PCR offers no advantage over culture for microbiologic diagnosis in cellulitis

PURPOSE

Most cases of cellulitis are traditionally attributed to β-hemolytic Streptococcus and Staphylococcus species, although in most cases, no organism is identified. Development of PCR using the conserved bacterial 16 S rRNA DNA permits identification of bacteria independent of conventional culture approaches and prior use of antibiotics.

METHODS

We used PCR-based techniques to identify cellulitis etiology using aspirate samples from affected skin. Saline was infiltrated and aspirated at the site of greatest erythema or at the cellulitic border. Samples were tested for 16 S rRNA DNA, and organism-specific probes used to identify bacteria commonly seen in skin infections.

RESULTS

Aspirates from 32 patients were studied, and 16 S rRNA DNA was detected in nine of these patient samples (28.1%). Bacterial species were identified by PCR methods in six of these nine samples (66.6%), with S. aureus and methicillin-resistant S. aureus (MRSA) identified in four and two, respectively, of these samples. Of the patients with positive aspirate bacterial cultures (3/9, 33.3%), S. aureus and coagulase-negative Staphylococcus (CoNS) were present on cultures of two of the three (both 66.6%) positive samples. Only in one of the three positive bacterial cultures did the PCR method detect the same organism as was detected by culture. Among patients with positive provider-collected clinical cultures, MRSA was the predominant organism (11/18, 61.1%) and when present, it was found as the sole organism. Where S. aureus or Streptococcus species were detected by molecular methods, clinical cultures yielded a positive result as well.

CONCLUSIONS

PCR-based techniques do not appear to be more sensitive than aspirate cultures for the detection of pathogens in cellulitis.

Phasic inhibition of dopamine uptake in nucleus accumbens induced by intravenous cocaine in freely behaving rats

A new approach combining fast-scan cyclic voltammetry with iontophoretic dopamine delivery was used in freely behaving rats to evaluate the time-course of dopamine uptake inhibition in nucleus accumbens induced by intravenous cocaine at a dose (1.0mg/kg) known to maintain self-administration behavior. Cocaine significantly increased the decay time of the dopamine response without altering its magnitude or time to peak. An increase in decay time was evident at 2 min, peaked at 6 min (+87%), and decreased to baseline at 18 min after a single cocaine injection. The change in decay time was similar in all rats and remained essentially the same, albeit slightly larger, for subsequent cocaine injections both within a session and over repeated sessions. The change in dopamine decay time did not correlate with cocaine-induced motor activation, which was maximal during the first minute after injection and decreased slowly over the next 20 min. Our data provide direct evidence for a phasic change in dopamine uptake induced by intravenous cocaine under behaviorally relevant conditions. The relatively slow and gradual development of dopamine uptake inhibition, which peaks at times when behaving rats self-inject cocaine, is inconsistent with the suggested role of this mechanism in the acute rewarding (euphoric) effects of self-injected cocaine, but supports its role in the activational and motivational aspects of drug-seeking and drug-taking behavior. Because intravenous cocaine enters the brain rapidly and peaks in neural tissue (1-2 min) long before it effectively inhibits dopamine uptake (6 min), it appears that some of the acute psychoemotional ("rush"), behavioral, autonomic, and neuronal effects of this drug, which are apparently resistant to dopamine receptor blockade, are mediated via rapid central or peripheral mechanisms independent of monoamine uptake.