INTRODUCTION

An abscess is a discrete or localised collection of pus, Incision and drainage of abscesses is probably the most common emergency procedure performed in general surgery. They occur in many parts of the body as superficial infections or as deep-seated infections associated with any internal organ. Many abscesses are caused by Staphylococcus aureus alone, but others are caused by mixed infections. Anaerobes are predominant isolates in intra-abdominal abscesses, and abscesses in the oral and anal areas.

Members of the "Streptococcus anginosus" group and Enterobacteriaceae are also frequently present in lesions at these sites.

Microbiology of Peritonisillar Abscess:

Peritonsillar abscess is characterized by a purulent secretion collected between the fibrous capsule of the palatine tonsil and the pharyngeal superior constrictor .Most of the peritonsillar abscess cases have a polymicrobial infection. Prevotella sp and Peptos-treptococcus sp found Bacteroids sp as the most frequent anaerobe present in the aspirates.^[1-4]Tonsil surface is covered by the bacteria present in the normal flora, and the most common are Streptococcus, Neisseria from aerobes, and Peptostreptococcus, Veilonella, Actino-myces and Fusobacterium from anaerobes, in the ratio of 1 aerobe for 100 anaerobes.

Retropharyngeal Abscess:

They are mainly polymicrobial infections containing common oropharyngeal microflora but not Enterobacteriaceae. Typically, they are caused by anaerobic organisms and beta-hemolytic streptococci (especially Streptococcus pyogenes), followed by viridans group streptococci, Staphylococcus aureus, Haemophilus influenzae and Streptococcus pneumoniae. Furthermore , the majority of spondylodiscitis cases are acquired by hematogenous spread, followed by direct external inoculation, whereas spread from contiguous tissues is comparably rare.^[5-6]

Microbiology of Brain Abscess :

Bacteria isolated from brain abscesses are usually mixtures of aerobes and obligate anaerobes, and the prevalent organism may vary depending upon geographical location, age and underlying medical condition.A brain abscess is initiated when microorganisms are introduced into cerebral tissue. Most infective agents gain access to the central nervous system either directly or via hematogenous spread.^[7]
In the pre-antibiotic era, bacteriological analysis revealed that S. aureus was causative organism in 25 to 30 percent of cases, Streptococci in 30 percent, coliform in 12 percent and no growth in over 50 percent .

The common organism reported have been Streptococci, Staphylococci and Anaerobic organism.The most commonly isolated organisms include Anaerobic streptococci, Anaerobic Gram negative bacilli, "Streptococcus anginosus" group, Enterobacteriaceae, Streptococcus pneumoniae, β-haemolytic streptococci, S. aureus. Otogenic infection was found to be the most common source of infection for anaerobic brain abscess. Chronic suppurative otitis media is still a major cause of brain abscess in developing country like India which is a benign and curable disease and should not be neglected.^[8,9]

Spinal Epidural Abscess :

The most common isolate is S. aureus, Staphylococcus epidermidis may be isolated in patients following invasive spinal manipulation. Streptococci (α-haemolytic, β-haemolytic and S. pneumoniae), Enterobacteriaceae and pseudomonads may also be isolated.

Skin and Subcutaneous Abscess:

The most common anaerobic bacteria are B. fragilis group (rectal), Prevotella and Porphyromonas spp. (oral) ^[10,11] facultative bacteria are S. aureus, S. pyogenes, Escherichia coli (rectal), Enterobacteriaceae.

Microbiology of Perirectal Abscess

The predominant anaerobes were as follows: Bacteroides fragilis group, Peptostreptococcus spp., Prevotella spp., Fusobacterium spp., Porphyromonas spp., and Clostridium spp.,. The predominant aerobic and facultative bacteria were as follows: Staphylococcus aureus, Streptococcus spp., and Escherichia coli.^[12-14]Surgical drainage is the therapy of choice of perirectal abscesses. This is important because the environment of an abscess is detrimental for many antimicrobial agents. The abscess capsule, the low pH, and the presence of binding proteins or inactivating enzymes (such as beta-lactamase) may impair the activities of many antimicrobial agents (especially).^[15]

Microbiology of Orofacial Abscess:

Odontogenic infections are always polymicrobial and are a mix of aerobic, facultative and strict anaerobes. Streptococcus viridians are the most common microorganism in dentoalveolar infection. The bacteria most commonly found in odontogenic infections are Streptococci which are aerobes and peptostreptococci, pigmented and non-pigmented prevotella and fusobacterium are anaerobes.^[16-19] Many investigations have demonstrated that Viridans streptococci, Peptostreptococcus, Prevotella, Porphyromonas and Fuso- bacterium are the organisms which are frequently isolated from orofacial odontogenic infection.Other gram- negative bacilli like Klebsiella, Proteus vulgaris were also isolated.^[20-22] The presence of anaerobes both cultivable and uncultivable tends to predominate. The vast majority of dental abscesses respond to surgical treatment, such as drainage of pus and elimination of the source of infection, with antibiotic use limited to severe spreading infections.

Scalp Abscess:

Polymicrobial infections also occur, involving Anaerobes ,β-haemolytic streptococci ,S. aureus, Enterobacteriaceae, Enterococci, Coagulase negative staphylococci [10]

Microbiology of Pyogenic Liver Abscess

The most frequent organism isolated from blood and abscess aspirate was Enterobacteriaceae (Klebsiella spp., followed by Escherichia coli), Bacteroides species, Clostridium species, Anaerobic streptococci, "S. anginosus" group, Enterococci, P. aeruginosa, B. pseudo-mallei (in endemic areas). ^[23-24] The most commonly used antibiotics were second- and third-generation cephalosporins with or without metroni-dazole. For patients with community-acquired liver abscess, the preferred regimen for empirical therapy is amoxicillin-clavulanate or ampicillin-sulbactam plus metronidazole to cover the usual bacteria (Enterobac- teriaceae, Bacteroides spp., enterococci) and possible Entamoeba histolytica.^[25]

Spleen Abscess:

Polymicrobial infection was present. The predominant aerobic and facultative isolates were E. coli, Proteus mirabilis, Streptococcus group D , K. pneumoniae and S. aureus. The predominant anaerobes were Pepto-streptococcus sp., Bacteroides spp., Fusobacterium spp. and Clostridium spp. S. aureus, K. pneumoniae and Streptococcus group Dwere associated with endocarditis, E. coli with urinary tract and abdominal infection, Bacteroides spp. and Clostridium spp. with abdominal infection and Fusobacterium spp. with respiratory infection.^[25]

Microbiology of Lung Abscess :

Monomicrobial abscesses are only occasionally identified and may be caused by bacteria such as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella spp., Pasteurella multocida, Enterobacteriaceae, Haemophilus influenzae (types b and c), Actinomyces spp., Nocardia spp., Rhodococcus equi, Burkholderia pseudomallei, Streptococcus anginosus group, Streptococcus pneumoniae, Le- gionella.^[26-29]

Microbiology of Intra Abdominal Abscess :

The normal flora of the human gastrointestinal tract is complex, consisting of hundreds of species of facultative and anaerobic bacteria . Obligate anaerobes including Bacteroides fragilis represent the predominant colonic flora. Of the facultative organisms present in the colon, Escherichia coli is most common. The normal colonic flora also consists of enterococci, streptococci, and various members of the family Enterobacteriaceae.^[30,31] Not surprisingly, the predominant pathogens in community-acquired intra- abdominal infections are members of the family Enterobacteriaceae (especially E. coli) and anaerobes (especially B. fragilis) Facultative gram-negative bacteria (e.g., E. coli) are thought to be responsible for early mortality associated with intra-abdominal sepsis, while anaerobes (e.g., B. fragilis) in combination with facultative organisms are important for abscess formation .Hence, in the treatment of intra-abdominal infections, particularly those arising from the lower gastrointestinal tract, antimicrobial coverage of both E. coli and B. fragilis is important. ^[32-34]

Microbiology of Renal and Perinephric Abscess

Abscess most often occurs in patients with diabetes mellitus (DM), urinary tract calculi or urinary tract ob- struction. Most of the causative pathogens are En- terobacteriaceae, such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Staphylococcus aureus and anaerobes. Anaerobic infections, monobacterial isolates included Bacteroides fragilis, Veillonella spp. , and Peptostreptococcus spp. Polymicrobial isolates included Peptostreptococcus and Prevotella spp. and Fusobacterium mortiferum and Prevotella melanino-genica.

Pilonidal Abscess:

They are common in children, and result from infection of a pilonidal sinus. Anaerobes and Enterobacteriaceae are usually isolated, but they may be caused by S. aureus and β-haemolytic streptococci.

Head and Neck Abscess:

Anaerobic bacteria: Prevotella and Porphyromonas spp., Fusobacterium spp., Peptostreptococcus spp. Facultative bacteria : S. pyogenes, S. aureus ^[35]

Retroperitoneal Abcess:

The predomiant aerobic and facultative isolates were Escherichia coli, Klebsiella pneumonia, Streptococcus group D , and Staphylococcus aureus. The predominant anaerobes were peptostreptococcus species, bacteriods fragilis group, prevotella species, and clostridium species ^[36]

The polymicrobial nature of abdominal, pelvic and skin and soft tissue (proximal to the oral or rectal areas) abscesses is apparent in the majority of patients, where the number of isolates in an infectious site varies between two and six1,2 .The average number of isolates is 3.6 in skin and soft tissue infections (2.6 anaerobes and 1.0 aerobe) per specimen,21–23 five in intra-abdominal infection (3.0 anaerobes and 2.0 aerobes) per specimen and four in pelvic infections (2.8 anaerobes and 1.2 aerobes) per specimen. Polymicrobial infections are known to be more pathogenic for experimental animals than those involving single organisms

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Received on 06.06.2016 Modified on 21.06.2016

Research J. Pharm. and Tech 2016; 9(10):1793-1796.

DOI: 10.5958/0974-360X.2016.00363.2