isolation and identification. Hence, this study aimed to study anaerobes causing respiratory tract infections and determine their antibiotic susceptibility.

MATERIALS & METHODS

Clinical specimens such as bronchial aspirates and pleural aspirates collected from patients with respiratory diseases attending Vallabhbhai Patel Chest Institute were processed, the anaerobes isolated were identified, and their susceptibilities to various groups of antimicrobials were studied using standard microbiological methods.

RESULTS

Three hundred and fourteen patients were included in the study, 154 males and 160 females. Of these 314 patients, 148 (47%) yielded anaerobes in their clinical samples. Seventy patients had more than one type of anaerobic organism. Hence, 235 isolates were recovered belonging to as many as 17 genera. The MIC of seven antibiotics on 154 isolates was tested. The isolates belonged mostly to the genera Bacteroides, Prevotella, Veillonella, and Actinomyces. Variable resistance was observed to most classes of antibiotics by many genera.

CONCLUSIONS

Metronidazole is commonly used against anaerobes, but the study showed that the isolates were 20-30% resistant to the antibiotic. Starting this as an empirical therapy might lead to treatment failure.

Construction of a Mutant in Prevotella melaninogenica Using the Conjugation Transfer Method with Escherichia coli

Prevotella melaninogenica is a bacterium that is resident in the oral cavity and upper respiratory tract and is associated with periodontal disease and aspiration pneumonia. Prevotella mutants are difficult to produce and only few reports have been reported. We examined several methods and many strains and succeeded in producing mutants in Prevotella melaninogenica GAI 07411. In this chapter, we will describe how to create a mutation of a target gene by carrying out conjugation transfer using Escherichia coli S17-1 as a donor and introducing a plasmid into P. melaninogenica.

Prevotella koreensis sp. nov., Isolated from Human Subgingival Dental Plaque of Periodontitis Lesion

A novel Gram-negative, obligately anaerobic, non-motile, non-spore forming, and rod-shaped bacterium, designated strain JS262^T, was isolated from human subgingival plaque of periodontitis lesion and was characterized by polyphasic taxonomic analysis. Comparison of 16S ribosomal RNA gene (16S rDNA) sequence revealed that the strain belonged to the genus Prevotella. The percent similarity of 16S rDNA of strain JS262^T was closest to those of Prevotella buccae ATCC 33574^T (89.1%) and Prevotella shahii JCM 12083^T (88.9%). The major fatty acids of strain JS262^T were C_16:0 (29.2%), iso-C_15:0 (19.2%), and anteiso-C_15:0 (16.9%). Complete genome of strain JS262^T was 2,691,540 bp in length and the G+C content was 43.9 mol%. Average nucleotide identity and genome-to-genome distance values between strain JS262^T and P. buccae ATCC 33574^T or P. loescheii DSM 19665^T were > 70.4% and > 30.1%, respectively. On the basis of these data, a novel Prevotella species is proposed: Prevotella koreensis sp. nov. The type strain of P. koreensis is JS262^T (= KCOM 3155^T = JCM 33298^T).

Involvement of PorK, a component of the type IX secretion system, in Prevotella melaninogenica pathogenicity

Prevotella melaninogenica is a gram-negative anaerobic commensal bacterium that resides in the human oral cavity and is isolated as a pathogen of suppurative diseases both inside and outside the mouth. However, little is known about the pathogenic factors of P. melaninogenica. The periodontal pathogens Porphyromonas gingivalis and Tanerella forsythia secrete virulence factors such as protease and bacterial cell surface proteins via a type IX secretion system (T9SS) that are involved in pathogenicity. P. melaninogenica also possesses all known orthologs of T9SS. In this study, a P. melaninogenica GAI 07411 mutant deficient in the orthologue of the T9SS-encoding gene, porK, was constructed. Hemagglutination and biofilm formation were decreased in the porK mutant. Furthermore, following growth on skim milk-containing medium, the diameters of the halos surrounding the porK mutant were smaller than those of the wild-type strain, suggesting a decrease in secretion of proteases outside the bacterium. To investigate this in detail, culture supernatants of wild-type and porK mutant strains were purified and compared by two-dimensional electrophoresis. In the mutant strain, fewer spots were detected, indicating fewer secreted proteins. In infection experiments, the mortality rate of mice inoculated with the porK mutant strain was significantly lower than in the wild-type strain. These results suggest that P. melaninogenica secretes potent virulence factors via the T9SS that contribute to its pathogenic ability.

Antibiotic susceptibility of 33 Prevotella strains isolated from Romanian patients with abscesses in head and neck spaces

The purpose of this study was to investigate the susceptibility of a series of 33 Prevotella strains isolated from patients with abscesses in the head and neck spaces, presented to one Romanian hospital. The Etest was applied to determine the value of the minimum inhibitory concentrations for: penicillin G, ampicillin, amoxicillin-clavulanate, metronidazole and clindamycin. In addition, the beta-lactamase activity was detected by the chromogenic cephalosporin disc method. The results indicated that 11 isolates were resistant to both penicillin G and ampicillin due to the beta-lactamase production. All the 33 Prevotella strains were susceptible to the other 3 antimicrobial agents tested, except for only one penicillin G - ampicillin resistant isolate of Prevotella buccae (MIC > 32 and MIC = 12 mg/L, respectively), which showed high resistance to clindamycin (MIC > 256 mg/L) too. Our data underline the necessity for antimicrobial testing including monitoring of beta-lactamase production in cases of oro-maxillo-facial mixed anaerobic infections where antimicrobial treatment is required in addition to the surgical drainage. The results of the study indicated that amoxicillin-clavulanate, like metronidazole, was fully active against the tested Prevotella strains. However, local and multicentre surveys on drug resistance among the clinically significant anaerobic isolates should be carried out periodically.

Anaerobes in nosocomial and community acquired pleural infections

Anaerobes are important causes of pleural space infections. The aim of the study is to evaluate the role of the anaerobic bacteria in pleural infections. The study involved 278 consecutive clinical samples sent to the Clinical Microbiology Laboratory of Tertiary Chest Hospital. Anaerobes were isolated in 39 community acquired and five nosocomial cases out of 278 anaerobic cultivations (15.8%). Total of 56 anaerobe strains were identified and 21 aerobes were accompanied to anaerobic isolates. Aerobe isolates were associated with anaerobic microorganisms in 19 cases (43.2%). Bacteroides species (21.4%) and Pseudomonas aeruginosa (33.3%) were the most common anaerobic and aerobic isolates.

How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy

Anaerobic bacteria are infrequent pulmonary pathogens, and, even then they are, they are almost never recovered due to the need for specimens uncontaminated by the upper airway flora and failure to do adequate anaerobic bacteriology. These bacteria are relatively common in selected types of lung infections including aspiration pneumonia, lung abscess, necrotizing pneumonia and emphyema. Preferred antibiotics for these infections based on clinical experience are clindamycin and any betalactam-betalactamase inhibitor.