Effect of inoculum size on in vitro activity of norfloxacin against fecal anaerobic bacteria. Rationale for selective decontamination of the digestive tract

Previous studies have shown that anaerobic bacteria are susceptible to norfloxacin at the levels attained in the feces. Conversely, studies in laboratory animals and neutropenic humans using norfloxacin for selective decontamination of the digestive tract have shown that norfloxacin markedly reduces the aerobic enteric flora without reducing fecal anaerobic flora. In an effort to resolve this paradox, the effect of a 10(9) colony-forming units (cfu)/ml inoculum, which is more reflective of actual fecal counts than the standard 10(5) cfu/ml inoculum, on the activity of norfloxacin against two fecal Escherichia coli isolates and 16 fecal anaerobic isolates was studied. The results showed a marked inoculum effect at 10(9) cfu/ml for most anaerobic isolates but not for the E. coli strains tested. At 256 micrograms/ml, all E. coli were killed while the anaerobic bacteria maintained colony counts greater than or equal to 10(9) cfu/ml. Hence, the lack of anaerobic activity (minimal inhibitory concentration greater than or equal to 512 micrograms/ml) at higher fecal inocula might explain the utility of norfloxacin in selective decontamination of the bowel.

Impact of prolonged incubation on disk diffusion susceptibility test results for Staphylococcus aureus

Because strains of Staphylococcus aureus that are resistant to penicillinase-resistant penicillins may be difficult to detect in the clinical laboratory, a variety of changes in methodology have been suggested to increase their detection. In 1984, the West Los Angeles Veterans Administration Medical Center experienced an increase in clinically significant strains of oxacillin-resistant S. aureus. To insure that such strains would not be missed by the disk diffusion test methods employed for routine testing, changes in methodology were insituted. These included interpreting zone diameters around oxacillin disks at 48 h of incubation. We collected 139 isolates from patients thought to have oxacillin-resistant S. aureus based on these test results and later retested the isolates using microdilution MIC testing. Only 85 isolates (61%) had microdilution oxacillin MICs of greater than or equal to 8.0 micrograms/ml, whereas 54 (39%) had oxacillin MICs of less than or equal to 2.0 micrograms/ml. A review of medical records revealed that in 1 year there were 98 patients with isolates appearing resistant by disk diffusion but not confirmed by microdilution MICs; many patients were placed in isolation and treated with specific antimicrobial agents. We conclude that incubation of oxacillin disk diffusion tests for longer than 24 h in conjunction with disregard for resistance to other classes of antimicrobial agents may result in an unacceptably high degree of false resistance results. Because the resistance of S. aureus has important therapeutic and infection control implications, it is necessary to recognize problems that may result in ambiguous or inaccurate susceptibility results.

Ciprofloxacin versus cinoxacin in therapy of urinary tract infections. A randomized, double-blind trial

In a prospective, randomized, double-blind trial, ciprofloxacin (250 mg orally, twice daily) was compared with cinoxacin (500 mg orally, twice daily) in 60 patients with urinary tract infections. Most patients were women with uncomplicated urinary tract infections. Escherichia coli was the most common isolate (36 patients). Clinical and microbiologic cure occurred in 20 of 24 (83 percent) evaluable patients treated with ciprofloxacin, compared with 15 of 21 (71 percent) evaluable patients treated with cinoxacin. Ciprofloxacin was well tolerated and had a low incidence of minor side effects that included Candida vaginitis, headache, and gastrointestinal intolerance. Relapse or failed therapy was not associated with the development of resistance.

Failure of rapid agglutination methods to detect oxacillin-resistant Staphylococcus aureus

Although a latex agglutination test (StaphAurex) and a hemagglutination test (Staphyloslide) correctly identified all strains of Staphylococcus aureus that were susceptible or had intermediate susceptibility to oxacillin, 17 of 73 (23%) and 18 of 73 (25%) strains of oxacillin-resistant S. aureus were not identified by StaphAurex and Staphyloslide, respectively. All strains not detected were resistant to trimethoprim-sulfamethoxazole and rifampin.

Susceptibility of Eikenella corrodens to newer and older quinolones

The susceptibilities of 44 clinical strains and a reference strain (ATCC 23834) of Eikenella corrodens were determined by agar dilution. All isolates were very susceptible (MICs, less than 2 micrograms/ml) to amifloxacin, ciprofloxacin, difloxacin, enoxacin, norfloxacin, ofloxacin, and Win 35439.

Susceptibility of bite wound bacteria to seven oral antimicrobial agents, including RU-985, a new erythromycin: considerations in choosing empiric therapy

The susceptibility of 93 aerobic and 59 anaerobic bacteria isolated from human and animal bite wounds was determined by agar dilution. No agent tested (penicillin, oxacillin, cephalexin, sulfamethoxazole-trimethoprim, minocycline, erythromycin, and RU-965) was consistently active against all isolates. A total of 21% of the Bacteroides species, all isolated from human bites, were resistant to penicillin; 14 and 18% of the Pasteurella multocida isolates were resistant to erythromycin and oxacillin, respectively.

Comparative in vitro activities of amoxicillin-clavulanic acid and imipenem against anaerobic bacteria isolated from community hospitals

The susceptibilities of recent clinical isolates of anaerobic bacteria from two community hospitals were determined. Thirty percent of pigmented Bacteroides species and bile-sensitive, nonpigmented Bacteroides species produced penicillinase and were resistant to amoxicillin. Cefoxitin and clindamycin showed good activity against most strains, with the exception of rare isolates of the Bacteroides fragilis group and some strains of Clostridium species. While amoxicillin was not active against B. fragilis and other members of the B. fragilis group, amoxicillin-clavulanic acid was very active against almost all of these organisms. Imipenem was the most potent agent against all strains tested.

Comparative in vitro inhibitory and killing activity of cefpirome, ceftazidime, and cefotaxime against Pseudomonas aeruginosa, enterococci, Staphylococcus epidermidis, and methicillin-susceptible and -resistant and tolerant and nontolerant Staphylococcus aureus

With a macrotube dilution method, MICs and MBCs were determined for three aminothiazolyl cephalosporins, cefpirome (HR 810), ceftazidime, and cefotaxime, against Pseudomonas aeruginosa, enterococci, Staphylococcus epidermidis, and methicillin-resistant, -susceptible, and -tolerant strains of Staphylococcus aureus. Comparatively, cefpirome was the most active agent against all gram-positive cocci, including enterococci and methicillin-resistant S. aureus, and was as active as ceftazidime against P. aeruginosa. MBCs of cefpirome were within two dilutions of the MICs for 91% of P. aeruginosa and 90% of gram-positive cocci strains tested, except methicillin-resistant S. aureus, for which the MBCs were within three dilutions for 90% of strains.

Comparative activity of the quinolones against anaerobic bacteria isolated at community hospitals

The in vitro activity of five quinolone compounds, amoxicillin, and clindamycin against 118 strains of anaerobic bacteria isolated at community hospitals was determined by an agar dilution method. Nalidixic acid and cinoxacin had poor activity, and norfloxacin and enoxacin showed relatively poor activity. Ciprofloxacin was active against Bacteroides fragilis, Fusobacterium species, Clostridium perfringens, and gram-positive cocci. At peak levels achievable in the feces, norfloxacin and enoxacin had moderate activity.

Comparative in vitro activity of cefbuperazone against anaerobic bacteria isolated from community hospitals

The activity of cefbuperazone against 266 strains of anaerobic bacteria was determined by the agar dilution method and compared with cefoxitin, moxalactam, piperacillin, and clindamycin. All strains were recent clinical isolates from community hospitals. All agents tested showed good activity against Bacteroides fragilis, Fusobacterium spp., Propionibacterium spp., Clostridium septicum, Clostridium perfringens, and the anaerobic, gram-positive cocci and gram-negative cocci. Cefbuperazone, cefoxitin, and moxalactam had poor activity against Bacteroides thetaiotaomicron, Bacteroides ovatus, and Bacteroides distasonis. The susceptibility of other Clostridium spp., Lactobacillus spp., and Eubacterium lentum was variable. Our community hospital isolates showed a difference in susceptibility patterns from those reported from university and research centers. This supports the recommendation that clinical microbiology laboratories, including those in community hospitals, need to perform susceptibility testing on representative clinical isolates.

Susceptibility of Eikenella corrodens to penicillin, apalcillin, and twelve new cephalosporins

The susceptibility of 29 strains of Eikenella corrodens to penicillin, apalcillin, and 12 new cephalosporins was determined by the agar dilution method. Most strains were resistant to cefsulodin, and some were resistant to apalcillin and cefpiramide. Although all strains were susceptible to the other cephalosporins tested, most of those drugs were as active as or less active than penicillin. Susceptibility testing of isolates should be performed whenever a cephalosporin is used to treat infections involving E. corrodens.

Specimen collection and transport, anaerobic culture techniques, and identification of anaerobes

Excellent progress has been made in recent years in the development and refinement of technical materials used for transporting specimens and growing and identifying anaerobes. Several good systems for maintaining swabs and vials for transporting liquid specimens are commercially available. Anaerobic bags are useful for transporting unusual specimens, such as tissue or bone, and are also a convenient way to incubate small numbers of plates. Several different types of anaerobic chambers, with or without gloves, and separately enclosed incubators are being used by an increasing number of laboratories. Prereduced anaerobically sterilized plates and biochemicals in tubes are available from several commercial sources. A new rapid identification microsystem based on tests for performed enzymes permits identification of many clinically significant anaerobes to the species level in 4 hr.

Brain abscess and cerebritis

Eighteen consecutive cases of brain abscess or cerebritis seen at the Veterans Administration Wadsworth Medical Center (Los Angeles, Calif.) during 1970-1982 were analyzed. Fifteen occurred after the computerized axial tomographic (CT) scanner for diagnosis and follow-up became available in 1976. The patient population included 14 individuals with significant underlying medical problems and with a clearly identifiable contiguous or distant source. Four patients had multiple brain abscesses; the most common site of involvement in the remaining 14 patients was the parietal lobe. Microorganisms were isolated from 14 patients and included a variety of aerobic and anaerobic bacteria. Of the 27 isolates, 12 were microaerophilic species or strictly anaerobic bacteria. Therapy was most often a combination of surgical drainage and antimicrobial agents. Usually the drug regimen included penicillin and chloramphenicol and, more recently, the combination of penicillin and metronidazole. One of the two patients with brain abscess treated with antimicrobial agents alone died. Two patients with presumed bacterial cerebritis improved with chemotherapy alone. This study reaffirms the important role of anaerobes in brain abscess. The advent of the CT scanner appears to have been a valuable development in both diagnosis and monitoring of therapy, but mortality (22%) still remains relatively high. Although metronidazole will likely prove to represent a significant advance in antimicrobial therapy, surgical drainage still appears to be the mainstay of therapy for treatment of established abscesses.

Role of anaerobic bacteria in bite-wound infections

The etiologic agents usually involved in wound infections due to human or animal bites are the aerobic skin flora of the victim, e.g., Staphylococcus aureus, and/or the aerobic oral flora of the biter, e.g., Pasteurella multocida. While anaerobic bacteria are predominant in the normal oral flora of humans and animals, their importance in the pathogenesis of bite-wound infections has not been stressed. Most investigators in this field have either not cultured these wounds for anaerobic bacteria or not utilized optimal culture techniques. In a series of studies on human and animal bite wounds, methods that are optimal for recovery of anaerobic bacteria were used. Anaerobes were found in significant quantities in 39% of animal bite wounds, 50% of human bite wounds, and 56% of clenched-fist injuries. Several species of anaerobes usually were present in the wounds and always were present in mixed culture with aerobic oral flora. The anaerobes most commonly isolated included Bacteroides asaccharolyticus, Bacteroides bivius, Bacteroides disiens, Bacteroides melaninogenicus, Bacteroides oralis, Bacteroides ruminicola, Bacteroides pneumosintes, Bacteroides ureolyticus, Fusobacterium nucleatum, Fusobacterium russii, Peptococcus species, Peptostreptococcus species, and Veillonella species. Initial, empiric antimicrobial therapy for bite wounds should be directed against potential anaerobic as well as aerobic pathogens.

Impact of cefoperazone therapy on fecal flora

To evaluate the effects of parenteral cefoperazone therapy upon human fecal flora, fecal specimens obtained from four patients before and during therapy (as well as after therapy for one patient) were cultured quantitatively for facultative, aerobic, and anaerobic bacteria and for fungi. Cefoperazone therapy was associated with major changes in fecal flora. There was suppression to undetectable levels or an appreciable reduction in all anaerobic bacteria as well as suppression of all initially detected Enterobacteriaceae. During therapy, there was acquisition or an increase in counts of Candida spp., so that these became the most numerous fecal microorganisms in all patients. In addition, Pseudomonas spp. and coagulase-negative Staphylococcus sp. were acquired by three patients. These marked alterations in flora have potentially important consequences.

Toxin-producing bacteria in infants. Lack of an association with sudden infant death syndrome

After finding enterotoxigenic (ET) Escherichia coli in two consecutive cases of sudden infant death syndrome (SIDS), we initiated a prospective search for ET E coli in SIDS in Manitoba; in addition, we looked for toxigenic Clostridium botulinum and C difficile. In a 21-month period, small- and large-bowel contents were obtained in 33 cases of SIDS, from 32 control subjects, and in ten suspected cases of SIDS. Neither C botulinum nor ET E coli was isolated from any of these; C difficile was cultured from postmortem bowel contents of two SIDS and seven control cases. The overall isolation rate of C difficile was 17%. Despite the fact that two of these cases had toxin detectable in the bowel contents, no evidence of colitis was found in any of the cases with C difficile. We conclude that C botulinum or ET E coli have only a small role, if any, in the etiology of SIDS, and that C difficile is found relatively commonly in the gastrointestinal tract of infants without apparent local or systemic effects.

Gram-negative anaerobic bacilli: Their role in infection and patterns of susceptibility to antimicrobial agents. II. Little-known Fusobacterium species and miscellaneous genera

Twenty infrequently reported species of gram-negative anaerobic bacilli other than Fusobacterium nucleatum, Fusobacterium necrophorum, and members of the genus Bacteroides were studied with regard to their role in infection and their susceptibility to antimicrobial agents. In addition, the literature regarding the recovery of these organisms from both the normal flora and infections of humans was reviewed. During a six-year period at the Wadsworth Clinical Anaerobic Bacteriology Research Laboratory (Veterans Administration Wadsworth Medical Center, Los Angeles, Calif.), 39 (6%) of 679 specimens obtained from anaerobic infections yielded "other gram-negative anaerobic bacilli" (OGNAB). Fusobacterium naviforme, Fusobacterium gonidiaformans, Fusobacterium varium, Fusobacterium mortiferum, and Fusobacterium russii were the most commonly isolated OGNAB. Most of the OGNAB tested were resistant to erythromycin, and most strains, except for F. varium, were susceptible to beta-lactam antibiotics and clindamycin. Chloramphenicol and metronidazole were active against all strains of OGNAB tested. Certain Fusobacterium species are undoubtedly previously unrecognized members of the normal flora of the oropharynx, upper respiratory tract, or urogenital tract and may be present in infections derived from these floras.

New medium selective for Fusobacterium species and differential for Fusobacterium necrophorum

Fusobacterium egg yolk agar is a new medium selective for Fusobacterium species and differential for Fusobacterium necrophorum. The medium is a Brucella Agar base (Difco Laboratories, Detroit, Mich.) containing vancomycin, neomycin, josamycin, and egg yolk. All species of fusobacteria grew with only minimal inhibition. The mean log difference in counts between Fusobacterium egg yolk agar and control media for 30 strains of seven species of fusobacteria was 0.1922. F. necrophorum typically showed a strong lipase reaction. Most other organisms were significantly inhibited by the medium.

The non-value of preoperative and intraoperative cultures in predicting the bacteriology of subsequent wound infection in patients undergoing major head and neck cancer surgery

A prospective study of patients undergoing major head and neck cancer surgery was undertaken to define the value of preoperative and intraoperative cultures in identifying the patient at "high risk" of wound infection and in predicting the bacteriology of wound infection. One or two days before surgery, the skin of the operative site on the neck, the oropharynx and anterior nares were swabbed. an intraoperative wound culture was obtained after the pharyngeal defect was closed and the wound irrigated with water. All cultures were processed for aerobes in the Anaerobic Bacteriology Research Laboratory at Wadsworth Hospital Center. Wound infections developed in 10 of 31 patients who received cefazolin prophylactically and 21 of 25 patients who received no perioperative antibiotics. Fifty-five percent of infected patients and 68% of noninfected patients demonstrated potential pathogens preoperatively. A potential pathogen isolated preoperatively or intraoperatively was subsequently recovered from 35% of infected wounds. The majority of infected wound cultures grew one or more additional pathogens. A poor correlation was also noted between preoperative nasal Staphylococcus aureus isolation and subsequent recovery from wound infections. We conclude that preoperative and intraoperative aerobic wound cultures are not predictive of the "high risk" patient or of the bacteriology of subsequent wound infection in major head and neck cancer surgery.

Gram-negative anaerobic bacilli: their role in infection and patterns of susceptibility to antimicrobial agents. I. Little-known Bacteroides species

The role in infection and the patterns of susceptibility to antimicrobial agents of 17 infrequently reported species of Bacteroides were studied. The findings of this research are summarized, and the literature dealing with recovery of these species from both the normal flora and infections of humans is reviewed. During a six-year period, 22% of 679 specimens from infections due to anaerobic bacteria that were studied by the authors yielded one or more of these "other Bacteroides species" (OBS). The most commonly isolated OBS were Bacteroides ruminicola subspecies brevis (63 patients), Bacteroides ureolyticus (38), Bacteroides bivius (26), and Bacteroides disiens (17). Appreciable resistance of some isolates to the beta-lactam antibiotics, erythromycin, and the tetracyclines was noted, whereas all strains were inhibited by chloramphenicol and metronidazole and almost all were inhibited by clindamycin. The data indicate that OBS are present in infection much more often than has been reported previously. The resistance of certain strains to some commonly used antimicrobial agents may necessitate a reassessment of the initial, empiric therapy of infections due to anaerobic bacteria.

Serious infection with Leptotrichia buccalis. Report of a case and review of the literature

Leptotrichia buccalis is an obligately anaerobic, gram-negative rod classified as a member of the family Bacteroidaceae. Organisms found in this family (Bacteroides and Fusobacteria) are frequent causes of severe infection in human beings. L. buccalis is a constituent of normal oral flora. Leptotrichia has rarely been recovered from mixed infections primarily of the head and neck. It has not previously been reported as a cause of serious infection in man. We report a case of cavitary pneumonia and septicemia caused by L. buccalis. The colonial morphology and gram stain of L. buccalis are characteristic. Definitive identification is made by gas-liquid chromatography. Leptotrichia have been shown to contain potent endotoxin. L. buccalis has the potential to be a virulent, pathogenic microorganism, especially in the compromised host.

Dog bite wounds and infection: a prospective clinical study

We prospectively studied 26 patients with 27 dog bite wounds who sought medical attention in the emergency department. Two distinct populations were found (Fishers Exact Test, P less than or equal to 0.001): 1) those who presented 8 hr to 12 hr post-injury were concerned about rabies or tetanus or surgical wound repair; and 2) those who presented more than 12 hr post-injury were concerned with infection. There was no difference (P > 0.05) in the bacteriology of the two groups. Of all wounds, 74% had aerobic pathogens isolated, including Streptococcus viridans (12 strains), Staphylococcus aureus (five strains), and Pasteurella multocida (eight strains); 41% had anaerobic pathogens isolated, including Bacteriodes species (five strains) and Fusobacterium species (five strains). Gram stains made from wound swabs were specific but insensitive predictor for bacterial growth. Empiric outpatient therapy with oral penicillin (17 patients) and/or dicloxacillin (four patients) was effective.

Bacteriology of rattlesnake venom and implications for therapy

Although the incidence of infection secondary to the bites of venomous snakes remains unknown, the routine use of prophylactic antimicrobial therapy is advocated. In this study, the venom from 15 rattlesnakes was cultured, and 58 aerobic and 28 anaerobic strains of bacteria were isolated. The most common species isolated were Pseudomonas aeruginosa, Proteus species, coagulase-negative staphylocci, and Clostridium species. Bacteroides fragilis was also recovered. When the fang sheaths of four additional rattlesnakes were retracted and the fangs of these snakes decontaminated, 50% of the samples of venom had no bacterial growth (P = 0.035). Until a clinical study is performed, the use of antimicrobial therapy that reflects that complex oral flora of rattlesnakes is still recommended in most cases of envenomization.

Cefoxitin for treatment of infections due to anaerobic bacteria

Twenty-seven patients with 29 infections due to anaerobic or mixed anaerobic-aerobic bacteria were treated with cefoxitin. From the 27 patients 99 isolates of anaerobic bacteria and 70 isolates of aerobic bacteria were recovered. Twelve pleuropulmonary infections, 12 soft tissue infections, three bone infections, and two intraabdominal infections were treated. Twenty-six of the 29 infections were completely or partially eradicated; the remaining three infections were unchanged. One-third of the patients experienced phlebitis; in two instances severe phlebitis caused discontinuation of therapy. In this study cefoxitin appeared to be an effective single agent for the therapy of infections due to specific anaerobic bacteria or to a mixed flora of anaerobic and aerobic bacteria.

Bacteriology of human and animal bite wounds

Seventy-three patients with bite wounds (16 patients with clenched-fist injuries, 18 with human bite wounds, and 39 with animal bites) were cultured aerobically and anaerobically. A total of 33 of 34 patients with human bites and clenched-fist injuries and 33 of 39 patients with animal bites had aerobic or facultative bacteria isolated from their wounds. A total of 224 strains of aerobic or facultative bacteria were isolated, the most frequent isolate being alpha-hemolytic streptococci (50 strains). Staphylococcus aureus was isolated from 18 wounds. Penicillin-resistant gram-negative rods were infrequently isolated (12 strains). Anaerobic bacteria were isolated in 18 of 34 human bite wounds and clenched-fist injuries and 16 of 39 animal bite wounds. A total of 88 anaerobic strains was isolated, the most common being various Bacteroides species (36 strains).