Itzhak Brook

Microbiology of Liver and Spleen Abscesses

To study the aerobic and anaerobic microbiology of liver and spleen abscesses and correlate the results with predisposing factors, potential causes and routes of infection, clinical and laboratory data of 48 patients with liver abscesses and 29 with spleen abscesses treated between 1970 and 1990 were reviewed retrospectively. In liver abscesses, a total of 116 isolates (2.4 isolates/specimen) was obtained; 43 were aerobic and facultative species (0.9 isolates/specimen) and 73 were anaerobic species or microaerophilic streptococci (1.5 isolates/specimen). Aerobic bacteria only were isolated from 12 (25%) abscesses, anaerobic bacteria only from eight (17%), and mixed aerobic and anaerobic bacteria from 28 (58%); polymicrobial infection was present in 38 (79%). The predominant aerobic and facultative isolates were Escherichia coli (11 isolates), Streptococcus group D (8), Klebsiella pneumoniae (5) and Staphylococcus aureus (4). The predominant anaerobes were Peptostreptococcus spp. (18 isolates), Bacteroides spp. (13), Fusobacterium spp. (10), Clostridium spp. (10) and Prevotella spp. (4). There were 12 isolates of micro-aerophilic streptococci. S. aureus and beta-haemolytic streptococci were associated with trauma; Streptococcus group D, K. pneumoniae and Clostridium spp. with biliary disease; and Bacteroides spp. and Clostridium spp. with colonic disease. In splenic abscesses, a total of 56 isolates (1.9 isolates/specimen) was obtained; 23 were aerobic and facultative species (0.8 isolates/specimen), 31 were anaerobic species or micro-aerophilic streptococci (1.1 isolates/specimen) and two were Candida albicans. Aerobic bacteria only were isolated from nine (31%) abscesses, anaerobic bacteria from eight (28%), mixed aerobic and anaerobic bacteria from 10 (34%) and C. albicans in two (7%); polymicrobial infection was present in 16 (55%). The predominant aerobic and facultative isolates were E. coli (5 isolates), Proteus mirabilis (3), Streptococcus group D (3), K. pneumoniae (3) and S. aureus (4). The predominant anaerobes were Peptostreptococcus spp. (11 isolates), Bacteroides spp. (5), Fusobacterium spp. (3) and Clostridium spp. (3). S. aureus, K. pneumoniae and Streptococcus group D were 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.

Minimum inhibitory concentrations of herbal essential oils and monolaurin for gram-positive and gram-negative bacteria.

New, safe antimicrobial agents are needed to prevent and overcome severe bacterial, viral, and fungal infections. Based on our previous experience and that of others, we postulated that herbal essential oils, such as those of origanum, and monolaurin offer such possibilities. We examined in vitro the cidal and/or static effects of oil of origanum, several other essential oils, and monolaurin on Staphylococcus aureus, Bacillus anthracis Sterne, Escherichia coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum proved cidal to all tested organisms with the exception of B. anthracis Sterne in which it was static. Monolaurin was cidal to S. aureus and M. terrae but not to E. coli and K. pneumoniae. Unlike the other two gram-negative organisms, H. pylori were extremely sensitive to monolaurin. Similar to origanum, monolaurin was static to B. anthracis Sterne. Because of their longstanding safety record, origanum and/or monolaurin, alone or combined with antibiotics, might prove useful in the prevention and treatment of severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.

Aerobic and anaerobic microbiology of peritonsillar abscess

Thirty-four aspirates of pus from peritonsillar abscesses that were studied for aerobic and anaerobic bacteria showed bacterial growth. A total 107 bacterial isolates (58 anaerobic and 49 aerobic and facultative) were recovered, accounting for 3.1 isolates per specimen (1.7 anaerobic and 1.4 aerobic and facultatives). Anaerobic bacteria only were present in 6 (18%) patients, aerobic and facultatives in 2 (6%), and mixed aerobic and anaerobic flora in 26 (76%). Single bacterial isolates were recovered in 4 infections, 2 of which were Streptococcus pyogenes and 2 were anaerobic bacteria. The predominant bacterial isolates were Staphylococcus aureus (6 isolates), Bacteroides sp (21 isolates, including 15 Bacteroides melaninogenicus group), and Peptostreptococcus sp (16) and S. pyogenes (10). beta-Lactamase-producing organisms were recovered from 13 (52%) of 25 specimens tested. This retrospective study highlights the polymicrobial nature and importance of anaerobic bacteria in peritonsillar abscess.

In vitro resistance of Bacillus anthracis Sterne to doxycycline, macrolides and quinolones.

Bacillus anthracis is a potential biological warfare agent. Its ability to develop resistance to antimicrobial agents currently recommended for the treatment of anthrax infection is a major concern. B. anthracis Sterne was grown from a live veterinary vaccine and used it to test for the development of resistance after 21 sequential subcultures in sub-inhibitory concentrations of doxycycline and three quinolones (ciprofloxacin, alatrofloxacin and gatifloxacin) and 15 sequential subcultures in sub-inhibitory concentrations of three macrolides (erythromycin, azithromycin and clarithromycin). After 21 subcultures the minimal inhibitory concentrations (MICs) increased from 0.1 to 1.6 mg/l for ciprofloxacin, from 1.6 to 12.5 mg/l for alatrofloxacin, from 0.025 to 1.6 mg/l for gatifloxacin and from 0.025 to 0.1 mg/l for doxycycline. After 15 passages of sequential subculturing with macrolides, the MICs increased from 12.5 to 12.5 or 50.0 mg/l for azithromycin, from 0.2 to 1.6 or 0.4 mg/l for clarithromycin and from 6.25 to 6.25 or 50 mg/l for erythromycin. After sequential passages with a single quinolone or doxycycline, each isolate was cross-tested for resistance using the other drugs. All isolates selected for resistance to one quinolone were also resistant to the other two quinolones, but not to doxycycline. The doxycycline-resistant isolate was not resistant to any quinolone.

Glucan: mechanisms involved in its "radioprotective" effect.

It has generally been accepted that most biologically derived agents that are radioprotective in the hemopoietic‐syndrome dose range (eg. endotoxin, Bacillus Calmette Guerin, Corynebacterium parvum, etc) exert their beneficial properties by enhancing hemopoietic recovery and hence, by regenerating the hosts ability to resist life‐threatening opportunistic infections. However, using glucan as a hemopoietic stimulant/radi‐oprotectant, we have demonstrated that host resistance to opportunistic infection is enhanced in these mice even prior to the detection of significant hemopoietic regeneration. This early enhanced resistance to microbial invasion in glucan‐treated irradiated mice could be correlated with enhanced and/or prolonged macrophage (but not granulocyte) function. These results suggest that early after irradiation glucan may mediate its radioprotection by enhancing resistance to microbial invasion via mechanisms not necessarily predicated on hemopoietic recovery. In addition, preliminary evidence suggests that glucan can also function as an effective free‐radical scavenger. Because macrophages have been shown to selectively phagocytize and sequester glucan, the possibility that these specific cells may be protected by virtue of glucans scavenging ability is also suggested.

Aerobic and Anaerobic Microbiology of Retroperitoneal Abscesses

The aerobic and anaerobic microbiology of various types of retroperitoneal abscesses was studied by review of the clinical and laboratory data for 161 patients treated between 1974 and 1990 for such abscesses. These included 109 anterior, 8 posterior, 21 retrofascial, and 23 pelvic retroperitoneal abscesses. A total of 472 organisms (2.9 isolates/specimen)--204 aerobic and facultative (1.3/specimen), and 268 anaerobic (1.7/specimen)--were recovered. Aerobes only were recovered from 34 abscesses (21%), anaerobes only from 34 (21%), and mixed aerobic and anaerobic bacteria from 93 (58%). Polymicrobial infection was present in 132 patients (82%). The predominant aerobic and facultative isolates were Escherichia coli (60 isolates), Klebsiella pneumoniae (20), Streptococcus group D (19), and Staphylococcus aureus (11). The predominant anaerobes were Peptostreptococcus species (95 isolates), Bacteroides fragilis group (66), Prevotella species (22), and Clostridium species (22). The number of anaerobes per site always was greater than the number of aerobic or facultative organisms and was especially high in pelvic abscesses. The number of aerobic and facultative organisms was especially high in pancreatic abscesses. These data highlight the polymicrobial aerobic-anaerobic nature of retroperitoneal abscesses.

Lack of influence of beta-lactamase-producing flora on recovery of group A streptococci after treatment of acute pharyngitis

Because production of beta-lactamase by normal pharyngeal flora could account for penicillin treatment failure, we studied the effect of anaerobic and aerobic beta-lactamase-producing bacteria on bacteriologic outcome in acute group A beta-hemolytic streptococcal (GABHS) pharyngitis. We compared 10-day courses of orally administered phenoxymethyl penicillin and amoxicillin-clavulanic acid, using a randomized, single-blind treatment protocol. Eligible patients were 2 to 16 years of age and had culture-proven acute GABHS pharyngitis; 89 patients (43 penicillin, 46 amoxicillin-clavulanic acid) were compliant with therapy. beta-Lactamase-producing organisms were isolated before therapy from the throats of 67% of patients treated with penicillin and 63% treated with amoxicillin-clavulanic acid. Throat cultures after completion of therapy were positive for GABHS in 7 (7.9%) of 89 patients. The initial GABHS T type persisted (treatment failure) in only 4 (4.5%) of 89 patients, including 3 (6.5%) of 46 who received amoxicillin-clavulanic acid and in 1 (2.3%) of 43 who received penicillin (not statistically significant). Bacteriologic treatment failure was unrelated to recovery of beta-lactamase-producing bacteria at the time of enrollment or after treatment. We conclude that beta-lactamase production by normal pharyngeal flora does not fully explain the failure of penicillin therapy for acute streptococcal pharyngitis. Using an antibiotic effective against beta-lactamase-producing bacteria will not eliminate the problem of bacteriologic treatment failure.

Management of Postirradiation Infection: Lessons Learned from Animal Models

Ionizing radiation depresses host defenses and enhances susceptibility to local and systemic infection due to endogenous or exogenous microorganisms. Exposure of mice to a lethal dose of ionizing 60Co-gamma radiation induces a dose-related reduction in the number of both aerobic and anaerobic bacteria from 10(10-12) to 10(4-6) per gram of stool within 4 days. The number of anaerobic bacteria stays low, but the number of Enterobacteriaceae per gram of stool increases significantly up to 10(9) by the 12th day after irradiation. This increase is associated with bacterial translocation of these organisms and fatal bacteremia. The use of quinolones in the irradiated animals was effective in controlling systemic endogenous Gram-negative infection after irradiation. Supplementation with penicillin prevented treatment failures due to Streptococcus spp. and increased survival. Quinolones given for 21 days also were effective in management of systemic exogenous infections due to orally ingested Klebsiella pneumoniae and Pseudomonas aeruginosa. Effectiveness of quinolones may be attributed to inhibition of exogenous organism growth within the gut lumen while preserving the anaerobic gut flora as well as their systemic antibacterial activity. Based on these findings, antimicrobial agents recommended for therapy of infection after exposure to irradiation are: ciprofloxacin, levofloxacin, ceftriaxone, cefepime, gentamicin +/- amoxicillin, or vancomycin.

Comparison of the microbiology of recurrent tonsillitis between children and adults

The microbial flora of recurrently inflamed tonsils removed from 25 children with recurrent episodes of tonsillar pharyngitis were compared to flora of tonsils removed from 23 adults suffering from similar illness. More bacterial isolates per tonsil were recovered in adults (10.2 per tonsil) than in children (8.4 per tonsil). The difference between these groups was due to a higher recovery rate in adults of Bacteroides melaninogenicus group (1.6 isolates per adult, 0.8 per child) and Bacteroides fragilis group (0.4 per adult, 0.2 per child). Conversely, Group A beta‐hemolytic streptococci were isolated in seven (28%) children as compared to their isolation in one (4%) adult. More isolates of beta‐lactamase‐producing organisms (BLPO) per tonsil were recovered in adults. Forty‐three BLPO were detected in 21 (91%) of the 23 tonsils removed from adults (1.9 isolates per patient) as compared to 31 isolates in 16 (64%) of the 25 tonsils removed from children (1.2 isolates per patient) (P=0.04). These findings suggest that the etiology of recurrent tonsillitis in adults may differ from that in children. The differences in the tonsillar flora may be due to the effect of many more courses of antimicrobials given over the years to adults and the changes in tonsillar tissue that occur in this age group.

Beta-lactamase-producing bacteria in head and neck infection.

We have summarized our experience in recovery of beta‐lactamase‐producing bacteria (BLPB) in head and neck infection (UNI). These HNI include conjunctivitis, serous and chronic otitis media, cholesteatoma, chronic mastoiditis, chronic sinusitis, adenoiditis, recurrent tonsillitis in children and adults, peritonsillar abscess, and retropharyngeal abscess.