Aberrant form of Pseudomonas aeruginosa in sputum and cerebrospinal fluid causing infection in a compromised patient

The necessity to revise Koch's postulates and its application to infectious and non-infectious diseases: a mini-review

Advances in the science have promoted all aspects of human's life; these, in turn, have changed many principles and scientific postulates. Koch's postulates, since the beginning of their implementation, have been one of the important subjects involving complications and misinterpretations regarding the causal relationship of microbe-hosts. These postulates have been shown not to be correct in some cases including the inability of some microbes to grow in the culture medium, viruses, or anaerobic bacteria. Today, due to some new scientific facts like the social behaviors of bacteria, such as quorum sensing, there are serious problems regarding the definition of whole microbial effects; these include microbiomes and viromes, as well as their interaction with the existing eukaryotics, the complicated relations between bacteria, L-forms, and cell wall-deficient bacteria, and the important role of microbes in the development of non-infectious diseases. So, the application of Koch's postulates to explain the causal relationships between host-microbes could be difficult. Therefore, nowadays, even the molecular Koch's postulates are not accountable. Also, according to the new scientific discoveries, various criteria such as changes in the immune system, pathology, and clinical findings, along with the results of daily laboratory tests, should be used to apply Koch's postulates in the etiologic studies. Otherwise, the possible etiologic relationships between the host-microbes cannot be verified due to numerous complications; certainly, the relationship between the doctor and the lab is ultimately weakened. Therefore, public health, prevention, and much of the antimicrobial treatments will also remain in a state of ambiguity.

Pharmacodynamic effects of subinhibitory antibiotic concentrations

The pharmacodynamics of antibiotics have become increasingly important for the determination of optimal dosing regimens. Studies over the past decade have demonstrated marked differences in the time course of antimicrobial activity for different classes of antibiotics both in vitro, in animals and in human trials. One of the explanations for the success of intermittent dosing regimens has been the delay in regrowth after the concentration has fallen under the MIC, the so called postantibiotic effect (PAE). In addition to the PAE, the success of discontinuous dosing regimens may be attributed to both the function of a normal host defence and to the effects of subinhibitory antibiotic concentrations (sub-MICs). It has been shown that there is a difference between the effects of sub-MICs following a suprainhibitory dose (postantibiotic sub-MIC effect; PA SME) and the effects of sub-MICs (SME) alone. It seems that the PA SME is more clinically relevant compared with the PAE, since exposure to suprainhibitory concentrations will always be followed by sub-MICs in vivo. A long PA SME could indicate that longer dosing intervals may be used for that antibiotic /bacterial combination and together with the known effects of sub-MICs on bacterial virulence and the influence of the immune system, it may explain the efficacy of antibiotics with short half-lives even of they are given infrequently.

Interaction of beta-lactam antibiotics with the bactericidal activity of leukocytes against Escherichia coli

The effect of beta-lactam antibiotics on phagocytosis and intracellular killing of four isogenic Escherichia coli strains differing in their 0- and K antigens was studied by adopting the rat polyvinyl-sponge model. The penicillins mezlocillin, ticarcillin and piperacillin rendered all four isogenic E. coli strains more susceptible to intraleukocyte killing; the cefalosporins tested exhibited inhomogenous effects; lamoxactam was marginally effective, whereas cefoxitin was completely ineffective; cefotaxime caused an increase in intracellular killing of the capsule-defective mutant only. The beta-lactam promoted increase in intracellular killing could be inhibited by alpha-methylmannoside but not by alpha-methylglucoside. Free-flow electrophoretic separation of mezlocillin-treated bacteria and guinea pig erythrocytes revealed that co-migration of E. coli and erythrocytes respectively could be inhibited by alpha-methylmannoside but not by alpha-methylglucoside. These data indicate that mezlocillin interferes with the mannose sensitive adhesins of E. coli.

Graft infection and bacteremia with a tolerant L-form of Streptococcus sanguis in a patient receiving hemodialysis

I report a case of a tolerant L-form Streptococcus sanguis infection involving an artificial vascular access site that was probably acquired from a nonhuman source; this is the first report of such an infection in a human. Gram stains from the infected access site and blood cultures revealed an aberrant form which could only be recovered by passage through hypertonic sucrose media before being reisolated and subsequently identified as S. sanguis. The same organism was isolated from a pet dog of the patient. The organism was also felt to be tolerant to penicillin. The patient was successfully treated by removal of the artificial graft and intravenous erythromycin therapy. Microorganisms acquired from nonhuman sources are potential pathogens in the immunocompromised patient.

Abnormal morphology of bacteria in the sputa of patients treated with antibiotics

Filaments of Klebsiella pneumoniae were observed by Gram stain in the sputum of a patient with a respiratory infection who was treated with half the usual dose of cefazolin. Identical filaments were observed in vitro when this strain was incubated with subminimum inhibitory concentrations of cefazolin. Large gram-positive cocci containing multiple cross walls were observed by electron microscopy in the sputum of a patient with a respiratory infection who was treated with ampicillin and gentamicin. Antibiotic administration was suspended the night before the sputum was obtained. The ultrastructure of these cocci was very similar to the ultrastructure of Staphylococcus aureus incubated with subminimum inhibitory concentrations of cephaloridine or oxacillin. It was suspected that the low dose of cefazolin and the intermittent therapy with ampicillin resulted in a subminimum inhibitory concentration of antibiotic in the respiratory tract which induced the the abnormal morphology of the bacteria observed in the sputum of both patients. The presence of abnormal forms of bacteria in the specimen of a patient, rather than in the culture of a specimen, has clinical significance.