CHICAGO—Many anaerobic bacteria are developing increased antibiotic resistance, according to research presented at the American Society for Microbiology’s 2001 Interscience Conference on Antimicrobial Agents and Chemotherapy. Although the most active antimicrobial agents are still effective against anaerobes, the stamina of these organisms against many antibiotics has risen markedly.

Also presented at the conference was evidence that bloodstream infections are increasingly attributable to gram-positive cocci, as well as information about the development of non-typeable coccal species. The importance of plumbing hygiene was underscored by presenters who described cases of ventilator-associated pneumonia linked to inadequate disinfection of an intensive care unit’s pipes. Another presentation on community-acquired pneumonia (CAP) indicated that a test involving C-reactive protein could help differentiate between different types of pneumonia.

ANAEROBIC RESISTANCE ON THE RISE

Some anaerobic microbes, particularly those in the Bacteroides fragilis group, have increased their resistance to certain antibacterial agents. Although this increased resistance has serious implications for clinicians, the revelation comes with the better news that resistant organisms are still susceptible to the most active antibacterial agents.

Data presented by D. W. Hecht involved clinical isolates from seven Illinois medical centers; included were various organisms in the B fragilis group, as well as Peptostreptococcus, Prevotella, and Clostridium species. The researchers tested the resistance of these isolates against a variety of antibiotics that are recommended for use against anaerobes.

They found that organisms in the B fragilis group showed strong resistance to penicillin (98%), clindamycin (21% to 50%), and piperacillin (14% to 75%); these organisms were less resistant to cefoxitin (8%) and trovafloxacin (10%). The other anaerobes studied showed lower, but still worrisome, levels of resistance to penicillin (3% to 60%), clindamycin (5% to 25%), and trovafloxacin (2% to 17%). For all anaerobes, the lowest rates of resistance were seen with metronidazole (0%), imipenem (0%), ertapenem (0.1%), piperacillin/tazobactam (0.7%), ticarcillin/clavulanate (0.7%), and ampicillin/sulbactam (2.9%).

GRAM–POSITIVE COCCI CAUSING BACTERMIA

Gram-positive cocci are responsible for an increasing proportion of bacterial bloodstream infections, a new three-year study has found. In contrast, the number of infections caused by coagulase-negative staphylococci, Streptococcus pneumoniae, and Escherichia coli is decreasing. The same study found that antimicrobial resistance was growing among enterococci and staphylococci.

M. A. Pfaller and colleagues evaluated information on 28,468 bacterial pathogens collected from 30 North American hospitals. They found that the rate of bacteremia due to Staphylococcus aureus had increased from 22.9% to 27.9%; the rate for Enterococcus species had risen from 9.5% to 10.3%. Decreases were seen in the rates for coagulase-negative staphylococci (from 12.8% to 10.8%), E coli (from 18.6% to 17.6%), and S pneumoniae (from 5.6% to 3.4%).

During the three-year study, S aureus and coagulase-negative staphylococci showed

decreased susceptibility to oxacillin, Enterococcus species displayed reduced susceptibility to vancomycin, and E coli developed increased resistance to ciprofloxacin.

NEW COCCAL SEROTYPES APPEAR

An effort to catalogue group B streptococci (GBS) to improve prenatal treatment strategies and monitor the distribution of streptococcal serotypes has resulted in a disturbing discovery: The number of non-typeable GBS serotypes has increased from 4.3% in 1996 to 10% in 2001.

J. A. Elliott and coworkers used pulse-field gel electrophoresis (PFGE) to analyze all 93 non-typeable GBS isolates found since 1996. They discovered that even within established serotypes, heterogeneity was apparent; there were five PFGE patterns with four or more non-typeable isolates. The researchers concluded that one or more new GBS serotypes have emerged within the United States and that this will complicate the development of new GBS vaccines.

PLUMBING HYGIENE CONTROLS P AERUGINOSA LEVELS

Good plumbing maintenance may be essential to preventing infectious disease outbreaks in medical intensive care units (MICUs). B. Page and colleagues described an episode in which bad maintenance led to Pseudomonas aeruginosa colonization in six patients treated in a 12-bed MICU during a three-month period. In three patients, ventilator-associated pneumonia due to carbapenem-resistant P aeruginosa resulted.

After the three cases of pneumonia were recognized, the researchers decided to culture the MICU’s hot and cold tap water. They found P aeruginosa in the water samples; these organisms had the same antibiotic phenotype and DNA profile as did the organisms found in the infected or colonized patients. Several of the unit’s faucets were contaminated as well.

Further investigation revealed that disinfection of the unit’s pipes, faucets, and tanks was supposed to occur monthly, but it had not been performed for three months before the outbreak. Disinfection of the pipes and tanks was undertaken, and the importance of the cleaning regimen was explained to maintenance workers. Afterwards, the organisms implicated in the outbreak were not detected in the MICU’s water or fixtures.

TEST TO HELP DIAGNOSE CAP

C-reactive protein may be used to distinguish between different types of CAP

E. García Vázquez and coworkers evaluated 258 patients who had pneumonia with a single etiologic diagnosis. They found that the mean C-reactive protein level was 16 mg/dL in patients with typical bacterial pneumonia, 12.6 mg/dL in those with atypical pneumonia, 14.4 mg/dL in those with viral pneumonia, and 25.2 mg/dL in those with Legionella pneumophila pneumonia. The researchers also noted that after correction for age and other risk factors, patients with L pneumophila pneumonia were 4.8 times more likely to have C-reactive protein levels of 10 mg/dL or higher than were those with other types of pneumonia. Furthermore, a cutoff of 10 mg/dL or higher had a sensitivity, specificity, positive predictive value, and negative predictive value of 0.9, 0.43, 0.17, and 0.97, respectively.

The researchers concluded that a C-reactive protein level below 10 mg/dL rules out L pneumophila pneumonia with great certainty. Given this, they suggest that assessing C-reactive protein could be a cost-effective part of CAP diagnosis.

—Owen McCarthy